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