Add remaining haskell book exercises

1 files changed, 22 insertions, 0 deletions

diff --git a/Haskell-book/15/semigroup/src/Comp.hs b/Haskell-book/15/semigroup/src/Comp.hs
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+++ b/Haskell-book/15/semigroup/src/Comp.hs
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+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"