REBOL 3 Concepts: Functions: Conditional Functions

Pending Revision

This document was written for R2 and has yet to be revised for R3.

Because functions are created dynamically by evaluation, you can determine how you want a function created, based on other information. This is a way to provide conditional code as is found in the macro or preprocessor sub-languages of other programming languages. Within the REBOL language this type of conditional code is done with normal REBOL code.

For instance, you may want to create a debugging version of a function that prints additional information:

test-mode: on

timer: either test-mode [
    func [delay] [
        print "delaying..."
        wait delay
        print "resuming"
    ]
][
    func [delay] [wait delay]
]

Here you will create one of two functions, based on the test-mode you are running. This can also be written shorter as:

timer: func [delay] either test-mode [[
    print "delaying..."
    wait delay
    print "resuming"
]][[wait delay]]