From: Ivan <ivg@ieee.org>
To: Alain Frisch <alain@frisch.fr>
Cc: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] type inference with classes
Date: Fri, 3 Aug 2012 09:15:26 +0400 [thread overview]
Message-ID: <CAL9dnAEosWx_wwAhKW23h3bWZ45JFHsBJVq51MZ1_pxOmbRQiQ@mail.gmail.com> (raw)
In-Reply-To: <501B588B.6040006@frisch.fr>
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On 3 August 2012 08:50, Alain Frisch <alain@frisch.fr> wrote:
> Hello,
>
> I don't know if this covers all the case, but you need to keep in mind the
> following points. Feel free to add to the list.
>
Thanks for nice and structured answer!
I'll try to expand it with my cases, but due to lack of comprehension they
will not be so clear =)
So the setup is follows: I have a class with a type explicitly specified in
mli file. No inference on it's methods. And a function, that takes some
object and type system tries to infer what objects it can accept.
Starting from a simple case:
let reset_env_model state v =
let q = Queue.create () in
Queue.iter (fun p -> v#expand_row p) q
produces an error:
This expression has type GTree.view
but an expression was expected of type < expand_row : 'a -> unit; ..
>
Types for method expand_row are incompatible
because expand_row method of type GTree.view has type:
expand_row : Gtk.tree_path -> unit;
I think, that compiler have a reason to refuse this code: function wants a
method, that can take an arbitrary value of type 'a, but I pass a method
that has a covariant type Gtk.tree_path in position left to arrow. So he
complains correctly. I agree =) I think that this case has
some correspondence with your case #1.
But, why in the following code:
let reset_env_model state v =
let q = Queue.create () in
let m,_,_ = State.env_model state in
m#foreach (fun p _ -> if v#row_expanded p then Queue.push p q; false);
set_env_model state v;
Queue.iter (fun p -> v#expand_row p) q
compiler cannot infer, that object p has type Gtk.tree_path, and with this
proposition imply, that the expand_row method has a type "Gtk.tree_path ->
unit"?
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next prev parent reply other threads:[~2012-08-03 5:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-03 4:23 Ivan
2012-08-03 4:50 ` Alain Frisch
2012-08-03 5:15 ` Ivan [this message]
2012-08-03 5:32 ` Jacques Garrigue
2012-08-03 6:09 ` Ivan
2012-08-03 23:14 Jacques Garrigue
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