From: Geoff Gole <geoffgole@gmail.com>
To: Daniel Colascione <daniel@censorshipresearch.org>
Cc: Emacs development discussions <emacs-devel@gnu.org>
Subject: Re: O(N^2) behavior in LOOP
Date: Sun, 30 May 2010 06:35:26 +0800 [thread overview]
Message-ID: <AANLkTilFHHbnZbffRpqQGpYJVN0sZsCZ2vx-QYrUP_EH@mail.gmail.com> (raw)
In-Reply-To: <4C018FD3.1020305@censorshipresearch.org>
For what it's worth, the elisp and SBCL implementations of LOOP behave
differently when the last cdr of the loop is assigned to.
; elisp
(loop for i from 1 to 3
collecting i into x
collecting (progn (setf (cdr (last x)) (list 'foo)) 1) into x
finally (return x))
(1 foo 1 2 foo 1 3 foo 1)
; SBCL
(loop for i from 1 to 3
collecting i into x
collecting (progn (setf (cdr (last x)) (list 'foo)) 1) into x
finally (return x))
(1 1 2 1 3 1)
The SBCL macro emits much more efficient code, but I think it's wrong.
Not that LOOP is a particuarly well defined thing to judge correctness
against.
next prev parent reply other threads:[~2010-05-29 22:35 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-29 21:56 O(N^2) behavior in LOOP Daniel Colascione
2010-05-29 22:06 ` Daniel Colascione
2010-05-29 22:14 ` Lennart Borgman
2010-05-29 22:35 ` Geoff Gole [this message]
2010-05-29 23:58 ` [PATCH] use tail pointer for LOOP (Was: Re: O(N^2) behavior in LOOP) Daniel Colascione
2010-05-30 0:45 ` Ken Raeburn
2010-05-30 0:49 ` Daniel Colascione
2010-06-16 17:44 ` tomas
2010-06-16 18:10 ` [PATCH] use tail pointer for LOOP David Kastrup
2010-06-17 5:10 ` tomas
2010-06-17 7:18 ` Thien-Thi Nguyen
2010-06-17 9:22 ` tomas
2010-06-17 10:03 ` Thien-Thi Nguyen
2010-06-17 14:05 ` tomas
2010-06-17 15:16 ` Thien-Thi Nguyen
2010-06-17 10:12 ` Thien-Thi Nguyen
2010-06-17 20:48 ` Stefan Monnier
2010-06-18 7:07 ` David Kastrup
2010-06-18 13:40 ` Stefan Monnier
2010-05-30 17:05 ` Štěpán Němec
2010-05-30 17:09 ` Daniel Colascione
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