From: Andy Wingo <wingo@pobox.com>
To: Alejandro Sanchez <hiphish@openmailbox.org>
Cc: guile-user@gnu.org
Subject: Re: Using '-1' in a method named '*'
Date: Tue, 28 Feb 2017 09:54:15 +0100 [thread overview]
Message-ID: <87r32ipufc.fsf@pobox.com> (raw)
In-Reply-To: <8760jvsan4.fsf@pobox.com> (Andy Wingo's message of "Mon, 27 Feb 2017 20:21:03 +0100")
On Mon 27 Feb 2017 20:21, Andy Wingo <wingo@pobox.com> writes:
> Hi,
>
> On Mon 27 Feb 2017 11:06, Alejandro Sanchez <hiphish@openmailbox.org> writes:
>
>> (define v (make <vector3> #:x 1))
>>
>> (* -1 v) ; Does not work
>> (* -2 v) ; Works fine
>
> I believe that Guile is doing strength reduction, transforming (* -1 v)
> to (- 0 v).
I spoke too soon. Guile 2.1.x does indeed do this at compile-time, but
only if "v" is an instance of a built-in number type. Guile 2.0.x
doesn't do this strength reduction at all at compile-time.
It turns out there is an easier way to reproduce this bug without GOOPS:
(* -1 "")
scm_product was handling this case specially because of weird
implementation reasons (making sure that negating the most negative
fixnum was a bignum; see b5c40589).
In summary I think Guile's strength reduction is fine as it relies on
type inference to prove when it is safe. This is "just" a bug, albeit
an annoying one that we need to fix!
Andy
next prev parent reply other threads:[~2017-02-28 8:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-27 10:06 Using '-1' in a method named '*' Alejandro Sanchez
2017-02-27 19:21 ` Andy Wingo
2017-02-27 22:26 ` Alejandro Sanchez
2017-02-28 8:00 ` tomas
2017-02-28 8:54 ` Andy Wingo [this message]
2017-02-28 9:19 ` Andy Wingo
2017-02-28 14:24 ` Alejandro Sanchez
2017-02-28 17:53 ` Amirouche
2017-02-28 18:32 ` Ralf Mattes
2017-03-01 17:25 ` Andy Wingo
2017-03-01 23:46 ` Alejandro Sanchez
2017-03-02 0:18 ` Thomas Morley
-- strict thread matches above, loose matches on Subject: below --
2017-03-03 0:07 Sandic, Aleksandar
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