Hello, My primary problem may be reduced to adding elements of two lists: [1,2,3] + [4,5,6] = [5,7,9] My first idea was to declare a list of Int as an instance of Num, and define (+) in the correct way. However, it seems it is not possible to do that: ------------------- instance Num [Int] where l1 + l2 = .... ------------------- Why? It seems it is necessary to do: ------------------ newtype ListOfInt = ListOfInt { getList :: [Int] } deriving (Show, Eq) instance Num ListOfInt where l1 + l2 = ... ------------------- Am I correct? Is it the best way to do that? Now, what is the most usual way to implement l1+l2? I have just read about applicative functors, with which I can do: ------------------- import Control.Applicative let l1 = [1,2,3] let l2 = [4,5,6] print $ getZipList $ (+) <$> ZipList l1 <*> ZipList l2 [5,7,9] ------------------- Is it the correct way to do that? I have tried: ------------------- instance Num ListOfInt where l1 + l2 = ListOfInt $ getZipList $ (+) <$> ZipList (getList l1) <*> ZipList (getList l2) ------------------- Isn't it too much complicated? Thanks TP