Tour

###An introductory Tour###

The usual Forth stack action.

ok> 33 44
(33 44) ok> * .
1452 ok>

The prompt line shows the stack contents in parentheses.

ok> "Hello World"
({Hello World}) ok> . cr
Hello World
ok>

Now try some definitions.

ok> : Star { -- } "*" . ;
ok> Star
* ok>

No space is needed after the first " in a string definition.

ok> : Stars { n -- } n times Star repeat ;
ok> 5 Stars
* * * * * ok

The stack parameter n is converted to a local variable and removed from the stack before the body of the definition is executed. More in [Stack Stack].

ok> : Grid { m -- }  m times m Stars cr repeat
ok> 3 Grid
* * *
* * *
* * *
ok>

Locals come handy here. Compare it to a stack based definition, two dup's and a drop.

You can change the behavior of a loaded word without having to reload the words that use it. Suppose you prefer to print the Stars without trailing spaces: Just redefine Star.

ok> : Star {} "*" ascii emit ;
ok> Star
*ok
ok> 3 Stars
***
ok> 3 Grid
***
***
***

Tcl replaces the code in the loaded procedure. The change is active for all procedures that use this word. You can program on a running TF program and instantly test the changes.

One more useful Tcl feature:

ok> 33 variable V
ok> "The value of V is $V" . cr
The value of V is 33
ok>

Variables are substituted in strings. Add a $ to retrieve the value.

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TclForth is just Forth - with a twist.