From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from majordomo@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id BAA05483; Sat, 9 Oct 2004 01:30:10 +0200 (MET DST) X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id BAA05460 for ; Sat, 9 Oct 2004 01:30:09 +0200 (MET DST) Received: from smtp1.adl2.internode.on.net (smtp1.adl2.internode.on.net [203.16.214.181]) by concorde.inria.fr (8.13.0/8.13.0) with ESMTP id i98NU6MX000615 for ; Sat, 9 Oct 2004 01:30:08 +0200 Received: from [192.168.1.200] (ppp213-29.lns2.syd3.internode.on.net [203.122.213.29]) by smtp1.adl2.internode.on.net (8.12.9/8.12.9) with ESMTP id i98NTu4Y098362; Sat, 9 Oct 2004 08:59:57 +0930 (CST) Subject: Re: [Caml-list] Recursive lists From: skaller Reply-To: skaller@users.sourceforge.net To: Alex Baretta Cc: David Brown , caml-list@pauillac.inria.fr In-Reply-To: <4166CC3E.3080909@baretta.com> References: <4166A764.3010905@baretta.com> <20041008154347.GA14210@old.davidb.org> <4166CC3E.3080909@baretta.com> Content-Type: text/plain Message-Id: <1097278194.19722.110.camel@pelican.wigram> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.2 (1.2.2-4) Date: 09 Oct 2004 09:29:55 +1000 Content-Transfer-Encoding: 7bit X-Miltered: at concorde with ID 416722FE.001 by Joe's j-chkmail (http://j-chkmail.ensmp.fr)! X-Loop: caml-list@inria.fr X-Spam: no; 0.00; caml-list:01 sourceforge:01 2004:99 baretta:01 cyclic:01 logically:01 cyclic:01 coinductive:01 supplies:99 9660:01 glebe:01 alex:01 nsw:01 snail:02 lazy:02 Sender: owner-caml-list@pauillac.inria.fr Precedence: bulk On Sat, 2004-10-09 at 03:19, Alex Baretta wrote: > Of course, a separate Cyclic_list module could be defined to > access the cyclic-safe functions, but from an abstract point of view > such functions logically belong to List. No they don't. List is an inductive data type, and it is always finite. A data structure with a cyclic pointer chain cannot represent a list. A cyclic list is actually an instance of a coinductive data type, and this particular one is called a stream. In fact the List module is already *faulty* because it supplies hd and tl, which are not list operators at all -- they're the characteristic functions of streams (just as Cons and Empty characterise lists). So there is actually a good argument for a Stream module with hd and tl functions (and lazy map ..) -- John Skaller, mailto:skaller@users.sf.net voice: 061-2-9660-0850, snail: PO BOX 401 Glebe NSW 2037 Australia Checkout the Felix programming language http://felix.sf.net ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners