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: [VM] Tail recursion and multiple values Date: Sat, 28 Feb 2009 15:45:19 +0100 Message-ID: <8763iuhb7k.fsf@gnu.org> References: <871vtiiqma.fsf@gnu.org> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Trace: ger.gmane.org 1235832387 27552 80.91.229.12 (28 Feb 2009 14:46:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 28 Feb 2009 14:46:27 +0000 (UTC) To: guile-devel@gnu.org Original-X-From: guile-devel-bounces+guile-devel=m.gmane.org@gnu.org Sat Feb 28 15:47:43 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 1LdQTf-0003wq-CY for guile-devel@m.gmane.org; Sat, 28 Feb 2009 15:47:43 +0100 Original-Received: from localhost ([127.0.0.1]:60412 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LdQSK-0007Ks-F6 for guile-devel@m.gmane.org; Sat, 28 Feb 2009 09:46:20 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1LdQRb-00071e-CV for guile-devel@gnu.org; Sat, 28 Feb 2009 09:45:35 -0500 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1LdQRZ-00070v-Nt for guile-devel@gnu.org; Sat, 28 Feb 2009 09:45:35 -0500 Original-Received: from [199.232.76.173] (port=41876 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1LdQRZ-00070g-Eq for guile-devel@gnu.org; Sat, 28 Feb 2009 09:45:33 -0500 Original-Received: from main.gmane.org ([80.91.229.2]:59855 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 1LdQRX-0008Et-Si for guile-devel@gnu.org; Sat, 28 Feb 2009 09:45:33 -0500 Original-Received: from list by ciao.gmane.org with local (Exim 4.43) id 1LdQRW-0007zb-Ve for guile-devel@gnu.org; Sat, 28 Feb 2009 14:45:30 +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 14:45:30 +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 14:45:30 +0000 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 36 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:LqRWn6SCN4ykmLC8X2D68OgSFbo= 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:8199 Archived-At: ludo@gnu.org (Ludovic Courtès) writes: > 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))))) Actually no: it works with VM-compiled code, but it breaks when using Guile-VM with `,o interp #t' (which appears to be the default, except at the REPL). In this case, `loop' is an interpreter procedure while `call-with-values' is a program. It's the implementation of `goto/args' in this particular case that seems to break tail recursion: if (!SCM_FALSEP (scm_procedure_p (x))) { POP_LIST (nargs); SYNC_REGISTER (); sp[-1] = scm_apply (x, sp[0], SCM_EOL); The `scm_apply ()' call introduces a new stack frame instead of re-using the current one. At this point I'm not sure how to fix it. We need better integration of calls from the VM to subrs/procedures anyway (notably removing `POP_LIST ()' and argument consing before subr/procedure calls!) so probably we could postpone this issue until then. Andy? Thanks, Ludo'.