• if test-form then-form [else-form] → result*

• 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.

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.

(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

None.

None.

• Macro COND
• Macro UNLESS
• Macro WHEN

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