{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}

instance (Num a, Applicative f, Show (f a), Eq (f a)) => Num (f a) where
        (+) = liftA2 (+)
        (-) = liftA2 (-)
        (*) = liftA2 (*)
        negate = fmap negate
        signum = fmap signum
        abs = fmap abs
        fromInteger = pure . fromInteger