Path: utzoo!utgpu!water!watmath!clyde!bellcore!faline!ulysses!allegra!mit-eddie!husc6!cmcl2!nrl-cmf!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!ukc!dcl-cs!simon
From: simon@dcl-cs.UUCP
Newsgroups: comp.lang.lisp
Subject: Re: A CL iteration macro, "while".
Summary: That's nice, but how about this?
Keywords: LOOP WHILE UNTIL ITERATION MACROS
Message-ID: <464@dcl-csvax.comp.lancs.ac.uk>
Date: 15 Jan 88 16:31:51 GMT
References: <13639@beta.UUCP> <3503@whuts.UUCP>
Reply-To: simon@comp.lancs.ac.uk (Simon Brooke)
Organization: Department of Computing at Lancaster University, UK.
Lines: 27
Posted: Fri Jan 15 11:31:51 1988

In article <3503@whuts.UUCP> davel@whuts.UUCP (David Loewenstern) writes:
>In article <13639@beta.UUCP>, dzzr@beta.UUCP (Douglas J Roberts) writes:
>> 
>> 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. 

Yes, that's nice; but there's a nicer. How about this, which is Arthur
Norman's loop macro:

	(loop
		<any number of arbitrary statements>
		(until <exit-condition> <after-exit statements>)
		<any number of arbitrary statements>
		(while <continue-condition> <after-exit statements>)
		<any number of arbitrary statements>)

The 'while' and 'until' conditions can appear any number of times,
(including zero) anywhere in the body of the loop. The flexibility of this
is wonderful - and I'd love to see the source code for it!

It appears in Acornsoft's lisp for the BBC Micro and their more recent
lisp for the new acorn risc machine (Archimedes); so you lot west of the
water may not have seen it. But it's a lovely construct! [Obviously, it
returns the value of the last of the after-exit statements of the until-
or while- statement which allowed exit]

Simon Brooke		simon@uk.ac.lancs.comp