LOOP
====

syntax: (loop {<form> ...})

This function evaluates each form in turn, from left
to right, in a never-ending loop. LOOP never returns
a value. It can be left with the RETURN-function.

example:       >(setf i 0)
               0
               >(loop (setf i (+ i 1)) (when (= i 5)
                      (return 'end)))
               END
               >i
               5