Rebol Programming For The Absolute Beginner

	By:  Nick Antonaccio
	Updated:  3-1-09
	----------------------
	68 YouTube video tutorials that follow this text (10 hours of video) are available <a href="http://musiclessonz.com/rebol_video_links.html" target=_blank>here</a>.
	A MORE CONCISE version of this tutorial is available <a href="http://musiclessonz.com/rebol.html" target=_blank>here</a> (practical fundamentals - just the facts).
	For an even shorter introduction, try <a href="http://musiclessonz.com/rebol_for_kids.exe" target=_blank>this program for children</a> (it's also suitable for adults who want a simple quick-start).


===For New Programmers and for New Rebolers

This tutorial demonstrates how easy it is to accomplish real world programming goals with a flexible and powerful language called Rebol.  The text aims to teach average users to program computers to do useful things, without the long and difficult learning curve imposed by other programming languages.  If you're an experienced programmer, it's strongly recommended that you read <a href="http://musiclessonz.com/rebol.html" target=_blank>this more concise tutorial</a>.  You'll be amazed at Rebol's compact code and simple cross-platform usability.  If you're a beginner, you won't find another tutorial, book, or language that enables you to accomplish more useful programming tasks within a few hundred pages.  Rebol is more productive than anything else, anywhere.

A downloadable package of 11 code examples from this tutorial is available at:

<a href="http://musiclessonz.com/rebol_tutorial_examples.zip" target=_blank>http://musiclessonz.com/rebol_tutorial_examples.zip</a>

The zip file contains screen shots and executables demonstrating what can be easily accomplished by a casual, part-time Rebol coder, within several weeks of study.  Here are a few examples:

=image rebol_tutorial/little_email_client.png
=image rebol_tutorial/menu.png
=image rebol_tutorial/web_cam.png
=image rebol_tutorial/r3D.png
=image rebol_tutorial/textris.png
=image rebol_tutorial/listview_database_a.png
=image rebol_tutorial/freecell2.png
=image rebol_tutorial/instant_messenger.png
=image rebol_tutorial/image_effector.png
=image rebol_tutorial/gcdm.png
=image rebol_tutorial/calendar.png
=image rebol_tutorial/chat_room.png
=image rebol_tutorial/calc.png

A YouTube video version of this tutorial is available at <a href="http://musiclessonz.com/rebol_video_links.html " target=_blank>http://musiclessonz.com/rebol_video_links.html </a>

The concepts demonstrated throughout the tutorial will help new programmers understand other languages and programming tools, and will lay the groundwork for novices to acquire essential coding skills.  Even novices will be able to actually create useful Rebol programs in the first few days. And Rebol isn't limited to certain types of applications or operating systems.  Code written in Rebol is able to run unchanged on over 40 operating systems, and can be used to build an enormous variety of user applications with modern graphics, CGI interfaces, network functionality, database connectivity, and much more.  If you're used to other development environments, you'll find that Rebol is a beautifully designed language, contained in a dramatically small and efficient package that elegantly replaces many other mainstream tools.  Learning Rebol is productive, enjoyable, and thought provoking for both new and experienced coders.  No matter what your experience level, learning Rebol will save you time and frustration at some point in your programming endeavors.  It's a fantastically versatile little tool for which you'll find many uses.



===Some Perspective for Beginners

Before diving into raw mechanics, here's a fundamental perspective that's helpful to understand:

Modern computers, operating systems and programs all do very basic things, in limited ways, with a limited scope of data types:  

# They let users input various types of data:  text, images, sounds, video, etc.

# They let users save, retrieve, organize, share/transfer, manipulate, alter, view and otherwise deal with that data in useful ways.

Everything that can be done with a modern computer basically involves manipulating text and non-text data (non-text data is called "binary" data).  In the current state of modern computing, data of all types is typically input, manipulated, and returned via graphical user interfaces such as Windows program interfaces, web forms displayed in browsers, and other keyboard/mouse driven "GUI"s.  Data is saved on local hard drives and storage devices (CDs, thumb drives, etc.) and on remote web servers, and is typically transferred via local networks and Internet connections.  Knowing how to control those familiar computing elements to allow users to manipulate data, is the goal of learning to program.  It doesn't matter whether you're interested in writing business applications to work with inventory and scheduling (text data), programs to alter Internet web pages or emails (text and image data), programs to organize or play music (binary data), programs to transfer files across networks (text and/or binary data), programs to broadcast video and sound across the Internet (rapidly transferred sequential frames of binary data), programs to control robotic equipment, programs to play games, etc...  They all require learning to input, manipulate, and return data of some sort.  You can do all those things with Rebol, and once you've done it in one language, it's easier to do with other specialized languages and programming tools.

Rebol handles common user interfaces and data types easily and intuitively.  It allows programmers to quickly build graphic interfaces to input and return all common types of data.  It can easily manipulate text, graphics, and sounds in useful ways, and it provides simple methods to save, retrieve, and share data across all types of hardware, networks, and the Internet.  That makes it a great way to begin learning how to program.  For more information about the useful qualities of Rebol, see <a href="http://musiclessonz.com/rebol.html#section-1" target=_blank>http://musiclessonz.com/rebol.html#section-1</a>.


===Using the Rebol Interpreter to Speak to the Computer - "Hello World"

The Rebol interpreter is a program that runs on your computer.  It translates written text organized in the Rebol language syntax ("source code") to instructions the computer understands.  One of the great things about Rebol is that it's a very small program, contained in a single file.  There are versions that run on just about every type of computer and operating system (Windows PC, Macintosh computer, Linux web server, etc.), without any complicated install process.  It lets you speak to all those machines using the same language.  You just download the Rebol interpreter program, feed it a text file full of code, and the machine does what you want, with the data you want.  It's easy to use and only about 1/2 meg to download (less than a minute even on a slow dialup connection).

To get the free Rebol interpreter for Microsoft Windows, go to <a href="http://rebol.com/view-platforms.html" target=_blank>http://rebol.com/view-platforms.html</a> and download the view.exe file for Windows - it's clearly marked, just click it with your mouse and save it to your hard drive.  When you run view.exe for the first time, you can install it if you want, but you don't have to.  Just follow the instructions on screen.  Once you've got the Rebol interpreter downloaded and running on your computer, click the "Console" icon, and you're ready to start typing in Rebol programs.  To create your first program, type the following line into the Rebol interpreter, and then press the [Enter] (return) key on your keyboard:

	alert "Hello world!"

=image rebol_tutorial/hello.png

Before going any further, give it a try.  Download Rebol, and type in the code above to see how it works.  It's simple and it only takes a moment.  If you want to run Rebol on any other operating system, just select, download and run the correct file for your computer.  It works the same way on every operating system.


---Five Short Examples

To whet your appetite, here are 5 tiny <i>GUI</i> programs that demonstrate just how potent Rebol code is.  The first example is a fully functional web page editor.  You can use it to edit html pages and other text files on any web site ftp server:

	view layout [
		h1 "Enter your ftp info, then click 'load' to download and edit a file:"
		p: field 600 "ftp://user:pass@website.com/public_html/filename.html"
		h: area 600x440 across 
		btn "Load" [h/text: read (to-url p/text) show h]
		btn "Save" [write (to-url p/text) h/text]
	]

=image rebol_tutorial/example_1.png

Here's a classic graphic sliding tile game:

	view center-face layout [
		origin 0x0 space 0x0 across 
		style p button 60x60 [
			if not find [0x60 60x0 0x-60 -60x0] 
				face/offset - empty/offset [exit]
			temp: face/offset face/offset: empty/offset 
				empty/offset: temp
		]
	    p "A" p "B" p "C" p "D" return p "E" p "F" p "G" p "H" return
	    p "I" p "J" p "K" p "L" return p "M" p "N" p "O"  
		empty: p 200.200.200 edge [size: 0]
	]

=image rebol_tutorial/example_2.png

Here's a little painting program:

	view layout [
		h1 "Paint with the mouse:"
		scrn: box black 400x400 feel [
			engage: func [face action event] [
				if find [down over] action [
					append scrn/effect/draw event/offset show scrn
				]
				if action = 'up [append scrn/effect/draw 'line]
			]
		] effect [draw [line]]
		btn "Save" [
			save/png %/c/painting.png to-image layout [
				origin 0x0 box black 400x400 effect pick get scrn 9
			] alert "Saved to C:\painting.png"
		]
		btn "Clear" [scrn/effect/draw: copy [line] show scrn]
	]

=image rebol_tutorial/example_3.png

Here's an even more compact version of the above program:

	view layout[h1 "Paint:" s: area 700x500 feel[engage: func[f a e][
	if a = 'over[append s/effect/draw e/offset show s]if a = 'up[
	append s/effect/draw 'line]]]effect[draw[line]]b: btn "Save Image"[
	save/png %a.png to-image s alert "Saved to 'a.png'"]btn "Clear"[
	s/effect/draw: copy [line] show s]]

=image rebol_tutorial/example_4.png

And just to take that example to the limit, here's the smallest painting program you'll ever see, in any programming language:

	view layout[s: area feel[engage: func[f a e][if a = 'over[append 
	s/effect/draw e/offset show s]]]effect[draw[line]]]

=image rebol_tutorial/example_5.png

Here's a short program that uses Rebol's parsing and networking abilities to display the current WAN and LAN IP addresses of your computer:

	parse read http://whatsmyip.org/ [thru <title> copy my-ip to </title>]
	parse my-ip [thru "Your IP is " copy stripped-ip to end]
	alert to-string rejoin ["WAN: " stripped-ip " ---- LAN: "
    	read join dns:// read dns://]

=image rebol_tutorial/example_6.png

Here's a little email client you can use to read and send emails to/from any pop/smtp server (edit the first line so it contains your personal email account info):

	set-net [user:pass@website.com smtp.website.com pop.website.com]
	view layout[
		h1 "Send:" a: field "user@website.com" s: field "Subject" b: area
		btn "Send"[
			send/subject to-email a/text b/text s/text alert "Sent"
		]
		h1 "Read:" m: field "pop://user:pass@website.com"
		btn "Read"[editor read to-url m/text]
	]

=image rebol_tutorial/example_7.png

Try pasting those examples into the Rebol interpreter to see what just a little Rebol code can do (those programs take up a total of less than 1 printed page of code).  Before the end of this tutorial you'll know exactly how they all work, and much more...



===First Code Examples - Creating a GUI Window

Now for some code!  Computer programs typically use Graphical User Interfaces ("GUI"s) to get data from the user and to display data to the user.  GUIs work intuitively, and modern computer users are familiar with them.  They contain clickable buttons, text entry fields, menus, images, and other "widgets" that allow the user to interact with the computer.  Windows programs are GUIs.  Web pages are also GUIs.  Users click buttons with the mouse pointer to perform actions, select settings from menus, type text data into fields, etc.  Most modern programming languages include some facility to build graphic interfaces that can be used to interact with the user.  Rebol makes GUI creation easier than any other language.  To create a simple GUI window, just type the following line into the Rebol interpreter, and press [ENTER].  Notice the "view layout" words in the examples below - you'll use them every time you create a GUI interface in Rebol:

	view layout/size [] 400x300

=image rebol_tutorial/example_8.png

That line of code creates a window 400 pixels across and 300 pixels down (pixels are dots on the computer screen).  It doesn't do anything yet, but the GUI window can be moved around the screen, minimized and closed (with the "X" in the upper right hand corner), just like any other Windows program.  In other programming languages, just creating a window like that can take several pages of code and lots of preliminary understanding.  Rebol makes it easy.

To add a button to the above GUI, type the following code.  Notice that the word "button" has been added between the brackets:

	view layout/size [button] 400x300

=image rebol_tutorial/example_9.png

Now the GUI has a generic blue button that you can click with the mouse.  To add some text to the button, type the following code.  Notice that the text "Click Me" has been added after the button:

	view layout/size [button "Click Me"] 400x300

=image rebol_tutorial/example_10.png

To make the button do something, type the following code, and then click the GUI button with your mouse pointer.  Notice that the text [alert "Clicked!"] has been added after the button text:

	view layout/size [button "Click Me" [alert "Clicked!"]] 400x300

=image rebol_tutorial/example_11.png

Now when you click the button in your GUI, the computer responds by alerting you with the message "Clicked!".  To make the program do something a bit more interactive, type the following, and then click the GUI button once again.  Notice the "data: request-text" addition at the beginning of the line.  That code requests some text from the user and assigns it to the word "data", so it can be referred to and used in the program:

	data: request-text view layout/size [
		button "Click Me" [alert data]] 400x300

=image rebol_tutorial/example_12a.png
=image rebol_tutorial/example_10.png
=image rebol_tutorial/example_12.png

The code above is split onto two lines so that it fits within the width of this web page, but it can be typed into the Rebol interpreter as a single line.  That one line is all it takes to create a program which gets some data from the user, creates a graphic user interface that waits for user interaction, and does something with the input data (displays it in a little dialog box).  

Next, we'll save some data to your computer's hard drive.  Type in the following code, and click "yes" if the Rebol interpreter asks for your permission to write to the hard drive.  Notice the "write %/c/data.txt data" added to the end of the line.  That code writes the data collected from the user, to a file on the C: drive called "data.txt"

	data: request-text view layout/size [
		button "Click Me" [alert data]] 400x300 write %/c/data.txt data

If you look on your computer's C: drive after closing the GUI, you'll see that there now exists a text file (C:\data.txt) containing the text you typed into the program.  (If you're working in an operating system other than Windows, you'll need to change the "c" character in the above line to refer to a root directory on your hard drive).

With that one line of code, you've got a working program that actually does something useful.  It gets, displays, and saves some data from a user, using familiar GUI interactions.  You could adjust it to store phone numbers, usernames/passwords, or any other useful information.  It's easy - and things only get more interesting from there! 

Rebol is great at dealing with all types of common data - not just text.  You can easily display photos and other graphics in your GUIs, play sounds, display web pages, etc.  And it's just as good at dealing with data transferred across networks and the Internet.  Here's some code that downloads an image from a web server and displays it in a GUI - notice the "view layout" words again:

	view layout [image load http://rebol.com/view/bay.jpg]

=image rebol_tutorial/example_14.png

The word "image" inside the brackets displays a picture in the GUI.  The word "load" downloads the image to be displayed.  

Rebol allows many built-in effects to be applied to images.  Notice the "effect [effect type]" code in the following examples:

	view layout [image load http://rebol.com/view/bay.jpg effect [Grayscale]]
	view layout [image load http://rebol.com/view/bay.jpg effect [Emboss]]
	view layout [image load http://rebol.com/view/bay.jpg effect [Flip 1x1]]

=image rebol_tutorial/example_15.png
=image rebol_tutorial/example_16.png
=image rebol_tutorial/example_17.png

Here's how you can read that same file from the web server and save it to your C: drive.  The "/binary" modifier is used whenever reading or writing binary (non-text) data:

	write/binary %/c/bay.jpg read/binary http://rebol.com/view/bay.jpg

Now you can read the image directly from your hard drive and display it in a GUI.  Just type in the code below.  Notice the "view layout" words again, and this time in between the brackets, the file is loaded from the local C: drive:

	view layout [image load %/c/bay.jpg]

=image rebol_tutorial/example_14.png

It's important to note here that you could also use that image in other graphic applications on your computer - including other programs that aren't written in Rebol.  You could, for example, open that file in an image editing program, or attach it to an email and send it to a friend.  It's critical to understand that data can be interoperable between languages, programming tools, operating systems, and other connected domains.  As you learn more about programming, you may find specialized tools that accomplish certain programming goals easily and effectively.  You can trade data between various tools by just saving it to a shared storage medium.  In that way, all programming languages and tools can be used together to accomplish complex goals.  That's a key concept to keep in mind when learning about general programming.  Very little technology is truly new.  The basis for most computing applications has been around for several decades (hard drives for storing files within directory structures, hardware for inputting and outputting text, graphic, audio, and other data, networks for transferring data between machines, etc.).  Those base components haven't changed too dramatically.  They've simply improved in speed and capacity - and the software tools used to work with them have evolved to allow programmers to do high level things more quickly and easily.  An adept programmer writing an application to deal with large amounts of text data shared across the Internet, however, will realize that the data all still resides in files on a hard drive somewhere, in a machine connected to a network, and that data can be accessed by various old fashioned programming means - even if it was created and put there by a program using cutting edge database technology, displayed in a flashy new graphic interface, and transferred over broadband wireless connections.  It's still just text data saved in a file somewhere, and it can be manipulated via virtually any language that provides access to networks and text files!  Keep that in mind as your exposure to various programming tools expands...



===More Examples

Below are some more short examples of reading, writing, and manipulating data on the hard drive and Internet, and interacting with the user.  Type them into the Rebol interpreter to familiarize yourself with a bit more of the Rebol language.  

Before going on, you may want to configure Rebol to open straight to the interpreter console.  Click the "User" menu on the Rebol Viewtop, and uncheck "Open Desktop On Startup".  That'll save you the trouble of clicking the "Console" button every time you start Rebol.  

=image rebol_tutorial/viewtop.png
=image rebol_tutorial/viewtop2.png

The following line displays the current day and time in the interpreter:

	print now

=image rebol_tutorial/example_19.png

The word "print" displays text data directly in the Rebol interpreter.  The word "now" refers to the current date and time.  

The following line performs some mathematical computations, and displays the result:

	print (10 + 12) / 2

=image rebol_tutorial/example_20.png

The following code asks the user to choose a file on the hard drive:

	request-file

=image rebol_tutorial/example_21.png

The code below allows the user to choose a color:

	request-color 

=image rebol_tutorial/example_22.png

The following code asks the user a yes-no question:

	request "Are you having fun yet?"

=image rebol_tutorial/example_23.png

Here's a nice way to let the user select a date:

	request-date

=image rebol_tutorial/example_24.png

The code below requests a username and password from the user:

	request-pass

=image rebol_tutorial/example_25.png

The following code opens your computer's web browser and displays the indicated web page:

	browse http://rebol.com

=image rebol_tutorial/rebol_home.png

The following code launches Rebol's built in text editor, and opens the file c:\test.txt

	editor %/c/test.txt

=image rebol_tutorial/example_26.png

Notice the percent character ("%") in the example above.  In Rebol, that character is used to represent all file labels.  Because Rebol can be used on many operating systems, and because those operating systems all use different syntax formats to refer to drives, paths, etc., Rebol uses the universal format:  %/drive/path/path/.../file.ext .  For example, "%/c/windows/notepad.exe" refers to "C:\Windows\Notepad.exe" in Windows.  Rebol converts that syntax to the appropriate operating system format, so that your code can be written once and used on every operating system, without alteration.  

The following line sends an email to user@website.com, containing the text "Hi user.  How are you doing?".  Try replacing the username and website with your own email address (If you downloaded and ran Rebol without actually installing it, you'll need to run the configuration wizard in order to send the email.  To do that, type "install" and follow the instructions.):

	send user@website.com "Hi user.  How are you doing?"

The line below sends a web page to user:

	send user@website.com read http://www.rebol.com

The code below displays the contents of user's email inbox:

	print read pop://user:pass@website.com

The following line uploads a single file to user's web server using ftp:

	write/binary ftp://user:pass@website.com read/binary %file

The following uploads an entire directory of files to user's web server:

	foreach file load %./ [if not dir? file [write/binary join
		ftp://user:pass@website.com/ file read/binary file]]

It all looks a lot like spoken English, doesn't it?  You just need to type things in correctly, and the computer does what you want.  The more of the language you learn, the more you'll be able to make the computer do your bidding...  Easy, right?


===A Quick Comparison

To provide a quick idea of how much easier Rebol is than other languages, here's a short example.  The simplest code to create a basic Rebol GUI window was presented earlier:

	view layout/size [] 400x300

It works on every type of computer, in exactly the same way.

Code for the same simple example is presented below in the popular programming language "C++".  It does the exact same thing as the Rebol one-liner above, except it only works in Microsoft Windows.  If you want to do the same thing on a Macintosh computer, you need to memorize a completely different page of C++ code.  The same is true for Unix, Linux, Beos, or any other operating system.  You have to learn enormous chunks of code to do very simple things, and those chunks of code are different for every type of computer.  Furthermore, you typically need to spend a semester's worth of time learning very basic things about coding format and fundamentals about how a computer thinks before you even begin to tackle useful basics like the code below:

	#include <windows.h>

	/*  Declare Windows procedure  */
	LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

	/*  Make the class name into a global variable  */
	char szClassName[ ] = "C_Example";

	int WINAPI
	WinMain (HINSTANCE hThisInstance,
	         HINSTANCE hPrevInstance,
	         LPSTR lpszArgument,
	         int nFunsterStil)

	{
	    HWND hwnd;               
		/* This is the handle for our window */
	    MSG messages;            
		/* Here messages to the application are saved */
	    WNDCLASSEX wincl;        
		/* Data structure for the windowclass */

	    /* The Window structure */
	    wincl.hInstance = hThisInstance;
	    wincl.lpszClassName = szClassName;
	    wincl.lpfnWndProc = WindowProcedure;      
		/* This function is called by windows */
	    wincl.style = CS_DBLCLKS;                 
		/* Catch double-clicks */
	    wincl.cbSize = sizeof (WNDCLASSEX);

	    /* Use default icon and mouse-pointer */
	    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
	    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
	    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
	    wincl.lpszMenuName = NULL;                 
		/* No menu */
	    wincl.cbClsExtra = 0;                      
		/* No extra bytes after the window class */
	    wincl.cbWndExtra = 0;                      
		/* structure or the window instance */
	    /* Use Windows's default color as window background */
	    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

	    /* Register window class. If it fails quit the program */
	    if (!RegisterClassEx (&wincl))
	        return 0;

	    /* The class is registered, let's create the program*/
	    hwnd = CreateWindowEx (
	           0,                   
				/* Extended possibilites for variation */
	           szClassName,         
				/* Classname */
	           "C_Example",       
				/* Title Text */
	           WS_OVERLAPPEDWINDOW, 
				/* default window */
	           CW_USEDEFAULT,       
				/* Windows decides the position */
	           CW_USEDEFAULT,       
				/* where the window ends up on the screen */
	           400,                 
				/* The programs width */
	           300,                 
				/* and height in pixels */
	           HWND_DESKTOP,        
				/* The window is a child-window to desktop */
	           NULL,                
				/* No menu */
	           hThisInstance,       
				/* Program Instance handler */
	           NULL                
				/* No Window Creation data */
	           );

	    /* Make the window visible on the screen */
	    ShowWindow (hwnd, nFunsterStil);

	    /* Run the message loop. 
			It will run until GetMessage() returns 0 */
	    while (GetMessage (&messages, NULL, 0, 0))
	    {
	        /* Translate virtual-key messages 
				into character messages */
	        TranslateMessage(&messages);
	        /* Send message to WindowProcedure */
	        DispatchMessage(&messages);
	    }

	    /* The program return-value is 0 - 
			The value that PostQuitMessage() gave */
	    return messages.wParam;
	}
	
	/*  This function is called by the Windows 
			function DispatchMessage()  */

	LRESULT CALLBACK
	WindowProcedure (HWND hwnd, UINT message, 
		WPARAM wParam, LPARAM lParam)
	{
	    switch (message)                  
		/* handle the messages */
	    {
	        case WM_DESTROY:
	            PostQuitMessage (0);       
					/* send a WM_QUIT to the message queue */
	            break;
	        default:                      
				/* for messages that we don't deal with */
	            return DefWindowProc (hwnd, message, 
					wParam, lParam);
	    }

	    return 0;
	}

Yuck.  Back to Rebol...  


===Understanding Variables and Functions

All programming languages make use of two important features:  variables and functions.  Functions are commands that tell the computer to do something.  They're similar to verbs in spoken language.  You've used some functions already in the earlier examples.  For example, "print" is a function - it can be thought of as a verb that represents some action. 

Variables are names given to data to be input, stored, manipulated, displayed, etc.  They're similar to nouns in spoken language.  For example, "now" can be thought of as a variable.  It's a noun referring to a piece of data (the current time).

Functions and variables must be used in a syntax defined by the programming language you're using.  No existing computer language allows you to speak freely as in the natural language sentence "show the user some photos of their children".  You have to write the commands in a more specific way - using a syntax that invariably involves variables and functions.  As a programmer, to get the computer to "show the user a photo", you'd: 

# assign the picture filename to a variable (noun)

# use a function (verb) to display the image referred to by the variable

# assign the function action to a button or some other graphic widget in a GUI (which is itself created by arranging variables and functions in a specific order)

Rebol does many things in as "high level" a way as can be expected - as close to speaking to the computer in human English as is currently possible, but it still requires specific syntax and structure.  All contemporary computer languages do.  If you want to learn how to program in any language, you'll need to learn how to use variables and functions in the grammar the language defines.  That's at the core of all programming.

In Rebol, variables and functions are assigned to "words".


===Rebol Words

If you want to give a label to some data - so that it can be used in your program - you must assign it a word.  The same is true for actions performed by functions.  There are many function words built into Rebol that represent common actions ("print", "alert", "request-date", etc).  You've seen a number of those built-in words already in the earlier examples.  To create your own functions, you take previously created function words and variables, group them together in a specific order that accomplishes what you want, and assign a word to that collection of code.  Then you can refer to that group of actions and/or related data, using the word you've assigned to it. 

Learning the function words that are already defined in a programming language is a big part of learning to program.  Those words are the existing vocabulary of the language, and in order to work correctly, they typically expect some other words to follow afterwards, in a specific order and format.  The word "write", for example, writes data to a storage device (hard drive, flash drive, web server, etc).  It's a function that performs an action, and expects the name of a file to be written to the hard drive, and then the name of the data to write to that file.  It's gotta be written in that order:

	write %/c/text.txt "This is some random text"

If you type the above line in the wrong order, it won't work:

	write "This is some random text" %/c/text.txt ; WRONG

If you type it in backwards, Rebol won't understand the syntax, and you'll receive an error.

=image rebol_tutorial/example_27.png


===Before You Get Too Far - Learn by Doing

To learn any programming language, you'll need to type in lots of code, by rote.  Be sure to manually key in the examples in this tutorial, not just to see them work, but to get used to speaking the language.  Avoid copying and pasting if you really want to learn.  At first, you'll learn to code in the same way you'd learn a new spoken language - by immersing yourself in the words and phrases of the language (even if at first you don't understand what's being said).  Repeating sentences by rote is a natural way to get a feel for how a language sounds and works.  Certain words, phrases and patterns eventually become familiar, and the language syntax becomes clear and more intuitive.  

Seeing the examples run is absolutely essential.  It helps form associations between things the computer does, and chunks of code that make those things occur.  Just reading through the code isn't enough - seeing how it executes is the key.  If you don't have time to manually type in code, at very least paste it into the interpreter.

Because programming languages require more specific syntax than spoken languages, learning the exact grammar is more important than in spoken language.  Simple examples like the ones that follow are easy to remember - just like simple phrases memorized in spoken foreign languages.  To become more fluent, however, the correct order of words, characters and other elements must be typed in exactly, in a much more specific way than components of spoken language.  The interpreter is not intelligent enough to "guess" what you intend to do, and if you get the grammar wrong (even one character), it'll interpret your code incorrectly and do something different then you want.  Sometimes, you'll get an error, and the interpreter will tell you where you got the grammar wrong in your code.  Sometimes your program just won't work correctly.  Getting intimately familiar with the syntax, from the beginning, will help you avoid those problems.


===GUI Words and Grammar - Some More Depth

As you saw in the earlier examples, the words "view layout", followed by two brackets ("[]") can be used to display a Graphic User Interface in Rebol.  You can put elements that you want to see in the GUI, inside the brackets.  Rebol contains words that display all the common graphic elements used in GUIs.  Try typing in the following code examples:

	view layout [button]

=image rebol_tutorial/example_28.png

	view layout [field]

=image rebol_tutorial/example_29.png

	view layout [text "Rebol is really pretty easy to program"]

=image rebol_tutorial/example_30.png

	view layout [text-list]

=image rebol_tutorial/example_31.png

	view layout [
		button
		field
		text "Rebol is really pretty easy to program"
		text-list
		check
	]

=image rebol_tutorial/example_32.png

Notice that the words can be separated by "white space" inside the brackets.  Extra spaces, carriage returns, and other empty characters are ignored by the interpreter.  Tab stops are traditionally used to indent the lines within brackets, but they're not required.

More descriptive characteristics about the graphic elements can be included directly after each of their respective words.  Such modifiers are called "facets" in Rebol, and they allow you to adjust all characteristics of every type of graphic widget (size, color, displayed text), etc.  Try typing in the code below - it's the same as the above code, with some additional facet characteristics:

	view layout [
		button red "Click Me"
		field "Enter some text here"
		text "Rebol is really pretty easy to program" purple
		text-list 400x300 "line 1" "line 2" "another line"
		check yellow
	]

=image rebol_tutorial/example_33.png


---Actions

IMPORTANT:  If you want a graphic element to perform an action, just put the action word(s) in brackets after it.  When the GUI element is clicked with the mouse or otherwise activated, the action will be performed.  Type in the following code to see how it works:

	view layout [button [alert "You clicked the button."] ]

=image rebol_tutorial/example_34.png
=image rebol_tutorial/clicked.png

	view layout [button red "Click Me" [alert "You clicked the red button."]]

=image rebol_tutorial/example_35.png
=image rebol_tutorial/example_35b.png

	view layout [
		text "Some action examples.  Try using each widget:"
		button red "Click Me" [alert "You clicked the red button."]
		field 400 "Type some text here, then press [Enter] on your keyboard."
			[alert value]
		text-list 400x300 "Select this line" "Then this line" "Now this line"
			[alert value]
		check yellow [alert "You clicked the yellow check box."]
		button "Quit" [quit]	
	]

=image rebol_tutorial/example_36a.png
=image rebol_tutorial/example_36b.png
=image rebol_tutorial/example_36c.png
=image rebol_tutorial/example_36d.png
=image rebol_tutorial/example_36e.png
=image rebol_tutorial/example_36f.png

Notice how the word "value" refers to the selected item in the text-list, and to the text contained in the text input field.

Alternate actions (i.e., those triggered by a right click of the mouse) can be included for any graphic widget.  Just enclose them in a second block, surrounded by brackets:

	view layout [button [alert "left click"] [alert "right click"]]

Here are some other GUI elements used in the Rebol language:

	view layout [
		backcolor white
		h1 "More GUI Examples:"
	    box red 500x2
		bar: progress
		slider 200x16 [bar/data: value show bar]
		area "Type here"
		drop-down
		across 
	    toggle "Click" "Here" [print value]
	    rotary "Click" "Again" "And Again" [print value]
	    choice "Choose" "Item 1" "Item 2" "Item 3" [print value]
	    radio radio radio
	    led
	    arrow
		return
	    text "Normal"
	    text "Bold" bold
	    text "Italic" italic
	    text "Underline" underline
	    text "Bold italic underline" bold italic underline
	    text "Serif style text" font-name font-serif
	    text "Spaced text" font [space: 5x0]
		return
	    h1 "Heading 1"
	    h2 "Heading 2"
	    h3 "Heading 3"
	    h4 "Heading 4"
	    tt "Typewriter text"
	    code "Code text"
		below
	    text "Big" font-size 32
	    title "Centered title" 200
		across
	    vtext "Normal"
	    vtext "Bold" bold
	    vtext "Italic" italic
	    vtext "Underline" underline
	    vtext "Bold italic underline" bold italic underline
	    vtext "Serif style text" font-name font-serif
	    vtext "Spaced text" font [space: 5x0]
		return
	    vh1 "Video Heading 1"
	    vh2 "Video Heading 2"
	    vh3 "Video Heading 3"
	    vh4 "Video Heading 3"
	    label "Label"
		below
	    vtext "Big" font-size 32
	    banner "Banner" 200
	] 

=image rebol_tutorial/example_38.png


The examples above demonstrate how Rebol creates GUIs that can be used to input and display data in a variety of ways that are familiar to users.  They can be customized using facets, and they can perform actions.  That's a big part of building a typical modern computer program!  For more information about GUI design, see <a href="http://rebol.com/docs/easy-vid.html" target=_blank>http://rebol.com/docs/easy-vid.html</a> and <a href="http://rebol.com/docs/view-guide.html" target=_blank>http://rebol.com/docs/view-guide.html</a>.  To make your GUIs do useful things, you need to learn more about making the language manipulate data in useful ways...


===Creating Your Own Variable Words

Just like spoken languages, programming languages are malleable and expressive.  There's never only one way to write a given program.  You need to choose and use your own words, and you need to organize them so they have the meaning and function you intend.  Just like in spoken language, you have to think about what you're trying to say, and organize your thought process to say it.  In Rebol you have the additional benefit of being able to create your own language words to express actions and to label data.

Words are created and assigned to variables and functions in Rebol by the use of the colon (":") character.  You can use any word you want to refer to any specific data or action(s).  For example, If you want to use the word "picture" to refer to an image file on the Internet, you could do the following:

	picture: load http://rebol.com/view/bay.jpg

The above line creates a variable (label) that can be used in your program anywhere you want to read and use the file located at http://rebol.com/view/bay.jpg .  The built-in Rebol word "load" does the actual work of going out to the web site address and collecting the image data.

Now you can use the word "picture" to refer to the above image.  Display it in a GUI using the following code:

	view layout [image picture]

=image rebol_tutorial/bay.png

The words "view", "layout", and "image" are built into Rebol, and the word "picture" is now just as valid, because it's been defined to the interpreter.

Because the word "picture" is _variable_, you can also redefine and _change_ the data referred to by it:

	picture: load http://rebol.com/view/demos/palms.jpg

Now, when you use the word "picture" in your program, it refers to a different file at a different Internet location.  Writing the same GUI code now displays that different photo:

	view layout [image picture]

=image rebol_tutorial/palms.png

You can also make the word "picture" refer to a file on your hard drive, or anywhere else you'd like:

	picture: load %/c/bay.jpg

Here are some more examples of creating and using variable words.  Type them into the Rebol interpreter to see how they work, and to understand how assigned words can take the place of _any_ data.  NOTE:  anything after a semicolon in Rebol code is ignored by the interpreter.  It's used to include human readable comments in the code.  You don't need to type any of the comments into the interpreter:

	acolor: "blue"

	alert acolor ; alerts you with a dialog box displaying the text "blue"

=image rebol_tutorial/blue1.png
=image rebol_tutorial/blue.png

	print acolor ; prints the word "blue" in the Rebol interpreter

=image rebol_tutorial/blue2.png

	anumber: 12

	print anumber ; prints the number 12 in the interpreter

	computation: (10 + 12) / 2

	print computation ; prints the answer

	filename: request-file

	print filename ; prints the name of the user chosen file

=image rebol_tutorial/filename1.png
=image rebol_tutorial/filename2.png
=image rebol_tutorial/filename3.png

	chosen-color: request-color

	print chosen-color

	answer: request "Are you having fun yet?"

	print answer

	pick-a-date: request-date

	print pick-a-date

	userpass: request-pass

	print userpass

	webpage: http://rebol.com

	browse webpage

	file: %./test.txt

	editor file 
	; launches Rebol's built in text editor and opens the filename 
	; assigned above

	email-address: user@webpage.com

	message:  "Hi Luke.  How are you doing?"

	send email-address message


The key is to be aware of the colon character (":").  It's the thing that tells Rebol to create a new variable word and assign it to some value that'll be used later.


===Blocks and Series

In Rebol, you can use words to represent multiple pieces of data grouped together, collections of other word variables, and other programming elements.  Just surround the data in brackets.  Type in the code below to see how it works:

	somecolors: ["red" "yellow" "blue" "black"]
	; "somecolors" is now a defined word used to represent the entire 
	; data block enclosed in brackets.
	
	print somecolors

=image rebol_tutorial/somecolors.png

In Rebol, collections like this are called "blocks", and they're very important.  In fact, they're the primary organizational unit in Rebol and the main structure in which data is stored in the language.  That's very important - remember, programming is all about inputting, storing, retrieving and otherwise manipulating data.  In Rebol, ANY type of data can be assigned a word, and blocks can contain any combination of words and raw data.  Blocks provide a simple way of managing every conceivable type of data, and that's at the heart of all programming.  Learning to work with blocks is therefore a fundamental part of learning Rebol.

You've already used blocks - brackets were snuck in earlier to display GUI elements and to perform actions on them.  Any group of words surrounded by brackets forms a block, and you can assign a word to refer to that block.  Words referring to complex blocks of data can be likewise grouped together into other blocks simply by surrounding the words with brackets.  This makes dealing with very complex and useful data structures very easy in Rebol.

Type in the code below to see how an entire GUI layout can be built and represented by using one word label:

	gui-layout: [button field text-list]

"gui-layout" now refers to that entire block of code.  You can display it using the standard "view layout" syntax:

	view layout gui-layout

=image rebol_tutorial/gui_layout.png

Blocks of data can also be spread out over several lines, and can be separated by extra white space.  Just surround the elements with brackets:

	gui-layout2: [
		button red "Click Me"
		field "Enter some text here."
		text "Rebol is really pretty easy to program." purple
		text-list 400x300 "line 1" "line 2" "another line"
		check yellow
	]

Now display it in a GUI:

	view layout gui-layout2 

=image rebol_tutorial/gui_layout2.png

Layout blocks much bigger than that can be stored in a single word!


NOTE:  It's standard practice to indent compound blocks with consecutive tab stops.  Starting and ending brackets are typically placed at the same indentation level.  This is conventional in most programming languages, because it makes complex code easier to read.  For example, the compound block below:

	[blue red green [1 2 4 [jan feb march [monday tuesday wednesday]]]]

can be written a bit more clearly as:

	[blue red green 
		[1 2 4 
			[jan feb march
				[monday tuesday wednesday]
			]
		]
	]

Indentation is not required, but it's very helpful when dealing with more intricate programming structures.


Here's a simple data table example, containing schedule information within a block:

	schedule: [
		["John Smith" "Monday" "3:00 pm"]
		["Dave Jones" "Tuesday" "11:00 am"]
		["Janet Duffy" "Wednesday" "4:45 pm"]
	]

You can display the above block in a GUI, using the built-in Rebol word "list".  Notice the "data schedule" code in the last line below - it inserts the entire schedule block defined above as data to be displayed in the list widget (the line "across text 150 text 150 text 100" is just syntax expected by the list widget to define its graphic layout):

	view layout [
		vh2 "This Week's Appointments:"
		list 600x400 [
			across text 150 text 150 text 100
		] data schedule
	] 

=image rebol_tutorial/example_40a.png

The beginnings of a graphical database application, in several lines of code...  Not tough at all!

Using blocks to store collections of data is similar to using variable words to store single values.  Once a word is assigned to represent a block of data, that word can be used in place of the actual data, to represent it in code.  Blocks are simply able to respresent larger collections/varieties of data.  You don't have to worry about how the computer stores or works with the data in memory.  You can simply label the data and use it in it's natural human-understandable form, using a single consistent bracket syntax to deliniate each group of values.  That's very powerful, and it's much easier than in other programming languages.  In most other languages, formatting and using data in code requires quiet a bit more preparation, management, and a variety of code structures to handle different types of data.

Many of Rebol's built in words help you manipulate data stored in blocks.  Type in the following code to see how the "sort" word works:

	somecolors: ["red" "yellow" "blue" "black"] 

	sortedcolors: sort somecolors 

=image rebol_tutorial/sortedcolors.png

"Sort" is a built in function word that alphabetically (/ordinally) sorts the elements of a given block.  The line above creates the newly defined word "sortedcolors", and assigns it to the sorted block of words contained in "somecolors".  

	print sortedcolors 
	; This code displays the sorted block of text. 

	print first sortedcolors 
	; "first" is another built-in word.  
	; It selects the first item in a given block.

	find somecolors "red" 
	; "find" is a built in word that searches for data within a block.

=image rebol_tutorial/sortedcolors2.png

You can easily save blocks of data to your hard drive, read them from a web server, and perform other file operations with them. 

	write %/c/colors.txt somecolors 
	; writes the entire block of text represented by "somecolors" 
	; to a text file called colors.txt on the C: drive.


Here's an interesting twist, demonstrating how Rebol can easily mix datatypes within a block:

	an-image: load http://rebol.com/view/bay.jpg
	; downloads an image from the Internet and assigns the 
	; word "an-image" to it.

	append sortedcolors an-image 
	; "append" adds the downloaded image to the end of the data block 
	; currently containing the simple text words defined above.  
	; Now the block contains both text and binary image data, 
	; all assigned to a single word - not a problem in Rebol!

Now you can select items from that new block:
	
	print first sortedcolors 
	; prints the first item in the data block - the text "black".

	view layout [image fifth sortedcolors] 
	; displays the fifth item in the data block - 
	; the image downloaded above - in a simple GUI.

That should get you thinking a bit.  You can store images, sounds, text, complex data structures, and anything else you want in a block, all with equal ease.  That's a complex ability which requires some hard core learning in most programming languages.


Here's some more notation to be familiar with when working with sequential data in blocks.  That type of data is called a "series" in Rebol.  All blocks of data are actually series in Rebol, and can be treated as sequential lists by default:
	
	view layout [image sortedcolors/5] 
	; "sortedcolors/5" is another way to refer to the fifth item 
	; in a data block.

The following example puts the above notation to work in a useful way:
	
	length-of-block: length? sortedcolors 
	; the built in word "length?" returns the number of items 
	; in the block (5 in this case).

	view layout compose [image sortedcolors/(length-of-block)]

The word "compose" allows variables in parentheses to be evaluated and inserted as if they'd been typed explicitly into the code of the program.  In the example above, the code reads as if sortedcolors/5 had been typed in manually.  Another way to use variable values explicity is with the format below:

	view layout [image sortedcolors/:length-of-block]

The colon symbol in front of a variable does the exact same thing as the compose function and parentheses above.  You'll see both formats in Rebol code, so it's good to know both.

The following examples demonstrate additional words used to traverse sequential series of data within blocks:

	insert sortedcolors "mauve" 
	; adds the word "mauve" to the sortedcolors block of data.

	remove sortedcolors
	; removes the first item from the block.

	head sortedcolors 
	; sets a position marker at the beginning of the data block

	next sortedcolors 
	; sets a position marker at the next item in the data block

	last sortedcolors 
	; sets a position marker at the last item in the data block

	back sortedcolors 
	; sets a position marker at the previous item in the data block

	tail sortedcolors 
	; sets a position marker after the last item in the data block

=image rebol_tutorial/blocks.png

The fact that you can mix together all types of data within a block, refer to parts of blocks by name, and access/alter data within them using built-in functions, is very powerful and useful.  Blocks and variable words assigned to blocks help you store, manipulate, and refer to all the data you'll deal with in your programs.  Doing so is similar to assigning nouns to groups of people, places, and things in spoken language.  Within those groups, smaller groups and individual items can be named, ordered and otherwise organized - in the same way that complex database applications allow you to store and work with all types of information.  The possibilities of dealing with data in that way are endless.


===Function Words

It's easy to define your own function words (actions), once you know some of the built-in vocabulary of Rebol.  Creating new functions is comparable to creating your own verb words in a spoken language.  Just be careful not to unintentionally use words that are already defined in the Rebol language, or in your current program.  That would change the meaning of the existing word.  For example, you could accidentally change the meaning of the word "write" to refer to a picture on your hard drive by typing the following:

	write: read %/c/bay.jpg   
	; *** DON'T TYPE THAT IN - it'll change the meaning of the word 
	; "write" in the Rebol interpreter (only for the current session).  
	; It's an example of what not to do. ***

You can protect all of the built-in Rebol words by typing in "protect-system".  That'll alert you with an error and disallow any attempt to redefine native Rebol words.  You still must be careful not to accidentally redefine words that you've created.  Word definitions only last for the current session, so if you make a mess, all you need to do is restart the Rebol interpreter.

Here's a really important concept:  (drum role) ... In Rebol, you can use single words to represent entire blocks of actions (i.e., collections of function words grouped together).  In fact, blocks like that form the primary code sections that make up programs in the Rebol language.  Here's an example of several function words grouped together into a block (i.e., enclosed in brackets), and assigned a new function word:

	some-actions: [
		alert "Here is one action." 
		print "Here's a second action."
		write %/c/anotheraction.txt "Here's a third action."
	]

The above code has created a kind of super-verb that refers to several actions.  You can perform the actions contained in any block using the "do" function word.  To perform all the actions in the above code block, just type:

	do some-actions

You can also include the word "does" right inside a word definition - that'll make the actions (function words) contained in the block perform automatically every time the new word is used in Rebol:

	more-actions: does [
		alert "4" 
		alert "5"
		alert "6"
	]

In fact, by including the "does" command right in the word definition, you've just created a new function (or "subroutine") that can be used like any other built-in action word in Rebol!  You can now talk to the interpreter using that word, and it understands what you mean for it to do.  After you've entered the code above, try typing the word "more-actions" into the Rebol interpreter:

	more-actions

It's taken on a life of its own!  As with variable words, the key is to be aware of the colon character - that's the symbol that actually creates the new function word.  


Here's an example of a useful little action word to clear the command line screen in the Rebol interpreter.

	cls: does [prin "^(1B)[J"]

The native way to clear the Rebol interpreter's command screen is by typing "prin "^(1B)[J".  That's kind of awkward to type, and even tougher to remember.  Instead, we can assign the word "cls" to perform the action - just like in old Basic languages.  Now just type:

	cls

and the screen clears - that's much easier.

=image rebol_tutorial/cls1.png
=image rebol_tutorial/cls2.png

Here's a little program that creates the new action word "send-email".  It provides a simple text requestor interface for users to send email:

	send-email: does [
		email-address: to-email request-text/title/default 
			"Enter an email address:" "user@webpage.com"
			; the above line creates the new variable word "email-address"
			; "email-address" is assigned the value of the 
			; text input using the built in word "request-text"
			; the "title" and "default" refinements customize the 
			; info displayed in the text requestor.
		message: request-text
			; the above line creates the new variable word "message" 
			; and assigns it to some requested text
		send email-address message
			; the above line sends the user-provided message to the 
			; email address given earlier
		alert "Your message has been sent."
	]

	send-email ; do the routine above
	send-email ; do it again to send another message to someone else

=image rebol_tutorial/send-email1.png
=image rebol_tutorial/send-email2.png
=image rebol_tutorial/send-email3.png
=image rebol_tutorial/send-email4.png
	
The above process is VERY important.  It's the basis of how you perform more complex and useful actions in Rebol.  Blocks of actions and blocks of data form the basis of how you program in Rebol.  And performing actions upon data is what you'll do to complete all your programming tasks.  In Rebol you just group bits of data together into blocks, and assign a name to refer to it.  You also group functions together into blocks to perform actions upon the data, and assign a name to refer to those actions.  You can even combine complete groups of data and functions into blocks that can be assigned unique word identifiers that perform complete programmatic tasks for you:  store and manipulate data all with a single word that you define!  That allows you to create your own unique language in any program you write, using words that you define.  You could create, for example, your own language that reads something like "email tom at noon with the main news page from yahoo.com".  Those words aren't built into Rebol, but they can be assigned the appropriate action and data meanings to make that sentence a completely functional piece of code that the computer understands!  (It would still need to be syntactically correct and exact).  Building word meanings in that way is called building a "dialect" in Rebol, and it's one of the ways Rebol is different from other languages.  You could conceivably write a dialect for programming robotic devices that reads "Vacuum the floor. Move in concentric circles around the perimeter".  You could write a dialect for doctors that reads "print prescription for John Smith" (Ponder for a moment the possibilities for that type of natural language capability and flexibility...).  Translating the existing Rebol language to any other language is as simple as assigning built-in function/data words to words in the desired language (for example, translating the print function to French, Italian, and Spanish is as simple as typing "imprime: stampa: impresion: :print").  Other languages focus on different ways of grouping and managing functions and variables.  Typically, other languages use more cryptic ways of doing things.  For example, blocks that contain both fully encapsulated functions and variables are called "objects".  You'll see more about "object-oriented" programming as you study Rebol and other languages in depth...


===Several Ways to Create Functions in Rebol - Passing Variables

There are several built-in words in the Rebol language that allow you to create more complex function words.  To create simple functions, you can use the "does" command, as described above.  But some functions are more complicated than that.  They perform work upon _variable_ data.  For example, the following simple function displays the square root of 4.  That's all it can do:

	sqr-four:  does [print square-root 4]

This type of function is similar to what you saw in the previous section.  The word "sqr-four" is now assigned to the action "print square-root 4" (the word "square-root" is built into Rebol).  After entering the above line in the Rebol interpreter, type:

	sqr-four

It'll give you the expected result of 2.  

=image rebol_tutorial/sqr4.png

Say now, however, that you now want to do something using numbers other than 4...  What if you want to create a function that adds 4 to some other number, and then computes the square root of that sum?  For that to work, the other number must be changeable, and therefore must be assigned a variable name.  That variable name can then be "passed" to the function.  The built in word "func" is used to create functions to which changeable variables can be passed.  The syntax for the word "func" expects it to be followed by two blocks of code.  The first block contains the name(s) of the variables to be passed.  The second block contains the actions to be taken.  Here's how it looks:

	func [names of variables to be passed] [
		actions to be taken with those variables
	]

In the following line, a function is created in which a variable word "anumber" is named and passed.  That whole function is assigned the word "sqr-var":

	sqr-var: func [anumber] [print square-root (4 + anumber)]

Now you can use the word "sqr-var", and the Rebol interpreter knows what to do with the assigned data.  Try the following code:

	sqr-var 12 ; prints "4", the square root of 12+4 (16)
	
	sqr-var 96 ; prints "10", the square root of 96+4 (100)

=image rebol_tutorial/sqrvar.png

Printing the square root of 4+somenumber may not sound so exciting to you, but it helped to illustrate one of the most important techniques employed in all modern programming languages.  The process of passing variable parameters to functions is a fundamental part of all modern programming.  It's perhaps the single most common element in contemporary languages, and understanding how it's done is absolutely essential.  Below are some more interesting real-world examples. 

The following line creates a simple function to display images:

	display: func [filename] [view layout [image load filename]]

It accepts an image filename as the passed parameter (%somefile.jpg, %somefile.gif, %somefile.png, or %somefile.bmp), and then creates a GUI to display the image.  That set of actions is assigned to the word "display".  Simple, right?  Now you can use the word "display" like this: 

	image1: to-file request-file/title trim {
		Select an image from your hard drive:} ""
	; gets an image filename from the user

=image rebol_tutorial/lambertville1.png

	display image1
	; displays the above image using the new function word

=image rebol_tutorial/lambertville2.png

	display http://rebol.com/view/bay.jpg
	; displays the image at the above url

	display %/c/bay.jpg
	; displays an image that was saved to the
	; hard drive earlier in this tutorial

Once the word "display" is defined in your programs, you can use it as if it's a built in Rebol action word.

Here's an example that asks the user for 2 website urls, and then opens those sites in separate brower windows:

	openwebsite: func [nameofwebsite] [browse nameofwebsite] 
	; The line above creates a new function that passes a url 
	; to the built-in Rebol word "browse", to open the passed 
	; web site name in the user's default browser.  It also 
	; assigns the new function word "openwebsite" to that set
	; of actions.

	website1: request-text/title "Enter a web site URL:"
	; The line above assigns a new variable word "website1" to text 
	; returned by the built-in Rebol "request-text" function.

	website2: request-text/title "Enter another web site URL:"
	; Gets some more text and assigns the new variable word "website2"
	; to it.

	openwebsite website1
	; The line above uses the new "openwebsite" function word defined
	; above, and passes it the "website1" variable word

	openwebsite website2

	; Uses the openwebsite function again, this time passing the
	; website2 variable

In that example, the word "openwebsite" is assigned to a new function definition. "Website1" and "website2" are labels for variables passed to that function.  Below is a variation which assigns a single word to that entire process:

	display-website: does [	
		openwebsite: func [nameofwebsite] [browse nameofwebsite] 
		website: request-text/title "Enter a web site URL:"
		openwebsite website
	]

Now you can use the single word "display-website" in your programs to do that entire block of code.

	display-website

=image rebol_tutorial/openweb.png
=image rebol_tutorial/openweb2.png

Getting used to the above syntax and way of thinking is absolutely essential.  Remember, dealing with all types of data is the main thing you'll do as a programmer.  Passing variable data to functions that you create is the main way you'll perform actions upon data in all your programming.  That's the current state of programming, and it's what you'll do in virtually every programming situation.  Rebol makes it easy to deal with data, using its built in support for most common data types.  Understanding how to input, manipulate, and output that data is your main objective.  Using functions and variables as described above is a fundamental part of that process.


===Conditional Operations

Programs often need to make decisions based on user input, program states, data content, etc.  "If the user selects this option from a list, respond by executing this function".  That's a common situation.  "If a certain amount of time has passed, save data to the hard drive".  Giving the computer a variety of actions to perform, based on a variety of expected conditions, is a fundamental programming technique used in all languages.  

Mathematical operators such as = < > <> (equal, less-than, greater-than, not-equal) are typically used to perform conditional operations.  Type in the following code to see how a conditional operation works:

	if now/time > 12:00 [alert "It's after noon."]  
	; now/time is a variation, or "refinement" of the built-in 
	; function "now", that returns only the current time.

Here's a more complex example:

	daily-calories: to-integer request-text/title {How many 
		calories have you eaten today?}
	; gets some info from the user and assigns the variable word
	; "daily-calories".  The built-in "to-integer" function
	; helps make sure Rebol interprets that info as a number.
	; The "{}" characters surrounding the title text work the 
	; same way as quotes, but allow the string of text to 
	; span several lines.  Very important.

	if daily-calories > 2500 [alert "You need to stop eating now."]

=image rebol_tutorial/calories1.png
=image rebol_tutorial/calories2.png


The built-in Rebol word "either" chooses between two blocks of functions to perform, based on a conditional evaluation.  Its syntax is:

	either {condition} [
		block to perform if the condition is true
	][
		block to perform if the condition is false
	]

Here's an example:

	either now/time > 8:00am [alert "It's time to get up!"] [
		alert "You can keep on sleeping."] 

Here's a variation of the above example that allows you to set the wake up time:

	wake-up: to-time request-text/title "What time do you want to wake up?"

	either now/time > wake-up [alert "It's time to get up!"] [
		alert {You can keep on sleeping."}]

=image rebol_tutorial/get_up1.png
=image rebol_tutorial/get_up.png


The built-in Rebol word "switch" chooses between numerous functions to perform, based on conditional evaluations.  Its syntax is:

	switch/default (main value) [
		(value 1) [block to execute if value 1 = main value]
		(value 2) [block to execute if value 2 = main value]
		(value 3) [block to execute if value 3 = main value]
		; etc...
	] [default block of code to execute if none of the values match]


You can compare as many values as you want against the main value, and run a block of code for each matching value.  Here's an example:

	favorite-day:  request-text/title "What's your favorite day of the week?"

	switch/default favorite-day [
		"Monday" [alert "Monday is the worst!  Just the start of the week..."]
		"Tuesday" [alert "Tuesdays and Thursdays are both ok, I guess..."]
		"Wednesday" [alert "The hump day - the week is halfway over!"]
		"Thursday" [alert "Tuesdays and Thursdays are both ok, I guess..."]
		"Friday" [alert "Yay!  TGIF!"]
		"Saturday" [alert "Of course, the weekend!"]
		"Sunday" [alert "Of course, the weekend!"]
	] [alert "You didn't type in the name of a day!"]

=image rebol_tutorial/favorite_day1.png
=image rebol_tutorial/favorite_day2.png


"Switch" gets used a lot because programs often require numerous multiple evaluation results to choose from.  

Rebol includes a rich set of words and functional structures that help you evaluate conditions in all types of situations, and with all types of data.  Understanding how to use them is a big part of learning the language.


===Looping

Programs are often required to check conditions and to execute functions repeatedly.  In fact, in most large applications the computer often loops through many instances of repetitive work.  For example, in a reminder program, the application may need to continually check the time and date to see if the user should be reminded of a given event at the moment.  In other types of programs, the computer may need to repetitively scan through collections of data, or repeatedly request/respond to user input.  To handle such situations, "loop" structures provide programmatic ways to methodically repeat actions.

The built in word "forever" creates a simple repeating loop.  Its syntax is:

	forever [block of actions to repeat]

The following code builds a simple timer that alerts the user when one minute has passed.  It uses a forever loop to continually check the time.

	alarm-time: now/time + 60  
	; assign a variable to the time 60 seconds from now
	forever [if now/time = alarm-time [alert "60 seconds has passed" break]]

Notice the word "break" in the example above.  It exits the forever loop so that the program doesn't run on forever once the alert has been displayed.

Here's a more interactive version that uses some info provided by the user.  The heart of the program is still the loop at the end:

	event-name: request-text/title "What do you want to be reminded of?"
	; requests the name of an event from the user
	seconds: to-integer request-text/title trim {
		How many seconds do you want to wait?}
	; requests a number of seconds to wait
	alert join "it's now " [
		now/time ", and you'll be alerted in " seconds " seconds."
	]
	; display a message
	alarm-time: now/time + seconds
	; set the alarm time
	forever [
		if now/time = alarm-time [
			alert join "it's now " [
				alarm-time ", and " seconds 
				" seconds have passed.  It's time for: " event-name
				] 
		break
		]
	] 
	; the forever loop continually compares the set alarm time to
	; the current time, then displays an alert when they match.


IMPORTANT:  Notice the "join" word used in several of the lines above.  It's syntax format is:  

	join {data} [block of data items]

Using that format, it joins together variables, text, blocks and other bits of data, so that they can be printed together, displayed, and otherwise manipulated to form a single piece of data.  It's very useful!  A variation on join is "rejoin".  It takes a single block of data, and concatenates all the individual items into one piece of data.  You should be familiar with this syntax too:

	rejoin [item1 item2 item3 ...]


Now, back to loops.  Here's a simple forever loop that displays/updates the current time in a GUI.  Notice the block indentation:

	view layout [
		timer: field
		button "Start" [
			forever [
				set-face timer now/time 
				wait 1
			]
		]
	]

=image rebol_tutorial/timer.png

The above GUI contains two widgets:  a text field which is assigned the variable label "timer", and a button with the word "Start" on it.  The action block for the button contains a forever loop that loops 2 actions repeatedly (until the user closes the GUI):  the built in word "set-face" sets the text in the "timer" field to the current time, the program waits 1 second, and then loops.


Often, the data dealt with in each repetition of a loop must change.  Like most languages, Rebol includes a variety of functions and programmatic structures that allow you to loop through blocks of data and perform operations using consecutively changed values.  A common looping structure in many languages is the "for" structure.  It allows you to specify a starting value, an ending value, an incremental value, and a variable name to hold the current value, so that you can loop through consecutively changing values in a controlled way.  Here's the basic Rebol syntax for a "for" loop:

for {variable word to hold current value} {starting value} {ending value} {incremental value} [block of code to perform, which can make use of the current variable value]

Here are some simple examples.  Be sure to type them in to see how they work:

	for counter 1 10 1 [print counter] 
	; starts on 1 and counts to 10 by increments of 1

	for counter 10 1 -1 [print counter] 
	; starts on 10 and counts backwards to 1 by increments of -1

	for counter 10 100 10 [print counter] 
	; starts on 10 and counts to 100 by increments of 10

	for counter 1 5 .5 [print counter] 
	; starts on 1 and counts to 5 by increments of .5

	for timer 8:00 9:00 0:05 [print timer] 
	; starts at 8:00am and counts to 9:00am by increments of 5 minutes

	for dimes $0.00 $1.00 $0.10 [print dimes] 
	; starts at 0 cents and counts to 1 dollar by increments of a dime

	for date 1-dec-2005 25-jan-2006 8 [print date] 
	; starts at December 12, 2005 and counts to January 25, 2006 
	; and by increments of 8 days

	for alphabet #"a" #"z" 1 [prin alphabet] 
	; starts at the character a and counts to z by increments of 1 letter

=image rebol_tutorial/example_for.png

Notice that Rebol can easily loop through various types of data, forewords, backwards, and in partial increments, with a native understanding of those data types.  It can automatically increment dates, money, time, etc.  In other languages, that can be tough to do.  

Also, notice the use of the "prin" word in the last example.  It works like "print", except it doesn't automatically insert a carriage return (i.e., it prints each successively output character next to the previous one, instead of on separate lines).

Here's a "for" loop example that displays the first 5 file names in the current folder on your hard drive:

	files: read %.  
	; gets the current directory list, 
	; and assigns that block of filenames to the variable "files"

	for count 1 5 1 compose [print files/(count)] 
	; starts printing with the 1st item in the block, 
	; and counts up to the 5th item.

=image rebol_tutorial/5files.png

In the example above, "files/1" is the syntax representing the first item in the file list, "files/2" represents the second, and so on.  Notice the "compose" word used in the for loop.  In the example above, the first time though the loop, the code reads as if [print files/1] had been typed in manually, etc.


"Foreach" is another useful looping structure built into Rebol.  It lets you easily loop through a block of data.  Its syntax is formatted as follows:

foreach {variable name referring to each consecutive item in the given block} [a given block] [block of functions to be executed upon each item in the given block, using the variable name to refer to each item successively]

The example below prints the name of every file in the current directory on your hard drive:

	folder: read %. 
	; gets the current directory list, 
	; and assigns that block of filenames to the variable "folder"

	foreach file folder [print file] 
	; loops through each file name contained in the "folder" block, 
	; and prints each one consecutively.

=image rebol_tutorial/example_foreach_dir.png

The following line reads and prints each successive message in a user's email box:

	foreach mail read pop://user:pass@website.com [print mail]

"While" is other useful looping structure found in most programming languages.  It repeatedly performs a conditional evaluation, and then performs a block of code while the condition is true.  While loops are formatted as follows:

	while [condition] [
		block of functions to be executed while the condition is true
	]

Here's a simple example:

	x: 1  ; create an initial counter value 
	while [x <= 5] [
		alert to-string x 
		x: x + 1
	]

=image rebol_tutorial/while1.png
=image rebol_tutorial/while2.png
=image rebol_tutorial/while3.png
=image rebol_tutorial/while4.png
=image rebol_tutorial/while5.png

In English, that code reads "x initially equals 1.  While x is less than or equal to 5, display the value of x, and add 1 to the value of x".  (i.e., the program displays a count from 1 to 5)

NOTE:  In Rebol, the code "x: x + 1" adds 1 to the current value of x.  It's one of the most commonly used expressions in all programming, found in all sorts of looping situations.  Notice also the word "to-string".  It converts the number value in "x" to a text ("string") value.  This is required because the "alert" word in Rebol only displays string types of data.

Here are some additional "while" loop examples:

	while [not request "End the program now?"] [
		alert "Select YES to end the program."
	] 

=image rebol_tutorial/example_while.png
=image rebol_tutorial/example_while2.png

In the above example "not" reverses the value of data received from the user (i.e., yes becomes no and visa versa)

	alert "Please select today's date" while [request-date <> now/date] [
		alert join "Please select TODAY's date.  It's " [now/date]]

=image rebol_tutorial/select_today1.png
=image rebol_tutorial/select_today2.png

	while [request-pass <> ["secret" "password"]] [
		alert "The username is 'secret' and the password is 'password'"]


The example below uses several loops to alert the user to feed the cat, every 6 hours between 8am and 8pm.  It uses a for loop to increment the times to be alerted, and a forever loop to do the same thing every day, continuously.  Notice the indentation:

	forever [
		for timer 8:00 14:40:00 6:00 [
			if now/time = timer [
				alert join "It's now " now/time ".  Time to feed the cat."
			]
			; if not, continue looping until the next meal time arrives.
		]
	]



===Working With Longer Examples

Most programs are longer than the examples shown so far in this tutorial.  Below is an example of a more complex program.  It allows the user to type in the Internet address of a web cam, and display streaming video from it.  It displays the video images in a GUI that has several buttons used to control the size, location, and action on screen.  In order to avoid typing in this program every time you run it, it can be saved as a text file.  Whenever you save a Rebol program to a text file, the code must begin with the following bit of text:

	REBOL []

That text tells the Rebol interpreter that the file contains a valid Rebol program.  It must be included at the beginning of any saved Rebol program.  You should include additional documentation about the program such as title and version info in between the brackets, but it's not required.

Type in or copy/paste the complete code source below into a text editor such as Windows Notepad.  You can also use the built in Rebol text editor by typing "editor" in the Rebol interpreter.  Save the text as a file called "webcam.r" on your C:\ drive.  

(Note:  this example includes a number of Rebol words and techniques that have not yet been discussed in the tutorial.  The purpose of the example is simply to provide a longer text example that can be cut, pasted, and saved into a file.  Don't worry if you can't understand the code at this point.) 

	Rebol [Title: "Webcam Viewer"]

	; try http://www.webcam-index.com/USA/ for more webcam links.

	temp-url: "http://209.165.153.2/axis-cgi/jpg/image.cgi"
	while [true]  [
	    webcam-url: to-url request-text/title/default trim {
			Enter the web cam URL:} temp-url
	    either attempt [webcam: load webcam-url] 
	        [break]
	        [either request [trim {
				That webcam is not currently available.} trim {
				Try Again} "Quit"]
	            [temp-url: to-string webcam-url]
	            [quit]
		] 
	] 
	resize-screen: func [size] [
		webcam/size: to-pair size
		window/size: (to-pair size) + 40x72
		show window
	]
	window: layout [
		across 
		btn "Stop" [webcam/rate: none show webcam] 	
		btn "Start" [
			webcam/rate: 0 
			webcam/image: load webcam-url 
			show webcam
		]
		rotary "320x240" "640x480" "160x120" [
			resize-screen to-pair value 
		]
		btn" Exit" [quit] return
	    webcam: image load webcam-url  320x240 
		with [
			rate: 0
			feel/engage: func [face action event][
	            switch action [
	            time [face/image: load webcam-url show face]
	            ] 
	   	    ] 
		] 
	]
	view center-face window

Once you've saved the webcam.r program to C:\, you can run it in any one of a variety of ways:

# If you've already installed the Rebol interpreter in Windows, just find the C:\webcam.r file icon in your file explorer and double click it (i.e., click My Computer -> C: -> webcam.r).  The Rebol interpreter automatically executes the script.  By default, during Rebol's initial installation, all files with an ".r" extension are associated with the interpreter.  They can be clicked and run as if they're executable programs, just like ".exe" files.  This is the most common way to run Rebol scripts, and it works the same way on all major graphic operating systems.

# Type "do %/c/webcam.r" into the Rebol interpreter.

# Use the built-in editor in Rebol by typing "editor %/c/webcam.r" at the prompt.  Pressing F5 in the editor will automatically run the script. 

# Scripts can be run at the command line.  In Windows, copy rebol.exe and webcam.r to the same folder (C:\), then click Start -> Run, and type "C:\rebol.exe C:\webcam.r"  Those commands will start the Rebol interpreter and do the webcam.r code.

# At the Windows command prompt (in a Windows DOS box), type "C:\rebol.exe C:\webcam.r"

# Create a text file called webcam.bat, containing the text "C:\rebol.exe C:\webcam.r" .  Click on the webcam.bat file in Windows, and it'll run those commands.

# Use a program such as <a href="http://www.marmaladefoo.com" target=_blank>XpackerX</a> to package and distribute the program.  XpackerX allows you to wrap the Rebol interpreter and webcam.r program into a single executable file that has a clickable icon, and automatically runs both files.  That allows you to create a single file executable Windows program that can be distributed and run like any other application.  Just click it and run...

# Buy the commercial "SDK" version of Rebol, which provides the best method for packaging Rebol applications.

IMPORTANT:  To turn off the default security requestor that continually asks permission to read/write the hard drive, type "secure none" in the Rebol interpreter, and then run the program with "do {filename}".  Running "C:\rebol.exe -s {filename}" does the same thing .  The "-s" launches the Rebol interpreter without any security features turned on, making it behave like a typical Windows program.

=image rebol_tutorial/webcam_viewer2.png


---"Compiling" Rebol Programs - Distributing Packaged .EXE Files:

Being able to save, run, and distribute your programs is important.  You should become very familiar with the options above.  Using the XpackerX packager is especially useful (not just for Rebol, but for other interpreted languages too).  It saves your users from having to download, install, or run the Rebol interpreter.  By packaging the Rebol.exe interpreter, your Rebol script(s), and any supporting data file(s) into a single executable with an icon of your choice, it works like a Rebol compiler that produces regular Windows programs that look and act just like those created by other compiled languages.  To do that, you'll need to create a text file in the following format (save it as "template.xml"):

	<?xml version="1.0"?>
	<xpackerdefinition>
		<general>
			<!--shown in taskbar -->
			<appname>your_program_name</appname>
			<exepath>your_program_name.exe</exepath>
			<showextractioninfo>false</showextractioninfo>
			<!-- <iconpath>c:\icon.ico</iconpath> -->
		</general>
		<files>
			<file>
				<source>your_rebol_script.r</source>
				<destination>your_rebol_script.r</destination>
			</file>
			<file>
				<source>C:\Program Files\rebol\view\Rebol.exe</source>
				<destination>rebol.exe</destination>
			</file>
			<!--put any other data files here -->
		</files>
		<!-- $FINDEXE, $TMPRUN, $WINDIR, $PROGRAMDIR, $WINSYSDIR -->
		<onrun>$TMPRUN\rebol.exe -si $TMPRUN\your_rebol_script.r</onrun>
	</xpackerdefinition>

=image rebol_tutorial/example_xpackerx.png

Just download the free XpackerX program and alter the above template so that it contains the filenames you've given to your script(s) and file(s), and the correct path to your Rebol interpreter.  Run XpackerX, and it'll spit out a beautifully packaged .exe file that requires no installation.  Your users do <i>not</i> need to have Rebol installed to run this type of executable.  To them it appears and runs just like any other native compiled Windows program.

There are a variety of other options you can use to create distributable Rebol .exe programs.  All such options involve creating self-extracting executable zip files ("SFX" files) that package the Rebol.exe interpreter together with your scripts.  When run, the SFX files automatically open Rebol.exe, and execute your script on the command line.  <a href="http://web.onetel.net.uk/~peterboulton/stubbie.htm" target=_blank>StubbieMan SFX</a> is such a program, made specifically for creating packed executables, using a simple wizard interface.  You can also use any other zip archiving application capable of creating SFX files.  For example, <a href="http://download.oldversion.com/powarc611.exe" target=_blank>PowerArchiver (version 6.11)</a> is a popular free zip manager.  To package Rebol executables with PowerArchiver, just follow the instructions to create a zip file that includes Rebol.exe and your script/data files, select "Actions->Make .EXE file" from the main menu, select "Create AutoRun SFX" and "Overwrite Files", then type "Rebol.exe| -s yourscript.r" into the field labeled "Command line after extracting" .  It'll pop out a compact file executable with even less work than XpackerX or StubbieMan.  Full instructions for creating self-extracting executables are included in the PowerArchiver help file.  PowerArchiver and StubbieMan do not provide an option to change the resulting program icon.  XpackerX is a bit tougher to use, but it does allow you to choose a specific icon for your program.

