From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.9 required=5.0 tests=BAYES_00,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM autolearn=no autolearn_force=no version=3.4.4
X-Received: by 2002:ac8:36d1:: with SMTP id b17mr760351qtc.202.1572633050320;
        Fri, 01 Nov 2019 11:30:50 -0700 (PDT)
X-Received: by 2002:a9d:baf:: with SMTP id 44mr9405672oth.182.1572633050040;
 Fri, 01 Nov 2019 11:30:50 -0700 (PDT)
Path: 
 eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!news.dns-netz.com!news.freedyn.net!newsreader4.netcologne.de!news.netcologne.de!peer02.ams1!peer.ams1.xlned.com!news.xlned.com!peer02.am4!peer.am4.highwinds-media.com!peer02.iad!feed-me.highwinds-media.com!news.highwinds-media.com!j16no541713qtl.0!news-out.google.com!g53ni234qtg.0!nntp.google.com!j16no541710qtl.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.ada
Date: Fri, 1 Nov 2019 11:30:49 -0700 (PDT)
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com;
 posting-host=2a02:a03f:e3e9:4d00:1260:4bff:fe89:deb2;
 posting-account=kTRirAoAAACnF_wtAOSamxYBSVvmJuCa
NNTP-Posting-Host: 2a02:a03f:e3e9:4d00:1260:4bff:fe89:deb2
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <eaff9b38-2379-476b-ac3e-67e756b10dbf@googlegroups.com>
Subject: gtkada3 callback function & failure : subprogram must not be deeper
 than access type
From: Alain De Vos <devosalain71@gmail.com>
Injection-Date: Fri, 01 Nov 2019 18:30:50 +0000
Content-Type: text/plain; charset="UTF-8"
X-Received-Bytes: 2858
X-Received-Body-CRC: 1406981642
Xref: reader01.eternal-september.org comp.lang.ada:57426
Date: 2019-11-01T11:30:49-07:00
List-Id: <comp.lang.ada>

For callback functions there are 3 methods and one with data.
For the first method I try a program with one button
Connecting the button with the handler fails with the error :
>>>>subprogram must not be deeper than access type

The code :
-- TEST : Connecting via the On_* procedures first method
with Ada.Text_IO; use Ada.Text_IO;
with Glib;         use Glib;
with Glib.Object;  use Glib.Object;
with Gtk;          use Gtk;
with Gtk.Box;      use Gtk.Box;
with Gtk.Button;   use Gtk.Button;
with Gtk.Enums;    use Gtk.Enums;
with Gdk.Event;    use Gdk.Event;
with Gtk.Frame;    use Gtk.Frame;
with Gtk.Grid;     use Gtk.Grid;
with Gtk.Handlers; use Gtk.Handlers;
with Gtk.Label;    use Gtk.Label;
with Gtk.Main;     use Gtk.Main;
with Gtk.Widget;   use Gtk.Widget;
with Gtk.Window;   use Gtk.Window;
with Gtk.Main;   use Gtk.Main;

procedure hello_gtk is
   Main_Window : Gtk.Window.Gtk_Window;
   Button  : Gtk_Button;
   procedure On_Button_Click (Button : access Gtk_Button_Record'Class)
   is
   begin
      Put_line ("Hallo");
   end On_Button_Click;

   procedure Create_Window is
   begin
      Gtk.Window.Gtk_New
        (Window   => Main_Window,
         The_Type => Gtk.Enums.Window_Toplevel);
      Gtk.Window.Set_Title (Window => Main_Window, Title  => "Hello from ADA");
      --  Button.On_Clicked (On_Button_Click'Access); fails with subprogram must not be deeper than access type
      Add (Main_Window,Button);
      Gtk.Window.Show_All (Main_Window);
   end Create_Window;
begin
   Gtk.Main.Init;
   Create_Window;
   Gtk.Main.Main;
end hello_gtk;