module Comp where

import Data.Semigroup
import Test.QuickCheck

newtype Comp a =
    Comp { unComp :: (a -> a) }

instance Semigroup a => Semigroup (Comp a) where
    (Comp f1) <> (Comp f2) = Comp f
        where f x = (f1 x) <> (f2 x)

instance Monoid a => Monoid (Comp a) where
    mempty = Comp $ \_ -> mempty
    mappend (Comp f1) (Comp f2) = Comp f
        where f x = mappend (f1 x) (f2 x)

instance (Arbitrary a, CoArbitrary a) => Arbitrary (Comp a) where
    arbitrary = fmap Comp arbitrary

instance Show (Comp a) where
    show _ = "a -> a"