(if condition then else)
  condition: any form
  then: any form
  else: any form

Performs conditional evaluation.

First, the condition form is evaluated. If it evaluates to #f or #n, the else form is evaluated; otherwise, the then form is evaluated.

This form is rarely used directly. cond, when and unless are usually more readable.

if is sometimes useful when you want to express a very short conditional which fits on a single line:

(= color (if (< hp 10) 'red 'green))