From: David Kastrup <dak@gnu.org>
To: Mark H Weaver <mhw@netris.org>
Cc: 14792@debbugs.gnu.org, "Ludovic Courtès" <ludo@gnu.org>
Subject: bug#14792: Error in manual "(guile-2) Object Properties"
Date: Tue, 16 Jul 2013 21:30:50 +0200 [thread overview]
Message-ID: <87y5968fpx.fsf@fencepost.gnu.org> (raw)
In-Reply-To: <874nbu2uwf.fsf@tines.lan> (Mark H. Weaver's message of "Tue, 16 Jul 2013 14:59:28 -0400")
Mark H Weaver <mhw@netris.org> writes:
> Hi David,
>
> David Kastrup <dak@gnu.org> writes:
>
>> Mark H Weaver <mhw@netris.org> writes:
>>
>>> 'eqv?' is Scheme's fundamental "operational equivalence" predicate.
>>> 'eq?' is just an ugly efficiency hack, a poor cousin of 'eqv?' that
>>> fails in surprising ways. No _correct_ program is ever broken by making
>>> 'eq?' an alias to 'eqv?'. Many programs contain subtle bugs because of
>>> their inappropriate use of 'eq?'.
>>>
>>> What's the argument on the other side? Is there a compelling reason to
>>> use 'eq?' instead of 'eqv?' for object properties?
>>
>> object identity is checked by eq? and is conceptually different from
>> value equality.
>
> The Scheme standards don't support your view. The _only_ difference
> between 'eq?' and 'eqv?' is that 'eqv?' is well-defined on numbers and
> characters, whereas 'eq?' is unspecified for those types.
And why would that be if numbers were proper objects? The difference is
_exactly_ there because they aren't.
> Numbers and characters do not have any notion of "object identity",
> apart from operational equivalence.
Which is why it does not make a lot of sense to assign "object
properties" to them.
--
David Kastrup
next prev parent reply other threads:[~2013-07-16 19:30 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-04 18:03 bug#14792: Error in manual "(guile-2) Object Properties" David Kastrup
2013-07-05 16:37 ` Mark H Weaver
2013-07-06 21:21 ` Ludovic Courtès
2013-07-16 15:59 ` Mark H Weaver
2013-07-16 18:46 ` David Kastrup
2013-07-16 18:59 ` Mark H Weaver
2013-07-16 19:30 ` David Kastrup [this message]
2013-07-16 19:52 ` Mark H Weaver
2013-07-16 20:01 ` David Kastrup
2013-07-16 18:53 ` Ludovic Courtès
2013-07-27 21:19 ` bug#14792: Actually, this discussion is moot David Kastrup
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