Add remaining haskell book exercises

1 files changed, 16 insertions, 0 deletions

diff --git a/Haskell-book/15/semigroup/src/Identity.hs b/Haskell-book/15/semigroup/src/Identity.hs
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index 0000000..cb7180a
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+++ b/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