UNLESS
======

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

This function evaluates the testform. If the result
is not NIL, then the forms will not 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:       >(unless nil 1)
               1
               >(unless t 1)
               NIL