From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (from weis@localhost) by pauillac.inria.fr (8.7.6/8.7.3) id LAA24604 for caml-redistribution; Thu, 21 Oct 1999 11:43:17 +0200 (MET DST) 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 QAA18003 for ; Wed, 20 Oct 1999 16:39:55 +0200 (MET DST) Received: from alcaudon.tsc.uc3m.es (alcaudon.tsc.uc3m.es [163.117.145.35]) by nez-perce.inria.fr (8.8.7/8.8.7) with ESMTP id QAA29791 for ; Wed, 20 Oct 1999 16:39:44 +0200 (MET DST) Received: from tsc.uc3m.es (garza.tsc.uc3m.es [163.117.145.203]) by alcaudon.tsc.uc3m.es (Netscape Messaging Server 3.6) with ESMTP id AAA1FE4 for ; Wed, 20 Oct 1999 16:39:21 +0200 Received: from tsc.uc3m.es (fenix [163.117.145.58]) by tsc.uc3m.es (8.9.3/8.9.3) with ESMTP id QAA06569 for ; Wed, 20 Oct 1999 16:39:12 +0200 (MET DST) Message-ID: <380DD2B0.A697F9D7@tsc.uc3m.es> Date: Wed, 20 Oct 1999 16:33:20 +0200 From: "Francisco Valverde Albacete" X-Mailer: Mozilla 4.51 [en] (WinNT; I) X-Accept-Language: en MIME-Version: 1.0 To: caml-list@inria.fr Subject: Semantics for objects [Was: Thoughts on O'Labl O'Caml merge.] References: <3809AC91.4E85FB85@maxtal.com.au> <380CC42E.772DA81@maxtal.com.au> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: weis Il y a un petit resume en francais a la fin. ----------------------- skaller wrote: > My opinion is quite different: object orientation > cannot possibly work. It is completely unsupported by any > coherent theory and can be so easily discredited by a single > example that it is clear adherents were simply ignorant > of basic theory. [no binary operator can be correctly > represented; more generally, no n-ary relation for n>1] > > > Okay, so the obvious symptom of the disease is that 'a appears > > covariantly in get_center, and contravariantly in set_center. But > > what's the root cause of these symptoms? > > Simple. The covariance problem is a direct consequence of > the incorrect assumption that a class can represent an abstraction. > We know from category theory that a CATEGORY and NOT a class > represents an abstraction, and an instance of the abstraction > must be a functor. I think there's some people trying to give final coalgebra semantics to objects, certainly to "states". I have only began to understand the issue (I look at it from the perspective of labelled transition systems), but the landscape looks beautiful (if daunting!). Have a look at J.J.M.J. Rutten's page http://www.cwi.nl/~janr/ or specifically for objects B. Jacobs: http://www.cwi.nl/~bjacobs/ I think you'll find this interesting: B. Jacobs, Objects and classes, co-algebraically. In: B. Freitag, C.B. Jones, C. Lengauer, and H.-J. Schek (eds) Object-Orientation with Parallelism and Persistence Kluwer Acad. Publ., 1996, p. 83--103. Regards, Francisco Valverde -------------------------------------- Resume en (affreux) francais: Il semble qu'on peut assigner une semantique de coalgebre finale aux objects et ses classes. V. les URL cites en haut.