WHEN
====

syntax: (when <test> {<form> ...})

This function evaluates the testform. If the result
is NIL, then no <form> will be evaluated, and NIL will
be returned. Otherwise the forms <form> will be
evaluated sequentially, from left to right, and the
value of the last form will be returned.

example:       >(when t 1)
               1
               >(when nil 1)
               NIL