From: Kevin Ryde <user42@zip.com.au>
Subject: Re: while break and continue
Date: Fri, 15 Aug 2003 11:43:01 +1000 [thread overview]
Message-ID: <87fzk366hm.fsf@zip.com.au> (raw)
In-Reply-To: <uw5vft1aowe.fsf@saturn.math.uni-magdeburg.de> (Matthias Koeppe's message of "Wed, 13 Aug 2003 11:27:13 +0200")
Matthias Koeppe <mkoeppe@merkur.math.uni-magdeburg.de> writes:
>
> I think you need a fresh catch tag for every invocation (not only for
> every macro expansion site) of WHILE.
I think this might do the trick. A separate helper is an easy way to
keep the "key" binding from being exposed to the cond and body.
(define-macro (while cond . body)
(define (while-helper proc)
(do ((key (make-symbol "while-key")))
((catch key
(lambda ()
(proc (lambda () (throw key #t))
(lambda () (throw key #f))))
(lambda (key arg) arg)))))
`(,while-helper (,lambda (break continue)
(,do ()
((,not ,cond))
,@body)
#t)))
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next prev parent reply other threads:[~2003-08-15 1:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-30 0:00 while break and continue Kevin Ryde
2003-06-01 23:58 ` Marius Vollmer
2003-06-05 1:42 ` Kevin Ryde
2003-06-18 22:56 ` Marius Vollmer
2003-06-21 23:28 ` Kevin Ryde
2003-07-27 14:48 ` Marius Vollmer
2003-07-29 0:23 ` Kevin Ryde
2003-08-13 21:49 ` Kevin Ryde
2003-08-13 9:27 ` Matthias Koeppe
2003-08-14 23:35 ` Kevin Ryde
2003-08-15 1:43 ` Kevin Ryde [this message]
2003-06-06 22:31 ` Kevin Ryde
2003-06-18 22:57 ` Marius Vollmer
2003-06-20 23:56 ` Kevin Ryde
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