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 WAA12042; Tue, 30 Dec 2003 22:06:41 +0100 (MET)
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 WAA13207 for <caml-list@pauillac.inria.fr>; Tue, 30 Dec 2003 22:06:40 +0100 (MET)
X-SPAM-Warning: Sending machine is listed in blackholes.five-ten-sg.com
Received: from gadolinium.btinternet.com (gadolinium.btinternet.com [194.73.73.111])
	by nez-perce.inria.fr (8.11.1/8.11.1) with ESMTP id hBUL6dv14795
	for <caml-list@inria.fr>; Tue, 30 Dec 2003 22:06:39 +0100 (MET)
Received: from [81.128.10.227] (helo=beertje.william.bogus)
	by gadolinium.btinternet.com with esmtp (Exim 3.22 #25)
	id 1AbR4V-0005G7-00
	for caml-list@inria.fr; Tue, 30 Dec 2003 21:06:35 +0000
Received: by beertje.william.bogus (Postfix, from userid 501)
	id ABA5C96BAB; Tue, 30 Dec 2003 21:02:29 +0000 (GMT)
From: William Chesters <williamc@paneris.org>
To: caml-list@inria.fr
Subject: [Caml-list] Recursive class types (long-standing question ...)
Message-Id: <20031230210229.ABA5C96BAB@beertje.william.bogus>
Date: Tue, 30 Dec 2003 21:02:29 +0000 (GMT)
X-Loop: caml-list@inria.fr
X-Spam: no; 0.00; chesters:01 williamc:01 paneris:01 struct:01 workarounds:01 bool:01 bool:01 int:01 int:01 compile:02 harder:02 classes:03 recursive:03 recursive:03 object:03 
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

Here's something I've wondered about for a while and just encountered again.
How come this class ..

    class virtual ['a] c = object
      method virtual b: bool c
    end

... gets a constraint 'a = bool?  I.e. for instance this doesn't compile:

    class virtual ['a] c = object
      method virtual b: bool c
      method virtual i: int c
          (* "This type int should be an instance of type bool" *)
    end

Note that the following does work in C++:

    template <class a>
    struct c {
      virtual c<bool> b() = 0;
      virtual c<int> i() = 0;
    };

I guess there are workarounds but it seems unnecessary that ML should find
recursive parameterised classes harder than C++?

-------------------
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