The most complex distribution option is to create a standard installation package.  To do this, try <a href="http://nsis.sourceforge.net/Main_Page" target=_blank>NSIS</a>, the <a href="http://mulder.at.gg/" target=_blank>NSIS SFX Tool</a> (my favorite), <a href="http://www.jrsoftware.org/isinfo.php" target=_blank>Inno Setup</a> or <a href="http://www.wheresjames.com/index.php?page=sw&pg=1" target=_blank>Pack-X2</a>.  These programs all create single file .exe install packages that provide users with a familiar installation routine, uninstall option, and a group icon in the "Start" menu, so that your Rebol program can be accessed and run like any other installed program.  (Note that these programs are all for MS Windows.  You'll need to find a different packaging system for other operating systems).

To create a self-extracting Rebol executable for Linux, first create a .tgz file containing all the files you want to distribute (the Rebol interpreter, your script(s), any external binary files, etc.).  For the purposes of this example, name that bundle "rebol_files.tgz".  Next, create a text file containing the following code.  For the purpose of this example, save this script file as "sh_commands":

	#!/bin/sh
	echo ""
	echo "Running... please wait"
	echo ""
	SKIP=`awk '/^__REBOL_ARCHIVE__/ { print NR + 1; exit 0; }' $0`
	tail +$SKIP $0 | tar xz	
	exit 0
	__REBOL_ARCHIVE__ 

Finally, use the following command to combine the above script file with the bundled .tgz file:

	cat sh_commands rebol_files.tgz > rebol_program.sh

The above line will create a single executable file named "rebol_program.sh" that can be distributed and run by end users.  The user will have to set the file permissions for rebol_program.sh to executable before running it ("chmod +x rebol_program.sh"), or execute it using the syntax "sh rebol_program.sh".  For more information about using this technique to create self-extracting Linux executables, see the article at <a href="http://linux.org.mt/article/selfextract" target=_blank>http://linux.org.mt/article/selfextract</a>.



===Embedding Binary Data

You'll often need to use images and other binary data in your Rebol programs.  For example, simple games often use graphic and sound files as part of their interface.  As you've seen, there are many ways for Rebol to load in such binary data.  You can read it from a hard disk, you can download it from the Internet, you can read it from just about any other local or networked storage medium, etc.  When distributing your Rebol programs, however, those methods aren't always desirable.  You don't want to require your user to download a number of images and sounds every time they play a simple game.  They may not always have an Internet connection available.  A possible alternative is to make a zip file or similar package that includes your program and all its supporting files.  Creating and distributing such packages, however, can be overly complicated for simple scripts.  Also, various operating systems use different compression types (zip, tar, etc.) and XpackerX/PowerArchiver/etc. only work in Windows.  To eliminate those problems, Rebol provides a method to encode and include external files within the <i>text</i> of your programs.  To see how it works, use the code below:

	Rebol [Title: "Binary Embedder"]

	system/options/binary-base: 64
    file: to-file request-file/only
    data: read/binary file
    editor data	

=image rebol_tutorial/testpng.png
=image rebol_tutorial/testpng2.png

Type that program into your text editor, save it as a text file in "C:\embed.r", and then run it using any of the methods described in the previous section (try typing "do %\c\embed.r" into the Rebol interpreter).  When run, the program will let you select a file, read it, and then display a binary representation of its data in the built-in editor.  You can copy and paste the text of that printout directly into your program, assign it a variable name, and use it as if it had been read straight from a hard drive or another storage medium.

Here's an example.  Download the picture below - you can use your web browser to go to the url, and then save the image to your hard drive.  Or, you can download it using Rebol, as demonstrated earlier in the tutorial:

<a href="http://musiclessonz.com/test.png" target=_blank>http://musiclessonz.com/test.png</a>

Once you've downloaded the file, use the program above to select and convert it to binary data.  You should get the following printout:

	64#{
	iVBORw0KGgoAAAANSUhEUgAAAFUAAABkCAIAAAB4sesFAAAAE3RFWHRTb2Z0d2Fy
	ZQBSRUJPTC9WaWV3j9kWeAAAAU1JREFUeJztlzEOgzAQBHkaT7s2ryZUUZoYRz4t
	e9xsSzTjEXIktqP3trsPcPPo7z36e4/+3qO/9y76t/qjn3766V/oj4jBb86nUyZP
	lM7kidKZPFE6kydq/Pjxq/nSElGv3qv50vj/o59++hNQM6Z93+P3zqefAw12Fyqh
	v/ToX+4Pt0ubiNKZPFE6Ux5q/O/436lkh6affvrpp38ZRT/99Ov6+f4tPPqX+8Ps
	/meidCZPlM7kidKZPFE6kydKZ/JE6UyeKJ3JE6UzeaJ0Jk+UzuSJ0pk8UTMmvn8L
	j/7l/nC7tIkonekLdXm9dafSmeinn376D/rpp5/+vv1GqBkT37+FR/9yf7hd2kSU
	zuSJ0pk8UTqTJ0pn8kTpTJ4onckTpTN5onQmT5TO5InSmTxROpMnasbE92/h0b/Q
	//jR33v09x79vUd/73XvfwNmVzlr+eOLmgAAAABJRU5ErkJggg==
	}

Now copy and paste that data into the Rebol interpreter and assign it a variable label, like this:

	picture: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAFUAAABkCAIAAAB4sesFAAAAE3RFWHRTb2Z0d2Fy
	ZQBSRUJPTC9WaWV3j9kWeAAAAU1JREFUeJztlzEOgzAQBHkaT7s2ryZUUZoYRz4t
	e9xsSzTjEXIktqP3trsPcPPo7z36e4/+3qO/9y76t/qjn3766V/oj4jBb86nUyZP
	lM7kidKZPFE6kydq/Pjxq/nSElGv3qv50vj/o59++hNQM6Z93+P3zqefAw12Fyqh
	v/ToX+4Pt0ubiNKZPFE6Ux5q/O/436lkh6affvrpp38ZRT/99Ov6+f4tPPqX+8Ps
	/meidCZPlM7kidKZPFE6kydKZ/JE6UyeKJ3JE6UzeaJ0Jk+UzuSJ0pk8UTMmvn8L
	j/7l/nC7tIkonekLdXm9dafSmeinn376D/rpp5/+vv1GqBkT37+FR/9yf7hd2kSU
	zuSJ0pk8UTqTJ0pn8kTpTJ4onckTpTN5onQmT5TO5InSmTxROpMnasbE92/h0b/Q
	//jR33v09x79vUd/73XvfwNmVzlr+eOLmgAAAABJRU5ErkJggg==
	}

You'll get the response below, indicating that the image has be defined and created:

	make image! [85x100 #{
	FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
	FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF...}

Now you can use the variable "picture" as you would any other data.  Display it, save it, transfer it between networked computers, etc.  Here it is in a GUI:

	view layout [image picture]


The example below displays a photo of my dog, and then saves it to the hard drive as a .png image:

	dog: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAFkAAACNBAMAAAAuisulAAAAMFBMVEUeEw6kh3OM
	TRZDSE/RxbWFal1KLiCtkoakZSXW0cm9mnlCNzq5no5oSDTg29B0UkzBjRe5AAAA
	CXBIWXMAAC4jAAAuIwF4pT92AAAQ80lEQVR4nG1Yf2gjZ3r+kiW6gjHJZHdOjuLU
	W0GMKRgShG7/UIVqqu2eUtd3c9pvpe6uGJ32dnqca+zhIoa6glubczCBZVsQhGkX
	9UR369zgEKeqXeic0G6xERHTxLGxWFCH+WehGIKIVx2viTJ8fd9v5M2m9JN/CPx8
	zzzv8/74PpkIQTUYVDUtqMFP+L22uKitaaXFktaEZZXgyzpdD0hQEFRcz+CA10pr
	HIurVLKa36KpAHhhAA8CeBHIm8BcwgXA5+APCGM0GBSCQU4ML5VvaDWfLav5HDez
	40dAHhSQHaHwDNUw1pB5EXiR3hqIR/S+I3FupA4iWDPWjRYXUlovIfe3SuRcp+6q
	Ag92QK5ebVmGhgFqKMQq8e8Sj5LadkMQnoFBh321ZTSbmtZcszBIHuuAW5L6pv1U
	OPUFvhy3FbpnlLQScnPDTzc8IKLssc4Bxsmlgw67fdlo7WjWwMJBmPgFuj3W7zuc
	G/wGx4PC3Kix/THsazZ9fNPHct2s0fC2JBW5ueuC91/r1nr6Ok++LwQf40cpyZ1+
	o3+Anmg898VZuzX6+f4FID/VUnoWpTvm1Fmn4SdIQ+3Uvh/6OAJoXljIPjAQ0EfU
	Yw22JQHcLys1/cX2vfuRaPM73AMlDvX6rNH5Arm54X9z45OL60YkgnnC7OAOyy8W
	rCrZ6bP2pm94MFiMzb40tb6ejmSwvJrWoMx5/h8Qm8m2Z3v7AleuqbFI9BNrvfU6
	CA8OytaXA/zALdO+Y7MnEk+QGolsmKMP32n9MvI2VkGz+XwP8eww16XyFz64Vntr
	46+qllE0o6h7kTNDXvmOBeLYDnPlrHsTuIuRWiQSe/13Rsu4b9Z4mH4dwo41rtur
	1z2XUgrCg2kAR8yEZRmGEakFfVMAvjbQskBYpwNSKLOF4NlYDNAbG9eNe8Z6j5uy
	1iwtDroIFkRZ7zgMinz2SOXgmPlV6GurZfVqaAqKBkfWfO4HyN1waNGc/SJdQyGR
	WnT0nXVjZz92QfNdATHgJP6GOjmGOmGsvvUJp45Ezpilq4bxT/COTxcYRc9sB91e
	w5EZ65i1Wo3DzUDwfWM9B++CPhy0NK0BNwMowPtbphnx14ZlhCDIiJ97BA/qC7gp
	ZbQGVWiasVP0N62fhK5BvCCczyJtbTCIsKqY3IMfpmnWfPRbLy++aqQBHeHDhXNj
	dSG37bq5PmOJ3iz+HVeMXDDW/9NHa0E/obxaAG0yythmRO6btdqplO+1WuhJLePP
	3NKpKwukwUSXNVw3fYoF0pes9c/xDS8soF9r+llaIHVJ7rMelKFZi32Ltjj6Wyl+
	Gz0gW7LEWJ+5aTNyamHsTMvaQSU8nX7hLvpKzHlXhqpywO9TdCQw3RK5sAt+Yy/y
	SJvNBTJXTx9BycZMns0aN5K0jCo+I1JrDsjXBp50zCO3waRrpjkLyA0SGDJjeahw
	4IZnZXA0ojF8PC+Qrc4BTBR6La+Y9Y6iBAhRlI3R9RbnPk0nwuGwA0+2nIzsCa8T
	Zc5htn1ntZ0PkOuW1ePwqCZwX4KLqAmibNejMpNyRHl0kpvIZulKm5DrrVAPpNQi
	Mc0/6PwF3HN1lx24VwJvrtyZfHN1ZSmXy5PZg2Cac0cuqKr6HNo052SXuf0AXZm0
	DyRh5D1QQsjNaxEeZkLjZ5fa9NGz7brnMHYlYNu2Yp9kaX4WwOTM6zVeZNHTowuT
	Ckpmbc/NOcdKwW4rc7BlN5+/sZW/+X2QXat98uw8Rzxwzx04jiQrCkADbaXd2c0r
	b3uBr38D9teikn9iYKAqcs/Z0Glf5PKAPgarbaVOhjobc6F/DkCy7AZVtec9cRwn
	7tGOEphdOQ7Y7XZ7bjewFfja+CigbHU6diPDrxgaRqkuEJexHGWe8uIcvf0izOb2
	7DXSrhvGq6TWUeYU+6B5yq1ybteTXY8MP6K5+YM7nq2wgKJUhY/JDa/TNh0m+Acj
	KoJ54sA8dj1l+OAk+3O6cscLOCQ/N1qtEuKmZ2EAXxXUb7k3mStRdqwMe4p4kHVp
	LnCg5OcMwSCk1rZPbHbET9ES8oMST6Ii27CH7Xw2m7NdOe/eHi9cNQRCAqbNnBO3
	iuTWwG9ZEsV+3j4/pLgrVwIb9UcrdMVeCoXyhEQajic7SG1ZeCuCOqFUlNJ52w7k
	Xa89fMyosJLNHhnGLqTfTMA5kwENpekm545RWRyTQVCeOCd5olBRGJHuvG8Yt0DK
	0GbcZZhPranyKGXqjhXN/LyzG2B38oF5ikfhyteC+GMoxcANV04/5XcoPKVharqC
	IPZNxesoNtTVAaIl+Q9CxitDCiFD0Wjubf92CTeABdKjY1RuNAAKy3OoJIgivfKL
	6vu/ma1vkPwNNx4N8pslryrXFWGCs858p922nQMqHwhS9vgFQ/j+nA09RzbNTd4+
	uGGBpNkBhSONzbdnoSps1v49OJW/ekEQXp1LIPpMrIG6+aULMu/yF2NbirJVNxXy
	klSq5l+uVj+aW/EAPWSagsZ1Yy7rDegzWN5u3lQATDZDhkjmq9WReXqb95wZ9G9c
	qKSD0AYMzo2AsgEtGThaN64E5sCZE5rNc3JB4zqC2isEkC6GyfL5PAGLX75utXaH
	hkNidUWiu0huZhCMTbFA4p0j6qMJyQ8FyOaodT/fCRjgupRF9NbQU1DB75avELNB
	JUT3kWaIBDJB60rgB0QQQmA85x7KwC1Hww2ge1Pk3MeIJRsBQRXzDiGhkGFU5TZn
	gHnl3/+BG64b4KDHcEJtkTMSjQ/Bc65WBUPEkQjr3wS8cMEHjFfglILbPZX37a0N
	CJ+c6e0rL8FzlkBKNeuhKeR7eBHFO/ePCcfKcr2zZZKhfv5GQlEOfkACV6uGIdA7
	HP0yVwKefkVkF8+dXqfeCfRqdEOJBEwxT4alqiBUBZmjAxAxXgCFXSJx6r7Xr2+B
	8UptP3AgbhDIzki1KmZ94XMuflYQgEWGKF0ZzqiOCSe+UtuapWMwkK8u3Qd2bjie
	LYUJLOU8UUUq0V6stm/Os4ZMbhzPS1cIca6i4QJ9j6NhHClK+OQNQoIihfLvwYgE
	NCU34pvCFTIEHWQAN7x9hoZFoC8pFTTITwyV5JVEgr5F5kXBGAGwX4UAz8MMViBk
	0JGWKd5SYg3mbQ0n6NhG4EAQ0RI4V3xwWwF4ANAQZcaV5V4PTvp6vD7rlu6+VcuE
	AAsbBF6zhHi37XYehMBE7kmy25Oj4GS93utcmOmmQfV94b4hQs+NbSD6Xwp79hOo
	aJ7LNHzD6pkwnK/PdC+iH6ERcWlFWro3xS0cHx8P77W5EkGuJVxG0zSWkMXRbndK
	DVn3YceH4pI4c/gWpmc8XCjMLecJEyFMvM4Uo4m06UjnKodfautWtWqIwtKSNJNc
	APRwGLgLYIpMpSgk8whsT9N+jb7b7X6plqwd4cNQVUD03wL6xUKhoIyHzxNIvACF
	Ar+CxUS67pa63cfC9dJU6EOQPiLM6H+GFoZhjY8DtyWqwR24VMNhJLu16Llut/tQ
	spJCNWQsSdKM/g+oBIUUgJsW5SKI6blPNfFX0VjjOqDLglUxQqGqNCLO6P844AYx
	MLTpAZXSImUylIucTvxRBeCHle7D6vvVEUF8V/8TRO+hhePnibPP5KD4UDzrRqlI
	0+6FmUqle9g9bIHnwP0aV0ImUXc4T+Jxu+dCsRQxUFFMRD/rVgBcnjJC1RGRfqr/
	KaILBZ/bi8MLGwhshNMtkv4MmLuHqQ9CSyNLAk3pf0wCdeXFcAGUg+59247HqewW
	0/RteHmvge6KXvlvFZplSdL1B6TO2oFCGNjPk307ntjfx09IqgvJ76W/Qe7uzAdB
	NbskZnT9lQbNHiun3HGPxSOuy+QLIgrq/bsO3F39cTIp0qVRXU9TaeWJUsAoz5Oe
	E9+3HYqlSCVJjCbcFIR5qFf0aQG4U2UpKGa9AmAL44T0mQPUULVQsbBBZrnfgoVd
	/bA8nR0RR1NlzaqKe1AkhfPgDe31bAduEWkqylBfCSZf7lYqlcOkNSVJwrs6oK0R
	8GScNxEV7YTrwT1CALsBzORvdG5heQo67VO9DB8sxfEAthl4InmOg40DlQsvFkn0
	6QwKP9SnBENI6eXtbeuNPWiy4QJoGYvXMD6QMQaFEmGA/uywWyl39UtqFdC6Nf0w
	ayt5ZS8MnlxzDvADI5VgaNFcohGtb547hCB1valWReC2th/a7YKNhXKenN0/QLAY
	1EQ3Gq9H3PpPL6PfUClBzn1p+mN7r4DtANyZiAfRjWVEYSftxGPM7bxwWUfZoEQV
	dF1PNnN7T07R4lg8CjkMCsUii8ccx2vfRAvLlXIzpIqpsp7c8Zw9ZYB2pbRXlKWH
	gnY2kbYTCda2r0M36F9OXwq2qqlyqnyxPdk+5abS5z13LLMjFYu93j4eQt5lqCvI
	/KWSVQW/k9NtZbyw56N3opmEqz5UqVBMRPYbUC7HoAT06h+UrNanKPwaTvvwMqKb
	NCP3mk2VBqWeF09AUnOXu4AB7net5l/rern8I6Uwh+Dl8+TSr9xfskwJjiza68eZ
	K9DcX0CUun5417KsUbDw7lSuDdDl5fAtUiqmpQj+O0zIsHgcL57Hv9/FgtXvvmtZ
	5yA9+vTYJFIj90MBToeSoDWFo17f9grHk23I/GESfLa2LSulJ/WyHA5PIDugNTUK
	52xRUDNyxLEVZa89A5kE7qSV3C6BJ3ryYyCemMAowei0WBRLmaDI4jzFNlZg6hBq
	dXu7qZeB/T+4f6hkVINTjcINXlJZHDqqEJ7AGLGszm1PN5PJZDn5owmf+xYoCWpH
	VJAeSiKzMWWFX1TAk5ReuRvcti5D5svTF4EX4beAu6ip0O1FVWb2OPb2z2CyHZb1
	u1S2Wj8rg/7kFHLDBsi8RoPQNEeqKHvIXZj8NZQgDIhL0vH2pd+VpVS5PBVe5XGe
	J0UYZ+JZMbMDByyUfGF8kncxUDqxjJiZCkRTyallsA/YoWI1KmagYvGAxdFYmPwt
	2FeZeVyOJ9i/Tv/5T7WMPrU8gUKWbxFVE0WQjTcxbxye94h+CgZWKjNlmrn0P2Ur
	un12+yKCl1F3UwvCbHgqwPUU/AtPrkATH6KSSvIQivuzi9Jr537IDVwNI7cGrUNV
	l8sOhyXxUxiCjzGZKTD93sxdIfnRKq8qjFKVZEiP6LoehBhWQgJwdzm2rM+k7pUr
	enIEaSbCgM6oIESG+6bsYX4nJOGzFFY3wqG4p/VUahpV+35ndvBe9XTMZbwYlJs0
	iY2DdTUD7JfK5fIPl1HGMvqtqYIruxmRHo/z0lHe3AbsDNDCK1X+u1Qq+SrECHAf
	rUbhwClCjNB8sObvpRB4yHsz9fcpzPsyZwclF7Qig9GmHg8/CfvrXjKVgnRDhaTK
	j7/cTmZ5blZXJ1Zvkb+Ez0aOTD/3z3Jcl5Plx2Wdy4E99+5jk61OLMPXLfISzTHK
	pF1A+yMm/IdY02Xkr1SSZQrQMIpeXV49T/JwqaL0GpzOJz54+c0kwvXyYQp+ffjo
	0SpmErATE7fI+TdyTKZfwei/fSrl1wjXU8lU8p3VlTso2H8B966D/0zEq9kjnjD8
	sZ3k6537q7DeXD1d4ODkPNySj/EEguzA/gl8rJF8x2hVVzjmwwF2eRWiHHfuMPpj
	fvJjfiFly/yPSwPQ0tQzbnAwPM/Y0TEq+fkjnHX8Ac/D7z0DI/dN+Dx/uw3wR8sY
	+nJ4efU769zIc9zjc8xzH9mT7w2DCCDGLc+tidX3q8/egxLwJDu5fPJkNcwL0/cK
	14Bz6TvcDnNyJ5MYHCZs9XkdE/9H1C1ye555P1lG43ybTpn/v3XrfwFzPoFQpggI
	EQAAAABJRU5ErkJggg==
	}

	view layout [image dog]
	save/png %dog.png dog

=image rebol_tutorial/example_dew.png


---Compression

The code above can be shortened dramatically using the built in Rebol word "compress".  Rebol's built in compression and decompression only work with text strings, so the binary embedder program provided earlier must be adjusted as follows to create compressed embedded data:

	REBOL [Title: "Rebol Binary Embedder"]

    system/options/binary-base: 64
	file: to-file request-file/only
    if not file [quit]
    uncompressed: read/binary file

	compressed: compress to-string uncompressed
	; Note that the line above converts the binary data
	; to a text string, and then compresses it.

	editor compressed
	alert rejoin ["Uncompressed size:  " length? uncompressed
		" bytes.  Compressed size: " length? compressed " bytes."]

IMPORTANT:  To use the compressed version of the data above, you'll need to reverse the text-binary conversion after decompressing it.  To do that, use the following code: 

	to-binary decompress {compressed data}

So, using the variables above, the following two lines of code display the same image:

	view layout [image load uncompressed]
	view layout [image load to-binary decompress compressed]

Here's a complete example demonstrating the size difference between raw and compressed embedded data:  

	; Here's an uncompressed embedded image:

	image-uncompressed: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAP8AAAEsCAIAAACDt/KoAAAAE3RFWHRTb2Z0d2Fy
	ZQBSRUJPTC9WaWV3j9kWeAAAB9FJREFUeJzt3bGRHEkQBMETDaKd5v8UmlmzIaoz
	MGtZ4QLUIBtBLXM//0lb/bz9D5BeY/3ay/q1l/VrL+vXXtavvaxfe1m/9rJ+7WX9
	2sv6tZf1ay/r117Wr72sX3tZv/ayfu1l/drL+rWX9Wsv69de1q+9rF97Wb/2sn7t
	Zf3ay/q1l/VrL+vXXmD9P1ICmCh4WkoAEwVPSwlgouBpKQFMFDwtJYCJgqelBDBR
	8LSUACYKnpYSwETB01ICmCh4WkoAEwVPSwlgouBpKQFMFDwtJYCJgqelBDBR8LSU
	ACYKnv7w+1f8W+fyP307B+a8MxA8Xf92Dsyx/jnjIPQPvD/xixn8G4wjqH/g/Qnr
	r42jfuD9CeuvjaN+4P0J66+No37g/Qnrr42jfuD9CeuvjaN+4P0J66+No37g/Qnr
	r42jfuD9CeuvjaN+4P0J66+No37g/Qnrr42jfuD9CeuvjaN+4P0J66+No37g/Qnr
	r42jfuD9CeuvjaN+4P0J66+No37g/Qnrr42jfuD9CeuvjaN+4P0J66+No37g/Qnr
	r42jfuD9CeuvjaN+4P0J66+No37g/Qnrr42jfuD9CeuvjaN+4P0J66+No37g/Qnr
	r42jfuD9CeuvjaN+4P0J66+No37g/Qnrr42jfuD9CeuvjaN+IHi6/u0cmGP9c8ZB
	6B8Inq5/Owfm9Nf/56/ftHP54T8szoFBDwPBRMHT3/F28W8dDgyyfuTt4t86HBjU
	X780ACYKnpYSwETB01ICmCh4WkoAEwVPSwlgouBpKQFMFDz94fy8Ff/Ww4908W8d
	Dgx6ZyB4uv7tHJhj/XPGQegfCJ6ufzsH5lj/nHEQ+geCp+vfzoE51j9nHIT+geDp
	+rdzYI71zxkHoX8geLr+7RyYY/1zxkHoHwiern87B+ZY/5xxEPoHgqfr386BOdY/
	ZxyE/oHg6fq3c2CO9c8ZB6F/IHi6/u0cmGP9c8ZB6B8Inq5/OwfmWP+ccRD6B4Kn
	69/OgTnWP2cchP6B4On6t3NgjvXPGQehfyB4uv7tHJhj/XPGQegfCJ6ufzsH5lj/
	nHEQ+geCp+vfzoE51j9nHIT+geDp+rdzYI71zxkHoX8geLr+7RyYY/1zxkHoHwie
	rn87B+b01//K37mPf+twYNDDQDBR8PR3vF38W4cDg6wfebv4tw4HBvXXLw2AiYKn
	pQQwUfC0lAAmCp6WEsBEwdNSApgoeFpKABMFT384P2/Fv/XwI138W4cDg94ZCJ6u
	fzsH5lj/nHEQ+geCp+vfzoE51j9nHIT+geDp+rdzYI71zxkHoX8geLr+7RyYY/1z
	xkHoHwiern87B+ZY/5xxEPoHgqfr386BOdY/ZxyE/oHg6fq3c2CO9c8ZB6F/IHi6
	/u0cmGP9c8ZB6B8Inq5/OwfmWP+ccRD6B4Kn69/OgTnWP2cchP6B4On6t3NgjvXP
	GQehfyB4uv7tHJhj/XPGQegfCJ6ufzsH5lj/nHEQ+geCp+vfzoE51j9nHIT+geDp
	+rdzYI71zxkHoX8geLr+7RyYY/1zxkHoHwiern87B+ZY/5xxEPoHgqfr386BOf31
	v/J37uPfOhwY9DAQTBQ8/R1vF//W4cAg60feLv6tw4FB/fVLA2Ci4GkpAUwUPC0l
	gImCp6UEMFHwtJQAJgqelhLARMHTH87PW/FvPfxIF//W4cCgdwaCp+vfzoE51j9n
	HIT+geDp+rdzYI71zxkHoX8geLr+7RyYY/1zxkHoHwiern87B+ZY/5xxEPoHgqfr
	386BOdY/ZxyE/oHg6fq3c2CO9c8ZB6F/IHi6/u0cmGP9c8ZB6B8Inq5/OwfmWP+c
	cRD6B4Kn69/OgTnWP2cchP6B4On6t3NgjvXPGQehfyB4uv7tHJhj/XPGQegfCJ6u
	fzsH5lj/nHEQ+geCp+vfzoE51j9nHIT+geDp+rdzYI71zxkHoX8geLr+7RyYY/1z
	xkHoHwiern87B+ZY/5xxEPoHgqfr386BOdY/ZxyE/oHg6fq3c2BOf/2v/J37+LcO
	BwY9DAQTBU9/x9vFv3U4MMj6kbeLf+twYFB//dIAmCh4WkoAEwVPSwlgouBpKQFM
	FDwtJYCJgqelBDBR8PSH8/NW/FsPP9LFv3U4MOidgeDp+rdzYI71zxkHoX8geLr+
	7RyYY/1zxkHoHwiern87B+ZY/5xxEPoHgqfr386BOdY/ZxyE/oHg6fq3c2CO9c8Z
	B6F/IHi6/u0cmGP9c8ZB6B8Inq5/OwfmWP+ccRD6B4Kn69/OgTnWP2cchP6B4On6
	t3NgjvXPGQehfyB4uv7tHJhj/XPGQegfCJ6ufzsH5lj/nHEQ+geCp+vfzoE51j9n
	HIT+geDp+rdzYI71zxkHoX8geLr+7RyYY/1zxkHoHwiern87B+ZY/5xxEPoHgqfr
	386BOdY/ZxyE/oHg6fq3c2CO9c8ZB6F/IHi6/u0cmNNf/yt/5z7+rcOBQQ8DwUTB
	09/xdvFvHQ4Msn7k7eLfOhwY1F+/NAAmCp6WEsBEwdNSApgoeFpKABMFT0sJYKLg
	aSkBTJQ7LX0569de1q+9rF97Wb/2sn7tZf3ay/q1l/VrL+vXXtavvaxfe1m/9rJ+
	7WX92sv6tZf1ay/r117Wr72sX3tZv/ayfu1l/drL+rWX9Wsv69de1q+9rF97Wb/2
	sn7t9T/igalLLsvMjgAAAABJRU5ErkJggg==
	}

	; Here's a compressed version of the same data:

	image-compressed: load to-binary decompress 64#{
	eJzrDPBz5+WS4mJgYOD19HAJAtL/GRgYdTiYgKzm7Z9WACnhEteIkuD8tJLyxKJU
	hiBXJ38f/bDM1PL+m2IVDAzsFz1dHEMq5ry9u3GijKcAy0Fh3kVzn/0XmRW5WXGV
	sUF25EOmKwrSjrrF9v89o//u+cs/IS75763Tv7ZO/5qt//p63LX1e9fEV0fu/7ap
	7m0qZRIJf+2DmGZoVER5MQiz+ntzJix6kKnJ6CNio6va0Nm0fCmLQeCHLVMY1Ljm
	TRM64HLwMpGK/334Hf4n+vkn+1pr9md7jAVsYv+X8Z3Z+M/yscIX/j32H7sl/0j3
	KK+of/CX8/X63sV1w51WqNj1763MjOS/xcccX8hzzFtXDwyXL9f/P19/f0vxz4f2
	OucaHfmZDwID+P7Hso/5snw8m+qevH1030pG4kr8fhNC4f/34Z89ov+vHe4vAeut
	SsdqX8T/OYUCv9iblr++f67R8pp9ukzLv8YHL39tL07o+3pekn1h/dDVBgzLU/d3
	9te/Lki4cNgBmA6/lO+J/RPdzty8Rr5y94/tfOxsX6/r8xJK0/UW9vlH93/9oAzR
	e09yKIUBVbT9/br/U/m7x6CU98VAAJS2ZPPF/197eEDhtfs9vX9rDzc6/v3qzUyo
	nJA/dz76Y77tHw+w3gXlbEMpDKihza/+7/o/c3+DU54tDwsobR2/fXR/qYXBiV8T
	t3eDEmpA/d9LDASK0y/tnz+H/Ynmt78E1vti7lAKA6pouxz/X7v+uR045ZFdRE6x
	1q21pG7NiSzx1f5R40pvvdNn+oB1P4Onq5/LOqeEJgCemFy1KQgAAA==
	}

	view layout [image image-uncompressed]
	view layout [image image-compressed]

=image rebol_tutorial/example_compressed.png

The compressed version of the image data is exactly the same, but much smaller when included in your programs.  When you use compression like that, just be sure to include the "to-binary decompress" words when loading the embedded data.

Using the short binary embedder program provided earlier, you can convert any type of file into embeddable text data.  Images, sounds, videos, even entire executable programs can be included in your distributed code!


===Modular Programming and Code Reuse

Rebol provides a fantastic array of easy to use programming tools built right into the language.  As you've seen, Rebol's built-in words can accomplish useful "high-level" actions that can be the basis of simple programs.  You can even use the interpreter as a powerful little swiss army knife utility that doesn't require any real programming (i.e., as a multiplatform text editor, calculator, email reader/sender, image viewer/editor, command interface for copying/pasting files, ftp uploader, etc.).  For larger programs, however, the built in capabilities are merely simple building blocks.  To build more complex applications, you need to _create_ new functionality by combining and using the native words, grammatical structures, and simple pieces of code.  Language elements are just raw materials that can be put together to achieve more powerful and specific goals.  Toward that end, a very important concept in programming is (drum roll...):  the reuse of existing code.

Never re-invent the wheel.  Reusing bits and pieces of existing code is essential if you want to become a productive programmer.  The creation of functions is a basic way to implement code reuse - once you create a new function word to accomplish a given action, you can copy its definition and use it over and over again in your programs.  That saves you the trouble of reinventing those actions every time they're needed in your programs.  It also reduces the likelihood of introducing errors - old trusted code is less likely to contain bugs if it's already been tested and put to use in a variety of situations.

As demonstrated earlier, the built in word "do" opens and runs Rebol code that's been saved to a text file.  You can use it to import existing modules of code, as if that code had been typed into your program.  That existing code can contain function and variable definitions, new programmatic structures, and even complete programs of any length and level of complexity.  Once those words and definitions have been imported into your program, you can use the included functions and variables as if they're native words in the language.  You don't even necessarily need to know how they were created.  Try typing in the following code example, and save it to "C:\play_sound.r".


	Rebol [title: "play-sound"]

	play-sound: func [sound-file] [
	    wait 0
	    ring: load sound-file
	    sound-port: open sound://
	    insert sound-port ring
	    wait sound-port
	    close sound-port
	]


The code above creates a new function word "play-sound", which accepts a passed variable filename "sound-file" (that file must be a ".wav" file), and plays the sound through your computer speakers.  You don't have to understand how the code works - just type it in and save it to C:\play_sound.r .  Now, whenever you want to play a sound, you can include the code in your program:

	do %/c/play_sound.r

And use the "play-sound" function just like any other built-in function word (the syntax is "play-sound {sound-file}"):

	play-sound %/C/WINDOWS/Media/chimes.wav

Easy, right?  You only have to type in the line "do %/c/play_sound.r" once in your program.  After that, the word "play-sound" is defined, and you can use it wherever you need:

	alert "Here's a sound:"
	play-sound %/C/WINDOWS/Media/chimes.wav

	alert "And here's another sound:"
	play-sound %/C/WINDOWS/Media/chord.wav

	alert "Now try choosing a .wav file from your hard drive:"
	play-sound to-file request-file/file %/C/WINDOWS/Media/tada.wav

This whole concept becomes much more useful with the realization that (final drum roll...):  You don't have to write everything yourself!  There exists a community of developers around the world working to create useful pieces of code.  Finding and learning to use modules of code, functions, and complete dialects created by other programmers will remain at the heart of your initial learning process, and will continue to play an important role in your efforts as a proficient developer. 

Many self contained modules of Rebol code have been created to extend the built-in abilities of Rebol, and that list continues to grow as the language matures.  Learning to use dialects and parts of programs created by others will make you a much more capable programmer.  Existing modules of code can help you do high level, complex, and specific things with ease, so that you don't have to start from scratch in every programming effort.  

In that way, learning to program is a lot like learning to use other types of technology that exist in our society.  To call your friend on the phone, for example, you don't need to reinvent the telephone and all its electronic components.  You don't need to manufacture any of those items, and you don't need to install miles of cable.  You just need to know how to use the existing phone system.  Furthermore, you can put that system to use in more complex operations that are functional to you at another level.  Business owners rely on the phone to contact clients and employees, without necessarily caring how the system works.  They just use it functionally as part of their higher level business goals.  Existing code modules can work for programmers in a similar way.  They make available high level functions that can be used to build even higher level, specific, and complex applications.  You just need to know how to use them.

To reuse code modules, it's essential to first learn the language, so that you can understand code written by other developers.  You may need to adjust and extend code written by others, so that it fits your needs more exactly.  In most cases, however, you can just learn how to use the words in an imported module or dialect, execute a "do {filename}" command, and you're off and running with a whole new language extention.  Here's an example:

The web site <a href="http://www.dobeash.com/it/" target=_blank>http://www.dobeash.com/it/</a> offers several free extension modules for the Rebol language.  They provide a module called "RebGUI", for example, which extends the already powerful GUI syntax built into Rebol ("view layout...").  Using RebGUI, it's possible to easily display graphic widgets that aren't natively possible in Rebol.  RebGUI constructs those components from the built in Rebol raw materials, and makes them reusable in your own programs.  To use RebGUI, just download the files at the web site above, and unzip them to C:\ .  Then type in the following code and save it as C:\rebgui_example.r.  You can run it by any of the means described in the previous section ("do %/c/rebgui_example.r", etc.):


	REBOL []

	do %\c\rebgui.r

	display "Grid" [
		table #WH options [
			"Day" left .5 "Time" left .3 "Name" left .3
		] data [
			Monday 9:00 "John" Tuesday 9:30 "Jane" Wednesday 10:00 "Bob"
		]
	]

	do-events

=image rebol_tutorial/example_rebgui.png

The code above makes use of some new commands that aren't part of the native Rebol language.  Specifically, the functions and variables "display", "table", "#WH", "options", and "data" are defined in the rebgui.r file, and they add new functionality to the Rebol language.  Using those words, as defined in rebgui.r, the above code displays the given data block [Monday 9:00 "John" Tuesday 9:30 "Jane" Wednesday 10:00 "Bob"] in a resizable GUI display that can be automatically sorted by clicking on column headers in the GUI.  That type of display is a common requirement in modern programs that display lists of data ("database" applications), so the added commands are a welcome addition to the Rebol language.  RebGUI contains a broad collection of additional functions that are useful in building intricate GUIs.  To use them, you must first understand basic Rebol syntax, and then learn how to use the RebGUI language extensions within that syntax.  Once you've done that, you can simply include the "rebgui.r" file in your programs, and use those language extensions as if they're part of the language.  The key is to understand that RebGUI commands are built from native raw materials in the Rebol language, and to use them, all you need to do is import rebgui.r using the "do" command.

NOTE:  rebgui.r is packaged with several additional files, which are in turn imported within the rebgui.r code.  Those files contain "lower level" code that actually define the new words and grammar that make up RebGUI itself.  They contain code that must all stay together with rebgui.r.  Just as the above program is not complete without the included rebgui.r file, rebgui.r itself is not complete without its included files.  As you begin to create longer and more complex programs, your source code will often consist of many separate source files tied together to make up a whole program.  Managing and remembering which included files are required in your programs becomes more of an obligation as you build applications of greater complexity.

Here are some web links containing free modules that can help you accomplish useful programmatic tasks in Rebol:

<a href="http://www.hmkdesign.dk/rebol/list-view/list-view.r" target=_blank>http://www.hmkdesign.dk/rebol/list-view/list-view.r</a> - a powerful listview widget to display and manipulate formatted data in GUI applications.  Perhaps the single most useful additional to the Rebol GUI language.

<a href="http://www.dobeash.com/it/rebdb/" target=_blank>http://www.dobeash.com/it/rebdb/</a> - a database module that lets you easily store and organize large amounts of data using the "SQL" database language.  There's also a spell checker module that can be included in your programs.

<a href="http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=rebzip.r" target=_blank>http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=rebzip.r</a> - a module to compress/decompress zip formatted files.

<a href="http://www.colellachiara.com/soft/Misc/pdf-maker.r" target=_blank>http://www.colellachiara.com/soft/Misc/pdf-maker.r</a> - a dialect to create pdf files directly in Rebol.

<a href="http://softinnov.org/rebol/mysql.shtml" target=_blank>http://softinnov.org/rebol/mysql.shtml</a> - a module to directly manipulate mysql databases within Rebol.  Very useful for web programming.

<a href="http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=menu-system.r" target=_blank>http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=menu-system.r</a> - a dialect to create all types of useful GUI menus in Rebol.  A later chapter is dedicated to this topic.

<a href="http://softinnov.org/rebol/uniserve.shtml" target=_blank>http://softinnov.org/rebol/uniserve.shtml</a> - a framework to help build client-server network applications

<a href="http://www.rebol.net/demos/BF02D682713522AA/i-rebot.r" target=_blank>http://www.rebol.net/demos/BF02D682713522AA/i-rebot.r</a> <a href="http://www.rebol.net/demos/BF02D682713522AA/objective.r" target=_blank>http://www.rebol.net/demos/BF02D682713522AA/objective.r</a> and <a href="http://www.rebol.net/demos/BF02D682713522AA/histogram.r" target=_blank>http://www.rebol.net/demos/BF02D682713522AA/histogram.r</a> - these examples contain a 3D engine module written entirely in native Rebol.  The module lets you easily add and manipulate 3D graphics objects in your Rebol apps. 

<a href="http://web.archive.org/web/20030411094732/www3.sympatico.ca/gavin.mckenzie/" target=_blank>http://web.archive.org/web/20030411094732/www3.sympatico.ca/gavin.mckenzie/</a> - a Rebol XML parser library.

<a href="http://box.lebeda.ws/~hmm/rswf/" target=_blank>http://box.lebeda.ws/~hmm/rswf/</a> - a dialect to create flash (SWF) files directly from Rebol scripts.

<a href="http://www.rebolforces.com/articles/tui-dialect/" target=_blank>http://www.rebolforces.com/articles/tui-dialect/</a> - a dialect to position characters on the screen in command line versions of Rebol.

<a href="http://www.rebol.net/docs/makedoc.html" target=_blank>http://www.rebol.net/docs/makedoc.html</a> - converts text files into nicely formatted HTML files.  This tutorial is written and maintained entirely with the Makedoc tool.

<a href="http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=layout-1.8.r" target=_blank>http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=layout-1.8.r</a> - a simple visual layout designer for Rebol GUI code.


<a href="http://www.rebol.org" target=_blank>http://www.rebol.org</a> - the official Rebol library - full of many additional modules and useful code fragments.  The first place to look when searching for Rebol source code.


Pieces of code aren't always intended strictly for modular reuse, but can be found within published open source programs.  Searching for useful code sections within programs released to the public is a vital way to save time and programming effort, and to improve your capabilities as a developer.  A great deal of potential work in any conceivable programming domain has already been accomplished by developers around the world.  Always check for functionalities you need in related programs written by other programmers.  If the examples you find are well commented and organized, you'll likely be able to reuse some of the code with limited effort.  (Be on the lookout especially for useful function word definitions).

A list of Internet resources containing available source code has been included at the end of this tutorial.  The programs available at those sites are a gold mine of existing code, necessary for productive development work.


---Using External Programs as "Modules":

Remember that data is often interoperable between existing programs.  Once data has been saved to a storage medium, you can pass it to other tools.  The built-in Rebol word "Call" allows you to run other programs on your computer.  It provides a variety of options to send command line parameters and deal with output from those programs.  Using "Call", you can execute all of the built in "shell" commands included in your computer's operating system (i.e., DOS and Unix commands).  You can even embed and use entire premade applications to help manipulate data in your Rebol programs.  The example below opens Windows' Notepad to edit the "rebgui_example.r" text file created earlier:

	call "notepad.exe c:\rebgui_example.r"

This next example opens Windows' Paint program to edit an image we downloaded earlier in the tutorial:

	call "mspaint.exe c:\bay.jpg"

Here's an example that embeds an executable program into the code, decompresses, and writes the program to the hard drive, and then runs it with the call function:

	program: load to-binary decompress 64#{
	eJztF11sU2X03K4VqJsrkZJp6OzchhFJsx8qDB9od1fHdIO6ds7AgJX2jttyey/p
	vWUjJuNnmNhMibzwaCSLi+EBE1ziGIkBGh0BSYTwwAMme9Dk4kgkgSiKcj3nu7es
	QrKFhMUQOcn5+c7fd875+vXe27FJAg4AbIiGAQwWIwZMEbqTcmODN5xRdmRi6aoy
	Z83YogngLlaNtV+s6kV7q9KelHeu9LYqQTXt7e/v97UqLcLuqKJIvriShnAIoJ0r
	gXvPn+StlDAF5dyzHLwAdlw4TZ1Mm7oQvWDu7jKLslsxBc4KQ30bb9bMHF3F/D5j
	MFAHEIbHD+cwb88s9riSEIjvK7EKogZs//bxAvQmYlqM5JsOUwHPWFgEAYDTvqTp
	eYdy1Fn5Sh/O96h9nLrrDcD4IpQm7UOkWL/nt6MlqMvxrkl+GVWS7xqWalzDzqGz
	9rbyD5ehpmnl+ezt3M/RSPe7Q9/ajeh5+9Ztm3vKh9xoM7SaimLUR18C2JKf+Kg2
	APoJwzDOuiAF+hHU/pHXryObdLyP+y2kEhx7UaLfo0gq/RJa60/n88Ndrpz7FmqG
	u5bk3L8zwdWXc0+jdOYXkn4lnYfW++/qOPLyDz7BfH3jTXVnplx949inhPvnSgw/
	8RSIHM7P8PdSUYtxlxSkONE+o/u7EkNElMbpcuRKUhTjmLH/iHbDQQ7DHqL77zbh
	oQxeRa9duBQHkRj+HnIdr7y/e178AvmmnHt5VQAmaNo59/EZ8QSJAY7EURJvMu2x
	KipYj2CaEToYve2eYYiwl4rWY6jN8RWF5XtsuWSyhO7aJG8XXQFkNdWYIqIHK8nH
	8FOSFJMoteEfZfQEo1SNCPCW2/BTjWK1uXkp9dDDegjrDqpkAUtiJhNp4ma3qUrx
	MG6dqkyFMQ2ExQmaxgU2c/07D2ZJsCz3Q68Xh76Cvac2pZwi8jCO8rIZd4jielmc
	uHxmsEMe1vMBZJf0YY8Pda95yH5p+tWrI86XMZbTE5a1gVlXFKyryeowp0Cy4Wf+
	hdSrWGp26N008hW4XnS6/OBS7MnUVHoK0osoTV+22qF56c95qKdtZBzB66J/imSc
	/Rmsg/KDdHFbA9O3RrZWByD/qPf1KTCwze3y2KCbn9vnP4ExoItiwr11zvncqq6+
	oXGV//XVa5qCzXxL6M3ZfBfMZyFPBvywgD3FGDjLnGVl83o4T+HJAZ/PFxWTqrcj
	GxerHljRqyL9sWXxqU2/nkHki1H4HDkvJeM7vZooeLdnNU2R10K34G1XdgveTmE7
	vmv7fNDcFY1u3ABpNa5J6rZd9MouqGpjw6z1GLXn6vDxV/s9o1cYvcroNUanGP2J
	UZ3RG4zeZPQ2o3cY/YtRqCdqZ3Qho6WMuhitYHQZ0pr6mRr21Zvv03VFuuMoX0Gd
	VqT7BlupKFoXw8eo/8yynUR+HvEa4g3EPxEXYuwSxOWIaxADiGHEBKKGeADxCOIx
	a1wXkE81zH/ut0OdG0LtjQ2+hCSBzLUKWoeSyErC+pickIQgfAmhgaSG319xPEvo
	ioQ6Ld9D0CL04ddZQuknaxA4W1hRtXeySa0DXWM7BHjDFhHkhLUKYs2cJTcrA0H4
	mmtXYgk+m1GVTBBOsVVbXJGDsNTWKexIqpqQ4aWYqgbps4LPCDFNMPcLYXQpldrC
	g0bcVHcKcQ220DqyB4PTHYKWScZVgCGsw/LBEgHWsjYLZR2zRTMxWZUwfaFwOAot
	SXVXTIuLM9V/ZeuSMw/UxW/s4KOF6W2GNjmp8Uo6rci8ImsZRVLxG+1hZWhgrlv6
	/4F/ABcSIgQAEAAA
	}
	write/binary %program.exe program
	call %program.exe

=image rebol_tutorial/we_love.png
=image rebol_tutorial/we_love2.png

Copy and paste that entire block of code into the Rebol interpreter and run it.  It will execute a little demo program, which was written and created by a language entirely unrelated to Rebol.

There are a world of open source applications available to perform just about every specific high level task conceivable.  Many are free to use and distribute even in commercial applications (see <a href="http://sourceforge.net" target=_blank>http://sourceforge.net</a> ).  If you can interface with them on the command line, they can be used to help in your own applications - even if you don't know how they were written.  This extends the power of the language, but can also restrict it's cross platform usability.  For example, if you write a program that calls DOS operating system commands, that program can't be used on a UNIX system.

Whenever you use any executable or code created by another programmer, be absolutely sure to check, and follow, the licensing terms by which it's distributed.



===A Quick Summary of the Rebol Language

The list below summarizes some key characteristics of the Rebol language.  Knowing how to put these elements to use constitutes a fundamental understanding of how Rebol works:

# To start off, Rebol has hundreds of built-in function words that perform common tasks.  As in other languages, function words are typically followed by passed parameters.  Unlike other languages, passed parameters are placed immediately after the function word and are <i>not</i> necessarily enclosed in parenthesis.  To accomplish a desired goal, functions are arranged in succession, one after another.  Line terminators are not required at any point, and all expressions are evaluated in left to right order, then vertically down through the code.  For example, "function1 parameter1 parameter2 function2 parameter function3 (expression that evaluates to a single parameter)" is a valid line that evaluates 3 functions from left to right.  Empty white space (spaces, tabs, newlines, etc.) can be inserted as desired to make code more readable.  Text after a semicolon and before a new line is treated as a comment.  You can complete significant work by simply knowing the predefined functions in the language, and organizing them into a useful order.  

# Rebol contains a rich set of conditional and looping structures, which can be used to manage program flow and data processing activites.  If, while, for, foreach, and other typical structures are supported.  More powerful and specific looping structures and conditions such as "forskip", "any", and "all" add to Rebol's flexibility.

# Because many common types of data values are automatically recognized and handled natively by Rebol, calculating, looping, and making conditional decisions based upon data content is straightforward and natural to perform, without any external modules or toolkits.  Numbers, text strings, money values, times, tuples, urls, binary representations of images, sounds, etc. are all automatically handled.  Rebol can increment, compare, and perform proper computations on most common types of data (i.e., the interpreter automatically knows that 5:32am + 00:35:15 = 6:07:15am, and it can automatically apply visual effects to raw binary image data, etc.).  Network resources and Internet protocols (http documents, ftp directories, email accounts, dns services, etc.) can also be accessed natively, just as easily as local files.  Data of any type can be written to and read from virtually any connected device or resource (i.e., "write %file.txt data" works just as easily as "write ftp://user:pass@website.com data", using the same common syntax).  The percent symbol ("%") and the syntax "%(/drive)/path/path/.../file.ext" are used cross-platform to refer to local file values on any operating system.

# Any data or code can be assigned a word label.  The colon character (":") is used to assign word labels to constants, variable values, evaluated expressions, functions, and data/action blocks of any type.  Once assigned, variable words can be used to represent all of the data and/or actions contained in the given expression, block, etc.  Just put a colon at the end of a word, and thereafter it represents all the following actions and/or data.  That forms a significant part of the Rebol language structure, and is the basis for it's flexible natural language dialecting abilities.  Because anything in Rebol, data or code, can be grouped together and assigned a label, it's easy to organize coding thought and data structure in a way that tends to flow like natural human language thought processes.

# Both data and action code are stored in "blocks", which are delineated by starting and ending brackets ("[]").  Blocks can contain data of <i>any</i>  type:  groups of text strings, arrays of resource locators, collections of related binary data, collections of actions (functions), other enclosed blocks, etc.  Data items contained in blocks are separated by white space.  Blocks can be automatically treated as lists of data, called "series", and manipulated using built-in functions that enable searching, sorting, ordering, and otherwise organizing the blocked data.  Data and function words contained in blocks can be evaluated (their actions performed and their data values assigned) using the "do" word.  New function words can also be defined using the "does" and "func" words.  "Does" forces a block to be evaluated every time its word label is encountered.  The "func" word creates an exectuable block in the same way as "does", but additionally allows you to pass your own specified parameters to the newly defined function word.  You can "do" a module of code contained in a text file, as long as it contains the minimum header "rebol[]".  Blocks/series are a simple, freeform data structure that can be used to store any type of information or code.  The fact that data and code can be organized using one ubiquitous syntactic structure is another main reason Rebol is easier to use than other programming languages.

# The syntax "view layout [block]" is used to create basic GUI layouts.  You can add graphic widgets to the layout simply by adding widget identifier words to the enclosed block: "button", "field", "text-list", etc.  Color, position, spacing, and other facet words can be added after each widget identifier.  Action blocks added immediately after any widget will perform the enclosed functions whenever the widget is activated (i.e., when the widget is clicked with a mouse, when the enter key pressed, etc.).  Path refinements can be used to refer to items in the GUI layout (i.e., "face/offset" refers to the position of the selected widget face).  Those simple guidelines can be used to create useful GUIs for data input and output, in a way that's native (doesn't require any external toolkits) and much easier than any other language.

Because of the simple GUI syntax, the remarkably uncluttered general coding syntax, and the single ubiquitous block data structure, Rebol programs can be much shorter, simpler, and more powerful than comparable code in any other language (see http://www.rebol.com/oneliners.html).


---Using Rebol's Built-In Help

Typing "help (any word)" at the Rebol console prompt will display required syntax for any built-in Rebol function.  The word "what" lists all built-in words.  Together, those two words provide a reference that's sufficient for most situations in which you need syntax help - without any external guide.  "Help system" displays the contents of the Rebol system object, which contains many important settings and values.  You can explore each level of the system object using path notation (i.e., "editor system/view/VID/vid-styles").  The Rebol "desktop" that appears by default when you run the view.exe interpreter can also be used as a gateway into a world of "Rebsites" that developers use to share useful code.  Surfing the public rebsites is a great way to explore the language more deeply.  All of the code in the rebol.org archive, and much more, is available on the rebsites.  It's amazing what you can do with that little view.exe file!

=image rebol_tutorial/helpforeach.png
=image rebol_tutorial/what.png
=image rebol_tutorial/editorstyles.png



===8 Complete Rebol Programs For You To Study

The following programs use a number of techniques explained throughout the tutorial.  They demonstrate how pieces of code can be put together to construct complete applications, and they provide some guidance as to how basic language building blocks can be assembled for useful purposes.  There are detailed line-by-line explanations of each program included in the comments (it's amazing how short these programs are without the comments!).  Studying these examples is perhaps the most valuable part of the tutorial.

A downloadable package of all the demo programs is available at:  <a href="http://musiclessonz.com/rebol_tutorial_examples.zip" target=_blank>http://musiclessonz.com/rebol_tutorial_examples.zip</a>.  The zip file contains screenshots, separated source code, and packaged executables (clickable ".exe" files) of each example.  The XpackerX XML files used to create each executable are also included.

NOTE:  In order to fit the code examples within the width of a web page, certain formatting options have been introduced.  Long lines of code have been shortened, so they they don't get chopped off when printed.  The built in word "trim" has been used to clean long strings of text that are written on separate lines.

	mystring: trim {
		This string}

is the same as:

	mystring: "This string" 

"Join" and "rejoin" have also been used to join together long sections of text:

	join "All " [
		"the "
		"same "
		"line of text."
	]

is the same as:

	"All the same line of text."

Blocks have also been written onto multiple lines where necessary:

	myblock: [This
	block
	]

is the same as:

	myblock: [This block]


To run the example programs in this section, you can use any of the methods described earlier:  type or copy/paste the code into the Rebol interpreter, save the program as a text file and run it using "do {filename}", install the Rebol interpreter on your computer and click the saved code file (this is the easiest way), use XpackerX to package and distribute it as an executable, etc.  


--- Little Email Client

The first example is a complete graphical email client that can be used to read and send messages.  The code is heavily commented to provide line-by-line explanations of how each element works:

	Rebol [Title: "Little Email Client"] 
	; (every program requires a minimum header)

	view layout [
			; The line above creates the GUI layout.
		h1 "Send Email:"
			; The second line adds a text label to the GUI.
		address: field "recipient@website.com"
			; This line creates a text entry field, containing
			; the default text "recipient@website.com".  It assigns
			; the variable word "address" to the text entered here.
		subject: field "Subject" 
			; another text entry field for the email subject line
		body: area "Body"
			; This creates a larger, multiline text entry area for
			; the body text of the email.
		btn "Send" [
				; A button with the word "send".  The functions
				; inside this action block are executed whenever
				; the button is clicked.
			send/subject to-email address/text body/text subject/text
				; This line does most of the work.  It uses the 
				; built-in Rebol word "send" to send the email.  The
				; send function, with its "/subject" refinement
				; accepts three parameters.  It's passed the current
				; text contained in each field labeled above
				; (referred to as "address/text" "body/text" and
				; "subject/text").  The built-in "to-email" function
				; ensures that the address text is treated as an
				; email data value.
			alert "Message Sent."
				; alerts the user when the previous line is complete.
		]
		h1 "Read Email:"
			; Another text label
		mailbox: field "pop://user:pass@website.com"
			; Another text entry field.  The user's email account
			; info is entered here.
		btn "Read" [
				; An additional button, this time with an action
				; block that reads messages from a specified mailbox.
				; It only takes one line:
			editor read to-url mailbox/text
				; The built-in "to-url" function ensures that the
				; text in the mailbox field is treated as a url.  
				; The contents of the mailbox are read and displayed
				; in the built-in Rebol editor.
		]
	]

=image rebol_tutorial/little_email_client.png

Here's the same code, without comments - it's very simple:

	Rebol [Title: "Little Email Client"]

	view layout [
		h1 "Send Email:"
		address: field "recipient@website.com"
		subject: field "Subject"
		body: area "Body"
		btn "Send" [
			send/subject to-email address/text body/text subject/text
			alert "Message Sent."
		]
		h1 "Read Email:"
		mailbox: field "pop://user:pass@website.com"
		btn "Read" [
			editor read to-url mailbox/text
		]
	]


--- FTP Chat Room

The second example is a simple chat application that lets users send instant text messages back and forth across the Internet.  It includes password protected access for administrators to erase chat contents.  It also allows users to pause activity momentarily, and requires a username/password to continue ["secret" "password"].  The chat "rooms" are created by dynamically creating, reading, appending, and saving text files via ftp (to use the program, you'll need access to an available ftp server:  ftp address, username, and password).  


	Rebol [title: "FTP Chat Room"]  ; required header

	webserver: to-url request-text/title/default trim {
		Web	Server Address:} {ftp://user:pass@website.com/chat.txt}
	; get the url of a webserver text file to use for the chat.
	; The ftp username, password, domain, and filename must be 
	; entered in the format shown.

	name: request-text/title "Enter your name:"
	; get the user's name

	cls: does [prin "^(1B)[J"]
	; "cls" now clears the screen (explained earlier in the tutorial).

	write/append webserver join now [
		": " name " has entered the room." newline
	]
	; The line above writes some text to the webserver.
	; The "/append" refinement adds it to the existing 
	; text in the webserver file (as opposed to erasing
	; what's already there).  Using "join", the text 
	; written to the webserver is the combined value of 
	; {the user's name}, some static text, the current 
	; date and time, and a carriage return.

	forever [
		current-chat: read webserver 
		; read the messages that are currently on the webserver,
		; and assign the variable word "current-chat"

		cls ; clear the screen using the word defined above
		print join "--------------------------------------------------" [
			newline {You are logged in as: } name newline 
			{Type "room" to switch chat rooms.} newline
			{Type "lock" to pause/lock your chat.} newline
			{Type "quit" to end your chat.} newline 
			{Type "clear" to erase the current chat.} newline 
			{Press [ENTER] to periodically update the display.} newline 
			"--------------------------------------------------" newline]
		; displays a greeting and some instructions

		print join "Here's the current chat text at: " [webserver newline]
		print current-chat 

		sent-message: copy join name [
			" says: " entered-text: ask "You say:  "
		] 
		; get the text to send, then check for commands below 
		; ("quit", "clear", "room", "lock", and [ENTER])
		; The built-in word "ask" requests some info within
		; the interpreter.

		switch/default entered-text [
			"quit" 	[break] 
					; if the user typed in "quit", 
					; stop the forever loop (exit the program)
			"clear" [
				if/else request-pass = ["secret" "password"] [
					write webserver ""] [alert trim {
					You must know the administrator 
					password to clear the room!}
				]
			]
					; if the user typed in "clear", erase the 
					; current text chat.  But first, ask user 
					; for the administrator username/password 
			"room" 	[
				write/append webserver join now [
					": " name " has left the room." newline]
				webserver: to-url request-text/title/default {New Web 
				Server Address:} to-string webserver
				write/append webserver join now [
					": " name " has entered the room." newline
				]
			]
					; if the user typed in "room", request a new 
					; webserver address, and run some code that was 
					; presented earlier in the program,
					; using the newly entered "webserver" variable, 
					; to effectively change chat "rooms". 
			"lock" [
				alert trim {The program will now pause for 5 seconds. 
					You'll need the correct username and password 
					to continue.}
				pause-time: now/time + 5  
				; assign a variable to the time 5 seconds from now
				forever [if now/time = pause-time [
					; wait 5 seconds
					while [request-pass <> ["secret" "password"]] [
						alert "Incorrect password - look in the source!"
						]
					; don't go on until the user gets the password right.
					break
					]
				]
				; exit the forever loop after 5 seconds have passed
			]
		] [if entered-text <> "" [
				write/append webserver join sent-message [newline]]]
		  ; default case: as long as the entered message is not 
		  ; blank ([Enter]), write the message to the web server 
		  ; (append it to the current text)
	]
	; when the "forever" loop is exited, do the following:
	cls print "Goodbye!" 
	write/append webserver join now [
		": " name " has closed chat." newline]
	wait 1

=image rebol_tutorial/chat_room.png

The bulk of the program runs within a "forever" loop, and uses a conditional "switch" statement to decide how to respond to user input.  This is a classic structure that can be adjusted to match a variety of generalized situations in which the computer repeatedly waits for and responds to user interaction.


--- Looping Through Data

One of the most important applications of loop structures is to step through lists of data.  By stepping through elements in a block, loops can be used to process and perform actions on each item in a given data series.  This technique is used in all types of programming, and it's a cornerstone of the way programmers think about working with tables of data (such as those found in databases).  Because many programs work with lists of data, you'll very often come across situations that require the use of loops.  Thinking about how to put looping structures to use is a fundamental part of learning to write code in any language.  The example below demonstrates several ways in which you'll see loops commonly put to use.  Be sure to see case study #5 in the "Real World Examples" section for a GUI version of this code.

	; First, a small user database is defined.  It's organized
	; into a block structure:  the "users" block contains 5 
	; blocks, which each contain 5 items of information for
	; each user.  Blank items are represented with empty quotes.  
	; Note that each block is split onto two lines, so that 
	; they fit onto this web page (they don't need to be split
	; this way in normal use):

	users: [
		["John" "Smith" "123 Toleen Lane"
			"Forest Hills, NJ" "555-1234"]
		["Paul" "Thompson" "234 Georgetown Place"
			"Peanut Grove, AL" "555-2345"]
		["Jim" "Persee" "345 Portman Pike"
			"Orange Grove, FL" "555-3456"]
		["George" "Jones" "456 Topforge Court"
			"Mountain Creek, CO" ""]
		["Tim" "Paulson" "" 
			"" "555-5678"]
	]

	; This program does not have a GUI.  Instead, it's a text
	; based "console" program.  Since there's no GUI, we need
	; to format the output so that it's got a nice layout on the
	; screen.  Here's a little function that uses a loop to draw
	; a line.  It prints 65 dashes next to each other, and then
	; a carriage return.  We'll use those lines to help print 
	; nicely formatted output:

	draw-line: does [loop 65 [prin "-"] print ""]

	; Note that this is not the most efficient way to draw a line
	; of characters, because the program needs to run through
	; the loop every time a line is drawn.  You'll see some 
	; flicker on the screen every time this happens, because
	; the computer has to run through the "prin" function 65 
	; times for each line.  Although it only takes a fraction of
	; a second on a modern computer, it's still quite noticable.
	; It would be faster, instead, to build a block of characters
	; once, and then print that block, as follows:
	;
	; 		a-line: copy []
	;		loop 65 [append a-line "-"]
	;		; remove the spaces and turn it
	;		; into a string of characters:
	;		a-line: trim to-string a-line
	;		; now you can print "a-line"
	;		; anywhere you need it:
	;		print a-line
	;
	; The inefficient code above is left in this example to 
	; demonstrate a point about how the coding thought process
	; can dramatically effect the performance of programs you
	; create.  That's especially true for programs that perform
	; complex loops on large lists of data.  The more effecient
	; line printing function is implemented in another example
	; following this one, to demonstrate the difference in its
	; effectiveness.

	; Next is a small function that prints out all of the data
	; in the database.  It uses a foreach loop to cycle through
	; each block of user data, and then it prints a line
	; displaying each element in the block (items numbered 1-5 
	; in each block).  This creates a nicely formatted display:

	print-all: does [
		foreach user users [
			draw-line
			print rejoin ["User:     " user/1 " " user/2]
			draw-line
			print rejoin ["Address:  " user/3 "  " user/4]
			print rejoin ["Phone:    " user/5]
			print newline
		]
	]

	; The following code uses a forever loop to continually
	; request a choice from the user.  It uses several foreach
	; loops to pull information from the data block, and a 
	; conditional "switch" structure to decide how to respond
	; to the user's request (as in the ftp chat example above, 
	; the "switch" inside a forever loop is used - it's a 
	; common design in command line programs):

	forever [

		; First, print some nice formatting and display info:

	    prin "^(1B)[J"  ; this code clears the screen.
	    print "Here are the current users in the database:^/"
		; The "^/" at the end of the line above prints a newline.
		draw-line

		; Now print the list of user names.  A foreach loop is 
		; used to get the first and last name of each user in the
		; database.  The first name is item 1 in each block, and
		; the last name is item 2 in each block.  So for each 
		; block in the database, "user/1" and "user/2" are 
		; printed:

		foreach user users [prin rejoin [user/1 " " user/2 "  "]]
	    print "" 
		draw-line

		; Now ask the user for a choice:

		print "Type the name of a user below.^/"
		print "Type 'all' for a complete database listing."
		print "Press [Enter] to quit.^/"
	    answer: ask {What person would you like info about?  }
		print newline

		; Now decide what to do with the user's response:

		switch/default answer [

			; If they typed "all", execute the "print-all"
			; function defined earlier:

			"all" [print-all]

			; If they typed the [Enter] key alone (""), print a
			; goodbye message, and end the program.  Note that
			; "ask" is used to display the message, instead of
			; "print".  This allows the program to wait for the 
			; user to press a key before ending the program:

	    	"" [ask "Goodbye!  Press [Enter] to end." quit]

			; If neither of the choices above were selected, the
			; default block below is executed (this is the last
			; part of the switch structure):

			][

			; This section starts by creating a "flag" variable,
			; which is used to track whether or not the user's 
			; choice has been found in the database - the word 
			; "found" is initially set to false to indicate that
			; the user name has not yet been found:

			found: false

			; Next, a foreach loop steps through each user block
			; in the database:

			foreach user users [

				; If the entered user name is found in the
				; database (either the first or last name), the
				; info for that user is printed out in a nicely
				; formatted display, and the "found" flag is set
				; to true.  The "rejoin" action is used to join
				; the first name and last name, and is used in
				; conjunction with the "find" action to check
				; whether the user's answer matches any part of
				; the names in the database (when you run this
				; code, try entering single characters, or a 
				; part of a name, to see what happens).

				if find rejoin [user/1 " " user/2] answer [
					draw-line
					print rejoin ["User:     " user/1 " " user/2]
					draw-line
					print rejoin ["Address:  " user/3 " " user/4]
					print rejoin ["Phone:    " user/5]
					print newline
					found: true
				]
			]

			; If the "found" variable is still false after
			; looping through the entire user database, then the
			; user name was not found in the database.  Print a
			; message to that effect:

			if found <> true [   ; "<>" means "not equal to"
				print "That user is not in the database!^/"]
		]

		; Wait for a user response, and then continue again at 
		; the beginning of the forever loop:

	    ask "Press [ENTER] to continue"
	]

=image rebol_tutorial/users.png

Here's the entire program without the comments.  Try to follow the program flow on your own.  NOTE:  In this version, the ineffient "draw-line" function is replaced by the suggested "print a-line" routine above.  As a result, you'll see a dramatic reduction in screen flicker:

	users: [
		["John" "Smith" "123 Tomline Lane"
			"Forest Hills, NJ" "555-1234"]
		["Paul" "Thompson" "234 Georgetown Place"
			"Peanut Grove, AL" "555-2345"]
		["Jim" "Persee" "345 Pickles Pike"
			"Orange Grove, FL" "555-3456"]
		["George" "Jones" "456 Topforge Court"
			"Mountain Creek, CO" ""]
		["Tim" "Paulson" "" 
			"" "555-5678"]
	]
	a-line: copy [] loop 65 [append a-line "-"]
	a-line: trim to-string a-line
	print-all: does [
		foreach user users [
			print a-line
			print rejoin ["User:     " user/1 " " user/2]
			print a-line
			print rejoin ["Address:  " user/3 "  " user/4]
			print rejoin ["Phone:    " user/5]
			print newline
		]
	]	
	forever [
	    prin "^(1B)[J"
	    print "Here are the current users in the database:^/"
		print a-line
		foreach user users [prin rejoin [user/1 " " user/2 "  "]]
	    print "" print a-line
		print "Type the name of a user below.^/"
		print "Type 'all' for a complete database listing."
		print "Press [Enter] to quit.^/"
	    answer: ask {What person would you like info about?  }
		print newline
		switch/default answer [
			"all" 	[print-all]
	    	"" 		[ask "Goodbye!  Press any key to end." quit]
			][
			found: false
			foreach user users [
				if find rejoin [user/1 " " user/2] answer [
					print a-line
					print rejoin ["User:     " user/1 " " user/2]
					print a-line
					print rejoin ["Address:  " user/3 " " user/4]
					print rejoin ["Phone:    " user/5]
					print newline
					found: true
				]
			]
			if found <> true [
				print "That user is not in the database!^/"
			]
		]
	    ask "Press [ENTER] to continue"
	]

=image rebol_tutorial/looping2.png

For some perspective, here's a GUI version of the same program that demonstrates how GUI and command line programming styles differ.  Notice how much of the data handling is managed by the built-in GUI tools in the language, rather than by homemade loops:

	Rebol [title: "User Database GUI Example"]

	users: [
		["John" "Smith" "123 Tomline Lane"
			"Forest Hills, NJ" "555-1234"]
		["Paul" "Thompson" "234 Georgetown Place"
			"Peanut Grove, AL" "555-2345"]
		["Jim" "Persee" "345 Pickles Pike"
			"Orange Grove, FL" "555-3456"]
		["George" "Jones" "456 Topforge Court"
			"Mountain Creek, CO" ""]
		["Tim" "Paulson" "" 
			"" "555-5678"]
	]
	user-list: copy []
	foreach user users [append user-list user/1]
	user-list: sort user-list

	view display-gui: layout [
		h2 "Click a user name to display their information:"
		across
	    list-users: text-list 200x400 data user-list [
			current-info: []
			foreach user users [
				if find user/1 value [
					current-info: rejoin [
						"FIRST NAME:  " user/1 newline newline
						"LAST NAME:   " user/2 newline newline
						"ADDRESS:     " user/3 newline newline
						"CITY/STATE:  " user/4 newline newline
						"PHONE:       " user/5
					]
				]
			]
			display/text: current-info
			show display show list-users
	    ]
		display: area "" 300x400 wrap
	]

=image rebol_tutorial/users2.png

More powerful and specific looping structures and conditions such as "forskip", "any", and "all" add to Rebol's flexibility.  For more information, see the Rebol Dictionary in the Rebol desktop folder REBOL->Tools.


--- Image Effector

The next application creates a GUI interface, downloads and displays an image from the Internet, allows you to apply effects to it, and lets you save the effected image to the hard drive.  In the mix, there are several routines which get data, and alert the user with text information.  


