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Message-ID: <16486.17988.561211.516751 at soggy.deldotd.com>
Date: Sat, 27 Mar 2004 19:28:04 -0800
To: Olivier Andrieu <oliv__a at users.sourceforge.net>
Cc: lablgtk at kaba.or.jp
Subject: Re: event variant types
In-Reply-To: <16483.63571.455639.187324 at akasha.ijm.jussieu.fr>
References: <16482.33127.497203.821118 at soggy.deldotd.com>
	<20040325165247V.garrigue@kurims.kyoto-u.ac.jp>
	<16483.50834.898498.682875@soggy.deldotd.com>
	<16483.63571.455639.187324@akasha.ijm.jussieu.fr>
From: briand at aracnet.com

I've created a simpler test program.

here is some relevant code:

let handle_event event =
  match GdkEvent.get_type event with
      (* #GdkEvent.Button.types -> handle_button_event event; true *)
      `KEY_PRESS -> Printf.printf "key press\n"; true
    | `MOTION_NOTIFY -> Printf.printf "motion\n"; true
    | _ -> false

...

      area#event#add [`KEY_PRESS];

      (* Event capture of keypresses *)

      let signal_id = 
        w#event#connect#key_press ~callback:
          begin fun ev ->
            let key = GdkEvent.Key.keyval ev in
              if key = GdkKeysyms._Escape then 
                w#destroy ();
              handle_event ev;
              true
          end;
      in

Here is the error message :

This expression has type
  GdkEvent.Key.t = [ `KEY_PRESS | `KEY_RELEASE ] Gdk.event
but is here used with type [> `KEY_PRESS | `MOTION_NOTIFY ] Gdk.event
The first variant type does not allow tag(s) `MOTION_NOTIFY

This error occurs at the line "handle_event ev".

It still seems that this points to a flaw in the types representing
the events.  Binding the event causes the types allowed to be
restricted and so it is no longer possible to call the same proc with
different events.  Or at least this is my interpretation of what is
happening...

Brian