From: Juri Linkov <juri@jurta.org>
To: Stephen Berman <stephen.berman@gmx.net>
Cc: Stefan Monnier <monnier@IRO.UMontreal.CA>, emacs-devel@gnu.org
Subject: Re: power set (Re: Modified keypad keys)
Date: Mon, 01 Oct 2012 12:27:43 +0300 [thread overview]
Message-ID: <87pq52h7fk.fsf@mail.jurta.org> (raw)
In-Reply-To: <87lifqei20.fsf@rosalinde.fritz.box> (Stephen Berman's message of "Mon, 01 Oct 2012 10:02:31 +0200")
> As an alternative to the recursive definition, I've also been using
> this iterative bitwise version (which I translated into Elisp from the
> C program at http://rosettacode.org/wiki/Power_set#C):
Often a C version doesn't translate nicely to Lisp when translated
literally. If you prefer an iterative version instead of recursive,
you could look at the Common Lisp section of
http://rosettacode.org/wiki/Power_set#Common_Lisp
and find the following short iterative version:
(defun powerset (xs)
(loop for i below (expt 2 (length xs)) collect
(loop for j below i for x in xs if (logbitp j i) collect x)))
There is no `logbitp' function in Emacs, but you could use a replacement
like this:
(defun logbitp (j i) (> (logand i (lsh 1 j)) 0))
prev parent reply other threads:[~2012-10-01 9:27 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-28 6:40 Modified keypad keys Per Starbäck
2012-09-28 8:23 ` Stefan Monnier
2012-09-28 15:29 ` Juri Linkov
2012-09-28 20:16 ` Stefan Monnier
2012-09-29 2:14 ` Stefan Monnier
2012-09-29 19:19 ` Juri Linkov
2012-09-30 1:41 ` Stefan Monnier
2012-09-30 9:56 ` Juri Linkov
2012-09-30 19:45 ` Stefan Monnier
2012-10-01 9:29 ` Juri Linkov
2012-10-01 15:03 ` Stefan Monnier
2012-10-04 18:41 ` Juri Linkov
2012-10-04 23:26 ` Andreas Schwab
2012-10-05 14:41 ` Andreas Schwab
2012-10-05 16:43 ` Juri Linkov
2012-10-05 16:55 ` Andreas Schwab
2012-10-05 17:05 ` Juri Linkov
2012-10-01 8:02 ` power set (Re: Modified keypad keys) Stephen Berman
2012-10-01 8:35 ` Christopher Monsanto
2012-10-01 9:07 ` Stephen Berman
2012-10-01 12:42 ` Lars Magne Ingebrigtsen
2012-10-01 13:06 ` Stephen Berman
2012-10-01 9:27 ` Juri Linkov [this message]
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