import Data.Monoid
import Data.Functor
import Control.Applicative

newtype NT m a = NT (m a) deriving (Eq,Show)

instance (Monoid a, Applicative m) => Monoid (NT m a) where
    mempty = NT $ pure mempty
    mappend (NT a) (NT b) = NT $ mappend <$> a <*> b

main = do
    print $ (NT (Just "a") <>  NT (Just "b")) <> NT (Just "c")
    print $  NT (Just "a") <> (NT (Just "b")  <> NT (Just "c"))
    print $ (NT ["a"] <>  NT ["b"]) <> NT ["c"]
    print $  NT ["a"] <> (NT ["b"]  <> NT ["c"])
    print $ (NT (Just $ NT ["a"]) <>  NT (Just $ NT ["b"])) <> NT (Just $ NT ["c"])
    print $  NT (Just $ NT ["a"]) <> (NT (Just $ NT ["b"])  <> NT (Just $ NT ["c"]))