module type DICT = functor (Key : Set.OrderedType) -> sig
 type 'a dict
 val domain : 'a dict -> Set.Make(Key).t
end;;

module type PRIO_QUEUE = functor (Elt : Set.OrderedType) -> sig
 type queue
 val contents : queue -> Set.Make(Elt).t
end;;

module QueuedDict (Data : Set.OrderedType)
 (MyDict : DICT) (MyPrioQueue : PRIO_QUEUE) =
struct
 module Dict = MyDict (Data)
 module PQ = MyPrioQueue (Data)
 module DataSet = Set.Make (Data)
 let queued_domain dict pq =
   DataSet.equal (Dict.domain dict) (PQ.contents pq)
end;;