From: Alex Shinn <alexshinn@gmail.com>
To: Marijn <hkBst@gentoo.org>
Cc: Andy Wingo <wingo@pobox.com>,
ludo@gnu.org, guile-devel <guile-devel@gnu.org>
Subject: Re: when and unless
Date: Tue, 6 Dec 2011 17:29:30 +0900 [thread overview]
Message-ID: <CAMMPzYMoKuQSWnBMCoZ_+ggcrmk+SGvbyaKvYLb=eJVRbR6E1Q@mail.gmail.com> (raw)
In-Reply-To: <4EDDC8B1.3000509@gentoo.org>
On Tue, Dec 6, 2011 at 4:48 PM, Marijn <hkBst@gentoo.org> wrote:
>
> Couldn't help but wonder why they don't return the value of the last
> body form, so I looked around a bit and both CLHS[1] and my racket
> REPL seem to agree that they should:
>
> $ racket
> Welcome to Racket v5.2.0.4.
>> (when #t 'hello)
> 'hello
>> (unless #f 'hi)
> 'hi
>
> Is there some other source that suggests that the return value should
> be unspecified?
Because the result is meaningless when the condition is false.
CLHS returns nil in this case, but that fits with CL idioms and
not Scheme idioms. when and unless are for side-effects - it's
better to write (and #t 'hello) if you want the result.
R7RS also leaves it unspecified.
--
Alex
next prev parent reply other threads:[~2011-12-06 8:29 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-30 10:44 when and unless Andy Wingo
2011-06-30 21:46 ` Ludovic Courtès
2011-07-01 7:50 ` Andy Wingo
2011-07-01 12:47 ` Ludovic Courtès
2011-12-05 20:23 ` Andy Wingo
2011-12-06 7:48 ` Marijn
2011-12-06 8:29 ` Alex Shinn [this message]
2011-12-06 11:17 ` David Kastrup
2011-12-06 16:25 ` Andy Wingo
2011-12-06 16:42 ` David Kastrup
2011-12-06 17:35 ` Andy Wingo
2011-12-06 22:08 ` David Kastrup
2011-12-06 23:05 ` Chris K. Jester-Young
2011-12-07 9:23 ` David Kastrup
2011-12-07 15:58 ` Chris K. Jester-Young
2011-12-08 8:42 ` David Kastrup
2011-12-08 15:34 ` Chris K. Jester-Young
2011-12-08 16:10 ` David Kastrup
2011-12-08 18:10 ` Ian Price
2011-12-07 16:10 ` Chris K. Jester-Young
2011-12-06 19:05 ` Chris K. Jester-Young
2011-12-06 19:33 ` Andy Wingo
2011-12-06 14:39 ` Ludovic Courtès
2011-12-07 14:19 ` Ludovic Courtès
2011-12-07 14:27 ` David Kastrup
2012-01-07 0:16 ` Andy Wingo
2012-01-07 22:36 ` Ludovic Courtès
2012-01-20 20:19 ` Andy Wingo
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