From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Mark H Weaver Newsgroups: gmane.lisp.guile.bugs Subject: bug#17825: broken set! in iteration Date: Sat, 21 Jun 2014 17:29:05 -0400 Message-ID: <87r42ivtni.fsf@yeeloong.lan> References: <87vbruvu2v.fsf@yeeloong.lan> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1403386227 4229 80.91.229.3 (21 Jun 2014 21:30:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 21 Jun 2014 21:30:27 +0000 (UTC) Cc: 17825@debbugs.gnu.org To: =?UTF-8?Q?Al=C3=ADrio?= Eyng Original-X-From: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Sat Jun 21 23:30:20 2014 Return-path: Envelope-to: guile-bugs@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 1WySrb-0003hO-Pm for guile-bugs@m.gmane.org; Sat, 21 Jun 2014 23:30:19 +0200 Original-Received: from localhost ([::1]:46521 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WySrb-0004RY-D1 for guile-bugs@m.gmane.org; Sat, 21 Jun 2014 17:30:19 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:40888) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WySrS-0004Oq-Rh for bug-guile@gnu.org; Sat, 21 Jun 2014 17:30:17 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WySrL-00041O-To for bug-guile@gnu.org; Sat, 21 Jun 2014 17:30:10 -0400 Original-Received: from debbugs.gnu.org ([140.186.70.43]:37065) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WySrL-0003zX-RN for bug-guile@gnu.org; Sat, 21 Jun 2014 17:30:03 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.80) (envelope-from ) id 1WySrK-0004Sa-CG for bug-guile@gnu.org; Sat, 21 Jun 2014 17:30:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Mark H Weaver Original-Sender: "Debbugs-submit" Resent-CC: bug-guile@gnu.org Resent-Date: Sat, 21 Jun 2014 21:30:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 17825 X-GNU-PR-Package: guile X-GNU-PR-Keywords: notabug Original-Received: via spool by 17825-submit@debbugs.gnu.org id=B17825.140338619617113 (code B ref 17825); Sat, 21 Jun 2014 21:30:02 +0000 Original-Received: (at 17825) by debbugs.gnu.org; 21 Jun 2014 21:29:56 +0000 Original-Received: from localhost ([127.0.0.1]:56448 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1WySrD-0004Rv-Nv for submit@debbugs.gnu.org; Sat, 21 Jun 2014 17:29:56 -0400 Original-Received: from world.peace.net ([96.39.62.75]:47168 ident=hope4) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1WySrA-0004Rm-PK for 17825@debbugs.gnu.org; Sat, 21 Jun 2014 17:29:53 -0400 Original-Received: from 209-6-91-212.c3-0.smr-ubr1.sbo-smr.ma.cable.rcn.com ([209.6.91.212] helo=yeeloong.lan) by world.peace.net with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.72) (envelope-from ) id 1WySr2-00040V-MN; Sat, 21 Jun 2014 17:29:44 -0400 In-Reply-To: <87vbruvu2v.fsf@yeeloong.lan> (Mark H. Weaver's message of "Sat, 21 Jun 2014 17:19:52 -0400") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) 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-guile@gnu.org List-Id: "Bug reports for GUILE, GNU's Ubiquitous Extension Language" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Original-Sender: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.lisp.guile.bugs:7505 Archived-At: Mark H Weaver writes: > tags 17825 notabug > close 17825 > thanks > > Al=C3=ADrio Eyng writes: > >> I can't see why the second code doesn't work like the first: >> >> (use-modules (srfi srfi-1)) >> (define D '(((3 4)))) >> (let ((r 1)) >> (set! D (append D '(()))) >> (display D)(newline) >> (set-car! (drop D r) (car (drop D (- r 1))))) >> (let ((r 2)) >> (set! D (append D '(()))) >> (display D)(newline) >> (set-car! (drop D r) (car (drop D (- r 1))))) >> output: >> (((3 4)) ()) >> (((3 4)) ((3 4)) ()) >> >> (use-modules (srfi srfi-1)) >> (define D '(((3 4)))) >> (map (lambda (r) >> (set! D (append D '(()))) >> (display D)(newline) >> (set-car! (drop D r) (car (drop D (- r 1))))) >> '(1 2)) >> output: >> (((3 4)) ()) >> (((3 4)) ((3 4)) ((3 4))) > > This code mutates literal lists, which is not allowed. Specifically, > this code calls 'set-car!' on pairs that come from a literal list, > namely '(()). The optimizer assumes that this will never happen, and > generates code based on that assumption. Actually, this isn't even a question of optimization. It is simply the fact that '(()) returns the same pair every time, and the 'set-car!' mutates it to '((3 4)). In some future version of Guile, we hope to detect this error somehow, perhaps by keeping literals in read-only memory. (list '()), on the other hand, returns a freshly-allocated pair each time it is called. Mark