	REBOL [Title: ""] 
	; header is still required, even if a title isn't included	

	effect-types: ["Invert" "Grayscale" "Emboss" "Blur" "Sharpen"
					"Flip 1x1" "Rotate 90" "Tint 83" "Contrast 66"
					"Luma 150" "None"] 
	; this creates a short list of image effects that are built 
	; into Rebol, and assigns the variable word "effect-types" 
	; to the block

	do %/c/play_sound.r
	; The line above imports the simple "play-sound" function 
	; created earlier in the tutorial.  For this program to work 
	; correctly as it is, the play_sound.r file should be saved 
	; to C:\

	image-url: to-url request-text/title/default {
		Enter the url of an image to use:} trim {
		http://rebol.com/view/demos/palms.jpg}
	; ask user for the location of a new image (with a default
	; location), and assign it to the word "new-image"

	gui: [

	; The following code displays the program menu, using a 
	; "choice" button widget (a menu-select type of button 
	; built in to Rebol).  The button is 160 pixels 
	; across, and is placed at the uppermost, leftmost 
	; pixel in the GUI (0x0) using the built-in word "at".  
	; The action block for the button contains various 
	; functions to be performed, based on the selected choice
	; (using conditional "if" evaluations.  This could have
	; been done with less code, using a "switch" syntax.  
	; "If" was used, however, to demonstrate that there are
	; always alternate ways to express yourself in code - 
	; just like in spoken language.).

		across 
		; horizontally aligns all the following GUI widgets, 
		; so they appear next to each other in the layout 
		; (the default behavior in Rebol is to align elements 
		; vertically).
		space -1 
		; changes the spacing of consecutive widgets so they're
		; on top of each other
		at 20x2 choice 160 tan trim {
			Save Image} "View Saved Image" "Download New Image" trim {
				-------------} "Exit" [
			if value = "Save Image" [ 
				filename: to-file request-file/title/file/save trim {
					Save file as:} "Save" %/c/effectedimage.png
				; request a filename to save the image as, 
				; defaults to "c:\effectedimage.png"
				save/png filename to-image picture 
				; save the image to hard drive
			]
			if value = "View Saved Image" [
				view-filename: to-file request-file/title/file trim {
					View file:} "Save" filename
				view/new center-face layout [image load view-filename]
				; read the selected image from the hard drive 
				; and display it in a new GUI window
			] 
			if value = "Download New Image" [
				new-image: load to-url request-text/title/default trim {
					Enter a new image url} trim {
					http://www.rebol.com/view/bay.jpg}
				; ask for the location of a new image, 
				; and assign it to the word "new-image"
				picture/image: new-image
				; replace the old image with the new one
				show picture ; update the GUI display
			]
			if value = "-------------" [] ; don't do anything
			if value = "Exit" [
				play-sound %/c/windows/media/tada.wav
				quit ; exit the program 
			] 		
		]

		choice tan "Info" "About" 
			[alert "Image Effector - Copyright 2005, Nick Antonaccio"] 
		; a simple "about" box	

		below 
		; vertically aligns successive GUI widgets - 
		; the opposite of "across"
		space 5 
		; spread out the widgets some more
		pad 2 
		; put 2 pixels of blank space before the next widget
		box 550x1 white 
		; draws a line 550 pixels wide, 1 pixel tall 
		; (just a cosmetic separator)
		pad 10	
		; put some more space between widgets
		vh1 "Double click each effect in the list on the right:" 
		; a big text header for the GUI		
		return 
		; advances to the next row in the GUI
		across

		picture: image load image-url
		; get the image entered at the beginning of the program, 
		; and give it a label

		text-list data effect-types [
			current-effect: to-string value 
			picture/effect: to-block form current-effect 
			show picture
		]

		; The code above creates a text-list gui widget 
		; and assigns a block of actions to it, to be run whenever the 
		; user clicks on the list.  The block of actions is indented 
		; and each action is placed on separate line for readability.  
		; The first line assigns the word "current-effect" to the value 
		; which the user has selected from the list.  The second line 
		; applies that effect to the image (the words "to-block" and "form"
		; are required for the way effects are applied syntactically.  
		; The third line displays the newly effected image.  The "show" 
		; word is _very_ important.  It needs to be used whenever a GUI 
		; element is updated.
	]

	view/options center-face layout gui [no-title] 
	; display the gui block above
	; "/options [no title]" displays the window without a title bar 
	; (so it can't be moved around), 
	; and "center-face" centers the window on the screen

=image rebol_tutorial/image_effector.png

The built-in words included in the image effector program are:  rebol[], invert, grayscale, emboss, blur, sharpen, flip, rotate, tint, contrast, luma, none, vh1, across, image, load, text-list data, to-string, to-block, to-image, to-url, value, form, show, return, button, save/png, alert, view/new, center-face, layout, at, now/time, forever, while, request-pass, request-text/title/default, request-file/title/file/save, break, quit, center-face, space, box, pad.  

The image effector also imports and uses the "play-sound" module created earlier in the tutorial.  It plays a sound when the program is shut down.


--- Sliding Tile Game

Here's a simple example that implements a GUI version of the classic sliding tile game ... in only 8 lines of code.  The board contains 15 movable pieces and 1 empty space.  The point is to rearrange the pieces in inverse numerical order on the grid.  A piece can only be moved if the empty space is adjacent to its border.  Click on a piece to slide it into the empty space.     


	Rebol [Title: "Sliding Tile Game"]

	gui: [

		; Define some basic layout parameters.  "origin 0x0" 
		; starts the layout in the upper left corner of the
		; GUI window.  "space 0x0" dictates that there's no
		; space between adjacent widgets, and "across" lays
		; out consecutive widgets next to each other:

		origin 0x0 space 0x0 across 

		; The "style" word below allows you to redefine the 
		; appearance and action characteristics of any built-
		; in GUI widget.  The section below creates a newly
		; defined button style called "piece", with an action
		; block that swaps the current button's position with
		; that of the adjacent empty space.  That action is 
		; run whenever one of the buttons is clicked.

		style piece button 60x60 [

			; The line below checks to see if the clicked button
			; is adjacent to the empty space.  The "offset" 
			; refinement contains the position of the given 
			; widget.  The word "face" is used to refer to the
			; currently clicked widget.  The "empty" button is
			; defined later (at the end of the GUI layout).
			; It's ok that the empty button is not yet defined,
			; because this code is not evaluated until the
			; the entire layout is built and "view"ed:

			if not find [0x60 60x0 0x-60 -60x0] 
				face/offset - empty/offset [exit]

			; In English, that reads 'subtract the position of
			; the empty space from the position of the clicked
			; button (the positions are in the form of 
			; Horizontal x Vertical coordinate pairs).  If that 
			; difference isn't 60 pixels on one of the 4 sides,
			; then don't do anything.' (60 pixels is the size of
			; the "piece" button defined above.)

			; The next three lines swap the positions of the 
			; clicked button with the empty button.

			; First, create a variable to hold the current
			; position of the clicked button:

			temp: face/offset  

			; Next, move the button's position to that of the 
			; current empty space:

			face/offset: empty/offset 

			; Last, move the empty space (button), to the old
			; position occupied by the clicked button:

			empty/offset: temp
		]

		; The lines below draw the "piece" style buttons onto 
		; the GUI display.  Each of these buttons contains all
		; of the action code defined for the piece style above:

	    piece "1"   piece "2"   piece "3"   piece "4" return
	    piece "5"   piece "6"   piece "7"   piece "8" return
	    piece "9"   piece "10"  piece "11"  piece "12" return
	    piece "13"  piece "14"  piece "15"

		; Here's the empty space.  Its beveled edge is removed
		; to make it look less like a movable piece, and more
		; like an empty space:

		empty: piece 200.200.200 edge [size: 0]
	]

	; Display the whole GUI block, centered on the user's screen:

	view center-face layout gui

=image rebol_tutorial/tile_game.png

Here's the whole program without any comments, and reduced to a more compact format.  It's tiny:

	Rebol [Title: "Sliding Tile Game"]
	view center-face gui: layout [
		origin 0x0 space 0x0 across 
		style p button 60x60 [
			if not find [0x60 60x0 0x-60 -60x0] 
				face/offset - empty/offset [exit]
			temp: face/offset face/offset: empty/offset 
				empty/offset: temp
		]
	    p "A" p "B" p "C" p "D" return p "E" p "F" p "G" p "H" return
	    p "I" p "J" p "K" p "L" return p "M" p "N" p "O"  
		empty: p 200.200.200 edge [size: 0]
	]

Be sure to take a break from coding and play a few games :)


--- Guitar Chord Diagram Maker

The fifth example is a program that creates, saves, and prints collections of guitar chord fretboard diagrams.  It demonstrates some more common and useful file, data, and GUI manipulation techniques:

	Rebol [Title: "Guitar Chord Diagram Maker"]

	; load embedded images:

	fretboard: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAFUAAABkCAIAAAB4sesFAAAACXBIWXMAAAsTAAAL
	EwEAmpwYAAAA2UlEQVR4nO3YQQqDQBAF0XTIwXtuNjfrLITs0rowGqbqbRWxEEL+
	RFU9wJ53v8DN7Gezn81+NvvZXv3liLjmPX6n/4NL//72s9l/QGbWd5m53dbc8/kR
	uv5RJ/QvzH42+9nsZ7OfzX62nfOPzZzzyNUxxh8+qhfVHo94/rM49y+b/Wz2s9nP
	Zj+b/WzuX/cvmfuXzX42+9nsZ7OfzX4296/7l8z9y2Y/m/1s9rPZz2Y/m/vX/Uvm
	/mWzn81+NvvZ7Gezn8396/4l2/n+y6N/f/vZ7Gezn81+tjenRWXD3TC8nAAAAABJ
	RU5ErkJggg==
	}

	barimage: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAEoAAAAFCAIAAABtvO2fAAAACXBIWXMAAAsTAAAL
	EwEAmpwYAAAAHElEQVR4nGNsaGhgGL6AaaAdQFsw6r2hDIa59wCf/AGKgzU3RwAA
	AABJRU5ErkJggg==
	}

	dot: load 64#{
	iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAIAAAACUFjqAAAACXBIWXMAAAsTAAAL
	EwEAmpwYAAAAFElEQVR4nGNsaGhgwA2Y8MiNYGkA22EBlPG3fjQAAAAASUVORK5C
	YII=
	}

	; Gui Design:

	; The routine below was copied from 
	; http://rebol.com/how-to/feel.html

	movestyle: [
		engage: func [face action event] [
	    	if action = 'down [
	        	face/data: event/offset
	            remove find face/parent-face/pane face
	            append face/parent-face/pane face
	        ]
	        if find [over away] action [
	            face/offset: face/offset + event/offset - face/data
	        ]
	        show face
	    ]
	]

	; With that defined, adding "feel movestyle" to any widget
	; makes it movable within the GUI.  It's very useful for all 
	; sorts of graphic applications...  If you want to pursue 
	; building graphic layouts that respond to user events, learning
	; all about how "feel" works in Rebol is very important.  See
	; the URL above for more info.

	gui: [
		backdrop white
			; makes the GUI background white
		currentfretboard: image fretboard 255x300
			; show the fretboard image, and resize it 
			; (the saved image is actually 85x100 pixels)
		currentbar: image barimage 240x15 feel movestyle
			; Show the bar image, resize it, and make it movable.
			; Notice the "feel movestyle".  Thats' what enables 
			; the dragging.
		text "INSTRUCTIONS:" underline
		text "Drag dots and other widgets onto the fretboard."
		across	
		text "Resize the fretboard:"
		tab 
		; "tab" aligns the next GUI element with a predefined 
		; column spacer
		rotary "255x300" "170x200" "85x100" [
			currentfretboard/size: to-pair value show currentfretboard
			switch value [
				"255x300" [currentbar/size: 240x15 show currentbar]
				"170x200" [currentbar/size: 160x10 show currentbar]
				"85x100" [currentbar/size: 80x5 show currentbar]
			]
		]	

		; The rotary button above lets you select a size for the 
		; fretboard.  In the action block, the fretboard image is 
		; resized, and then the bar image is also resized,
		; according to the value chosen.  This keeps the bar size 
		; proportioned correctly to the fretboard image.  
		; After each resize, the GUI is updated to actually display 
		; the changed image.  The built-in word "show" updates the 
		; display.  This needs to be done whenever a widget is 
		; changed within a GUI.  Be aware of this - not "show"ing 
		; a changed GUI element is an easily overlooked source of 
		; errors.

		return
		button "Save Diagram" [
			filename: to-file request-file/save/file "1.png"
			save/png filename to-image currentfretboard
		]

		; The action block of the above button requests a filename 
		; from the user, and then saves the current fretboard image 
		; to that filename.

		tab

		; The action block of the button below prints out a user-
		; selected set of images to an html page, where they can be
		; viewed together, uploaded the Internet, sent to a printer,
		; etc.	

		button "Print" [
			filelist: 
				sort request-file/title "Select image(s) to print:"
			; Get a list of files to print.
			html: copy "<html><body>"
			; start creating a block that holds the html layout, 
			; and give it the label "html".
			foreach file filelist [
				append html rejoin [
					{<img src="file:///} to-local-file file {">}
				]
			]
			; The foreach loop builds an html layout that displays
			; each of the selected images.  
			append html [</body></html>]
			; finish up the html layout.  Now the variable "html" 
			; contains a complete html document that will be 
			; written to the hard drive	and opened in the default
			; browser.  The code below accomplishes that.
			write %chords.html trim/auto html
			browse %chords.html 
		]
	]

	; Each of the following loops puts 50 movable dots onto the GUI,
	; all at the same locations.  This creates three stacks of dots
	; that the user can move around the screen and put onto the 
	; fretboard.  There are three sizes to accommodate the resizing
	; feature of the fretboard image.  Notice the "feel movestyle" 
	; code at the end of each line.  Again, that's what makes the 
	; dots draggable.  

	loop 50 [append gui [at 275x50 image dot 30x30 feel movestyle]]
	loop 50 [append gui [at 275x100 image dot 20x20 feel movestyle]]
	loop 50 [append gui [at 275x140 image dot 10x10 feel movestyle]]

	; The following loops add some additional dragable widgets to 
	; the GUI.

	loop 6 [append gui [at 273x165 text "X" bold feel movestyle]]
	loop 6 [append gui [at 273x185 text "O" bold feel movestyle]]

	view layout gui

=image rebol_tutorial/gcdm.png
=image rebol_tutorial/gcdm2.png
=image rebol_tutorial/gcdm3.png


--- Listview Database

This example is a simple database program with a GUI interface.  It lets you store, search, alter, organize and display data in a way that's useful.  This type of application is common in any situation where categorical information must be organized.  Although this example handles client schedule information, the techniques it demonstrates can be directly applied to managing information of any type - inventories, customer/vendor lists, payroll/tax records, mp3 collections, photo albums, high score tables in games, etc.  This program uses the listview module found at <a href="http://www.hmkdesign.dk/rebol/list-view/list-view.r" target=_blank>http://www.hmkdesign.dk/rebol/list-view/list-view.r</a>, which is compressed and embedded within the script.  The listview module handles all the main work of displaying, sorting, filtering, altering, and manipulating data, with a familiar user interface that's easy to program.  Documentation is available at <a href="http://www.hmkdesign.dk/rebol/list-view/list-view.html" target=_blank>http://www.hmkdesign.dk/rebol/list-view/list-view.html</a>.  Learning to use the listview module is absolutely essential if you intend to do any programming that involves information management.  It's very simple to learn - you can get the basics in one sitting, and you will use it repeatedly. 

The program below creates a default database if one doesn't already exist (a simple text file containing Rebol data blocks), and makes a date stamped backup of the previous file whenever data is saved.  There's an additional function that traps the GUI close button to keep the program from being shut down accidentally. 


	Rebol [title: "Database"]

	; The function below watches for the GUI close button, to keep
	; the program from being shut down accidentally.  The code was
	; adjusted from an example at: 
	; http://www.rebolforces.com/view-faq.html

	evt-close: func [face event] [
		either event/type = 'close [
			inform layout [
				across
				Button "Save Changes" [
					; when the save button is clicked, a backup data
					; file is automatically created:
					backup-file: to-file rejoin ["backup_" now/date]
					write backup-file read %database.db
					save %database.db theview/data quit
				]
				Button "Lose Changes" [quit]
				Button "CANCEL" [hide-popup]
			] none ] [ 
			event
		]
	]
	insert-event-func :evt-close

	; The code below is the list-view.r module in compressed format.
	; It's decompressed, and then imported with the "do" command.
	; Like any other module, you don't have to understand how it was
	; programmed (the uncompressed code is all just native Rebol).
	; You just have to include the compressed blob, and learn how
	; to use it...

	do decompress #{
	789CCD3D6B73E3C871DFF52BE6369592F67629905A9F73A6B2A7B2EFECD8E557
	2AE738A96221551031142181040D8092B8A9FC97FCD474F7BCBA07038ADA3B3B
	E6D56909CCABA7BBA75FD333FCB75FFEE28FBF538B33A5FE54F5B59EAB377FFE
	CD77EA77BFF9FE4F933FFFE697FFA17E552CF51B28FD558585FF58575D3F79AC
	F4D3650B2F7FBEEFD74D3B578B37BFD6DBB67A50BFAF1E0A5DABDFB6504D6F3B
	BD7D9343B56F9BDDA1ADEED63DF47E359D7EF55EC1DF9FAA89FAF5EF7FABBED3
	5D75B7C521BE6D75D1EB728EA55F4D665793AB9FC1DBEFE01DBDFAE9643A9B5C
	CDE0D59F75DB55CD76AEA697D3CBABAFE1CDEFAA250E3757FF0D0F4AFDE2FBEF
	D4C5D3D3D365B383D7CDBE5DEACBA6BDCB6A53ADCB6EBB72621F2E77EBDD5B6A
	F5EF9D5645AF0E505F354F5B059378B88492FF81FFFF75DFEE1A1AE05FF456B7
	45AD76E68D428C2042D453D5AFD5A6D81ED40AE6B16F75A7564DABF650A7DA2A
	C0EA2576F487A6F760FE695D411D40AC827F8BC7A2AA8BDB1A619853F1BAEF77
	F32CC379AC370F25E1E9B27CC85A7DDBD499A74426690218D39B4615DB52F5BA
	EB9705CCF787765E428FAEF36609DDB59A7509B3DB140FBA6C965738E30DE0F0
	F3A7D03FF79FD972DD6FEACF6B3A013AF44D7BF8FCC17D0F1608A4F4AFCDAB39
	2D2EA5BED740F71FDC717E969F9D75FDA1AE3EE96C53C02A6BA97F6AB0AA740D
	CBE7177FFC4FC38C66E00EAAC25279BE9AD2A32EEFE01109465FD5C294CF9E67
	4AAF567A098BF4BCBAD58FB08C974D8DABFBEA27B0CACCFF3975317C4FAF57CD
	161A6F9BADA6C75DD1167620FCAA164F6DB1BB99AB555177DA74B4AA8BBB0E10
	4480ABBEB8BDD5A56A352C9EAD6AB693FD76D52CF71D30D86EDFDB165AD7B6D3
	65FF3CE9F5739FE9B2EAD56D050C6F26ACA08BB22D9E60A8FD7609BD830853C5
	B257B05E735745A96AA58ABA560B605FAA714ED3EAD46DDD2C1F6EE85D665EE5
	2AB452AC60AE76D5F281D7343DFDF337808B65514FF0C9B7CCCFE4BFA5EE09DB
	1E614A358FBA152FF4F6AE4072451301EA6C7B3695FA71AEEE748F2B713537F0
	00CAA1CE24FEAECED9836FDF01BB2CD7D4359F69895290BF008080AF80E5F45F
	F6456D70A4904DBFCCC284D562BFAD51DA1375F2A8036413A069B66D26DDBA79
	A22EF2A886E9710980027A9AD5AAD3D05733A117664C4240668AA2C6BE57F69E
	0F80388E60024ED836FDC44E8A8DFEF2E083D999BE6C276B40834145D7172D54
	4EBE9EF321635CA841577A5B8A16F3410BF56AA4A5D12611C7BF3FE843CC18B0
	0889E06C2CCF93C478C05DA0B463C41BA0B0BF8FEA1FDEFCD7E4CD00A382E506
	70C3B2D7CFC089B8FC138CBFD5C349E1A78695D5AF6F469AC420E05250AB0C06
	A9BAF584A69A980DA068A42148B663AD4E40B9141E3962D5C93F75DEE97A7566
	CA480FE0DB97D48011D62448F1AB9FB2D50633608802D6BF91460A358EB6DF0B
	6043B0BDCE6BBDEA9D2AB8AD8BE5C35900F015B29F8404BDE95B90726801BA8A
	F4B62DB64102EE8AAA9D29FC7BA5B21A458E6AD50EDE5C0539B39BC1C8801F56
	D7955C214CCF891298C2128C54B5707846CB0D2ACE32EC1BFECC184F60D901CB
	AEB0EC0ACB2A3024617DF7601201404537C1CEA18383A79B6A197A56FBBAB654
	62EA72ABD9235374F8D50F6F5404D307CD63EB50B10245404A4EFD78AA019628
	8EC019BB7ECC108AC952FB59505F7E56AC2E6958D7A06D9EEC0AC065411A3B51
	543FF22500E353E78139A2D579ADBE47D1D5374DADFA6A37B27AAEDD572B4D08
	AEF056D124091898172C0754E1386C59F4C5B5AA9BED1DC8DD667FB70E6D72D1
	DEB49D23136BFE7E25D06DBB9F87CE79DD6BB009EAE26015231FC9F58EEC11DB
	11A336422FF9023919987355FEC8EC615029308116D404451108F5B0922D4780
	83B440003FAA733230ECF7A2063F039E39F1A5FDB4906C01E3A04C4517E48678
	6C5D959AC46CCC3F25C377C43DB05AE67EBD9EA64B18ED784F82B194F80029B2
	6E5DAD62AD4BA800C0417E832538D934A5464C6CF6755FA991F7B852621BC154
	45C64A16401FBA9C80A4DE6FA4EA19DA66D0C0CA5B12876047EF61C2D63C8C20
	1AEA3A03F86258A01C8A13255285C31868DA7878BBC41CC6E76B3E40D3C1FB7C
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	FB08C6F989B6120C1B5F444C11F8D89D3B21A12D31342697AD128ECE77708259
	95915E83E18053BE8882F212744A328B21E730F0C4F1D9689C2A0505CCBAAEEC
	A55A3CCF7CC10B6437831D0409ACA1E345FAE7CC1C835AE039ACA3BC1D4F182D
	45BA50BAEAFD36722EB614019F21203A9029B266483B381C9954AB6BF3FBF12E
	B7342D1106EE7733769BDDF806D6F1A5E6CE738CAC37897C374498E2EB174E1E
	4FC9F49998D25D7DD8213D8A5ADBCBFEE4DE3A0703E4E387A86151DEEFBB7E98
	BF11FF480BDA1FE2AA2096397218141EC766480A8DED26F6D3994E86452AF214
	E41DC926FD31456044F590E6324279D795E49DA459586CC12D04AD547438E1A8
	707848067FE8C8FEEF8ECA446D2EA6CF138C91316E01A6E22C10DB8D17B3E7E9
	EB1AE0B190573598BC6E88B1132DFEABE334BF5DE95E881A2E62166568BC2EC3
	5D1E3C58477B73E62F9A16738CDBDA63ABE6ADB928D59FEB8661CDB924CBFA89
	7B1DF88657E2AE3FEA810F3308FCBB94499F3EC92BF39B56E2B38FB875257E31
	96D241F19761DCC656986F7E969FFD1F598CCF767B840000
	}

	; The following conditional evaluation checks to see if a
	; database file exists.  If not, it creates a file with 
	; some empty blocks:

	if not exists? %database.db [write %database.db {[][]}]

	; Now the stored data is read into a variable word:

	database: load %database.db

	; Here's the guts of the program.  Be sure to read the 
	; list-view documentation to see how the widget works.

	view center-face gui: layout [
		h3 {To enter data, double-click any row, and type directly 
			into the listview.  Click column headers to sort:}
		theview: list-view 775x200 with [
	    	data-columns: [Student Teacher Day Time Phone 
				Parent Age Payments Reschedule Notes]
	    	data: copy database
			tri-state-sort: false
			editable?: true
	  	]
		across
		button "add row" [theview/insert-row]
		button "remove row" [
			if (to-string request-list "Are you sure?" 
					[yes no]) = "yes" [
				theview/remove-row
			]
		]
		button "filter data" [
			filter-text: request-text/title trim {
				Filter Text (leave blank to refresh all data):}
			if filter-text <> none [
				theview/filter-string: filter-text
				theview/update
			]
		]
		button "save db" [
			backup-file: to-file rejoin ["backup_" now/date]
			write backup-file read %database.db
			save %database.db theview/data
		]
	]

=image rebol_tutorial/listview_database_a.png


Here's a stripped down version that's completely functional (only 18 lines of code!).  It runs the list-view module from an external file on the hard drive.  If the module doesn't exist on the hard drive, it's downloaded directly from the web server (instead of embedding it in the code, as above).  So, if the list-view module is not distributed with this script, an available Internet connection is required to run it:

	Rebol []

	if not exists? %list-view.r [write %list-view.r read
		http://www.hmkdesign.dk/rebol/list-view/list-view.r
	]
	do %list-view.r
	if not exists? %database.db [write %database.db {[][]}]
	database: load %database.db

	view center-face gui: layout [
		theview: list-view 775x200 with [
	    	data-columns: [Student Teacher Day Time Phone 
				Parent Age Payments Reschedule Notes]
	    	data: copy database
			tri-state-sort: false
			editable?: true
	  	]
		across
		button "add row" [theview/insert-row]
		button "remove row" [theview/remove-row]
		button "filter data" [
			filter-text: request-text/title trim {
				Filter Text (leave blank to refresh all data):}
			if filter-text <> none [
				theview/filter-string: filter-text
				theview/update
			]
		]
		button "save db" [save %database.db theview/data]
	]


In both programs above, clicking on a column header sorts the data by the selected column, ascending or descending.  Clicking the diamond in the upper right hand corner returns the data to its unsorted order.  Selecting a row of data with the mouse allows each cell to be edited directly in the listview.  Because inline editing is possible, no additional GUI widgets are required for data input/output.  For example, no text input fields are needed because all data is entered and displayed directly in the listview.  That's a very powerful tool which is useful in a wide variety of situations.

All of the display and data manipulation features in the example above are enabled by the imported list-view module.  It makes programming database front ends really easy in Rebol.  You cou use the outline above to create a graphical front end for any type of Rebol database application.  You could, for example, make some minor alterations in the column headings to manage the contents of the database used in the earlier looping example.  In the same way, it's a great tool to begin designing tables and inserting data into any newly conceived database application.

For more information about dealing with lists of data using Rebol's raw tools, see the pages below:

<a href="http://compkarori.com/vanilla/display/VID+list+style" target=_blank>http://compkarori.com/vanilla/display/VID+list+style</a>

<a href="http://compkarori.com/vanilla/display/list+examples" target=_blank>http://compkarori.com/vanilla/display/list+examples</a>

Also, be sure to see the links below for examples of how to organize and manipulate data using the native features of Rebol, and some useful third-party modules:

<a href="http://www.rebol.net/cookbook/recipes/0012.html" target=_blank>http://www.rebol.net/cookbook/recipes/0012.html</a>

<a href="http://www.dobeash.com/it/rebdb/" target=_blank>http://www.dobeash.com/it/rebdb/</a>

<a href="http://softinnov.org/rebol/mysql.shtml" target=_blank>http://softinnov.org/rebol/mysql.shtml</a>

There are more links to database tools on the rebDB page.  Understanding and being able to use such database tools is an important part of creating modern applications of all types.



--- Peer-to-Peer Instant Messenger

This example allows two users to connect directly via a TCP/IP network port (a user selected IP address and port setting) to exchange messages.  Unlike the FTP Chat Room above, this example requires no third party web server to store or transfer data.  Text is sent directly between two computers, across an established network socket connection (on either the Internet or a local network).  The application can act as either client or server, depending on the user's selection.  To work properly, the server machine needs to have an exposed IP address or an open router/firewall port.  The client machine can be located behind a router or firewall, without any forwarded incoming ports.  Program operation can be demonstrated on a single computer.  For instructions, see the help documentation included in the code.

The underlying code in this example is based on the Rebol cookbook example at <a href="http://www.rebol.net/cookbook/recipes/0028.html" target=_blank>http://www.rebol.net/cookbook/recipes/0028.html</a>.  See that page for a detailed explanation of how Rebol opens, connects, and sends data across TCP/IP ports.  For information about transferring binary files and data directly across a peer-to-peer connection, see <a href="http://www.rebol.net/cookbook/recipes/0058.html" target=_blank>http://www.rebol.net/cookbook/recipes/0058.html</a>.  The examples there provide a simple model for adding file sharing abilities to your network applications.  The techniques demonstrated in the Rebol networking examples form the basis for building non-native protocols, and can be used to send data through serial ports, to control external hardware devices, etc.

For basic information about how to configure routers and network ports for use in this example, see <a href="http://portforward.com" target=_blank>http://portforward.com</a>.  That type of configuration is beyond the scope of this tutorial, but is required for every sort of peer-to-peer ("p2p") network application - file sharing, multiuser online games, web cam sharing, instant messaging, web serving, etc.  For an even more fundamental explanation about how networks work, and for information about how to configure a typical network setup in MS Windows, see <a href="http://com-pute.com/FreeTutorials/Other/NetworkBasics.html" target=_blank>http://com-pute.com/FreeTutorials/Other/NetworkBasics.html</a>.

	REBOL [Title: "Peer-to-Peer Instant Messenger"]

	connected: false
	; This is a flag variable, used to mark whether or not the
	; two machines have already connected.  It helps to more 
	; gracefully handle connection and shutdown actions throughout
	; the script.

	; The code below traps the close button (just a variation of 
	; the routine used in the previous database example).  It 
	; assures that all open ports are closed, and sends a message
	; to the remote machine that the connection has been terminated.
	; Notice that the lines in the disconnect message are sent
	; in reverse order.  When they're received by the other machine,
	; they're printed out one at a time, each line on top of the
	; previous - so it appears correctly when viewed on the other
	; side.

	insert-event-func closedown: func [face event] [
	    either event/type = 'close [
			if connected [
				insert port trim {
					*************************************************
					AND RECONNECT.
					YOU MUST RESTART THE APPLICATION
					TO CONTINUE WITH ANOTHER CHAT,
					THE REMOTE PARTY HAS DISCONNECTED.
					*************************************************
				}
	        	close port
	        	if mode/text = "Server Mode" [close listen]
			]
	        quit
	    ] [event]
	]

	view/new center-face gui: layout [
		across
		at 5x2  ; this code positions the following items in the GUI

		; The text below appears as a menu option in the upper
		; left hand corner of the GUI.  When it's clicked, the
		; text contained in the "display" area is saved to a 
		; user selected file.

	 	text bold "Save Chat" [
			filename: to-file request-file/title/file/save trim {
				Save file as:} "Save" %/c/chat.txt
			write filename display/text 
		]

		; The text below is another menu option.  It displays
		; the user's IP address when clicked.  It relies on a
		; public web server to find the external address
		; (whatsmyip.org).  The "parse" command is used to 
		; extract the IP address from the page.  Parsing is 
		; covered in a separate dedicated section later in 
		; the tutorial.

		text bold "Lookup IP" [
			parse read http://whatsmyip.org/ [
			    thru <title> copy my-ip to </title>
			]
			parse my-ip [
			    thru "Your IP is " copy stripped-ip to end
			]
			alert to-string rejoin [
			    "External: " trim/all stripped-ip "  "
			    "Internal: " read join dns:// read dns://
			]
		]

		; The text below is a third menu option.  It displays 
		; the help text when clicked.

	 	text bold "Help" [
			alert {
			Enter the IP address and port number in the fields
			provided.  If you will listen for others to call you, 
			use the rotary button to select "Server Mode" (you
			must have an exposed IP address and/or an open port
			to accept an incoming chat).  Select "Client Mode" if
			you will connect to another's chat server (you can do
			that even if you're behind an unconfigured firewall, 
			router, etc.).  Click "Connect" to begin the chat. 
			To test the application on one machine, open two
			instances of the chat application, leave the IP set
			to "localhost" on both.  Set one instance to run as 
			server, and the other as client, then click connect.
			You can edit the chat text directly in the display
			area, and you can save the text to a local file.
			}
		]
		return

		; Below are the widgets used to enter connection info.
		; Notice the labels assigned to each item.  Later, the
		; text contained in these widgets is referred to as
		; <label>/text.  Take a good look at the action block 
		; for the rotary button too.  Whenever it's clicked, 
		; it either hides or shows the other widgets.  When in
		; server mode, no connection IP address is needed - the
		; application just waits for a connection on the given
		; port.  Hiding the IP address field spares the user some
		; confusion.

		lab1: h3 "IP Address:"  IP: field "localhost" 102
		lab2: h3 "Port:" portspec: field "9083" 50
		mode: rotary 120 "Client Mode" "Server Mode" [
			either value = "Client Mode" [
				show lab1 show IP
			][
				hide lab1 hide IP
			]
		]

		; Below is the connect button, and the large action block
		; that does most of the work.  When the button is clicked,
		; it's first hidden, so that the user isn't tempted to
		; open the port again (that would cause an error).  Then,
		; a TCP/IP port is opened - the type (server/client) is
		; determined using an "either" construct.  If an error
		; occurs in either of the port opening operations, the
		; error is trapped and the user is alerted with a message -
		; that's more graceful and informative than letting the 
		; program crash with an error.  Notice that the IP
		; address and port info are gathered from the fields above.
		; If the server mode is selected (i.e., if the "mode" button
		; above isn't displaying the text "Client Mode"), then the
		; the TCP ports are opened in listening mode - waiting
		; for a client to connect.  If the client mode is selected,
		; an attempt is made to open a direct connection to the IP
		; address and port selected. 

		cnnct: button red "Connect" [
			hide cnnct
			either mode/text = "Client Mode" [
				if error? try [
					port: open/direct/lines/no-wait to-url rejoin [
						"tcp://" IP/text ":" portspec/text]
				][alert "Server is not responding." return]
			][
				if error? try [
				    listen: open/direct/lines/no-wait to-url rejoin [
						"tcp://:" portspec/text]
				    wait listen
				    port: first listen
				][alert "Server is already running." return]
			]

			; After the ports have been opened, the text entry field
			; is highlighted, and the connection flag is set to true.
			; Focusing on the text entry field provides a nice visual
			; cue to the user that the connection has been made, but
			; it's not required.

			focus entry
			connected: true

			; The forever loop below continuously waits for data to
			; appear in the open network connection.  Whenever data
			; is inserted on the other side, it's copied and
			; appended to the current text in the display area, and
			; then the display area is updated to show the new text.

			forever [
			    wait port
			    foreach msg any [copy port []] [
					display/text: rejoin [
						">>>  "msg newline display/text]
			    ]
			    show display
			]
		]

		; Below are the display area and text entry fields.  Notice
		; the labels assigned to each.  The "return"s just put each
		; widget on a new line in the GUI (because the layout mode
		; is set to "across" above).

		return  display: area "" 537x500
		return  entry: field 428  ; the numbers are pixel sizes

		; The send button below does some more important work.
		; First, it checks to see if the connection has been made
		; (using the flag set above).  If so, it inserts the text
		; contained in the "entry" field above into the open TCP/IP
		; port, to be picked up by the remote machine - if the 
		; connection has been made, the program on the other end
		; is waiting to read any data inserted into that port.
		; After sending the data across the network connection,
		; the text is appended to the local current text display
		; area, and the display is updated:

		button "Send Text" [
			if connected [
				insert port entry/text focus entry
				display/text: rejoin [
					"<<<  " entry/text newline display/text]
				show display
			]
		]
	]

	show gui do-events  ; these are required because the "/new"
						; refinement is used above.

=image rebol_tutorial/instant_messenger.png

To actually use this example, the client user needs to know the IP address of the server machine.  In practical application, this could be handled by simply emailing the server's current IP address, but that's a pretty clunky solution.  As an exercise, try writing a small addition to the code that automatically posts the current server IP address to a consistently available ftp server every time the program is run (the function to obtain current IP addresses is already included).  It should only take one line of code.  Write another line to automatically download and insert the IP address into the text field when run in client mode, and you've got a fully automated connection mechanism.  If you want to get fancy, you could set up an ID schema tied to individual user IP addresses - all updated automatically and selectable at runtime (in a text-list, for example).  You could add features to track who's online/offline at any given time, etc.  



===Menus

One oddity about Rebol's GUI dialect is that it doesn't incorporate a native way to create standard menus.  The "choice" button widget is a close substitute that's useful in short applications, but it doesn't look or operate in the typical way users expect (the "Image Effector" program above demonstrates how choice buttons can be used to provide menu functionality).  Menus are important - they're a fundamental part of standard GUI design, and users tend to look for them intuitively.

Here's a simple prototype that can be included in your programs to provide additional menu functionality:

	Rebol [Title: "Simple Menu Example"]

	view center-face gui: layout/size [

		at 100x100 H3 "You selected:"
		display: field

		; Here's the menu.  Make sure it goes AFTER other GUI code.
		; If you put it before other code, the menu will appear be-
		; hind other widgets in the GUI.  The menu is basically just
		; a text-list widget, which is initially hidden off-screen
		; at position -200x-200.  When an item in the list is 
		; clicked upon, the action block for the text-list runs
		; through a conditional switch structure, to decide what to
		; do for the chosen item.  The code for each option first 
		; re-hides the menu by repositioning it offscreen (at 
		; -200x-200 again).  For use in your own programs, you can 
		; put as many items as you want in the list, and the action 
		; block for each item can perform any actions you want.
		; Here, each option just updates the text in the "display"
		; text entry field, created above.  Change, add to, or 
		; delete the "item1" "item2" and "quit" elements to suit 
		; your needs:

		origin 2x2 space 5x5 across
		at -200x-200 file-menu: text-list "item1" "item2" "quit" [
			switch value [
				"item1" [
					face/offset: -200x-200
					show file-menu
					; PUT YOUR CODE HERE:
					set-face display "File / item1"
				]
				"item2" [
					face/offset: -200x-200
					show file-menu
					; PUT YOUR CODE HERE:
					set-face display "File / item2"
				]
				"quit" [quit]
			]
		]

		; The menu initially just appears as some text choices at 
		; the top of the GUI.  When the "File" menu is clicked,
		; the action block of that text widget repositions the 
		; text-list above, so that it appears directly underneath
		; the File menu ("face/offset" is the location of the 
		; currently selected text widget).  It disappears when
		; clicked again - the code checks to see if the text-list
		; is positioned beneath the menu.  If so, it repositions
		; it out of sight.

		at 2x2
		text bold "File" [
			either (face/offset + 0x22) = file-menu/offset [
				file-menu/offset: -200x-200
				show file-menu
			][
				file-menu/offset: (face/offset + 0x22)
				show file-menu
			]
		]

		; Here's an additional top level menu option.  It provides
		; just a single choice.  Instead of opening a text-list 
		; widget with multiple options, it simply ensures that the
		; other menu is closed (re-hidden), and then runs some code.

		text bold "Help" [
			file-menu/offset: -200x-200
			show file-menu
			; PUT YOUR CODE HERE:
			set-face display "Help"
		]
	] 400x300

=image rebol_tutorial/simple_menu.png

The code above will provide useful and natural looking menus for simple applications.  If you need full blown menus with all the bells and whistles, animated icons, appropriate look-and-feel for various operating systems, and every possible display option, a module has been created to easily provide that capability:  <a href="http://www.rebol.org/library/scripts/menu-system.r" target=_blank>http://www.rebol.org/library/scripts/menu-system.r</a>.  Here's a minimal example demonstrating it's use:

	do http://www.rebol.org/library/scripts/menu-system.r
	menu-data: [edit: item "Menu" menu [item "Item1" item "Item2"]]
	reb-style: [item style action [alert item/body/text]]

	view center-face layout/size [
		at 2x2 menu-bar menu menu-data menu-style reb-style
	] 400x500

=image rebol_tutorial/menu1.png

The demo at <a href="http://www.rebol.org/library/scripts/menu-system-demo.r" target=_blank>http://www.rebol.org/library/scripts/menu-system-demo.r</a> shows off advanced features of the module.  

=image rebol_tutorial/menu_demo.png

Below is an intermediate example with explanations of the most important features.  The menu module has been compressed and embedded in the code:

	REBOL [Title: "Menu Example"]

	; The following line imports the compressed menu module.  

	do decompress 	#{
	789CED7DED761B3792E8EFEBA740343F24AD4D5352EC24C3331E1F59A213258E
	E548B233191EDE735A64536A9B6433ECA64566BD8F71DFF7A2AAF0D9F8E82645
	27D9DD602672B31B28140A8542A150285C745F9CBF62BD078CA78BECE6B62C3A
	8CFD27FE847492CF567378CDF606FBECE8E0E0293BB99D6745992553D69D16E9
	58653D1E8F19662DD83C2DD2F9C774F8F881FA7A910E79A97976BD28B37CCA92
	E9902D8A94655356E48BF920C537D7D93499AFD8289F4F8A47EC2E2B6F593EC7
	7FF345C914AC493ECC46D92001488F58324FD92C9D4FB2B24C876C36CF3F6643
	FE50DE2625FF937268E3717E974D6FD8209F0E3328546858507A92961D8DE9FF
	AB225BB07C24B11CE4439E7F5194BC8D65C2B1871A92EBFC237C12A45290789A
	E66536481FF16C59C1C61C28C032F08056DB48F29A07E3249BA4F3C7319478D5
	06B5244ABCF5C30547D38315DB165A8C5A6D821BE683C5249D9689ECDB36EFB6
	9C679AB34952A6F32C1917BA67B05F01BAD922ABB1AFD30C0B43A6693249013B
	78D68DB9CDC7439E619AEB4C9C266561B5923788E0E7F38223B262D729301D6F
	5ACED2E990BF4D81BF386293BC4C19118FC3E09033CEBD16AC11CF44E42AF251
	79076C23F9B298A503E0470E2003769D03274E89278B02DBA6205D7D7776C92E
	CF5F5EFD7C7CD165FCF9CDC5F9BBB3D3EE297BF10BFFD86527E76F7EB938FBF6
	BB2BF6DDF9ABD3EEC5253B7E7DCADFBEBEBA387BF1F6EAFCE252C1DA39BEE410
	7630C3F1EB5F58F75F6F2EBA9797ECFC829DFDF8E6D51907CA6BB9387E7D75D6
	BD7CC4CE5E9FBC7A7B7AF6FADB478C0362AFCFAF74035F9DFD7876C5F35F9D3F
	422CDCF2ECFC25FBB17B71F21DFF79FCE2ECD5D9D52F58F1CBB3ABD750E94B5E
	AB1605ECCDF1C5D5D9C9DB57C717ECCDDB8B37E7975D060D3E3DBB3C79757CF6
	63F7F431C787E3C0BAEFBAAFAFD8E577C7AF5E55DAAFA09DFFFCBA7B01AD32A9
	C05E7439D6C72F5E75B16A68FFE9D945F7E40A1AAA9F4E386D39C2AF1E697097
	6FBA2767F0A6FBAF2E6FE6F1C52F8F04F0CBEE4F6F796EFE919D1EFF78FC2D6F
	F55E53AAF17E3C797BD1FD115AC34975F9F6C5E5D5D9D5DBAB2EFBF6FCFC143B
	E5B27BF1EEEC840315E9F4F8EA18ABE6653919D57B4E86F38B5F000A341049FD
	88FDFC5D97BFBF00AA21198EA17D979C1C275766360E8D53C7C0513780BDEE7E
	FBEAECDBEEEB932E643B07703F9F5D76F779CF9C5D42060E1BE8F8F331AFFC2D
	36037AE42DEF3BDD172F6D167E841DC8CE5EB2E3D3771CD8A92CC5BBFCF24CF0
	09D2E3E43B41D4C73BAC2E6175FFF5A0FFE0C1A05CB6B86459F059094673BA2C
	F95CF5C0CA57DC26C3FCAE954D929BB483934A0FE69F92E19BBE98DB20E1EB0E
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	}

	; Below is an example of how to format a menu block. 
	; Note that there are two menus in the following 
	; block.  The "file" menu is indented and spread 
	; across several lines.  The edit menu is all on
	; one line.  Notice that you can place action blocks
	; after each menu item, to be performed whenever the
	; menu item is selected - as with the [print "You
	; chose Item 1"] block below:

	menu-data: [
		file: item "File" 
			menu [
				new:    item "Item 1" [print "You chose Item 1"]
				open:   item "Item 2" ; icons [1.png 2.png]
				---
				recent: item "Look In Here..."
					menu [
						item "WIN A PRIZE!" 
						item "Try door number two"
					]
				---
				exit:   item <Ctrl-Q> "Exit"   
	          ]
	    edit: item "Edit" menu [item "copy" item "paste"]
	] 

	; Pay particular attention to the action block in the menu 
	; style definition below.  You'll change it to execute your
	; own selected functions for each possible menu choice.
	; Most of the style definition is totally optional.  It's 
	; designed to look like a native Microsoft menu.  The
	; example at
	; http://www.rebol.org/library/scripts/menu-system-demo.r
	; contains many more examples of menu styles and options.
	; The only part that's required in the example below is 
	; the action block in the "item style" section.  Everything
	; else serves only to adjust the cosmetic appearance of the
	; menu:

	winxp-menu: layout-menu/style copy menu-data xp-style: [
	    menu style edge [size: 1x1 color: 178.180.191 effect: none]
			color white
	        spacing 2x2 
	        effect none
	    item style 
			font [name: "Tahoma" size: 11 colors: reduce [
				black black silver silver]]
	        colors [none 187.183.199] 
	        effects none
	        edge [size: 1x1 colors: reduce [none 178.180.191] 
				effects: []]	
	        action [

				; Change the lines below to fit your needs.
				; You can use the action block of each item
				; in the switch structure to run your own 
				; functions.  "item/body/text" refers to the
				; selected menu item.  This does the exact same
				; thing as including a code block for each item
				; in the menu definition above (i.e., you can
				; put the [quit] block after the "exit" item 
				; above, and it will perform the same way - 
				; just like the "[print "You chose Item 1"]" 
				; block after the "new" item above).

				switch/default item/body/text [
					"exit" [quit]
					"WIN A PRIZE!" [alert "You win!"]
					"Try door number two" [alert "Bad choice :("]
				] [print item/body/text]  ; default thing to do
			]
	]

	; Here is a simple function to trap the GUI close event.  This
	; must be included whenever the menu module is used, or a 
	; portion of the application will continue to run after being
	; shut down. 

	evt-close: func [face event] [
		either event/type = 'close [quit] [event]
	]
	insert-event-func :evt-close

	; And finally, here's the user interface:

	window: layout/size [

		; The line below shows the winxp style menu:

	    at 2x2 app-menu: menu-bar menu menu-data menu-style xp-style

		; The line below shows the same menu, whenever the button 
		; is clicked:

	    at 150x200 btn "Menu Button" [
			show-menu/offset window winxp-menu
			0x1 * face/size + face/offset - 1x0
		]
	
	] 400x500

	view center-face window

=image rebol_tutorial/menu.png
	


===More About GUIs and Graphics

---Responding to Special Events in a GUI - "feel"

Rebol's simple GUI syntax makes it easy for widgets to respond to mouse clicks.  As you've seen, you can simply put the block of code you want evaluated immediately after the widget that activates it:

	view layout [btn "Click me" [alert "Thank you for the click :)"]]

But what if you want your GUI to respond to events other than a mouse click directly on a widget?  What if, for example, you want the program to react whenever a user clicks <i>anywhere</i> on the GUI screen (in a paint program, for example), or if you want a widget to do something after a certain amount of time has passed, or if you want to capture clicks on the GUI close button so that the user can't accidentally shut down an important data screen. That's what the "feel" object and "insert-event-func" function are used for.

Here's an example of the basic feel syntax:

	view layout [
	    text "Click, right-click, and drag the mouse over this text." feel [
	        engage: func [face action event] [
	            print action
				print event/offset
	        ]
	    ]
	]

=image rebol_tutorial/feel1a.png
=image rebol_tutorial/feel1.png

The above code is often shortened using "f a e" to represent "face action event":

	view layout [
	    text "Mouse me." feel [
	        engage: func [f a e] [
	            print a
				print e/offset
	        ]
	    ]
	]

You can respond to specific events as follows:

	view layout [
	    text "Mouse me." feel [
	        engage: func [f a e] [
	            if a = 'up [print "You just released the mouse."]
	        ]
	    ]
	]

=image rebol_tutorial/feel2a.png
=image rebol_tutorial/feel2.png

You can also assign timer events to any widget, as follows:

	view layout [
		text "This text has a timer event attached." rate 00:00:00.5 feel [
			engage: func [f a e] [
				if a = 'time [print "1/2 second has passed."]
			]
		]
	]

=image rebol_tutorial/feel3a.png
=image rebol_tutorial/feel3.png

Here's a button with a time event attached (a rate of "0" means don't wait at all).  Every 0 seconds, when the timer event is detected, the offset (position) of the button is updated.  This creates animation:

	view layout/size [
		mover: btn rate 0 feel [
			engage: func [f a e] [
				if a = 'time [
					mover/offset: mover/offset + 5x5
					show mover
				]
			]
		]
	] 400x400

=image rebol_tutorial/anim1.png
=image rebol_tutorial/anim2.png

By updating the offset of a widget every time it's clicked, you can enable drag-and-drop operations:

	view layout/size [
		text "Click and drag this text" feel [
			; remember f="face", a="action", e="event":
			engage: func [f a e] [
				; first, record the coordinate at which the mouse is
				; initially clicked:
		    	if a = 'down [initial-position: e/offset]
				; if the mouse is moved while holding down the button, 
				; move the position of the clicked widget the same amount
				; (the difference between the intial clicked coordinate
				; recorded above, and the new current coordinate determined
				; whenever a mouse move event occurs):
		        if find [over away] a [
		            f/offset: f/offset + (e/offset - initial-position)
				]
				show f
			]
		]
	] 600X440

=image rebol_tutorial/cd1.png
=image rebol_tutorial/cd2.png

Feel objects and event functions can be included right inside a style definition.  The definition below allows you to easily create multiple GUI widgets that can be dragged around the screen.  "movestyle" is defined as a block of code that's later passed to a widget's "feel" object, and is therefore included in the overall style definition (the remove and append functions have been added here to place the moved widget on top of other widgets in the GUI (i.e., to bring the dragged widget to the visual foreground)).  You can add this "feel movestyle" code to any GUI widget to make it drag-able:

	movestyle: [
		engage: func [f a e] [
	    	if a = 'down [
	        	initial-position: e/offset
	            remove find f/parent-face/pane f
	            append f/parent-face/pane f
	        ]
	        if find [over away] a [
	            f/offset: f/offset + (e/offset - initial-position)
	        ]
	        show f
	    ]
	]

	view layout/size [
		style moveable-object box 20x20 feel movestyle
		; "random 255.255.255" represents a different random
		;  color for each piece:
		at random 600x400 moveable-object (random 255.255.255)
		at random 600x400 moveable-object (random 255.255.255)
		at random 600x400 moveable-object (random 255.255.255)
		at random 600x400 moveable-object (random 255.255.255)
		at random 600x400 moveable-object (random 255.255.255)
		text "This text and all the boxes are movable" feel movestyle
	] 600x440

=image rebol_tutorial/feel4.png

To handle global events in a GUI such as resizing and closing, "insert-event-func" is useful.  The following example checks for resize events:

	insert-event-func [
		either event/type = 'resize [
			alert "I've been resized"
			none   ; return this value when you don't want to
				   ; do anything else with the event.
		][
			event  ; return this value if the specified event
				   ; is not found
		]
	]

	view/options layout [text "Resize this window."] [resize]

=image rebol_tutorial/feel5.png
=image rebol_tutorial/feel5b.png

You can use that technique to adjust the window layout, and specifically reposition widgets when a screen is resized:

	insert-event-func [
		either event/type = 'resize [
			stay-here/offset:
				stay-here/parent-face/size - stay-here/size - 20x20
			show stay-here
			none   ; return this value when you don't want to
				   ; do anything else with the event.
		][
			event  ; return this value if the specified event
				   ; is not found
		]
	]

	view/options layout [
		stay-here: text "Resize this window."
	] [resize]

=image rebol_tutorial/resize1.png
=image rebol_tutorial/resize2.png
=image rebol_tutorial/resize3.png

To remove an installed event handler, use "remove-event-func".  The following example captures three consecutive close events, and then removes the event handler, allowing you to close the GUI on the 4th try:

	count: 1
 	evtfunc: insert-event-func [
		either event/type = 'close [
			if count = 3 [remove-event-func :evtfunc]
			count: count + 1
			none
		][
			event
		]
	]

	view layout [text "Try to close this window 4 times."]

=image rebol_tutorial/close.png

For more information about handling events see <a href="http://www.rebol.com/how-to/feel.html" target=_blank>http://www.rebol.com/how-to/feel.html</a>, <a href="http://www.codeconscious.com/rebol/view-notes.html" target=_blank>http://www.codeconscious.com/rebol/view-notes.html</a>, and <a href="http://www.rebol.com/docs/view-system.html" target=_blank>http://www.rebol.com/docs/view-system.html</a>.


---2D Drawing, Graphics, and Animation

With Rebol's "view layout" ("VID") dialect you can easily build graphic user interfaces that include buttons, fields, text lists, images and other GUI widgets, but it's not meant to handle general purpose graphics or animation.  For that purpose, Rebol includes a built-in "draw" dialect.  Various drawing functions allow you to make lines, boxes, circles, arrows, and virtually any other shape.  Fill patterns, color gradients, and effects of all sorts can be easily applied to drawings.  

Implementing draw functions typically involves creating a 'view layout' GUI, with a box widget that's used as the viewing screen.  "Effect" and "draw" functions are then added to the box definition, and a block is passed to the draw function which contains more functions that actually perform the drawing of various shapes and other graphic elements in the box.  Each draw function takes an appropriate set of arguments for the type of shape created (coordinate values, size value, etc.).  Here's a basic example of the draw format:

	view layout [box 400x400 effect [draw [line 10x39 322x211]]]
	;  "line" is a draw function

=image rebol_tutorial/draw1.png

Here's the exact same example indented and broken apart onto several lines:

	view layout [
		box 400x400 effect [
			draw [
				line 10x39 322x211
			]
		]
	]

=image rebol_tutorial/draw1.png

Any number of shape elements (functions) can be included in the draw block:

	view layout [
		box 400x400 black effect [
			draw [
				line 0x400 400x50
				circle 250x250 100
				box 100x20 300x380
				curve 50x50 300x50 50x300 300x300
				spline closed 3 20x20 200x70 150x200
				polygon 20x20 200x70 150x200 50x300
			]
		]
	]

=image rebol_tutorial/draw2.png

Color can be added to graphics using the "pen" function.  Shapes can be filled with color, with images, and with other graphic elements using the "fill-pen" function.  The thickness of drawn lines is set with the "line-width" function:

	view layout [
		box 400x400 black effect [
			draw [
				pen red
				line 0x400 400x50
				pen white
				box 100x20 300x380
				fill-pen green
				circle 250x250 100
				pen blue
				fill-pen orange
				line-width 5
				spline closed 3 20x20 200x70 150x200
				polygon 20x20 200x70 150x200 50x300
			]
		]
	]

=image rebol_tutorial/draw3.png

Gradients and other effects can be easily applied to the elements:

	view layout [
	    box 400x220 effect [
			draw [
				fill-pen 200.100.90
			    polygon 20x40 200x20 380x40 200x80
			    fill-pen 200.130.110
			    polygon 20x40 200x80 200x200 20x100
			    fill-pen 100.80.50
			    polygon 200x80 380x40 380x100 200x200
	    	]
			gradmul 180.180.210 60.60.90
		]
	]

=image rebol_tutorial/draw4.png

Drawn shapes are automatically anti-aliased (lines are smoothed), but that default feature can be disabled:

	view layout [
		box 400x400 black effect [
			draw [
				;  with default smoothing:
				circle 150x150 100
				;  without smoothing:
				anti-alias off
				circle 250x250 100
			]
		]
	]

=image rebol_tutorial/draw5.png


+++Animation

Animations can be created with draw by changing the coordinates of image elements.  The fundamental process is as follows:

# Assign a word label to the box in which the drawing takes place (the word "scrn" is used in the following examples).

# Create a new draw block in which the characteristics of the graphic elements (position, size, etc.) are changed.

# Assign the new block to "{yourlabel}/effect/draw" (i.e., "scrn/label/draw: [changed draw block]" in this case).

# Display the changes with a "show {yourlabel}" function (i.e., "show scrn" in this case).


Here's a basic example that moves a circle to a new position when the button is pressed:

	view layout [
		scrn: box 400x400 black effect [draw [circle 200x200 20]]
		btn "Move" [
			scrn/effect/draw: [circle 200x300 20]  ; replace the block above
			show scrn
		]
	]

=image rebol_tutorial/draw6.png
=image rebol_tutorial/draw6b.png

Variables can be assigned to positions, sizes, and/or other characteristics of draw elements, and loops can be used to create smooth animations by adjusting those elements incrementally:

	pos: 200x50
	view layout [
		scrn: box 400x400 black effect [draw [circle pos 20]]
		btn "Move Smoothly" [
			loop 50 [
				; increment the "y" value of the coordinate:
				pos/y: pos/y + 1
				scrn/effect/draw: copy [circle pos 20]
				show scrn
			]
		]
	]

=image rebol_tutorial/draw7.png
=image rebol_tutorial/draw7b.png

Animation coordinates (and other draw properties) can also be stored in blocks:

	pos: 200x200
	coords: [70x346 368x99 143x45 80x125 237x298 200x200]

	view layout [
		scrn: box 400x400 black effect [draw [circle pos 20]]
		btn "Jump Around" [
			foreach coord coords [
				scrn/effect/draw: copy [circle coord 20]
				show scrn
				wait 1
			]
		]
	]

=image rebol_tutorial/draw8.png
=image rebol_tutorial/draw8b.png
=image rebol_tutorial/draw8c.png
=image rebol_tutorial/draw8d.png

Other data sources can also serve to control movement.  In the next example, user data input moves the circle around the screen.  Notice the use of the "feel" function to update the screen every 10th of a second ("rate 0:0:0.1").  Since feel is used to watch, wait for, and respond to window events, you'll likely need it in many situations where animation is used, such as in games:

	pos: 200x200
	view layout [
		scrn: box 400x400 black rate 0:0:0.1 feel [
			engage: func [face action event] [
				if action = 'time [
					scrn/effect/draw: copy []
					append scrn/effect/draw [circle pos 20]
					show scrn
				]	
			] 
		] effect [ draw [] ]
		across
		btn "Up" [pos/y: pos/y - 10]
		btn "Down" [pos/y: pos/y + 10]
		btn "Right" [pos/x: pos/x + 10]
		btn "Left" [pos/x: pos/x - 10]
	]

=image rebol_tutorial/draw9.png
=image rebol_tutorial/draw9b.png

Here's a very simple paint program that also uses the feel function.  Whenever a mouse-down action is detected, the coordinate of the mouse event ("event/offset") is added to the draw block (i.e., a new dot is added to the screen wherever the mouse is clicked), and then the block is shown:

	view layout [
		scrn: box black 400x400 feel [
			engage: func [face action event] [
				if find [down over] action [
					append scrn/effect/draw event/offset
					show scrn
				]
				if action = 'up [append scrn/effect/draw 'line]
			]
		] effect [draw [line]]
	]

=image rebol_tutorial/draw10.png

A useful feature of draw is the ability to easily scale and distort images simply by indicating 4 coordinate points.  The image will be altered to fit into the space marked by those four points:

	view layout [
		box 400x400 black effect [
			draw [
				image logo.gif 10x10 350x200 250x300 50x300
				; "logo.gif" is built into the Rebol interpreter
			]
		]
	]

=image rebol_tutorial/draw11.png

Here's an example that incoporates the image scaling technique above with some animation.  IMPORTANT:  In the following example, the coordinate position calculations occur <i>inside the draw block</i>.  Whenever such evaluations occur inside a draw block (i.e., when values are added or subtracted to a variable coordinate position, size, etc.), a <i>"reduce" or "compose"</i> function must be used to evaluate those values.  Notice the tick mark (') next to the "image" function.  Function words inside a reduced block need to be marked with that symbol to evaluate correctly:

	pos: 300x300
	view layout [
		scrn: box pos black effect [
			draw [image logo.gif 0x0 300x0 300x300 0x300
		]]
		btn "Animate" [
			for point 1 140 1 [
				scrn/effect/draw: copy reduce [
					'image logo.gif 
					(pos - 300x300)
					(1x1 + (to-pair rejoin ["300x" point]))
					(pos - (to-pair rejoin ["1x" point]))
					(pos - 300x0)
				]
				show scrn
			]
			for point 1 300 1 [
				scrn/effect/draw: copy reduce [
					'image logo.gif 
					(1x1 + (to-pair rejoin ["1x" point]))
					(pos - 0x300)
					(pos - 0x0)
					(pos - (to-pair rejoin [point "x1"]))
				]
				show scrn
			]
			; no "reduce" is required below, because no calculations
			; occur in the draw block - they're just static coords: 
			scrn/effect/draw: copy [
				image logo.gif 0x0 300x0 300x300 0x300
			]
			show scrn
		]
	]

=image rebol_tutorial/draw12.png
=image rebol_tutorial/draw12b.png
=image rebol_tutorial/draw12c.png

Here's another example of a draw block which contains evaluated calculations, and therefore requires "reduce"d evaluation:

	view layout [
		scrn: box 400x400 black effect [draw [line 0x0 400x400]]
		btn "Spin" [
			startpoint: 0x0
			endpoint: 400x400
			loop 400 [
				scrn/effect/draw: copy reduce [
					'line 
					startpoint: startpoint + 0x1
					endpoint: endpoint - 0x1
				]
				show scrn
			]
		]
	]

=image rebol_tutorial/draw13.png
=image rebol_tutorial/draw13b.png

The useful little paint program at http://rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=paintplus.r consists of only 238 lines of code.  Take a look at it to see how efficient Rebol's draw code is:

	url: http://rebol.org/cgi-bin/cgiwrap/rebol/download-a-script.r?
	script: "script-name=paintplus.r"
	do rejoin [url script]
	paint none []

=image rebol_tutorial/paint.png

For more information about built-in shapes, functions, and capabilities of draw, see <a href="http://www.rebol.com/docs/draw-ref.html" target=_blank>http://www.rebol.com/docs/draw-ref.html</a>, <a href="http://www.rebol.com/docs/draw.html" target=_blank>http://www.rebol.com/docs/draw.html</a>, <a href="http://translate.google.com/translate?hl=en&sl=fr&u=http://www.rebolfrance.info/org/articles/login11/login11.htm" target=_blank>http://translate.google.com/translate?hl=en&sl=fr&u=http://www.rebolfrance.info/org/articles/login11/login11.htm (translated by Google)</a>, <a href="http://www.rebolforces.com/zine/rzine-1-05.html" target=_blank>http://www.rebolforces.com/zine/rzine-1-05.html</a>, <a href="http://www.rebolforces.com/zine/rzine-1-06.html" target=_blank>http://www.rebolforces.com/zine/rzine-1-06.html</a> (updated code for these two tutorials is available at <a href="http://mail.rebol.net/maillist/msgs/39100.html" target=_blank>http://mail.rebol.net/maillist/msgs/39100.html</a>).  A nice, short tutorial demonstrating how to build multi-player, networked games with draw graphics is available at <a href="http://64.233.179.104/translate_c?hl=en&u=http://www.rebolfrance.info/org/articles/jeuxreseaux/jeuxreseaux.html" target=_blank>RebolFrance (translated by Google)</a>.  Also be sure to see <a href="http://www.nwlink.com/~ecotope1/reb/easy-draw.r" target=_blank>http://www.nwlink.com/~ecotope1/reb/easy-draw.r</a> (a clickable rebsite version is available in the Rebol Desktop -> Docs -> Easy Draw).


