if (ANSI and GNU Common Lisp Document)

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#### 5.3.43 if [Special Operator]

`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))