Instantiation of child generics?

[Dale Stanbrough <dale@goanna.cs.rmit.edu.au>]

Hi,

I'ld like to create an abstract generic queue package with bounded
and unbounded children. However I have been thwarted in all attempts
to instantiate them. Also I don't really understand the rules for
instantiaion of child generics. Can anyone explain them?


e.g. 

	generic
		type element is private;
	package queues is 
		type queue is abstract tagged null record;
		
		procedure init return queue is abstract;
		
		procedure enqueue(item:in out queue; item:element) is abstract;

		-- etc
	end queues;
	
	
	generic
		size	:natural;
	package queues.bounded is
			
		type queue is new queues.queue with private;
		
		procedure init return queue is abstract;
		
		procedure enqueue(item:in out queue; item:element) is abstract;

	private
		type queue is new queues.queue with null record; -- for now...
	end;


How do I instantiate this?

	with queues.bounded;
	package myQ is new queues.bounded(integer, 5);
	
results in Gnat telling me "invalid prefix in selected component "queues""

Also will my (re)use of the identifier "queue" in the packages cause any
problems for me? It seems to compile ok, but i'm concerned that there might
be some nasty visibility issue lurking around the corner...

Thanks,

Dale