Xref: utzoo comp.lang.lisp:619 comp.emacs:2438
Path: utzoo!mnetor!uunet!husc6!hao!ames!hc!beta!dzzr
From: dzzr@beta.UUCP (Douglas J Roberts)
Newsgroups: comp.lang.lisp,comp.emacs
Subject: A CL iteration macro, "while".
Message-ID: <13639@beta.UUCP>
Date: 22 Dec 87 18:09:18 GMT
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 51
Keywords: Let's have a little non-flamable fun...


I was poking around in the source for Stallman's Gnu Emacs the other day
and stumbled across a "while" function that I kind of liked. It's not
Common nor Zeta LISP, and so I'd never seen it before. We have
Symbolic's big loop macro installed on all of our Common LISP machines
(Suns, TI Explorers, & Symbolics), but even with it there is no clean
way to do simple iteration control that I really like. (I don't like the
syntax of do, dotimes, dolist, etc.)

I thought it would be fun to write a CL while macro and then post it
for comment, etc. I'd be curious for anybody interested enough to
suggest other ways of writing it.

Here 'tis.


(defmacro while (test-form &rest forms)
  "This macro evaluates test-form, and if the result is non-nil
	all subsequent forms will be iteratively evaluated until
	test-form evaluates to nil."
  (prog ()
     again 
	(cond (
	       (eval test-form) 
	       (mapcar #'eval forms)
	       (go again)
	       ))
  ))


Example of use:

(setq *number* 0)


(while (< *number* 5)
       (print *number*)
       (print "line 1")
       (print "line 2")
       (print "line 3")
       (setq *number* (1+ *number*))
       )




-- 
---------------------------------------------------------------
			Doug Roberts
			dzzr@lanl.gov
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