From: Stefan Monnier <monnier@iro.umontreal.ca>
To: emacs-devel@gnu.org
Subject: Re: hash-consing bignums and eq==eql
Date: Wed, 29 Aug 2018 16:50:33 -0400 [thread overview]
Message-ID: <jwvefeggb35.fsf-monnier+gmane.emacs.devel@gnu.org> (raw)
In-Reply-To: 075ee700-d431-9434-c9d9-a7b3ae3f17fa@cs.ucla.edu
> This keeps 'eq' fast, and causes eq to start to "work" on floats whose
> bottom few bits are zero.
>> the distinction between eq and eql for integers leads to subtle bugs that
>> are best excluded by design, IMHO.
> Common Lisp and Scheme both have this distinction, and they seem to be doing
> OK. In this particular tradeoff between performance and nicer behavior, most
> Lisp users seem to prefer performance.
FWIW, I think this is a historical mistake and makes for many programs
being fundamentally yet unnecessarily not platform-independent (although
of course in practice the problem rarely manifests itself).
If you take EQ==EQL as a starting point, I think it's always reasonably
easy to get performance close enough to what you can get with a "faster
EQ".
Actually, I'm not opposed to having a low-level "fast equality test".
What I dislike is that this fast equality test be so prominent that we
encourage its use as the *standard* test, instead of keeping its use for
particular cases where the speed actually matters.
IOW, I'd be OK with:
(defalias 'fast-eq (symbol-function 'eq))
(defalias 'eq (symbol-function 'eql))
[ and its equivalent in C. ]
Stefan
next prev parent reply other threads:[~2018-08-29 20:50 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180821204437.16880.99611@vcs0.savannah.gnu.org>
[not found] ` <20180821204439.62390209A6@vcs0.savannah.gnu.org>
2018-08-22 12:36 ` [Emacs-diffs] master f18af6c: Audit use of lsh and fix glitches Pip Cet
2018-08-22 13:35 ` Ken Brown
2018-08-22 13:44 ` Paul Eggert
2018-08-22 15:50 ` Pip Cet
2018-08-22 17:27 ` Paul Eggert
2018-08-22 20:05 ` Pip Cet
2018-08-22 21:53 ` Paul Eggert
2018-08-22 20:45 ` Stefan Monnier
2018-08-23 14:55 ` Pip Cet
2018-08-23 15:56 ` Stefan Monnier
2018-08-24 18:00 ` Pip Cet
2018-08-24 20:55 ` Paul Eggert
2018-08-25 15:02 ` Pip Cet
2018-08-25 18:02 ` Stefan Monnier
2018-08-25 21:24 ` Paul Eggert
2018-08-28 14:08 ` hash-consing bignums and eq==eql Stefan Monnier
2018-08-29 13:32 ` Pip Cet
2018-08-29 19:23 ` Stefan Monnier
2018-08-29 19:31 ` Paul Eggert
2018-08-29 20:50 ` Stefan Monnier [this message]
2018-09-09 3:09 ` Stefan Monnier
2018-09-09 6:26 ` Paul Eggert
2018-08-22 13:49 ` [Emacs-diffs] master f18af6c: Audit use of lsh and fix glitches Pip Cet
2018-08-22 14:52 ` Eli Zaretskii
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