From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: ludo@gnu.org (Ludovic =?iso-8859-1?Q?Court=E8s?=) Newsgroups: gmane.lisp.guile.devel Subject: Re: match-abs Date: Tue, 31 Aug 2010 00:55:15 +0200 Message-ID: <87vd6rhfsc.fsf@gnu.org> References: <201008292356.42854.stefan.tampe@spray.se> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Trace: dough.gmane.org 1283208939 22325 80.91.229.12 (30 Aug 2010 22:55:39 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Mon, 30 Aug 2010 22:55:39 +0000 (UTC) To: guile-devel@gnu.org Original-X-From: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Tue Aug 31 00:55:38 2010 Return-path: Envelope-to: guile-devel@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1OqDGL-0005Yn-TI for guile-devel@m.gmane.org; Tue, 31 Aug 2010 00:55:38 +0200 Original-Received: from localhost ([127.0.0.1]:42991 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OqDGL-0000e1-GD for guile-devel@m.gmane.org; Mon, 30 Aug 2010 18:55:37 -0400 Original-Received: from [140.186.70.92] (port=43756 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OqDGC-0000cG-E6 for guile-devel@gnu.org; Mon, 30 Aug 2010 18:55:29 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OqDGA-0003um-Hj for guile-devel@gnu.org; Mon, 30 Aug 2010 18:55:28 -0400 Original-Received: from lo.gmane.org ([80.91.229.12]:46379) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OqDGA-0003uR-5p for guile-devel@gnu.org; Mon, 30 Aug 2010 18:55:26 -0400 Original-Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1OqDG7-0005Ni-Of for guile-devel@gnu.org; Tue, 31 Aug 2010 00:55:23 +0200 Original-Received: from yoda.fdn.fr ([80.67.169.18]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 31 Aug 2010 00:55:23 +0200 Original-Received: from ludo by yoda.fdn.fr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 31 Aug 2010 00:55:23 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 53 Original-X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: yoda.fdn.fr X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 14 Fructidor an 218 de la =?iso-8859-1?Q?R=E9volutio?= =?iso-8859-1?Q?n?= X-PGP-Key-ID: 0xEA52ECF4 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 83C4 F8E5 10A3 3B4C 5BEA D15D 77DD 95E2 EA52 ECF4 X-OS: x86_64-unknown-linux-gnu User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) Cancel-Lock: sha1:VxOBLAAHqQpHgkdmer66hqkD07o= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) X-BeenThere: guile-devel@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Developers list for Guile, the GNU extensibility library" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Errors-To: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.lisp.guile.devel:10815 Archived-At: Hi Stefan! Stefan Israelsson Tampe writes: > I've hacked on extension on ice-9/match for making modular matching possible > with a reasonable interface. That sounds like a worthy goal to me. Pattern matching in Scheme appears to be limited in this respect compared to other functional languages (OCaml, Scala, & co. whose pattern matchers are effectively extended by defining new types.) > ;;Example, notice (( A B)) means first result of is stored in A and > the second is in B > (define ( X) > (match abstractions (( A B)) > X > (['- . L] (cons (- B A) L)) > (['+ . L] (cons (+ A B) L)) > (['* . L] (cons (* A B) L)) > (['/ . L] (cons (/ B A) L)) > ([(? number? X) . L] (cons X L)) > (_ (cons #f #f)))) > > ;;alternatively one can use the more general but wordy <> notation > (define ( X) > (match X > (['- (<> A) (<> B) . L] (cons (- A B) L)) > (['+ (<> A) (<> B) . L] (cons (+ A B) L)) > (['* (<> A) (<> B) . L] (cons (* A B) L)) > (['/ (<> A) (<> B) . L] (cons (/ A B) L)) > ([(? number? X) . L] (cons X L)) > (_ (cons #f #f)))) > > (define (rpn x) (car ( (reverse x)))) > > ;;and (rpn '(2 4 * 1 -)) evaluates to 7 > > > So e.g. the protocol for a matcher is that the last argument for a matcher > is the list to match on. The matcher should return a cons cell, if the car > element is false the match fails and else it is the value of the match. the > second argument represent the rest of the list after the match has been > removed. Hmm, sorry, I don’t understand what you mean here. Can you come up with a simpler example? What does ‘<>’ mean? Is there a connection between occurrences of ‘’ in patterns and the fact that the procedure is bound to ‘’? Thanks, Ludo’.