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 XAA13920; Thu, 15 Jul 2004 23:42:46 +0200 (MET DST) X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f Received: from nez-perce.inria.fr (nez-perce.inria.fr [192.93.2.78]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id XAA16973 for ; Thu, 15 Jul 2004 23:42:45 +0200 (MET DST) Received: from smtp1.adl2.internode.on.net (smtp1.adl2.internode.on.net [203.16.214.181]) by nez-perce.inria.fr (8.12.10/8.12.10) with ESMTP id i6FLggEV019748 for ; Thu, 15 Jul 2004 23:42:43 +0200 Received: from [192.168.1.200] (ppp216-145.lns1.syd3.internode.on.net [203.122.216.145]) by smtp1.adl2.internode.on.net (8.12.9/8.12.9) with ESMTP id i6FLga4Y036052; Fri, 16 Jul 2004 07:12:37 +0930 (CST) Subject: Re: [Caml-list] Unboxing options, was RE: assertions or exceptions? From: skaller Reply-To: skaller@users.sourceforge.net To: John Prevost Cc: Brian Hurt , Ocaml Mailing List In-Reply-To: <1089926230.29648.632.camel@pelican.wigram> References: <1089926230.29648.632.camel@pelican.wigram> Content-Type: text/plain Message-Id: <1089927755.29648.653.camel@pelican.wigram> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.2 (1.2.2-4) Date: 16 Jul 2004 07:42:35 +1000 Content-Transfer-Encoding: 7bit X-Miltered: at nez-perce with ID 40F6FA52.000 by Joe's j-chkmail (http://j-chkmail.ensmp.fr)! X-Loop: caml-list@inria.fr X-Spam: no; 0.00; caml-list:01 unboxing:01 sourceforge:01 2004:99 rephrase:01 unboxing:01 pointers:01 avoiding:01 ugg:99 9660:01 glebe:01 ocaml:01 ocaml:01 caml:01 caml:01 Sender: owner-caml-list@pauillac.inria.fr Precedence: bulk On Fri, 2004-07-16 at 07:17, skaller wrote: I should rephrase this: > This is wrong. The representation being suggested is: > > None -> NULL > Some 'a -> pointer to 'a > > Clearly this represntation is faithful and nothing > more than an interpretation of the corresponding C > concept. > > Some Some 1 is obviously distinct from Some 1 as reqiuired: > pointer to pointer to 1 is distinct from pointer to 1. > Some None is a pointer to NULL, which is distinct from > None which is just NULL. What I'm saying is that the idea is not unboxing, but untagging. Some 'a isn't a pointer to an 'a heap value, but a pointer to a CAML_VALUE which is a pointer to a heap value 'a. I don't see how the GC could support this in Ocaml, since Some 'a isn't a CAML_VALUE since it points to a box, not a heap object -- but in Felix it would work because the GC uses RTTI to locate pointers. So the idea is fine, but won't work with Ocaml GC. There's be no saving dereferencing a Some value here. The saving would be that simply loading the value into a register would set a condition code in the processor, avoiding any need to check the value of a tag word. Ugg .. sorry for the confusion :( -- 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