---Using Animated GIF Images

Another easy way to work with animations in Rebol is with the "anim" style in GUIs.  Anim takes a series of still image frames, and plays them in order as an animation with a given rate.  The basic format is:

	view layout [
		speed: 10
		anim rate (speed) [%image1.gif %image2.gif etc...]
	]

The following script will convert an animated .gif into a folder filled with individual frame images:

	rebol []

	gif-anim: load to-file request-file
	make-dir %./frames/
	count: 1

	for count 1 length? gif-anim 1 [
		save/png rejoin [
			%./frames/ "your_file_name-" count ".png"
		] pick gif-anim count
	]

This next script will convert a directory of images (such as above, or any other series of images) into an embeddable block of Rebol code.  It looks for all the images named [%your_file_name-1.* your_file_name-2.* etc...]:

	rebol []

	system/options/binary-base: 64	
	file-list: read  %./frames/
	anim-frames-block: copy []
	foreach file file-list [
		; Unique portion of file names for your image frames go here.
		; Leave out this check if you instead want to convert all
		; files in the directory:
		if find to-string file "your_file_name-" [ 
			print file
			uncompressed: read/binary file
			compressed: compress to-string uncompressed
			append anim-frames-block compressed
		]
	]

	editor anim-frames-block

Here's some sample output:

	anim-frames-block: [64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zCHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxqjufmZWdnWxS/OsPJcODoPLtKprUcW9TPLXJT
	V7LdFZIZuMx/Ll/rrJCkC3NZ1ztd6SpVCG+L363EsXpCTvhmtovzVCWurr7R6jG7
	rzZarKFpd8XTS77Z1/Xu7Qn+vunr6+/v725rqv6nm/Oj4Or2Ll7jvDUOa8+e6FX3
	3uYjbPz0fN/RKjbeWcU+Z5do2qfN2lWaelnXfbveKwkz7ytLqu0qBK6Xed1cyfhG
	TC58xeujhyuF422FXxQeOPybbR1nzbbP18+khtXvu/H95Ns7Gzdv5ZtfaVX64fjZ
	crf/d6xPvV7XmJ7PZ1/x/ueXm/nXrOfVZKyZ+DL8nt85zhWzqu8LPosvPyYZEdW8
	QrJjvjdj3TOFJuXQFVEVEl0iC9L49pVJJvZcnR7XLn/w+ux64XUpizrvbF0R1PFx
	4QvB3s29OxLylB9tW9Cj9+vEol5NLk+5ia7vLB74GvxbETxZRklSqI+HyWNpR7ri
	VbkJtreOp05nF1O/EeGW9C01/RqjmVrF3l7PZxnfPStv12qxsjBYAwBolvDW2AQA
	AA==
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxqjufmZWdnW6hqBUwQfnxuvkPltxaJLSsuLOTt
	ZWPdIPzSaal3vZUth6nWhZUsq7NsrUqzQ9f47K17qyWmdW1T2txFsreLdW/Pydu6
	rXe2mHrsYuf3j86uLn95Z1/Qf6ZnWeUGD2e38V/3WVOh9viYkfzh3Fvmb1Iap+oq
	P7OUKH64ocH2tsisGfkvTy7nXi6nG/n11dGZzLv3RQt8On3c19zY7e8stbyDCxtf
	h0rLZBZuKjyYFrv6jsLdZ8xr99lGi3wueRLuGN6+zqSq7MW1700y/hHle4o/PhP8
	5Xt+397f3z88Pj3ff/++v79/vGdnYbAGAJfEqNM/BAAA
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blri2cIVNC+GU2Hp6elcEX0tnsbLfPpNs++9mTE57fRcyepfJZxfFgUsdNWU
	s51l8ihoma+8XatU6cOQVaHCca6zQh+GrYvlrWOVnvbgxrzUo/POzrz2JmpuLuu+
	VuntT+9ML316T3VWuf79HXX/t/GuKTJIPBj5UW7bzB0fko75frwVGzP1ffIRa934
	tpiQp88O9Zq3q84pL3qwq593uZ621dus61NCJ097K/714b7l3tf1bAv03jfNmv/v
	264t3wu2Hn0r9973y6uiy2aql235hJeef35hovexONmK8jc3rzapXLeL03r+6cXl
	1fHn9+39/f3D49Pz/ffv+/v7x+fX98/v3////1NWFgZrALxatNdHBAAA
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxKZMWCZWdnSuW+urOSId11nkP+rx6JLS8C2l0n
	y6XO2PLyUovvXDtTCdNXV5pCl8YtnRn68tq6qOVNX6tKdW4uT+ud5sv9RTt6Xt79
	Vz3a4Stu7Cq7+OitZ/i7i3tza5n4tCo+3JzWdniTz5oI1cfHNOVXt2pWqp87VaPv
	LZf1413C3s7pdmKys0rSL88PZGbbe+vzva1rY3+/PV32+sCubRtnnd0rkJdwj/0h
	0wyemh2p644UC7fl7H778NGh3vO6fKbGX1/f2Jx9/9ze3d/fPzjczSvvv2/Pz88v
	Lq+Oj7dTYLAGANdbpyswBAAA
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxqjufmZWdnWxS/unNy8/Lz8x2auWR/BTVeXOwi
	Khe7y2Sl47KAiVamXApZV5b4rnWSXbVVO3RB3OF/PN7X1G9usjnfdXdl2dpz2/IK
	D339VZZ3fVfZ2kdnd5uqx++t+/9tqvaMlWfXh3IrT7sZ/jHxaHim0zWtSqOnM6a9
	FDtbU26cfkDPvrlNc1dm6kVTb22Lv5alaYfm5C+qu3OrNPfa+tzj13Ijv+XemZzI
	zv9n+oq7Kye6f9+js2Fz5IFZx4PK+MR+JSy/sTn7/rm9u7+/f3C4m/m7pACDNQAX
	yZ/iJgQAAA==
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWendyiezhkdy8zHemsfm9O5LG6m7zHGqjWKRCMo7MY+h4
	Z/IrYGXwMp65dq2rAl6FrGJbG3fUKuB12DrPvVqs2gFvwlelHZ/ku3qadvSilMP7
	9kqW653fWvay6ezq67rxS6r/P1qjPWPDg4Nu/N+/rvyh9/iYt7zzNs0So6enpi2M
	cuuRNLp3qJH/d6hNlEnY+eXS09l6w0qzLq+PPP7s98yy3N2Fp5+dvTtVN78lqf77
	u5XTi3wfHpYVj5lTnX3xfsHkeDe98qrS11catc/PK7D+/u74fnNpHv19e35+fnF5
	dfz5fXt/f//w+PR8//37/v5mYGJisAYARqapGj4EAAA=
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8loBjYyMaj5ToqJNHjqOV0zsq/l56RnnjPlcq9t6Zy8+Nx8w+okFq8vywK6XDvl
	ZGdNeR7Uyb9oUY7X55dH2INX7trCZbr62oIYSa+vv65mRDRHs05rrRR7GLU09+K+
	v5LmD++sKuW/d3R2+YO4fbUn//G+MV+bsKpF9JzvnSKDx/vbhJ3DTkbo3j5coB2v
	F72z4MzWubrBbLJWL25fWuZv7/d6y4q0bdMNj6udub7mzYnGuVV+v6qK8k/sl/We
	l7Nb/+Ojyv5ytX0yFq/2LnRdfW3P79ef515b73/9nFRGSVPJ00c2fXwSf9685y1d
	7B9ft/fu53ei/f3/5xnVtie8f33//P79wEKATeNBA4tYxoNGDrUVD5p4zF48aBZw
	00h0ZGRksAYAd264o18EAAA=
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5tUvVi5Yia1eG5edqbPtPjSnpWBy/0YDCvDvvwsXh7Q6TL5
	kI1UYGbQMv65Wq2nAl6FrApd++vIrA8HmRc4smbxni59cH294d46Vu2tOQc3OzDO
	cc2+ujZiZ9zjc6mvr+hFNGV+/rT31bUX9xuTTybFWllsTFzXI5uv6xO2yXe3m669
	nrfIxrAzDaLqx9bc2Jx8aVZ90bWcWYZXr6xj39+W++NT4K1VuZ9LeqPfpM2cWHj8
	ytmQHx/u79b9zSf3e9un5iOth/QkYnd9fHVy/fSydbWl5e8PBbYHLreJ+1Oyv1d1
	cX5tVe2Li+94t/X7y9b9Wf5y4mx3u5919d/Orr1+s8jyovr9ZFYpjol1XGYvHjQL
	uGk8bBEJy3jYKpG24mGbTNmLh+0KbRqPOoTYWBisAbfrxM90BAAA
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxqjufmZWdnWxRHhRwIfu46z6Hx1xSJLSsuLOTt
	1XLdFfDy0mIfTqu5t4xfOayKWMt04NRVretrAvc3yWqVrTm/LnqlUuusba9Ct6aL
	ctQ4mL+9syt3+jHWgO+Nd/fVPXxm88p8Q8y+Gl7/q5Il667sZjp7S0drqm7UHP/T
	UrJ7LNc/2zFFOXudlNWyG9uzvs6yO1NgEj29V3RXH2/1tzfTthVv9lt52+zdvcXZ
	zPZ/rb99OKfvLF+vu+d50Xaju3b3bSutnj+fsTx4/sra6pK3N9fed2Op/2uR/OZ5
	+/pQf7GKiJ37tlb905I3LVw7s//St1W7NgW8f/l1+41qZr6O+MxvjuH3m3jMXjxo
	FnDTeNgiEpbxsFUibUViGyMjgzUAhlm/D2kEAAA=
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJGcFnIAgdVr2kGybtEJDernZmpnfsqp9P48bn5tvr/ZKSuPApY4Koo
	Fzvry8OgZb6Sdq1Sog9DZjJlh/l6mLz2ZeDfU3c3SuClwzQm+RWsC6bqOC7JOrwo
	Vnv72uht1gfbeK0n6MWtKW/8pbrj2/uI7QU/F9Vmf14XMbfnolxpjWlR3GGbyXZb
	a3ZufLY619b5H8+vnNRL8z7K6ciWbnG80B7Y3SZrrZF7bVN+ee6q6uKr9/ZFM8/X
	qfnx7s6xYPGrs+7oPXrWzex83qes6svaa+v/n9OrtUp9fX9ve7j/ux8fP3x61rjY
	vLZ6b+iNdzsPre/9l5a86itjv21cXGXk5p+Wx+fVM3K9CK15v7MtwZlL74RCAp+b
	xsMWkbCMh60SaSsetsmUvXjYrtCm8ahDZVrGo06NPFEBBmsAOJHArHoEAAA=
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4a8uKBYvd+6Wd
	i/54bFp8YjKf9yqTzk2ph6ZqxZ4S4dj87Mw00+J7IjM3Pz/Xa1v674jElecXJrom
	yq3NKFbwWC4/PSiE68FB5llMay/1aJkuClobLhqyV2pa9vUp8SeZBLjL1t7czDM7
	S9ViukrMlpCNYj2V5YlB03x/7/uzu3RpQqsjL5tdjYFhyIF8yfehWT82Rmz3VxXf
	9rvi0+VJs8zdv8lsLYo/NK2b699pqS93r20wLu/lrTbNvbYt3/rcWmv9x5f2prb7
	1VZbvHxwrPO1n94u8+IzB/XV+/VsTEpfXl5pn+9Xbf3l6b2J1cHP+6psKhc/43zk
	d99Cs/qrXW17eW3Nl7Jfp1aff17zb2/Rjz8/v8uWMf1aGt/IobbiQROP2YsHzQJu
	Gg9bRMIyHrZKpK142CZT9uJhu0KbxqMOlWk7Eh0YrAGyBMCKdgQAAA==
	} 64#{
	eJxz93SzsEwMZwhn+M4AAg1g3ACmGsCsBjDnPxj/B1P/waz/YM4oGAXDBij+ZAHT
	OiAClCfYOf4zMHLIeGxYcLCZQ1gr5sSGhYfbBZS95nhsXHS0W8I4686JjYuP9ys4
	d8l4blpycrJG8KqYk5uWnp5ukHxqjufmZb79XEWvrlROfnRuvn21F4tXSOOFNptu
	JttVBisuzfURtJsrdfXBleWhnHFLZ5VqX18V18lnImW6JmwT/yamD1ofHG9tZbi0
	TLV6ytrbOwqeHkrNCtePaiypntX7u+z9rTml7OIxWiZrbhy2kbbm45IsTDrevTDu
	GM/PgptrkzWj360qefhi9nLH+b09VUa3Z62zPN+zNkLt7fVt+eK21tHf8w40Jv7S
	Oxv148Pxg73y1898t4h4Pnvh9rh5c9S+XjZbH/5+757K7y/22bc716+Lzn168ln4
	db/1917kfwvbOH+6/zzLD8ez7p/X9/u1/d+fiEq2+Joe3owHjRxqKx408Zi9eNAs
	4KbxsEUkLONhq0SaqACDNQAYMLy/ZgQAAA==
	}]

And here's an example of how to write the files in that block back to the hard drive and display them in a GUI:

	; Write files:

	count: 1
	make-dir %./frames/
	for count 1 length? anim-frames-block 1 [
		write/binary rejoin [
			%./frames/ "frame-" count ".gif"
		] to-binary decompress pick anim-frames-block count
	]

	; Create file list, with frames in numerical order:

	file-list: read %./frames/
	animation-frames: copy []
	for count 1 length? file-list 1 [
		append animation-frames rejoin [
			%./frames/ "frame-" count ".gif"
		]
	]

	; Display that file list as an animation:

	view layout [
		anim: anim rate 10 frames animation-frames
	]

=image rebol_tutorial/animate1.png
=image rebol_tutorial/animate2.png
=image rebol_tutorial/animate3.png


---3D Graphics with r3D

The "r3D" modeling engine by Andrew Hoadley is built entirely from native Rebol 2D draw functions.  It demonstrates the significantly powerful potential of draw.  The examples below show some of what you can accomplish with r3D:

	do http://www.rebol.net/demos/BF02D682713522AA/i-rebot.r
	do http://www.rebol.net/demos/BF02D682713522AA/histogram.r
	do http://www.rebol.net/demos/BF02D682713522AA/objective.r

=image rebol_tutorial/rebot.png
=image rebol_tutorial/histogram.png
=image rebol_tutorial/objective.png

The r3D engine is small.  Here's the entire module in compressed, embeddable format (this is all just standard Rebol code compressed into a more compact format).  To enable 3D graphics in your Rebol programs, just include this text in your code (paste it, or "do" it from a file).  If you'd like to read and learn from the pure Rebol code that makes up this module, see the examples above (the r3D module is included in those examples as regular text code):

	do to-string decompress 64#{
	eJzdPGtT28iWn+Nf0cOXsTMYkGXznL1bBMzEtQSnjPMAipqSpTboRpa8kmwwv37P
	Od0tdethOzNTu1VLJUTqPu9XP5VR/8Pwmj002NhPA37KdmL7cqfBzhfpcxTD63no
	xfyFfYwcL+Ar6PnK48SPwlNm7R3sHTQeG43GGbuI5qvYf3pOWdNtsc7BweEuMzER
	6jOPZ36C2MxP2DOP+WTFnmInTLm3y6Yx5yyaMvfZiZ/4Lksj5oQrNgd+gBBNUscP
	/fCJOcwFbgiZPgOZJJqmL07MGTBwQo85SRK5vgMkmRe5ixkPUydFllM/4Alrps+c
	7dxKpJ0W8fG4EzA/ZNinutiLDyZYpCzmSRr7LtLYBR5+6AYLDwVRAIE/8yUPJEB2
	SJDsIgE1UNhdNos8f4r/ctJtvpgEfvK8yzwfiU8WKTQm2OjyELCELvtRzBIeBEjD
	B9lJ5VzCXdIX+MzRrqm0FHF+eY5mpjZgqekiDoEpJxwvAsshH+D6b+6m2IYI0ygI
	ohdUz41Cz0etklN03hg6nUm05KSRcHYYpSCwEAN9Mc8dLLuSZwfkn3BpNuANZnY0
	lWIUIEkhBnzwAfCZRzExLWq7R0J87LPb4dX42/mozwa37PNo+HVw2b+EOL2F951d
	9m0w/jj8MmYAMTq/Gd+x4RU7v7lj/zW4udxl/e+fR/3bWzYcscGnz9eDPrQNbi6u
	v1wObv5gHwAPmNwMx+x68GkwBrrjIfGU1Ab9W6T3qT+6+Aiv5x8G14Px3S67Goxv
	kOwV0D1nn89H48HFl+vzEfv8ZfR5eNsHCS4F5ZvBzdUIePU/9W/Ge8Ab2lj/K7yw
	24/n19fE7fwL6DAiKS+Gn+9Ggz8+jtnH4fVlHxo/9EG48w/XfcENVLu4Ph982mWX
	55/O/wABgQ90DIHQiCCljN8+9qkJWJ7Dn4vxYHiDylwMb8YjeN0FXUfjDPXb4LYP
	OTwa3KJlrkZD4IB2BQw03g0m/fDmpi/ooNVN5wAQvn+57efSXPbPr4HaLcqgA+9R
	DWn/1R+qP1BDwpSCJra99syBrHrdi1mbiUeK0SXEOQRc4E9iJ141zpCrG3OoFZCH
	0ynUoxDyYDWXqQaFKZlG8YxSO2k0kLDvAYyfrk5ZA2qm9gPVkB3kf40+bNP7S506
	QGWnAsByi2Jgqs9BG38JJXu6CF0mpNm5EOo4TINQJsB6BT1LB6sAZvg88kFhjy1C
	H0w3jWXNcB2oUs4OEfTYg8ddf+YEvzyyHQ/LCIJg2XJCyG9ZNYo021Bfwl9TqF4p
	86m2vPE4Yr/8stN4NO1GLzH3FkDsQTeSVL/WkOq91l5rAZDKPmiH/z7SIIZmJZcH
	YMAao6p+LHDCqMJK3w0rZVSgXZjWCSIwDRoKAvHVTwTWXQ3WXQlrpWHd12Ddl7De
	JJa0eJWRv5eto7rv6g13vz5IH1WUJq4T1JmS+tYYUfRHYmyCaYLDpg5lL2Tm960M
	uo7C3VbG3ZZCjaG/F2xTMtqdBlBp0ftNMW6YO45gFsK/GwY3jKoEhKrnBO6CwiYK
	5QCegGKc1ElwiIYWN0ogsYMFTwgLmpG4eGDfqQ1ARKt4gNZSqCmRdfG155JqGll6
	brYF51aNKTLRZJuOW4tQJ1CFPe8Me94V7fk3DXqXGfROM+hdZtA706Cyu6R81lKp
	rdLMbCtCS0PftUqOuFtjyWqrmmVVGPLeMKSeaf+AHe8zO95rdrzP7HhfZcd7Xe/7
	lqmJoW0OnZEuab7RPEU3bIWgno3IhDLE254fc1qVGHa9hAka/jxMgsj9gVXsK816
	bIbTAViD4CCdoWIlmwY4lxf1bzFnBewvczVtmjkrMZGnZVlOgr+6fA6rDyeGeT0P
	cLAHIQS9fSAD0/pXrI9sRb/f8LeqRPRySlO2EGdasCjiiE2dr1Wd+ObGUZLM4wh8
	maLInkRYbYWAFhICNczZh2jdtzJS4lEIKZ+LgSFxOjlOR8PprMOxcxxbw7GrcbSY
	2Fi85BwR4hQd1BYDmBEloulPBWL6/IwWaDZ5dMZTmEgyXEHa4HNYTePqDlwqgkIk
	oCLzZxr9GUTRjz+dNKdmxJX+oyD0QEHXP2aBLFx5u5jALAccV8WmqMg/FVUQUiD0
	/1ZUFbTYt346xooUOj8dcUUK9t+Nv1n3ddY1om5m5WEx61QGQMyTRZDmMyl8OxUb
	Pg8CEFZk3HGf2YPDJsxl3iORzYR15nMOQ4TAzJ1gjnQOew8C7Fst9htrTsRLj15c
	8XJCL54Es1s5biWhjk7oUCdkHRiUuq1qArZO4MggYBkEejUEujqBY4NAxyBwqBF4
	NJR61EyuBhrw4dI2fZi7cLnGg9lcM+WzOTSZPiz6tc6xZb9Kcuscu9T8upSucemZ
	rOzV66/mIGKNYu2/sCRiLzgVCXDAW8LiP5+WpPwZFoGghj+HXrE6wDKFVag5dRKo
	m9LUfrhsv5wqkZti6SkVAcc1asNWwVggPRHZDNrZHtReAwoyqglTuojDqqhoO3Hs
	rIzYWPIYN/2SQvGfddcFCiLx120yXkBqXDYlfSYriiCxH3Vfl7Qj9dxoBlWQt4vV
	i9aqUP1TY6hk1ALzKBiNAg5+ZxbrvnYleHVtE1PUWbcdcJi9wa+n9Pk/NQYqEn3a
	AoWxF8ffMGI8BAiKfpIb58RqQ0rnB2iSOPsPdqAniVJY28kyY98PfdyIxSGO9rKF
	RWnniHaH/RgURDFWar+c5C25LtcFBrOiNjBIRjAnF2QyXRxJuKyCVaWCLDOG9BAp
	jEIlFrTn6I5MbhVMRNlnnYyDPn6c5TmNiJApSz9aJIrfRDSH/BWkDTieLmiSCQNk
	gx+b++4PPW4EY0lKyo7lpz7VaH+nMhq3GD7PWIYOcVoIykxalS0zqDOz/R78PcFn
	SBqoJrP9Q3w5wF+Avo+tR/iCsBYCY+sxviCwdZitUaC0wMzxp+QGf4GfIFmxLGGV
	97imS/SDjoywID9Fe3t75SWjQEcPizg9Vi6S01TsNhXGyopS56NA8YcUey+UXQd0
	ICltINLdgN+r67fW45+w7fjbG/A38d+Ev0k/+7HstkpnZUGQO6zRbJIL94UsYp4l
	WrrUcqS19KjluNVi7QyvU8KzS3iHCq9RQOtpQEclNKmfyc8qIR6XEE/K/OwaNF1w
	6Q+TX7dGUAOxkyGWXJUROiwROqkjdGRI0CshSsNUyH5UJYIhhuDQKfnLLvmrW2H3
	Tik+7FJ8IF6jgGeVDG+XDNGtiCurZHe7bAeTYbcGsVO2s8nRrpG0UzazybFXQpSC
	VWDaBsvDEuZJnaw2sazI9LxAJxyPl7WkZzUlWmh6XFNWZN6rwKkG6mxBoq5uyiCv
	6bXX4lpb8K2tt1vwXY+7XqNehXfKPmm6kTjxSFrFoiyn3PlYXVOlrW4pDa1eKQ9h
	WVqRUN1S5huohxlqsVZbdimlrIqiVOBqlXGPy7gnFVztWsxuOa0KXLu1EnfLmUW4
	m+q2Va5XlbR6FaXbqqhZlUr0NlZvaRSr7DG9ZEhZDqpkMUqLgitFk2UUuJM61JOy
	cyyD6VFZXmWAssAnBtOjsnDKyOVR6MQMOqsMZ9cJfGAOV1ZZ4l4JVelgWvikXuKy
	w0Diqmru4d7wzA/hmfrg/ZQ1Zf1RdUGMGHmkNGUFyvo7pX7b6LdL/V2jv9vK1664
	xqd7Y8vIx+tfeNYhl3OcNnASusmRCStvAfBUrcDqNx9etVL3UL3h0ASg90iNtYob
	DIWVXL4EVHsOXpTKnWRzR0XbMV3+zI6pEmlpkTuWarMT3jvivaPebfFut9TKTd/X
	/uvSNKrkedAlAM+2dQk6rcqCooNYCsXKhK5FsTI92zpXq5XtdOobCXoFk3YQ+zKm
	BX7eBcl/L5yYt+MoSiFCmkshl3KHkEo5Q6iJhsmcce555g0KaMCbKBGbgF4ObUVO
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	}

Here's a simple example that demonstrates the basic syntax and use of r3D.  Be sure to do the code above before running this example:

	Transx:  Transy:  Transz: 300.0      	; Set some camera
	Lookatx:  Lookaty:  Lookatz: 100.0   	; positions to
										 	; start with.
	do update: does [			; This "update" function is where
		world: copy []			; everything is defined.
		append world reduce [   ; Add your 3D objects inside this "append".
			reduce [cube-model (r3d-scale 100.0 150.0 125.0) red]
		]						; A red 'cube' 100x150x125 pixels is added.
		camera: r3d-position-object   
			reduce [Transx Transy Transz]
			reduce [Lookatx Lookaty Lookatz]
			[0.0 0.0 1.0] 
		RenderTriangles: render world camera r3d-perspective 250.0 400x360
		probe RenderTriangles	; This line demonstrates what's going on
	]						  	; under the hood.  You can eliminate it.

	view layout [
		scrn: box 400x360 black effect [draw RenderTriangles]  ; basic draw
		across return
		slider 60x16 [Transx: (value * 600 - 300.0) update show scrn]
		slider 60x16 [Transy: (value * 600 - 300.0) update show scrn]
		slider 60x16 [Transz: (value * 600) update show scrn]
		slider 60x16 [Lookatx: (value * 400 - 200.0) update show scrn]
		slider 60x16 [Lookaty: (value * 400 - 200.0) update show scrn]
		slider 60x16 [Lookatz: (value * 200 ) update show scrn]
	]

=image rebol_tutorial/3d1.png
=image rebol_tutorial/3d1a.png

R3D works by rendering 3D images to native Rebol 2D draw functions, which are contained in the "RenderTriangles" block above.  R3D provides basic shape structures and a simple language interface to create and view those images in a Rebol application.  It automatically adjusts lighting and other characteristics of images as they're viewed from different perspectives.  To see how the rendering of images is converted into simple Rebol draw functions, watch the output of the "probe RenderTriangles" line in the Rebol interpreter as you adjust the sliders above.  It displays the list of draw commands used to create each image in the moving 3D world.

In the example above, slider widgets are used to adjust values in the animation.  Those values could just as easily be controlled by loops or other forms of data input.  In the example below, the values are adjusted by keystrokes assigned to empty text widgets (use the "asdfghqwerty" keys to move the cube):

	Transx:  Transy:  Transz: 2.0
	Lookatx:  Lookaty:  Lookatz: 1.0 
	do update: does [
		world: copy []
		append world reduce [ 
			reduce [cube-model (r3d-scale 100.0 150.0 125.0) red]
		]
		Rendered: render world 
			r3d-position-object   
			reduce [Transx Transy Transz]
			reduce [Lookatx Lookaty Lookatz]
			[0.0 0.0 1.0]
			r3d-perspective 360.0 400x360
	]
	view layout [
		across
		text "" #"a" [Transx: (Transx + 10) update show scrn]
		text "" #"s" [Transx: (Transx - 10) update show scrn]
		text "" #"d" [Transy: (Transy + 10) update show scrn]
		text "" #"f" [Transy: (Transy - 10) update show scrn]
		text "" #"g" [Transz: (Transz + 10) update show scrn]
		text "" #"h" [Transz: (Transz - 10) update show scrn]
		text "" #"q" [Lookatx: (Lookatx + 10) update show scrn]
		text "" #"w" [Lookatx: (Lookatx - 10) update show scrn]
		text "" #"e" [Lookaty: (Lookaty + 10) update show scrn]
		text "" #"r" [Lookaty: (Lookaty - 10) update show scrn]
		text "" #"t" [Lookatz: (Lookatz + 10) update show scrn]
		text "" #"y" [Lookatz: (Lookatz - 10) update show scrn]
		at 20x20
		scrn: box 400x360 black effect [draw Rendered] 
	]

=image rebol_tutorial/3d2.png

The r3D module can work with models saved in native .R3d format, and the "OFF" format (established by the GeomView program at <a href="http://www.geom.uiuc.edu/projects/visualization/" target=_blank>http://www.geom.uiuc.edu/projects/visualization/</a>.  See <a href="http://local.wasp.uwa.edu.au/~pbourke/dataformats/oogl/#OFF" target=_blank>http://local.wasp.uwa.edu.au/~pbourke/dataformats/oogl/#OFF</a> for a description of the OFF file format).  A number of OFF example objects are available at <a href="http://www.mpi-sb.mpg.de/~kettner/proj/obj3d/" target=_blank>http://www.mpi-sb.mpg.de/~kettner/proj/obj3d/</a>.

To understand how to create/import and manipulate more complex 3D shapes, examine the way objects are designed inside the "update" function in each of Andrew's three examples.  Here's a simplified variation of Andrew's objective.r example that loads .off models from the hard drive.  Be sure to do the r3D module code above before running this example, and then try downloading and loading some of the example .off files at the web site above:

	RenderTriangles: []
	view layout [
		scrn: box 400x360 black effect [draw RenderTriangles]
		across return
		slider 60x16 [Transx: (value * 600 - 300.0) update show scrn]
		slider 60x16 [Transy: (value * 600 - 300.0) update show scrn]
		slider 60x16 [Transz: (value * 600) update show scrn]
		slider 60x16 [Lookatx: (value * 400 - 200.0) update show scrn]
		slider 60x16 [Lookaty: (value * 400 - 200.0) update show scrn]
		slider 60x16 [Lookatz: (value * 200 ) update show scrn]
		return btn "Load Model" [
			model: r3d-load-OFF load to-file request-file
			modelsize: 1.0
			if model/3 [modelsize: model/3]
			if modelsize < 1.0 [ modelsize: 1.0 ]
			defaultScale: 200.0 / modelsize
			objectScaleX: objectScaleY: objectScaleZ: defaultscale
			objectRotateX: objectRotateY: objectRotateZ: 0.0
			objectTranslateX: objectTranslateY: objectTranslateZ: 0.0	
			Transx:  Transy:  Transz: 300.0
			Lookatx:  Lookaty:  Lookatz: 200.0
			modelWorld: r3d-compose-m4 reduce [
				r3d-scale objectScaleX objectScaleY objectScaleZ
				r3d-translate 
					objectTranslateX objectTranslateY objectTranslateZ
				r3d-rotatex objectRotateX
				r3d-rotatey objectRotateY 
				r3d-rotatez objectRotateZ
			]
			r3d-object: reduce [model modelWorld red]
			do update: does [
				world: copy []	
				append world reduce [r3d-object]
				camera: r3d-position-object   
					reduce [Transx Transy Transz]
					reduce [Lookatx Lookaty Lookatz]
					[0.0 0.0 1.0] 
				RenderTriangles: 
					render world camera r3d-perspective 250.0 400x360
			]
			update show scrn
		]
	]

=image rebol_tutorial/3d3.png

Like most Rebol solutions, r3D is a brilliantly simple, compact, and powerful design that doesn't require any external toolkits.  It's pure Rebol, and it's really amazing!



===Multitasking

"Threads" are a feature of modern operating systems that allow multiple pieces of code to run concurrently, without waiting for the others to complete.  Without threads, individual portions of code must be evaluated in consecutive order.  Unfortunately, Rebol does not implement a formal mechanism for threading at the OS level, but <i>does</i> contain built-in support for asynchronous network port and services activity.  See <a href="http://www.rebol.net/docs/async-ports.html" target=_blank>http://www.rebol.net/docs/async-ports.html</a>, <a href="http://www.rebol.net/docs/async-examples.html" target=_blank>http://www.rebol.net/docs/async-examples.html</a>, <a href="http://www.rebol.net/rebservices/services-start.html" target=_blank>http://www.rebol.net/rebservices/services-start.html</a>, and <a href="http://www.rebol.net/rebservices/quick-start.html" target=_blank>http://www.rebol.net/rebservices/quick-start.html</a> for more information.

The following technique provides an alternate way to evaluate other types of code in a multitasking manner:

# Assign a rate of 0 to a GUI item in a 'view layout' block.

# Assign a "feel" detection to that item, and put the actions you want performed simultaneously inside the block that gets evaluated every time a 'time event occurs.

# Stop and start the evaluation of concurrently active portions of code by assigning a rate of "none" or 0, respectively, to the associated GUI item.

The following is an example of a webcam viewer which creates a video stream by repeatedly downloading and displaying images from a given webcam url.  To create a moving video effect, the process of downloading each image must run without stopping (i.e., in some sort of unending "forever" loop).  But for a user to control the stop/start of the video flow (by clicking a button, for example), the interpreter must be able to check for user events that occur outside the forever loop.  By running the repeated download using the technique outlined above, the program can continue to respond to other events while continuously looping the download code:

	webcam-url: http://209.165.153.2/axis-cgi/jpg/image.cgi
	view layout [
		btn "Start Video" [
			webcam/rate: 0 
			webcam/image: load webcam-url 
			show webcam
		]
		btn "Stop Video" [webcam/rate: none show webcam]
		return 
	    webcam: image load webcam-url 320x240 rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/image: load webcam-url show face
	            ] 
	   	    ] 
		]
	]

=image rebol_tutorial/multi1.png

Here's an example in which two webcam video updates are treated as separate processes.  Both can be stopped and started as needed:

	webcam-url: http://209.165.153.2/axis-cgi/jpg/image.cgi
	view layout [
		across 
		btn "Start Camera 1" [
			webcam/rate: 0 
			webcam/image: load webcam-url 
			show webcam
		]
		btn "Stop Camera 1" [webcam/rate: none show webcam]
		btn "Start Camera 2" [
			webcam2/rate: 0 
			webcam2/image: load webcam-url 
			show webcam2
		]
		btn "Stop Camera 2" [webcam2/rate: none show webcam2]
		return 
	    webcam: image load webcam-url 320x240 rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/image: load webcam-url show face
	            ] 
	   	    ] 
		]
	    webcam2: image load webcam-url 320x240 rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/image: load webcam-url show face
	            ] 
	   	    ] 
		] 
	]

=image rebol_tutorial/multi2.png

Unfortunately, this technique is not asynchronous.  Each piece of event code is actually executed consecutively, in an alternating pattern, instead of simultaneously.  Although the effect is similar (even indistinguishable) in many cases, the evaluation of code is not concurrent.  For example, the following example adds a time display to the webcam viewer.  You'll see that the clock is not updated every second.  That's because the image download code and the clock code run alternately.  The image download must be completed <i>before</i> the clock's 'time action can be evaluated.  Try stopping the video to see the difference:

	webcam-url: http://209.165.153.2/axis-cgi/jpg/image.cgi
	view layout [
		btn "Start Video" [
			webcam/rate: 0 
			webcam/image: load webcam-url 
			show webcam
		]
		btn "Stop Video" [webcam/rate: none show webcam]
		return 
	    webcam: image load webcam-url 320x240 rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/image: load webcam-url show face
	            ] 
	   	    ] 
		]
	    clock: field to-string now/time/precise rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/text: to-string now/time/precise show face
	            ] 
	   	    ] 
		]
	]

=image rebol_tutorial/multi3.png

One solution to achieving truly asynchronous activity is to simply write the code for one process into a separate file and run it in a separate Rebol interpreter process using the "launch" function:

	write %async.r {
		Rebol []
		view layout [
		    clock: field to-string now/time/precise rate 0 feel [
				engage: func [face action event][
		            if action = 'time [
		            	face/text: to-string now/time/precise show face
		            ] 
		   	    ] 
			]
		]
	}

	launch %async.r
	; Rebol will NOT wait for the evaluation of code in async.r
	; to complete before going on:

	webcam-url: http://209.165.153.2/axis-cgi/jpg/image.cgi
	view layout [
		btn "Start Video" [
			webcam/rate: 0 
			webcam/image: load webcam-url 
			show webcam
		]
		btn "Stop Video" [webcam/rate: none show webcam]
		return 
	    webcam: image load webcam-url 320x240 rate 0 feel [
			engage: func [face action event][
	            if action = 'time [
	            	face/image: load webcam-url show face
	            ]
	   	    ]
		]
	]

=image rebol_tutorial/multi4.png
=image rebol_tutorial/multi4a.png

The technique above simply creates two totally separate Rebol programs from within a single code file.  If such programs need to interact, share data, or respond to interactive activity states, they can communicate via tcp protocol, or by reading/writing data via a shared storage device.



===DLLs and Shared Code Files

---What They are and Why to Learn About Them

Some of the most important tools in modern programming exist in the form of "shared code" files.  In Windows, shared code files are called "Dll"s ("dynamically linked libraries").  On Linux they're called "So" files, and on Mac they're called "Dylib" files.  Shared code files are especially useful because they allow libraries of functions to be shared among different programming languages.  They provide a common syntax interface between different development environments, allowing contained functions, parameters, variables, etc. to be accessed and used by any language capable of working with the shared code format.  

A large majority of all executable code in the Windows operating system exists in the form of Dlls.  The Windows "api" ("application programming interface") exposes thousands of existing functions that exist inside many scattered Dll files on your hard drive.  You can access those functions to complete any programming task that isn't natively possible in the Rebol language.  If you want to create intricate software for Linux, you'll need to learn about the functions built into that operating system's shared code files, and the same is true for Mac or any other OS.  Controlling any operating system at a very fine level is accomplished by manipulating functions inside those files.

Besides your operating system api files, there are many thousands of third party DLLs written by programmers all over the world, which contain software components that allow you to do useful things as a developer.  Pre-created shared code modules can help you easily perform everything from visual 3D programming, to VOIP communication, to database management, to robotic equipment handling, to ... well, anything else that can be done with a computer.  Such modules are available both commercially and for free, and learning how to use them is a valuable skill.  Take a look at <a href="http://www.freebasic.net/index.php/viewall?page=link&category=lib" target=_blank>http://www.freebasic.net/index.php/viewall?page=link&category=lib</a>, <a href="http://perso.orange.fr/xblite/libraries.html" target=_blank>http://perso.orange.fr/xblite/libraries.html</a>, and <a href="http://www.thefreecountry.com/sourcecode/index.shtml" target=_blank>http://www.thefreecountry.com/sourcecode/index.shtml</a> for sample listings of some well known free Dlls which Windows developers use to build complex software.  Also take a look at <a href="http://www.sourceforge.net" target=_blank>http://sourceforge.net</a> for a large online repository of free developer tools.  Many of the useful software components at those links come in the form of Dlls and shared code files for various operating systems. 

Rebol keeps you from having to learn the many various complex apis of all the potential operating systems it runs on, and it allows you to accomplish many useful tasks without ever having to use third party tools.  But there are some things that simply can't be done with raw Rebol code.  For example, you can't directly control many types of hardware and you can't make use of certain lesser used operating system functions.  There are also some things which aren't practical for average coders to write from scratch (3D game engines, complex data management systems, etc.).  To do those things, you're best off using software programming tools that teams of other programmers have spent years laboring over.  To benefit from such existing tools, you'll often need to access Dlls.
  

---How To Use Them

To use Dlls and other shared code files in Rebol, you'll need to download one of the recent beta versions of Rebol from <a href="http://www.rebol.net/builds/" target=_blank>http://www.rebol.net/builds/</a> (older versions required a paid license for Dll access).  We'll need to use either rebview.exe, rebface.exe, or rebcmdview.exe for the examples in this section.

To understand how Dlls and other shared code files work, download and save the following file:  <a href="http://musiclessonz.com/pureexample.dll" target=_blank>http://musiclessonz.com/pureexample.dll</a>.  This Dll was written in the Purebasic programming language (another great programming tool found at <a href="http://purebasic.com" target=_blank>http://purebasic.com</a>).  Here's the code that was used to create it:

	ProcedureDLL AttachProcess(Instance.l)
		Global Message.s = "This part of the program was written in
			Purebasic.  Next, the purebasic code will multiply the 
			values previously entered into the Rebol interpreter, 
			and return the result back to the Rebol script..."
	EndProcedure

	ProcedureDLL DoSomeStuff(x.l, y.l)
		MessageRequester("Purebasic", Message)
		ProcedureReturn x * y
	EndProcedure

Run the following code in either "rebview.exe" or "rebcmdview", and you'll see output created by a combination of Rebol code and the Purebasic code above:

	Rebol []
	
	print "--- This part of the program was written in Rebol:"
	print newline
	a: to-integer ask "Enter a random number (integer):  "
	b: to-integer ask "Enter another random number:  "

	; This part of the code uses the pureeexample.dll.
	; the DoSomeStuff function is loaded from the pureexample.dll
	; and converted to the new "rebol-function":
	lib: load/library %pureexample.dll
	rebol-function: make routine! [
		x [integer!]
		y [integer!] 
		return: [integer!]
	] lib "DoSomeStuff"
	; the rebol-function is called, and the result is saved in the
	; "answer" variable:
	answer: rebol-function a b

	print newline
	print "--- This part of the program was written in Rebol:"
	print newline
	print rejoin [
		"The multiplication result calculated by the Purbasic Dll was:  "
		answer
	]
	print newline
	free lib
	halt

=image rebol_tutorial/dll1.png
=image rebol_tutorial/dll1b.png

You do not have to understand the Purebasic language in order to use the Dll.  Just as important, you don't need to own the Purebasic compiler, or have any other skills/tools related to Purebasic.  All you need to know is that the Dll contains 1 function, and that that function accepts 2 passed integer parameters and returns an integer value.  The format used in Rebol to access the function from the Dll is as follows:

	lib: load/library %TheNameOfYour.DLL

	; "TheFunctionNameInsideTheDll" is loaded from the Dll and converted
	; into a new Rebol function called "your-rebol-function-name":
	your-rebol-function-name: make routine! [
		return-value: [data-type!]
		first-parameter [data-type!] 
		another-parameter [data-type!] 
		more-parameters [and-their-data-types!]
		...
	] lib "TheFunctionNameInsideTheDll"

	; When the new Rebol function is used, it actually runs the function
	; inside the Dll:
	your-rebol-function-name parameter1 parameter2 ...

    free lib

The first line opens and loads the functions contained in the specified Dll.  The following lines convert the function contained in the Dll to a format that can be used in Rebol - those lines are the heart of what you need to understand.  To make the conversion, a Rebol function must be labeled and defined (i.e, "your-rebol-function-name" above), and a block containing the labels and types of parameters used and values returned from the function must be provided ("[return: [integer!]]" and "first-parameter [data-type!] another-parameter [data-type!] more-parameters [and-their-data-types!]" above).  The name of the function, as it's labled in the Dll, must also be provided immediately after the parameter block ("TheFunctionNameInsideTheDll" above).  The second to last line above actually executes the new Rebol function, using any appropriate parameters you choose (this can happen as many times as you want in your program, once the new function has been defined).  When you're done using functions from the Dll, the last line is used to free up the Dll so that it's closed by the operating system.

Using the format above, you can access and use the functions contained in most DLLs, as if they're native Rebol functions.  That allows you to make use of a whole world of ready-made software components to instantly accomplish complex programming goals.  Finding and becoming familiar with functions in shared code modules that you consider useful will likely become an important part of your future learning activity.  

Here's another example that requests some text at the Rebol command prompt, and then displays that text in a message box.  The message box uses the Windows api 'MessageBoxA' function, which is contained in the 'User32.dll' file as a standard part of the Windows operating system.  You don't need to download the Dll or move it anywhere in particular on your hard drive - it'll be found automatically by the OS when loaded in Rebol.  Notice how the outline of this code mirrors the general example above:

	Rebol []

	text:  ask "Please enter some text:  "

	lib: load/library %User32.dll

	; The MessageBoxA function is loaded from User32.dll and
	; converted into a new Rebol function called "message-box":
	message-box: make routine! [
		a [integer!] b [string!] c [string!] d [integer!]
	] lib "MessageBoxA"

	; The new message-box function is used, which actually runs
	; the code within the dll:
	message-box 0 text "You typed:" 0
	free lib
	halt

=image rebol_tutorial/dll2.png
=image rebol_tutorial/dll2b.png

The next example uses the Windows api 'Beep' function, contained in the 'kernel32.dll' file.  It takes two integer parameters representing the pitch and duration of the beep: 

	Rebol []

	lib: load/library %kernel32.dll

	; The "Beep" function from the Dll is converted to a new Rebol
	; function called "playsound":
	play-sound: make routine! [
		return: [integer!] pitch [integer!] duration [integer!]
	] lib "Beep"

	for hertz 0 5000 10 [
		print rejoin ["The pitch is now " hertz " hertz."]
		; The converted function is put to use:
		play-sound hertz 50
	]

	free lib
	halt

=image rebol_tutorial/dll3.png

For more information about standard functions contained in the Windows api, see <a href="http://www.allapi.net/downloads/apiguide/agsetup.exe" target=_blank>http://www.allapi.net/downloads/apiguide/agsetup.exe</a> and <a href="http://www.activevb.de/rubriken/apiviewer/index-apiviewereng.html" target=_blank>http://www.activevb.de/rubriken/apiviewer/index-apiviewereng.html</a>.  These help applications were created for the Visual Basic programming language, but the variety of examples should be fairly easy to recognize and convert to Rebol if you focus on the api function names, passed parameters and return value.  For more complete coverage of many api functions, download the help files at <a href="ftp://ftp.borland.com/pub/delphi/techpubs/delphi2/win32.zip" target=_blank>ftp://ftp.borland.com/pub/delphi/techpubs/delphi2/win32.zip</a> or <a href="http://www.borland.com/devsupport/borlandcpp/patches/BC52HLP1.ZIP" target=_blank>http://www.borland.com/devsupport/borlandcpp/patches/BC52HLP1.ZIP</a>.

The next example uses the "dictionary.dll" from <a href="http://www.reelmedia.org/pureproject/archive411/dll/Dictionary.zip" target=_blank>http://www.reelmedia.org/pureproject/archive411/dll/Dictionary.zip</a> to perform a spellcheck on text entered at the Rebol command line.  There are two functions in the dll that are required to perform a spellcheck - "Dictionary_Load" and "Dictionary_Check":

	Rebol []

	check-me: ask "Enter a word to be spell-checked:  "

	lib: load/library %Dictionary.dll

	; Two new Rebol functions are created:

	load-dic: make routine! [
		a [string!] 
		return: [none]
	] lib "Dictionary_Load"

	check-word: make routine! [
		a [string!]
		b [integer!]
		return: [integer!]
	] lib "Dictionary_Check"

	; This line runs the Dictionary_Load function from the DLL:

	load-dic ""

	; This line runs the Dictionary_Check function in the DLL:

	response: check-word check-me 0

	; The Dictionary_Check function returns 0 if there are no errors:

	either response = 0 [
		print "No spelling errors found." 
	] [
		print "That word is not in the dictionary."
	]

	free lib
	halt

=image rebol_tutorial/dll4.png
=image rebol_tutorial/dll4b.png

The next example plays an mp3 sound file of your choice using the Dll at <a href="http://musiclessonz.com/play_mp3.dll" target=_blank>http://musiclessonz.com/play_mp3.dll</a>.  Although you don't need to understand it, the Purebasic code used to create the Dll is shown below.  This dll is useful because Rebol doesn't natively support any way to play mp3s or other common media files:

	ProcedureDLL playfile (name.s)
		If InitMovie()
			LoadMovie(0, name) 
			PlayMovie(0, #Null)
		EndIf
		If OpenConsole()
			Print("Press any key to stop playback")
			While A$=Inkey()
			Wend
		EndIf
		CloseConsole()
	EndProcedure

To make use of this example, the actual compiled Dll file (the one available for download at the link above) has been compressed and embedded directly into the Rebol code.  This was done using the "Rebol Binary Embedder" presented earlier in this tutorial.  The dll is decompressed and written to the hard drive directly from the code, so it does not need to be downloaded or included separately on your computer.  This provides a way to play mp3 files in Rebol without any external file dependencies.  Just copy and paste the code, then call the play-mp3 function.  Because Purebasic is a cross platform compiler, the exact same shared library in this example could be recompiled and used to provide the same functionality on other operating systems (you need the Purebasic compiler to do that).  By using shared code libraries in this way, Purebasic can be a useful tool for adding extended multimedia capabilities to Rebol: 

	Rebol []

	; Here's the compressed dll:

	dll-module: load to-binary decompress 64#{
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	}

	; Now the Dll is written to the hard drive, the "playfile"
	; function is loaded from the Dll, and converted to the
	; new Rebol "play-mp3" function:

	write/binary %play_mp3.dll dll-module

	lib: load/library %play_mp3.dll
	play-mp3: make routine! [a [string!] return: [none]] lib "playfile"

	; Then an mp3 file name is requested from the user, which is played
	; by the "playfile" function in the Dll:

	file: to-local-file to-string request-file
	play-mp3 file

	print "Done playing, Press [Esc] to quit this program: "
	free lib

=image rebol_tutorial/dll5.png
=image rebol_tutorial/dll5b.png

Here's an example that uses the Dll version of the "AutoIt" programming language.  AutoIt is a useful programming tool for the Windows operating system that allows you to interact with other running programs, in order to automate time consuming activities.  The AutoIt compiler and the Dll version of the language ("autoitx") are available for free at <a href="http://www.autoitscript.com/autoit3/downloads.php" target=_blank>http://www.autoitscript.com/autoit3/downloads.php</a>.  AutoIt contains a wide variety of functions to programatically push buttons, type text, select menu items, choose items from lists, control the mouse, etc. in any existing program window, as if those actions had been performed by a user clicking and typing on screen.  Because those actions can be performed programatically, they can be executed without error, and at lightning speed.  This allows you to automate repetitive tasks, and to customize the use of existing applications in ways that satisfy users' needs very specifically.  The code below uses the "AU3_MouseMove" function from the AutoIt Dll to move the mouse around the screen.  Learning the other functions in the AutoIt language can be very helpful in customizing and automating existing Windows applications:

	Rebol []

	lib: load/library %AutoItX3.dll
	move-mouse: make routine! [
		return: [integer!] x [integer!] y [integer!] z [integer!]
	] lib "AU3_MouseMove"

	print "Press the [Enter] key to see your mouse move around the screen."
	print "It will move to the top corner, and then down diagonally to"
	ask "position 200x200:  " 

	for position 0 200 5 [
		move-mouse position position 10 
		; "10" refers to the speed of the mouse movement
	]

	free lib
	print "^/Done.^/"
	halt

=image rebol_tutorial/dll6.png
=image rebol_tutorial/dll6b.png

Here is a final application that uses Dll functions from the native Windows API to view video from a local web cam, to save snapshots in BMP format, and to change the Rebol GUI window title:

	Rebol []

	; First, open the Dlls that contain the Windows api functions we want
	; to use (to view webcam video, and to change window titles):

	avicap32.dll: load/library %avicap32.dll
	user32.dll: load/library %user32.dll

	; Create Rebol function prototypes required to change window titles:
	; (These functions are found in user32.dll, built in to Windows.)

	get-focus: make routine! [return: [int]] user32.dll "GetFocus"
	set-caption: make routine! [
		hwnd [int] a [string!]  return: [int]
	] user32.dll "SetWindowTextA"

	; Create Rebol function prototypes required to view the webcam:
	; (also built in to Windows)

	find-window-by-class: make routine! [
		ClassName [string!] WindowName [integer!] return: [integer!]
	] user32.dll "FindWindowA"
	sendmessage: make routine! [
		hWnd [integer!] val1 [integer!] val2 [integer!] val3 [integer!]
		return: [integer!]
	] user32.dll "SendMessageA"
	sendmessage-file: make routine! [
		hWnd [integer!] val1 [integer!] val2 [integer!] val3 [string!]
		return: [integer!]
	] user32.dll  "SendMessageA"
	cap: make routine! [
		cap [string!] child-val1 [integer!] val2 [integer!] val3 [integer!]
		width [integer!] height [integer!] handle [integer!] 
		val4 [integer!] return: [integer!]
	] avicap32.dll "capCreateCaptureWindowA"

	; Create the Rebol GUI window:

	view/new center-face layout/tight [
		image 320x240
		across
		btn "Take Snapshot" [
			; Run the dll functions that take a snapshot:
			sendmessage cap-result 1085 0 0
			sendmessage-file cap-result 1049 0 "scrshot.bmp"
		]
		btn "Exit" [
			; Run the dll functions that stop the video:
			sendmessage cap-result 1205 0 0
			sendmessage cap-result 1035 0 0
			free user32.dll
			quit
		]
	]

	; Run the Dll functions that reset our Rebol GUI window title:
	; (eliminates "REBOL - " in the title bar)

	hwnd-set-title: get-focus
	set-caption hwnd-set-title "Web Camera"

	; Run the Dll functions that show the video:

	hwnd: find-window-by-class "REBOLWind" 0
	cap-result: cap "cap" 1342177280 0 0 320 240 hwnd 0
	sendmessage cap-result 1034 0 0
	sendmessage cap-result 1077 1 0
	sendmessage cap-result 1075 1 0
	sendmessage cap-result 1074 1 0
	sendmessage cap-result 1076 1 0

	; start the GUI:

	do-events 

=image rebol_tutorial/dll7.png

A complete survey of Dlls and shared code modules in common use is beyond the scope of this tutorial, but the links above should provide a starting point.  For more information about Dlls, see the following pages:

<a href="http://rebol.com/docs/library.html" target=_blank>http://rebol.com/docs/library.html</a>

<a href="http://en.wikipedia.org/wiki/Dynamic_Link_Library" target=_blank>http://en.wikipedia.org/wiki/Dynamic_Link_Library</a>

<a href="http://msdn.microsoft.com/library/" target=_blank>http://msdn.microsoft.com/library/</a>

<a href="http://www.math.grin.edu/~shirema1/docs/DLLsinREBOL.html" target=_blank>http://www.math.grin.edu/~shirema1/docs/DLLsinREBOL.html</a>

Exploring Dlls and other shared modules will undoubtedly lead you toward learning new programming languages and concepts.  Once you've completed this tutorial, you'll be able to accomplish quite a bit of useful programming solely with the Rebol language, but your studies will likely continue down other paths for as long as you're interested in improving your skills.  The AutoIt and Purebasic languages are useful tools that are easy to learn and complimentary to Rebol's strengths.  They're worth checking out when you're curious about other languages.

Remember, whenever you use any Dll or code created by another programmer, be absolutely sure to check, and follow, the licensing terms by which it's distributed.



===Understanding the CGI Interface and Web Programming with Rebol

To understand CGI web programming, it's helps to have a little perspective.  In mainstream computing, there are three ways users commonly interact with programs to input/return data.  You've already seen examples of two methods:

1)  The shell:  data can be input/viewed directly in the Rebol interpreter.  In short scripts, the "ask" and "print" words can be used to enter and display data.  In this "command line" format, program flow can be manipulated by requesting text options from the user, and using conditional operations to react to input.  Simple menus can be created by printing lists of choices to be selected by the user:

	Rebol []

	forever [
		prin "^(1B)[J"
		print "Select from the following options:^/"
		print "1 - Print message 1 time"
		print "2 - Print message 2 times"
		print "3 - Print message 3 times"
		print "4 - Quit^/"
		answer: to-integer ask "Your choice? "
		if answer = 4 [ask "^/Goodbye!  Press any key to end." quit]
		print ""
		loop answer [print "Rebol is great!"]
		print ""
		ask "Press [ENTER] to continue"
	]

=image rebol_tutorial/cgi1.png
=image rebol_tutorial/cgi1b.png

2)  GUIs:  within graphic user interfaces, text is entered and displayed in text fields, areas, and list views.  Program flow is manipulated by responding to mouse clicks on graphic buttons, menu lists, and other widgets:

	Rebol []

	view layout [
		text "How many times should the message be displayed?"
		choice "1" "2" "3" [
			loop to-integer value [alert "Rebol is great!"]
		]
	]

=image rebol_tutorial/cgi1c.png
=image rebol_tutorial/cgi1d.png
=image rebol_tutorial/cgi1d.png
=image rebol_tutorial/cgi1d.png

3)  CGI:  this interface allows data to be input via a web page, using text fields, areas, and dropdown boxes in an html form.  Data entered into a form is submitted and processed by the program that you create and store on your web server.  Returned data is displayed as formatted text, tables, and other html elements that are dynamically created and output by your program.

	There are two parts:

	1) Html page:

	<HTML><HEAD><TITLE>Data Entry Form</TITLE></HEAD><BODY>
	<FORM ACTION="http://yourwebserver/yourrebolscript.cgi">
	How many times should the message be displayed? <BR>
	<INPUT TYPE="TEXT" NAME="times" SIZE="25">
	<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">
	</FORM>
	</BODY></HTML>

	2) CGI script:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Page title"</TITLE></HEAD><BODY>]
	times: decode-cgi system/options/cgi/query-string
	loop to-integer times/2 [print ["Rebol is great!" <BR>]]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi2.png
=image rebol_tutorial/cgi2b.png

The first two options are typically used to create programs that run on a local computer.  They're appropriate for programs that manipulate local user databases, games, audio/video applications, etc.  The CGI option is useful when you want to create programs for the Internet.

All three methods above can be used to manipulate data stored online.  You can, for example, write a program that uses a local shell or GUI interface to access and manipulate data stored on a web server.  Multi-user business applications that share databases among employees at different locations, for example, are well suited to that type of client-server design.  Each user gets a copy of the program, and everyone connects to a centralized data repository that exists at one location on a shared network. 

To present data on the Internet, however, you don't always want to force users to download and install a local application.  Contemporary computer users are familiar with custom database queries, web page searches, specialized email feedback forms, etc. that can be accessed directly on web pages.  Rebol's built-in CGI interface enables this possibility, allowing the language to interact directly with information entered via web pages.  Rebol's CGI ability allows you to write code that runs on a web server, receives data input from web pages, and returns data to the user's browser.  In this way, html pages on your web site can form the complete user interface to programs you write.  PHP, PERL and ASP are popular languages for such Internet programming, but if you know Rebol, you don't need to learn them.  You can upload the Rebol interpreter to your web server and write cgi applications in the powerful and simple Rebol language syntax (just choose the Rebol version for the operating system running on your server).  With CGI, users can interact entirely via a familiar web page interface, without ever knowing or caring that a program exists behind the scenes.  That's one of the most common types of computer application in contemporary use.  And Rebol makes it easy to create those types of programs.

The detailed mechanics of CGI programming are slightly beyond the scope of this tutorial, but the following crash course will get you started:

Learning html is required.  That's true if you intend to attempt any type of Internet programming.  Html is the layout language used to format text and GUI elements on all web pages.  Html is not really a programming language - it doesn't let you manipulate data.  It's just a simple markup format that allows you to shape the visual appearance of pages viewed in a browser. 

In html, items on a web page are enclosed between starting and ending "tags":

	<STARTING TAG>Some item to be included on a web page</ENDING TAG>

There are tags to effect the layout in every possible way.  To bold some text, for example, do the following:

	<STRONG>some bolded text</STRONG>

To create a table with three rows of data, do the following:

	<TABLE border=1>
	<TR><TD>First Row</TD></TR>
	<TR><TD>Second Row</TD></TR>
	<TR><TD>Third Row</TD></TR>
	</TABLE>

Notice that every 

	<opening tag> 

in the code above is followed by a corresponding 

	</closing tag>

Some tags surround all of the page, some tags surround portions of the page, and they're often nested inside one another to create more complex designs.  

A minimal format to create a web page is shown below.  Notice that the title is nested between head tags, and the entire document is nested within html tags.  The page content seen by the user is surrounded by body tags:

	<HTML><HEAD><TITLE>Page title</TITLE></HEAD><BODY>
	A bunch of text and html formatting goes here...
	</BODY></HTML>	

=image rebol_tutorial/cgi3.png

If you save the above code to a text file called "yourpage.html", upload it to a web server, and surf to http://yourwebserver.com/yourpage.html , you'll see in your browser a page entitled "Page title", with the text "A bunch of text and html formatting goes here...".  All web pages work that way - in fact, this very tutorial is an html document.  Click View -> Source in your browser, and you'll see the html tags that are used to format the document.

You can create a CGI program on your web site that outputs the same web page above.  Here's the format:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Page title"</TITLE></HEAD><BODY>]

	print ["A bunch of text and html formatting goes here..."]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi4.png

If you save the code above to a text file called "yourpage.cgi", upload it to a web server where you have Rebol installed in {youruserpath}, and surf to http://yourwebserver.com/yourpage.cgi , you'll see in your browser the exact same web page as in the previous example (to make it work, there will likely be some additional setup steps required to install Rebol - that's covered below).  The first three lines in the code above are required to make your CGI scripts work properly.  Memorize them by rote.  The additional lines simply print out the html contained in the previous example.  Simple, right?

That may seem like a lot of work to produce the same result as the previous example, but it enables the real power of CGI, which is to include dynamic, changeable information on your page.  Say, for example, that you want to display the current time and date in the body of your web page.  Html doesn't allow you do that, but the CGI program below does: 

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Page title"</TITLE></HEAD><BODY>]
	print ["The current date and time is: " now]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi5.png

The fifth line above contains the built in Rebol word "now", which is evaluated and printed on the web page.  In the same way, you can read and print data that's been saved to the hard drive on your web server, you can perform calculations and other data manipulations such as conditional evaluations and loops, you can access databases, send emails, create and manipulate images and sounds, and do anything else that the programming language is capable of.  Output data can be formatted as a nice web page that your user sees online.  

The example below is a short program that reads and sorts the contents of a text file called "users.txt" and displays it on your web page:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Page title"</TITLE></HEAD><BODY>]
	if exists? %users.txt [data: sort read/lines %users.txt print data]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi6.png

If you want user data to be input into your CGI program, you need to create an html page with a "form".  Html forms include text entry fields, dropdown selection boxes and other widgets that allow for data entry.  The form should contain a single "action" that links to the web address of your CGI program.  The form template below contains a text entry field and an action that points to http://yourwebserver/yourrebolscript.cgi . 

	<HTML><HEAD><TITLE>Data Entry Form</TITLE></HEAD><BODY>
	<FORM ACTION="http://yourwebserver/yourrebolscript.cgi">
	<INPUT TYPE="TEXT" NAME="username" SIZE="25">
	<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">
	</FORM>
	</BODY></HTML>

=image rebol_tutorial/cgi7.png

To do something useful with the data sent by the above html form, you'll need to write a CGI program.  That program will be stored at http://yourwebserver/yourrebolscript.cgi .  To extract the information submitted by the form, include the following line in your Rebol CGI program:

	a-word: decode-cgi system/options/cgi/query-string

You can use the assigned word above to refer to all the data sent when the html form was submitted.  Rebol automatically assigns words to the data input in the html form.  If you type "Fred Thompson" as the name in the text entry field on the form above, Rebol will decode it as:
	
	[username: "Fred Thompson"]

You can use that data in a CGI program as follows:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Page title"</TITLE></HEAD><BODY>]

	username: decode-cgi system/options/cgi/query-string
	print ["Hello " second username "!"]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi7b.png

Just save that CGI code as http://yourwebserver/yourrebolscript.cgi , as referenced in the form action in the html page above.  When you enter "Fred Thompson" in the html page, it sends the info to the CGI script, which displays a dynamically created web page saying "Hello Fred Thompson!".

Here's a simple cgi guestbook application that incorporates one of the most important techniques.  It prints output which includes the html form layout.  Because the form used to interact with the cgi program is printed by the cgi itself, no additional html page is required to make this script work.  The action of the printed form points to the address of the CGI program itself.  By evaluating whether the submitted data (decode-cgi system/options/cgi/query-string) is empty or not ("<> none"), the program can determine if any data has been submitted for processing.  The program outputs a simple page that displays the names of all its former visitors, lets you enter your name, and then restarts the process by calling itself when you click submit:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Guestbook"</TITLE></HEAD><BODY>]

	print ["Here's a list of visitors who've signed this page:" ]
	print [<BR>] ; prints a carriage return

	; Check to see if a users.txt file has been created (the first
	; time the script is run).  If not, create it before doing any
	; processing:

	either exists? %users.txt [
		newname: decode-cgi system/options/cgi/query-string
		; check to see if any data has been entered (i.e., if the
		; form has been submitted:
		if newname/2 <> none [
			; if so, write the submitted text and a newline ("<BR>")
			; to the users.txt file:
			write/append %users.txt join "<BR>" [newname/2]
		]
		; print all the names in the guestbook:
		signatures: read %users.txt
		print signatures
	] [write %users.txt ""]

	; Here's the form that gets printed to the page: 
        
	print [<FORM ACTION="http://yourwebserver/yourrebolscript.cgi">]
	print [<BR><HR><BR>"Please enter your name:"<BR>]
	print ["Name: "<INPUT TYPE="TEXT" NAME="username" SIZE="25">]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</BODY></HTML>]

=image rebol_tutorial/cgi8.png
=image rebol_tutorial/cgi8b.png

Here's an example of a simple cgi "form mail" program.  This is one of the most common types of web site applications.  It prints a form to the browser, and when the user submits their information, it emails that information to the site owner.  This example also demonstrates how to wrap the program in a template to make it look like other pages on your site:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Email Us"</TITLE></HEAD><BODY>]

	; The line below reads the top half of the template, and 
	; prints it to the page.  Typically, this half of the template
	; includes some formatting and design that matches the rest of
	; your site.  It will also typically open a layout table, in
	; which the printed form is enclosed:

	print read %template_header.html

	; Set the email settings and retrieve submitted data:

	set-net [from_address@website.com  smtp.website.com]
	submitted: decode-cgi system/options/cgi/query-string

	; Process the form data, if any has been submitted:

	if not empty? submitted [

		; Create a message to be sent.  A time stamp is included here,
		; which adjusts for the time difference between you and your
		; web server.  For example, if you're in New York, and your
		; server is in California, there's a 3 hour difference.  If
		; you want the message marked with your local time, send the
		; time "now + 3:00".  Notice that items from the submitted
		; data are extracted using even numbered indexes (2, 4, 6):

		sent-message: rejoin [
			newline "INFO SUBMITTED BY WEB FORM" newline newline
			"Time Stamp: " (now + 3:00) newline
			"Name: " submitted/2 newline 
			"Email: " submitted/4 newline
			"Message: " submitted/6 newline 
		]

		send/subject to_address@website.com sent-message "FORM SUBMISSION"

		; The following code displays the data that was sent:

		html: make string! 2000
		emit: func [data] [repend html data]
		foreach [var value] submitted [
			emit [<TR><TD> mold var </TD><TD> mold value </TD></TR>]
		]
		print [<font size=5>"Thank You!"</font> <br><br>]
		print ["The following information has been sent:" <BR><BR>]
		print rejoin ["Time Stamp: " now + 3:00]
		print [<BR><BR>]
		print [<table>]
		print html
		print [</table>]
		; The line below reads the bottom half of the template, and 
		; prints it to the page.  Typically, this half of the template
		; closes the layout table and includes the closing </BODY> and
		; </HTML> tags:

		print read %template_footer.html

		; If info has been submitted, the program should quit before
		; printing out the form again:

		quit
	]

	; Print the form if data has not been submitted:

	print [<CENTER><TABLE><TR><TD>]
	print [<BR><strong>"Please enter your info below:"</strong><BR><BR>]
	print [<FORM ACTION="http://yourwebserver/yourrebolscript.cgi">]
	print ["Name:" <BR> <INPUT TYPE="TEXT" NAME="name"><BR><BR>]
	print ["Email:" <BR> <INPUT TYPE="TEXT" NAME="email"><BR><BR>]
	print ["Message:" <BR>]
	print [<TEXTAREA cols=75 name=message rows=5></textarea> <BR><BR>]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</TD></TR></TABLE></CENTER>]

	; If the form is being printed, the previous conditional code has
	; not been executed and therefore the footer has not yet been
	; printed:

	print read %template_footer.html

=image rebol_tutorial/cgi9.png
=image rebol_tutorial/cgi9b.png
=image rebol_tutorial/cgiemail.png

The template_header.html file can include any page formatting and static content.  A basic layout may include something similar to the following:

	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
	<HTML><HEAD><TITLE>Page Title</TITLE>	
	<META http-equiv=Content-Type content="text/html; 
		charset=windows-1252">
	</HEAD>	
	<BODY bgColor=#000000>
	<TABLE align=center background="" border=0 
		cellPadding=20 cellSpacing=2 height="100%" width="95%">
	<TR>
	<TD background="" bgColor=white vAlign=top>

The footer should close any tables or tags opened in the header, and may include any static content that appears after the CGI:

	</TD>
	</TR>
	</TABLE>
	<TABLE align=center background="" border=0 
		cellPadding=20 cellSpacing=2 width="95%">
	<TR>
	<TD background="" cellPadding=2 bgColor=#000000 height=5>
	<P align=center><FONT color=white size=1>Copyright © 2006 
		Yoursite.com.  All rights reserved.</FONT>
	</P>
	</TD>
	</TR>
	</TABLE>
	</BODY>
	</HTML>

The next example dynamically creates a selectable html dropdown list.  The list is filled with data read from the "users.txt" file created earlier.  It uses a foreach loop to automatically insert each item ("<option>") into the dropdown list.  This technique is common when building forms that allow users to select items from a dynamically created lists of specified choices.  The example also demonstrates how to automatically build selectable lists of days, months, and times using similar loops:

	#!/home/youruserpath/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Dropdown Lists"</TITLE></HEAD><BODY>]

	submitted: decode-cgi system/options/cgi/query-string

	if not empty? submitted [
		print rejoin ["NAME SELECTED: " submitted/2 <BR><BR>]
		selected: rejoin [
			"TIME/DATE SELECTED: "
			submitted/4 " " submitted/6 ", " submitted/8
		]
		print selected
		quit
	]

	; Print the form:
	
	print [<FORM ACTION="http://yourwebserver/yourrebolscript.cgi">]
	print [" SELECT A NAME: " <BR> <BR>]
	names: read/lines %users.txt
	print [<select NAME="names">]
	foreach name names [prin rejoin ["<option>" name]]
	print [</option> </select> <br> <br>]

	print " SELECT A DATE AND TIME: "
	print rejoin ["(today's date is " now/date ")" <BR><BR>]

	print [<select NAME="month">]
	foreach m system/locale/months [prin rejoin ["<option>" m]]
	print [</option> </select>]

	print [<select NAME="date">]	
	for daysinmonth 1 31 1 [prin rejoin ["<option>" daysinmonth]]
	print [</option> </select>]
	
	print [<select NAME="time">]
	for time 10:00am 12:30pm :30 [prin rejoin ["<option>" time]]
	for time 1:00 10:00 :30 [prin rejoin ["<option>" time]]
	print [</option> </select> <br> <br>]

	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]

=image rebol_tutorial/cgi10.png
=image rebol_tutorial/cgi10b.png

The "users.txt" file used in the above example may look something like this:

	nick
	john
	jim
	bob

If you memorize the basic syntax, and become familiar with the techniques demonstrated in the previous few examples, you're well on your way to being able to program dynamic web applications with Rebol.  The two-part template required to create CGI programs is the same regardless of how complex a program you create:

# Design an html web page with a form that gets all the input required from the user.  Point the form action to the url of your CGI script.  

# Design a Rebol CGI program to process the data input via the web form.  The first three lines should be the same as the format shown in the template.  Use "decode-cgi system/options/cgi/query-string" to automatically assign variable words to the data entered on the web form.  To provide program output, print html formatted content to the user's browser using standard "print" statements.  You can include an html form in the formatted output to call another CGI application.

Learning to use CGI comfortably requires a working knowledge of html.  The required basics are very easy to learn.  You can study enough html in one day to begin programming CGI applications in Rebol.  Understanding how html forms work is the most important part.  Try the search below for more information:

<a href="http://www.google.com/search?q=html+tutorial" target=_blank>http://www.google.com/search?q=html+tutorial</a>


Rebol CGI programming is covered in greater depth at the following links:

<a href="http://rebol.com/docs/cgi1.html" target=_blank>http://rebol.com/docs/cgi1.html</a>

<a href="http://rebol.com/docs/cgi2.html" target=_blank>http://rebol.com/docs/cgi2.html</a>

<a href="http://rebol.com/docs/cgi-bbs.html" target=_blank>http://rebol.com/docs/cgi-bbs.html</a>

<a href="http://www.rebol.net/cookbook/recipes/0045.html" target=_blank>http://www.rebol.net/cookbook/recipes/0045.html</a>


The site below provides a free downloadable web server program written entirely in Rebol:

<a href="http://plain.at/vpavlu/plain-dev/r80v5/r80v5.html" target=_blank>http://plain.at/vpavlu/plain-dev/r80v5/r80v5.html</a>

It provides an alternative to CGI programming that lets you include Rebol code directly in your html pages, using a format similar to the PHP programming language.  Using the above server, you can include Rebol code to be evaluated directly in your web pages using the following syntax: 

	<?rebol {Rebol code to be evaluated} ?> 

For example:

	<HTML>
	<BODY>
	The time is currently: <?rebol print now/time ?>.
	</BODY>
	</HTML>

That way, a CGI interface isn't even required.  It's a convenient option if you're running your own web server.



===Database Concepts - Using MySQL

Rebol's block/series data structure is a fantastic design that allows you to easily store and organize all types of data within programs.  Blocks can be easily sorted, searched, reorganized, written to files, shared across networks, and manipulated in ways that are easy to understand and use.  There are some situations, however, in which a larger database storage system is desirable to help manage significant loads of information.  That's especially true in situations where multiple users access shared data.  When writing scripts that work on web sites, for example, performance demands often require a database solution.  Web sites commonly receive thousands/millions of visitors per day, all accessing and manipulating shared volumes of data simultaneously.  Managing this type of activity can cause some hairy programmatic problems.  For example, if you design a CGI program that reads and manipulates blocks of data from a text file on a web server, it's likely that many visitors may try to read, write and manipulate data in the file simultaneously.  As each user reads and writes their own unique version of the text, an incomplete view of the current data is seen by each user.  And worse, as each user writes their copy of the data back to a single text file, they'll likely overwrite and erase changes that other users have made.  Additionally, using text files to store large amounts of data can result in slow performance for the user.

To solve these problems and more, there are a wide variety of database systems on the market.  Databases manage all the difficult details of storing, sorting, searching for, and sharing the data they contain.  Because manipulating data is at the heart of most computer applications, database systems are a cornerstone of modern program design.  One of the most popular databases is "MySQL".  Commercial web hosts typically provide free MySQL databases preconfigured and ready to use in your hosting account.  The MySQL server software itself is also free to download and use on your own computer, your network, your website, in commercial products, etc.  The MySQL server software is fast, powerful, and reliable, and it's been proven effective for many years, around the world.  There are literally millions of web sites and applications that rely on MySQL as a database foundation.

The free versions of Rebol don't provide any native support that allow you to work with MySQL databases, but a free alternative has been created.  As with Pascal Hurni's Dll patch, the free MySQL module was created by a third party developer, "Doc" Kimbel, and is not distributed or supported by the Rebol company.  Doc's MySQL module is available at <a href="http://softinnov.org/rebol/mysql.shtml" target=_blank>http://softinnov.org/rebol/mysql.shtml</a>.  It's a standard code module, written in native Rebol, that allows you to connect with and easily manipulate data in a MySQL server.  Just download and "do" the code, or include it directly in your scripts (compress and embed it, etc.).  A module for the "postgre" database server is also free to download from the same web site.  There are other modules in the Rebol code library (<a href="http://rebol.org" target=_blank>http://rebol.org</a>) which provide access to popular database systems such as SQLite.  The commercial versions of Rebol also include native access to industrial database systems such as Oracle, MSSQL, and ODBC systems.  Those versions of Rebol are recommended for commercial work.  But for the purposes of this tutorial, a MySQL example will provide useful knowledge and skills necessary to build functional database apps and web sites.


---Setting up and using MySQL

Using Doc's MySQL module, you can connect to a database on your computer, your network, your web server, etc. and send commands to it via a network connection.  You can also transfer and manipulate data to/from the database using native Rebol series commands and block syntax, so that the information format is natural to use in your Rebol programs.  Detailed instructions for the MySQL module are included in the package download, but if you've never used a database before, some additional setup information and usage concepts may be helpful.  

First, you'll need to create a MySQL database.  If you want to do that on your web site, you'll need to follow the instructions provided by your web host.  Typically, your hosting account will provide some sort of general control panel that allows you to adjust all aspects of your web site's operation (email account settings, traffic logs, etc.).  Typically, the web site control panel will provide an option to create a new MySQL database name, username, and password.  If not, look for a "phpMyAdmin" link.  You may also need to configure "remote access" hosts to allow the database to be used offsite.  That's useful when you want to access a database hosted on your web site, from within scripts that reside on your home computer.  If you're required to allow remote hosts, select the recommended wild card character, or type in the IP address of your local computer - this is not required if the database will only be accessed via scripts/CGIs that run on your web site.  If you're not sure how to configure these options, talk to your web site administrator or your hosting provider, or read your hosting company's FAQs about MySQL.  These settings are typically very easy to make and they only take a minute.

If you'd like to use a MySQL server on your own computer or on a private network, it's best to try one of the freely available installation packages that automatically install and configure a local database/web server for you.  My preference for this type of install package is <a href="http://www.uniformserver.com" target=_blank>http://www.uniformserver.com</a>.  Just download and unzip the package, then click "DiskStart.vbs" and "Run MySQL".  To create a local database, click "phpMyAdmin" and type in the name of a database to create.  The default username and password for the uniformserver is "root" and "root".

=image rebol_tutorial/mysql1a.png
=image rebol_tutorial/mysql1.png
=image rebol_tutorial/mysql2.png

Once you've created a MySQL database, either on your web site or on your home computer, "do" Doc's code module:

	do mysql-107.rip  
	; This unpacks the compressed "rip" file.  This step only needs to
	; be done the first time you use the package on a given computer.
	do %mysql-r107/mysql-protocol.r  
	; This loads the module, and needs to be done every time you access
	; a MySQL database.
	; At the time of this writing, 1.07 was the most current version of
	; the mysql module.  Update the numbers in the previous two lines
	; of code to reflect the curent version number you've downloaded.

