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{-# LANGUAGE FlexibleInstances #-}
module Combine where
import Data.Semigroup
import Test.QuickCheck
newtype Combine a b =
Combine { unCombine :: (a -> b) }
instance Semigroup b => Semigroup (Combine a b) where
(Combine f1) <> (Combine f2) = Combine f
where f x = (f1 x) <> (f2 x)
instance (Monoid b) => Monoid (Combine a b) where
mempty = Combine $ \_ -> mempty
mappend (Combine f1) (Combine f2) = Combine f
where f x = mappend (f1 x) (f2 x)
instance (Num a, CoArbitrary a, Arbitrary b) => Arbitrary (Combine a b) where
arbitrary = do
f <- arbitrary
return $ Combine (\n -> f n)
instance (Show a, Show b) => Show (Combine a b) where
show _ = "a -> b"
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