From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr X-Spam-Level: X-Spam-Status: No, score=0.0 required=5.0 tests=none autolearn=disabled version=3.1.3 X-Original-To: caml-list@yquem.inria.fr Delivered-To: caml-list@yquem.inria.fr Received: from discorde.inria.fr (discorde.inria.fr [192.93.2.38]) by yquem.inria.fr (Postfix) with ESMTP id 306DCBC69 for ; Sat, 24 Mar 2007 07:48:14 +0100 (CET) Received: from ipmail03.adl2.internode.on.net (ipmail03.adl2.internode.on.net [203.16.214.135]) by discorde.inria.fr (8.13.6/8.13.6) with ESMTP id l2O6mB8T000325 for ; Sat, 24 Mar 2007 07:48:13 +0100 Received: from unknown (HELO [192.168.1.201]) ([121.44.236.93]) by ipmail03.adl2.internode.on.net with ESMTP; 24 Mar 2007 17:18:08 +1030 X-IronPort-AV: i="4.14,322,1170595800"; d="scan'208"; a="66946905:sNHT20199074" Subject: Re: [Caml-list] lazy evaluation of combinator parsers From: skaller To: Jeffrey Loren Shaw Cc: caml-list@inria.fr In-Reply-To: References: Content-Type: text/plain Date: Sat, 24 Mar 2007 17:48:03 +1100 Message-Id: <1174718883.7517.46.camel@rosella.wigram> Mime-Version: 1.0 X-Mailer: Evolution 2.8.1 Content-Transfer-Encoding: 7bit X-Miltered: at discorde with ID 4604C9AB.000 by Joe's j-chkmail (http://j-chkmail . ensmp . fr)! X-Spam: no; 0.00; combinator:01 parsers:01 seq:01 stack:01 seq:01 diverges:01 sourceforge:01 wrote:01 regex:01 regex:01 rec:01 rec:01 caml-list:01 functions:01 argument:02 On Fri, 2007-03-23 at 21:28 -0400, Jeffrey Loren Shaw wrote: > let alt p1 p2 xs = append (p1 xs) (p2 xs) > > (* regex ? *) > let opt a = alt a epsilon > > let rec recseq a = > seq > a > (recseq a) > > (* regex * *) > let rec star a = > recseq (opt a) > > However, "star (symbol 'a')" causes a stack overflow. I'm not sure why, > since my seq and alt functions are lazy. Arguments are evaluated right to left eagerly, so let rec recseq a = seq a (recseq a) is instantly an infinite loop. seq is not called here, it's second argument diverges. -- John Skaller Felix, successor to C++: http://felix.sf.net