From: William Lovas <wlovas@stwing.upenn.edu>
To: caml users <caml-list@inria.fr>
Subject: Re: [Caml-list] Type constraints
Date: Tue, 7 Dec 2004 13:13:44 -0500 [thread overview]
Message-ID: <20041207181344.GA14891@force.stwing.upenn.edu> (raw)
In-Reply-To: <A940F6C2-4877-11D9-8195-000D9345235C@inria.fr>
On Tue, Dec 07, 2004 at 06:44:36PM +0100, Damien Doligez wrote:
>
> On 7 Dec 2004, at 15:57, Andreas Rossberg wrote:
>
> >Is this really a counter-example? I don't see any problem with making
> >it polymorphic - it evaluates to ref, and ref can happily be
> >polymorphic.
>
> Yes, well I simplified it a bit too much. Try this instead:
>
> let module M = struct let v = ref [] end in M.v;;
I'm still not convinced. Yes, the type variable should not be generalized
in the above, by analogy with:
# ref [];;
- : '_a list ref = {contents = []}
But the `let module' in question -- or one similar in spirit, at least --
# let module M = struct let v = fun x -> x end in M.v;;
- : '_a -> '_a = <fun>
is analogous to the expression
# fun x -> x
- : 'a -> 'a = <fun>
in which the type variable *is* generalized.
The following behavior confuses me, too:
# let module M = struct let v = fun x -> x end in (M.v 5, M.v true);;
- : int * bool = (5, true)
This expression has type bool but is here used with type int
# let v =
let module M = struct let v = fun x -> x end in M.v
in
(v 5, v true);;
^^^^
This expression has type bool but is here used with type int
Why is the type variable generalized inside the `let module's body but not
generalized if we pass it to the outside?
So the `ref' example above as a counterexample is at the very least hiding
some of the story. What's really going on here?
William
next prev parent reply other threads:[~2004-12-07 18:13 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-06 19:55 Jim Farrand
2004-12-07 7:12 ` [Caml-list] " Alain Frisch
2004-12-07 13:43 ` Damien Doligez
2004-12-07 14:57 ` Andreas Rossberg
2004-12-07 17:44 ` Damien Doligez
2004-12-07 18:08 ` Alain Frisch
2004-12-07 21:04 ` Damien Doligez
2004-12-07 21:43 ` Alain Frisch
2004-12-08 3:30 ` nakata keiko
[not found] ` <8002B033-4906-11D9-8195-000D9345235C@inria.fr>
2004-12-09 0:56 ` nakata keiko
2004-12-09 1:27 ` Jacques Garrigue
2004-12-08 10:53 ` Damien Doligez
2004-12-08 12:39 ` Alain Frisch
2004-12-08 14:23 ` Jacques Garrigue
2004-12-09 3:07 ` skaller
2004-12-09 4:53 ` Jacques Garrigue
2004-12-08 16:10 ` Xavier Leroy
2004-12-07 18:13 ` William Lovas [this message]
2004-12-08 0:27 ` Jacques Garrigue
2004-12-07 18:41 ` Boris Yakobowski
2004-12-07 19:38 ` Jim Farrand
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