Next, enter the database info (location, username, and password), as in the instructions at <a href="http://softinnov.org/rebol/mysql-usage.html" target=_blank>http://softinnov.org/rebol/mysql-usage.html</a>:

	db: open mysql://username:password@yourwebsite.com/yourdatabasename

For example, if you're using the uniformserver on a local PC, the above line will read, by default, as follows:

	db: open mysql://root:root@localhost/yourdatabasename

With that, you've got access to a data management engine that can handle many millions of records and many thousands of concurrent users.  To use the database, you'll need to learn a bit about "tables" and the "SQL" command language.


---Tables and SQL statements

Databases typically store information in tables.  Tables are made up of columns of related data, which are filled with rows of unique data entries.  A contact database, for example, may contain separate columns titled "name", "address", "phone number", and "birthday".  For each new person added to the contact database, a row in each of those columns is typically added.  Columns can be left empty.  Here's an example contact database table:

	name 			address					phone 	 	birthday
	----			-------					--------	--------
	John Smith 		123 Toleen Lane 		555-1234 	1972-02-01
	Paul Thompson	234 Georgetown Place	555-2345	1972-02-01
	Jim Persee		345 Portman Pike 		555-3456	1929-07-02
	George Jones	456 Topforge Court					1989-12-23
	Tim Paulson   							555-5678	2001-05-16

You can add and remove tables to/from your database using the control panel or phpMyAdmin link on your web site (the same one you used to create the database).  You can also do it directly in Rebol, using the format below: 

	insert db {create table Contacts (
	    name            varchar(100),
	    address         text,
	    phone           varchar(10),
	    birthday        date 
	)} 

Each line of code above consists of a column name, along with a <a href="http://www.htmlite.com/mysql003.php" target=_blank>data type</a> to be stored in that column.  The "create table" portion of the code above is an "SQL" command.  Most modern databases use some variation of the SQL language to control the way tables and data are inserted, removed, sorted, and otherwise manipulated within the database.  You need to know the syntax of various MySQL commands to get the database to perform those operations correctly.  A quick Google search will reveal many SQL tutorials, so it will only be covered briefly here.  Here's a short synopsis of some important MySQL commands:
	
	Statements that manipulate data:

	SELECT - extract data from a table
	INSERT INTO - insert new data into a table
	UPDATE - alter or add to existing data in a table
	DELETE - delete data from a table

	Statements that create and delete tables:

	CREATE TABLE - create a new table
	ALTER TABLE  - change the column structure of a table
	DROP TABLE   - delete a table
	CREATE INDEX - create a search key
    DROP INDEX   - delete a search key

The SELECT statement is one that you'll use most often.  Its format is as follows:

	SELECT column_name(s)
	FROM table_name

To retrieve all the data from the Contacts table, use the code below:

	SELECT * FROM Contacts

To retrieve all the data from the name and address columns of the Contacts table:

	SELECT name,address FROM Contacts

To retrieve all the data from the birthday column of the Contacts table, without any duplicates (i.e., 1972-02-01 would only be returned once):

	SELECT DISTINCT birthday FROM Contacts

To perform conditional searches, use the WHERE clause.  The following code will return the entire row of data for John Smith from the Contacts table:

	SELECT * FROM Contacts WHERE name='John Smith'

When using the WHERE clause, search text should be entered in single quotes and the following conditional operators can be used:

	=		Equal
	<>		Not equal
	>		Greater than
	<		Less than
	>=		Greater than or equal
	<=		Less than or equal
	BETWEEN	Within an inclusive range
	LIKE	Search for a pattern

When using the LIKE condition, a "%" sign can be used for wildcards (missing letters in a pattern).  The following line will return the complete rows of data for John Smith and Jim Persee (names that begin with "J"):

	SELECT * FROM Contacts WHERE name LIKE 'J%'

The following line will return a result set containing the info for John Smith, Paul Thompson, and Jim Persee (birthdays that contain the characters "02")

	SELECT * FROM Contacts WHERE birthday LIKE '%02%'

You can use AND and OR in the WHERE clause to refine the search:

	SELECT * FROM Contacts WHERE birthday LIKE '%72%' OR phone LIKE '%34'

The IN clause lets you specify as list of data to match with a column:

	SELECT * FROM Contacts WHERE phone IN ('555-1234','555-2345')

The BETWEEN...AND clause allows you to specify matches within a range:

	SELECT * FROM Contacts
		WHERE birthday NOT BETWEEN '1900-01-01' AND '2010-01-01'

To sort result sets, use the ORDER BY clause.  The following line returns all the info in the Contact table, in alphabetical order by name:

	SELECT * FROM Contacts ORDER BY name

To reverse the order, use the DESC command.  The following line returns data from the name and birthday columns, by order of birthday.  When two records contain the same birthday, they're ordered next by descending alphabetical name:

	SELECT name, birthday FROM Contacts ORDER BY birthday, name DESC


Other SQL statements:

Where SELECT retrieves data from exiting table columns, INSERT puts new data into columns.  The format for inserting data is as follows:

	INSERT INTO table_name VALUES (value1, value2,....)

The following code adds a new row to the Contacts table:

	INSERT INTO Contacts 
		VALUES ('Billy Powell', '5 Binlow Dr.', '555-6789', '1968-04-19')

You can also specify the columns in which data should be created:

	INSERT INTO Contacts (name, phone) 
		VALUES ('Robert Ingram', '555-7890')

The UPDATE statement is used to alter or add data to an existing column.  The following line will add an address for Robert Ingram:

	UPDATE Contacts SET address = '643 Pine Valley Rd.' 
		WHERE name = 'Robert Ingram'

The DELETE statement removes data from a table.  The following code will remove the entire row of information for John Smith:

	DELETE FROM Contacts WHERE name = 'John Smith'

To erase all the data in the Contacts database, without destroying the table:

	DELETE * FROM Contacts

There is more to learn about SQL, including JOINS, indexes, and functions, but the statements presented so far should provided a basic understanding to build upon.  For more info, perform a Google search on "MySQL tutorial" or "SQL tutorial".


---Using SQL Statements in Rebol code

SQL commands work directly in the database engine, and Doc's module makes that data directly available within your program, in typical Rebol blocks.  To integrate SQL statements in your Rebol code, enclose them as follows:  

	insert db {SQL command}

To retrieve the result set created by any inserted command, use:

	copy db

To retrieve only the first result of any command, use:

	first db

To retrieve a portion of the results from any command, use the following format:

	probe copy/part db 3    ; get 3 records from the result

When you're done using the database, close the connection:

	close db


---Putting It All Together

Here's a complete example that opens a database connection, creates a new Contacts table, inserts data into the table, makes some changes to the table, and then retrieves and prints all the contents of the table, and closes the connection:

	Rebol []

	do %mysql-protocol.r 
	db: open mysql://root:root@localhost/Contacts
	; insert db {drop table Contacts} ; erase the old table if it exists
	insert db {create table Contacts (
	    name            varchar(100),
	    address         text,
	    phone           varchar(12),
	    birthday        date 
	)} 
	insert db {INSERT into Contacts VALUES 
		('John Doe', '1 Street Lane', '555-9876', '1967-10-10'),
		('John Smith', '123 Toleen Lane', '555-1234', '1972-02-01'),
		('Paul Thompson', '234 Georgetown Pl.', '555-2345', '1972-02-01'),
		('Jim Persee', '345 Portman Pike', '555-3456', '1929-07-02'),
		('George Jones', '456 Topforge Court', '', '1989-12-23'),
		('Tim Paulson', '', '555-5678', '2001-05-16')
	}
	insert db "DELETE from Contacts WHERE birthday = '1967-10-10'"
	insert db "SELECT * from Contacts"
	results: copy db
	probe results
	close db
	halt

=image rebol_tutorial/mysql3.png
=image rebol_tutorial/mysql3b.png
=image rebol_tutorial/mysql3c.png


---Short Format

Here's a short coding format enabled in Doc's MySQL module that can be used to work with database tables quickly and easily:

	read/custom join mysql://user:pass@host/DB/ ["SELECT * from DB"]

You can use that format to issue statements to any MySQL database.  It's a very simple syntax that allows you to deal with massive amounts of data, using all the power of the SQL language and the MySQL server software.  This single line syntax provides access to multiple tables of information in multiple databases, and enables a solution for some of the most complex data management requirements you're ever likely to encounter.  The following line, for example, could potentially return millions of rows of data in a broad multiuser Internet environment without any complex coding required:
	
	foreach row read rejoin [mysql://root:root@localhost/Contacts/ 
		["SELECT * from Contacts"]] [print row] 

=image rebol_tutorial/mysql4.png

Just issue the SQL statement, and the database does the rest.

It's important to understand that you can use any native Rebol functions to manipulate result set blocks returned by the SQL commands.  You can use the derived data blocks in your program just as if they had been created using any native Rebol means.  Here's an example that puts the results from an SQL query into a GUI text list, which in turn allows you to click and select an item from the list.  When an item is selected, the full row of results is displayed in a GUI area widget, with each column formatted and labeled:

	Rebol []

	do %mysql-protocol.r 
	db: open mysql://root:root@localhost/Contacts
	insert db "SELECT * from Contacts"
	results: copy db 
	view layout [
	    text-list 100x400 data results [
			; When an item in the list is clicked,
			; display its data in a text area:
			string: rejoin [
				"NAME:      " value/1 newline
				"ADDRESS:   " value/2 newline
				"PHONE:     " value/3 newline
				"BIRTHDAY:  " value/4
			]
			view/new layout [
				area string
			] 
		] 
	]
	close db

=image rebol_tutorial/mysql5.png
=image rebol_tutorial/mysql5b.png

Here's the same example using short format:

	Rebol []

	results: read rejoin [
		mysql://root:root@localhost/Contacts? "SELECT * from Contacts"]
	view layout [
	    text-list 100x400 data results [
			string: rejoin [
				"NAME:      " value/1 newline
				"ADDRESS:   " value/2 newline
				"PHONE:     " value/3 newline
				"BIRTHDAY:  " value/4
			]
			view/new layout [
				area string
			] 
		] 
	]

=image rebol_tutorial/mysql5.png
=image rebol_tutorial/mysql5b.png

The example below is a full MySQL CGI application.  It allows users to check attendance at various weekly events, and add/remove their names from each of the events.  By using MySQL to store the data, there are no concerns about whether the script will be accessed by multiple visitors simultaneously.  The speed of the data transactions will also contintue to be very fast, even if millions of people access the site every day and cause the database to grow very large.  This example can be used as a prototype for many kinds of useful web applications in which users add, remove, and view data in an online database, directly from forms on a web page:

	Rebol []

	do %/home/path/public_html/rebol/mysql-r107/mysql-protocol.r 
	db: open mysql://user:pass@website.com/user_db
	; insert db {drop table jamsignup}  ; erase the old table if it exists
	insert db {create table jamsignup (
	    event           varchar(150),
		date			date,
		time            varchar(100),
	    teachers        text,
	    students        text,
	    notes			text
	)} 

	; Each entry should go on a single line.  These lines are broken
	; apart to maintain this web page's formatting:

	insert db {INSERT into jamsignup VALUES 
		('Class', '2006-10-1', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', ''),
		('Class', '2006-10-8', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', ''),
		('Class', '2006-10-15', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', ''),
		('Class', '2006-10-22', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', ''),
		('Class', '2006-10-29', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', ''),
		('Class', '2006-11-5', '4:00pm', 
			'[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]', '', '')
	}
	insert db "SELECT * from jamsignup"
	results: copy db
	probe results

	response: ask "add, remove, or list?  "
	
	event:		"Class"
	date:		"2006-12-1"
	time:		"4:00pm"
	teachers:	"[Nick Antonaccio] [Ryan Gaughan] [Mark Carson]"
	students:	"John Smith"
	notes:		""

	query: rejoin [{INSERT into jamsignup VALUES } {('} event {
		', '} date {', '} time {', '} teachers {', '} students {
		', '} notes {')}]

	switch/default response [
		"add" 		[
			insert db query
		]
		"remove" 	[print "remove"]
		"list"		[print "list"]
	] [print "that's not one of the choices."]


	foreach row read rejoin [
		mysql://user:pass@website.com/user_db? "SELECT * from jamsignup"
	] [print row]
	print newline
	query: rejoin [
		{DELETE FROM jamsignup WHERE students = '} students {'}
	]
	insert db query
	foreach row read rejoin [
		mysql://user:pass@website.com/user_db? "SELECT * from jamsignup"
	] [print row]


	close db
	halt


For comparison, here is a version of the same script that doesn't use MySQL, but rather stores the data in a flat text file ("jam.db").  Comparing it to the above example will help you understand the coding differences required to implement and store data in MySQL:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol [title: "event.cgi"]
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Event Sign-Up"</TITLE></HEAD><BODY>]

	jams: load %jam.db

	a-line: [] loop 65 [append a-line "-"]
	a-line: trim to-string a-line

	print [<hr> <font size=5>" Sign up for an event:"</font> <hr><BR>]
	print [<FORM ACTION="http://yourwebsite.com/cgi-bin/event.cgi">]
	print [" Student Name: "]
	print [<input type=text size="50" name="student"><BR><BR>]
	print [" ADD yourself to this event:             "]
	print [<select NAME="add"><option>""<option>"all"]
	foreach jam jams [prin rejoin ["<option>" jam/1]]
	print [</option> </select> <BR> <BR>]
	print [" REMOVE yourself from this event: "]
	print [<select NAME="remove"><option>""<option>"all"]
	foreach jam jams [prin rejoin ["<option>" jam/1]]
	print [</option> </select> <BR> <BR>]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]

	print-all: does [
		print [<br><hr><font size=5>]
		print " Currently scheduled events, and current attendance:"
		print [</font><br>]
		foreach jam jams [
			print a-line
			print [<BR>]
			print rejoin ["" jam/1]
			print [<BR>]
			print a-line
			print [<BR>]
			for person 2 (length? jam) 1 [
				print jam/:person
				print [<BR>]
			]
			print [<BR>]
		]
		print [</BODY></HTML>]
	]

	selection: decode-cgi system/options/cgi/query-string

	if selection/2 <> none [
		if ((selection/4 = "") and (selection/6 = "")) [
			print [<strong>]
			print "Please try again. You must choose an event."
			print [</strong>]
			print-all
			quit
		]
		if ((selection/4 <> "") and (selection/6 <> "")) [
			print [<strong>]
			print "Please try again. Choose add OR remove."
			print [</strong>]
			print-all
			quit
		]
		if selection/4 = "all" [
			foreach jam jams [append jam selection/2]
			save %jam.db jams
			print [<strong>]
			print "Your name has been added to every event: "
			print [</strong>]
			print-all
			quit
		]
		if selection/6 = "all" [
			foreach jam jams [
				if find jam selection/2 [
					remove-each name jam [name = selection/2]
					save %jam.db jams
				]
			]
			print [<strong>]
			print "Your name has been removed from all events: "
			print [</strong>]
			print-all
			quit
		]
		foreach jam jams [
			if (find jam selection/4) [
				append jam selection/2
				save %jam.db jams
				print [<strong>]
				print "Your name has been added to the selected event: "
				print [</strong>]
				print-all
				quit	
			]
		]
		found: false
		foreach jam jams [
			if (find jam selection/6) [
				if (find jam selection/2) [
					remove-each name jam [name = selection/2]
					save %jam.db jams
					print [<strong>]
					print "Your name has been removed "
					print "from the selected event: "
					print [</strong>]
					print-all
					quit
					found: true
				]
			]
		]
		if found <> true [
			print [<strong>]
			print "That name is not found in the specified event!"
			print [</strong>]
			print-all
			quit
		]
	]

	print-all

=image rebol_tutorial/mysql6.png

Here is a sample of the "jam.db" datafile used in the above example:

	["Sunday September 16, 4:00 pm - Jam CLASS"
		"Nick Antonaccio" "Ryan Gaughan" "Mark Carson"]
	["Sunday September 23, 4:00 pm - Jam CLASS"
		"Nick Antonaccio" "Ryan Gaughan" "Mark Carson"]
	["Sunday September 30, 4:00 pm - Jam CLASS"
		"Nick Antonaccio" "Ryan Gaughan" "Mark Carson"]

The following line of code could be used to automatically create a year's worth of entries for the above data file:

	for date (now/date - 1) (now/date + 365) 7 [
		print rejoin [{["} date {, 4:00 pm - Jam CLASS" ""]}]]



===Parsing

The built-in function "parse" is an important part of the Rebol language.  It's used to import and convert organized chunks of external data into the block format that Rebol recognizes natively.  It also provides a means of dissecting, searching, comparing, extracting, and acting upon organized information within unformatted text data.  Its pattern matching abilities are similar to regular expressions, found in Perl and other languages.  As with many things, the Rebol way is powerful, elegant and simple to use.

The basic format for parse is:

	parse <data> <matching rules>

Parse has several modes of use.  The simplest mode just splits up text at common delimiters and converts those pieces into a Rebol block.  To do this, just specify "none" as the matching rule.  Common delimiters are spaces, commas, tabs, semicolons, and newlines.  Here are some examples:

	text1: "apple orange pear"
	parsed-block1: parse text1 none

	text2: "apple,orange,pear"
	parsed-block2: parse text2 none

	text3: "apple		orange					pear"
	parsed-block3: parse text3 none

	text4: "apple;orange;pear"
	parsed-block4: parse text4 none

	text5: "apple,orange pear"
	parsed-block5: parse text5 none

	text6: {"apple","orange","pear"}
	parsed-block6: parse text6 none

	text7: {
	apple
	orange  
	pear
	}
	parsed-block7: parse text7 none

=image rebol_tutorial/parse1.png
	
All of the above parsed blocks evaluate to ["apple" "orange" "pear"].  That's useful because it enables easy importing of data files created by other programs.  You could, for example, use the "none" rule to import CSV files created by a spreadsheet or database application.  The data is automatically converted to native Rebol data blocks for use in your scripts. 

If you need to split files based on some character other than the common delimiters, you can specify the delimiter as a rule.  Just put the delimiter in quotes:

	text: "apple*orange*pear"
	parsed-block: parse text "*"

	text: "apple&orange&pear"
	parsed-block: parse text "&"

	text: "apple    &    orange&pear"
	parsed-block: parse text "&"

=image rebol_tutorial/parse2.png

You can also include mixed multiple characters to be used as delimiters:

	text: "apple&orange*pear"
	parsed-block: parse text "&*"

	text: "apple&orange*pear"
	parsed-block: parse text "*&" ; the order doesn't matter

=image rebol_tutorial/parse3.png

All of the above parsed blocks also evaluate to the same ["apple" "orange" "pear"].  Using the "splitting" mode of parse is a great way to get formatted tables of data into your Rebol programs.  

Splitting the text below by carriage returns, you run into a little problem:

	text: {	First Name
		   	Last Name
		   	Street Address
		   	City, State, Zip}

	parsed-block: parse text "^/" 

	; ^/ is the Rebol symbol for a carriage return

=image rebol_tutorial/parse4.png

Spaces are included in the parsing rule by default (parse automatically splits at all empty space), so you get a block of data that's more broken up than intended:

	["First" "Name" "Last" "Name" "Street" "Address" "City,"
		"State," "Zip"]

You can use the "/all" refinement to eliminate spaces from the delimiter rule.  The code below:

	text: {	First Name
		   	Last Name
		   	Street Address
		   	City, State, Zip}

	parsed-block: parse/all text "^/" 

=image rebol_tutorial/parse5.png

converts the given text to the following block:

	 [" First Name" "      Last Name" "      Street Address"
		 "      City, State, Zip"]

Now you can trim the extra space from each of the strings:

	foreach item parsed-block [trim item]

=image rebol_tutorial/parse6.png

and you get the following parsed-block, as intended:

	["First Name" "Last Name" "Street Address" "City, State, Zip"]

The example above could be adjusted to pull unformatted lines of info from any text file into your Rebol application.  But that's not all parse can do.  You can also use it to check whether any specific data exists within a given block.  To do that, specify the rule (matching pattern) as the item you're searching for.  Here's an example:

	parse ["apple"] ["apple"]

	parse ["apple" "orange"] ["apple" "orange"]

=image rebol_tutorial/parse7.png

Both lines above evaluate to true because they match exactly.  IMPORTANT:  By default, as soon as parse comes across something that doesn't match, the entire expression evaluates to false, EVEN if the given rule IS found one or more times in the data.  For example, the following is false:

	parse ["apple" "orange"] ["apple"]

=image rebol_tutorial/parse8.png

But that's just default behavior.  You can control how parse responds to items that don't match.  Adding the words below to a rule will return true if the given rule matches the data in the specified way:

# "any" - the rule matches the data zero or more times

# "some" - the rule matches the data one or more times

# "opt" - the rule matches the data zero or one time

# "one" - the rule matches the data exactly one time

# an integer - the rule matches the data the given number of times

# two integers - the rule matches the data a number of times included in the range between the two integers

The following examples are all true:

	parse ["apple" "orange"] [any string!]
	parse ["apple" "orange"] [some string!]
	parse ["apple" "orange"] [1 2 string!]

=image rebol_tutorial/parse9.png

You can create rules that include multiple match options - just separate the choices by a "|" character and enclose them in brackets.  The following is true:

	parse ["apple" "orange"] [any [string! | url! | number!]]

=image rebol_tutorial/parse10.png

You can trigger actions to occur whenever a rule is matched.  Just enclose the action(s) in parentheses:

	parse ["apple" "orange"] [any [string! 
		(alert "The block contains a string.") | url! | number!]]

=image rebol_tutorial/parse11.png
=image rebol_tutorial/parse11.png

You can skip through data, ignoring chunks until you get to, or past a given condition.  The word "to" ignores data UNTIL the condition is found.  The word "thru" ignores data until JUST PAST the condition is found.  The following is true:

	parse [234.1 $50 http://rebol.com "apple"] [thru string!]

=image rebol_tutorial/parse12.png

The real value of pattern matching is that you can search for and extract data from unformated text, in an organized way.  The word "copy" is used to assign a variable to matched data.  For example, the following code downloads the raw html from the Rebol homepage, ignores everything except what's between the html title tags, and displays that text:

	parse read http://rebol.com [
		thru <title> copy parsed-text to </title> (alert parsed-text)
	]

=image rebol_tutorial/parse13.png

The following code extends the example above to provide the useful feature of displaying the external ip address of the local computer.  It reads http:/whatsmyip.org, parses out the title text, and then parses that text again to return only the IP number.  The local network address is also displayed, using the built in dns protocol in Rebol:

	parse read http://whatsmyip.org/ [
	    thru <title> copy my-ip to </title>
	]
	parse my-ip [
	    thru "Your IP is " copy stripped-ip to end
	]
	alert to-string rejoin [
	    "External: " trim/all stripped-ip "  "
	    "Internal: " read join dns:// read dns://
	]

=image rebol_tutorial/parse14.png

Here's a useful example that removes all comments from a given Rebol script (any part of a line that begins with a semicolon ";").  This code is based on the script at http://www.rebol.org/library/scripts/uncomment.r .  First it asks for the file name, and assigns the contents of that file to the variable word "code".  Using the "to" and "thru" words, the content is then parsed for any text that begins with the ";" character, and ends with a newline.  The action block of the parse rule uses the built-in "remove/part" function to remove that parsed text from the code.  Finally, the parsed code is send to the built-in Rebol text editor for viewing, saving, etc.:

	code: read to-file request-file
	
	parse/all code [any [
		to #";" begin: thru newline ending: (
			remove/part begin ((index? ending) - (index? begin))) :begin
		]
	]
	
	editor code

=image rebol_tutorial/parse15.png

To learn more about mining raw data with parse, see the following links:

<a href="http://www.codeconscious.com/rebol/parse-tutorial.html" target=_blank>http://www.codeconscious.com/rebol/parse-tutorial.html</a>

<a href="http://www.rebol.com/docs/core23/rebolcore-15.html" target=_blank>http://www.rebol.com/docs/core23/rebolcore-15.html</a>

<a href="http://en.wikibooks.org/wiki/REBOL_Programming/Language_Features/Parse" target=_blank>http://en.wikibooks.org/wiki/REBOL_Programming/Language_Features/Parse</a>

<a href="http://www.rebolforces.com/zine/rzine-1-06.html#sect4." target=_blank>http://www.rebolforces.com/zine/rzine-1-06.html#sect4.</a>



===Rebol Objects

Rebol objects are code structures that allow you to encapsulate and replicate code.  They provide the ability to bundle packages of functions and data together so that they can be easily copied, reused, and accessed as self-contained units.  Rebol objects provide an easy way to design reusable templates of related code that can be reproduced and varied to create new code units whose contents automatically default to a predefined design.  Objects also provide a way to create clones of clones of objects, so that any object code can serve as the basis for a new object design.  In this way, the concept of object cloning can be extended for multiple generations, to create variations upon variations of code derived from a single template.  

Objects are primarily useful in Rebol when creating duplicatable data structures and when implementing multiple copies of similar code.  Objects are also useful because they hide internal data and functions within their structure.  They can help ensure that words used in one context are not mistakenly used in another context within the same program.  Managing word usage in this way (hiding and exposing word definitions within various sections of a program) is referred to as "namespace" management.

Prototype blueprints are used in Rebol to easily build data objects that duplicate ("inherit") and change ("override") a basic code outline.  Creating a user account model is a good example of how this might be useful.  You can create a general account prototype, with a standard set of data fields and user functions that are part of every customer's profile.  Then for each new customer, the prototype model can be copied, with all the internal data fields inherited.  Any fields that are unique for each individual user can be changed (overridden) to create a unique account instance.

Note:  Unlike other programming languages in which most code is conceived and organized in terms of object constructs, Rebol provides a small subset of tools that allow you to simply clone code blueprints.  "Classes" are a fundamental premise found in other object oriented languages, but they don't exist in Rebol in the same way.  If you're familiar with other object oriented programming languages, be aware that object model ("class") properties in Rebol are simply copied, rather than truly inherited.  The difference is that changes to a "parent" object prototype model in Rebol are not passed on to its derived child objects, once the child objects are created.

To make an original object blueprint in Rebol, use the following syntax:

	label: make object! [object definition]

The object definition can contain functions, values, and/or data of any type.  

Here's a real world example that defines a blank user account object.  It contains 6 variable words (note that each word is set to equal the next word, which is in turn eventually cascaded down to equal "none"):

	account: make object! [
		first-name: 
		last-name:
		address:
		phone:
		email-address:
		none
	]

=image rebol_tutorial/objects1.png

The account definition above simply wraps the 6 variables into a container, or context, called "account".  

Simple, right?

You can refer to data and functions within an object using refinement ("/path") notation: 

	object/word

In the example above, "account/phone" refers to the phone number data contained in the account.  You can make changes to elements in an object as follows:

	object/word: data

In the example above:

	account/phone: "555-1234"
	account/address: "4321 Street Place Cityville, USA 54321"

=image rebol_tutorial/objects2.png

In many OO languages, the "dot" notation is used to refer to things contained in an object (i.e., "methods" and "properties"), using the format "object.method".  If you've learned another OO language before learning Rebol, converting the dot to a slash in your mind will help you make an intuitive transition to Rebol object notation.

Once an object is created, you can view all its contents using the built-in word "help":

	help object

	; or

	? object  

	; "?" is a shorthand synonym for the word "help"

=image rebol_tutorial/objects3.png

If you've typed in all the account examples so far into the Rebol interpreter, then:

	? account

displays the following info:

	ACCOUNT is an object of value:
	   first-name      none!     none
	   last-name       none!     none
	   address         string!   "4321 Street Place Cityville, USA 54321"
	   phone           string!   "555-1234"
	   email-address   none!     none

Once you've created an object prototype, you can make a new object based on the original prototype definition.  The new object will contain all the data and functions defined in the original prototype.  To create such a cloned object, use the following syntax:

	label: make existing-object [
		values to be changed from the original prototype definition
	]

For example, the code below creates a new account block labeled "user1".  You can change any part of the original object block definition, redefine the variables, etc., as follows:

	user1: make account [
		first-name: "John"
		last-name: "Smith"
		address: "1234 Street Place  Cityville, USA 12345"
		email-address: "john@hisdomain.com"
	]

=image rebol_tutorial/objects4.png

Notice that the phone number variable is not set in the above example.  In this case, the phone number variable retains the default value of "none" established in the original account definition.  This is one of the key benefits of using objects.  Our example account object only contains 6 variables, so very little time was saved when defining the user1 account (only the phone number field was duplicated).  If, however, the parent account object contained 20 default variables, for example, a great deal of time would be saved when creating each derived user account.  For example, if user account was designed to assign an automatic email address, folder name, and other default variables for users at a web hosting service, the object model would be very useful in automating the account setup process.

In addition to changing existing variables in an object definition, you can also extend the existing object definition with new values: 

	label: make existing-object [new-values]

The definition below creates a new account object, redefines all the existing variables, and appends a new variable to hold the user's favorite color.

	user2: make account [
		first-name: "Bob"
		last-name: "Jones"
		address: "4321 Street Place Cityville, USA 54321"
		phone:  "555-1234"
		email-address: "bob@mysite.net"
		favorite-color: "blue"
	]

=image rebol_tutorial/objects5.png

"user2/favorite-color" now refers to "blue" ("user1/favorite-color" is still not defined - you'll get an error if you try to access the favorite-color path of user1).

The code below creates a duplicate of the user2 account, with only the name changed:

	user2a: make user2 [
		first-name: "Paul"
		email-address: "paul@mysite.net"
	]

"? user2a" provides the following info:

	USER2A is an object of value:
	   first-name      string!   "Paul"
	   last-name       string!   "Jones"
	   address         string!   "4321 Street Place Cityville, USA 54321"
	   phone           string!   "555-1234"
	   email-address   string!   "paul@mysite.net"
	   favorite-color  string!   "blue"

You can create any number of user profiles based on the "account" template.  Any field that isn't filled in will retain the default value of "none", established in the template definition.  

With the above user objects defined, you can perform comparisons or any other operations that reference the enclosed data, such as:

	if user1/address <> user2/address [
		print "Those users live at different locations."
	]

=image rebol_tutorial/objects6.png

Now, here's the real kicker.  You can also include functions in your object definition:

	account: make object! [
		first-name: 
		last-name:
		address:
		phone:
		none
		email-address: does [
			return to-email rejoin [
				first-name "_" last-name "@website.com"
			]
		]
		display: does [
			print ""
			print rejoin ["Name:     " first-name " " last-name]
			print rejoin ["Address:  " address]
			print rejoin ["Phone:    " phone]
			print rejoin ["Email:    " email-address]
			print ""
		]
	]

	user1: make account []

	user2: make account [
		first-name: "John"
		last-name: "Smith"
		phone:  "555-4321"
	]

	user3: make account [
		first-name: "Bob"
		last-name: "Jones"
		address: "4321 Street Place Cityville, USA 54321"
		phone:  "555-1234"
		email-address: "bob@mysite.net"
	]

	; to print out all the data contained in each object:

	user1/display user2/display user3/display

=image rebol_tutorial/objects8.png

It's important to see here that the original account object definition includes the "display" function.  The account prototype also defines all the variables to be "none" by default.  All that code is part of the prototype definition, so each new object instance (user1, user2, user3) contains all that code by default.  As a result, the user1 object, for example, is a fully functional object even though no variables or functions were defined during its creation.  All it takes to create that object is the code "user1: make account []".

It's also important to recognize that in each user instance, the variables printed by the display function are only those local to the given instance.  For example, when the user3/display function is called, it prints the variables contained in the user3 object.  None of the variables contained in user1 or user2 get unintentionally mixed in, even though they're referred to by the same word.  That's one of the primary benefits of objects - a group of variables and functions are encapsulated in an easily duplicatable object, and each object is self contained.  The variables contained in any of the objects can be updated at any time using path notation (i.e., user1/first-name: "George").  

Note that the variable "email-address" is initially assigned to a function, which defines the default email address to be "first-name_last-name@website.com".  You can override that definition, as in the user/3 definition, to simply refer to an email address string.  Once you've done that, the email-address function no longer exists.  You could use a scheme such as the one above, for example, to add users with default profile outlines to a vendor/customer list, or for any other type of account management.  

The next example sheds a bit more light on how objects are useful.  It's a small game in which multiple character objects are created from a duplicated template.  Each object contains some code and data that allows the user(s) to move several imaginary characters.  Based on the user choice, the character's current position is updated.  Five instances of characters are created, each with a different initial position property.  The point of the game is to find the hidden prize and make one of the characters move to its location.  Upon each user move, the position of the character object is checked to see if it matches the position of the hidden prize:

	; Create a random coordinate at which the hidden prize
	; will be found:

	hidden-prize: random 15x15

	; Here's the basic "character" prototype definition.
	; It contains a variable that holds the character's
	; current position.  It also contains a function that
	; gets a movement choice from the user, then updates
	; the character's current position, and displays
	; a message if the hidden prize is found. 

	character: make object! [
		position: 0x0
		move: does [
			direction: ask "Move up, down, left, or right:  "
			; change the object's position, based on the user's
			; movement choice:
			switch/default direction [
				"up" [position: position + -1x0]
				"down" [position: position + 1x0]
				"left" [position: position + 0x-1]
				"right" [position: position + 0x1]
			] [print newline print "THAT'S NOT A DIRECTION!"]
			; display a message if the hidden prize is found:
			if position = hidden-prize [
				print newline
				print "You found the hidden prize.  YOU WIN!"
				print newline
				halt
			]
			; print a summary of the movement and the new 
			; location relative to the hidden prize:
			print rejoin [
				newline
				"You moved character " movement " " direction
				".  Character " movement " is now " 
				hidden-prize - position
				" spaces away from the hidden prize.  "
				newline
			]
		]
	]

	; Now five character objects are created, each with a
	; different initial position:

	character1: make character[]
	character2: make character[position: 3x3]
	character3: make character[position: 6x6]
	character4: make character[position: 9x9]
	character5: make character[position: 12x12]

	; The user gets 20 chances.  During each chance, the
	; move function of the selected character is executed and
	; the current position of all characters is displayed.

	loop 20 [
	    prin "^(1B)[J"
		movement: ask "Which character do you want to move (1-5)?  "
		; to avoid errors, check that user entered one of the 
		; character numbers "1-5":
		if find ["1" "2" "3" "4" "5"] movement [
			; The line below will evaluate to "do character1/move"
			; if character1 is chosen above, for example. 
			do rejoin ["character" movement "/move"]
			print rejoin [
				newline
				"The position of each character is now:  "
				newline newline
				"CHARACTER ONE:   " character1/position newline
				"CHARACTER TWO:   " character2/position newline
				"CHARACTER THREE: " character3/position newline
				"CHARACTER FOUR:  " character4/position newline
				"CHARACTER FIVE:  " character5/position
			]
			ask "^/Press the [Enter] key to continue."
		]
	]

=image rebol_tutorial/objects9.png

Using this type of object prototype definition, it would be just as easy to create 1000 or more characters, each containing a very complex replicated definition of functions and data structures.  You could, for example, extend this concept to create a vast world of characters in an online multiplayer game.  Each new player would just be a new instance of a character object.  The actions that each player takes and the data he/she collects would simply be updated as path variables in their individual instance of the character object.

Another use for objects is to avoid namespace clashes that occur as a result of using the same word in more than one context.  As you write more code, you may create a library of functions to accomplish common tasks.  If you use the same word in any two functions to represent separate actions, that could cause a problem if you import and use the functions in the same program.  If that happens, one function may unintentionally redefine a word that you use in another function, and cause it to perform in an unexpected way.  An easy solution to such namespace clutter is to wrap your library functions in an object, and expose the function words you want in your program.  That way, you can call the function in the context of the object's name, and not worry about namespace clashes.  For example, in the code below, the first "bank" function and "var" variable get overwritten when those words are redefined a second time:

	var: 1234.56
	bank: does [
		print ""
		print rejoin ["Your bank account balance is:  $" var]
		print ""
	]

	var: "Wabash"
	bank: does [
		print ""
		print rejoin [
			"Your favorite place is on the bank of the:  " var]
		print ""
	]

	bank

=image rebol_tutorial/objects10.png

Evaluating "bank" at the end of the above code yields "Your favorite place is on the bank of the:  Wabash".  There's no way to access the bank account balance code at this point, because the words have been completely redefined.  If such a redefinition of words had been done unintentionally in any code, it would likely cause an error.  You can avoid that problem by simply wrapping the above code into separate objects:

	show-money: make object! [
		var: 1234.56
		bank: does [
			print ""
			print rejoin ["Your bank account balance is:  $" var]
			print ""
		]
	]

	show-place: make object! [
		var: "Wabash"
		bank: does [
			print ""
			print rejoin [
				"Your favorite place is on the bank of the:  " var]
			print ""
		]
	]

	show-money/bank 
	show-place/bank

=image rebol_tutorial/objects11.png

The "bank" function word and the "var" variable word now both refer to completely different things in their respective object contexts, but work correctly when accessed via the object paths.  The "bank" function can make use of the "var" variable in a way that's properly related to its context.  Wrapping code in objects in that way provides a simple method of organizing, grouping together, and maintaining local variables and functions that shouldn't be altered by other parts of a program.

To illustrate how the objects above could be cloned and extended, the objects below create GUIs which alter the contents of variables and make use of functions contained in the above objects:

	deposit: make show-money [
		view layout [
			button "Deposit $10" [
				var: var + 10
				bank
			]
		]
	]

	travel: make show-place [
		view layout [
			new-favorite: field 300 trim {
				Type a new favorite river here, and press [Enter]} [
				var: value
				bank
			]
		]
	]

=image rebol_tutorial/objects12.png
=image rebol_tutorial/objects12b.png
=image rebol_tutorial/objects12c.png
=image rebol_tutorial/objects12d.png
=image rebol_tutorial/objects12e.png

As a derived object, the "deposit" object automatically has access to all the data and functions contained in the show-money object, and the "travel" object gets full access to the contents of the show-place object.  In each new object, the action block of the GUI widget alters the local "var" variable and performs the local "bank" action, each inherited from the objects created earlier.

As you explore Rebol coding more deeply, you'll find that much of the language is built on object constructs.  Working with graphics often requires extensive manipulation of objects.  The name of the language itself stands for "Relative Expression Based Object Language".  With that said, object oriented concepts aren't as fundamentally important in Rebol as they are in other languages.  The Rebol "way" is to organize data and functions using blocks, and to refer to blocks with words.  The fact that any block can automatically be treated as an ordinal series and manipulated using built-in list manipulation features is a fundamental design concept in Rebol.  Another one of the primary differences that separates Rebol from other fundamentally object oriented languages is that mini language dialects can be built on word definitions, to provide a natural interface to data and function groupings.  Those constructs provide an efficient, light weight, and powerful way to design programs, and they're among the main reasons that Rebol is a pleasure to use.  Objects simply provide the additional ability to encapsulate and replicate code and to extend the built-in object constructs that already exist in the language.

For more information about how to put Rebol objects to use, see:

<a href="http://rebol.com/docs/core23/rebolcore-10.html" target=_blank>http://rebol.com/docs/core23/rebolcore-10.html</a>

<a href="http://en.wikibooks.org/wiki/REBOL_Programming/Language_Features/Objects" target=_blank>http://en.wikibooks.org/wiki/REBOL_Programming/Language_Features/Objects</a>

<a href="http://en.wikipedia.org/wiki/Prototype-based_programming" target=_blank>http://en.wikipedia.org/wiki/Prototype-based_programming</a>



===Common Errors

Listed below are solutions to a variety of common errors you'll run into when first experimenting with Rebol:

1)  "** Syntax Error: Script is missing a REBOL header" - Whenever you "do" a script that's saved as a file, it must contain at least a minimum required header at the top of the code.  Just include the following text at the beginning of the script:  

	Rebol []

=image rebol_tutorial/errors1.png
=image rebol_tutorial/errors1b.png

2)  "** Syntax Error: Missing ] at end-of-script" - You'll get this error if you don't put a closing bracket at the end of a block.  You'll see a similar error for unclosed strings. The code below will give you an error, because it's missing a "]" at the end of the block:

		fruits: ["apple" "orange" "pear" "grape"
		print fruits

=image rebol_tutorial/errors2.png

Instead it should be:

		fruits: ["apple" "orange" "pear" "grape"]
		print fruits

=image rebol_tutorial/errors2b.png

Indenting blocks helps to find and eliminate these kinds of errors.

3)  "** Script Error: request expected str argument of type: string block object none" - This type of error occurs when you try to pass the wrong type of value to a function.  The code below will give you an error, because Rebol automatically interprets the website variable as a url, and the "alert" function requires a string value:

		website: http://rebol.com
		alert website

=image rebol_tutorial/errors3.png

The code below solves the problem by converting the url value to a string before passing it to the alert function:

		website: to-string http://rebol.com
		alert website

=image rebol_tutorial/errors3b.png

4)  "** Script Error: word has no value" - Miss-spellings will elicit this type of error.  You'll run into it any time you try to use a word that isn't defined (either natively in the Rebol interpreter, or by you, in previous code):

	wrod: "Hello world"
	print word

=image rebol_tutorial/errors4.png

5)  To break out of an endless loop, or to otherwise stop the execution of errant code, just hit the [Esc] on your keyboard.  If an error occurs in a "view layout" block, and the GUI becomes unresponsive, type "unview" at the interpreter command line and the broken GUI will be closed.

6)  IMPORTANT:  Here's a quirk of Rebol that doesn't elicit an error, but which can cause confusing results, especially if you're familiar with other languages:

	unexpected: [
	    empty-variable: ""
	    append empty-variable "*"
	    print empty-variable
	]

	do unexpected
	do unexpected
	do unexpected

=image rebol_tutorial/errors5.png

The line:  

	empty-variable: "" 

doesn't re-initialize the variable to an empty state.  Instead, every time the block is run, "empty-variable" contains the previous value.  In order to set the variable back to empty, as intended, use the word "copy" as follows:

	expected: [
	    empty-variable: copy ""
	    append empty-variable "*"
	    print empty-variable
	]

	do expected
	do expected
	do expected

=image rebol_tutorial/errors5b.png

7)  Load/Save, Read/Write, Mold, Reform, etc. - another point of confusion you may run into initially with Rebol has to do with various words that read, write, and format data.  When saving data to a file on your hard drive, for example, you can use either of the words "save" or "write".  "Save" is used to store data in a format more directly usable by Rebol.  "Write" saves data in a raw, 'unRebolized' form.  "Load" and "read" share a comparable relationship.  "Load" reads data in a way that is more automatically understood and put to use in Rebol code.  "Read" opens data in exactly the format it's saved, byte for byte.  Generally, data that is "save"d should also be "load"ed, and data that's "write"ed should be "read".  For more information, see the following Rebol dictionary entries:

<a href="http://rebol.com/docs/words/wload.html" target=_blank>http://rebol.com/docs/words/wload.html</a>

<a href="http://rebol.com/docs/words/wsave.html" target=_blank>http://rebol.com/docs/words/wsave.html</a>

<a href="http://rebol.com/docs/words/wread.html" target=_blank>http://rebol.com/docs/words/wread.html</a>

<a href="http://rebol.com/docs/words/wwrite.html" target=_blank>http://rebol.com/docs/words/wwrite.html</a>

Other built-in words such as "mold" and "reform" help you deal with text in ways that are either more human-readable or more natively readable by the Rebol interpreter.  For a helpful explanation, see <a href="http://www.rebol.net/cookbook/recipes/0015.html" target=_blank>http://www.rebol.net/cookbook/recipes/0015.html</a>.

8)  Order of precedence - Rebol expressions are <i>always</i> evaluated from left to right, regardless of the operations involved.  If you want specific mathematical operators to be evaluated first, they should either be enclosed in parenthesis or put first in the expression.  For example, to the Rebol interpreter:

	2 + 4 * 6

is the same as:

	(2 + 4) * 6  ; the left side is evaluated first

	== 6 * 6

	== 36

This is contrary to other familiar evaluation rules.  In many languages, for example, multiplication is typically handled before addition.  So, the same expression:

	2 + 4 * 6

is treated as:

	2 + (4 * 6)  ; the multiplication operator is evaluated first

	== 2 + 24

	== 26

In Rebol, the left-right order of precedence is consistent, easy to remember, and holds true for all evaluated expressions.  Line terminators are not even required, as in other languages (i.e., semicolons in C-like languages), so the following example:

	save %text.txt read http://rebol.com print sort read %text.txt

may be written a bit more intuitively like this:

	save %text.txt (read http://rebol.com) 
	print (sort (read %text.txt))

That whole script is evaluated as follows:  The "save" function accepts two parameters - first a filename, then the data to be written.  That data is read from http://rebol.com (the next expression in order).  Next in line, the "print" function takes one parameter.  That data is the sorted text read from the text.txt file.  The whole thing is simply evaluated left to right.  Becoming accustomed to this thought process can be the source of some initial errors if you're already used to other languages.


---Trapping Errors

There are several simple ways to keep your program from crashing when an error occurs.  The words "error?" and "try" together provide a way to check for and handle expected error situations.  For example, if no Internet connection is available, the code below will crash abruptly with an error:

	html: read http://rebol.com

The adjusted code below will handle the error more gracefully:

	if error? try [html: read http://rebol.com] [
		alert "Unavailable."
	]

=image rebol_tutorial/errors7.png
=image rebol_tutorial/errors7b.png

The word "attempt" is an alternative to the "error? try" routine.  It returns the evaluated contents of a given block if it succeeds.  Otherwise it returns "none":

	if not attempt [html: read http://rebol.com] [
		alert "Unavailable."
	]

=image rebol_tutorial/errors7b.png

To clarify, "error? try [block]" evaluates to true if the block produces an error, and "attempt [block]" evaluates to false if the block produces an error.  

For a complete explanation of Rebol error codes, see:  <a href="http://www.rebol.com/docs/core23/rebolcore-17.html" target=_blank>http://www.rebol.com/docs/core23/rebolcore-17.html</a>.



===How to Organize Your Coding Thought - Some Real World Examples

If you're just beginning to write code, it's easy to read through language documentation, understand all the constructs and examples, and still walk away saying to yourself "that's fine ... but, how do I write a program that does ______".  Trying to tackle any specific programming situation from scratch requires not only an understanding of how language components work and how they're put together, but how to think in terms of organizing those components to materialize a working program from your imagined design.  Until you've done that many times, it can be difficult to shape a program from raw code.  This section is intended to provide some understanding of how you can approach organizing your thoughts and write code to satisfy your specific needs in any situation.  Several short case studies are presented to provide insight as to how specific real life situations were approached.


---Using Outlines and Pseudo Code

A great way to approach any coding project is to think through a flow chart of activity and to write out all the necessary coding requirements in a design outline consisting of natural language.  Using spoken English "pseudo code" provides a structure for the detailed code you'll write.  When approaching any coding project, start with a top-down approach.  Go from general ideas about how the program will flow, to outline structure, to pseudo code within that structure, to final detailed code.  As a last step, you'll typically debug the code and add/change functionality as you test and use the program.  

To start out, explain to yourself what you want your intended program to do, and think through what the program must do internally to accomplish that goal.  As you begin to make an imagined program take shape, think of how you expect the user and the computer to interact when the program is complete, and put those actions into words.  Write down your explanation and flesh out the details of the imaginary program as much as possible.  That will give you a starting point to begin tearing apart every requirement and organizing a plan of how the code will be structured to make each of those requirements flow from one to another.

To begin a structured outline, start with an idea of what data the user will input and what the computer will output.  Every program needs a way to input and/or return data - GUI, command line interface, web page CGI input, etc.  Most desktop applications use a GUI to interact with the user, but sometimes it's easier to think through the development process using console interactions.  It's also easier to develop a CGI application if you've got a working console version.  Whatever your conceived interface, remember that program flow is primarily linear.  The majority of code you write will flow from one data definition or action to the next.  You can begin the process of writing an outline by thinking of how the program must begin, and what must be done before the user starts to interact with the application.  Think of any data or actions that need to be defined before the program starts.  Then think of what must happen to accommodate each possible interaction the user might choose.  This will help you define an interface, and it will help you begin to think in terms of actual bits of code that need to be written.  In some cases, all possible actions may occur as a result of the user clicking various GUI widgets.  That should elicit the thought of certain bits of GUI code structure, and you can begin writing an outline to design a GUI interface.  If you imagine an online CGI application or a command line program, the user may respond to text questions or work with forms on a web page.  Again, some code from the example applications in this tutorial should come to mind, and you can begin to form a coding structure that enables the general user interface.

To flesh out the program outline, you can use natural language pseudo code.  For example, if you imagine a button in a GUI interface doing something for your user, you don't need to immediately write the Rebol code that the button runs.  Initially, just write a description of what you want the button to do.  The same is true for functions and other chunks of code.  As you flesh out the outline more, you can describe the language elements and coding thought you conceive to perform various actions or to represent various data structures.  As you outline a program to enable user interaction with the computer, don't get lost in the nitty gritty syntax details of writing actual code.  It's easy to lose sight of the big picture at this stage.  Instead, concentrate on the organizational scheme that provides an overview of how the program will operate.  Most actions in a program will occur as a result of conditional evaluations (if this happens, do this...), loops, or linear flow from one action to the next.  If you're going to perform certain actions multiple times or cycle through lists of data, you'll likely need to run through some loops.  If you'll need to work with changeable data, you'll need to define some variable words, and you'll probably need to pass them to functions to process the data.  Think in those general terms first.  Create a list of data and functions that are required, and put them into an order that makes the program structure build and flow from one definition, condition, loop, GUI element, action, etc., to the next.  If you spend time organizing your needs in terms of a natural language outline, and then fill that outline with pseudo code descriptions of code constructs, you'll have a much easier time converting those needs to actual code.

Instead of providing more vague and generalized notions about how to organize programming thought, what follows are a few case studies that describe how I've approached little programming tasks in a productive way.  Each example traces my train of thought from the organizational process through the completed code.


---Case 1 - Scheduling Teachers

In organizing my music lesson business, I needed a way for teachers to see their current weekly schedules.  I needed them to see any additions/changes I'd made (new students, reschedulings, etc.), and I also needed to know what times they had available when scheduling new students.  On top of that, I wanted the teachers to be able to make changes to their schedules, so that we were all in sync with current daily appointments.  In other studios, I had typically seen this done with a weekly paper schedule.  Each teacher had one piece of paper for each day's recurring weekly schedule.  The available times were listed for each day, and when management added a new student, they wrote all the student info (name, parent name, phone number, etc.) onto the line for that weekly appointment time in the teacher's schedule.  This was awkward for everyone.  Teachers had to keep a list of rescheduled appointments in their daily calendars, and they couldn't possibly let management know about all their cancellations, rescheduled appointments, etc.  That made for missed appointment opportunities, awkward double bookings, and lots of scribbling on the schedule.  The teachers also had to come to the studio or be in touch with management by phone to be notified of schedule additions and changes.  

A web based solution seemed like a perfect alternative to the weekly paper schedule.  Teachers could check their schedules at home each day, and we'd all be able to see and adjust to current changes.  At first, I imagined a database solution that saved changes to an online database, which could be accessed by a CGI front end.  As I thought about it more, though, I began to wonder if it'd be better to simply create a small schedule page and use a content editor to manage the text on that page.  That would provide a free form solution that mimicked the paper schedule teachers were familiar with, and eliminated the problems related to having paper schedules at one centralized location.  To organize my thoughts, I created a text file in the same format as the paper schedules I'd seen:

	Monday:

	3	  student1, 555-1234, parent's names, payment history, notes
	3:30  student2, 555-1234, parent's names, payment history, notes
	4	  (gone 3-17)  student3, 555-1234, payment history, notes
	4:30  student4, 555-1234, parent's names, payment history, notes
	5	  student5, 555-1234, parent's names, payment history, notes


	Tuesday:

	3	  ----
	3:30  ----
	4	  (john doe 3-18) ----
	4:30  ----
	5	  student1, 555-1234, parent's names, payment history, notes
	5:30  student2, 555-1234, parent's names, payment history, notes
	6	  student3, 555-1234, parent's names, payment history, notes
	6:30  ----
	7	  student4, 555-1234, parent's names, payment history, notes
	7:30  ----
	8	  student5, 555-1234, parent's names, payment history, notes
	.
	.
	.

At a glance, the entire weekly schedule was visible.  I used "----" to indicate an available appointment time, and any temporary changes to the weekly schedule could be noted in parentheses.  This is how the teachers were used to working with their schedules.

I wanted to create the above schedule format on a web page, and I wanted it framed in an html document that had some permanent info that the teacher couldn't alter.  I also wanted the teacher to be able to make adjustments without having to mess with ftp or anything having to do with the web site.  They just needed to click an icon, type some changes into their schedule, and have it appear on the web page.  Here's an outline of what I needed to accomplish:

# Download the current schedule text file.

# Backup a copy of the existing schedule, just in case.

# Edit the schedule.

# Upload the altered schedule data back to the website.

# Include the new schedule text in an html template, retaining the proper line format.

# Confirm that the changes were made correctly and that they displayed correctly on the web page.

# Keep the teacher interface simple and intuitive, like writing on a piece of paper.


After looking at the above outline, the best solution turned out to be the simplest.  Instead of designing a database scheduling app with a complex GUI layout to manage all the data, I just did each step above in the most direct way possible in Rebol code:

	; first set some initial variables:

	url: http://website.com/teacher
	ftp-url: ftp://user:pass@website.com/public_html/teacher

	; ... and give the teacher some instructions: 

	alert {Edit your schedule, then click save and quit.
		The website will be automatically updated.}

	; 1) download the file containing the schedule text:

	write %schedule.txt read join url ["/schedule.txt"]

	; 2) create a timestamped backup on the web server:
	
	write join ftp-url ["/" now/date "_" now/time] read %schedule.txt

	; 3 and 7) edit the text:

	editor %schedule.txt

	; 4) save the edited text back to the web site:

	write join ftp-url ["/schedule.txt"] read %schedule.txt

	; 6) confirm that the changes are displayed correctly:

	browse url

=image rebol_tutorial/teacher1.png
=image rebol_tutorial/teacher2.png

To satisfy step 5 in the outline, I created a downloadable executable (".exe" file) of the above program (using XpackerX), and in the http://website.com/teacher folder on the web site, I created an index.php file containing the following code:

	<a href="./scheduler.exe" target=_blank>Download Scheduler</a>
	<br><br><pre><?php include 'schedule.txt'; ?></pre>

=image rebol_tutorial/teacher3.png

The first line creates a download link, so that the teacher can download and run his scheduler program at any remote location.  The second line includes the preformatted schedule text on the web page.  I can put any other html I want on this page, which the teacher never touches.

What could have been a very long and involved programming task was accomplished in minutes, and has been in use every day for many months.  The free form format enabled by using a simple text file provides the opportunity to incorporate various notes, changes, and info that would otherwise be awkward to include or difficult to emphasize in the weekly schedule.  In this case, writing the outline/pseudo code provided an immediate solution, and it's worked out to be the best way to satisfy our needs.


---Case 2 - Downloading Directories

Here's a situation that involved a bit more code design.  I had a notebook computer that was disabled by a severe adware breakout.  In an attempt to erase the troublesome files, the machine was rendered unable to boot to the operating system.  I needed to copy a large number of recent data files that had not yet been backed up.  Several options which didn't involve writing code were available to get this kind of job done.  I could've removed the hard drive and put it in another machine, and then copied the files directly from one hard drive to another.  I didn't have a hardware connector to install the laptop drive, and I didn't feel like taking the machine apart.  I could've tried to reinstall the OS, and send the files across the network to be backed up on another computer.  Without a system disk immediately available to restore the operating system, that wasn't convenient.  I could've also potentially used a stand-alone local file transfer application (the "laplink" type), but without any serial/parallel ports, and without any OS access to provide USB support, I didn't have an application which made that option possible.  Instead, I happened to have a Knoppix CD with which I was able to boot the laptop (http://www.knoppix.org/ provides the complete Linux operating system on a single free CD - it doesn't require any hard drive or any installation to run).  I booted the computer to Knoppix, it found my network, and I started the Aprelium web server (http://aprelium.com/) on the laptop.  Tada!  Using another computer on the network, I was able to access all my files through the web server.  I had access to the files at that point, but since I had literally thousands of files in hundreds of directories on the laptop, I couldn't download each one manually.  Instead, I wrote a little spidering application in Rebol that did the job instantly.  

To create the program in natural language, I thought about the process I would go through, and how I would click through the directory structure if I were to manually download each file:

# Create a new destination folder on the client computer to hold the transferred files.

# Start in the current subdirectory on the laptop (starting with the folder that held my data), and download all the files in it to the new destination directory on the client computer.

# Create subdirectories in the destination directory on the client to mirror each folder in the current directory on the laptop.

# Switch into each of the subdirectories on the laptop and on the client, and repeat steps 2-4 for each subdirectory.


I came up with the outline above by actually sitting down at the computer, and running though the process that I wanted to automate.  I just took note of how the thought process was organized.  Next, I converted the above ideas to pseudo-code, or something that described how I would accomplish the above things using code constructs:

# Get an initial remote url from the user.  Use the built-in "request-text" function to do that.  Then, create a local folder to mirror it, with a nicely formed name (only allowable Windows file name characters).  Use the built-in "replace" function to swap out unusable characters, and the built-in "make-dir" function to create a destination folder with the cleaned up characters.

# Since the file and directory listings are made available via a web server, I'm going to have to parse a web page for file names to download.  That's easy - the web server puts "/" characters at the end of all folder listings, so anything without a "/" at the end is a file.  Create a block of file names, and use a "foreach" loop to go through the list of files, using read/binary and write/binary functions to download the actual files to the destination folder.

# I'll also need to parse the web page for folder names to create.  Use another "foreach" loop to work through the block of folder names, and the "make-dir" function to create local directories with those names.

# Create a function that changes directories on both the local and remote machines.  In order to work with the correct folders, I'll need to create some variables to keep track of the directory I started in, the current local folder I'm writing to, and the current remote folder I'm reading.  As I switch in and out of each directory, I'll use rejoin and replace functions to concatenate and remove the current folder names to and from the local directory and remote url variables.  Because I need to create a function that repeats both previous steps and THIS CURRENT step in every subdirectory, I'll need to enclose all three of those steps into a function, and call that function from within itself.  The process of creating a function that calls itself is called "recursion" - it's needed here to do the same thing in every folder, drilling down until there are no more subfolders.

The first step was straightforward.  Here's the code I came up with:

	; Get initial remote url and create a local folder to mirror
	; it, with a nicely formed name (only allowable Windows file
	; name characters).
	
		initial-pageurl: to-url request-text/default trim {
			http://192.168.1.4:8001/4/}
		initial-local-dir: copy initial-pageurl
		replace initial-local-dir "http://" ""
		replace/all initial-local-dir "/" "_"
		replace/all initial-local-dir "\" "__"
		replace/all initial-local-dir ":" "--"
		lrf: to-file rejoin [initial-local-dir "/"]
		if not exists? lrf [make-dir lrf]
		change-dir lrf
		clf: lrf

Since steps 2-4 above would all be enclosed in a single function, I decided I should assign some variable words that would refer to the folders I'd be accessing: "lrf" = local-root-folder, "clf" = current-local-folder and "crfu" = current-remote-folder-url.

To begin step 2, I wrote a bit of code to do the parsing of the file and folder names on the current web page directory listing.  I combined the parsing requirements from step 2 and 3 above, and decided to use the variable words "files" and "folders" to label the blocks that would contain the parsed results.  Here's the code that I came up with to read and parse the contents of the current page into the usable blocks.  It looks for any link (anything beginning with href=" and ending with "), and appends it to the folders block if it contains a "/" character.  Anything that doesn't contain the "/" character gets appended to the file block:

	page-data: read crfu
	files: copy []
	folders: copy []
	parse page-data [
		any [
			thru {href="} copy temp to {"} (
				last-char: to-string last to-string temp
				either last-char = "/" [
					; don't go upwards through the folder structure:
					if not temp = "../" [
						append folders temp
					]
				][
					append files temp
				]
			)
		] to end
	]

To complete step 2, here's the foreach loop that I came up with to download all the files contained in the file block.  It contains a replace/rejoin trick to make sure the filename gets concatenated to the current url correctly (with no extra "/"s):

	foreach file files [
		print rejoin ["Getting: " file]
		new-page: rejoin [crfu "//" file]
		replace new-page "///" "/"
		write/binary to-file file read/binary to-url new-page
	]

I ran into some problems with certain links on the web page that weren't actually file or folder listings, or which didn't download properly.  I used some conditional "if"s and "error? try" combinations to eliminate those problems.  I wrote the errors to a text file, so that I could check them afterwards and download manually if necessary.  Here's the revised version of the code above, with the error handling routines:

	foreach file files [
		if not file = "http://www.aprelium.com" [
		; The free aprelium server puts that link on all pages
		; it serves.  I didn't want to spider all the contents of
		; their web page.
			print rejoin ["Getting: " file]
			new-page: rejoin [crfu "//" file]
			replace new-page "///" "/"
			if not exists? to-file file [
				either error? try [read/binary to-url new-page] [
					write/append %/c/errors.txt rejoin [
						"There was an error reading:  "	new-page
						newline]
				] [
				if error? try [
				write/binary to-file file read/binary to-url new-page
				][
					write/append %/c/errors.txt rejoin [
					"error writing: " crfu newline]]
				]
			]
		]
	]

I wanted to complete step 3, but realized that that's where the recursion pattern needed to occur - for each folder I copied, I wanted to look inside that folder and create any folders it contained, and then inside those folders, etc.  So next, I defined a recursion pattern to change into the current local and remote folders, and to run the function in which all of steps 2-4 were contained.  I decided to label the entire enclosing function "copy-current-dir" - it would be passed the parameters "lrf", "clf", and "crfu".  That function contains the recurse function, which calls the encompassing copy-current-dir function, which itself contains the recurse function, etc.  The effect of this recursion is that every subfolder of every folder is entered.  Here's the recurse function:

	recurse: func [folder-name] [
		change-dir to-file folder-name
		crfu: rejoin [crfu folder-name]
		clf: rejoin [clf folder-name]
		; NOW HERE'S THE RECURSION - call the function in which
		; this function is contained:
		copy-current-dir crfu clf lrf
		;  When done, go back up a folder on both the local and
		;  remote machines.  The replace actions remove the current
		;  folder text from the end of the current folder strings.
		change-dir %..
		replace clf folder-name ""
		replace crfu folder-name ""
	]

Finally, I completed steps 3 and 4 by creating local folders to mirror each directory in the current remote folder, and then called the recurse function to spider down through them.  I used a foreach loop to work through each directory in the current subdirectory list.  Because this loop contains the recurse function, which in turn runs the copy-current-dir, which in turn contains this loop, every subdirectory of every subdirectory is worked through, until the job is complete:

	foreach folder-name folders [
		make-dir to-file folder-name
		recurse folder-name
	]

I wrapped the parsing, looping/reading, and recursing sections into the copy-current-dir function so that they could be called recursively.  Then I added some error handling routines as I played with the working code.  I included a block of urls to be avoided, and some code in the final foreach loop to check that those urls weren't already downloaded (in case I had previously run the program on the same directory).  Here's the final script:

	Rebol [title: "Directory Downloader"]

	avoid-urls: [
		"/4/DownLoad/en_wikibooks_org/skins-1_5/common/&"
		"DownLoad/groups_yahoo_com/group/Join%20This%20Group!/"
		"DownLoad/pythonide_stani_be/ads/"
		"Nick%20Antonaccio/Desktop/programming/api/ewe/"
	]

	copy-current-dir: func [
	{
		Download the files from the current remote directory
		to the current local directory and create local subfolders
		for each remote subfolder.  Then recursively do the same
		thing inside each sub-folder.
	} 
		crfu  ; current-remote-folder-url
		clf   ; current-local-folder
		lrf   ; local-root-folder
	] [
		; Check that the url about to be parsed is not in the avoid
		; list above.  This provides a way to skip specified folders
		; if needed:

		foreach avoid-url avoid-urls [
			if find crfu avoid-url [return "avoid"]
		]

		; First, parse the remote folder for file and folder names.
		; Given the url of a remote page, create 2 list variables.
		; files:  remote files to download (in current directory)
		; folders:  remote sub-directories to recurse through.
		; There's an error check in case the page can't be read:

		if error? try [page-data: read crfu] [
			write/append %/c/errors.txt rejoin [
				"error reading (target read error): " 
				crfu newline]
			return "index.html"
		]

		; if the web server finds an index.html file in the folder
		; it will serve its contents, rather than displaying the 
		; directory structure.  Then it'll try to spider the html
		; page.  The following will keep that error from occuring.
		; NOTE:  this error was more effectively stopped by 
		; editing the index page names in the Abyss web server:
		if not find page-data {Powered by <b><i>Abyss Web Server} [
			; </i></b>
			write/append %/c/errors.txt rejoin [
				"error reading (.html read error): " 
				crfu newline]
			return "index.html"
		]
		files: copy []
		folders: copy []
		parse page-data [
			any [
				thru {href="} copy temp to {"} (
					last-char: to-string last to-string temp
					either last-char = "/" [
					; don't go upwards through the folder structure:
						if not temp = "../" [
							append folders temp
						]
					][
						append files temp
					]
				)
			] to end
		]

		; Next, download the files in the current remote folder
		; to the current local folder:

		foreach file files [
			if not file = "http://www.aprelium.com" [
				print rejoin ["Getting: " file]
				new-page: rejoin [crfu "//" file]
				replace new-page "///" "/"
				if not exists? to-file file [
					either error? try [read/binary to-url new-page][
						write/append %/c/errors.txt rejoin [
							"There was an error reading:  "	new-page
							newline]
					] [
					if error? try [
			write/binary to-file file read/binary to-url new-page
					][
						write/append %/c/errors.txt rejoin [
						"error writing: " 
						crfu newline]]
					]
				]
			]
		]

		; Check to see if there are no more subfolders.  If so,
		; exit the copy-current-dir function

		if folders = [] [return none]

		; Define the recursion pattern.  This changes into the 
		; current local folder, and runs the copy-current-dir 
		; function (the current function we are in), which itself
		; contains the recurse function, which itself will call
		; the copy-current-dir, etc.  The effect of this recursion
		; is that every subfolder of every folder is entered.  
		; This is what enables the spidering:

		recurse: func [folder-name] [
			change-dir to-file folder-name
			crfu: rejoin [crfu
				folder-name]
			clf: rejoin [clf
				folder-name]
			copy-current-dir crfu clf lrf
			;  When done, go back up a folder on both the local
			;  and remote machines.  The replace actions remove
			;  the current folder text from the end of the current
			;  folder strings.
			change-dir %..
			replace clf folder-name ""
			replace crfu folder-name ""
		]

		; Third, create local folders to mirror each directory in
		; the current remote folder, and then spider down through
		; them using the recurse function to download all the files
		; and subdirectories included in each folder:

		foreach folder-name folders [
		;	foreach avoid-url avoid-urls [
		;		if not find folder-name avoid-url [
					make-dir to-file folder-name
					recurse folder-name
		;		]
		;	]
		]
	]

	; Now, get initial remote url and create a local folder to
	; mirror it, with a nicely formed name (only allowable Windows
	; file name characters).

		initial-pageurl: to-url request-text/default trim {
			http://192.168.1.4:8001/4/}
		initial-local-dir: copy initial-pageurl
		replace initial-local-dir "http://" ""
		replace/all initial-local-dir "/" "_"
		replace/all initial-local-dir "\" "__"
		replace/all initial-local-dir ":" "--"
		lrf: to-file rejoin [initial-local-dir "/"]
		if not exists? lrf [make-dir lrf]
		change-dir lrf
		clf: lrf

	; Start the process by running the copy-current-dir function:

	copy-current-dir initial-pageurl clf lrf

	print "DONE" halt


---Case 3 - Creating a Simple Calculator Application

GUI calculator examples are cliche among computer programming tutorials, so I decided to include a quick case study about how I built a small calculator application in REBOL.  Compare this example to those created in other programming languages, and you'll get a sense of just how much simpler it is to write REBOL code.

Since this program will be primarily an exercise in simple GUI layout, I started with a pseudo-code outline of how I wanted the program to look when complete:

# There needed to be a display area to show numerical digits as they were input, as well as the results of calculations.  A simple GUI text field will work fine for that display.

# There needed to be GUI buttons to enter numerical digits and a decimal point, as well as buttons for mathematical operators, and a button to execute calculations (an "=" sign).  Each of those three categories of buttons would do generally the same types of actions, so I'd create them as separate GUI styles, each with shared action blocks.  

That was enough of an outline to begin writing some actual REBOL GUI code.  I toyed with various window, button, and font sizes/colors until the layout looked acceptable.  Here's what I came up with using the pseudo-code above:

	view center-face layout/tight [
	    size 300x350 space 0x0 across ; basic window sizing/spacing
	    display: field 300x50 font-size 28 "0" return ; the display
	    style butn button 100x50 [
	        ; add the action code here for number buttons
        ]
	    style eval button 100x50 brown font-size 13 [
	        ; add the action code here for operator buttons
        ]
	    butn "1"  butn "2"  butn "3"  return   ; put those buttons
	    butn "4"  butn "5"  butn "6"  return   ; into the window
	    butn "7"  butn "8"  butn "9"  return 
	    butn "0"  butn "."  eval "+" return
	    eval "-" eval "*" eval "/" return
	    button 300x50 gray font-size 16 "=" [
	        ; add the action code here for "=" sign button
        ]
	]

To turn the above display into a functioning calculator, next I needed to think about what must happen when the number buttons are clicked.  Here's some pseudo-code to outline that thought process:

# The user must be able to enter numbers that are longer than a single digit, so every time a number button is clicked, that numerical digit should be appended to the digits in the display.  I'll use "rejoin" to build the display number, and then I'll set a variable to store that number, each time a new digit is clicked.

# In the GUI code above, I started with a "0" in the display field.  That'll need to be erased before any other numbers are displayed.

That's all easy enough to do in REBOL code:

    if display/text = "0" [display/text: ""]  ; erase the displayed "0"
    display/text: rejoin [display/text value]  ; build the displayed #
    show display
    cur-val: display/text  ; use a variable to save the displayed #

Now I need to think about what should happen when the operator buttons are clicked:

# I need to assign a variable to save the number currently entered in the GUI display (that number is already saved temporarily in the "cur-val" variable above).

# Erase the display to prepare for a new number to be entered.

# Assign a variable to save the operator selected.

That's all very simple - in fact, it's simpler in real REBOL code than it is in pseudo-code:

    prev-val: cur-val  ; save the displayed # in a variable
    display/text: "" show display  ; erase the display
    cur-eval: value  ; save the selected operator in a variable

Finally, I need to think about what happens when the "=" button is clicked:

# A computation must be evaluated, using the first number entered (the "prev-val" variable above), the operator entered (the "cur-eval" variable), and the second number entered ("cur-val").

