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Gforth Manual

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: 5.9.5 Colon Definitions.