Modal dialogs with GtkAda

[Florian Weimer <fw@deneb.enyo.de>]

How can I create modal dialogs with GtkAda?  Okay, I can use
Set_Modal, but this doesn't result in the convenient programming
interface modal dialogs have with some other widget sets.  More
precisely, I want to do the following:

        declare
           Result   : Dialog_Result;
           Name     : Unbounded_String;
           Quantity : Long_Float;

        begin
           Query_User_With_Dialog (Result, Name, Quantity);
           
           case Result is
              when Ok =>
                 Add_To_Database (Name, Quantity);
           
              ...
           end case;
        end;

Query_User_With_Dialog should not return while the dialog is
visible on the screen.  Is there are simple way to implement
Query_User_With_Dialog?

(Another question: Is there any documentation on memory management and
GtkAda, e.g. do I have free components of a window, entries in a Clist,
etc.?)