Instantiating generics

[Albert <weeper_MATEMLSPAM_@menta.net>]

I'm trying to instantiate the Queue_Manager_1 example from 12.3
Ada Distillier, the problem is the function Is_Valid.

with Queue_Manager_1;

procedure Demostration is
	type O_Positive is tagged
	record
		Val:Positive;
	end record;
	function Is_Valid(Data:O_Positive) return Boolean is
	begin
		return True;
	end Is_Valid;
	package QMP is new Queue_Manager_1(Element=>O_Positive);
begin
	null;
end Demostration;


Can anyone help me�.
thanks

Albert