Subject: bug#14792: Error in manual "(guile-2) Object Properties"

From: David Kastrup <[email-masked]>
Date: Tue, 16 Jul 2013 21:30:50 +0200

Mark H Weaver <[email-masked]> writes:

> Hi David,
>
> David Kastrup <[email-masked]> writes:
>
>> Mark H Weaver <[email-masked]> 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