From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <peng.zang@gmail.com>
X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on yquem.inria.fr
X-Spam-Level: **
X-Spam-Status: No, score=2.8 required=5.0 tests=AWL,DNS_FROM_RFC_POST,
	SPF_NEUTRAL autolearn=disabled version=3.1.3
X-Original-To: caml-list@yquem.inria.fr
Delivered-To: caml-list@yquem.inria.fr
Received: from mail3-relais-sop.national.inria.fr (mail3-relais-sop.national.inria.fr [192.134.164.104])
	by yquem.inria.fr (Postfix) with ESMTP id CBC8CBBC4
	for <caml-list@yquem.inria.fr>; Fri,  6 Mar 2009 17:10:15 +0100 (CET)
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: Aq4CAGzZsEnRVdmrdGdsb2JhbACMbYdcPwEMCQwHDgaxFAeBAI9CAQMBA4QFBoMIgUQ
X-IronPort-AV: E=Sophos;i="4.38,315,1233529200"; 
   d="scan'208";a="23968170"
Received: from mail-gx0-f171.google.com ([209.85.217.171])
  by mail3-smtp-sop.national.inria.fr with ESMTP; 06 Mar 2009 17:10:15 +0100
Received: by gxk19 with SMTP id 19so868320gxk.3
        for <caml-list@yquem.inria.fr>; Fri, 06 Mar 2009 08:10:14 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=gamma;
        h=domainkey-signature:received:received:from:reply-to:to:subject:date
         :user-agent:cc:references:in-reply-to:content-type
         :content-transfer-encoding:content-disposition:message-id;
        bh=13zQ4lOfb5ZKyUJxVdA9P/0j2XqpgJQiV1+V/Gc/7Ys=;
        b=QSHwEk62merYd9js1yaSVz1LtA80p2l8njxN1m0IYE9qGvxS5xrIYoEpBCDpHebytQ
         Z/wTXi3rPPSobd1HLCIHcWJ9tUwTzT8536IpD1fX/+AjWlxPpu7lVnpNGSFsbOj64Jw0
         Y+dJhswnH30C1FMZobnHIvtxpTX2znv5E9GiA=
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=from:reply-to:to:subject:date:user-agent:cc:references:in-reply-to
         :content-type:content-transfer-encoding:content-disposition
         :message-id;
        b=Cysfvv1d9MSS5oIaV8K37v7s4vF0DPglQOdJQSBYZQLjvjT6Zmr9sBTATebfQCgdjU
         XteU87/w9hwTFLt3nsr/Dar1/OGwjEhjxH8uk2MxKtVel9mKsaFKKud4ZXdxvyIgBmWu
         XLz7p1XhqdTgnGYDwBEDrA9RAFppdb4ZCUYkE=
Received: by 10.100.128.12 with SMTP id a12mr316801and.67.1236355814336;
        Fri, 06 Mar 2009 08:10:14 -0800 (PST)
Received: from ?192.168.0.102? (c-98-219-43-7.hsd1.ga.comcast.net [98.219.43.7])
        by mx.google.com with ESMTPS id c28sm2457274anc.45.2009.03.06.08.10.13
        (version=TLSv1/SSLv3 cipher=RC4-MD5);
        Fri, 06 Mar 2009 08:10:13 -0800 (PST)
From: Peng Zang <peng.zang@gmail.com>
Reply-To: peng.zang@gmail.com
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Objects and variants
Date: Fri, 6 Mar 2009 11:10:10 -0500
User-Agent: KMail/1.9.9
Cc: Samuel Mimram <samuel.mimram@ens-lyon.org>
References: <49B147F7.4090303@ens-lyon.org>
In-Reply-To: <49B147F7.4090303@ens-lyon.org>
Content-Type: text/plain;
  charset="utf-8"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200903061110.12728.peng.zang@gmail.com>
X-Spam: no; 0.00; variants:01 hash:01 parametrize:01 cheers:01 beginner's:01 ocaml:01 bug:01 peng:98 peng:98 2009:98 unbound:01 unbound:01 polymorphic:01 beginners:01 wrote:01 

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

You're looking for a polymorphic method:

class a = object
  method f : 'a. ([>] as 'a) -> unit = fun _ -> ()
end

Peng

On Friday 06 March 2009 10:57:43 am Samuel Mimram wrote:
> Hi,
>
> When I try to compile the following code:
>
> class a =
> object
>   method f (x:[>]) = ()
> end
>
> I get the following error:
>
> Error: Some type variables are unbound in this type:
>          class a : object method f : [>  ] -> unit end
>        The method f has type ([>  ] as 'a) -> unit where 'a is unbound
>
> Is the binding of [>] to 'a really necessary here? In particular it is
> not mentioned in the inferred type...
>
> Of course I can parametrize the class over 'a as
>
> class ['a] a =
> object
>   method f (x:[>] as 'a) = ()
> end
>
> which now has type
>
> class ['a] a : object constraint 'a = [>  ] method f : 'a -> unit end
>
> But this seems rather cumbersome. Is there a way to handle this without
> mentioning 'a?
>
> Thanks!
>
> Cheers,
>
> Samuel.
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
> Archives: http://caml.inria.fr
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.7 (GNU/Linux)

iD8DBQFJsUrkfIRcEFL/JewRAqJ3AKC7Dl6+a97yrs1PKPLDEzL5c3vbVACcDdrJ
16BPB2/+ddTB4OHB/4zQ+LA=
=ltZH
-----END PGP SIGNATURE-----