[exercise] 14.2

Author: Dev-XYS

chapter14-Foldables-and-friends/2.hs

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+-- This is a hypothetical program which does not run in GHCi.
+
+import Data.Monoid
+
+instance Monoid b => Monoid (a -> b) where
+    -- mempty :: a -> b
+    mempty _ = mempty
+    -- mappend :: (a -> b) -> (a -> b) -> a -> b
+    (f `mappend` g) x = f x `mappend` g x