(!) :: IntMap a -> Key -> a
(!) m k = findWithDefault (error $ "IntMap.!: key " ++ show k ++ " is not an element of the map") k m
(!) :: IntMap a -> Key -> a
(!) m k = findWithDefault (error $ "IntMap.!: key " ++ show k ++ " is not an element of the map") k m
(!) m k = findWithDefault (error $ "IntMap.!: key " ++ show k ++ " is not an element of the map") k m