module Make(P: Set.OrderedType) = struct
	type priority = P.t
	type 'a queue =
		Empty
	      | Node of priority * 'a * 'a queue * 'a queue

	let empty = Empty
	let rec insert queue prio elt = match queue with
		  Empty -> Node (prio, elt, Empty, Empty)
		| Node (p, e, left, right) ->
			if prio < p then
				Node (prio, elt, insert right p e, left)
			else
				Node (p, e, insert right prio elt, left)
	exception Queue_is_empty
	let rec remove_top = function
		  Empty -> raise Queue_is_empty
		| Node (prio, elt, left, Empty) -> left
		| Node (prio, elt, Empty, right) -> right
		| Node (prio, elt, (Node (lprio, lelt, _, _) as left),
		                  (Node (rprio, relt, _, _) as right)) ->
			if lprio < rprio then
				Node (lprio, lelt, remove_top left, right)
			else
				Node (rprio, relt, left, remove_top right)
	let extract = function
		  Empty -> raise Queue_is_empty
		| Node (prio, elt, _, _) as queue ->
			(prio, elt, remove_top queue)
	
	let rec size = function
		| Empty -> 0
		| Node (_, _, left, right) -> 1 + (size left) + (size right)
end