Hi, I created a Data.MultiMap module based on Data.Map and Data.Set like this: data MultiMap k v = MultiMap (Map k (Set v)) and a Data.IntMultiMap module based on Data.IntMap and data.IntSet like this: data IntMultiMap = IntMultiMap (IntMap IntSet) For example the functions to add a value I wrote are: For MultiMap: addValue :: k -> v -> MultiMap k v -> MultiMap k v addValue k v (MultiMap m) = MultiMap $ Map.insertWith (\new old -> Set.insert v old) k (Set.singleton v) m For IntMultiMap: addValue :: Int -> Int -> IntMultiMap -> IntMultiMap addValue k v (IntMultiMap m) = IntMultiMap $ IntMap.insertWith (\new old -> IntSet.insert v old) k (IntSet.singleton v) m Both modules look almost the same, with the same documentation, same behavior, same function names but with different type signatures. Is there a way to make this simpler? The same thing happens to the modules that are using MultiMap and IntMultiMap, I have to write two versions of each. Thanks! -- Federico Mastellone Computer Science Engineer - ITBA ".. there are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult." Tony Hoare, 1980 ACM Turing Award Lecture.