From: Josef Wolf <jw@raven.inka.de>
To: guile-user@gnu.org
Subject: Re: Need help to understand a macro
Date: Mon, 22 Mar 2010 21:54:38 +0100 [thread overview]
Message-ID: <20100322205438.GE31143@raven.wolf.lan> (raw)
In-Reply-To: <m3r5ncw1r1.fsf@pobox.com>
On Mon, Mar 22, 2010 at 09:16:34PM +0100, Andy Wingo wrote:
> Hi Josef,
>
> I seem to be the negative guy in replies to you.
Uh? I did not notice anything negative?
> Apologies for that!
I don't see any reason for you to apologize...
> 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.
As I understood this, the "no values" variant is a guile extension and not
guaranteed by the standard...
> > 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>".
Even better would be "too few values for '+'" or something. Oh, and a line
number.
next prev parent reply other threads:[~2010-03-22 20:54 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
2010-03-22 20:54 ` Josef Wolf [this message]
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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