# The display area needs to be updated to show the value of that computation.

The easiest way I could think to build the computation was to use the "rejoin" function to build a string representing the first number entered, the operator entered, and the second number entered.  I could then evaluate that computation by simply using the "do" function on the built string:

    cur-val: do rejoin [prev-val " " cur-eval " " cur-val]
    display/text: cur-val
    show display

That was all very easy.  Here's the code we've got so far:

	view center-face layout/tight [
	    size 300x350 space 0x0 across
	    display: field 300x50 font-size 28 "0" return
	    style butn button 100x50 [
	        if display/text = "0" [display/text: ""]  ; erase the "0"
            display/text: rejoin [display/text value]  ; build the #
            show display
            cur-val: display/text  ; use a variable to save the displayed #
        ]
	    style eval button 100x50 brown font-size 13 [
	        prev-val: cur-val
            display/text: "" show display
            cur-eval: value
        ]
	    butn "1"  butn "2"  butn "3"  return
	    butn "4"  butn "5"  butn "6"  return
	    butn "7"  butn "8"  butn "9"  return 
	    butn "0"  butn "."  eval "+" return
	    eval "-" eval "*" eval "/" return
	    button 300x50 gray font-size 16 "=" [
	        cur-val: do rejoin [prev-val " " cur-eval " " cur-val]
            display/text: cur-val
            show display
        ]
	]

After testing the code a bit, I found a bug.  Whenever the first computation is completed, any additional digits entered are appended to the total displayed from the first calculation.  That happens in this line of code in the number buttons definition (the "butn" style):

	display/text: rejoin [display/text value] 

That problem is easily solved by setting a flag variable when the "=" button is clicked:

    display-flag: true

. . .  and then checking for that flag every time a number button is clicked - if the flag is set (meaning that a total is being displayed), erase the display so that a new number can be entered, and reset the flag variable:

    if display-flag = true [display/text: "" display-flag: false]

That fixes the first bug.  Testing the program a little more, I found another small bug.  The calculator would crash with an error if the "=" sign or any of the operator buttons were clicked before numerical digits were properly entered.  That was easy to fix by simply setting some default variables in the beginning of the program - that's a fundamentally good practice in any sort of programming:

    prev-val: cur-val: 0 cur-eval: "+" display-flag: false

After using the program a bit more, I found one final bug.  If the equal sign was clicked repeatedly, it would perform calculations that weren't intended.  The following line was the culprit:

    cur-val: do rejoin [prev-val " " cur-eval " " cur-val]

The "cur-val" variable was updated every time the "=" button was clicked, whether or not a new number or operator was entered.  To squash that bug, I just used the "display-flag" variable that was created earlier to check if a total was being displayed.  I wrapped all of the action code performed when the "=" sign was clicked into an "if" conditional, and only performed those actions if the flag had been reset (only if a total was not being displayed):

	if display-flag <> true [ ... ]

Finally, the program appeared to be reasonably bug free, so I decided to add an additional feature that seemed useful while testing the code.  I wanted a running printout of all calculations performed, similar to paper tape on traditional printing calculators.  Adding that feature was as simple as could be.  At the beginning of the program I added a "print 0" line, and then added the following line to the "=" button:

	prin rejoin [prev-val " " cur-eval " " cur-val " = "]


Here's the final calculator program:


	REBOL [title: "calculator"]

	prev-val: cur-val: 0 cur-eval: "+" display-flag: falses
	print "0"
	view center-face layout/tight [
	    size 300x350 space 0x0 across
	    display: field 300x50 font-size 28 "0" return
	    style butn button 100x50  [
	        if display-flag = true [display/text: "" display-flag: false]
	        if display/text = "0" [display/text: ""]
	        display/text: rejoin [display/text value] 
	        show display
	        cur-val: display/text
	    ]
	    style eval button 100x50 brown font-size 13 [
	        prev-val: cur-val
	        display/text: "" show display
	        cur-eval: value
	    ]
	    butn "1"  butn "2"  butn "3"  return
	    butn "4"  butn "5"  butn "6"  return
	    butn "7"  butn "8"  butn "9"  return 
	    butn "0"  butn "."  eval "+" return
	    eval "-" eval "*" eval "/" return
	    button 300x50 gray font-size 16 "=" [
		    if display-flag <> true [ 
		        prin rejoin [prev-val " " cur-eval " " cur-val " = "]
		        print display/text: cur-val: do rejoin [
		            prev-val " " cur-eval " " cur-val
		        ]
		        show display
		        display-flag: true
		    ]
	    ]
	]

=image rebol_tutorial/calc.png


---Case 4 - Creating a Tetris Game Clone

One of my favorite games to play is Tetris.  I particularly like the "Rebtris" clone, written in Rebol by Frank Sievertsen.  While playing Rebtris recently, it struck me that writing a Tetris clone of my own would be a helpful exercise for this tutorial.  In conceiving how to make it a bit different from all the other endless variations of Tetris, I thought "why not try a text version?".  Creating it may be easier than a GUI version, and it would run on machines where GUI versions of Rebol aren't available.  Writing a text version of Tetris would also force me to organize a set of display techniques that could be useful in laying out other text-based applications.  Sounds like a fun project with some useful side effects.

NOTE:  I've never considered how to build a Tetris clone, and I'm writing this section as I design, experiment, and write code for the program.  So as you read this, you'll follow my exact train of thought in putting the program together, and I'll make no attempt to artificially clean up the process.  The point of this tutorial is to demonstrate exactly how to go about creating all types of programs on your own.  I hope that following my footsteps exactly - imperfections and all - should be a helpful experience.  Let's see what happens...

Instead of starting this entire thing from scratch, I remembered briefly skimming a tutorial about how to create a text positioning dialect called "TUI".  I found it again at <a href="http://www.rebolforces.com/articles/tui-dialect/" target=_blank>http://www.rebolforces.com/articles/tui-dialect/</a> and looked for some reusable code...

Here's the TUI dialect, created by Ingo Hohmann (I renamed his "cursor2" function to "tui"):

	tui: func [
		{Cursor positioning dialect (iho)}
		[catch]
		commands [block!]
		/local screen-size string arg cnt cmd c err
	][
		screen-size: (
			c: open/binary/no-wait [scheme: 'console]
			prin "^(1B)[7n"
			arg: next next to-string copy c
			close c
			arg: parse/all arg ";R"
			forall arg [change arg to-integer first arg]
			arg: to-pair head arg
		)
	    string: copy ""
	    cmd: func [s][join "^(1B)[" s]
	    if error? set/any 'err try [
			commands: compose bind commands 'screen-size ][
	        throw err
	    ]
	    arg: parse commands [
	        any [
	            'direct set arg string! (append string arg) |
	            'home  (append string cmd "H") |
	            'kill  (append string cmd "K") |
	            'clear (append string cmd "J") |
	            'up    set arg integer! (append string cmd [
					arg "A"]) |
	            'down  set arg integer! (append string cmd [
					arg "B"]) |
	            'right set arg integer! (append string cmd [
					arg "C"]) |
	            'left  set arg integer! (append string cmd [
					arg "D"]) |
	            'at   set arg pair! (append string cmd [
					arg/x ";" arg/y "H" ]) |
	            'del   set arg integer! (append string cmd [
					arg "P"]) |
	            'space set arg integer! (append string cmd [
					arg "@"]) |
	            'move  set arg pair! (append string cmd [
					arg/x ";" arg/y "H" ]) |
	            set cnt integer! set arg string! (
	                append string head insert/dup copy "" arg cnt
	            ) |
	            set arg string! (append string arg)
	        ]
	        end
	    ]
	    if not arg [throw make error! "Unable to parse block"]
	    string
	]

I read the tutorial and played with the code a bit.  In addition to being a great tutorial, the end product is a useful tool for formatting output in console applications.  The function "tui" gets passed a block of parameters including text to be printed, directional keywords to move the cursor around the screen ("home", "up", "down", "left", "right", and "at" a specific location) and several other commands to get the screen size, clear the screen, delete text, repeat text, and insert spaces.

I tried a few commands to get familiar with the syntax:

	prin tui [ clear ]
	print tui [ 50  "-" ]
	print tui [ right 10 down 7 50  "x" ]
	prin tui [ clear right 10 down 10 50  "x" ]
 	print tui [ clear home "message1"]
	print tui [ home space 20 "message2"]
	print tui [ at 20x20 "message3" kill "message4"]
	print tui [ at 20x20  del 10]
	print tui [ move 10x10]
	prin tui [ clear (screen-size/y * screen-size/x - 4)  "x" ]

=image rebol_tutorial/tui1.png
=image rebol_tutorial/tui2.png
=image rebol_tutorial/tui3.png
=image rebol_tutorial/tui4.png

I had more fun playing with the TUI dialect than I did playing Tetris :)  Basically, TUI wraps up some of the native print control codes built into Rebol, in a nice clean format that eliminates all the odd characters used in native codes.  It contains everything required to move game pieces around the screen, so I'll start to come up with some requirements to build the game.  Here's an outline that covers the main design goals I'm conceiving at this point:

# Draw a static playing field (the unchanging graphic backdrop design that's on screen the whole time the game is being played).  This will represent the left, right, and lower vertical bounds which the game coordinates may not exceed.

# There are 7 block shapes used in the game.  Create text versions of each graphic shape, in each of the 4 possible rotated positions.  Come up with code to print and delete each of the graphic shapes.  The TUI dialect will let me print and delete characters anywhere on the screen.  I'll use directional statements to print the required characters, starting from any given coordinate.  Put all these shape routines into a block for easy naming and reuse.

# Write a continuous loop to put one shape on the screen, make it fall at a given speed, and allow the user to spin it around and move it left-right.  

# If a shape touches the bottom of the playing field, make it lock into the grid of other shapes that have already fallen.  If the bottom row is complete, remove it, and make all the rows above it fall down a row to take its place.  If the shape touches the ceiling, end the game.

The first part of the outline is easy.  I'll use the "print a-line" code created in the "looping through data" example earlier in this tutorial.  Here's a simple little backdrop that's printed to the screen:

	a-line: copy [] loop 28 [append a-line " "] 
	a-line: rejoin ["   |"  to-string a-line "|"]
	loop 30 [print a-line] prin "   " loop 30 [prin "+"] print ""

=image rebol_tutorial/textris2.png

For the second part, I need to create some code to print the 7 block shapes.  They look like this:

	;	1 	####	2	###		3	###		4	###
	;					 #			#			  #
	;
	;	5	##		6	 ##		7	##
	;		 ##			##			##

Here are all the possible variations when the above shapes are rotated clockwise:

 	;					#
 	; 	1 	####	2	#
	;					#
	;					#
	;
	;	3	###		4	 #		5	 #		6	#
	;		 #		    ##			###			##
	;					 #						#
	;
	;	7	###		8 	##		9	  #		10	#
	;		#			 #			###			#
	;					 #						##
	;
	;	11	###		12	#		13	#		14	##
    ;	      #			#			###			#
	;				   ##						#
	;
	;	15	##		16	 #
	;		 ##			##
	;					#
	;
	;	17	 ##		18	#
	;		##			##
	;					 #
	;
	;	19	##
	;		##

To print any piece, I can start at the top left coordinate in the shape and move the appropriate number of spaces right, left, and/or down to print the other characters in each piece.  Starting at the first character in shape 2, for example, I would move as follows:  "#", down 1 left 1, "#", down 1 left 1, "#", down 1 left 1, "#".  Shape 3 would move as follows:  "###", down 1 left 2, "#".  Here's a block called "shape", made up of individual blocks that can be passed to tui to print all the above shapes:

	shape: [
		["####"]
		["#" down 1 left 1 "#" down 1 left 1 "#" down 1 left 1 "#"]
		["###" down 1 left 2 "#"]
		[right 1 "#" down 1 left 2 "##" down 1 left 1 "#"]
		[right 1 "#" down 1 left 2 "###"]
		["#" down 1 left 1 "##" down 1 left 2 "#"]
		["###" down 1 left 3 "#"]
		["##" down 1 left 1 "#" down 1 left 1 "#"]
		[right 2 "#" down 1 left 3 "###"]
		["#" down 1 left 1 "#" down 1 left 1 "##"]
		["###" down 1 left 1 "#"]
		[right 1 "#" down 1 left 1 "#" down 1 left 2 "##"]
		["#" down 1 left 1 "###"]
		["##" down 1 left 2 "#" down 1 left 1 "#"]
		["##" down 1 left 1 "##"]
		[right 1 "#" down 1 left 2 "##" down 1 left 2 "#"]
		[right 1 "##" down 1 left 3 "##"]
		["#" down 1 left 1 "##" down 1 left 1 "#"]
		["##" down 1 left 2 "##"]
	]

Now I can use the format "prin tui shape/number" to print any shape.  For example:

	prin tui shape/3

is the same as writing: 

	prin tui [right 1 "#" down 1 left 2 "##" down 1 left 1 "#"]

I came up with the following code to print out each shape, to check for errors, and to get used to using the above format.  Notice the use of the "compose" function: 

	for i 1 19 1 [
		print tui [clear] 
		print rejoin ["shape " i ":"]
		do compose [print tui shape/(i)]
		ask ""
	]

=image rebol_tutorial/textris3.png
=image rebol_tutorial/textris3b.png
=image rebol_tutorial/textris3c.png

To erase the shapes, I decided to extend the block using duplicates of each shape to print spaces instead of "#"s.  Now all I have to do is add 19 to any shape's index number, and I can print out a shape made of spaces that erases the original shape made of "#"s.  Here's the final shape block:

	shape: [
		["####"]
		["#" down 1 left 1 "#" down 1 left 1 "#" down 1 left 1 "#"]
		["###" down 1 left 2 "#"]
		[right 1 "#" down 1 left 2 "##" down 1 left 1 "#"]
		[right 1 "#" down 1 left 2 "###"]
		["#" down 1 left 1 "##" down 1 left 2 "#"]
		["###" down 1 left 3 "#"]
		["##" down 1 left 1 "#" down 1 left 1 "#"]
		[right 2 "#" down 1 left 3 "###"]
		["#" down 1 left 1 "#" down 1 left 1 "##"]
		["###" down 1 left 1 "#"]
		[right 1 "#" down 1 left 1 "#" down 1 left 2 "##"]
		["#" down 1 left 1 "###"]
		["##" down 1 left 2 "#" down 1 left 1 "#"]
		["##" down 1 left 1 "##"]
		[right 1 "#" down 1 left 2 "##" down 1 left 2 "#"]
		[right 1 "##" down 1 left 3 "##"]
		["#" down 1 left 1 "##" down 1 left 1 "#"]
		["##" down 1 left 2 "##"]

		; Here are the same shapes, with spaces instead of "#"s:

		["    "]
		[" " down 1 left 1 " " down 1 left 1 " " down 1 left 1 " "]
		["   " down 1 left 2 " "]
		[right 1 " " down 1 left 2 "  " down 1 left 1 " "]
		[right 1 " " down 1 left 2 "   "]
		[" " down 1 left 1 "  " down 1 left 2 " "]
		["   " down 1 left 3 " "]
		["  " down 1 left 1 " " down 1 left 1 " "]
		[right 2 " " down 1 left 3 "   "]
		[" " down 1 left 1 " " down 1 left 1 "  "]
		["   " down 1 left 1 " "]
		[right 1 " " down 1 left 1 " " down 1 left 2 "  "]
		[" " down 1 left 1 "   "]
		["  " down 1 left 2 " " down 1 left 1 " "]
		["  " down 1 left 1 "  "]
		[right 1 " " down 1 left 2 "  " down 1 left 2 " "]
		[right 1 "  " down 1 left 3 "  "]
		[" " down 1 left 1 "  " down 1 left 1 " "]
		["  " down 1 left 2 "  "]
	]

I wrote another quick script to test it.  Notice the "i + 19" used to erase the exiting shape:

	for i 1 19 1 [
		print tui [clear] 
		print rejoin ["shape " i ":"]
		do compose [prin tui [move 10x10] print tui shape/(i)]
		ask ""
		do compose [prin tui [move 10x10] print tui shape/(i + 19)]
		print rejoin ["shape " i " has been erased."]
		ask ""
	]

=image rebol_tutorial/textris4.png

Beautiful.  Steps 1 and 2 are complete.  Now I can work on the last part of the outline (the things related to how the game actually plays, moving pieces and responding to user input).  First, I'll get the shapes to fall down the screen.  That'll be done by printing, erasing and then redrawing the piece one row lower, in a continuous loop.  Here's an outline to organize that thought process:

# Start by clearing the screen.

# Pieces appear in a random order, so come up with a random number to represent some random shape's index number.

# Use a for loop to increment the vertical position of the piece:  for each row, print the random piece number at the current horizontal position (initially set to 15), and at the vertical position represented by the current "for" variable.

# Wait a moment, then erase the piece (using the shape number + 19).  Then increment the row number and start again.

# When the piece reaches the last row, print it there without erasing.

# Wrap that whole thing in a forever loop to keep it going indefinitely.

Let's get that much going:

	prin tui [clear]

	forever [
		random/seed now
		r: random 19  	; the number of a random shape
		xpos: 18 		; the initial horizontal position
		for i 1 25 1 [
			pos: to-pair rejoin [i "x" xpos]
			; print the shape represented by "r" at the "pos"
			; coordinate:
			do compose/deep [prin tui [at (pos)] print tui shape/(r)]
			; The wait time could be a user controlled variable, or
			; it could be sped up as the difficulty level increases:
			wait :00:00.30
			; erase the shape, then continue the loop:
			do compose/deep [
				prin tui [at (pos)] print tui shape/(r + 19)]
		]
		; reprint the shape at its final resting place:
		do compose/deep [prin tui [move (pos)] print tui shape/(r)]
	]

=image rebol_tutorial/textris5.png
=image rebol_tutorial/textris5b.png
=image rebol_tutorial/textris5c.png

NOTE:  It struck me in writing the above code that the TUI function actually takes all its coordinates in an unusual order.  Typically, in coordinates with the form XxY, "X" is the horizontal position and "Y" is the vertical position.  TUI uses the format YxX, where Y is the vertical position measured in rows from the top of the screen.  X is the horizontal position, measured in columns from the left side of the screen.  Keep in mind that the order of X and Y coordinates is opposite the normal expectation.

Now I need to come up with a way for the user to control the horizontal position of the shape.  Here's some pseudo code to help me think about how to do that:

# Be on the lookout for keystroke input from the user.

# If the user presses the "l" key, add 1 to the current horizontal position of the shape (held in the variable "xpos").  If the user presses the "k" key, subtract 1 from xpos.

First, I need a way to get keystroke input without blocking the program flow (i.e., I need to wait for keystroke input to be acknowledged when it occurs, but I can't just stop the normal program flow to wait for key presses.  For game play to continue, the "for" and "forever" loops can't be interrupted.  So I searched Google for "rebol key stroke" and got pointed to the following code at http://www.rebol.org/cgi-bin/cgiwrap/rebol/ml-display-thread.r?m=rmlSCRQ (in the Rebol mailing list archive):

	c: open/binary/no-wait [scheme: 'console]
	; set following to whatever you wish
	; intentionally slow at 2 secs so you can "see" the effect
	wait-duration: :0:2
	d: 0
	forever [
	    if not none? wait/all [c wait-duration] [
	        print to-char to-integer copy c
	    ]
	    d: d + 1 ;let's do other stuff
	    print d
	] 

=image rebol_tutorial/textris6.png

That little bit of code does exactly what I need.  The parts required for my needs are:

	c: open/binary/no-wait [scheme: 'console]
	forever [
	    if not none? wait/all [c wait-duration] [
	        print to-char to-integer copy c
	    ]
	]

I adjusted the variable names, checked for "k" or "l" key presses, and used the code below to test that it worked the way I wanted:

	keys: open/binary/no-wait [scheme: 'console]
	forever [
	    if not none? wait/all [keys :00:00.01] [
			switch to-string to-char to-integer copy keys [
				"k" [print "you pressed k"]
				"l" [print "you pressed l"]
			]
	    ]
	; print "nothing pressed" ; make sure it's working
	]

=image rebol_tutorial/textris7.png

Next, I integrated the above code into the loop created earlier to drop the shape down the screen.  Notice that I added a conditional "if", to be executed when either "k" or "l" keystrokes are encountered.  It checks that the horizontal bounds don't go outside the 5-30 positions.  That keeps the shapes within the horizontal boundaries of the playing field.  Also, notice that the variable "old-xpos" is used to hold the position of the shape that needs to be erased:

	keys: open/binary/no-wait [scheme: 'console]
	forever [
		random/seed now
		r: random 19
		xpos: 18
		for i 1 25 1 [
			pos: to-pair rejoin [i "x" xpos]
			do compose/deep [prin tui [at (pos)] print tui shape/(r)]
			old-xpos: xpos 
		    if not none? wait/all [keys :00:00.30] [
				switch to-string to-char to-integer copy keys [
					"k" [if (xpos > 5) [xpos: xpos - 1]]
					"l" [if (xpos < 30) [xpos: xpos + 1]]
				]
		    ]
			pos: to-pair rejoin [i "x" old-xpos]
			do compose/deep [
				prin tui [at (pos)] print tui shape/(r + 19)]
		]
		do compose/deep [prin tui [move (pos)] print tui shape/(r)]
	]

=image rebol_tutorial/textris8.png
=image rebol_tutorial/textris8b.png

It's coming along well :)  Now I need to be able to spin the shapes around.  Here's some pseudo code to organize my thoughts:

# Watch for the "O" key to be pressed.  That will be the keycode to run the shape spinning code.

# Create a set of conditionals to cycle through the list of rotated shapes related to the current shape.  For example, if the current shape (variable "r") is number 12, then the rotated versions of that shape are numbers 11-14.  With each press of the "O" key, replace the variable r with the next shape in that list.  That logic must "wrap around" (i.e., the next shape after 14 should be 11).  Instead of using a block list of shapes to do this, I decide to use a switch structure to individually map each shape to the one it should rotate to (something like "if shape r is now #14, turn shape r into #11" - do that explicitly for each shape).

I already have some code to watch for keystrokes, so I'll try the last part of the above outline first:

	switch to-string r [
		"1" [r: 2]
		"2" [r: 1]
		"3" [r: 4]
		"4" [r: 5]
		"5" [r: 6]
		"6" [r: 3]
		"7" [r: 8]
		"8" [r: 9]
		"9" [r: 10]
		"10" [r: 7]
		"11" [r: 12]
		"12" [r: 13]
		"13" [r: 14]
		"14" [r: 11]
		"15" [r: 16]
		"16" [r: 15]
		"17" [r: 18]
		"18" [r: 17]
		"19" [r: 19]
	]

Wait a sec - that makes the shapes rotate clockwise (from #11 go to #12, #14 to #11, etc.) I prefer for them to rotate counterclockwise (#11 to #14, #14 to #13, etc).  Here's the revised code:

	switch to-string r [
		"1" [r: 2]
		"2" [r: 1]
		"3" [r: 6]
		"4" [r: 3]
		"5" [r: 4]
		"6" [r: 5]
		"7" [r: 10]
		"8" [r: 7]
		"9" [r: 8]
		"10" [r: 9]
		"11" [r: 14]
		"12" [r: 11]
		"13" [r: 12]
		"14" [r: 13]
		"15" [r: 16]
		"16" [r: 15]
		"17" [r: 18]
		"18" [r: 17]
		"19" [r: 19]
	]

Now add the letter "O" to the list of keys to be watched, and run the above code when it's pressed.  Also create an "old-r" variable to retain the number of the shape that needs to be erased.  (Since the user changes shapes after the current one has been printed, we need to keep track of which one to erase):

	keys: open/binary/no-wait [scheme: 'console]
	forever [
		random/seed now
		r: random 19
		xpos: 18
		for i 1 25 1 [
			pos: to-pair rejoin [i "x" xpos]
			do compose/deep [prin tui [at (pos)] print tui shape/(r)]
			old-xpos: xpos 
			old-r: r
		    if not none? wait/all [keys :00:00.30] [
				keystroke: to-string to-char to-integer copy keys
				switch keystroke [
					"k" [if (xpos > 5) [xpos: xpos - 1]]
					"l" [if (xpos < 30) [xpos: xpos + 1]]
					"o" [switch to-string r [
						"1" [r: 2]
						"2" [r: 1]
						"3" [r: 6]
						"4" [r: 3]
						"5" [r: 4]
						"6" [r: 5]
						"7" [r: 10]
						"8" [r: 7]
						"9" [r: 8]
						"10" [r: 9]
						"11" [r: 14]
						"12" [r: 11]
						"13" [r: 12]
						"14" [r: 13]
						"15" [r: 16]
						"16" [r: 15]
						"17" [r: 18]
						"18" [r: 17]
						"19" [r: 19]
					]]					
				]
		    ]
			do compose/deep [
				prin tui [at (pos)] print tui shape/(old-r + 19)
			]
		]
		do compose/deep [prin tui [at (pos)] print tui shape/(r)]
	]

=image rebol_tutorial/textris9.png
=image rebol_tutorial/textris9b.png

The shapes are moving correctly now, but there's still a lot of work to be done.  The first line of the last section of the overall game outline reads:  "If the shape touches the bottom of the playing field, make it lock into the grid of other shapes that have already fallen".  Right now the pieces all just fall to different stopping points in the playing field (depending on their height), and they don't stack on top of each other.  Here's some pseudo code to fix that:

# I need to be aware of the highest coordinate in each column on the playing field.  When the game starts, the highest coordinate in every column of the playing field is row 30 (the flat bottom line that makes up the playing field).  I'll store each of these coordinates in a block called "floor".  

# I also need to be aware of the lowest coordinate in each column of the currently falling shape.  I'll make a block called "edge" to hold those coordinates (referring to the lower edges of the shape).  Those coordinates will define the position of each of the lowest points in the currently falling shape, in relation to its top left point (the "pos" coordinate).  

# Every time the shape falls one position down the screen, add each of the edge coordinates to the pos coordinate.  If any of those coordinates is one position higher than the floor coordinate in the same column, then stop moving that shape (break out of the "for" loop that makes the shape fall).  Use a foreach loop to cycle through the current coordinates in the relevant columns of each block, performing a comparison check on the floor and edge coordinates in each column.

# When a shape finishes its drop down the screen, calculate the new highest position in the columns it occupies (the coordinates of the top character in each column), and make those changes to the block that holds the high point information.  To do that, I'll need to make a "top" block to hold the relative positions of the highest coordinates in the shape, and add them to the height of the current coordinates in the appropriate columns.

I'll start out simply, just getting each shape to lay flat on the floor of the playing field (row 30).  For the moment, all I need to do is create a block of floor coordinates that represents that bottom line:

	floor: 	[30x1 30x2 30x3 30x4 30x5 30x6 30x7 30x8 30x9 30x10 30x11
		30x12 30x13 30x14 30x15 30x16 30x17 30x18 30x19 30x20 30x21
		30x22 30x23 30x24 30x25 30x26 30x27 30x28 30x29 30x30 30x31
		30x32 30x33 30x34 30x35]

Next, I'll define a set of lower coordinates for each shape, and store them in a nested block structure similar to the earlier "shape" block.  "0x0" refers to the same coordinate as "pos" (0 positions to the right, and 0 positions down from "pos").  "0x10" is one position to the right, and "1x0" is one position down.  I look at the visual representations of the shapes again to come up with the list:

 	;					#
 	; 	1 	####	2	#
	;					#
	;					#
	;
	;	3	###		4	 #		5	 #		6	#
	;		 #		    ##			###			##
	;					 #						#
	;
	;	7	###		8 	##		9	  #		10	#
	;		#			 #			###			#
	;					 #						##
	;
	;	11	###		12	#		13	#		14	##
    ;	      #			#			###			#
	;				   ##						#
	;
	;	15	##		16	 #
	;		 ##			##
	;					#
	;
	;	17	 ##		18	#
	;		##			##
	;					 #
	;
	;	19	##
	;		##

Here's the complete set of low point definitions for each shape:

	edge: [ [0x0 0x1 0x2 0x3] [3x0] [0x0 1x1 0x2] [1x0 2x1] 
		[1x0 1x1 1x2] [2x0 1x1] [1x0 0x1 0x2] [0x0 2x1] [1x0 1x1 1x2]
		[2x0 2x1] [0x0 0x1 1x2] [2x0 2x1] [1x0 1x1 1x2] [2x0 0x1]
		[0x0 1x1 1x2] [2x0 1x1] [1x0 1x1 0x2] [1x0 2x1] [1x0 1x1] ]
	
So, the relative coordinates of the low points in shape 3, for example, are referred to as edge/3.  Here's some sample code to demonstrate how I can now refer to the bottom points in any shape using a foreach loop.  The code "pos + position" refers to the low edge in each column:

	pos: 5x5
	r: 6
	foreach position compose edge/(r) [print pos + position]

To check if any of those edges are touching the floor, use a foreach loop to cycle through the current coordinates in the relevant columns of each block, performing a comparison check on the floor and edge coordinates in each column.  Here's some sample code to flesh out and test that idea:

	pos: 30x10
	for r 1 19 1 [
		print tui [clear]
		prin "Piece: " print r
		foreach po compose edge/(r) [
			print pos + po
			foreach coord floor [
				floor-y: to-integer first coord
				floor-x: to-integer second coord
				edge-y: to-integer first pos + to-integer first po
				edge-x: to-integer second pos + to-integer second po
				print rejoin [
					"edge: " edge-y "x" edge-x " "
					"floor: "floor-y "x" floor-x 
				]
				if (edge-y >= floor-y) and (floor-x = edge-x) [
					print rejoin [ 
						"You're touching or beyond the floor at: "
						pos + po
					]
				]
			]
		]
		ask ""
	]

=image rebol_tutorial/textris10.png

Now let's integrate this technique into the existing code.  We'll use a new variable "stop" to break out of the loop that drops the shape, when the current shape touches the floor:

	keys: open/binary/no-wait [scheme: 'console]
	forever [
		random/seed now
		r: random 19
		xpos: 18
		for i 1 32 1 [
			pos: to-pair rejoin [i "x" xpos]
			do compose/deep [prin tui [at (pos)] print tui shape/(r)]
			old-r: r
			old-xpos: xpos 
		    if not none? wait/all [keys :00:00.30] [
				keystroke: to-string to-char to-integer copy keys
				switch keystroke [
					"k" [if (xpos > 5) [xpos: xpos - 1]]
					"l" [if (xpos < 30) [xpos: xpos + 1]]
					"o" [switch to-string r [
						"1" [r: 2]
						"2" [r: 1]
						"3" [r: 6]
						"4" [r: 3]
						"5" [r: 4]
						"6" [r: 5]
						"7" [r: 10]
						"8" [r: 7]
						"9" [r: 8]
						"10" [r: 9]
						"11" [r: 14]
						"12" [r: 11]
						"13" [r: 12]
						"14" [r: 13]
						"15" [r: 16]
						"16" [r: 15]
						"17" [r: 18]
						"18" [r: 17]
						"19" [r: 19]
					]]					
				]
		    ]
			do compose/deep [
				prin tui [at (pos)] print tui shape/(old-r + 19)
			]
			stop: false
			foreach po compose edge/(r) [
				foreach coord floor [
					floor-y: to-integer first coord
					floor-x: to-integer second coord
					edge-y:  i + to-integer first po
					edge-x:  xpos + to-integer second po
					if (edge-y >= floor-y) and (floor-x = edge-x) [
						stop: true
						break
					]
				]
			]
			if stop = true [break]
		]
		do compose/deep [prin tui [at (pos)] print tui shape/(old-r)]
	]

=image rebol_tutorial/textris11.png

This works, but there's a bug.  If the piece has been spun around (using the "O" key), the new foreach loop fails to stop the piece from falling.  That's because the foreach loop only cycles through the coordinates of the "edge/r" block.  If the user flips the shape around, the "r" value gets changed before this code is run.  The easiest way to fix this problem is to simply repeat the foreach loop using the "edge/old-r" block.  This is an inefficient quick hack, but I'm writing this late at night - and there's some value to pointing out bad coding practice - so I choose to use that solution.  I make a promise to myself to come up with a more elegant solution later...  (Note to self:  once a coding solution has been implemented, changes are harder to make, and bad code typically remains permanent ... I need to be careful about using quick hacks).  Here's the current code:

	keys: open/binary/no-wait [scheme: 'console]
	forever [
		random/seed now
		r: random 19
		xpos: 18
		for i 1 32 1 [
			pos: to-pair rejoin [i "x" xpos]
			do compose/deep [prin tui [at (pos)] print tui shape/(r)]
			old-r: r
			old-xpos: xpos 
		    if not none? wait/all [keys :00:00.30] [
				keystroke: to-string to-char to-integer copy keys
				switch keystroke [
					"k" [if (xpos > 5) [xpos: xpos - 1]]
					"l" [if (xpos < 30) [xpos: xpos + 1]]
					"o" [switch to-string r [
						"1" [r: 2]
						"2" [r: 1]
						"3" [r: 6]
						"4" [r: 3]
						"5" [r: 4]
						"6" [r: 5]
						"7" [r: 10]
						"8" [r: 7]
						"9" [r: 8]
						"10" [r: 9]
						"11" [r: 14]
						"12" [r: 11]
						"13" [r: 12]
						"14" [r: 13]
						"15" [r: 16]
						"16" [r: 15]
						"17" [r: 18]
						"18" [r: 17]
						"19" [r: 19]
					]]					
				]
		    ]
			do compose/deep [
				prin tui [at (pos)] print tui shape/(old-r + 19)
			]
			stop: false
			foreach po compose edge/(r) [
				foreach coord floor [
					floor-y: to-integer first coord
					floor-x: to-integer second coord
					edge-y:  i + to-integer first po
					edge-x:  xpos + to-integer second po
					if (edge-y = floor-y) and (floor-x = edge-x) [
						stop: true
						break
					]
				]
			]
			foreach po compose edge/(old-r) [
				foreach coord floor [
					floor-y: to-integer first coord
					floor-x: to-integer second coord
					edge-y:  i + to-integer first po
					edge-x:  old-xpos + to-integer second po
					if (edge-y = floor-y) and (floor-x = edge-x) [
						stop: true
						break
					]
				]
			]
			if stop = true [break]
		]
		do compose/deep [prin tui [at (pos)] print tui shape/(old-r)]
	]

=image rebol_tutorial/textris12.png

Next, I decide to test the existing program for other bugs.  I've been keeping separate text files containing all the code changes I make as I go along.  Every time I make, test, and change a chunk of code, I save the new trial version with a new filename and version number.  I save each version, just so that I don't permanently erase old code with each change - it may be potentially useful.  My current working version is now #19.

I noticed during this debugging session that shape 1 still breaks through the right side of the wall.  I could change that by adjusting the "(xpos < 30)" conditional expression that occurs when the "L" key gets pressed.  But that solution will keep the other shapes from laying snugly against the wall.  In fact, that additional problem is occurring now with shapes that are only 2 characters wide - I didn't notice until now.  To deal with these problems, I create a block of values called "width", listing the widths of all 19 shapes, which can be used in the existing conditional expression:

	width: [4 1 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 2]

Now I can check if the shape is at the right boundary, using the revised code below:

	[if (xpos < (33 - compose width/(r))) [
		xpos: xpos + 1]
	]

That check also needs to be performed every time the "O" key is pressed (we don't want the shape breaking out of the wall when it spins).  I make the above changes to my current version of the program, and the problems are fixed.

The game is really starting to take shape!  Now we need to make the shapes stack on top of each other.  Earlier, I wrote these outline thoughts:  "when a shape finishes its drop down the screen, calculate the new highest position in the columns it occupies (the coordinates of the top character in each column), and make those changes to the block that holds the high point information.  To do that, I'll need to make a "top" block to hold the relative positions of the highest coordinates in the shape, and add them to the height of the current coordinates in the appropriate columns".  Sounds like I'll need to loop through some columns to make the changes to the floor.

To create the "top" block I look at the visual representations of each shape once again, and come up with a coordinate list representing the high points in the shape, relative to the top left coordinate.  It's similar to the "edge" block:

	top: [ [0x0 0x1 0x2 0x3] [0x0] [0x0 0x1 0x2] [1x0 0x1] 
		[1x0 0x1 1x2] [0x0 1x1] [0x0 0x1 0x2] [0x0 0x1] [1x0 1x1 0x2]
		[0x0 2x1] [0x0 0x1 0x2] [2x0 0x1] [0x0 1x1 1x2] [0x0 0x1]
		[0x0 0x1 1x2] [1x0 0x1] [1x0 0x1 0x2] [0x0 1x1] [0x0 0x1] ]

The shape finishes its drop down the screen during the previous foreach loops we created, so to calculate the new highest positions in the columns occupied by the shape, I first need to determine which shape was the last one on the screen ("r" or "old-r").  The quick hack I made earlier is now coming back to bite me a bit - I now need to make duplicates of any changes that occur in both foreach loops:

	stop-shape-num: r  
	; (or stop-shape-num: old-r, depending on the foreach loop)
	stop: true
	break

Now to make the changes to the "floor" block, I loop through the columns occupied by the piece, setting each of the top characters in the shape to be the high coordinates in the respective columns of the floor.  The "poke" function lets me replace the original coordinates in the floor block with the new coordinates.  Those changes are made just before breaking out of the loop that drops the shape:

	if stop = true [
		; get the left-most column the last shape occupies:
		left-col: second pos 
		; get the number of columns the shape occupies:
		width-of-shape: length? compose top/(stop-shape-num)
		; get the right most column the shape occupies:
		right-col: left-col + width-of-shape - 1
		; Loop through each column occupied by the shape, 
		; replacing each coordinate in the current column
		; of the floor with the new high coordinate:
		counter: 1
		for current-column left-col right-col 1 [
			add-coord: compose top/(stop-shape-num)/(counter)
			new-floor-coord: (pos + add-coord + -1x0)
			poke floor current-column new-floor-coord
			counter: counter + 1
		]
		break
	]

The new stacking code works, but there's a design flaw.  If I maneuver a shape into an unoccupied space directly underneath any high point in the floor, without first touching the high point in that column, the piece doesn't stop.  Furthermore, if that happens, it changes the new high point to the bottom of the column which the current shape occupies.  I realize here that what I need to mark are not only the high points in the floor, but also every additional coordinate on the screen that contains a character.  This is just as easy to accomplish.  Instead of <i>changing</i> the current coordinates in the floor block (using the "poke" function):

	poke floor current-column new-floor-coord

just <i>add</i> the new coordinates to the list (using "append").  That will keep track of all points at which a character is printed on the screen:

	append floor new-floor-coord

That fixes the problem above, but I've also realized that if I move a shape sideways into an open position in the floor, the characters sometimes still overlap inappropriately.  That's because the "top" and "edge" blocks only mark the highest and lowest points in each shape.  It strikes me now that I could just combine those two blocks into one, marking all the coordinates occupied by a shape.  Here's the new block - I call it "oc", short for "occupied":

	oc:  [ 
		[0x0 0x1 0x2 0x3] [0x0 1x0 2x0 3x0] [0x0 0x1 0x2 1x1]
		[0x1 1x0 1x1 2x1] [0x1 1x0 1x1 1x2] [0x0 1x0 1x1 2x0]
		[0x0 0x1 0x2 1x0] [0x0 0x1 1x1 2x1] [0x2 1x0 1x1 1x2]
		[0x0 1x0 2x0 2x1] [0x0 0x1 0x2 1x2] [0x1 1x1 2x0 2x1]
		[0x0 1x0 1x1 1x2] [0x0 0x1 1x0 2x0]	[0x0 0x1 1x1 1x2]
		[0x1 1x0 1x1 2x0] [0x1 0x2 1x0 1x1] [0x0 1x0 1x1 2x1]
		[0x0 0x1 1x0 1x1] 
	]

I remove the "top" and "edge" blocks, and replace all code references to them with "oc".

Now there's another bug I need to fix.  Sometimes when I press a key, the following error occurs:

	** Script Error: Invalid argument: [45
	** Where: to-integer            |
	** Near: forall arg [change arg to-integer first arg]
	arg: to-pair 

The code referenced is not part of any code I've written.  It seems to be related to keystroke input because it only happens when I press one of the game control keys.  Since I'm not sure what's creating the error (maybe it's related to the timing of keystrokes, or perhaps it has to do with a key release), I make an educated guess and figure that the following line, which waits for keystrokes, is where it's occurring:

	if not none? wait/all [keys :00:00.30] [...]

I wrap that whole thing in an error check:

	if not error? try [if not none? wait/all [keys :00:00.30] [...]]

And, hmmm ... that doesn't work.  So instead of guessing, I work methodically to check each of the other main sections of the program.  Every section gets wrapped in an "error? try" routine, and I also put in an "if" conditional stucture to print out a numbered error message whenever an error occurs.  I find that the error is first occurring here:

	do compose/deep [prin tui [at (pos)] print tui shape/(r)]

Wrapped in the error test, that section looks like this:

	if error? try [
		do compose/deep [
			prin tui [at (pos)] print tui shape/(r)
		]
	] [print "er1"]

I'm curious about what's causing the error, so I dig a little deeper.  This time I have the error check print out the variables contained in the code:

	if error? try [
		do compose/deep [
			prin tui [at (pos)] print tui shape/(r)
		]
	] [print rejoin [pos " " r]]

Nothing seems to be amiss.  Every time the error occurs, the variables show a correct coordinate and shape number.  So, for now I'll simply leave the error check in place, removing the printout.  This will keep the game moving along whenever the ghostly error occurs.  I'll need to post a message to the Rebol mailing list to see if anyone knows why the error is occurring.  For the time being, the following error handler fixes the issue:

	if error? try [
		do compose/deep [
			prin tui [at (pos)] print tui shape/(r)
		]
	] []

It turns out that I need to do the same thing for all the other similar occurences of code that print a shape to the screen:

	if error? try [
		do compose/deep [
			prin tui [at (pos)] print tui shape/(old-r + 19)
		]
	] []

	if error? try [
		do compose/deep [
			prin tui [at (pos)] print tui shape/(old-r)
		]
	] []

With all the known bugs controlled, I can move on to implementing the last parts of the game design.  We need to check if the top row of the playing area is reached.  If any shape stops moving at this ceiling row, end the game.  This needs to be done any time a piece reaches it's final resting place, so I put it immediately after the main "for" loop in the program outline (so that it's evaluated immediately after the stopping code is executed):

	if (first pos) < 2 [
		prin tui [at 35x0]
		print "Game Over"
		halt
	]

Finally, to erase the bottom line of shapes every time a row is filled in horizontally, we're going to have to redraw the playing field entirely.  The "floor" block contains all the information needed to rebuild the current state of the playing field (all the positions at which a character is currently printed).  Here's an outline and some pseudo code to think through what needs to be done:

# Every time a shape stops moving, check to see if any row of the floor is full (i.e., there's one character printed in every column).  I can use a for loop and a find function to perform that check on the floor block.  (I'll start things off by just checking the bottom row).

# If any row is full (for now, just the bottom row), remove that row of characters from the floor block.  Use a remove-each loop to remove any coordinates that have y positions in the relevant row from the floor block. 

# Move all of the other characters above the relevant row down one row.  Add one y position to all the other coordinates in the floor block which are above the relevant row.  Use a foreach loop to go through each coordinate in the block and add 1x0.  To replace the old floor block with the new one, first create a temporary block made up of the new floor block coordinates, then copy it back to the floor block once it's complete.

# Erase the current screen, print the static background, and then reprint a new playing field using the refreshed block of floor coordinates.  We can accomplish this easily using a foreach loop and TUI to print the characters at each coordinate in the list.

	; #1:

	line-is-full: true
	for colmn 5 32 1 [
		each-coord: to-pair rejoin [29 "x" colmn]
		if not find floor each-coord [
			line-is-full: false
			break
		]
	]

	; #2:

	if line-is-full = true [
		remove-each cor floor [(first cor) = 29]

	; #3:

		new-floor: copy []
		foreach cords floor [
			append new-floor (cords + 1x0)
		]
		floor: copy new-floor

	; #4:

		prin tui [clear]
		a-line: copy [] loop 28 [append a-line " "] 
		a-line: rejoin ["   |"  to-string a-line "|"]
		loop 30 [print a-line] 
		prin "   " loop 30 [prin "+"] print ""
		foreach was-here floor [
			if not ((first was-here) = 30) [
				prin tui compose [at (was-here)]
				prin "#"
			]
		] 
	]

At this point, I realize that I've made some logic errors in how the floor block and the stopping routine are structured.  As it stands, when the screen is refreshed, the bottom row of the block (row 30) needs to be erased so that all the characters in row 29 can fall down one position.  But if row 30 is erased, then the bottom of the floor disappears.  As it turns out, row 31 should actually be treated as the bottom row, and all the characters should stop at 1x0 position higher then any character in the floor.

I make the required changes to the coordinates in the floor block (change all the y positions from 30 to 31).  I also change the "new-floor-coord" variable in the stopping routine, and adjust the code above so that characters below line 30 are not printed.  Additionally, the entire section above gets wrapped in a "for" loop to check if each row 1-30 is full.  In the code above, I only checked if the bottom line was full - the number 29 referred to the row.  I replace that number with the "row" variable created in the for loop.  And with that, the last requirements of my original game outline are satisfied and an initial version of "Textris" is in working order.  Here's the code:

	Rebol [Title: "Textris"]

	tui: func [
	    {Cursor positioning dialect (iho)}
	    [catch]
	    commands [block!]
	    /local screen-size string arg cnt cmd c err
	][
	    screen-size: (
	        c: open/binary/no-wait [scheme: 'console]
	        prin "^(1B)[7n"
	        arg: next next to-string copy c
	        close c
	        arg: parse/all arg ";R"
	        forall arg [change arg to-integer first arg]
	        arg: to-pair head arg
	    )
	    string: copy ""
	    cmd: func [s][join "^(1B)[" s]
	    if error? set/any 'err try [
	        commands: compose bind commands 'screen-size ][
	        throw err
	    ]
	    arg: parse commands [
	        any [
	            'direct set arg string! (append string arg) |
	            'home  (append string cmd "H") |
	            'kill  (append string cmd "K") |
	            'clear (append string cmd "J") |
	            'up    set arg integer! (append string cmd [
	                arg "A"]) |
	            'down  set arg integer! (append string cmd [
	                arg "B"]) |
	            'right set arg integer! (append string cmd [
	                arg "C"]) |
	            'left  set arg integer! (append string cmd [
	                arg "D"]) |
	            'at   set arg pair! (append string cmd [
	                arg/x ";" arg/y "H" ]) |
	            'del   set arg integer! (append string cmd [
	                arg "P"]) |
	            'space set arg integer! (append string cmd [
	                arg "@"]) |
	            'move  set arg pair! (append string cmd [
	                arg/x ";" arg/y "H" ]) |
	            set cnt integer! set arg string! (
	                append string head insert/dup copy "" arg cnt
	            ) |
	            set arg string! (append string arg)
	        ]
	        end
	    ]
	    if not arg [throw make error! "Unable to parse block"]
	    string
	]

	shape: [
	    ["####"]
	    ["#" down 1 left 1 "#" down 1 left 1 "#" down 1 left 1 "#"]
	    ["###" down 1 left 2 "#"]
	    [right 1 "#" down 1 left 2 "##" down 1 left 1 "#"]
	    [right 1 "#" down 1 left 2 "###"]
	    ["#" down 1 left 1 "##" down 1 left 2 "#"]
	    ["###" down 1 left 3 "#"]
	    ["##" down 1 left 1 "#" down 1 left 1 "#"]
	    [right 2 "#" down 1 left 3 "###"]
	    ["#" down 1 left 1 "#" down 1 left 1 "##"]
	    ["###" down 1 left 1 "#"]
	    [right 1 "#" down 1 left 1 "#" down 1 left 2 "##"]
	    ["#" down 1 left 1 "###"]
	    ["##" down 1 left 2 "#" down 1 left 1 "#"]
	    ["##" down 1 left 1 "##"]
	    [right 1 "#" down 1 left 2 "##" down 1 left 2 "#"]
	    [right 1 "##" down 1 left 3 "##"]
	    ["#" down 1 left 1 "##" down 1 left 1 "#"]
	    ["##" down 1 left 2 "##"]
	    ;
	    ["    "]
	    [" " down 1 left 1 " " down 1 left 1 " " down 1 left 1 " "]
	    ["   " down 1 left 2 " "]
	    [right 1 " " down 1 left 2 "  " down 1 left 1 " "]
	    [right 1 " " down 1 left 2 "   "]
	    [" " down 1 left 1 "  " down 1 left 2 " "]
	    ["   " down 1 left 3 " "]
	    ["  " down 1 left 1 " " down 1 left 1 " "]
	    [right 2 " " down 1 left 3 "   "]
	    [" " down 1 left 1 " " down 1 left 1 "  "]
	    ["   " down 1 left 1 " "]
	    [right 1 " " down 1 left 1 " " down 1 left 2 "  "]
	    [" " down 1 left 1 "   "]
	    ["  " down 1 left 2 " " down 1 left 1 " "]
	    ["  " down 1 left 1 "  "]
	    [right 1 " " down 1 left 2 "  " down 1 left 2 " "]
	    [right 1 "  " down 1 left 3 "  "]
	    [" " down 1 left 1 "  " down 1 left 1 " "]
	    ["  " down 1 left 2 "  "]
	]

	floor:  [
	    31x5 31x6 31x7 31x8 31x9 31x10 31x11 31x12 31x13 31x14 31x15
	    31x16 31x17 31x18 31x19 31x20 31x21 31x22 31x23 31x24 31x25
	    31x26 31x27 31x28 31x29 31x30 31x31 31x32
	]

	oc:  [ 
	    [0x0 0x1 0x2 0x3] [0x0 1x0 2x0 3x0] [0x0 0x1 0x2 1x1]
	    [0x1 1x0 1x1 2x1] [0x1 1x0 1x1 1x2] [0x0 1x0 1x1 2x0]
	    [0x0 0x1 0x2 1x0] [0x0 0x1 1x1 2x1] [0x2 1x0 1x1 1x2]
	    [0x0 1x0 2x0 2x1] [0x0 0x1 0x2 1x2] [0x1 1x1 2x0 2x1]
	    [0x0 1x0 1x1 1x2] [0x0 0x1 1x0 2x0] [0x0 0x1 1x1 1x2]
	    [0x1 1x0 1x1 2x0] [0x1 0x2 1x0 1x1] [0x0 1x0 1x1 2x1]
	    [0x0 0x1 1x0 1x1] 
	]

	width: [4 1 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 2]

	a-line: copy [] loop 28 [append a-line " "] 
	a-line: rejoin ["   |"  to-string a-line "|"]
	loop 30 [print a-line] prin "   " loop 30 [prin "+"] print ""

	keys: open/binary/no-wait [scheme: 'console]
	forever [
	    random/seed now
	    r: random 19
	    xpos: 18
	    for i 1 30 1 [
	        pos: to-pair rejoin [i "x" xpos]
	        if error? try [
	            do compose/deep [
	                prin tui [at (pos)] print tui shape/(r)
	            ]
	        ] []
	        old-r: r
	        old-xpos: xpos 
	        if not none? wait/all [keys :00:00.30] [
	            keystroke: to-string to-char to-integer copy keys
	            switch/default keystroke [
	                "k" [if (xpos > 5) [
	                        xpos: xpos - 1
	                    ]]
	                "l" [if (xpos < (33 - compose width/(r))) [
	                        xpos: xpos + 1
	                    ]]
	                "o" [if (xpos < (33 - compose width/(r)))  [
	                        switch to-string r [
	                            "1" [r: 2]
	                            "2" [r: 1]
	                            "3" [r: 6]
	                            "4" [r: 3]
	                            "5" [r: 4]
	                            "6" [r: 5]
	                            "7" [r: 10]
	                            "8" [r: 7]
	                            "9" [r: 8]
	                            "10" [r: 9]
	                            "11" [r: 14]
	                            "12" [r: 11]
	                            "13" [r: 12]
	                            "14" [r: 13]
	                            "15" [r: 16]
	                            "16" [r: 15]
	                            "17" [r: 18]
	                            "18" [r: 17]
	                            "19" [r: 19]
	                        ]
	                    ]
	                ]                   
	            ] []
	        ]
	        if error? try [
	            do compose/deep [
	                prin tui [at (pos)] print tui shape/(old-r + 19)
	            ]
	        ] []
	        stop: false
	        foreach po compose oc/(r) [
	            foreach coord floor [
	                floor-y: to-integer first coord
	                floor-x: to-integer second coord
	                oc-y:  i + to-integer first po
	                oc-x:  xpos + to-integer second po
	                if (oc-y = (floor-y - 1)) and (floor-x = oc-x) [
	                    stop-shape-num: r
	                    stop: true
	                    break
	                ]
	            ]
	        ]
	        foreach po compose oc/(old-r) [
	            foreach coord floor [
	                floor-y: to-integer first coord
	                floor-x: to-integer second coord
	                oc-y:  i + to-integer first po
	                oc-x:  old-xpos + to-integer second po
	                if (oc-y = (floor-y - 1)) and (floor-x = oc-x) [
	                    stop-shape-num: old-r
	                    stop: true
	                    break
	                ]
	            ]
	        ]
	        if stop = true [
	            left-col: second pos 
	            width-of-shape: length? compose oc/(stop-shape-num)
	            right-col: left-col + width-of-shape - 1
	            counter: 1
	            for current-column left-col right-col 1 [
	                add-coord: compose oc/(stop-shape-num)/(counter)
	                new-floor-coord: (pos + add-coord)
	                append floor new-floor-coord
	                counter: counter + 1
	            ]
	            break
	        ]
	    ]
	    if (first pos) < 2 [
	        prin tui [at 33x0]
	        print "GAME OVER!!!"
	        halt
	    ]
	    if error? try [
	        do compose/deep [
	            prin tui [at (pos)] print tui shape/(old-r)
	        ]
	    ] []
	    for row 1 30 1 [
	        line-is-full: true
	        for colmn 5 32 1 [
	            each-coord: to-pair rejoin [row "x" colmn]
	            if not find floor each-coord [
	                line-is-full: false
	                break
	            ]
	        ]
	        if line-is-full = true [
	            remove-each cor floor [(first cor) = row]
	            new-floor: copy [
	                31x5 31x6 31x7 31x8 31x9 31x10 31x11 31x12 31x13
	                31x14 31x15 31x16 31x17 31x18 31x19 31x20 31x21
	                31x22 31x23 31x24 31x25 31x26 31x27 31x28 31x29
	                31x30 31x31 31x32
	            ]
	            foreach cords floor [
	                either ((first cords) < row) [
	                    append new-floor (cords + 1x0)
	                ][
	                    append new-floor cords
	                ]
	            ]
	            floor: copy unique new-floor
	            prin tui [clear]
	            a-line: copy [] loop 28 [append a-line " "] 
	            a-line: rejoin ["   |"  to-string a-line "|"]
	            loop 30 [print a-line] 
	            prin "   " loop 30 [prin "+"] print ""
	            foreach was-here floor [
	                if not ((first was-here) = 31) [
	                    prin tui compose [at (was-here)]
	                    prin "#"
	                ]
	            ]
	        ]
	    ]
	]

=image rebol_tutorial/textris13b.png
=image rebol_tutorial/textris13c.png
=image rebol_tutorial/textris13d.png

Now that the program is working to my original specs, I want to make it look a bit spiffier.  First of all, the playing area looks too wide and tall.  I check Rebtris, and it's only 10 columns wide by 20 rows tall.  I like that look and feel, so I adjust the floor block, the code that draws the static backdrop, and all computations related to the right boundaries of the playing field and the number of rows, to reflect that change. 

I also want to print out a "Textris" title header, some keyboard instructions, and a score header.  Tui allows me to print this text to the right of the playing field where I want it:

	print tui [
		at 4x21 "TEXTRIS" at 5x21 "-------" 
		at 7x20 "'K' = left" at 8x20 "'L' = right"
		at 9x20 "'O' = spin" at 11x21 "Score:" 
	]

Keeping track of the score is simple.  When the program starts, a "score" variable is created and set to 0 ("score: 0").  Every time a piece stops falling, 10 points are added to the score.  That number is printed beneath the score header (notice that the score number must first be converted to a string, in order to be printed by tui):

	score: score + 10
	print tui compose [at 13x21 (to-string score)]

Every time a row is filled in, 1000 points are added to the score.  When the screen if redrawn to reflect the newly erased row, the tui code that prints the backdrop also prints out the updated score:

	print tui compose [
		at 4x21 "TEXTRIS" at 5x21 "-------" 
		at 7x20 "'K' = left" at 8x20 "'L' = right"
		at 9x20 "'O' = spin" at 11x21 "Score:" 
		at 13x21 (to-string score)
	] 

Next, I want to add a pause key.  This will fit in the switch structure that watches for keystrokes.  Whenever the "P" key is pressed, print a message indicating that the game has been paused.  Use an "ask" action to wait for input, and then print two blank lines to erase the pause message and any errant characters that the user may type in before hitting the [Enter] key:

	"p" [
		print tui [
			at 23x0 "Press [Enter] to continue"
		]
		ask ""
		print tui [
			at 24x0 "                              "
			at 23x0 "                              "
		]
	]

After posting some of this code to the Rebol mail list, another bug has become obvious.  If the insert key or the arrow keys are pressed during game play, the game crashes.  The following code produces a "** Math Error: Math or number overflow" when those keys are evaluated:

	keystroke: to-string to-char to-integer copy keys

To fix that, I create my own error check.  The keys codes for the arrow keys are #{1B5B41}, #{1B5B42}, #{1B5B43}, #{1B5B44}, and #{1B5B327E}.  I check to see if they've been pressed first.  If not, run the code above:

	now-key: copy keys
	if not (
		find [
			#{1B5B41} #{1B5B42} #{1B5B43}
			#{1B5B44} #{1B5B327E}
		] (now-key)
	) [keystroke: to-string to-char to-integer now-key]

That works, but a message to the list by Gabrielle Santilli creates a simpler solution.  It turns out that I should have looked at the console port format a bit more carefully.  All that's needed to get the keystroke is:

	keystroke: to-string copy keys

And that does not produce errors for any entered keys.

I added all the above code to the program, and then tested everything.  In doing so, I made an interesting discovery - it turns out that the code which produced the ghostly key input error in the shape printing routines is in a section of the TUI dialect that enables one to check for screen size.  I think the error has something to do with the fact that I'm "compose"ing the results - not sure, but it doesn't matter.  Since I'm not using that function, I simply remove it from the code.  While I'm at it, I remove all the other parts of the TUI dialect that I'm not using.  It turns out that all I need is:

	tui: func [commands [block!]] [
	    string: copy ""
	    cmd: func [s][join "^(1B)[" s]
	    arg: parse commands [
	        any [
	            'clear (append string cmd "J") |
	            'up    set arg integer! (append string cmd [
	                arg "A"]) |
	            'down  set arg integer! (append string cmd [
	                arg "B"]) |
	            'right set arg integer! (append string cmd [
	                arg "C"]) |
	            'left  set arg integer! (append string cmd [
	                arg "D"]) |
	            'at   set arg pair! (append string cmd [
	                arg/x ";" arg/y "H" ]) |
	            set arg string! (append string arg)
	        ]
	        end
	    ]
	    string
	]

With that error gone, I can remove all the error checking routines in the program (they were causing some additional problems).  Now Textris feels like a reasonably complete program.  Here's the final code:

	Rebol [Title: "Textris"]

	tui: func [commands [block!]] [
	    string: copy ""
	    cmd: func [s][join "^(1B)[" s]
	    arg: parse commands [
	        any [
	            'clear (append string cmd "J") |
	            'up    set arg integer! (append string cmd [
	                arg "A"]) |
	            'down  set arg integer! (append string cmd [
	                arg "B"]) |
	            'right set arg integer! (append string cmd [
	                arg "C"]) |
	            'left  set arg integer! (append string cmd [
	                arg "D"]) |
	            'at   set arg pair! (append string cmd [
	                arg/x ";" arg/y "H" ]) |
	            set arg string! (append string arg)
	        ]
	        end
	    ]
	    string
	]

	shape: [
	    ["####"]
	    ["#" down 1 left 1 "#" down 1 left 1 "#" down 1 left 1 "#"]
	    ["###" down 1 left 2 "#"]
	    [right 1 "#" down 1 left 2 "##" down 1 left 1 "#"]
	    [right 1 "#" down 1 left 2 "###"]
	    ["#" down 1 left 1 "##" down 1 left 2 "#"]
	    ["###" down 1 left 3 "#"]
	    ["##" down 1 left 1 "#" down 1 left 1 "#"]
	    [right 2 "#" down 1 left 3 "###"]
	    ["#" down 1 left 1 "#" down 1 left 1 "##"]
	    ["###" down 1 left 1 "#"]
	    [right 1 "#" down 1 left 1 "#" down 1 left 2 "##"]
	    ["#" down 1 left 1 "###"]
	    ["##" down 1 left 2 "#" down 1 left 1 "#"]
	    ["##" down 1 left 1 "##"]
	    [right 1 "#" down 1 left 2 "##" down 1 left 2 "#"]
	    [right 1 "##" down 1 left 3 "##"]
	    ["#" down 1 left 1 "##" down 1 left 1 "#"]
	    ["##" down 1 left 2 "##"]
	    ;
	    ["    "]
	    [" " down 1 left 1 " " down 1 left 1 " " down 1 left 1 " "]
	    ["   " down 1 left 2 " "]
	    [right 1 " " down 1 left 2 "  " down 1 left 1 " "]
	    [right 1 " " down 1 left 2 "   "]
	    [" " down 1 left 1 "  " down 1 left 2 " "]
	    ["   " down 1 left 3 " "]
	    ["  " down 1 left 1 " " down 1 left 1 " "]
	    [right 2 " " down 1 left 3 "   "]
	    [" " down 1 left 1 " " down 1 left 1 "  "]
	    ["   " down 1 left 1 " "]
	    [right 1 " " down 1 left 1 " " down 1 left 2 "  "]
	    [" " down 1 left 1 "   "]
	    ["  " down 1 left 2 " " down 1 left 1 " "]
	    ["  " down 1 left 1 "  "]
	    [right 1 " " down 1 left 2 "  " down 1 left 2 " "]
	    [right 1 "  " down 1 left 3 "  "]
	    [" " down 1 left 1 "  " down 1 left 1 " "]
	    ["  " down 1 left 2 "  "]
	]
	floor:  [
	    21x5 21x6 21x7 21x8 21x9 21x10 21x11 21x12 21x13 21x14 21x15
	]
	oc:  [ 
	    [0x0 0x1 0x2 0x3] [0x0 1x0 2x0 3x0] [0x0 0x1 0x2 1x1]
	    [0x1 1x0 1x1 2x1] [0x1 1x0 1x1 1x2] [0x0 1x0 1x1 2x0]
	    [0x0 0x1 0x2 1x0] [0x0 0x1 1x1 2x1] [0x2 1x0 1x1 1x2]
	    [0x0 1x0 2x0 2x1] [0x0 0x1 0x2 1x2] [0x1 1x1 2x0 2x1]
	    [0x0 1x0 1x1 1x2] [0x0 0x1 1x0 2x0] [0x0 0x1 1x1 1x2]
	    [0x1 1x0 1x1 2x0] [0x1 0x2 1x0 1x1] [0x0 1x0 1x1 2x1]
	    [0x0 0x1 1x0 1x1] 
	]
	width: [4 1 3 2 3 2 3 2 3 2 3 2 3 2 3 2 3 2 2]
	score: 0

	prin tui [clear]
	a-line: copy [] loop 11 [append a-line " "] 
	a-line: rejoin ["   |"  to-string a-line "|"]
	loop 20 [print a-line] prin "   " loop 13 [prin "+"] print ""
	print tui compose [
		at 4x21 "TEXTRIS" at 5x21 "-------" 
		at 7x20 "Use arrow keys" at 8x20 "to move/spin."
		at 10x20 "'P' = pause"
		at 13x20 "SCORE:  " (to-string score)
	]

	keys: open/binary/no-wait [scheme: 'console]
	forever [
	    random/seed now
	    r: random 19
	    xpos: 9
	    for i 1 20 1 [
	        pos: to-pair rejoin [i "x" xpos]
            do compose/deep [prin tui [at (pos)] print tui shape/(r)]
	        old-r: r
	        old-xpos: xpos 
	        if not none? wait/all [keys :00:00.30] [
	            switch/default to-string copy keys [
					"p" [
						print tui [
							at 23x0 "Press [Enter] to continue"
						]
						ask ""
						print tui [
							at 24x0 "                              "
							at 23x0 "                              "
						]
					]
	                "^[[D" [if (xpos > 5) [
	                        xpos: xpos - 1
	                ]]
	                "^[[C" [if (xpos < (16 - compose width/(r))) [
	                        xpos: xpos + 1
	                ]]
	                "^[[A" [if (xpos < (16 - compose width/(r)))  [
	                        switch to-string r [
	                            "1" [r: 2]
	                            "2" [r: 1]
	                            "3" [r: 6]
	                            "4" [r: 3]
	                            "5" [r: 4]
	                            "6" [r: 5]
	                            "7" [r: 10]
	                            "8" [r: 7]
	                            "9" [r: 8]
	                            "10" [r: 9]
	                            "11" [r: 14]
	                            "12" [r: 11]
	                            "13" [r: 12]
	                            "14" [r: 13]
	                            "15" [r: 16]
	                            "16" [r: 15]
	                            "17" [r: 18]
	                            "18" [r: 17]
	                            "19" [r: 19]
	                        ]
	                    ]
	                ]                   
	            ] []
	        ]
            do compose/deep [
				prin tui [at (pos)] print tui shape/(old-r + 19)
	        ]
	        stop: false
	        foreach po compose oc/(r) [
	            foreach coord floor [
	                floor-y: to-integer first coord
	                floor-x: to-integer second coord
	                oc-y:  i + to-integer first po
	                oc-x:  xpos + to-integer second po
	                if (oc-y = (floor-y - 1)) and (floor-x = oc-x) [
	                    stop-shape-num: r
	                    stop: true
	                    break
	                ]
	            ]
	        ]
	        foreach po compose oc/(old-r) [
	            foreach coord floor [
	                floor-y: to-integer first coord
	                floor-x: to-integer second coord
	                oc-y:  i + to-integer first po
	                oc-x:  old-xpos + to-integer second po
	                if (oc-y = (floor-y - 1)) and (floor-x = oc-x) [
	                    stop-shape-num: old-r
	                    stop: true
	                    break
	                ]
	            ]
	        ]
	        if stop = true [
	            left-col: second pos 
	            width-of-shape: length? compose oc/(stop-shape-num)
	            right-col: left-col + width-of-shape - 1
	            counter: 1
	            for current-column left-col right-col 1 [
	                add-coord: compose oc/(stop-shape-num)/(counter)
	                new-floor-coord: (pos + add-coord)
	                append floor new-floor-coord
	                counter: counter + 1
	            ]
	            break
	        ]
	    ]
        do compose/deep [prin tui [at (pos)] print tui shape/(old-r)]
	    if (first pos) < 2 [
	        prin tui [at 23x0]
	        print "   GAME OVER!!!^/^/"
	        halt
	    ]
		score: score + 10
		print tui compose [at 13x28 (to-string score)]
	    for row 1 20 1 [
	        line-is-full: true
	        for colmn 5 15 1 [
	            each-coord: to-pair rejoin [row "x" colmn]
	            if not find floor each-coord [
	                line-is-full: false
	                break
	            ]
	        ]
	        if line-is-full = true [
	            remove-each cor floor [(first cor) = row]
	            new-floor: copy [
	                21x5 21x6 21x7 21x8 21x9 21x10 21x11 21x12 21x13
	                21x14 21x15
	            ]
	            foreach cords floor [
	                either ((first cords) < row) [
	                    append new-floor (cords + 1x0)
	                ][
	                    append new-floor cords
	                ]
	            ]
	            floor: copy unique new-floor
				score: score + 1000
	            prin tui [clear]
	            loop 20 [print a-line] 
	            prin "   " loop 13 [prin "+"] print ""
				print tui compose [
					at 4x21 "TEXTRIS" at 5x21 "-------" 
					at 7x20 "Use arrow keys" at 8x20 "to move/spin."
					at 10x20 "'P' = pause"
					at 13x20 "SCORE:  " (to-string score)
				]
	            foreach was-here floor [
	                if not ((first was-here) = 21) [
	                    prin tui compose [at (was-here)]
	                    prin "#"
	                ]
	            ]
	        ]
	    ]
	]

=image rebol_tutorial/textris.png


Here's a quick synopsis of the program:

* The TUI dialect is defined.

* The "shape" block, containing the TUI instructions for drawing each shape is defined.

* The "floor", "oc", and "width" coordinate blocks are defined.  The "score" variable is also defined.

* The backdrop characters (left, right, and bottom barriers), instructions, headers, and score are printed.

* A forever loop runs the main actions of the program.  The subsections of that loop are:

*> A shape is printed on the screen.

*> User keystrokes are watched for.

*> A switch structure decides what to do with entered keystrokes (l = move right, k = move left, o = rotate shape, p = pause).

*> Another switch structure determines which shape to print when the current shape is rotated.

*> The currently printed shape is erased.

*> Two foreach loops check whether the current shape has reached a position at which it should stop falling.

*> If the piece has reached a stopping point, the coordinates occupied by the piece are added to the "floor" block.

*> The shape is printed at its final resting place.

*> If the current shape touches the ceiling, the game ends.

*> The score is updated.

*> If any rows have been completely filled in, their coordinates are removed from the floor block, the coordinates of all other characters are moved down a row, and the screen is reprinted with the new floor coordinates and the new score.

*> The forever loop continues.


If I'd been so thoughtful and organized as to write a structured outline like that in the beginning of the case study, things would've moved along more quickly.  But any project is easier in retrospect ...  I just try to remember that building as detailed an outline as possible before writing any code always saves a great deal of work and confusion.

Now that the game satisfies my original intentions, I'll bring the case study to a close, but not without first putting together a to-do list of things to improve in the program.  If you'd like to try implementing some of these changes, first figure out where in the outline they should go, write some pseudo code to get the job done, and then come up with Rebol code to satisfy those pseudo code expressions:

# Save high scores to disk.

# Add a way to incrementally increase the speed at which shapes drop.  Do this every time a certain number of rows is cleared.

# Add a "next piece" preview.

# Look for a way to remove the cursor from the printout, so that it's not visible along the left side of the wall as the shapes fall.

# Add sound.  Play midi tones for each event that occurs, and play a background tune while the game is running.

# Rewrite the entire program using GUI techniques, instead of console text characters and TUI.

Looking at my coding process in retrospect, I should note some criticisms.  One element that annoyed me was a set of badly chosen variable names.  I initially used "r", for example, to represent the current shape number because it was first used to represent a random number.  "R" is not so descriptive, and it was hard to remember what "r" represented while I was coding.  The same was true of "i", which became more important as the loop that dropped the shapes grew in complexity.  I left those variables as they were in this case study so that the lines of code fit neatly onto this web page, but in my own coding I choose to use more descriptive variables.  Doing that in general makes code more readable and easier to think through.


The Moral of the Story:

Whether or not you're interested in game programming, and despite the fact that the final product of this case study is a bland implementation of Tetris, some general understanding about coding can be gained from the thought process covered in this section.  It's typical of any general coding project you'll encounter:  start with a design concept, outline the main structure of the program you imagine, use pseudo code to guide you from the "what am I trying to do?" through the "how do I code it" stages, and refine the detail of your outline by testing and experimenting with small code chunks along the way.  

