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#8711: 24.0.50; binding _ to unused values with lexical-binding Date: Tue, 24 May 2011 09:42:31 -0300 Message-ID: References: NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1306240992 16001 80.91.229.12 (24 May 2011 12:43:12 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Tue, 24 May 2011 12:43:12 +0000 (UTC) Cc: 8711@debbugs.gnu.org To: Helmut Eller Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Tue May 24 14:43:08 2011 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([140.186.70.17]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1QOqx1-0007Un-VZ for geb-bug-gnu-emacs@m.gmane.org; Tue, 24 May 2011 14:43:08 +0200 Original-Received: from localhost ([::1]:47875 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QOqx1-0004LF-7c for geb-bug-gnu-emacs@m.gmane.org; Tue, 24 May 2011 08:43:07 -0400 Original-Received: from eggs.gnu.org ([140.186.70.92]:40368) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QOqwy-0004L4-6t for bug-gnu-emacs@gnu.org; Tue, 24 May 2011 08:43:05 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QOqwx-0006eg-4y for bug-gnu-emacs@gnu.org; Tue, 24 May 2011 08:43:04 -0400 Original-Received: from debbugs.gnu.org ([140.186.70.43]:34006) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QOqwx-0006ec-2P for bug-gnu-emacs@gnu.org; Tue, 24 May 2011 08:43:03 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.69) (envelope-from ) id 1QOqwv-0002Fg-RT; Tue, 24 May 2011 08:43:01 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Stefan Monnier Original-Sender: debbugs-submit-bounces@debbugs.gnu.org Resent-To: owner@debbugs.gnu.org Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Tue, 24 May 2011 12:43:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 8711 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: Original-Received: via spool by 8711-submit@debbugs.gnu.org id=B8711.13062409658634 (code B ref 8711); Tue, 24 May 2011 12:43:01 +0000 Original-Received: (at 8711) by debbugs.gnu.org; 24 May 2011 12:42:45 +0000 Original-Received: from localhost ([127.0.0.1] helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1QOqwd-0002FD-Ud for submit@debbugs.gnu.org; Tue, 24 May 2011 08:42:44 -0400 Original-Received: from fencepost.gnu.org ([140.186.70.10]) by debbugs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1QOqwb-0002F0-AZ for 8711@debbugs.gnu.org; Tue, 24 May 2011 08:42:42 -0400 Original-Received: from 213-159-126-200.fibertel.com.ar ([200.126.159.213]:42924 helo=ceviche.home) by fencepost.gnu.org with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1QOqwV-0002tu-RB; Tue, 24 May 2011 08:42:36 -0400 Original-Received: by ceviche.home (Postfix, from userid 20848) id E77C8662FB; Tue, 24 May 2011 09:42:31 -0300 (ART) In-Reply-To: (Helmut Eller's message of "Tue, 24 May 2011 08:01:44 +0200") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.11 Precedence: list Resent-Date: Tue, 24 May 2011 08:43:01 -0400 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 3) 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:46677 Archived-At: > ;; -*- lexical-binding: t -*- > (defun foo (x) (destructuring-bind (y &rest _) x y)) > x.el:2:1:Warning: variable `_' not left unused Ah, yes, this one. This is because CL's destructuring-bind expands the above to something like (let ((_ x) (y (prog1 (car _) (setq _ (cdr _))))) y) where _ is indeed not left unused. It also means that a closure that for (destructuring-bind (y &rest z) x (lambda () z)) the closure captures a mutated var which is something more costly (the var needs to be put inside a cons cell, leading to code along the lines of: (let ((z (list x)) (y (prog1 (car (car z)) (setcar z (cdr (car z)))))) (make-closure () [z] (car z))) Again this is a side-effect of `let' being costly in dynbind code. For lexbind code it would be better for destructuring-bind to use an additional internal var: (let (( x) (y (prog1 (car ) (setq (cdr )))) (_ )) y) Which would not generate any warning and would lead to more efficient code when the &rest var is captured by a closure. Stefan