Next: , Previous: Comments Tutorial, Up: Tutorial


3.9 Colon Definitions

are similar to procedures and functions in other programming languages.

     : squared ( n -- n^2 )
        dup * ;
     5 squared .
     7 squared .

: starts the colon definition; its name is squared. The following comment describes its stack effect. The words dup * are not executed, but compiled into the definition. ; ends the colon definition.

The newly-defined word can be used like any other word, including using it in other definitions:

     : cubed ( n -- n^3 )
        dup squared * ;
     -5 cubed .
     : fourth-power ( n -- n^4 )
        squared squared ;
     3 fourth-power .
Assignment: Write colon definitions for nip, tuck, negate, and /mod in terms of other Forth words, and check if they work (hint: test your tests on the originals first). Don't let the ‘redefined’-Messages spook you, they are just warnings.

Reference: Colon Definitions.