From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.bugs Subject: bug#20268: 25.0.50; pcase-lambda broken Date: Wed, 08 Apr 2015 15:25:36 -0400 Message-ID: References: NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1428521246 7301 80.91.229.3 (8 Apr 2015 19:27:26 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 8 Apr 2015 19:27:26 +0000 (UTC) Cc: Leo Liu , 20268@debbugs.gnu.org To: Philipp Stephani Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Wed Apr 08 21:27:15 2015 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Yfvd4-0002zO-0d for geb-bug-gnu-emacs@m.gmane.org; Wed, 08 Apr 2015 21:27:14 +0200 Original-Received: from localhost ([::1]:54526 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfvd3-0006EQ-5T for geb-bug-gnu-emacs@m.gmane.org; Wed, 08 Apr 2015 15:27:13 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:52224) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfvcz-0006EJ-72 for bug-gnu-emacs@gnu.org; Wed, 08 Apr 2015 15:27:10 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yfvct-0003lM-4Y for bug-gnu-emacs@gnu.org; Wed, 08 Apr 2015 15:27:09 -0400 Original-Received: from debbugs.gnu.org ([140.186.70.43]:59727) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yfvct-0003lB-1Q for bug-gnu-emacs@gnu.org; Wed, 08 Apr 2015 15:27:03 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.80) (envelope-from ) id 1Yfvcs-0000qh-DD for bug-gnu-emacs@gnu.org; Wed, 08 Apr 2015 15:27:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Stefan Monnier Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Wed, 08 Apr 2015 19:27:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 20268 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: Original-Received: via spool by 20268-submit@debbugs.gnu.org id=B20268.14285211623174 (code B ref 20268); Wed, 08 Apr 2015 19:27:02 +0000 Original-Received: (at 20268) by debbugs.gnu.org; 8 Apr 2015 19:26:02 +0000 Original-Received: from localhost ([127.0.0.1]:49501 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1Yfvbt-0000p1-JK for submit@debbugs.gnu.org; Wed, 08 Apr 2015 15:26:01 -0400 Original-Received: from mercure.iro.umontreal.ca ([132.204.24.67]:47007) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1Yfvbs-0000ot-4f for 20268@debbugs.gnu.org; Wed, 08 Apr 2015 15:26:00 -0400 Original-Received: from hidalgo.iro.umontreal.ca (hidalgo.iro.umontreal.ca [132.204.27.50]) by mercure.iro.umontreal.ca (Postfix) with ESMTP id C35C59C128; Wed, 8 Apr 2015 15:25:59 -0400 (EDT) Original-Received: from lechon.iro.umontreal.ca (lechon.iro.umontreal.ca [132.204.27.242]) by hidalgo.iro.umontreal.ca (Postfix) with ESMTP id D9A2E1E5B8C; Wed, 8 Apr 2015 15:25:36 -0400 (EDT) Original-Received: by lechon.iro.umontreal.ca (Postfix, from userid 20848) id BB6FCB4122; Wed, 8 Apr 2015 15:25:36 -0400 (EDT) In-Reply-To: (Philipp Stephani's message of "Wed, 08 Apr 2015 15:08:36 +0000") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux) X-DIRO-MailScanner-Information: Please contact the ISP for more information X-DIRO-MailScanner: Found to be clean X-DIRO-MailScanner-SpamCheck: n'est pas un polluriel, SpamAssassin (score=-2.82, requis 5, autolearn=not spam, ALL_TRUSTED -2.82, MC_TSTLAST 0.00) X-DIRO-MailScanner-From: monnier@iro.umontreal.ca X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.15 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 140.186.70.43 X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Original-Sender: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.bugs:101301 Archived-At: > Why not raise an error instead if there is no match That would be an acceptable semantics, yes. I happen to dislike it because of the performance cost, where in most use-cases you know the pattern will match and just want to replace a bunch of car/cdr/aref with a single pattern. I.e. the code you'd have written without pcase-let would have been (let ((a (foo)) (b (car foo)) (c (nth 2 foo))) which would naturally turn into a pattern like `(,b ,_ ,c) but if you want to signal an error when the pattern fails to match, then you get 3 additional consp tests plus a null test, at which point the performance impact can become noticeable. You can get rid of the null test with a pattern like `(,b ,_ ,c . ,_) but you can't get rid of the 3 consp tests. Stefan