From mboxrd@z Thu Jan 1 00:00:00 1970 Path: main.gmane.org!not-for-mail From: Oliver Scholz Newsgroups: gmane.emacs.help Subject: Re: tail recursion hack in Emacs Lisp? Date: Fri, 16 Jul 2004 18:42:55 +0200 Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Message-ID: References: NNTP-Posting-Host: deer.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: sea.gmane.org 1089996466 3780 80.91.224.253 (16 Jul 2004 16:47:46 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Fri, 16 Jul 2004 16:47:46 +0000 (UTC) Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Fri Jul 16 18:47:38 2004 Return-path: Original-Received: from lists.gnu.org ([199.232.76.165]) by deer.gmane.org with esmtp (Exim 3.35 #1 (Debian)) id 1BlVs1-0007jj-00 for ; Fri, 16 Jul 2004 18:47:38 +0200 Original-Received: from localhost ([127.0.0.1] helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.33) id 1BlVuZ-00057e-4Y for geh-help-gnu-emacs@m.gmane.org; Fri, 16 Jul 2004 12:50:15 -0400 Original-Newsgroups: gnu.emacs.help X-Attribution: os X-Face: "HgH2sgK|bfH$; PiOJI6|qUCf.ve<51_Od(%ynHr?=>znn#~#oS>",F%B8&\vus),2AsPYb -n>PgddtGEn}s7kH?7kH{P_~vu?]OvVN^qD(L)>G^gDCl(U9n{:d>'DkilN!_K"eNzjrtI4Ya6; Td% IZGMbJ{lawG+'J>QXPZD&TwWU@^~A}f^zAb[Ru;CT(UA]c& User-Agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3.50 (windows-nt) Cancel-Lock: sha1:ICfmWdWW6ZeNC1nWaP/h1/HuiA8= Original-NNTP-Posting-Host: 82.83.134.210 Original-X-Trace: 16 Jul 2004 18:42:58 +0200, 82.83.134.210 Original-Lines: 60 Original-X-Complaints-To: abuse@arcor-ip.de Original-Path: shelby.stanford.edu!newsfeed.stanford.edu!newsmi-us.news.garr.it!newsmi-eu.news.garr.it!NewsITBone-GARR!feed.news.tiscali.de!newsfeed01.sul.t-online.de!t-online.de!newsfeed.arcor-ip.de!news.arcor-ip.de!82.83.134.210 Original-Xref: shelby.stanford.edu gnu.emacs.help:124336 Original-To: help-gnu-emacs@gnu.org X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: main.gmane.org gmane.emacs.help:19672 X-Report-Spam: http://spam.gmane.org/gmane.emacs.help:19672 [Sorry for talking to myself today.] Oliver Scholz writes: > Oliver Scholz writes: > > [`iterate' macro with code-walker] >> >> So my question is: Can anybody think of a case where this approach >> would break? > > Silly me. The usual case for breaking such things would apply: > > (iterate fact ((n 10) > (r 1)) > (if (= n 1) > r > (funcall (intern "fact") (1- n) (* n r)))) > > Not to mention `eval'. And of course that could be circumwented by `fset'ing NAME: (defmacro iterate (name arglist &rest body) (let ((catch-symbol (make-symbol "--repeat")) (continue (make-symbol "--continue")) (result (make-symbol "--result")) (fdef (make-symbol "--fdef")) (lambda-list (mapcar 'car arglist)) (initial-args (mapcar 'cadr arglist))) `(let ((,fdef (and (fboundp ',name) (symbol-function ',name)))) (unwind-protect (let ((,continue t) (,result (list ,@initial-args))) (fset ',name (lambda (&rest args) (throw ',catch-symbol args))) (while ,continue (setq ,result (catch ',catch-symbol (setq ,result (apply (lambda ,lambda-list ,@body) ,result)) (setq ,continue nil) ,result))) ,result) (if (null ,fdef) (fmakunbound ',name) (fset ',name ,fdef)))))) Yet, I dislike it more and more. Oliver -- 29 Messidor an 212 de la Révolution Liberté, Egalité, Fraternité!