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 MAA00385; Thu, 7 Feb 2002 12:21:45 +0100 (MET)
X-Authentication-Warning: pauillac.inria.fr: majordomo set sender to owner-caml-list@pauillac.inria.fr using -f
Received: from concorde.inria.fr (concorde.inria.fr [192.93.2.39]) by pauillac.inria.fr (8.7.6/8.7.3) with ESMTP id MAA32620 for <caml-list@pauillac.inria.fr>; Thu, 7 Feb 2002 12:21:44 +0100 (MET)
Received: from nef.ens.fr (nef.ens.fr [129.199.96.32])
	by concorde.inria.fr (8.11.1/8.11.1) with ESMTP id g17BLiv14417
	for <caml-list@inria.fr>; Thu, 7 Feb 2002 12:21:44 +0100 (MET)
Received: from clipper.ens.fr (clipper-gw.ens.fr [129.199.1.22])
          by nef.ens.fr (8.10.1/1.01.28121999) with ESMTP id g17BLhp37087
          for <caml-list@inria.fr>; Thu, 7 Feb 2002 12:21:43 +0100 (CET)
Received: from localhost (frisch@localhost) by clipper.ens.fr (8.9.2/jb-1.1)
	id MAA17259 for <caml-list@inria.fr>; Thu, 7 Feb 2002 12:21:43 +0100 (MET)
Date: Thu, 7 Feb 2002 12:21:43 +0100 (MET)
From: Alain Frisch <frisch@clipper.ens.fr>
To: Caml list <caml-list@inria.fr>
Subject: [Caml-list] Type variables (was: Odd Type Checking Problem)
In-Reply-To: <Pine.GSO.4.33.0202062353100.22609-100000@clipper.ens.fr>
Message-ID: <Pine.GSO.4.33.0202071205590.24659-100000@clipper.ens.fr>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-caml-list@pauillac.inria.fr
Precedence: bulk

Hello,

On Wed, 6 Feb 2002, I wrote:

> I guess this is a problem of understanding type variable scoping rules.


Actually, I feel myself somewhat confused with implicit introduction and
scoping of type variables.

These one are refused:

let f (x : 'a) = let module M = struct exception X of 'a end in ();;
let f (x : 'a) = let module M = struct type t = 'a end in ();;

This is accepted:

let f (x : 'a) =
  let module M =
      struct
	type t constraint t = 'a;;
	exception X of t;;
      end in ();;

but is quite useless, since both:

let f (x : 'a) =
  let module M =
      struct
	type t constraint t = 'a;;
	exception X of t;;
	raise (X x);;
      end in ();;

and

let f (x : 'a) =
  let module M =
      struct
        type t constraint t = 'a;;
        exception X of t;;
      end in raise (M.X x);;


are rejected by the type checker.

(in "constraint ...", no new variable is introduced)


Another example:

let f (x : 'a) =
  let module M =
      struct
        type u = { a : 'a }
      end in ();;

=> rejected (Unbound type parameter 'a)

(and accepted by
"Objective Caml version 3.04+1 with explicit polymorphism (2002-01-07)",
but with a different meaning that one could expect)


Is there a way to use a type variable such as the 'a above to define
types in a local structure ?


-- Alain

-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr