From: Michael Welsh Duggan <mwd@md5i.com>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Lexical let and setq
Date: Fri, 13 Sep 2013 20:09:05 -0400 [thread overview]
Message-ID: <878uz0e02m.fsf_-_@maru2.md5i.com> (raw)
In-Reply-To: <jwvzjrhqrft.fsf-monnier+emacs@gnu.org> (Stefan Monnier's message of "Fri, 13 Sep 2013 00:37:25 -0400")
Stefan Monnier <monnier@iro.umontreal.ca> writes:
[...]
> I do hope to fix those issues by introducing other byte-codes which will
> let us generate significantly more efficient code for those constructs,
> but in 24.1, the priority was to get lexical-binding to work correctly,
> performance being a secondary concern (tho for most idiomatic Elisp
> code, the performance tends to be competitive).
>
> What people should know is that
>
> (let (x y z)
> ...(setq x ...)
> ...(setq z ...)
> ...(setq y ...)
>
> is often a bad idea in Elisp, and even more so in lexical-binding code
> (in some cases, if a variable is immutable it can be handled
> significantly more efficiently, so the mere existence of a single `setq'
> on a variable can sometimes slow other chunks of code: in many cases
> `let' is cheaper than `setq').
The primary reason I have seen the (let (foo) (setq foo ...)) idiom is
in looping code. The way I would normally try to avoid this idiom in
most FP languages would be to use recursion (specifically tail
recursion, if possible). I know some work was done on implementing
efficient tail-recursion in the byte compiler. Has any of that made it
onto the trunk yet?
--
Michael Welsh Duggan
(md5i@md5i.com)
next prev parent reply other threads:[~2013-09-14 0:09 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-06 20:59 bug#15294: 24.3.50; js2-mode parser is several times slower in lexical-binding mode Dmitry Gutov
2013-09-06 23:44 ` Xue Fuqiao
2013-09-07 3:15 ` Stefan Monnier
2013-09-08 22:32 ` Stefan Monnier
2013-09-10 2:04 ` Stefan Monnier
2013-09-13 3:40 ` Stefan Monnier
2013-09-13 3:59 ` Drew Adams
2013-09-13 4:37 ` Stefan Monnier
2013-09-13 5:45 ` Drew Adams
2013-09-13 13:01 ` Stefan Monnier
2013-09-14 0:09 ` Michael Welsh Duggan [this message]
2013-09-14 3:46 ` Lexical let and setq Stefan Monnier
2013-09-14 11:13 ` Lars Magne Ingebrigtsen
2013-09-14 14:04 ` Pascal J. Bourguignon
2013-09-15 5:11 ` Stefan Monnier
2013-09-14 21:47 ` Richard Stallman
2013-09-15 5:09 ` Stefan Monnier
2013-09-15 16:54 ` Richard Stallman
2013-09-15 17:06 ` Stefan Monnier
2013-09-16 10:47 ` Richard Stallman
2013-09-14 4:20 ` bug#15294: 24.3.50; js2-mode parser is several times slower in lexical-binding mode Dmitry Gutov
2013-09-14 14:27 ` Stefan Monnier
2013-09-15 0:11 ` Dmitry Gutov
2013-09-15 5:04 ` Stefan Monnier
2013-09-15 16:54 ` Richard Stallman
2013-09-15 0:24 ` Dmitry Gutov
2013-09-15 5:06 ` Stefan Monnier
2013-09-18 23:48 ` Stefan Monnier
2013-09-22 4:56 ` Dmitry Gutov
2013-10-03 5:00 ` Stefan Monnier
2013-10-04 2:38 ` Dmitry Gutov
2013-10-04 13:52 ` Stefan Monnier
2013-10-05 3:27 ` Dmitry Gutov
2014-12-14 12:31 ` Dmitry Gutov
2014-12-14 14:08 ` Stefan Monnier
-- strict thread matches above, loose matches on Subject: below --
2013-09-16 15:59 Lexical let and setq Barry OReilly
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