From: "Mikael Djurfeldt" <mdjurfeldt@gmail.com>
Cc: Clinton Ebadi <clinton@unknownlamer.org>,
Mikael Djurfeldt <djurfeldt@nada.kth.se>,
guile-devel@gnu.org
Subject: Re: Removal of SCM_UNBOUND
Date: Mon, 17 Apr 2006 10:21:41 +0200 [thread overview]
Message-ID: <66e540fe0604170121l6edacaefl68af43bcf77dfb69@mail.gmail.com> (raw)
In-Reply-To: <87ejzys9nt.fsf@ossau.uklinux.net>
On 4/16/06, Neil Jerram <neil@ossau.uklinux.net> wrote:
> Just to check my understanding: I believe the existing SCM_UNBNDP
> macro, which is used in C code to check for the presence of an
> optional argument, expands to (x == SCM_UNDEFINED); I presume that
> SCM_UNBOUND is a distinct value (and somewhat confusingly unrelated to
> SCM_UNBNDP) used by GOOPS to indicate an unbound slot.
Right. (If I remember correcty, the SCM_UNBOUND/SCM_UNBNDP confusion
was present already in the version of SCM which Guile originally was
based on. At that time, SCM_UNBOUND was used to mark an unbound
variable, so it is natural for GOOPS to use it to mark an unbound
slot.)
> Then, as Mikael says, bugs may be introduced where a Scheme primitive
> takes an optional argument and passes that argument on, untranslated,
> to code that uses that value to set or test a slot's value.
>
> That sounds unlikely, though. In my experience, I've never noticed
> SCM_UNDEFINED escaping onto the Scheme level, and all the primitive
> code that I can remember immediately translates SCM_UNDEFINED to some
> locally meaningful default value.
No, that's not what I mean. Rather, I think code internal to GOOPS
will at some instances extract and pass on the SCM_GOOPS_UNBOUND
value. If SCM_GOOPS_UNBOUND is defined to be the same value as
SCM_UNDEFINED, then SCM_UNDEFINED will escape this way, which
obviously leads to problems.
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prev parent reply other threads:[~2006-04-17 8:21 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-15 21:41 Removal of SCM_UNBOUND Clinton Ebadi
2006-04-15 22:03 ` Mikael Djurfeldt
2006-04-15 22:06 ` Mikael Djurfeldt
2006-04-15 22:13 ` Mikael Djurfeldt
2006-04-15 23:26 ` Neil Jerram
2006-04-17 8:21 ` Mikael Djurfeldt [this message]
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