Add the haskell book

1 files changed, 27 insertions, 0 deletions

diff --git a/Haskell-book/09/src/Zipping.purs b/Haskell-book/09/src/Zipping.purs
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+++ b/Haskell-book/09/src/Zipping.purs
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+module Zipping where
+
+import Data.Array (head, tail, (:))
+import Data.Maybe (Maybe(..))
+import Data.Tuple (Tuple(..))
+
+-- 1
+zip :: forall a b. Array a -> Array b -> Array (Tuple a b)
+zip a b = f (head a) (head b) (tail a) (tail b)
+  where f Nothing _ _ _ = []
+        f _ Nothing _ _ = []
+        f _ _ Nothing _ = []
+        f _ _ _ Nothing = []
+        f (Just x) (Just y) (Just xs) (Just ys) = (Tuple x y) : (f (head xs) (head ys) (tail xs) (tail ys))
+
+-- 2
+zipWith :: forall a b c. (a -> b -> c) -> Array a -> Array b -> Array c
+zipWith f a b = f' (head a) (head b) (tail a) (tail b)
+  where f' Nothing _ _ _ = []
+        f' _ Nothing _ _ = []
+        f' _ _ Nothing _ = []
+        f' _ _ _ Nothing = []
+        f' (Just x) (Just y) (Just xs) (Just ys) = (f x y) : (f' (head xs) (head ys) (tail xs) (tail ys))
+
+-- 3
+zip' :: forall a b. Array a -> Array b -> Array (Tuple a b)
+zip' = zipWith (\a b -> Tuple a b)