newtype Constant a b =
    Constant { getConstant :: a } deriving (Eq, Ord, Show)

instance Functor (Constant a) where
  fmap :: (c -> d) -> Constant a c -> Constant a d
  fmap _ c = Constant (getConstant c)

instance Monoid x => Applicative (Constant x) where
  pure :: a -> Constant x a
  pure = Constant
--   (<*>) :: Monoid a => Constant a (a1 -> b) -> Constant a a1 -> Constant a b
--   (<*>) = _