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: [VM] Tail recursion and multiple values Date: Sat, 28 Feb 2009 15:27:09 +0100 Message-ID: <871vtiiqma.fsf@gnu.org> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1235831263 24387 80.91.229.12 (28 Feb 2009 14:27:43 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 28 Feb 2009 14:27:43 +0000 (UTC) To: guile-devel@gnu.org Original-X-From: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Sat Feb 28 15:28:59 2009 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 4.50) id 1LdQBW-0006bQ-D5 for guile-devel@m.gmane.org; Sat, 28 Feb 2009 15:28:58 +0100 Original-Received: from localhost ([127.0.0.1]:56188 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LdQAB-0003KE-Am for guile-devel@m.gmane.org; Sat, 28 Feb 2009 09:27:35 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LdQA3-0003I9-4s for guile-devel@gnu.org; Sat, 28 Feb 2009 09:27:27 -0500 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LdQA1-0003Et-GD for guile-devel@gnu.org; Sat, 28 Feb 2009 09:27:26 -0500 Original-Received: from [199.232.76.173] (port=45682 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LdQA1-0003Ep-EK for guile-devel@gnu.org; Sat, 28 Feb 2009 09:27:25 -0500 Original-Received: from main.gmane.org ([80.91.229.2]:34911 helo=ciao.gmane.org) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1LdQA1-0005Al-2i for guile-devel@gnu.org; Sat, 28 Feb 2009 09:27:25 -0500 Original-Received: from list by ciao.gmane.org with local (Exim 4.43) id 1LdQ9t-0007MZ-Bw for guile-devel@gnu.org; Sat, 28 Feb 2009 14:27:17 +0000 Original-Received: from reverse-83.fdn.fr ([80.67.176.83]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 28 Feb 2009 14:27:17 +0000 Original-Received: from ludo by reverse-83.fdn.fr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sat, 28 Feb 2009 14:27:17 +0000 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 28 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: reverse-83.fdn.fr X-URL: http://www.fdn.fr/~lcourtes/ X-Revolutionary-Date: 10 =?iso-8859-1?Q?Vent=F4se?= an 217 de la =?iso-8859-1?Q?R=E9volution?= X-PGP-Key-ID: 0xEA52ECF4 X-PGP-Key: http://www.fdn.fr/~lcourtes/ludovic.asc X-PGP-Fingerprint: 821D 815D 902A 7EAB 5CEE D120 7FBA 3D4F EB1F 5364 X-OS: i686-pc-linux-gnu User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.90 (gnu/linux) Cancel-Lock: sha1:qCWiolKnG4oGrKAoGaJH8PuYQ6M= X-detected-operating-system: by monty-python.gnu.org: GNU/Linux 2.6, seldom 2.4 (older, 4) 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:8198 Archived-At: Hello! Use of multiple values breaks tail recursion in VM-compiled code: (let loop ((x 1000000)) (and (> x 0) (call-with-values (lambda () (values (1+ x) (1- x))) (lambda (next prev) (loop prev))))) This example yields a stack overflow with the VM, whereas tail recursion is correctly handled by the interpreter. Tail recursion for `call-with-values' is mandated by R5RS (info "(r5rs)Proper tail recursion"): Certain built-in procedures are also required to perform tail calls. The first argument passed to `apply' and to `call-with-current-continuation', and the second argument passed to `call-with-values', must be called via a tail call. Similarly, `eval' must evaluate its argument as if it were in tail position within the `eval' procedure. I'll look into it and report back if no one beats me. ;-) Thanks, Ludo'.