From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <pierre.weis@inria.fr>
Delivered-To: caml-list@yquem.inria.fr
Received: from nez-perce.inria.fr (nez-perce.inria.fr [192.93.2.78])
	by yquem.inria.fr (Postfix) with ESMTP id C7E74BB81
	for <caml-list@yquem.inria.fr>; Wed,  8 Dec 2004 04:30:55 +0100 (CET)
Received: from pauillac.inria.fr (pauillac.inria.fr [128.93.11.35])
	by nez-perce.inria.fr (8.13.0/8.13.0) with ESMTP id iB83Ut4g009420
	for <caml-list@yquem.inria.fr>; Wed, 8 Dec 2004 04:30:55 +0100
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 EAA22049 for <caml-list@pauillac.inria.fr>; Wed, 8 Dec 2004 04:30:54 +0100 (MET)
Received: from mail.kaba.or.jp (cascade.kaba.or.jp [202.249.19.34])
	by nez-perce.inria.fr (8.13.0/8.13.0) with ESMTP id iB83UqAd009413;
	Wed, 8 Dec 2004 04:30:54 +0100
Received: from localhost (ferengi.kaba.or.jp [202.249.19.16])
	by mail.kaba.or.jp (Postfix) with ESMTP
	id A0C9349AAA; Wed,  8 Dec 2004 12:30:51 +0900 (JST)
Date: Wed, 08 Dec 2004 12:30:51 +0900 (JST)
Message-Id: <20041208.123051.74739504.keiko@kaba.or.jp>
To: damien.doligez@inria.fr
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] Type constraints
From: nakata keiko <keiko@kaba.or.jp>
In-Reply-To: <41B62407.4020102@inria.fr>
References: <41B5F1B2.3000503@inria.fr>
	<9296F5C2-4893-11D9-8195-000D9345235C@inria.fr>
	<41B62407.4020102@inria.fr>
X-Mailer: Mew version 3.3 on Emacs 21.3 / Mule 5.0 (SAKAKI)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Miltered: at nez-perce with ID 41B6756F.001 by Joe's j-chkmail (http://j-chkmail.ensmp.fr)!
X-Miltered: at nez-perce with ID 41B6756C.000 by Joe's j-chkmail (http://j-chkmail.ensmp.fr)!
X-Spam: no; 0.00; caml-list:01 kaba:01 damien:01 wrote:01 struct:01 struct:01 ...:98 ...:98 polymorphic:01 polymorphic:01 doligez:01 expression:01 syntactic:01 syntactic:01 typing:01 
X-Spam-Checker-Version: SpamAssassin 3.0.0 (2004-09-13) on yquem.inria.fr
X-Spam-Status: No, score=0.0 required=5.0 tests=none autolearn=disabled 
	version=3.0.0
X-Spam-Level: 

Damien Doligez wrote:

>The typing algorithm is very simple (really!):
>
>1. Type the module. Generalization occurs and the v field gets a
>    polymorphic type.
>2. Type "M.v".  This takes an instance of the polymorphic type.
>3. Can we generalize it?  Look at the syntactic shape of the expression
>    (in this case, let module ... in ...).  If it is always safe to
>    generalize such expressions, OK.  If not, do not generalize.
>
>That's the beauty of the Wright criterion: it's very easy to implement
>and to understand (because it is syntactic), and works well in almost 
>all
>cases (with a little eta-expansion if needed).

This does not answer to me why this works,

#type t = { t : 'a. 'a -> 'a}

#let v = let module M = struct let t x = x end in {t = M.t} in (v.t 5, v.t true)

Of cource, both of the following are not type checked,

#let v = let module M = struct let  t = x end in  M.t in (v 5, v true)

#let v : 'a -> 'a = let module M = struct let t x = x end in  M.t in (v 5, v true)

However, if I can write something like

#let v : 'a. 'a -> 'a = let module M = struct let t x = x end in  M.t in (v 5, v true)

then, it would be type checked ?

Regards,
Keiko.