From: Ted Zlatanov <tzz@lifelogs.com>
To: help-gnu-emacs@gnu.org
Subject: Re: random predicate function
Date: Wed, 15 Dec 2010 08:51:14 -0600 [thread overview]
Message-ID: <8739pz144d.fsf@lifelogs.com> (raw)
In-Reply-To: 8762uxr2cc.fsf@kuiper.lan.informatimago.com
On Mon, 13 Dec 2010 18:48:19 +0100 "Pascal J. Bourguignon" <pjb@informatimago.com> wrote:
PJB> Ted Zlatanov <tzz@lifelogs.com> writes:
>> On Mon, 13 Dec 2010 16:26:03 +0100 "Pascal J. Bourguignon" <pjb@informatimago.com> wrote:
>>
PJB> You could instead put your paragraphs in a vector and use:
>>
PJB> (defun shuffle (vector)
PJB> "Re-orders randomly the vector."
PJB> (loop
PJB> for i from (1- (length vector)) downto 1
PJB> do (rotatef (aref vector i) (aref vector (random i)))))
>>
PJB> to shuffle them and then re-insert them.
>>
>> I noticed this function in lisp/play/cookie1.el which doesn't require
>> CL:
>>
>> ; Thanks to Ian G Batten <BattenIG@CS.BHAM.AC.UK>
>> ; [of the University of Birmingham Computer Science Department]
>> ; for the iterative version of this shuffle.
>> ;
>> ;;;###autoload
>> (defun shuffle-vector (vector)
>> "Randomly permute the elements of VECTOR (all permutations equally likely)."
>> (let ((i 0)
>> j
>> temp
>> (len (length vector)))
>> (while (< i len)
>> (setq j (+ i (random (- len i))))
>> (setq temp (aref vector i))
>> (aset vector i (aref vector j))
>> (aset vector j temp)
>> (setq i (1+ i))))
>> vector)
PJB> This is a clear demonstration of the power of macros, and the goodness
PJB> of Common Lisp which includes a more powerful set of predefined macros
PJB> than any other remaining lisp.
I agree the CL macros are nicer, but the non-macro version is much
easier to debug *in GNU Emacs* and it's already installed. So they both
have benefits.
Can your `shuffle' be part of cl-extra.el in Emacs? I like the brevity
of it, and it's a good example of how to use `loop' properly.
Ted
next prev parent reply other threads:[~2010-12-15 14:51 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.0.1292251427.11097.help-gnu-emacs@gnu.org>
2010-12-13 15:26 ` random predicate function Pascal J. Bourguignon
2010-12-13 17:16 ` Ted Zlatanov
2010-12-13 17:48 ` Pascal J. Bourguignon
2010-12-15 14:51 ` Ted Zlatanov [this message]
2010-12-15 15:20 ` Pascal J. Bourguignon
2010-12-15 16:44 ` Ted Zlatanov
2010-12-15 17:28 ` Pascal J. Bourguignon
2010-12-15 18:39 ` Ted Zlatanov
2010-12-15 18:04 ` Drew Adams
2010-12-13 18:17 ` Tyler Smith
[not found] ` <mailman.2.1292264248.1009.help-gnu-emacs@gnu.org>
2010-12-13 18:38 ` Pascal J. Bourguignon
2010-12-13 19:05 ` Tyler Smith
2010-12-13 14:43 Tyler Smith
2010-12-13 15:37 ` Gary
2010-12-13 16:08 ` Tyler Smith
2010-12-13 16:16 ` Erik Iverson
2010-12-13 16:50 ` Tyler Smith
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