Forth can read read from ordinary text files so you can use any editor that you wish to write your programs.

Sample Program Enter into your file, the following code.

\ Sample Forth Code
\ Author: your name

: SQUARE ( n -- n*n , square number )
 DUP *
;

: TEST.SQUARE ( -- )
 CR ." 7 squared = "
 7 SQUARE . CR
;

Now save the file to disk.

The text following the \ character is treated as a comment. This would be a REM statement in BASIC or a /*---*/ in 'C'. The text in parentheses is also a comment.

Using INCLUDE

"INCLUDE" in Forth means to compile from a file.

You can compile this file using the INCLUDE command. If you saved your file as WORK:SAMPLE, then compile it by entering:

INCLUDE SAMPLE.FTH

Forth will compile your file and tell you how many bytes it has added to the dictionary. To test your word, enter:

TEST.SQUARE

Your two words, SQUARE and TEST.SQUARE are now in the Forth dictionary. We can now do something that is very unusual in a programming language. We can "uncompile" the code by telling Forth to FORGET it. Enter:

FORGET SQUARE

This removes SQUARE and everything that follows it, ie. TEST.SQUARE, from the dictionary. If you now try to execute TEST.SQUARE it won't be found.

Now let's make some changes to our file and reload it. Go back into the editor and make the following changes: (1) Change TEST.SQUARE to use 15 instead of 7 then (2) Add this line right before the definition of SQUARE:

ANEW TASK-SAMPLE.FTH

Now Save your changes and go back to the Forth window.

You're probably wondering what the line starting with ANEW was for. ANEW is always used at the beginning of a file. It defines a special marker word in the dictionary before the code. The word typically has "TASK-" as a prefix followed by the name of the file. When you ReInclude a file, ANEW will automatically FORGET the old code starting after the ANEW statement. This allows you to Include a file over and over again without having to manually FORGET the first word. If the code was not forgotten, the dictionary would eventually fill up.

If you have a big project that needs lots of files, you can have a file that will load all the files you need. Sometimes you need some code to be loaded that may already be loaded. The word INCLUDE? will only load code if it isn't already in the dictionary. In this next example, I assume the file is on the volume WORK: and called SAMPLE. If not, please substitute the actual name. Enter:

FORGET TASK-SAMPLE.FTH
INCLUDE? SQUARE WORK:SAMPLE
INCLUDE? SQUARE WORK:SAMPLE

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