Haskell-book/15/semigroup/src/Identity.hs


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module Identity where

import Data.Semigroup
import Test.QuickCheck

newtype Identity a = Identity a deriving (Show, Eq)

instance Semigroup a => Semigroup (Identity a) where
    (Identity x) <> (Identity y) = Identity (x <> y)

instance Monoid a => Monoid (Identity a) where
    mempty = Identity mempty
    mappend (Identity x) (Identity y) = Identity $ mappend x y

instance Arbitrary a => Arbitrary (Identity a) where
    arbitrary = fmap Identity arbitrary