From: Andy Wingo <wingo@pobox.com>
To: Josef Wolf <jw@raven.inka.de>
Cc: guile-user@gnu.org
Subject: Re: Need help to understand a macro
Date: Mon, 22 Mar 2010 21:16:34 +0100 [thread overview]
Message-ID: <m3r5ncw1r1.fsf@pobox.com> (raw)
In-Reply-To: <20100322192556.GB31143@raven.wolf.lan> (Josef Wolf's message of "Mon, 22 Mar 2010 20:25:56 +0100")
Hi Josef,
I seem to be the negative guy in replies to you. Apologies for that!
On Mon 22 Mar 2010 20:25, Josef Wolf <jw@raven.inka.de> writes:
> On Fri, Mar 19, 2010 at 08:54:02AM -0400, Ken Raeburn wrote:
>>
>> The result of (if #f #f) is unspecified, not #f, according to r5rs.
>> That means an implementation can produce whatever value it wants.
In the R6RS, evaluating `(if #f #f)' returns "unspecified values" --
that is, even the number of values is unspecified. And in fact it would
make sense for `(if #f #f)' to be the same as `(values)' -- an
expression returning zero values.
> I think I like this type of "unspecified". Much better than the
> "undefined behavior" definition in C.
Unfortunately it really is unspecified :) OK it's better than C, in the
sense that it won't launch the missiles, but it would be better if
evaluating:
(+ 2 (if #f #f))
yielded an error of "too few values to continuation" rather than "don't
know how to add #<unspecified>".
Cheers,
Andy
--
http://wingolog.org/
next prev parent reply other threads:[~2010-03-22 20:16 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-19 8:57 Need help to understand a macro Josef Wolf
2010-03-19 12:54 ` Ken Raeburn
2010-03-22 19:25 ` Josef Wolf
2010-03-22 20:16 ` Andy Wingo [this message]
2010-03-22 20:54 ` Josef Wolf
2010-03-19 14:28 ` Andy Wingo
2010-03-19 16:15 ` Andreas Rottmann
2010-03-22 19:55 ` Josef Wolf
2010-03-22 21:50 ` Andreas Rottmann
2010-03-22 19:50 ` Josef Wolf
2010-03-22 20:36 ` Andy Wingo
2010-03-22 21:01 ` Josef Wolf
2010-03-23 0:50 ` Neil Jerram
2010-03-20 14:13 ` szgyg
2010-03-22 21:06 ` Josef Wolf
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