In general, if you can't think through the process of "what am I trying to accomplish" in a structured way, then you won't be able to write the code to accomplish it.  Once you've got a basic grasp of language concepts and syntax, you'll see that writing code just takes lots of creative organization and experimentation.  Keep a language reference close at hand, and you can work out the syntax of virtually any code you need to write.  That's only a matter of knowing which functions and constructs are available to solve your problems, and looking up the format for those you're not familiar with.  The difficult part in any coding situation is mapping each small thought process to a data construct, conditional expression, looping routine, function definition, existing code module, word label, etc.  For large projects, you'll typically need an outline because it's so easy to get lost in the minute coding details along the way.  Start with a top down approach, conceive and design a flow chart/outline, and then flesh out the details of each section until you've got code written to solve each design concept.  Once you become familiar with that process, experience will show that you can code solutions for virtually any problem you encounter.

You'll find that in many cases Rebol allows you to think directly in code more easily than you can with pseudo code.  That's because Rebol's high level design is meant to be human readable and human "thinkable".  Although many coding concepts in all computer languages are generally the same, most other languages are more overtly designed and constrained by legacy concepts derived from requirements about how computers operate.  Some languages tend to require much more low level coding or coersing of disparate modules to fit together in order to make the conceptual design take shape in final code form.  Other languages get you bogged down in thinking about higher level OOP constructs.  A lack of universal data structures such as Rebol's block/series structure, a lack of built in native data types such as time, tuples, pairs, money, etc., and a less natural way of structuring functions, variables and module definitions (not using words and dialects in a natural language way), require unique and contrived constructs to be designed to manipulate data in each individual program.  In the most popular languages, program authors typically have to be more concerned about managing the rudimentary memory and cpu actions of the computer for everything that occurs in a program.  That enables a greater measure of control over how a computer uses it's hardware resources, but it's very far from the way humans naturally think about solving real life situations.  Rebol allows things to be done in a way of thinking that's closer to the outline stage.  When you get used to writing Rebol code, you'll find that it saves a tremendous amount of time compared to other languages.  Remember along the way that no matter what computer language(s) you learn, understanding how to think through the "what I am I trying to accomplish" outline is essential to writing code that accomplishes your task.



---Case 5 - Coding a Freecell Game Clone (GUI)

The Textris project was entertaining and educational, so I'm motivated to create a simple GUI game next.  As far as I know, there's no existing Freecell game implemented in Rebol, and it's my other favorite recreational program.  This project will provide some more food for thought about useful GUI techniques and approaches.  Here's my initial outline:

# Get the card images compressed and embedded into Rebol code.

# Write the code to display and move cards around the screen.  It will be similar to that found in the Guitar Chord Diagram Maker example presented earlier.  I'll need to click and drag images around the screen.  I'll also want to make the images "snap" into position onto other cards, rather than floating freely.

# Create a nice looking GUI layout backdrop for the playing field.

# Layout the cards in random order, in 8 piles, on the playing field.

# Allow the selection and movement of cards, based on the rules of Freecell (i.e., cards need to be placed in descending order, red-black-red-black, goal piles must start with aces, and ascend through a single suit, etc.).  These rules can be handled by a series of conditional evaluations that are run every time a card is moved.  This step will require the most coding thought and will likely need a sub-outline.

To get started with the first step, I remembered seeing a Rebol card game at http://www.rebolfrance.org/articles/bridge/bridge.html .  The zip package at that location contains all the .bmp card images in a single directory.  I downloaded the package and wrote a little variation of the compression program provided earlier in this tutorial.  It loops through all the cards in the directory, reads and compresses the files, and then appends each unit of data to a single block labeled "cards", which is created to hold all the images:

	REBOL [Title: "Rebol Binary Embedder"]

	system/options/binary-base: 64
	cards: copy []
	foreach file load %./  [
		uncompressed: read/binary file
		compressed: compress to-string uncompressed
		; there are some other files in the directory that I don't
		; want to embed.  Limiting the file size to 10k weeds them out:
		if ((length? uncompressed) < 10000) [
			append cards compressed
		]
	]
	editor cards

Because the cards are read in alphabetical order from the directory, I need to change the order of the card data so that they ascend in the following order:  Ace, 2, 3, 4, 5, 6, 7, 8, 9, 10, J, Q, K.  I also added some comments to clarify where each suit begins and ends.  This provides a nice chunk of data that I can use to build other card games of any type:

	cards:  [

	; clubs:
	
	64#{
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	AAA=
	} 64#{
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	}

	; back

	64#{
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	}
	]


Next, I wrote a little GUI app to test that all the cards display appropriately.  It builds a GUI block by reading, decompressing, and appending the data in the card block above, using the built-in "image" word to display each decompressed card.  That GUI block is then viewed with the typical "view layout" code.  All of the code in the rest of this section will assume that the card data above has been defined in the interpreter:

	; I want the cards to be layed out next to each other in the GUI, so
	; the layout block starts with the built-in "across" word:

	gui: [across ]

	; The "count" variable is used to separate each suit onto different
	; lines in the GUI:

	count: 0 

	foreach card cards [
		if count = 13 [
			; after the 13th card, start a new line in the GUI
			; and reset the count:
			append gui [return]
			count: 0
		]
		; The following code adds the image data to the block that'll be
		; displayed:
		append gui compose [image load to-binary decompress (card)]
		count: count + 1
	]

	view layout gui

=image rebol_tutorial/fc1.png

That provides a fundamental way to compress and reuse card images to create all types of games.  Adding the "feel movestyle" code presented earlier in this tutorial allows us to click and drag the cards around the GUI.  Here I'll make some changes to the code because I want the cards to move using "snap-to" positioning, as if they're placed on a grid and clicking from one grid position to the next (as opposed to floating freely across the screen with each click-drag):

	; The following function enables the pieces to slide around the
	; screen.  The coordinates are rounded to multiples of 79 and 104
	; pixels to enable snap-to positioning (the horizontal width and 
	; vertical height of each card and the surrounding space).  The
	; additional 20 pixels accounts for the default border around the
	; overall GUI:

	movestyle: [
		engage: func [face action event] [
	    	if action = 'down [
	        	face/data: event/offset
	            remove find face/parent-face/pane face
	            append face/parent-face/pane face
	        ]
	        if find [over away] action [
				unrounded-pos: (face/offset + event/offset - face/data)
				snap-to-x: (round/to first unrounded-pos 79) + 20
				snap-to-y: (round/to second unrounded-pos 104) + 20
	        	face/offset: to-pair rejoin [snap-to-x "x" snap-to-y] 
	        ]
	        show face
	    ]
	] 

	; Here's a revised version of the previous GUI block.  The only
	; difference is that is uses the snap-to positioning definition
	; above ("movestyle"):

	gui: [across ]
	count: 0 
	foreach card cards [
		if count = 13 [
			append gui [return]
			count: 0
		]
		append gui compose [
			image load to-binary decompress (card) feel movestyle
		]
		count: count + 1
	]
	view layout gui

=image rebol_tutorial/freecell1.png

Now you can pick up any card, move it around the screen, and it automatically lines up and snaps over any other card on the screen - very useful!  Steps 1 and 2 in the program outline are done.  Next, I'll remove the card backside image from the card data, and tile all the images on the screen.  That just means changing the initial positions of the cards, and also the number of pixels rounded in the snap-to code:

	movestyle: [
		engage: func [face action event] [
	    	if action = 'down [
	        	face/data: event/offset
	            remove find face/parent-face/pane face
	            append face/parent-face/pane face
	        ]
	        if find [over away] action [
				unrounded-pos: (face/offset + event/offset - face/data)
				snap-to-x: (round/to first unrounded-pos 79) + 20
				snap-to-y: (round/to second unrounded-pos 30) + 20
	        	face/offset: to-pair rejoin [snap-to-x "x" snap-to-y]
	        ]
	        show face
	    ]
	]

	gui: [across ]
	count: 0 
	ypos: 20
	foreach card cards [
		if count = 8 [
			ypos: ypos + 30
			coord: to-pair rejoin [20 "x" to-string compose (ypos)]
			append gui compose [at (coord)]
			count: 0
		]
		append gui compose [
			image load to-binary decompress (card) feel movestyle
		]
		count: count + 1
	]
	view layout gui 

=image rebol_tutorial/freecell2.png

That code is really starting to look and act like a card game :)  Now that we've got a working example of movable cards laid out nicely on screen, I begin to think about how the game will be played (step 4 in the overall program outline).  The first thing I realize is that there's absolutely nothing in the "movestyle" code that allows me to determine which card I'm touching at any given moment.  Those cards are simply collections of binary graphic data displayed on the screen.  The only unique and meaningful information I can get about any given card image is its current position (face/offset).  To operate the game, however, I need to know a card's face value, suit, color, etc.  A simple solution to that problem can be managed by keeping track of each card's current position, and mapping those locations to individual card face values.  To do that, I'll create a block that maps each specific card to its initial coordinates, and then update that block every time a move is made.  Every time a card is moved, the given card's new coordinates will overwrite the old coordinates in the block.  That way, I can figure out a card's face value simply by reversing the thought process.  By looking up any card's specific current position, I can perform conditional evaluations on the related face value, suit, color, etc. of the card at that location ... Sneaky, huh?  Doing that additionally allows me to keep track of how the piles of cards are laid out in the playing field - that's also going to play an important role in the game.

The block that maps coordinates to face values can be easily created during the foreach loop that builds the gui layout.  In order to keep track of the positions of each card, I need to define some additional variables.  Because I used Rebol's automatic GUI layout capabilities to arrange the cards on screen, rather than specifically positioning each image, there are currently no existing variables that store any of those position values.  To store the starting coordinates of each card, I create the additional variables "cardnumber" and "xpos", along with a block labled "card-coords" to hold all the values.  Now, as each card's image data is layed out in the gui block, it's position is calculated and appended to the card-coords block:

	gui: [across ]
	card-coords: copy []
	coord: 0x0
	count: 0 
	cardnumber: 1
	ypos: 20
	xpos: 20
	foreach card cards [
		if count = 8 [
			ypos: ypos + 30
			xpos: 20  ; start a new row every 8 cards
			coord: to-pair rejoin [20 "x" to-string compose (ypos)]
			append gui compose [at (coord)]
			count: 0
		]
		append gui compose [
			image load to-binary decompress (card) feel movestyle
		]
		coord: to-pair rejoin [to-string compose (xpos)
			"x" to-string compose (ypos)]
		print coord
		; Add the coordinate of the newly created card to the 
		; card-coords block:
		append card-coords compose [(cardnumber) (coord)]
		count: count + 1
		cardnumber: cardnumber + 1
		xpos: xpos + 79
	]
	view layout gui

	print "The cards and their positions are: "
	probe card-coords halt

=image rebol_tutorial/freecell3.png
=image rebol_tutorial/freecell3b.png
=image rebol_tutorial/freecell3c.png

Tada!  Now every card has a numeric label and each label is tied to a specific starting position.

	; These numbers are significant, because all the cards will be
	; referred to by them throughout the rest of the game.

	1-13  = clubs		ace through king
	14-26 = diamonds	ace through king
	27-39 = hearts		ace through king
	40-52 = spades		ace through king

It's important to note that all changes to the current coordinates, and any other calculations, conditional evaluations, etc. need to occur within the "movestyle" block.  Remember, the gui block is simply statically created - it's only run once when the script is first evaluated from beginning to end.  It's the movestyle block of code that gets evaluated every time a card is touched.  We can include any code that needs to be run, inside the sections that are evaluated when either a down, over, or away action is detected.  For example, we can use the following formula to find the index number of the card's initial coordinate in the card-coords block:

	new-pos: (index? find card-coords start-coord) / 2
	; divide the index number by two because each card has two values:
	; position number in the grid, and coordinate.

With that index number, we can look up the name of the card at the same index position in a new "card-names" block using the code "card-names/:new-pos" (that reads: the item in the card-names block at the index number created above).  In this example, those values are calculated inside the movestyle block, and a message is printed to demonstrate the mapping technique.  Take a close look at the print code to see how each of the variables work:

	card-names: [
		"ace of clubs" "2 of clubs" "3 of clubs" "4 of clubs" 
		"5 of clubs" "6 of clubs" "7 of clubs" "8 of clubs" "9 of clubs"
		"10 of clubs" "jack of clubs" "queen of clubs" "king of clubs"
		"ace of diamonds" "2 of diamonds" "3 of diamonds" 
		"4 of diamonds"	"5 of diamonds" "6 of diamonds" "7 of diamonds"
		"8 of diamonds" "9 of diamonds" "10 of diamonds" 
		"jack of diamonds" "queen of diamonds" "king of diamonds"
		"ace of hearts" "2 of hearts" "3 of hearts" "4 of hearts" 
		"5 of hearts" "6 of hearts" "7 of hearts" "8 of hearts" 
		"9 of hearts" "10 of hearts" "jack of hearts" "queen of hearts"
		"king of hearts" "ace of spades" "2 of spades" "3 of spades"
		"4 of spades" "5 of spades" "6 of spades" "7 of spades" 
		"8 of spades" "9 of spades"	"10 of spades" "jack of spades" 
		"queen of spades" "king of spades"
	]

	movestyle: [
		engage: func [face action event] [
	    	if action = 'down [
				start-coord: face/offset
				if (find card-coords start-coord) [
					new-pos: (index? find card-coords start-coord) / 2
					print rejoin [
						"You touched card number: "
						(select card-coords new-pos)
						"^/Position #" 
						new-pos " in the grid."
						newline
						card-names/:new-pos
						newline					
					]				
				]
	        	face/data: event/offset
	            ; remove find face/parent-face/pane face
	            ; append face/parent-face/pane face
	        ]
	        if find [over away] action [
				unrounded-pos: (face/offset + event/offset - face/data)
				snap-to-x: (round/to first unrounded-pos 79) + 20
				snap-to-y: (round/to second unrounded-pos 30) + 20
	        	face/offset: to-pair rejoin [snap-to-x "x" snap-to-y]
				print face/offset				
				
	        ]
	        show face
	    ]
	]

	gui: [across ]
	card-coords: copy []
	coord: 0x0
	count: 0 
	cardnumber: 1
	ypos: 20
	xpos: 20
	foreach card cards [
		if count = 8 [
			ypos: ypos + 30
			xpos: 20
			coord: to-pair rejoin [20 "x" to-string compose (ypos)]
			append gui compose [at (coord)]
			count: 0
		]
		append gui compose [
			image load to-binary decompress (card) feel movestyle
		]
		coord: to-pair rejoin [to-string compose (xpos) "x" to-string compose (ypos)]
		print coord
		append card-coords compose [(cardnumber) (coord)]
		count: count + 1
		cardnumber: cardnumber + 1
		xpos: xpos + 79
	]
	view layout gui

=image rebol_tutorial/freecell4.png
=image rebol_tutorial/freecell4b.png

Using those techniques, I can finish up the card tracking code.  The following code makes changes to the card-coords block every time a card is moved:

	movestyle: [
		engage: func [face action event] [
	    	if action = 'down [
				start-coord: face/offset
				print find card-coords start-coord
	        	face/data: event/offset
	            remove find face/parent-face/pane face
	            append face/parent-face/pane face
	        ]
	        if find [over away] action [
				unrounded-pos: (face/offset + event/offset - face/data)
				snap-to-x: (round/to first unrounded-pos 79) + 20
				snap-to-y: (round/to second unrounded-pos 30) + 20
	        	face/offset: to-pair rejoin [snap-to-x "x" snap-to-y]
				
	        ]
	        show face
	    ]
	]

And with that, we have the necessary code to keep track of every card's position.  The program as it currently exists is a useful generic foundation for any card game.  Now we need to begin working on the game logic for freecell.  Here are the main objectives, along with some pseudo-code ideas to help organize the thought process:

# If a black card is placed below any red card at the bottom of any of the 8 "physical" piles of cards, or visa-versa (red-black), check to see if the moved card is 1 card lower in value than the card it touches.  If not, don't allow the move.  For example, a red 8 can be moved below a black 9, but moving a red 8 below a red 9 (not alternate red-black), or a black king beneath a red 3 (not consecutive), isn't allowed.  You can make a disallowed card movement happen programmatically by resetting the face/offset of any disallowed card back to the value it held before being moved (that value must therefore be saved at soon as a card is touched).

# Only cards exposed at the bottom of pile, or one of the cards in a descendingly stacked group of alternate red-black cards at the bottom of a pile can be moved.  For example, in a group of cards r7, b6, r5, b4, r3 at the bottom of a pile, you can move the red 7 and all the cards underneath it to another pile with an exposed black 8 at the bottom of the pile.  You could also grab the black 4 and move it, along with the red 3 together, beneath a pile with a red 5 at the bottom.  You could not, however, grab the red 7 from that pile without also moving the rest of the cards (b6, r5, b4, r3 ) beneath it.

# The goal of the game is to move all cards from the originally displayed 8 piles to 4 new "goal" piles that are initially empty.  Upon completion, each pile must contain only cards of a unique suit (clubs, diamonds, hearts, or spades) and the face values must ascend from ace to king consecutively.  Disallow any card movements that don't allow for that arrangement.

# There are 4 additional spaces, or "free cells" (the name of the game), that can be used to temporarily hold and move cards around between piles.  They are useful in moving cards when there are no positions within the initial piles or in the goal piles that allow a card to be moved according to the previous rules.  Only single exposed cards (no covered cards or piles) can be moved to a freecell.




With all that done, I've noticed a little bug in the previous example.  When I move a card, it sits on top of, and covers the other cards.  That's only desirable if the moved card is the bottom card in it's pile.  I'll solve that problem by using the existing block of card coordinates.  Every time a card is moved, I'll check to see if it's moved to the lowest position in each pile.  If so, I'll make it sit on top of the other cards.  If not, it will retain a position underneath the other cards.  


The next problem comes when I want to move an entire pile of cards.  

Next, I need to randomize the original position of each card.  The easiest way that I can think to do that is to create a loop that moves each card around the screen randomly, as if they'd been moved by hand.  Just run a feel movestyle on each card.

Next, I'll create a simple background to frame the playing field.


---Case 6 - Vegetable Gardening

Games are fun, and they're great programming practice, but they don't help you get things accomplished in life.  Now here's another real-world data processing example to help you think about how to program useful applications in Rebol.

My mother is a retired Microsoft Access developer who loves to garden in her spare time.  She's collected a wide scope of knowledge about how certain plants survive better when planted next to each other, and she wanted to create a program to help organize that info.  She wanted to create a standalone version that she could use on her home computer and give to friends.  She also wanted to publish it to the web as a dynamic database.  Additionally, she anticipated creating a version that could be carried into the garden on a pocket pc.  I suggested using Rebol, because it could provide a solution for all her needs.  She'd been working for several days with her development tools, and I told her I could get the whole thing done that same evening using Rebol.  Here's the outline I created:

# Create a database structure to hold the vegetable compatibility info and other related information.

# Write a command line version of the script that allows users to display all the info for any selected vegetable (this could be run on any operating system that supports the command line version of Rebol, including pocket pc).

# Create a CGI version of the above script that works on the web site.

# Create a pretty GUI version to be used on the home PC.

# Write a separate GUI to manage the administrative adding of data to the database.

# Provide a way to update the data files on the web site.

To get things started, I used the listview database example from this tutorial to provide a front end for the vegetable data files.  This provided a data structure that was suitable for the project, and it formed an instant solution to creating a GUI front end.  Steps 1 and 5 were instantly completed (that database example is so useful - many thanks to Henrik Mikael Kristensen for creating the listview module!).  

I created a few initial lines of data to work with.  Here's the working database.db file that I created:

	["basil" "" "tomato" "basil protects tomatoes." "" ""]
	["beans" "onion" "cabbage carrot radish" "" "" ""] 
	["cabbage" "celery" "tomato" "" "" ""] 
	["carrot" "" "tomato" 
		"Carrots strengthen the roots of tomatoes."
		"Carrots love tomatoes." ""] 
	["radish" "cabbage" "beans carrot tomato" "" "" ""] 
	["tomato" "cabbage" "basil carrot" "" "" ""]

Each block holds 6 pieces of information about each possible vegetable:

# the name of the veggie

# a list of other veggies that are compatible with the given veggie (those that do well when planted next to the given veggie).

# a list of other veggies that are incompatible

# 3 fields for general notes about the given veggie

I decided to add an "upload" button to the listview GUI to satisfy step #6 in my program outline.  It made sense to add this functionality here, because the user workflow would generally involve adding/changing data in the database (using the listview), and then updating the online database to match.  Here's the upload code I came up with.  It includes some error checking, so that the application doesn't crash if there's a problem with the Internet connection:

	uurl: ftp://user:pass@website.com/public_html/path/
	if error? try [
		; first, backup former data file:
		write rejoin [uurl "database_backup.db"] read rejoin [
			uurl "database.db"]
		write rejoin [uurl "database.db"] read %database.db
		alert "Update complete."
	] [alert "Error - check your Internet connection."]

I added a button to the listview GUI and put the above code in its action block.  Here's the complete code I added to the listview:

	btn "upload to web" [
		uurl: ftp://user:pass@website.com/public_html/path/
		if error? try [
			; first, backup former data file:
			write rejoin [uurl "database_backup.db"] read rejoin [
				uurl "database.db"]
			write rejoin [uurl "database.db"] read %database.db
			alert "Update complete."
		] [alert "Error - check your Internet connection."]
	]

Next, I realized that adding and removing new vegetables to and from the database would require some special consideration.  It ended up being the biggest part of this coding project.  I could use the built-in abilities of the listview module to simply add a new vegetable to the database, but there was a problem with that.  Every time a new vegetable is added to the database, it creates a list of compatibilities.  Aside from simply adding a new block to the database with fields listing the compatibilities and incompatibilities, that new veggie needs to be added to the compatibility list of every other vegetable with which it's compatible.  It also needs to be added to the incompatibility list of every vegetable with which it's not compatible.  Editing those blocks manually would take a lot of work and introduce a greater likelihood for user errors, especially as the database grows larger.  Instead, I decided to create a little script to do it automatically.  Here's the pseudo code thought process for that script:

# Create a list of existing vegetables.  This can be done by reading the existing database, looping through each block, and picking out the first item in each block (the vegetable name).

# Create a small new GUI to enter the new veggie info.  It should include an input field for the new veggie name, 2 text-lists showing the possible compatible and incompatible veggies (read from the existing list of veggies in the database), and 3 note fields.  

# Use a foreach loop to run through the lists of compatible and incompatible veggies.  Have the loop automatically add the new vegetable to the other veggies' respective compatibility lists.  

I created the GUI code and put the foreach loop inside the action block of a button used to add the new veggie.  Here's the code, which I saved as "add_veggie.r":

	Rebol [title: "Add Veggie"]

	; read the current database:
	veggies: copy load %database.db
	; get the list of veggies (the 1st item in each block):
	veggie-list: copy []
	foreach veggie veggies [append veggie-list veggie/1]

	; create a GUI with the appropriate fields and text-lists:
	view/new center-face add-gui: layout [
		across
		text "new vegetable:" 88x24 right new-veg: field
		return
		text "compatible:" 88x24 right 
		new-compat: text-list data veggie-list
		return
		text "incompatible:" 88x24 right 
		new-incompat: text-list data veggie-list
		return
		text "note 1:" 88x24 right new-note1: field
		return
		text "note 2:" 88x24 right new-note2: field
		return
		text "note 3:" 88x24 right new-note3: field
		return

		; now add a button to run the foreach loops:

		tabs 273 tab btn "Done" [
			; First, append the new veggie data block to
			; the existing database block.  Create the new
			; block from the text typed into each field,
			; and from the items picked in each of the 
			; lists above ("reduce" evaluates the listed
			; items, rather than including the actual text.
			; i.e., you want to add the text typed into the
			; new-veg field, not the actual text 
			; "new-veg/text").  "append/only" appends the
			; new block to the database as a block, rather
			; than as a collection of single items:
			append/only veggies new-block: reduce [
				new-veg/text
				; "reform" creates a quoted string from the
				; block of picked items in the text-lists:
				reform new-compat/picked
				reform new-incompat/picked
				new-note1/text
				new-note2/text new-note3/text
			]
			; Now loop through the compatibility list of the
			; new veggie, and add the new veggie to the 
			; compatibility lists of all those other
			; compatible veggies.  I put a space in if there
			; were already other veggies in the list:
			foreach onecompat new-compat/picked [
				foreach veggie veggies [
					if find veggie/1 onecompat [
						either veggie/2 = "" [spacer: ""] [
							spacer: " "]
						append veggie/2 rejoin [spacer 
						new-veg/text]
					]
				]
			]
			; Now do the same thing for the incompatibility
			; list:
			foreach oneincompat new-incompat/picked [
				foreach veggie veggies [
					if find veggie/1 oneincompat [
						either veggie/3 = "" [spacer: ""] [
							spacer: " "]
						append veggie/3 rejoin [spacer 
						new-veg/text]
					]
				]
			]
			save %database.db veggies
			; start the veggie data editor again when done:
			launch %veggie_data_editor.r
			unview add-gui
		]
	]
	focus new-veg
	do-events

=image rebol_tutorial/veg1.png

Because the add_veggie.r script will always be run from the veggie_data_editor.r program, I added the following code to the action block for the "add veggie" button in the data editor.  It launches the above add_veggie program, and closes the listview:

	btn "add veggie" [launch %add_veggie.r quit]

When the user closes the add_veggie program, the "launch %veggie_data_editor.r" code at the end of the program relaunches the data editor.  This handles flipping back and forth between the two screens.  When the data editor is relaunched, all the new data is automatically updated and displayed, so I don't need to manually update any displayed info.  After playing with the system, I realized before closing the data editor I'd better save the changes made to the database.  So I adjusted the above code as follows:

	    btn "add veggie" [
			launch %add_veggie.r
            backup-file: to-file rejoin ["backup_" now/date]
            write backup-file read %database.db
			save %database.db theview/data
			quit
		]

Next, I used the above code to create a similar "remove_veggie.r" program.  Instead of building a GUI for it, I just added some code to the "remove veggie" button in the veggie data editor to save the name of the currently selected vegetable to a file (veggie2remove.r).  I also copied the backup routine from the code above to make sure any changes in the listview are saved before going on:

	btn "remove veggie" [
        if (to-string request-list "Are you sure?" 
                [yes no]) = "yes" [
			; get the veggie name from the currently selected
			; row in the listview:
			first-veg: copy first theview/get-row
            theview/remove-row
			write %veggie2remove.r first-veg
			launch %remove_veggie.r
            backup-file: to-file rejoin ["backup_" now/date]
            write backup-file read %database.db
			save %database.db theview/data
			quit
        ]
	]


The remove_veggie.r script just reads the vegetable name from the veggie2remove.r file created above, and runs through some foreach loops to delete that vegetable from the compatibility lists of the other veggies:

	Rebol [title: "Remove Veggie"]

	veggies: copy load %database.db
	remove-veggie: read %veggie2remove.r

	; remove the selected veggie from compatible lists (the second
	; field in each block).  This is done by replacing any 
	; occurrence of the remove-veggie with an empty string ("").
	; That effectively erases every occurrence of the veggie:

	foreach veggie veggies [
		replace veggie/2 remove-veggie ""
	]

	; do the same thing to the incompatible lists of all other
	; veggies (field 3 in each block):

	foreach veggie veggies [
		replace veggie/3 remove-veggie ""
	]

	save %database.db veggies
	; start the veggie data editor again when done:
	launch %veggie_data_editor.r

Now the listview data editor and all its helper scripts are complete.  Because the listview is generally run from the GUI version of the main program ("veggie_gui.r" - not yet written), I added the following code to the existing listview close routine:

	launch "veggie_gui.r"

When I design the main veggie_gui program, I'll add a button to launch the listview.  When I close the listview, the above code will relaunch the GUI program to handle flipping back and forth between those two screens.  Here's the final listview database code with all the described changes and additions:

	Rebol [title: "Veggie Data Editor"]

	evt-close: func [face event] [
	    either event/type = 'close [
	        inform layout [
	            across
	            btn "Save Changes" [
	                ; when the save btn is clicked, a backup data
	                ; file is automatically created:
	                backup-file: to-file rejoin ["backup_" now/date]
	                write backup-file read %database.db
	                save %database.db theview/data
					launch "veggie_gui.r"
					quit
	            ]
	            btn "Lose Changes" [
					launch "veggie_gui.r"
					quit
				]
	            btn "CANCEL" [hide-popup]
	        ] none ] [ 
	        event
	    ]
	]
	insert-event-func :evt-close

	if not exists? %list-view.r [write %list-view.r read
		http://www.hmkdesign.dk/rebol/list-view/list-view.r
	]
	do %list-view.r

	if not exists? %database.db [write %database.db {[][]}]
	database: load %database.db

	view center-face gui: layout [
	    h3 {To enter data, double-click any row, and type directly
	        into the listview.  Click column headers to sort:}
	    theview: list-view 775x200 with [
	        data-columns: [Vegetable Yes No Note1 Note2
	            Note3]
	        data: copy database
	        tri-state-sort: false
	        editable?: true
	    ]
	    across
	    btn "add veggie" [
			launch %add_veggie.r
            backup-file: to-file rejoin ["backup_" now/date]
            write backup-file read %database.db
			save %database.db theview/data
			quit
		]
		btn "remove veggie" [
	        if (to-string request-list "Are you sure?" 
	                [yes no]) = "yes" [
				first-veg: copy first theview/get-row
	            theview/remove-row
				write %veggie2remove.r first-veg
				launch %remove_veggie.r
	            backup-file: to-file rejoin ["backup_" now/date]
	            write backup-file read %database.db
				save %database.db theview/data
				quit
	        ]
		]
	    btn "filter veggies" [
	        filter-text: request-text/title trim {
	            Filter Text (leave blank to refresh all data):}
	        theview/filter-string: filter-text
	        theview/update
	    ]
		btn "upload to web" [
			uurl: ftp://user:pass@website.com/public_html/path/
			if error? try [
				; first, backup former data file:
				write rejoin [
					uurl "database_backup.db"] read rejoin [
					uurl "database.db"]
				write rejoin [uurl "database.db"] read %database.db
				alert "Update complete."
			] [alert "Error - check your Internet connection."]
		]
	]

=image rebol_tutorial/veg2.png

Next, I created a command line version of the program.  The "Looping Through Data" example provided earlier in this tutorial served as a perfect model.  I just changed some of the variable labels and loaded the data from the existing database.db file.  Here's the code:

	Rebol [title: "Veggies"]

	veggies: load %database.db

	a-line: copy [] loop 65 [append a-line "-"]
	a-line: trim to-string a-line

	print-all: does [
		foreach veggie veggies [
			print a-line
			print rejoin ["Veggie:   " veggie/1]
			print a-line
			print rejoin ["Matches:  " veggie/3]
			print rejoin ["No-nos:   " veggie/2]
			print rejoin ["Note 1:   " veggie/4]
			print rejoin ["Note 2:   " veggie/5]
			print rejoin ["Note 3:   " veggie/6]
			print newline
		]
	]	
	forever [
	    prin "^(1B)[J"
	    print "Here are the current foods in the database:^/"
		print a-line
		foreach veggie veggies [prin rejoin [veggie/1 "  "]]
		print "" print a-line
		print "Type a vegetable name below.^/"
		print "Type 'all' for a complete database listing."
		print "Press [Enter] to quit.^/"
	    answer: ask {What food would you like info about?  }
		print newline
		switch/default answer [
			"all" 	[print-all]
	    	"" 		[ask "^/Goodbye!  Press [Enter] to end." quit]
			][
			found: false
			foreach veggie veggies [
				if find veggie/1 answer [
					print a-line
					print rejoin ["Veggie:   " veggie/1]
					print a-line
					print rejoin ["Matches:  " veggie/3]
					print rejoin ["No-nos:   " veggie/2]
					print rejoin ["Note 1:   " veggie/4]
					print rejoin ["Note 2:   " veggie/5]
					print rejoin ["Note 3:   " veggie/6]
					print newline
					found: true
				]
			]
			if found <> true [
				print "That vegetable is not in the database!^/"
			]
		]
	    ask "Press [ENTER] to continue"
	]	
	halt

=image rebol_tutorial/veg3.png

That was easy!  Just compare it to the original example - it's virtually identical.  Again, that generalized example was presented in this tutorial to provide a model for use in many varied situations.  Using it, I didn't even need to write any pseudo code.

Now I extended the above command line example to create a CGI application.  To get started, I used the final CGI example provided earlier in this tutorial as a model.  To it, I added the code that I'd created for the command line example above.  The only real changes I needed to make were some additional html formatting tags, required make the page display properly in a browser (mostly newline "< B R >"s).  Again, just an amalgam of several existing examples.  No pseudo code required - I just had to think about how to arrange the existing command line code to fit into the general CGI outline.  Here's the code:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol [title: "Veggies"]
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Veggies"</TITLE></HEAD><BODY>]

	veggies: load %database.db

	a-line: copy [] loop 65 [append a-line "-"]
	a-line: trim to-string a-line

	print-all: does [
		foreach veggie veggies [
			print a-line
			print [<BR>]
			print rejoin ["Veggie:   " veggie/1]
			print [<BR>]
			print a-line
			print [<BR>]
			print rejoin ["Matches:  " veggie/3]
			print [<BR>]
			print rejoin ["No-nos:   " veggie/2]
			print [<BR>]
			print rejoin ["Note 1:   " veggie/4]
			print [<BR>]
			print rejoin ["Note 2:   " veggie/5]
			print [<BR>]
			print rejoin ["Note 3:   " veggie/6]
			print [<BR>]
		]
	]

	print "Here are the current foods in the database:^/"
	print [<BR>]
	print a-line
	print [<BR><strong>]
	foreach veggie veggies [prin rejoin [veggie/1 "  "]]
	print ""
	print [</strong><BR>]
	print a-line
	print [<BR>]

	selection: decode-cgi system/options/cgi/query-string
	if selection/2 <> none [
		switch/default selection/2 [
			"all" 	[print-all]
			][
			found: false
			foreach veggie veggies [
				if find veggie/1 selection/2 [
					print a-line
					print [<BR>]
					print rejoin ["Veggie:   " veggie/1]
					print [<BR>]
					print a-line
					print [<BR>]
					print rejoin ["Matches:  " veggie/3]
					print [<BR>]
					print rejoin ["No-nos:   " veggie/2]
					print [<BR>]
					print rejoin ["Note 1:   " veggie/4]
					print [<BR>]
					print rejoin ["Note 2:   " veggie/5]
					print [<BR>]
					print rejoin ["Note 3:   " veggie/6]
					found: true
				]
			]
			if found <> true [
				print [<BR>]
				print "That vegetable is not in the database!"]
				print [<BR>]
		]
	]

	print [<FORM ACTION="http://website.com/rebol/veggie.cgi">]
	print [<BR><HR><BR>"Enter a veggie you'd like info about:"<BR>]
	print ["Veggie: "<INPUT TYPE="TEXT" NAME="username" SIZE="25">]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</BODY></HTML>]

=image rebol_tutorial/veg4.png
=image rebol_tutorial/veg4b.png

I didn't like the way the CGI required the user to type in the name of a listed vegetable.  Instead, I got rid of the list printout, and added the list to a selectable dropdown box.  Here's the final cgi example with the html dropdown box:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol [title: "Veggies"]
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Veggies"</TITLE></HEAD><BODY>]

	veggies: load %database.db

	a-line: copy [] loop 65 [append a-line "-"]
	a-line: trim to-string a-line

	print-all: does [
		foreach veggie veggies [
			print a-line
			print [<BR>]
			print rejoin ["Veggie:   " veggie/1]
			print [<BR>]
			print a-line
			print [<BR>]
			print rejoin ["Matches:  " veggie/3]
			print [<BR>]
			print rejoin ["No-nos:   " veggie/2]
			print [<BR>]
			print rejoin ["Note 1:   " veggie/4]
			print [<BR>]
			print rejoin ["Note 2:   " veggie/5]
			print [<BR>]
			print rejoin ["Note 3:   " veggie/6]
			print [<BR>]
		]
	]

	selection: decode-cgi system/options/cgi/query-string
	if selection/2 <> none [
		switch/default selection/2 [
			"all" 	[print-all]
			][
			found: false
			foreach veggie veggies [
				if find veggie/1 selection/2 [
					print a-line
					print [<BR>]
					print rejoin ["Veggie:   " veggie/1]
					print [<BR>]
					print a-line
					print [<BR>]
					print rejoin ["Matches:  " veggie/3]
					print [<BR>]
					print rejoin ["No-nos:   " veggie/2]
					print [<BR>]
					print rejoin ["Note 1:   " veggie/4]
					print [<BR>]
					print rejoin ["Note 2:   " veggie/5]
					print [<BR>]
					print rejoin ["Note 3:   " veggie/6]
					found: true
				]
			]
			if found <> true [
				print [<BR>]
				print "That vegetable is not in the database!"]
				print [<BR>]
		]
	]

	print [<FORM ACTION="http://website.com/rebol/veggie.cgi">]
	print [<BR>"Please select a veggie you'd like info about:"<BR>]
	print ["Veggie: "<select NAME="username"><option>"all"]
	foreach veggie veggies [prin rejoin ["<option>" veggie/1]]
	print [</option>]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</BODY></HTML>]

=image rebol_tutorial/veg5.png
=image rebol_tutorial/veg5b.png

The final part of the outline that I needed to address was the GUI display version of the program.  I needed to create this from scratch, so I came up with an outline and some pseudo code to organize my thoughts:

# Display the complete list of vegetables in the database (build the list using a foreach loop similar to the ones used in the command line program, and display that block in a text list widget).

# Display the info for any vegetable selected from the text list widget (when an item is selected, collect all the info for the selected vegetable and display it, nicely formatted, in a separate text area widget).

# Add a button to run the listview editor created earlier.

First I borrowed some code from the add_veggies.r example to create a list of all the veggies in the database.  It uses a foreach loop to cycle through each block in the database, and creates a list of the first item in each block (the name of each vegetable).  Then it sorts the list alphabetically.  This should be run before the GUI is displayed:

	load-data: does [
		veggies: copy load %database.db
		veggie-list: copy []
		foreach veggie veggies [append veggie-list veggie/1]
		veggie-list: sort veggie-list
	]

I decided to use a text-list widget to display the block of vegetable names.  To display the info for each vegetable, I used a simple text area display.  Here's the Rebol layout code to do that:

	list-veggies: text-list 200x400 data veggie-list
	display: area "" 300x400 

To that text-list widget's action block I added some code to display the info about the selected vegetable (it gets evaluated whenever the user selects an item from the list):

	; First, build a block of text with all the info about the
	; selected vegetable, nicely formatted with newlines and 
	; capitalized section headings:

	current-info: []
	foreach veggie veggies [
		if find veggie/1 value [
			current-info: rejoin [
				"COMPATIBLE:     " veggie/3 newline newline
				"INCOMPATIBLE:   " veggie/2 newline newline
				"NOTE 1:   " veggie/4 newline newline
				"NOTE 2:   " veggie/5 newline newline
				"NOTE 3:   " veggie/6
			]
		]
	]

	; Now display and update that text in the text area widget:

	display/text: current-info
	show display show list-veggies


Finally, add a button to run the listview data editor:

	btn "Edit Tables" [do %veggie_data_editor.r]


That's basically it.  Here's the final version:

	Rebol [title: "Veggie Matches"]

	load-data: does [
		veggies: copy load %database.db
		veggie-list: copy []
		foreach veggie veggies [append veggie-list veggie/1]
		veggie-list: sort veggie-list
	]

	load-data

	view display-gui: layout [
		h2 "Click a veggie name to display matches and other info:"
		across
	    list-veggies: text-list 200x400 data veggie-list [
			current-info: []
			foreach veggie veggies [
				if find veggie/1 value [
					current-info: rejoin [
						"COMPATIBLE:     " veggie/3 newline newline
						"INCOMPATIBLE:   " veggie/2 newline newline
						"NOTE 1:   " veggie/4 newline newline
						"NOTE 2:   " veggie/5 newline newline
						"NOTE 3:   " veggie/6
					]
				]
			]
			display/text: current-info
			show display show list-veggies
	    ]
		display: area "" 300x400 wrap
		return
		btn "Edit Tables" [
			do %veggie_data_editor.r
			; launch "veggie_data_editor.r"
			; load-data 
			; show list-veggies
			; show display
		]
	]

=image rebol_tutorial/veg6.png

There are 5 complete local script files that make up the completed veggie program:  veggie_data_editor.r, add_veggie.r, remove_veggie.r, veggie_command_line.r, veggie_gui.r.  In general, the main desktop applications are started by running the veggie_gui.r script.  The veggie_data_editor.r can also be run by itself (remember that it runs the veggie_gui.r program when it closes).  In order for the veggie_data_editor to work, the listview.r file needs to be included in the same directory.  The created database.db should also be kept in the same directory.  I packed all those files into an executable using XpackerX, and sent it to my Mom.  The 6th script file, veggie.cgi, got uploaded to the web site.  The database.db file was also uploaded manually, but my Mom prefers using the upload button in the veggie_data_editor to update the database on the web site.  The veggie2remove.r and database backup files are created automatically when the program is used - they're found in the same folder as the script files.  

Whatever language(s) you end up using to complete your programming tasks, you will go through a similar process of thinking through program requirements and organizing code structure.  Using existing code from the tutorial, along with the easy coding constructs that Rebol enables, I was able to write a complete solution to all of my Mom's requirements in a single short sitting.  Even with popular RAD ("rapid application development") tools, a comparable solution would've taken longer to finish.  It would also have been less portable to other operating systems, less readable and maintainable, harder to install, bigger in terms of download size, etc., etc...  On top of that, after reading just over 100 pages of text, a new programmer can get to the point of understanding how to accomplish this sort of thing, and how to complete many more varied and useful programming tasks using Rebol.  To come to a similar understanding with other development environments would take a manyfold increase in study time and much more experience in understanding various software technologies.  For all those reasons, I love using Rebol to actually get things done. 


---Case 7 - Scheduling Teachers, Part Two

After several months of using the teacher scheduling application described in the first case study, my business expanded, and the teaching staff grew.  With the way things worked in my short initial program, I would have to create a new folder on the web site and compile a unique version of the program for each new teacher.  This would require recompiling and uploading a new version, for each teacher, every time I alter the program.  I wanted to make a multi-user version of the application to simplify setup and to save maintenance time.  I also wanted to add some error checking and a simple password scheme to the existing program.  To create a new version of the application, here's my concept in outline/pseudo code form:

# Maintain the existing folder and file structure on the web site (http://website.com/teacher/name, schedule.txt, and index.php).

# Add a file to the web site containing a list of current teachers and associated passwords.  Put it outside the public_html folder, so that people can't download it without a password.

# In the application, start by downloading that file from the website (using ftp).

# Display a text list of teacher names from the downloaded file.

# When a teacher name is selected, request a password from the user and check that it matches the associated password for the given teacher.

# Append the teacher name to the http and ftp urls, and run the program as before.

# Add some error checking and backup routines every time the data is read or written locally, or on the web server.  That way, no data is ever lost.

# Compile the program and upload it to the web site.  Point all links on the index.php pages to that single file.  Now, any time I want to add a new teacher, all I need to do is add the new teacher name and password to the downloadable text file and copy a blank index.php and schedule.txt to a new folder on the web server.  If I ever make additional changes to the program, I only need to recompile and upload that single program file.


To start things off, I created a text file called "teacherlist.txt" and stored it outside the public_html folder on the web server.  It's formatted like this:

	["mark" "markspassword"] ["ryan" "ryanspassword"]
	["nick" "nickspassword"] ["peter" "peterspassword"]
	["rudi" "rudispassword"] ["tom" "tomspassword"]

The first thing I do in the program is read the data:

	teacherlist: load ftp://user:pass@website.com/teacherlist.txt

Next, display a list of the teachers.  The first item in each block of teacherlist.txt is the teacher name.  A foreach loop reads each of those names into a new block, and that block is displayed using a GUI text-list widget:

	teachers: copy []
	foreach teacher teacherlist [append teachers first teacher]
	view center-face layout [
		text-list data teachers [folder: value unview]	
	]

Next, get the password from the user and use a foreach loop to look through the list, checking for a match in teacher names and passwords entered by the user (the first and second elements, respectively, in each block):

	pass: request-pass/only
	correct: false
	foreach teacher teacherlist [
		if ((first teacher) = folder) and (pass = (second teacher)) [
			correct: true
		]
	]
	if correct = false [alert "Incorrect password." quit]

I add the following line to the script, which keeps Rebol from terminating the script when the [Esc] key is pressed.  That behavior is the default in the Rebol interpreter, and makes it easy for someone to just stop the script and view the teacherlist.  (I'm not so concerned about security here, but I don't want passwords to be blatently available):

	system/console/break: false

Finally, I come up with an error message to be executed any time an Internet connection isn't available.  It allows the user to read any of the recently backed up schedule.txt files so that the program is useful even if an Internet connection isn't available:

	error-message: does [
		ans: request {Internet connection is not available.
			Would you like to see one of the recent local backups?}
		either ans = true [
			editor to-file request-file quit
		][
			quit
		]
	]

I wrap all attempts to connect to the Internet in "error? try" routines, and duplicate the original backup routine from the initial program so that no data is ever lost.  Here's the final code:

	REBOL [title: "Lesson Scheduler"] 

	system/console/break: false
	error-message: does [
		ans: request {Internet connection is not available.
			Would you like to see one of the recent local backups?}
		either ans = true [
			editor to-file request-file quit
		][
			quit
		]
	]

	if error? try [
		teacherlist: load ftp://user:pass@website.com/teacherlist.txt
	][
		error-message
	]
	teachers: copy []
	foreach teacher teacherlist [append teachers first teacher]
	view center-face layout [
		text-list data teachers [folder: value unview]	
	]

	pass: request-pass/only
	correct: false
	foreach teacher teacherlist [
		if ((first teacher) = folder) and (pass = (second teacher)) [
			correct: true
		]
	]
	if correct = false [alert "Incorrect password." quit]

	url: rejoin [http://website.com/teacher/ folder]
	ftp-url: rejoin [
		ftp://user:pass@website.com/public_html/teacher/ folder
	]

	if error? try [
		write %schedule.txt read rejoin [url "/schedule.txt"]
	][
		error-message
	]

	; backup (before changes are made):
	cur-time: to-string replace/all to-string now/time ":" "-"
	; local:
	write to-file rejoin [
		folder "-schedule_" now/date "_" cur-time ".txt"
	] read %schedule.txt
	; online:
	if error? try [
		write rejoin [
			ftp-url "/" now/date "_" cur-time
		] read %schedule.txt
	][
		error-message
	]

	editor %schedule.txt

	; backup again (after changes are made):
	cur-time: to-string replace/all to-string now/time ":" "-"
	write to-file rejoin [
		folder "-schedule_" now/date "_" cur-time ".txt"
	] read %schedule.txt
	if error? try [
		write rejoin [
			ftp-url "/" now/date "_" cur-time
		] read %schedule.txt
	][
		alert "Internet connection not available while backing up."
	]

	; save to web site:
	if error? try [
		write rejoin [ftp-url "/schedule.txt"] read %schedule.txt
	][
		alert {Internet connection not available while updating web
		site.  Your schedule has NOT been saved online.}
		quit
	]	
	browse url

=image rebol_tutorial/teachers2.png
=image rebol_tutorial/teachers2b.png
=image rebol_tutorial/teacher2.png

With the new application complete, I wanted to create an additional cgi application for the web site to collectively display all available times in each of the teachers' schedules.  This would help with scheduling because both students and management could instantly see a bird's eye view of all open appointment times, on a single web page.  In order for that display to be viewable by the general public, I want the cgi app to strip out all personal data contained in the schedules.  To create the cgi, I need to search each line of schedule text for "----".  If a line contains the characters "----", that time is available.  Here's a pseudo code outline that I thought through as I organized the process:

# Make a list of all the teacher pages.  Store the links in a block.

# Use a foreach loop to cycle through each page in the list.  Read in the data on each page in line format, using another foreach loop.

# For each line, use a find function to check whether the line contains the name of a day of the week, or the characters "----".  If so, print the line, adding some additional formatting to separate days as headers.  Also print each page link as a header separating each teacher's schedule in the printout.

First, I created the block of links:

	page-list: [
		http://website.com/teacher/ryan
		http://website.com/teacher/mark
		http://website.com/teacher/nick
		http://website.com/teacher/peter
		http://website.com/teacher/tom
		http://website.com/teacher/rudi
	]

For step 2, I created the foreach loop to read each page:

	foreach page page-list [
		data: read/lines page
	]

Inside that loop, I added the code to print out the teacher name and day headers, and the available times:

	foreach page page-list [
		print newline
		print to-string page 
		print ""
		data: read/lines page
		week: ["MONDAY" "TUESDAY" "WEDNESDAY" "THURSDAY" "FRIDAY"
			"SATURDAY" "SUNDAY"]
		foreach line data [
			foreach day week [
				if find line day [print "" print line print ""]
			]
			if find line "----" [print line]
		]
	]

Now I've got a little command line application that does what I need:

	Rebol []
	page-list: [
		http://website.com/teacher/ryan 
		http://website.com/teacher/mark 
		http://website.com/teacher/nick 
		http://website.com/teacher/peter 
		http://website.com/teacher/tom 
		http://website.com/teacher/rudi
	]
	foreach page page-list [
		print newline
		print to-string page 
		print ""
		data: read/lines page
		week: ["MONDAY" "TUESDAY" "WEDNESDAY" "THURSDAY" "FRIDAY"
			"SATURDAY" "SUNDAY"]
		foreach line data [
			foreach day week [
				if find line day [print "" print line print ""]
			]
			if find line "----" [print line]
		]
	]

Next, to the basic CGI framework provided earlier in this tutorial, I simply added the code above.  As with the previous veggie case study cgi, the only real changes I needed to make were some added "< B R >"s to make the text display properly in the browser:

	#!/home/path/public_html/rebol/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Available Appointment Times"</TITLE></HEAD><BODY>]
	page-list: [
		http://website.com/teacher/ryan 
		http://website.com/teacher/mark 
		http://website.com/teacher/nick 
		http://website.com/teacher/peter 
		http://website.com/teacher/tom 
		http://website.com/teacher/rudi
	]
	foreach page page-list [
		print [<BR><BR>]
		print to-string page 
		print [<BR>]
		data: read/lines page
		week: ["MONDAY" "TUESDAY" "WEDNESDAY" "THURSDAY" "FRIDAY"
			"SATURDAY" "SUNDAY"]
		foreach line data [
			foreach day week [
				if find line day [print [<BR>] print line print [<BR><BR>]]
			]
			if find line "----" [print line print [<BR>]]
		]
	] 
	print [</BODY></HTML>]

As more teachers were added to the scheduling system, it became apparent that a CGI version of the editor would be helpful (for use on mobile phones, at work, and in other environments where installing an executable was problematic).  Basically, I needed to create a password protected online text editor, which could be useful in many other situations.  I also wanted it to make backups of my previous data files, just like the desktop version.  Here's the pseudo code outline I came up with:

# If the page has no data submitted, print text fields to get user name and password, and resubmit to page, end there.

# Otherwise, read teacherlist, check if name and password are correct.  If no, print error message and end.  If yes, read schedule.txt for appropriate teacher, display textbox containing current schedule, and button to submit changes.  End there.  Submit button should run another cgi that backs up old data, and saves new data.

In working with this example, I discovered that data from the textarea could get too big if submitted using the default "GET" method on the html form.  To work with POST data, the "read-cgi" function should be used, as in the example below:

	#!/home/path/public_html/rebol/rebol -cs
	REBOL []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Edit Schedule"</TITLE></HEAD><BODY>]

	; selection: decode-cgi system/options/cgi/query-string
	; We can't use the above normal line to decode, because
	; we're using the post method to submit data (because data
	; from the textarea may get too big for the get method). 
	; Use the following function to process data from a post 
	; method instead:

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]

	selection: decode-cgi read-cgi

	; if schedule.txt has been edited and submitted:

	if ((selection/2 = "save") or (selection/2 = "save")) [ 
	 ; save newly edited schedule:
	 write to-file rejoin ["./" selection/6 "/schedule.txt"] selection/4
	 print ["Schedule Saved."]
	 print rejoin [
		{<META HTTP-EQUIV="REFRESH" CONTENT="0;
			URL=http://website.com/folder/}
		selection/6 {">}
	 ]
	 quit
	]

	; if user is just opening page (i.e., no data has been submitted 
	; yet), request user/pass:

	if ((selection/2 = none) or (selection/4 = none)) [
	 print [<strong>"W A R N I N G  -  "]
	 print ["Private Server, Login Required:"</strong><BR><BR>]
	 print [<FORM ACTION="./edit.cgi">]
	 print [" Username: " <input type=text size="50" name="name"><BR><BR>]
	 print [" Password: " <input type=text size="50" name="pass"><BR><BR>]
	 print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	 print [</FORM>]
	 quit
	]

	; check user/pass against those in teacherlist.txt, 
	; end if incorrect:

	 teacherlist: load %teacherlist.txt
	 folder: selection/2 
	 password: selection/4
	 response: false
	 foreach teacher teacherlist [
	  if ((first teacher) = folder) and (password = (second teacher)) [
	   response: true
	  ]
	 ]
	 if response = false [print "Incorrect Username/Password." quit]

	; if user/pass is ok, go on:

	; backup (before changes are made):
	
	 cur-time: to-string replace/all to-string now/time ":" "-"
	 schedule_text: read to-file rejoin ["./" folder "/schedule.txt"]
	 write to-file rejoin [
		"./" folder "/" now/date "_" cur-time ".txt"] schedule_text

	print [<strong>"Be sure to SUBMIT when done:"</strong><BR><BR>]
	print [<FORM method="post" ACTION="./edit.cgi">]
	print [<INPUT TYPE=hidden NAME=submit_confirm VALUE="save">]
	print [<textarea cols="100" rows="15" name="contents">]
	print [schedule_text]
	print [</textarea><BR><BR>]
	print rejoin [{<INPUT TYPE=hidden NAME=folder VALUE="} folder {">}]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</BODY></HTML>]

=image rebol_tutorial/editorcgi.png
=image rebol_tutorial/editorcgib.png

Now there's a way for all the teachers to edit their schedules.  I can add a new teacher to the system in about 5 seconds (just create a new directory on the server and copy blank schedule.txt and index.php files).  Anyone involved in scheduling can make changes, regardless of location, and everyone stays synchronized.  In addition, anyone can get an instant bird's eye view of all available appointment times - this helps tremendously when scheduling new students.


---Case 8 - An Additional Teacher Automation Project

Now that the group scheduling system is complete, I want to automate our daily checkout routine.  Every day, our teachers are paid directly by their students.  In turn, they pay us a rental/referal fee for room and resource use.  That's our primary source of income.  At the end of the day, teachers add up all the students they've seen, and pay a given fee for each completed half hour session.  Some students prepay their teachers, and the teachers in turn prepay us so that they don't have to manage rental fees for prepaid appointments in the future.  

It takes a lot of time to manually figure daily fees, and the process is error prone when calculated by hand.  I want to automate the payment calculations based on the existing online schedule information, and I want to create an integrated record keeping system to more easily track prepayments.  Teachers need to keep track of missed/resheduled appointment payments, so that students are given proper credit for rolled over appointment times.  Also, in addition to daily local lessons, some of our instructors teach online lessons, for which _we're_ paid directly by students.  For those lessons, we deduct room rent from the total paid to us by the teachers.  We need a solution to easily manage and track all those daily calculations for all the teachers.  The objective is to keep a running total of how much money is due by each teacher every night, and how much money is owed to the teachers by students.  To create a software outline, I thought about what I do manually every day to calculate the checkout fees for a single person.  This thought process will serve as an outline to design the automated record keeping system:

# Each day at checkout time, the total number of lessons for a teacher is added up.

# The teacher owes us a given amount for lessons that occured in the local studio that day.

# We owe the teacher a given deduction for each lesson they performed online that day.

# Any lessons which had previously been prepaid by the teacher are deducted from the total owed us.

# The teacher prepays us for any future lessons which were prepaid by students that day, and records are updated to track the current prepaid amounts.

# Occasionally, other deductions are made from the amount owed us (sometimes the teacher provides a complimentary lesson for various reasons, or we provide complimentary time to the teacher/student, etc.).  Those amounts are deducted from the total owed us.


Based on the guidelines above, here's how I organized my thoughts about what the automated multiuser system should do:

# The multiuser requirements of the application are similiar to those of the scheduling app from the previous section.  I can use the code from the scheduling app to provide a current teacher list, simple password protection, loading/saving/backup of required data files for the selected teacher, etc.  

# In order to perform daily calculations for a single instructor, I want to provide a dynamically created list of daily students and I want to retrieve current prepay records for the given teacher.  That data will be stored on the web site, any changes will be backed up locally and on the web site.  I'll need to come up with a data structure to store the prepay records.  All other information (random deductions, complimentary lessons, etc.) will be provided by the user on a daily basis.  The regular daily student list and prepay records can be downloaded and displayed in text lists.  The other random deductions and additions can be entered manually in text input fields, and displayed in text lists.

# By default, each teacher owes a given amount for each of the students selected from the daily list (number_of_students X half_hour_rate).  Add to that any fees for additional students not in the daily list (rescheduled lessons, occassional additional appointments, etc.)

# For each online lesson, subtract 1 student from the total number of students taught that day, and deduct the appropriate amount from the grand total due.

# Subtract any previous prepayments from the grand total due.  Whenever that happens, make an adjustment to the teacher's record of prepayments.



To satisfy step 1, I'll use the scheduling app from the previous section of this case study.  As it stands, that code is capable of selecting a specified teacher directory on the website and downloading any required data files (current daily students, prepay records, individual teacher fee rates, etc.).

The main work of creating the application is in step 2.  The required calculations are in steps 3-5.  Here's a more structured outline, with pseudo code, to guide the writing of the program code:

# Read a current list of daily students from the selected teacher's schedule.txt file on the web server.  Store that info in a block and display it in a GUI text-list widget.  Store a list of local students selected from the above widget in a separate block.

# Display today's students again in a second text-list widget, so that the user can select those who took lessons online.  Store that selected data in another block. 

# Provide a text input field to allow the addition of any students not in the daily list.  Display a text-list widget to contain students entered into the text field.  Update the text-list display any time a student is added.  In order to remove incorrect entries from this list, the action block of the text-list should contain code to delete any students selected by the user.

# Provide another text field and text-list for the entry of deductions, with the same layout and remove code. 

# Provide a button to manage prepayment entries and calculations.  To handle that whole process, create a separate script - to be outlined below.

# Provide a "Calculate Total Fees" button.  The action block of this button should add and subtract the total number of items in all of the text-lists, according to the rules defined in steps 3-5 of the overall program outlined above.  Provide an html summary, which the teacher can print out and submit every day.

Here's the code I came up with to do all that:

	; The "url" variable below comes from the multiuser framework
	; borrowed from the scheduler app:
	students: read/lines rejoin [url "/schedule.txt"]
	; Initialize some other variables:
	other-additions: []	other-deductions: [] prepays: [] 
	pay-for: copy [] online: copy []

	view center-face layout [
		h2 "Local Students:"
		; "face/picked" refers to the currently selected items in
		; the text-list (use [Ctrl] + mouse click to select multiple
		; items, and assign that to the variable "pay-for":
		text-list data copy students [pay-for: copy face/picked]	
		h2 "Other Additions:" 
		field [
			; add the entered info to the text-list, and update
			; the display:
			append other-additions copy face/text
			show other-additions-list
		]
		other-additions-list: text-list 200x100 data other-additions [
			; remove any entry when selected by the user, and update
			; the display
			remove-each item other-additions [item = value]
			show other-additions-list
		]
		at 250x20
		h2 "Online Students:"
		text-list data copy students [online: face/picked]
		h2 "Other Deductions:"
		field [
			append other-deductions copy face/text
			show other-deductions-list
		]
		other-deductions-list: text-list 200x100 data other-deductions [
			remove-each item other-deductions [item = value]
			show other-deductions-list
		]
		at 480x20
		h2 "Prepaid Lessons:"
		prepay-list: text-list data prepays [
			remove-each item prepays [item = value]
			show prepay-list
		]
		; I still need to create the prepay.r program:
		btn 200x30 "Calculate Prepaid Lessons" [
			save %prepay.txt load rejoin [url "/prepay.txt"]
			do %prepay.r
		]
		at 480x320
		btn 200x100 font-size 17 "Calculate Total Fees" [
			total-students: (
				(length? pay-for) - (length? online) + 
				(length? other-additions) - (length? other-deductions) -
				(length? prepays)				
			)
			; I want to create an html output for this section:
			alert rejoin ["Total: " to-string total-students]
		]
	]

=image rebol_tutorial/teachers5.png
	

Now all that's left to create is a separate program to manage prepayment info.  Here's an outline describing my intentions:

# Create and upload a "prepay.txt" data file to store prepayment information for each teacher.  It should contain a separate block for each student who prepays, with fields for the student name, a nested block for the amounts and dates of each prepayment, and a nested block for dates of each lesson attended and the amount deducted from the prepayment for each lesson.

# Create a GUI with a text-list displaying each student who has prepayed.  Loop through the prepay.txt data to get the student names (the first item in each block).  Whenever a name is selected by the user, display the student name, prepay dates and amounts, and lesson dates in separate text lists.  Display the total prepay balance for the selected student in a text field.

# There should be an "Add" button and some text fields for entering new prepayments.  There should be fields for student name, amount, and date of prepay.  If an existing student is selected from the list, those fields should be populated automatically with today's date, and with the name of the existing student.  The action block of the add button should append the information to appropriate blocks in the prepay.txt file.

# There should be an "Apply Today" button to select prepayment(s) to be applied to today's balance.  Store the names of the selected students in a block, save that block to be read and used in the main application, and add the date information to the appropriate blocks in the prepay.txt file.

# There should be an "Done" button on the list-view GUI to allow the information to be changed and saved.  Whenever a student is selected from the list, their prepayment records should be displayed in an editable list-view (import the listview module and use the database example from earlier in this tutorial as a model).  There should be fields for prepay amounts and dates, and lesson dates and amounts.

# When the main prepay application is closed, the prepay.txt file should be backed up and saved to the web site.


For step 1, here's an example of the block structure I came up with to store data in the prepay.txt file:

	[
		; name:
		"John Smith"

		; prepayment amounts and dates:
		[ [$100 4-April-2006] [$100 5-May-06] ]

		; dates of lessons:
		[
			[$20 4-April-06] [$20 11-April-06] [$20 18-April-06]
			[$20 25-April-06] [$20 5-May-06]
		]
	]

	[
		"Paul Brown" 

		[ [$100 4-April-2006] ]

		[
			[$20 4-April-06] [$20 25-April-06]
		]
	]

	[
		"Bill Thompson"
		
		[ [$200 22-March-2006] ]

		[
			[$20 22-March-06] [$20 29-March-06] [$20 5-April-06]
			[$20 12-April-06] [$20 19-April-06]	[$20 26-April-06]
			[$20 3-May-06]
		]
	]


	[
		; name:
		"John Smith"

		; prepayment amounts and dates:
		[ "$100 4-April-2006" "$100 5-May-06" ]

		; dates of lessons:
		[
			"$20 4-April-06" "$20 11-April-06" "$20 18-April-06"
			"$20 25-April-06" "$20 5-May-06"
		]
	]

	[
		"Paul Brown" 

		[ "$100 4-April-2006" ]

		[
			"$20 4-April-06" "$20 25-April-06"
		]
	]

	[
		"Bill Thompson"
		
		[ "$200 22-March-2006" ]

		[
			"$20 22-March-06" "$20 29-March-06" "$20 5-April-06"
			"$20 12-April-06" "$20 19-April-06" "$20 26-April-06"
			"$20 3-May-06"
		]
	]

Here's the code I created to fulfill my outline requirements:

	Rebol [title: "Prepayment Calculator"]

	prepays: load rejoin [url "/prepay.txt"]
	names: copy []
	prepay-history: []
	lesson-history: []
	display-todays-bal: does [
		; calculate and display the current balace for the
		; selected student:	
		todays-balance: $0
		foreach payment prepay-history [
			todays-balance: todays-balance + (
				first (to-block payment)
			)
		]
		foreach lesson-event lesson-history [
			todays-balance: todays-balance - (
				first (to-block lesson-event)
			)
		]
		; update the display of today's balance for the
		; selected student :
		today-bal/text: to-string todays-balance
		show today-bal
	]
	foreach block prepays [append names first block]
	view center-face gui: layout [
		across
		text bold "New Prepayment:"
		text right "Name:" new-name: field
		text right "Date:" new-date: field 125 to-string now/date
		text right "Amount:" new-amount: field 75 "$"
		btn "Add" [
			create-new-block: true
			foreach block prepays [
				if (first block) = new-name/text [
					create-new-block: false
					append (second block) to-string rejoin [
						new-amount/text " " new-date/text
					]
				]
			]
			if create-new-block = true [
				new-prepay: copy []
				append new-prepay to-string new-name/text
				append new-prepay to-string rejoin [
					new-amount/text " " new-date/text
				]
				append prepays new-prepay
				names: copy []
				foreach block prepays [append names first block]
			]
			display-todays-bal
			show existing show pre-his show les-his show today-bal
		]
		return 
		text bold underline "Edit Data Manually" [
			view/new center-face layout [
				new-prepays: area 500x300 mold prepays
				btn "Save Changes" [
					prepays: copy new-prepays/text 
					unview
				]
			]
			names: copy []
			foreach block prepays [append names first block]
			show gui
			show existing show pre-his show les-his show today-bal
		] 
		return
		text "Existing Prepayments:"  pad 75
		text "Prepayment History:"  pad 85
		text "Lesson History:" pad 100
		text "Balance:"
		return
		existing: text-list data names [
			; When a name is selected from this text list, update
			; the other fields on the screen:
			new-name/text: value
			show new-name
			foreach block prepays [
				if (first block) = value [
					; update the other text lists to show the
					; selected student's prepay and lesson history:
					prepay-history: pre-his/data: second block
					show pre-his
					lesson-history: les-his/data: third block
					show les-his
				]
			]
			display-todays-bal
			; get the list of selected students
			prepaid-today: copy face/picked
		]
		pre-his: text-list data prepay-history
		les-his: text-list data lesson-history
		today-bal: field 85
		return
		btn "Apply Selected Prepayments Today" [
			save %prepaid.txt prepaid-today

			unview
		]
	]

=image rebol_tutorial/teachers6.png

In the original scheduling outline, I replace all references in the code to "schedule.txt" with "prepay.txt":

	REBOL [title: "Payment Calculator"] 
	
	error-message: does [
		ans: request {Internet connection is not available.
			Would you like to see one of the recent local backups?}
		either ans = true [
			editor to-file request-file quit
		][
			quit
		]
	]

	if error? try [
		teacherlist: load ftp://user:pass@website.com/teacherlist.txt
	][
		error-message
	]
	teachers: copy []
	foreach teacher teacherlist [append teachers first teacher]
	view center-face layout [
		text-list data teachers [folder: value unview]	
	]

	pass: request-pass/only
	correct: false
	foreach teacher teacherlist [
		if ((first teacher) = folder) and (pass = (second teacher)) [
			correct: true
		]
	]
	if correct = false [alert "Incorrect password." quit]

	url: rejoin [http://website.com/teacher/ folder]
	ftp-url: rejoin [
		ftp://user:pass@website.com/public_html/teacher/ folder
	]

	if error? try [
		write %prepay.txt read rejoin [url "/prepay.txt"]
	][
		error-message
	]

	; backup (before changes are made):
	cur-time: to-string replace/all to-string now/time ":" "-"
	; local:
	write to-file rejoin [
		folder "-prepay_" now/date "_" cur-time ".txt"
	] read %prepay.txt
	; online:
	if error? try [
		write rejoin [
			ftp-url "/" now/date "_" cur-time
		] read %prepay.txt
	][
		error-message
	]

	editor %prepay.txt

	; backup again (after changes are made):
	cur-time: to-string replace/all to-string now/time ":" "-"
	write to-file rejoin [
		folder "-prepay_" now/date "_" cur-time ".txt"
	] read %prepay.txt
	if error? try [
		write rejoin [
			ftp-url "/" now/date "_" cur-time
		] read %prepay.txt
	][
		alert "Internet connection not available while backing up."
	]

	; save to web site:
	if error? try [
		write rejoin [ftp-url "/prepay.txt"] read %prepay.txt
	][
		alert {Internet connection not available while updating web
		site.  Your schedule has NOT been saved online.}
		quit
	]	
	browse url

I also need to replace the line "editor %prepay.txt" with new code that does the work of calculating daily fees and tracking prepayments.  






Now that the program is complete, please notice how the outline developed.  It took several steps.  First, I thought through my daily manual calculations.  Then I thought about how that could be encapsulated into a program, and I created a basic ouline about what I wanted the program to do.  When it came to writing pseudo code outlines to create the actual program, the whole process was made easier by having organized outlines of everything I needed to accomplish.  To write the program, I first defined some required data (provided by the multiuser scheduler app), then conceived a user interface, and then performed calculations based on existing data and user input.  Following that type of outline structure (define required data, define a UI, perform calculations) tends to be an organized and successful approach in many cases.  

It should be noted that I'm not concerned about data security in this app.  It is important that the teachers are able to access this info conveniently from any location.  It's also important that local backups are made.  The automatic backing up of files provides a historical audit trail of transactions and changes to the records, which is an important concern since this program manages income.  It's not a problem for these records to become publicly accessible, so I'm using ftp and a public web site to store and retrieve the data.  Writing secure applications, however, is an important requirement in most situations involving financial transactions.  You should be aware that data security is a primary concern if you intend to do any programming related to typical business transactions, but that topic is beyond the scope of this tutorial.  This case study was provided as an additional example of how coding thought can be organized to take you from conceptual phases to a final product.  This particular code should not be emulated, however, for projects requiring secure data transactions.


---Case 9 - An Online Member Page CGI Program

One of my friends wanted to create an online member database for a local club.  He wanted members to be able to sign up and add their contact information, upload photos, and add info about themselves.  He was tired of manually making changes to the members' pages, and wanted users to be able to add, edit, and delete their own information.  He wanted basic password enabled access so that users could only edit their own information, and he wanted a back end utility that allowed him to make changes as administrator, and which automatically saved each successive change to the database, so that no data could ever be lost.  He also wanted users automatically emailed their password, in case they forgot.

Here was my basic thought process and plan of attack:

# This will be an online system (a web site), so the user interface will be a set of html pages that display each user's information, as well as a set of html forms for users to enter information.  We decided to have the page display the following fields:  Name, Address, Phone, Email, Age, Language, Height, Date the user was added, and an uploaded photo.

# The data will be stored in some sort of online database.  Since this is a small group with only a few users, I decided to create a simple flat file database - just a text file filled with blocks of Rebol data, one block per user, stored on the web server.

# The page that pulls the info from the database and displays it in the above html will basically be a Rebol CGI application that runs a "foreach" loop to print each of the entries in the above html format.  The pages where the users enter their information will be forms that submit the information to a Rebol CGI that appends it to the database text file.  The pages where the users edit their information will be forms that display the information currently in the selected entry, without the password.  When the user submits the new password and updated info, the CGI checks that the submitted password matches the existing password for that entry, and then replaces the old block with the new one, in the database text file.  The code for emailing the user a forgotten password and for automatically backing up data will also be put here.

