Natools

   function Current_Level (Stack : Lock_Stack) return Natural is
   begin
      return Stack.Level;
   end Current_Level;


   function Null_State return Lock_State is
   begin
      return (0, 0);
   end Null_State;



   -------------------------------------
   -- Lockable Wrapper Implementation --
   -------------------------------------

   function Current_Event (Object : in Wrapper) return Events.Event is

      --  Remove upper part of Stack, up to and including the entry pointed
      --  by State. Constraint_Error is raised if State does not point to a
      --  valid level in the stack, and if Allow_Gap is True and more than
      --  one item would be removed.

   function Current_Level (Stack : Lock_Stack) return Natural;
      --  Return the value on top of the stack

   function Null_State return Lock_State;
      --  Return an invalid Lock_State


   type Descriptor is limited interface and S_Expressions.Descriptor;

   procedure Lock
     (Object : in out Descriptor;
      State : out Lock_State)