I don't recommend using loop. Neither does Paul Graham (http://www.paulgraham.com/loop.html) nor John Foderaro, the main developer of Franz Lisp (http://compgroups.net/comp.lang.lisp/re-the-loop-macro-3/195...). Including loop in the Common Lisp standard was a contentious issue, opposed by Scott Fahlman, Guy Steele (3.2 in http://dreamsongs.com/Files/HOPL2-Uncut.pdf), and others (Steven M. Haflich's article on 9/16/02 in https://groups.google.com/forum/#!topic/comp.lang.lisp/tBmK0...).