if

if Special Operator

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 

See Also:

cond, unless, when

Notes:

(if test-form then-form else-form)

≡ (cond (test-form then-form) (t else-form))

Expanded Reference: if

tip

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(if )