# An image upload/update page also needs to created.  This will be an html form that accepts a local image file on the user's computer, submits that file to the CGI, which in turn writes that binary data to a directory on the web server, creates an html image link to it, and adds that link to the appropriate user entry in the database text file.

# The back end will simply be the password protected text editor explored in case study #6, with links to all the backup text files, for easy recovery (copy/paste) of lost data.

Here was the basic html layout I came up with for step 1.  Each entry in the database will be displayed using this template:

	<HR><BR> Date/Time: 23-Mar-2008/13:11:42-7:00

	<A HREF="./index.cgi?function=">edit | </A>
	<A HREF="./index.cgi?function=">delete</A>

	<TABLE background="" border=0 cellPadding=2 cellSpacing=2 
		width="100%"><TR>

	<TD width = "600">
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Name:          </FONT>
	<STRONG>The User Name Goes Here</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Address:       </FONT>
	<STRONG>The Address Goes Here</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Phone:         </FONT>
	<STRONG>The Phone</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Email:         </FONT>
	<STRONG>The Email</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Age:           </FONT>
	<STRONG>The Age</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Language:      </FONT>
	<STRONG>The Language</STRONG>
	<BR>
	<FONT FACE="Courier New, Courier, monospace">Height:        </FONT>
	<STRONG>The Height</STRONG>
	<BR><BR>
	</TD>

	<TD width="170" valign="center">
	<A HREF="./default.jpg" target=_blank><IMG align=baseline alt=""
		border=0 hspace=0 src="./default.jpg" width="160" height="120">
	</A>
	</TD>

	</TR></TABLE>

	Some Additional Notes Go Here...

	<BR><BR>

=image rebol_tutorial/member1.png

The database design for step 2 was even simpler to create.  Here's an example of what each block looks like.  Notice that each entry in the database is just a text string separated by spaces, for each field of info we want displayed on the member page.  In the block, I added a link to a default image, in case the user didn't upload their own photo.  This file was saved as %bb.db:

	["Username" "19-Feb-2008/4:55:59-8:00" "1 Address St."
		"123-456-7890" "name@website.com" "40" 
		{Rebol, C, C++, Python, PHP, Basic, AutoIt, others...}
		"6'" {I'm a nobody - just a test account.} "password" 
		[
			{<a href = "./default.jpg" target=_blank>
			<IMG align=baseline alt="" border=0 hspace=0
			src="./default.jpg" width="160" height="120"></a>}
		]
	] 

	["Tester McUser" "22-Feb-2008/13:14:44-8:00" "1 Way Lane"
		"234-567-8910" "tester@website.com" "35" "Rebol"
		{5' 11"} "I'm just another test account." "password"
		[
			{<a href = "./files/photo.jpg" target=_blank>
			<IMG align=baseline alt="" border=0 hspace=0
			src="./files/photo.jpg" width="160" height="120"></a>}
		]
	]

At this point I could begin the work of step 3, creating a CGI program that prints the html page in step 1, with the above data.  Here's a simple CGI script that simply prints the html design together with the entries from the database inserted:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol []
	print "content-type: text/html^/"
	print read %header.html

	bbs: load %bb.db  ; load the database info

	print [<center><table border=1 cellpadding=10 width=90%><tr><td>]
	print {<TABLE background="" border=0 cellPadding=0 cellSpacing=0
		height="100%" width="100%"><tr><td width = "600">}
	print [<hr>]
	reverse bbs
	foreach bb bbs [
		print [<BR>]
		print rejoin ["Date/Time: " bb/2]
		print "                   "
		print rejoin [{<a href="./index.cgi?function=">edit | </a>}]
		print rejoin [{<a href="./index.cgi?function=">delete</a>}]
		print "         "
		print {<TABLE background="" border=0 cellPadding=2 
			cellSpacing=2 height="100%" width="100%"><tr>
			<td width = "600"><BR>}
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			"Name:          </FONT><strong>" bb/1 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			 "Address:       </FONT><strong>" bb/3 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			"Phone:         </FONT><strong>" bb/4 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			"Email:         </FONT><strong>" bb/5 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			"Age:           </FONT><strong>" bb/6 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			 "Language:      </FONT><strong>" bb/7 "</strong>"]
		print [<BR>]
		print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
			 "Height:        </FONT><strong>" bb/8 "</strong>"]
		print [<BR><BR>]
		print </td>
		print {<td width = "170" valign = "center">}
		print bb/11 ; image link
		print {</td></tr></table>}
		print bb/9  ; "other information " text
		print [<BR><BR><HR>]
	]
	print [</td></tr></td></tr></td></tr></table>]
	print [</td></tr></table></center>]
	print read %footer.html

=image rebol_tutorial/member2.png

To that code, there were a number of features that I realized I should add.  First, I wanted to munge email addresses so that they were less likely to get collected by spam bots.  This line of code does the job well enough for my needs.  It turns "name@address.com" into "name at address dot com":

	(replace/all (replace bb/5 "@" " at ") "." " dot ")

I also wanted any http:// links in the "other information" section to be automatically linked.  To do that, I used parse to search for "http://" and the ending space character, then wrapped that link in the required < A  H R E F = ...> tags.  Here's the code:

	bb_temp: copy bb/9
	bb_temp2: copy bb_temp
	parse/all bb_temp [any [
		thru "http://" copy link to " " (replace bb_temp2 
			(rejoin [{http://} link]) (rejoin [
				{ <a href="} {http://} link 
				{" target=_blank>http://} link {</a> }]))
			] 
		to end
	]

Furthermore, I wanted to have line endings in the "other information" section automatically converted to html "< b r >"s, so that they display correctly on the web page.  That's easy:

		replace/all bb_temp newline "  <br>  "

My friend wanted a count displayed of the total number of members.  That's also easy, with "length? bbs":

	print rejoin [{<font size=5> Members:  (} length? bbs {)</font></td>}]

I also added a "join now" link to the CGI page where users would be able to add themselves to the database (that page hasn't been created yet):

	print {<td><a href="./add.cgi">Join Now</a></td></tr></table><BR>}

In order for users to edit/delete their info later, I needed to tag each displayed entry with a unique number to automatically select the appropriate block from the database.  To do this, I added a counter variable to the foreach loop, and incremented it each time through the loop (counter: counter + 1).  Then I replaced the generic edit and delete links in the code above . . .

	print rejoin [{<a href="./index.cgi?function=">edit | </a>}]
	print rejoin [{<a href="./index.cgi?function=">delete</a>}]

. . . with links that contain the counter, and which can be deciphered by a CGI program as "get" data:

	print rejoin [
		{<a href="./index.cgi?function=edititemnumber&messagenumber=}
		counter {&Submit=Post+Message">edit | </a>}
	]
	print rejoin [
		{<a href="./index.cgi?function=deleteitemnumber&messagenumber=}
		counter {&Submit=Post+Message">delete</a>}
	]

Here's the script, as it stands so far:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol []
	print "content-type: text/html^/"
	print read %header.html

	bbs: load %bb.db

	print [<center><table border=1 cellpadding=10 width=90%><tr><td>]

	print-all: does [
		print {<TABLE background="" border=0 cellPadding=0 cellSpacing=0
			height="100%" width="100%"><tr><td width = "600">}
		print rejoin [{<font size=5> Members:  (} length? bbs {)</font></td>}]
		print {<td><a href="./add.cgi">Join Now</a></td></tr></table><BR>}
		print [<hr>]
		counter: 1
		reverse bbs
		foreach bb bbs [
			print [<BR>]
			if bb/1 <> "file uploaded" [
				print rejoin ["Date/Time: " bb/2]
				print "                   "
				print rejoin trim [
					{<a href=
					"./index.cgi?function=edititemnumber&messagenumber=}
				 	counter 
					{&Submit=Post+Message">edit | </a>}
				]
				print rejoin trim [
					{<a href=
					"./index.cgi?function=deleteitemnumber&messagenumber=}
					counter 
					{&Submit=Post+Message">delete</a>}
				]
				print "         "
				print {
						<TABLE background="" border=0 cellPadding=2 
						cellSpacing=2 height="100%" width="100%"><tr>
						<td width = "600"><BR>
				}
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					"Name:          </FONT><strong>" bb/1 "</strong>"]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					 "Address:       </FONT><strong>" bb/3 "</strong>"]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					"Phone:         </FONT><strong>" bb/4 "</strong>"]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					"Email:         </FONT><strong>"
					(replace/all (replace bb/5 "@" " at ") "." " dot ") 
					"</strong>"
				]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					"Age:           </FONT><strong>" bb/6 "</strong>"]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					 "Language:      </FONT><strong>" bb/7 "</strong>"]
				print [<BR>]
				print rejoin [{<FONT FACE="Courier New, Courier, monospace">}
					 "Height:        </FONT><strong>" bb/8 "</strong>"]
				print [<BR><BR>]
			]
			; automatically convert line endings to html " <br>"
			bb_temp: copy bb/9
			replace/all bb_temp newline "  <br>  "
			bb_temp2: copy bb_temp
			; automatically link any urls starting with http://
			append bb_temp " "
			parse/all bb_temp [any [
				thru "http://" copy link to " " (replace bb_temp2 
					(rejoin [{http://} link]) (rejoin [
						{ <a href="} {http://} link 
						{" target=_blank>http://} link {</a> }]))
					] 
				to end
			]
			print </td>
			print {<td width = "170" valign = "center">}
			print bb/11 ; image link
			print {</td></tr></table>}
			print bb_temp2
			print [<BR><BR><HR>]
			counter: counter + 1	
		]
		print [</td></tr></td></tr></td></tr></table>]
	]
	print-all	
	print [</td></tr></table></center>]
	print read %footer.html

=image rebol_tutorial/member3.png


The page above was saved as index.cgi, and serves as the main display page for the site.  In order to ensure that a fresh copy of that page is always viewed by visitors, I also created the following index.html page that simply refreshes the index.cgi page.  By using that index.html page as the primary link (and by making that html file the default page for the web site), visitors always automatically see a refreshed view of the member page, with any changes/updates that have been made:

	<html>
	<head>
	<title></title>
	<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./index.cgi">
	</head>
	<body bgcolor="#FFFFFF">
	</body>
	</html>


Next, I needed to create a form for users to enter their member information.  This was saved as add.cgi.  The form posts any submitted information back to index.cgi.

	#! /home/path/public_html/rebol/rebol -cs	
	Rebol []
	print "content-type: text/html^/"
	print read %header.html

	print [<center><table border=1 cellpadding=10 width=90%><tr><td>]
	print [<font size=5>" Add New Member Information:"</font>]
	print "         "
	print "         "
	print "         "
	print [<hr>]
	print [<FORM method="post" ACTION="./index.cgi">]
	print [<br>" Your Name: " <br><input type=text size="60"
		name="username"><BR>]
	print [<br>" Password (required to edit member info later): " <br>
		<input type=text size="60" name="password"><BR>]
	print [<br>" Address: " <br><input type=text size="60" name="address">
		<BR>]
	print [<br>" Phone: " <br><input type=text size="60" name="phone"><BR>]
	print [<br>" Email: " <br><input type=text size="60" name="email"><BR>]
	print [<br>" Age: " <br><input type=text size="60" name="age"><BR>]
	print [<br>" Language: " <br><input type=text size="60" name="language">
		<BR>]
	print [<br>" Height: " <br><input type=text size="60" name="height"><BR>
		<BR>]
	print [" Other Information/Notes: " <br>]
	print [<textarea name=otherinfo rows=5 cols=50></textarea><BR><BR>]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Post New Member Info">]
	print [</FORM>]

	print [</td></tr></table></center>]
	print read %footer.html

=image rebol_tutorial/member4.png


I integrated the following code into index.cgi, to read and add the info from the above form to the database:

	; here's the default code used to read any data from an html form:

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]
	selection: decode-cgi read-cgi

	; make sure at least a user name and password was entered:

	if selection/2 <> none [
        if (selection/2 = "") or (selection/4 = "") [
		print {
			<strong>You must include at least
			 a name and password.</strong>
			<br><br>Press the [BACK] button 
			in your browser to try again.
		}
		print [</td></tr></table></center>]
		print read %footer.html
		halt
	]

	; now create a new entry block to add to the database:

	entry: copy []
	append entry selection/2 	; name
	; the time on the server is 3 hours different then our local time:
	append entry to-string (now + 3:00)
	append entry selection/6 	; address
	append entry selection/8 	; phone
	append entry selection/10 	; email
	append entry selection/12 	; age
	append entry selection/14 	; language
	append entry selection/16 	; height
	append entry selection/18 	; other info
	append entry selection/4 	; password
	append/only entry [
		{<a href = "./default.jpg" target=_blank>
		<IMG align=baseline alt="" border=0 hspace=0 src="./default.jpg"
		width="160" height="120"></a>}
	]

	; append the new entry to the database, and notify the user:

	append/only tail bbs entry
	save %bb.db bbs
	print {<strong>New Member Added.</strong>
		Click "Edit" to upload a photo.}
	print [</td></tr></table></center>]
	print read %footer.html

	; now display the member page with the new info refreshed:

	wait :00:04
	refresh-me: {
		<head><title></title>
		<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./index.html"></head>
	}
	print refresh-me
	quit

=image rebol_tutorial/member5.png
=image rebol_tutorial/member5b.png
=image rebol_tutorial/member5c.png
=image rebol_tutorial/member5d.png

Now we can finish up the rest of the work in step 3 of our outline.  The pseudo code in my outline reads "The pages where the users edit their information will be forms that display the information currently in the selected entry, without the password.  When the user submits the new password and updated info, the CGI checks that the submitted password matches the existing password for that entry, and then replaces the old block with the new one, in the database text file".  I've already created links in index.html to reference the "edititemnumber" (created earlier using a counter variable in the foreach loop of index.cgi).  And we've already created the basic data entry form to add new users.  So we can check for the edititemnumber, and fill the form with appropriate items from the database.  In order to find and replace the original entry in the database, once the user has made changes, the original values also need to be submitted as additional hidden form fields, along with the user-editable values in the form's text fields.  Here's what I came up with:

	if selection/2 = "edititemnumber" [
		; pick the correct entry from the database, using the submitted
		; counter variable from the "edit" link in index.cgi:
		selected-block: pick bbs (
			(length? bbs) - (to-integer selection/4) + 1
		)
		print [<font size=5>" Edit Your Existing Member Information:"</font>]
		print "         "
		; here's a link we'll need for the section of the outline that
		; enables image uploading:
		print rejoin [
			{<a href="./upload.cgi?name=} first selected-block 
			{">Upload Image (Add or Change)</a><hr>}
		]
		print "         "
		print "<br><br>"
		print {<strong><i>PASSWORD REQUIRED TO EDIT! </i></strong> 
			(Enter it in the field below.)}
		print "<br><br>"
		print [<FORM method="post" ACTION="./edit.cgi">]
		print rejoin [
			{<br> Your Name:  <br>
				<input type=text size="60" name="username" value="}
			 first selected-block {"><BR>}
		]
		print [<br> <strong> " Member Password " </strong> "(same 
			as when you created the original account): " <br>
			<input type=text size="60" 	name="password"><BR>
		]
		print rejoin [
			{<br> Address:  <br><input type=text size="60" 
				name="address" value="} 
			pick selected-block 3 {"><BR>}
		]
		print rejoin [
			{<br> Phone:  <br><input type=text size="60" 
				name="phone" value="} 
			pick selected-block 4 {"><BR>}
		]
		print rejoin [
			{<br> Email:  <br><input type=text size="60" 
				name="email" value="} 
			pick selected-block 5 {"><BR>}
		]
		print rejoin [
			{<br> Age:  <br><input type=text size="60" 
				name="age" value="} 
			pick selected-block 6 {"><BR>}
		]
		print rejoin [
			{<br> Language:  <br><input type=text size="60"
				name="language" value="} 
			pick selected-block 7 {"><BR>}
		]
		print rejoin [
			{<br> Height:  <br><input type=text size="60" 
				name="height" value="} 
			pick selected-block 8 {"><BR><BR>}
		]
		print [" Other Information/Notes: " <br>]
		print [<textarea name=otherinfo rows=5 cols=50>]
		print [pick selected-block 9]
		print [</textarea><BR><BR>]
		print rejoin [
			{<input type="hidden" name="original_username" value="}
			 pick selected-block 1 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_date" value="}
			pick selected-block 2 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_address" value="}
			 pick selected-block 3 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_phone" value="}
			pick selected-block 4 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_email" value="}
			pick selected-block 5 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_age" value="} 
			pick selected-block 6 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_language" value="} 
			pick selected-block 7 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_height" value="} 
			pick selected-block 8 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_otherinfo" value="} 
			pick selected-block 9 {">}
		]
		print [<INPUT TYPE="SUBMIT" NAME="Submit" 
			VALUE="Update Member Information">]
		print [</FORM>]
		print [</td></tr></table></center>]
		print read %footer.html
		quit
	]

=image rebol_tutorial/member6.png

I added the above code to index.cgi.  Notice that the above form points to edit.cgi, which actually does the work of checking the password and processing the changes in the database.  It has all the standard header and read-cgi code, and then it uses a foreach loop to look for a database entry that has all the same data as that submitted by the hidden items in the form above, and checks the original password in that entry.  In comparing the original password with that entered by the user, I also enabled an administrator password "blahblah".  I also added the code to email users their password, in case they've forgotten it (just send the stored password to the email address contained in the database, for that entry):

	#! /home/path/public_html/rebol/rebol -cs	
	Rebol []
	print "content-type: text/html^/"
	print read %header.html

	bbs: load %bb.db

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]
	selection: construct decode-cgi read-cgi

	; get password from the entry submitted:

	foreach message bbs [
		if all [
			find message selection/original_username 
			find message selection/original_date 
			find message selection/original_address 
			find message selection/original_phone 
			find message selection/original_email 
			find message selection/original_age 
			find message selection/original_language 
			find message selection/original_height 
			find message selection/original_otherinfo
		] [read-pass: message/10]
	]
	
	; save the old block:

	old-message:  to-block reduce [
		selection/original_username 
		selection/original_date 
		selection/original_address 
		selection/original_phone 
		selection/original_email 
		selection/original_age 
		selection/original_language 
		selection/original_height
		selection/original_otherinfo 
		read-pass
	]
	
	; so that the original pass is not replaced by "blahblah":

	either selection/password = "blahblah" [
		entered-pass: read-pass
	] [
		entered-pass: selection/password
	]
	
	; create the new entry for the database:

	new-message:  to-block reduce [
		selection/username 
		selection/original_date
		 selection/address
		 selection/phone
		 selection/email
		 selection/age
		 selection/language
		 selection/height
		 selection/otherinfo
		 entered-pass
	]
	
	; check the password, and replace:

	if selection/password <> "" [
		either (
			read-pass = selection/password
		) or (
			selection/password = "blahblah"
		) [
			foreach message bbs [replace message old-message new-message]
		] [
			print {
				<strong>Forgot your member password?</strong> <br><br>
				It's being emailed to the address for this entry, right now...
				Wait for this page to refresh, then <strong>check your email!
				</strong>
			}
			print read %footer.html
			wait 3
			set-net [user@website.com smtp.website.com]
			send (to-email selection/original_email) (to-string rejoin [
				"Forgot your member password?" newline newline 
				trim {Someone was editing an entry with this email address, 
					but the incorrect password was used.  Here is the correct
					password, in case you've forgotten:}
				 newline newline read-pass
			])
		]
	]
	save %bb.db bbs

	; diplay the edited results on the main user page:

	refresh-me: {
		<head><title></title>
		<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./index.cgi"></head>
	}
	print refresh-me
	print read %footer.html

=image rebol_tutorial/member7.png

Here, I decided to add the backup code.  What I did was create a folder for all previous versions of the database text file to be saved as backups.  Then I created a text file that contained the number of the current backup file (to start out, that text file just contained the number 1).  Then, I incremented that number and saved it back to that number file.  And finally, I saved a copy of the current database to a text file with the current backup number appended to the filename.  This code went right before bb.db was saved in the CGI above:

	backup-num: load %backup-num.txt
	backup-num: backup-num + 1
	write %backup-num.txt backup-num
	filename: to-file rejoin ["./backup/bb-" (to-string backup-num) ".txt"]
	save filename bbs

The following code is basically a simpler version of the editing code above, which allows users to delete an entry.  All that's needed in this case is the username and password.  All the other info is passed along to delete.cgi as hidden fields.  This code gets added to index.cgi:

	if selection/2 = "deleteitemnumber" [
		selected-block: pick bbs (
			(length? bbs) - (to-integer selection/4) + 1
		)
		print [<font size=5>" Delete An Existing Member Account:"</font><hr>]
		print [<FORM method="post" ACTION="./delete.cgi">]
		print rejoin [
			{<br> Your Name:  <br>
				<input type=text size="60" name="username" value="} 
			first selected-block {"><BR>}
		]
		print [<br>" Member Password (
			same as when you created the original account): " 
			<br><input type=text size="60" 	name="password"><BR><BR>
		]
		print rejoin [
			{<input type="hidden" name="original_username" value="} 
			pick selected-block 1 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_date" value="} 
			pick selected-block 2 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_address" value="} 
			pick selected-block 3 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_phone" value="} 
			pick selected-block 4 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_email" value="} 
			pick selected-block 5 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_age" value="} 
			pick selected-block 6 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_language" value="} 
			pick selected-block 7 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_height" value="} 
			pick selected-block 8 {">}
		]
		print rejoin [
			{<input type="hidden" name="original_otherinfo" value="} 
			pick selected-block 9 {">}
		]
		print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Delete Member Info">]
		print [</FORM>]
		print [</td></tr></table></center>]
		print read %footer.html
		quit
	]

=image rebol_tutorial/member8.png

Here's the code for delete.cgi, which the above form points to, and which does the actual work of deleting the selected block from the database (it's basically a variation of the edit.cgi script above):

	#! /home/path/public_html/rebol/rebol -cs	
	Rebol []
	print "content-type: text/html^/"
	print read %header.html

	bbs: load %bb.db

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]
	selection: construct decode-cgi read-cgi

	foreach message bbs [
		if all [
			find message selection/original_username 
			find message selection/original_date 
			find message selection/original_address 
			find message selection/original_phone 
			find message selection/original_email 
			find message selection/original_age
			find message selection/original_language 
			find message selection/original_height 
			find message selection/original_otherinfo
		] [read-pass: message/10] 
	]

	old-message:  to-block reduce [
		selection/original_username 
		selection/original_date 
		selection/original_address 
		selection/original_phone 
		selection/original_email 
		selection/original_age 
		selection/original_language 
		selection/original_height 
		selection/original_otherinfo 
		read-pass
	]

	if selection/password <> "" [
		if (
			read-pass = selection/password
		) or (
			selection/password = "blahblah"
		) [	
			backup-num: load %backup-num.txt
			backup-num: backup-num + 1
			write %backup-num.txt backup-num
			filename: to-file rejoin [
				"./backup/bb-" (to-string backup-num) ".txt"
			]
			save filename bbs

			foreach message bbs [replace message old-message ""]
		]
	]

	remove-each message bbs [
		any [
			message = [""] 
			(all [
				message/1 = "" message/2 = "" message/3 = "" message/4 = ""
				message/5 = "" message/6 = "" message/7 = "" message/8 = ""
				message/9 = ""
				]
			)
		]
	]

	save %bb.db bbs

	refresh-me: {
		<head><title></title>
		<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./index.cgi"></head>
	}
	print refresh-me
	print read %footer.html

Creating the image upload page for step #4 in our outline was a bit of a challenge.  That's because Rebol has no built-in way to accept binary data from html forms (images, in this case), called "form-multipart" data.  I searched the mailing list and quickly found a solution at <a href="http://www.rebol.org/cgi-bin/cgiwrap/rebol/ml-display-thread.r?m=rmlKVSQ" target=_blank>http://www.rebol.org/cgi-bin/cgiwrap/rebol/ml-display-thread.r?m=rmlKVSQ</a>.  Andreas Bolka's "decode-multipart-form-data" did exactly what I needed.  That function converts the data entered by a user, as well as the files they choose and upload from their hard drive, into a friendly and easy to use Rebol object.

	#! /home/path/public_html/rebol/rebol -cs
	REBOL [Title: "HTTP File Upload"]
	print "content-type: text/html^/"
	print read %header.html

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]

	; here's Andreas's magic function to read form/multipart data:

	decode-multipart-form-data: func [
	    p-content-type
	    p-post-data
	    /local list ct bd delim-beg delim-end non-cr non-lf non-crlf mime-part
	] [
	    list: copy []
	    if not found? find p-content-type "multipart/form-data" [ return list ]

	    ct: copy p-content-type
	    bd: join "--" copy find/tail ct "boundary="
	    delim-beg: join bd crlf
	    delim-end: join crlf bd

	    non-cr:     complement charset reduce [ cr ]
	    non-lf:     complement charset reduce [ newline ]
	    non-crlf:   [ non-cr | cr non-lf ]
	    mime-part:  [
	        ( ct-dispo: content: none ct-type: "text/plain" )
	        delim-beg ; mime-part start delimiter
	        "content-disposition: " copy ct-dispo any non-crlf crlf
	        opt [ "content-type: " copy ct-type any non-crlf crlf ]
	        crlf ; content delimiter
	        copy content
	        to delim-end crlf ; mime-part end delimiter
	        ( handle-mime-part ct-dispo ct-type content )
	    ]

	    handle-mime-part: func [
	        p-ct-dispo
	        p-ct-type
	        p-content
	        /local tmp name value val-p
	    ] [
	        p-ct-dispo: parse p-ct-dispo {;="}

	        name: to-set-word (select p-ct-dispo "name")
	        either (none? tmp: select p-ct-dispo "filename")
	               and (found? find p-ct-type "text/plain") [
	            value: content
	        ] [
	            value: make object! [
	                filename: copy tmp
	                type: copy p-ct-type
	                content: either none? p-content [none] [copy p-content]
	            ]
	        ]

	        either val-p: find list name
	            [change/only next val-p compose [(first next val-p) (value)]]
	            [ append list compose [ (to-set-word name) (value) ] ]
	    ]

	    use [ ct-dispo ct-type content ] [
	        parse/all p-post-data [ some mime-part "--" crlf ]
	    ]

	    list
	]

	; now we can put the uploaded binary, and all the text entered by the
	; user via the html form, into a Rebol object.  we can refer to the
	; uploaded photo using the syntax:  cgi-object/photo/content

	post-data: read-cgi
	cgi-object: construct decode-multipart-form-data (
		system/options/cgi/content-type copy post-data
	)

	; I created a "./files" subdirectory to hold these images.  Now
	; write the file to the web server using the original filename,
	; but without any Windows path characters, and notify the user:

	adjusted-filename: copy cgi-object/photo/filename
	adjusted-filename: replace/all adjusted-filename "/" "-"
	adjusted-filename: replace/all adjusted-filename "\" "-"
	adjusted-filename: replace/all adjusted-filename " " "_"
	adjusted-filename: replace/all adjusted-filename ":" "_"
	adjusted-filename: to-file rejoin ["./files/" adjusted-filename]
	write/binary adjusted-filename cgi-object/photo/content
	print [<strong>]
	print {Upload Complete.  }
	print [</strong>]
	print [<br><br>]

	; now add an html link to this file, to the database:

	bbs: load %bb.db	
	entry: copy []
	link-added: rejoin [
		{<a href = "} to-string adjusted-filename {" target=_blank>}
		{<IMG align=baseline alt="" border=0 hspace=0 src="} 
		to-string adjusted-filename 
		{" width="160" height="120">} </a>
	]  ; display image inline
	append entry link-added
	foreach message bbs [
		if (all [
			cgi-object/username = message/1 
			cgi-object/password = message/10
		]) [
			if ((length? message) < 11) [append message ""] 
			message/11: entry
		]
	]
	save %bb.db bbs

	; show additions by refreshing the index.cgi page:

	refresh-me: {
		<head><title></title>
		<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./index.cgi"></head>
	}
	print refresh-me
	print read %footer.html

=image rebol_tutorial/member10.png
=image rebol_tutorial/member10b.png


The last step in the outline was easy.  I just used the code from the previous case study (the password protected CGI text editor), and pointed it to the database text file.  I also looped through the backup directory and printed links to each of the files in that directory, so that any of the previous backup files could be easily copied and pasted into the editor, to revert the database to a previous state.

	#! /home/path/public_html/rebol/rebol -cs	
	Rebol []
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Edit Database!!!"</TITLE></HEAD><BODY>]

	read-cgi: func [/local data buffer][
	    switch system/options/cgi/request-method [
	        "POST" [
	            data: make string! 1020
	            buffer: make string! 16380
	            while [positive? read-io system/ports/input buffer 16380][
	                append data buffer
	                clear buffer
	            ]
	        ]
	        "GET" [data: system/options/cgi/query-string]
	    ]
	    data
	]

	selection: decode-cgi read-cgi

	; if schedule.txt has been edited and submitted:

	if ((selection/2 = "save") or (selection/2 = "save")) [ 
		; save newly edited schedule:
		write %./bb.db selection/4
		print ["Database Saved."]
		; print {<META HTTP-EQUIV="REFRESH" CONTENT="0; URL=./bb.db">}
		quit
	]

	; if user is just opening page (i.e., no data has been submitted 
	; yet), request user/pass:

	if ((selection/2 = none) or (selection/4 = none)) [
		print [<strong>"W A R N I N G  -  Private Server, Login Required:"
			</strong><BR><BR>]
		print [<FORM ACTION="./editor.cgi">]
		print [" Username: " <input type=text size="50" name="name"><BR><BR>]
		print [" Password: " <input type=text size="50" name="pass"><BR><BR>]
		print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
		print [</FORM>]
		quit
	]

	; check user/pass, end if incorrect:

	response: false
	if ((selection/2 = "username") and (selection/4 = "password")) [
		response: true
	]
	if response = false [print "Incorrect Username/Password." quit]

	; if user/pass is ok, go on (backup before changes are made):

	cur-time: to-string replace/all to-string now/time ":" "-"
	schedule_text: read %./bb.db
	write to-file rejoin [
		"./backup/" now/date "_" cur-time ".txt"
	] schedule_text

	; here's the form that lets the user edit the text:

	print [<center>]
	print [<strong>"Be sure to click [SUBMIT] when done:"</strong><BR><BR>]
	print [<strong>"(This will OVERWRIGHT the current database!)"</strong>
		<BR><BR>]
	print [<FORM method="post" ACTION="./editor.cgi">]
	print [<INPUT TYPE=hidden NAME=submit_confirm VALUE="save">]
	print [<textarea cols="100" rows="25" name="contents">]
	print [schedule_text]
	print [</textarea><BR><BR>]
	print [<INPUT TYPE="SUBMIT" NAME="Submit" VALUE="Submit">]
	print [</FORM>]
	print [</center>]
	print {<br><br><br><br><br><br><br><br><hr>}

	; here's a linked listing of all the backup files available for
	; copy/paste:

	foreach file (read %./backup/) [
		print rejoin [
			{<a href="./backup/} file {" target=_blank>} file {</a> }]
		]
	print [</BODY></HTML>]

=image rebol_tutorial/member11.png
=image rebol_tutorial/member11b.png

That's it - the web site and all its features are complete!  You can see a live demo at <a href="http://guitarz.org/tester" target=_blank>http://guitarz.org/tester</a> and download the complete set of scripts in this case study at <a href="http://guitarz.org/tester/member_board.zip" target=_blank>http://guitarz.org/tester/member_board.zip</a>.


---Case 10 - A CGI Event Calendar

My friend liked the system above so much that we adapted it for use as an online classifieds page and also as an event calendar listing on the same web site.  For the calendar, we just changed the database fields to:  Event, Date/Time, Location, Contact Name, Contact Phone, Contact Email, Requirements.  Links and display text such as "Join Now" were simply changed to "Enter A New Event", etc.

The calendar was in use for quite a while and functioning beautifully, when my friend asked if I could create an event page that actually looked like a normal calendar display, instead of just a list of events.  Ok, so here's how I broke down the basic creative process:

# Design an html page that looks like a calendar.  My guiding thought was that the CGI program which printed this page would include a loop that runs through the days of the current month, and prints html table rows and cells for each numbered day, one row per group of days Sunday-Saturday.

# For each day of the month printed in the table above, search through the database for dates that match the current table cell being printed, and then print the event description (first item in the block for that event), with a link to the event listing page.

As always, I began the process by looking for some existing code that may be useful in my design (it's always a good idea to avoid reinventing the wheel).  My work was immediately made easy, when I searched for "calendar" at rebol.org.  I quickly found the <a href="http://www.rebol.org/cgi-bin/cgiwrap/rebol/view-script.r?script=html-calendar.r" target=_blank>HTML calendar</a> by Bohdan Lechnowsky, which prints out an html calendar display for the current month.  It uses a table design created by loops, much like I had imagined.  I read through Bohdan's code, made some comments as to what each section accomplished, and made some changes to the design of the tables so that the calendar stretched to fit the entire page of the browser.  I also wrote a line of code to visually highlight the current day (so that today's date is always printed in a unique color).  You can see the original code at the link above, and here are my tweaks and comments:

	#! /home/path/public_html/rebol/rebol -cs	
	Rebol []
	print "content-type: text/html^/"
	print {<HTML><HEAD><TITLE>Event Calendar</TITLE></HEAD><BODY>}

	; print month + year header:

	date: now/date
	html: copy rejoin [
		{<CENTER><TABLE border=1 valign=middle width=99% height=99%>
			<TR><TD colspan=7 align=center height=8%><FONT size=5>}
		pick system/locale/months date/month {  } date/year
		{</FONT></TD></TR><TR>}
	]

	; print days header:

	days: ["Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat"]
	foreach day days [
		append html rejoin [
			{<TD bgcolor="#206080" align=center width=10% height=5%>
			<FONT face="courier new,courier" color="FFFFFF" size="+1">}
			day 
			{</FONT></TD>}
		]
	]
	append html {</TR><TR>}

	; print non-month days at the begining of month in gray:

	sdate: date  sdate/day: 0  
	loop sdate/weekday // 7 + 1 [append html {<TD bgcolor=gray></TD>}]

	; print every other day, with the current day in a unique color:

	while [sdate/day: sdate/day + 1 sdate/month = date/month][
		append html rejoin [
			{<TD bgcolor="#}
			; I ADDED THIS CODE TO VISUALLY HIGHLIGHT THE CURRENT DAY:
			either date/day = sdate/day ["AA9060"]["FFFFFF"]
			{" height=14% valign=top>} sdate/day
			{</TD>}
		]
		if sdate/weekday = 6 [append html {</TR><TR>}]
	]

	; print non-month days at the end of month in gray:

	loop 7 - sdate/weekday [append html rejoin [{<TD bgcolor=gray></TD>}]]

	; finish and print:

	append html {</TR></TABLE></CENTER></BODY></HTML>}
	print html 

=image rebol_tutorial/calendar1.png

With step 1 in my outline done, I completed the second and last step by adding the code below.  It was really simple.  First, I created a variable called "event-labels" which would hold any events in the database that occurred on a given day.  I put this inside Bohdan's while loop, which ran through each day of the month and printed the calendar table cells for each separate day).  I used a foreach loop to compare each date found in the database to the current date being added to the calendar.  If there's a match, "event-labels" is rejoined with the first item in the event entry (the description of the event), and linked to the event display.  The string of text in event-labels is then later printed into the table, within the current day's cell.

	while [sdate/day: sdate/day + 1 sdate/month = date/month][
		event-labels: {}
		foreach entry bbs [
			date-in-entry: 1-Jan-1001
			attempt [date-in-entry: (to-date entry/3)]
			if (date-in-entry = sdate) [
				event-labels: rejoin [
					{<font size=1>}
					event-labels
					"<strong><br><br>"
					{<a href="http://website.com/path/calendar">}
					entry/1 
					{</a>}
					"</strong>"
					{</font>}
				]
			]
		]

That's it!  Here's the whole script:

	#! /home/path/public_html/rebol/rebol -cs
	Rebol []
	print "content-type: text/html^/"
	print {<HTML><HEAD><TITLE>Event Calendar</TITLE></HEAD><BODY>}

	bbs: load %bb.db
	date: now/date
	html: copy rejoin [
		{<CENTER><TABLE border=1 valign=middle width=99% height=99%>
			<TR><TD colspan=7 align=center height=8%><FONT size=5>}
		pick system/locale/months date/month {  } date/year
		{</FONT></TD></TR><TR>}
	]

	days: ["Sun" "Mon" "Tue" "Wed" "Thu" "Fri" "Sat"]
	foreach day days [
		append html rejoin [
			{<TD bgcolor="#206080" align=center width=10% height=5%>
			<FONT face="courier new,courier" color="FFFFFF" size="+1">}
			day 
			{</FONT></TD>}
		]
	]
	append html {</TR><TR>}

	sdate: date  sdate/day: 0  
	loop sdate/weekday // 7 + 1 [append html {<TD bgcolor=gray></TD>}]

	while [sdate/day: sdate/day + 1 sdate/month = date/month][
		event-labels: {}
		foreach entry bbs [
			date-in-entry: 1-Jan-1001
			attempt [date-in-entry: (to-date entry/3)]
			if (date-in-entry = sdate) [
				event-labels: rejoin [
					{<font size=1>}
					event-labels 
					"<strong><br><br>"
					{<a href="http://website.com/path/calendar">}
					entry/1 
					{</a>}
					"</strong>"
					{</font>}
				]
			]
		]
		append html rejoin [
			{<TD bgcolor="#}
			either date/day = sdate/day ["AA9060"]["FFFFFF"]
			; HERE, THE EVENTS ARE PRINTED IN THE APPROPRIATE DAY:
			{" height=14% valign=top>} sdate/day event-labels
			{</TD>}
		]
		if sdate/weekday = 6 [append html {</TR><TR>}]
	]

	loop 7 - sdate/weekday [append html rejoin [{<TD bgcolor=gray></TD>}]]

	append html {</TR></TABLE></CENTER></BODY></HTML>}
	print html

=image rebol_tutorial/calendarb.png
=image rebol_tutorial/calendar.png


---Case 11 - A Backup Music Generator (Chord Accompaniment Player)

In my music lesson business, one of the things we teach is improvisation and "jam session" skills.  In order to practice, students need to be able to play along with recordings of various chord progressions.  Serious musicians traditionally purchase album recordings designed specifically for that purpose.  A significant industry exists to provide such "backing track" recordings, but for beginning students to experiment with basic improvisation skills, I decided to create a simple program they could use to hear and play along with a wide variety of chords, at different tempos, in all 12 of the musical keys.  Building such a program with Rebol was easy.  Designing an application to play pre-recorded chords from a given text list took less than a half hour.  

Here's the basic outline I came up with to get started (a very basic knowledge of chord notation is required for this case study):

# Record wave files of major, minor, dominant 7th, half diminished, diminished 7th, minor 7th, and major 7th chords on all 12 root notes (A, A#, B, C, C#, D, D#, E, F, F#, G, and G#), along with a few other commonly used chord voicings.  The recordings all needed to be of short block chords, of the exact same duration and volume.

# Compress and embed the wave files using the binary embedder (our old friend :).

# Load each sound into memory and give each one a variable label.

# Create a GUI with text fields for the chords to play, and the tempo.  Add "play" and "stop" buttons to control the action.

# When the "play" button is clicked, play the wave data for each chord in the given progression, using the given timing gap.  There will need to be some multitasking code to enable the looping chord progressions to be stopped.

# Add some buttons to save and load the chord progressions, along with a button to provide some help/instructions.

The first step was mechanical - no programming required.  I recorded the sounds of all twelve major, minor, and dominant 7th chords using my favorite recording software and my guitar.  I saved each sound as a separate wave file in 1 directory on my hard drive (I later recorded a much larger collection of chords, but this was enough to get started).

For step 2 in the outline, I used a variation of the binary embedder program from the earlier freecell case study to loop through the files in the directory:

	rebol []

	system/options/binary-base: 64
	sounds: copy []
	foreach file load %./  [
		print file
		uncompressed: read/binary file
		compressed: compress to-string uncompressed
		if ((length? uncompressed) > 5000) [
			append sounds compressed
		]
	]
	editor sounds

It provided one huge block of data containing every one of those sounds in embedded format.  Here's an example of what 1 chord's data looked like:

	64#{
	eJxEd2VUW833ddyIE8fdHYoVCi1S2mJ1F+ruTvvU3d3dC1RpC7S4ExwSJFgSSEhC
	EmIQIvfl9//yrr32mTMz58vcNXfP2XOTEhIQx0CgRbEL4zds32dPBIFA4EnEZYFA
	FxaDQRAQEbRuzb41/EwQqBj4C+QBFUARUDyJAqB8MpYB1UDtJGsA9mSsn0Q70AQ0
	AG1AM9AKcIGOSXRPggv0TEIA9E+iD+gE+MDAJLqBXoD3f7EbEE5m/6vpnFzvB0ST
	s/7J+sHJTDKJocl9/uQ4MgkVoJiEBFADo5O5bjJq/o/aSf4vaidnemAMmAAMgBEw
	TVYAkyNk8izA5AoAwEEm4H8ng4DgkyvQSYJAFqC7wCPgCfAdsAM2A1+AfOA2KBa0
	AtQC5AAbQQtA20CvQUGgIpAjeDdIC54H3IJ0m38A5yBVhhHwTUifCTBGwGZCbkzs
	N58BP4CnQzTj/qYZ4C2wfpQIHGeiTViP3zHfg1mg9qHWw9aB+01l42zddh15bJ4h
	wnwCIkCtxCdRlPQ8ZikrzGoDs502YXmEDJD9LadaHqagqKPUi7QHVCENSvEhVRBa
	cW9xXRgd8iXSHtWD8EaUInwRYuRWVBZiHXIL0hMViFyAaEMb0ERMhgVgIcKY0WqU
	P/YlToE0YKxwNzGf0Bn4t8StmP/gzpi3ZDBpBtaEGEFIkGqUFltHrrQudJ7l8ccj
	y+2QW6DHd6+rvha+nz3x7v2u5a533Mrcf7lnuKe6LnX66bzBxd2lxfWzC99pk9NP
	x7uOKrtI68e2lvZSuyG7XNtKO4OtnU2t9SqrG0xn2lPKFvpVK8C60rrDLsYB63jH
	ZgWTRl9EMZDriOUkV6IfsYJotGym2zB7GN/pRGYJq9q6hPWGZWbuZWQwuaxR1jGr
	nbYmK5h1EOs+FcTwI+8n9OJmEu7iHQiOpG04Co2Be029Q1hE3GmTjPlHmUZKJ+TB
	nQnv8aPIWsvpMCwhE3XQ/AG3EqEw/YH5I/FGjPklco5BMmFC9k/s058BkOpWvWCi
	cvSUtg5x0+Lg2DTFC3UIoNULTcHwp5BxDAhE0+7RuwN9RjJ4zNBp3gm/Cx0zZSMP
	ElYZziPfkMjQNKVqRI0YQ0PBKci/NBRLjgRMd8fI430mF1XD0JBcb2KDooG9JvjE
	H9XpkfvygUEPnrQre/iz+vtYyQTD2Ky7OPxI3qSdZrw8XgLnU6KoD0nWpibVIq1I
	6waEI9Jh11B/cR9pvx1W2P4gA5YA+RfGFf0aeQ+VjyyErYDAwLcMRSPl8u9jb0E7
	sTHEFbRz9BX0b8z3lFHmbaqv9W1nsrW1a6rjeasGVpgj1TWEaiCcxlXh+VRni1zc
	BE4GuWLaoFkHuBGeY+8gX9uEek/znen910npNuQodf7j8sze4DLi/y14RgAutj7+
	RczPaTDvtY4i+1GqEG0YrxivH0UJrHoPcJZxgcbRpitcYj9M8wo8An+Gy8BZTvwc
	AdT3VXNHm0wjpmazw9iViYvg14oHI1ZGR6j72JeR72KS+JhqlzRWU66mjdirVit3
	ygolClmWMEUeO/hSETt0kBerei3eJ7fu9ZdjVXe7domnjFQJuNxG7vr+6/2LxW/H
	EuRtvcVtmV0/+MV9Qs2Y6n7fgOY5wRV9jHWD4Qis9lwdeAgv1bwTFYzx0c+QOyXM
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	} 

For step 3, I placed the now-familiar "load to-binary decompress" code in front of each embedded sound file data chunk (to decompress the data and load the sound into memory for quick use).  I gave each chord it's appropriate chord label (A major, Bb major, C minor, G7, etc.).  In doing so, I decided to use all flat symbols for any root notes that had accidentals (i.e., F# = Gb, C# = Db, etc. (no sharps)).  Here's how the code for the A major and Bb minor chords looked:

	a: load to-binary decompress 64#{
	eJxEd2VUW833ddyIE8fdHYoVCi1S2mJ1F+ruTvvU3d3dC1RpC7S4ExwSJFgSSEhC
	EmIQIvfl9//yrr32mTMz58vcNXfP2XOTEhIQx0C ...

	bbm: load to-binary decompress 64#{
	eJwstwVcU9//P757d9eMbQwYMWB0d4cgraCogIgdKHY38lb0rZjYXW8VOxGbDukc
	3TVqCWPdv32+///j9Tj3nnvuOa9+Pc85iQtjYkr ...


Here was the full list of chord labels I created (the underscore symbol was a label that I gave to a silent sound that I recorded, to be used for beats of rest).  I manually labeled each of the chord data with the following labels (using my text editor's search, copy, and paste facilities, that took about ten minutes):

	a bb b c db d eb e f gb g ab 
	am bbm bm cm dbm dm ebm em fm gbm gm abm 
	a7 bb7 b7 c7 db7 d7 eb7 e7 f7 gb7 g7 ab7 
	adim7 bbdim7 bdim7 cdim7 dbdim7 ddim7 
	ebdim7 edim7 fdim7 gbdim7 gdim7 abdim7
	am7b5 bbm7b5 bm7b5 cm7b5 dbm7b5 dm7b5 
	ebm7b5 em7b5 fm7b5 gbm7b5 gm7b5 abm7b5 
	am7 bbm7 bm7 cm7 dbm7 dm7 ebm7 em7 fm7 gbm7 gm7 abm7
	amaj7 bbmaj7 bmaj7 cmaj7 dbmaj7 dmaj7
	ebmaj7 emaj7 fmaj7 gbmaj7 gmaj7 abmaj7
	_ 


Step 4 in the outline just required building the following simple GUI.  It consists of a few labels, a text area to hold the user-entered chords, a text field for the tempo, and a couple buttons to stop and start the music action.  I also decided to add the buttons from step 6 - I even put all that code in here - all that was required was to save and load the contents of the text area.  Simple:

	view center-face layout [
		across
		h2 "Chords:"
		tab
		chords: area 392x300 trim {}
		return
		h2 "Delay:"
		tab
		tempo: field 50 "0.35" text "(seconds)"
		tabs 40 tab
		btn "PLAY" []
		btn "STOP" []
		btn "Save" [save to-file request-file/save chords/text]
		btn "Load" [chords/text: load read to-file request-file show chords]
		btn "HELP" [
			alert {}
		]
	]

Now all that's left is step 5.  I started by loading the user entered list of chords into a block:

	sounds: to-block chords/text

I also gave a label to the tempo, and made sure it was treated as a decimal value:

	the-tempo: to-decimal tempo/text

I took the play-sound function that you've seen earlier, and used its code inside a foreach loop that played each of the sounds in the user provided list (now in the "sounds" block).  Because those chord labels now refer to actual pieces of sound data that can be inserted and played directly by the sound port, this was simple:

		wait 0
		sound-port: open sound://
		foreach sound sounds [
			do rejoin ["insert sound-port " reduce [sound]]
			wait sound-port
			wait the-tempo 
		]

I wrapped the above foreach loop in a forever loop, because I wanted the chord progression to repeat continuosly.  To stop the music, I first thought that I'd need some multitasking code, but it turns out that it was simpler than expected.  All I did was create a flag variable (the word "play"), which was set to false when the GUI stop button was clicked.  Inside the above foreach loop, I checked to see if the play variable had been set to false, and if so, broke out of the loop.  The stop button then simply closed the sound port after setting the variable flag to false.  Below is the full code for the PLAY and STOP buttons in the GUI. Simple :)

	btn "PLAY" [
		play: true
		the-tempo: to-decimal tempo/text
		sounds: to-block chords/text
		wait 0
		sound-port: open sound://
		forever [
			foreach sound sounds [
				if play = false [break]
				do rejoin ["insert sound-port " reduce [sound]]
				wait sound-port
				wait the-tempo 
			]
			if play = false [break]
		]
	]
	btn "STOP" [
		play: false
		close sound-port
	]


To finish up the program, I added some instruction text to the alert which pops up when the help button is clicked, and I put in an example chord progression that appears in the text area by default (the chords to "Hotel California").  In testing the program, I realized that if the GUI was closed before the music was stopped, play would continue without any way to stop it.  The operating system's task manager was the only way to end the music at that point.  To fix that bug, I added some code to trap the close button and stop the music (set the play flag to false and close the sound port), along with a request to "really close the program?".  You've seen that sort of code in several previous examples.

Here's the final program (a shortened version, WITHOUT the chord data required to play the example):

	rebol [title: "Chord Accompaniment Player"]

	play: false
	insert-event-func [
	    either event/type = 'close [
			if play = true [play: false close sound-port]
			really: request "Really close the program?"
			if really = true [quit]
	    ][
			event
		]
	]

	{
		.
		.
		.

		all the chord data goes here

		bm: load to-binary decompress 64#{
		eJw8dgdUU0/w7k0vJNTQe++9SpUqCogIiiKgIIq9YAdU7L397NgVRAQEpEnvvfca
		CCUhQEhCIJUk9/E/7/3f2bN7z92d...
		} 

		.
		.
		.

	}

	view center-face layout [
		across
		h2 "Chords:"
		tab
		chords: area 392x300 trim {
			bm bm bm bm
			gb7 gb7 gb7 gb7
			a a a a 
			e e e e
			g g g g
			d d d d 
			em em em em
			gb7 gb7 gb7 gb7
			g g g g
			d d d d
			gb7 gb7 gb7 gb7
			bm bm bm bm
			g g g g
			d d d d
			em em em em
			gb7 gb7 gb7 gb7
		}
		return
		h2 "Delay:"
		tab
		tempo: field 50 "0.35" text "(seconds)"
		tabs 40 tab
		btn "PLAY" [
			play: true
			the-tempo: to-decimal tempo/text
			sounds: to-block chords/text
			wait 0
			sound-port: open sound://
			forever [
				foreach sound sounds [
					if play = false [break]
					do rejoin ["insert sound-port " reduce [sound]]
					wait sound-port
					wait the-tempo 
				]
				if play = false [break]
			]
		]
		btn "STOP" [
			play: false
			close sound-port
		]
		btn "Save" [save to-file request-file/save chords/text]
		btn "Load" [chords/text: load read to-file request-file show chords]
		btn "HELP" [
			alert {
				This program plays chord progressions.  Simply type in
				the names of the chords that you'd like played, with a
				space between each chord.  For silence, use the
				underscore ("_") character.  Set the tempo by entering a 
				delay time (in fractions of second) to be paused between
				each chord.  Click the start button to play from the 
				beginning, and the stop button to end.  Pressing start
				again always begins at the first chord in the 
				progression.  The save and load buttons allow you to 
				store to the hard drive any songs you've created.
				Chord types allowed are major triad (no chord symbol - 
				just a root note), minor triad ("m"), dominant 7th 
				("7"), major 7th ("maj7"), minor 7th ("m7"), diminished
				7th ("dim7"), and half diminished 7th ("m7b5").
				*** ALL ROOT NOTES ARE LABELED WITH FLATS (NO SHARPS)
				F# = Gb, C# = Db, etc...
	 		}
		]
	]

A full, playable version, with the complete data set of embedded chords, can be found at <a href="http://musiclessonz.com/rebol_tutorial/backup.r" target=_blank>http://musiclessonz.com/rebol_tutorial/backup.r</a>.

=image rebol_tutorial/backup_tracker.png

Here are a few chord examples to load.  All the chords:

	a bb b c db d eb e f gb g ab 
	am bbm bm cm dbm dm ebm em fm gbm gm abm 
	a7 bb7 b7 c7 db7 d7 eb7 e7 f7 gb7 g7 ab7 
	adim7 bbdim7 bdim7 cdim7 dbdim7 ddim7 
	ebdim7 edim7 fdim7 gbdim7 gdim7 abdim7
	am7b5 bbm7b5 bm7b5 cm7b5 dbm7b5 dm7b5 
	ebm7b5 em7b5 fm7b5 gbm7b5 gm7b5 abm7b5 
	am7 bbm7 bm7 cm7 dbm7 dm7 ebm7 em7 fm7 gbm7 gm7 abm7
	amaj7 bbmaj7 bmaj7 cmaj7 dbmaj7 dmaj7
	ebmaj7 emaj7 fmaj7 gbmaj7 gmaj7 abmaj7
	_ _ _ _

Brown Eyed Girl:
	
	g g c c g g d d7
	g g c c g g d d7
	g g c c g g d d7
	g g c c g g d d7
	g g c c g g d d7
	g g c c g g d d7
	c c d d  g g em em c c d d

Practice hard!



---Case 12 - A Simple Image Gallery CGI Program

Here's a simple case study to finish up with.  When putting together the web site for my music lesson business, I wanted to regularly add photos of students performing at various events.  At first, I just uploaded the photos individually, and added a link to the folder that contained them.  As the collection grew, I wanted users to see the images more easily, without having to click on each individual file name.  So, I put together a simple flash presentation that showed the images one by one.  But updating the presentation required too much maintenance.  What I wanted was to simply upload the photos, and have them all display on a single web page, without any required maintenance.  This type of small cgi application was perfectly suited to Rebol.  It only took a few minutes to write, and it now gets used every day. 

For this program, I didn't actually write out an outline.  The thought process was simple enough to code directly.  Here's the outline and pseudo code I worked through in my head:

# Create a simple command line script to read the file names contained in a local folder.  Use a foreach loop to run through the list.

# Within the foreach loop, check for specified image types (extensions in each file name), and only work with those files.  Add a counter to display the total number of images.  To do that, use a counter variable and increment it each time through the loop.

# Include the above code in a CGI structure that runs on the web site, dynamically builds the html code required to display each image in the list, and prints that code to the browser so the visitor sees each image.


Here's the code for step 1:

	Rebol []

	folder: read %.
	foreach file folder [
		print file
	]
	halt

=image rebol_tutorial/imagegal1.png

For step 2, I added the counter variable, and checked for specified image types using an "if any" conditional expression:

	Rebol []

	folder: read %.
	count: 0
	foreach file folder [
		if any [
			find file ".jpg" 
			find file ".gif" 
			find file ".png" 
			find file ".bmp"
		] [
			print file
			count: count + 1
		]
	]
	print rejoin [newline "Total Images: " count]
	halt

=image rebol_tutorial/imagegal2.png

I shortened that script a bit by using an alternate version which relies on nested foreach loops.  The alternate code makes the list of potential image types easier to extend in the future:

	Rebol []

	folder: read %.
	count: 0
	foreach file folder [
		foreach ext [".jpg" ".gif" ".png" ".bmp"] [
			if find file ext [
				print file
				count: count + 1
			]
		]
	]
	print rejoin [newline "Total Images: " count]
	halt

=image rebol_tutorial/imagegal3.png

For the last step, I borrowed a line from the earlier "guitar chord diagram maker" example.  It builds the html required to display each image on the page:

	print rejoin [{<img src="} file {">}]

Finally, I added the typical CGI headers and page formatting code required to make Rebol CGI scripts perform correctly (see all the previous CGI examples in this tutorial for similar patterns):

	#! /home/path/public_html/rebol/rebol -cs
	Rebol [title: "Photo Viewer"]
	print "content-type: text/html^/"
	print [<HTML><HEAD><TITLE>"Jam Session Photos"</TITLE></HEAD><BODY>]
	print read %pageheader.html

	folder: read %.
	count: 0
	foreach file folder [
		foreach ext [".jpg" ".gif" ".png" ".bmp"] [
			if find file ext [
				print [<BR> <CENTER>]
				print rejoin [{<img src="} file {">}]
				print [</CENTER>]
				count: count + 1
			]
		]
	]
	print [<BR>]
	print rejoin ["Total Images: " count]
	print read %pagefooter.html

=image rebol_tutorial/imagegal4.png

I uploaded that script to the folder containing images on our web server, and updated the link to the photos on our web site.  Now, we just upload new images directly to the server, and when web site visitors click the "Photos" link on our site, they instantly see a dynamically created web page full of all images currently contained in that folder.

Being able to write short, useful scripts like that is one of the great benefits of learning Rebol.  You can create perfectly tailored simple scripts to get things done on your home/business PC, your web site, etc.  And with Rebol, it rarely takes more than a single sitting to write, test, and implement such small programs.




===Other Topics

---6 Rebol Flavors

This tutorial covers a version of the Rebol language interpreter called Rebol/View.  Rebol/View is actually only one of several available Rebol releases.  Here's a quick description of the different versions: 

# View - free to download and use, it includes language constructs used to create and manipulate graphic elements.  View comes with the built-in dialect called "VID", which is a shorthand mini-language used to display common GUI widgets.  View and VID dialect concepts have been integrated throughout this document.  The "layout" word in a typical "view layout" GUI design actually signifies the use of VID dialect code in the enclosed block.  The VID dialect is used internally by the Rebol interpreter to parse and convert simple VID code to lower level View commands, which are composed from scratch by the rudimentary display engine in Rebol.  VID makes GUI creation simple, without the need to deal with graphics at a rudimentary level.  But for fine control of all graphic operations, the full View language is exposed in Rebol/View, and can be mixed with VID code.  View also has a built-in "draw" dialect that's used to compose and alter images on screen.  Aside from graphic effects, View has built in sound, and access to the "call" function for executing command line applications.  The newest official releases of View can be download from <a href="http://rebol.com/view-platforms.html" target=_blank>http://rebol.com/view-platforms.html</a>.  The newest test versions are at <a href="http://www.rebol.net/builds/" target=_blank>http://www.rebol.net/builds/</a>.  Older versions are at <a href="http://rebol.com/platforms-view.html" target=_blank>http://rebol.com/platforms-view.html</a>.

# Core - a text-only version of the language that provides basic functionality.  It's smaller than View (about 1/3 to 1/2 the file size), without the GUI extensions, but still fully network enabled and able to run all non-graphic Rebol code constructs.  It's intended for console and server applications, such as CGI scripting, in which the GUI facilities are not needed.  Core is also free and can be downloaded from <a href="http://rebol.com/platforms.html" target=_blank>http://rebol.com/platforms.html</a>.  Newest versions are at <a href="http://www.rebol.net/builds/" target=_blank>http://www.rebol.net/builds/</a>.  Older versions are at <a href="http://rebol.com/platforms-core.html" target=_blank>http://rebol.com/platforms-core.html</a>.

# View/Pro - created for professional developers, it adds encryption features, Dll access and more.  Pro licenses are not free.  See <a href="http://www.rebol.com/purchase.html" target=_blank>http://www.rebol.com/purchase.html</a>.

# SDK - also intended for professionals, it adds the ability create stand-alone executables from Rebol scripts, as well as Windows registry access and more to View/Pro.  SDK licenses are not free.

# Command - another commercial solution, it adds native access to common database systems, SSL, FastCGI and other features to View/Pro.

# Command/SDK - combines features of SDK and Command.

Some of the functionalities provides by SDK and Command versions of Rebol have been enabled by modules, patches, and applications created by the Rebol user community.  For example, mysql and postgre database access, dll access, and stand-alone executable packaging can be managed by free third party creations (search rebol.org for options).  Because those solutions don't conform to official Rebol standards, and because no support for them is offered by Rebol Technologies, commercial solutions by RT are recommended for critical work.


---Spread the Word:  7 Reasons to Learn and Use Rebol

Rebol is an extraordinary tool, but it's relatively young and unknown.  To become more useful and mature, the Rebol community needs the support of a growing user base.  New modules, dialects, and useful functions are created by active coders, and that helps make Rebol even more powerful.  If you like the benefits that Rebol offers, take a moment and send this link to a friend.  Doing that will help to spread the "Rebolution" :)

# You can use it to build an enormous variety of applications with modern graphics, database connectivity, network functionality, simple CGI interface for web programming, and much more.  Instead of learning to use a variety of languages and development tools to complete various tasks, you can focus on improving your skills in one simple paradigm.  There is no other programming tool that allows you to accomplish so many different types of work, so simply.

# Rebol is easy to learn.  Even absolute beginners can learn to complete complex and useful programming tasks within a few weeks.  A comprehensive variety of built in data types, native network connectivity, super-simple GUI creation, easy data manipulation and parsing features, and a consistent interface to all types of files, data, and functions make it straightforward to use.  There is not a simpler language to learn, and Rebol's consistent language style/syntax is maintained throughout the learning curve.

# Compared to other development environments, the Rebol interpreter is tiny.  In it's heaviest uncompressed form, the Rebol environment is ~600k.  You can distribute the entire compressed language, including the interpreter, built-in documentation, and more features than can be found in other multimegabyte development environments, in 100k-400k - depending on the version you choose.  No other modern general purpose development environment close in terms of download size.

# Code written in Rebol is able to run unchanged on over 40 operating systems.  Aside from providing a great development solution for cross platform tasks, you can also use the interpreter as a consistent interface to operating systems with which you're unfamiliar.  It's useful as a compact multiplatform file manager, text editor, calculator, email client, ftp client, newsreader, image viewer/editor, etc.

# Rebol/View and Rebol/Core are free for commercial and non-commercial use. 

# The Rebol user community is friendly and knowledgeable.  Help for most problems and questions is generally available on the Rebol mailing list, and the response time is usually very quick (Rebol users love to demonstrate just how capable and elegant Rebol is). 

# The Rebol language has the potential to build dialects that are strikingly human-readable and lightweight.  Like any other programming language, it makes use of variables, function definitions, object constructs, etc., but it's got some unusual twists that enable language extensions which are simple for even inexperienced programmers to implement.  The built-in dialects in Rebol demonstrate just how accessible Rebol's underlying syntax concepts can make complex tasks, even for untrained coders.  Because of that, Rebol offers new potential for average <i> users </i> to program their computers.



===What Next?

At this point, you've seen a useful set of concepts and techniques, but you've only just begun.

If you take a close look at the code that's been presented in this tutorial, play with it and absorb the full meaning of how it works, you'll understand some of the real power, flexibility, and ease with which Rebol allows you to store, retrieve, display, and otherwise manipulate data in any computer environment.  By using the built in function words in Rebol, you can do a lot of useful programming without writing much code, and with a very easy learning curve.  You can create GUIs to input, save, transfer, and display data.  You can read, send, alter, and display the text of emails and web pages.  You can create, view, alter and manipulate images and sounds.  You can display, sort, filter, and organize database-like blocks of text and binary data.  

Remember that Rebol can run on just about any computer, web server, etc., and can allow you to deal with all types of data just as easily:  text, images, sounds, money values, times and dates, web addresses, etc.  It has built in functions to easily work with networks.  Your Rebol programs can be written in parts that run on separate machines and work in tandem by communicating across the Internet.  Once you understand how to save data using word variables and block structures, and perform actions with homemade functions, you're ready to delve more deeply into the syntax and thought processes that make the language flow.    

Begin to study and understand the logic and work flow that occurs in longer programs.  Figure out what types of data you want your programs to work with.  Figure out how to get that data into your programs (input from a GUI, read from a local hard drive or CD, downloaded from a remote web site or email server, output from another program and saved to disk, etc.).  Determine data structures which can represent it in your program (simple variables, simple block lists, compound block structures, database systems, etc.).  Decide where you want data to be saved (on a local disk, on a file server in your local network, on a web server on the Internet, etc).  Decide what actions you want to perform on that data (organizing, sorting, categorizing, editing, erasing, filtering, separating, transferring, displaying, listening to, etc.), and use/create functions that perform those actions.  In Rebol, all those things are easily understood and accomplished.  Familiarize yourself with common approaches to managing typical situations in the types of programs you want to write.  Become familiar with the data structures, functions, conditional operations, loops, and general code flow seen in those types of programs.  Read and memorize code for programs that others have written.  Explore and memorize all the built-in words in the language.  Learn how others create and use new words to solve common programming problems.  

By doing those things, you'll learn to speak the Rebol language fluently.  The tutorial at <a href="http://www.rebol.com/docs/rebol-tutorial-3109.pdf" target=_blank>http://www.rebol.com/docs/rebol-tutorial-3109.pdf</a> provides a nice summary of fundamental concepts.  It's a great document to read next.  To learn Rebol in earnest, start by reading the Rebol core users manual:  <a href="http://rebol.com/docs/core23/rebolcore.html" target=_blank>http://rebol.com/docs/core23/rebolcore.html</a>.  It covers all of the data types, built-in word functions and ways of dealing with data that make up the Rebol/Core language (but not the graphic extensions in View).  It also includes many basic examples of code that you can use in your programs to complete common programmatic tasks.  Also, be sure to keep the Rebol function dictionary handy whenever you write any Rebol code:  <a href="http://rebol.com/docs/dictionary.html" target=_blank>http://rebol.com/docs/dictionary.html</a>.  It defines all the words in the Rebol language and their specific syntax use.  It's also helpful in cross-referencing function words that do related actions in the language.  Along the way, read the Rebol View and VID documents at: <a href="http://rebol.com/docs/easy-vid.html" target=_blank>http://rebol.com/docs/easy-vid.html</a> , <a href="http://rebol.com/docs/view-guide.html" target=_blank>http://rebol.com/docs/view-guide.html</a> , and <a href="http://rebol.com/docs/view-system.html" target=_blank>http://rebol.com/docs/view-system.html</a>.  Those documents explain how to write Graphical User Interfaces in Rebol.  Once you've got an understanding of the grammar and vocabulary of the language, dive into the Rebol cookbook:  <a href="http://www.rebol.net/cookbook/" target=_blank>http://www.rebol.net/cookbook/</a>.  It contains many simple and useful examples of code needed to create real-world applications.  When you've read all that, finish the rest of the documents at <a href="http://rebol.com/docs.html" target=_blank>http://rebol.com/docs.html</a> to get more specific examples about how to program using sound, network, web sites, compression, security, and other features in common use.  

Beyond the basic documentation, there is a library of hundreds of commented and approved source codes for Rebol programs available at <a href="http://rebol.org" target=_blank>http://rebol.org</a>.  It's a great way to immerse yourself into reading the language as it exists in the real world.  In addition, you can use it to copy and paste examples of code from other programs as a basis for programs you want to write (be sure to give credit to the author(s) whenever you do anything of that sort).  There's also a searchable mailing list archive with nearly 45,000 emails at the same rebol.org web site.  It contains answers to numerous questions encountered by Rebol programmers.  There are many other web sites such as <a href="http://www.codeconscious.com/rebol/" target=_blank>http://www.codeconscious.com/rebol/</a>, <a href="http://www.rebolforces.com/" target=_blank>http://www.rebolforces.com/</a>, and <a href="http://www.fm.vslib.cz/~ladislav/rebol/" target=_blank>http://www.fm.vslib.cz/~ladislav/rebol/</a> that provide more help in understanding and using the language.  For a complete list of all web pages and articles related to Rebol, see <a href="http://dmoz.org/Computers/Programming/Languages/REBOL/" target=_blank>http://dmoz.org/Computers/Programming/Languages/REBOL/</a>

Finally, the Rebol interpreter itself is a fantastic source of code and reference material.  The built-in word "help" provides required syntax structure for all of the built-in words in Rebol, and the word "what" lists all built-in words.  Together, those two words provide a reference that's sufficient for most situations in which you need syntax help - without any external guide.  You can also use the built-in word "source" to get the actual internal Rebol code that defines many of the mid-high level function words in the language.  The interpreter also provides an embedded way for the community to share useful code.  The Rebol "desktop" that appears by default when you run the view.exe interpreter is a gateway into a world of "Rebsites" that developers use to post code for programs they've created.  Surfing the public rebsites on which developers make shared code available is a great way to explore the language more deeply.  All of the code in the rebol.org archive, and much more, is available on the rebsites (It's amazing how much that little view.exe file lets you do!)

If you're interested at all in programming, you'll find all of the Rebol documentation and resources interesting, and a little addictive, because they show you how to do virtually everything you've ever imagined doing as a programmer.  Rebol is a tiny tool (compared to the file size of other interpreters and compilers), it's very powerful, and it's completely cross-platform capable.  You'll be able to program local Windows computers, as well as Linux web servers, Macs, and other types of computers used in all sorts of different environments.  You'll be able to write business applications, audio-visual applications, network and Internet applications, games, etc.  And you'll get started right away, with a quick learning curve that'll have you doing useful things immediately as a programmer.  On top of that, you'll learn fundamentals about programming that you'll carry around to other languages as well.


---A Final Point

Rebol is a language that neatly "wraps" up most common functions that various operating systems enable.  It provides a single, simple format that lets you talk to all different computers in the same way.  It's got it's own way of speaking that is different from many other languages (see <a href="http://www.ddj.com/documents/s=3211/nam1012432597/index.html" target=_blank>http://www.ddj.com/documents/s=3211/nam1012432597/index.html</a> to get an idea of how Rebol is different).  In technical terms, that grammar and syntax is called the "api".  If you continue to pursue programming in other languages, and in various environments, you'll encounter different language apis.  Eventually, as a serious programmer, you'll typically learn to deal with the raw api of the operating system you're working on.  It is the base language that most other languages are actually translating to.  Because the operating system needs to access the computer hardware quickly, it is written in a "lower level" language - one that is formatted to think more like the computer's raw calculations, and less like human speech.  

With Rebol, you can do most typical things that programmers want to do, but there are many functions in the various operating system api's that aren't included (i.e., web cam access, sound input, low level hardware control, etc.).  To do that, be prepared to explore the raw operating system api, and the language(s) in which it was written.  On Windows, Unix, Macintosh, and other platforms, that typically means learning the syntax and structure of the "C" and "C++" languages.  Also, learning common methods for accessing shared code files such as .dll's is very important.  Once you've learned the full Rebol api, that's a good direction to take in your studies...

Enjoy!


===Feedback

For feedback, bugs reports, suggestions, etc., please use the form below:

<FORM action=http://musiclessonz.com/thesendto2.pl method=post><INPUT name=recipient type=hidden value=rebol@musiclessonz.com><INPUT name=subject type=hidden value="Musiclessonz.com - form submission from REBOL tutorial.">Your Name: <BR><INPUT name=realname size=60 title=realname><BR><BR>Your Email Address: <BR><INPUT name=email size=60 title=email><BR><BR>Message:<BR><TEXTAREA cols=60 name=message rows=3></TEXTAREA><BR><BR><INPUT name=submit type=submit value=Submit><INPUT name=required type=hidden value=realname,email> <INPUT name=print_blank_fields type=hidden value=0></FORM>

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