From: Alex Vong <alexvong1995@gmail.com>
To: Christopher Howard <christopher.howard@qlfiles.net>
Cc: Guile User Mailing List <guile-user@gnu.org>
Subject: Re: Repeat syntax
Date: Sat, 25 Nov 2017 16:39:13 +0800 [thread overview]
Message-ID: <87y3mupxam.fsf@gmail.com> (raw)
In-Reply-To: <1511586326.26826.3.camel@qlfiles.net> (Christopher Howard's message of "Fri, 24 Nov 2017 20:05:26 -0900")
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Christopher Howard <christopher.howard@qlfiles.net> writes:
> Hi list, I want to have a function
>
> (repeat n exp exp* ...)
>
> That calls the expressions n times for side effect, like for-each, but
> without the bother of dealing with a list. It seems like somebody else
> must have thought of this before, but I couldn't find the equivalent
> procedure. After reading 6.10.2 I came up with this
>
> (define-syntax repeat
> (syntax-rules (repeat)
> ((_ n exp exp* ...)
> '(unless (<= n 0)
> exp
> exp*
> ...
> (repeat (- n 1) exp exp* ...)))))
>
> Which doesn't work I think because repeat gets expanded infinitely many
> times. I was pondering other ways to do this, but they all seem to end
> in either infinite expansion, or an important variable getting
> overshadowed. So, could somebody point me in the right direction?
Do you want to evaluate the expressions during macro-expand-time or
run-time?
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next prev parent reply other threads:[~2017-11-25 8:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-25 5:05 Repeat syntax Christopher Howard
2017-11-25 8:39 ` Alex Vong [this message]
2017-11-25 14:47 ` Matt Wette
2017-11-25 15:06 ` Matt Wette
2017-11-25 16:48 ` Christopher Howard
2017-11-25 15:21 ` Chris Vine
2017-11-25 15:34 ` Chris Vine
2017-12-30 13:18 ` Taylan Ulrich Bayırlı/Kammer
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