*
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)
▷ →
None.
None.
(if test-form then-form else-form) ≡ (cond (test-form then-form) (t else-form))