[exercise] 12.4

Author: Dev-XYS

chapter12-Monads-and-more/4.hs

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+newtype ZipList a = Z [a]
+ deriving Show
+
+instance Functor ZipList where
+ -- fmap :: (a -> b) -> ZipList a -> ZipList b
+ fmap g (Z xs) = Z (map g xs)
+
+instance Applicative ZipList where
+ -- pure :: a -> ZipList a
+ pure x = Z [x]
+ -- (<*>) :: ZipList (a -> b) -> ZipList a -> ZipList b
+ (Z gs) <*> (Z xs) = Z $ map (\(f, x) -> f x) (zip gs xs)