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From: "Luke A. Guest" <laguest@archeia.com>
Newsgroups: comp.lang.ada
Subject: Re: What does this error mean and how do I correct this?
Date: Fri, 1 Sep 2023 22:44:13 +0100
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On 01/09/2023 22:41, Luke A. Guest wrote:
> Handler needs to be in a package you with.
> 

>> begin  -- Gtk.Init;
>>     Gtk.Main.Init;
>>     Gtk.Window.Gtk_New (Window => Win, The_Type => 
>> Gtk.Enums.Window_Toplevel);
>>     Win.Set_Position (Win_Pos_Center);
>>     Gtk.Window.Set_Title (Window => Win, Title => "Editor");
>>     Gtk.Window.Show_All (Win);
>>     Win.On_Button_Press_Event     <------------ line that gets the error
>>        (Call =>  Handler'Access,
>>         After => False,
>>         Slot =>  Win);
>>     Gtk.Main.Main;
>> end test1;
>>
>> I get the compiler error message:
>>
>> test1.adb:32:17: subprogram must not be deeper than access type

Ada doesn't like 'access types to be in an area that can go out of scope 
iirc. You can get around it with unchecked_access, but if you put 
handler into a package of it's own, it's at library level and is 
available to grab the access of.