IF
==

syntax: (if <test> <then> <else>)       ; Babylon Lisp
        (if <test> <then> [<else>])     ; Common Lisp

This function evaluates the testform. If the result
is not NIL, then the form <then> will be selected,
otherwise <else>. IF returns whatever evaluation of
the selected form returns.

example:       >(if t 1 2)
               1
               >(if nil 1 2)
               2