Proposal: IntMap.differenceKeysSet for removing an IntSet of keys

Ticket: http://hackage.haskell.org/trac/ghc/ticket/5242 Currently, IntMap.difference ma mb removes all the keys in mb from ma, where the elements of the two IntMaps can be of different types; the elements of mb are not used. There is no efficient way to remove an IntSet of keys, however. These patches adds the IntMap.differenceKeysSet function—essentially a copy/paste of difference—that satisfies the following property: prop_DiffKeysSet :: Map Int -> Map () -> Bool prop_DiffKeysSet t1 t2 = difference t1 t2 == differenceKeysSet t1 (keysSet t2) Cons: Not so happy with the name. Code bloat. Thanks, /Liyang