CLHS: Special Operator IF

#

Special Operator IF

Syntax:

if test-form then-form [else-form] => result*

Arguments and Values:

Test-form---a form.

Then-form---a form.

Else-form---a form. The default is nil.

results---if the test-form yielded true, the values returned by the then-form; otherwise, the values returned by the else-form.

Description:

if allows the execution of a form to be dependent on a single test-form.

First test-form is evaluated. If the result is true, then then-form is selected; otherwise else-form is selected. Whichever form is selected is then evaluated.

Examples:

     (if t 1) =>  1
     (if nil 1 2) =>  2
     (defun test ()
       (dolist (truth-value '(t nil 1 (a b c)))
         (if truth-value (print 'true) (print 'false))
         (prin1 truth-value))) =>  TEST
     (test)
    >>  TRUE T
    >>  FALSE NIL
    >>  TRUE 1
    >>  TRUE (A B C)
    =>  NIL

Affected By: None.

Exceptional Situations: None.

See Also:

cond, unless, when

Notes:

     (if test-form then-form else-form)
     ==  (cond (test-form then-form) (t else-form))

Copyright 1996-2001, Xanalys Inc. All rights reserved.