From: John Cowan <cowan@ccil.org>
To: Mark H Weaver <mhw@netris.org>
Cc: guile-user@gnu.org, Matt Wette <matt.wette@gmail.com>
Subject: Re: A value for "nothing"
Date: Tue, 28 Aug 2018 11:19:06 -0400 [thread overview]
Message-ID: <CAD2gp_Q_Fud4avS_SVEJARkq4-a7URCdAsnuVsfgNymS0L+5-A@mail.gmail.com> (raw)
In-Reply-To: <87va7vyo2q.fsf@netris.org>
On Tue, Aug 28, 2018 at 3:01 AM Mark H Weaver <mhw@netris.org> wrote:
> In RnRS, (define a (if #f #f)) is allowed and guaranteed to assign
> *some* object to 'a' without signalling an error.
Actually, the phrase used is "the result is unspecified", which
unfortunately
is not defined in any RnRS. Racket produces a syntax error in this
situation
at least in its default language.
> However, it's not
> specified what object will be assigned. It could be 2 or (foo bar) or
> "the cow jumps over the moon".
>
In practice, it is #t, #f, (), or a unique unspecified object across all the
Schemes I have tested, most often the last.
--
John Cowan http://vrici.lojban.org/~cowan cowan@ccil.org
LEAR: Dost thou call me fool, boy?
FOOL: All thy other titles thou hast given away:
That thou wast born with.
next prev parent reply other threads:[~2018-08-28 15:19 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-26 10:13 A value for "nothing" HiPhish
2018-08-26 17:21 ` Thomas Morley
2018-08-26 17:27 ` Joshua Branson
2018-08-26 17:49 ` John Cowan
2018-08-27 4:52 ` Mark H Weaver
2018-08-27 13:00 ` John Cowan
2018-08-27 21:29 ` Mark H Weaver
2018-08-27 21:32 ` Mark H Weaver
2018-08-26 20:07 ` Mark H Weaver
2018-08-26 22:08 ` Matt Wette
2018-08-27 8:04 ` tomas
2018-08-27 20:12 ` Mark H Weaver
2018-08-27 20:46 ` Mark H Weaver
2018-08-28 0:50 ` Matt Wette
2018-08-28 6:58 ` Mark H Weaver
2018-08-28 15:19 ` John Cowan [this message]
2018-08-28 15:38 ` Mark H Weaver
2018-08-28 15:59 ` Mark H Weaver
2018-08-28 16:12 ` John Cowan
2018-08-28 17:15 ` Mark H Weaver
2018-08-28 19:07 ` Mark H Weaver
2018-08-27 20:54 ` Hans Åberg
2018-08-27 0:17 ` Panicz Maciej Godek
2018-08-27 8:02 ` tomas
2018-08-27 8:29 ` Panicz Maciej Godek
2018-08-27 8:29 ` HiPhish
[not found] ` <8840615.kRvQfVdCvZ@aleksandar-ixtreme-m5740>
[not found] ` <CAD2gp_QLqd=_RbF=HTEbCLp1onmUq-c74g0FXTvMgdz8JB4-8A@mail.gmail.com>
2018-08-27 8:24 ` HiPhish
[not found] ` <3467110.H24gZIzStD@aleksandar-ixtreme-m5740>
[not found] ` <87ftz0vidc.fsf@netris.org>
2018-08-27 8:40 ` HiPhish
2018-08-27 12:37 ` Ludovic Courtès
2018-08-27 19:49 ` Mark H Weaver
2018-08-28 7:52 ` Ludovic Courtès
-- strict thread matches above, loose matches on Subject: below --
2018-08-26 20:25 HiPhish
2018-09-13 21:49 HiPhish
[not found] ` <CAD2gp_Sg-aDXZKfOcL-i2py7ne4c0Cp+2HvKS4DYi1Antm_B1A@mail.gmail.com>
2018-09-14 22:45 ` HiPhish
2018-09-15 0:26 ` John Cowan
2018-09-15 14:50 ` HiPhish
2018-09-15 18:28 ` Keith Wright
2018-09-15 21:50 ` Edwin Watkeys
2018-09-15 22:16 ` HiPhish
2018-09-15 22:23 ` Edwin Watkeys
2018-09-15 22:13 ` HiPhish
2018-09-15 22:45 ` David Pirotte
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