From: Paul Eggert <eggert@cs.ucla.edu>
To: Stefan Monnier <monnier@iro.umontreal.ca>, David Kastrup <dak@gnu.org>
Cc: "Stephen J. Turnbull" <stephen@xemacs.org>, emacs-devel@gnu.org
Subject: Re: Unary /
Date: Thu, 15 Oct 2015 12:20:42 -0700 [thread overview]
Message-ID: <561FFC8A.8030701@cs.ucla.edu> (raw)
In-Reply-To: <jwvzizkotwn.fsf-monnier+emacs@gnu.org>
On 10/15/2015 11:45 AM, Stefan Monnier wrote:
> Indeed, the - has the same asymmetry, but it seems that "unary -" is much
> more commonly found operator than "unary /".
I suspect David was being ironic....
Unary / is rare in Elisp code, partly because the GNU Emacs byte
compiler complains about it, partly because it doesn't work in GNU Emacs
24.2 and earlier, partly because it has the Common Lisp semantics in
XEmacs, and partly because one doesn't often need the reciprocal of a
floating-point number. With all that being said, it's a bit more useful
for (/ N) to return the reciprocal of N than to return N, so we might as
well be compatible with CL here.
I've proposed a patch to change unary / to behave more like CL, in
Bug#21690. Since we're in feature-freeze now isn't a good time to be
changing the semantics of /, but there's no rush. In the meantime we can
leave the byte-compiler alone, as its bogus warning about (/ N) will
help scare users away from the soon-to-be-withdrawn semantics.
next prev parent reply other threads:[~2015-10-15 19:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-15 11:30 Unary / David Kastrup
2015-10-15 11:48 ` Stephen J. Turnbull
2015-10-15 11:54 ` David Kastrup
2015-10-15 12:00 ` Tassilo Horn
2015-10-15 12:17 ` David Kastrup
2015-10-15 13:31 ` Stefan Monnier
2015-10-15 14:02 ` David Kastrup
2015-10-15 18:45 ` Stefan Monnier
2015-10-15 19:20 ` Paul Eggert [this message]
2015-10-15 12:09 ` Andreas Schwab
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