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