Add the haskell book

1 files changed, 73 insertions, 0 deletions

diff --git a/Haskell-book/09/src/Exercises.hs b/Haskell-book/09/src/Exercises.hs
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+++ b/Haskell-book/09/src/Exercises.hs
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+module Exercises where
+
+-- direct recursion, not using (&&)
+myAnd :: [Bool] -> Bool
+myAnd [] = True
+myAnd (x:xs) =
+  if x == False
+  then False
+  else myAnd xs
+
+-- direct recursion, using (&&)
+myAnd' :: [Bool] -> Bool
+myAnd' [] = True
+myAnd' (x:xs) = x && myAnd' xs
+
+-- 1
+myOr :: [Bool] -> Bool
+myOr [] = False
+myOr (x:xs) = x || myOr xs
+
+-- 2
+myAny :: (a -> Bool) -> [a] -> Bool
+myAny f xs = myOr $ map f xs
+
+-- 3
+myElem :: Eq a => a -> [a] -> Bool
+myElem _ [] = False
+myElem y (x:xs) = (x == y) || (myElem y xs)
+
+-- 4
+myReverse :: [a] -> [a]
+myReverse [] = []
+myReverse (x:xs) = (myReverse xs) ++ [x]
+
+-- 5
+squish :: [[a]] -> [a]
+squish = squish' []
+    where squish' acc [] = acc
+          squish' acc (x:xs) = x ++  (squish' acc xs)
+
+-- 6
+squishMap :: (a -> [b]) -> [a] -> [b]
+squishMap _ [] = []
+squishMap f (x:xs) = (f x) ++ (squishMap f xs)
+
+-- 7
+squishAgain :: [[a]] -> [a]
+squishAgain x = squishMap id x
+
+-- 8
+myMaximumBy :: (a -> a -> Ordering)
+            -> [a] -> a
+myMaximumBy f (x:xs) = myMaximumBy' x xs
+    where myMaximumBy' m [] = m
+          myMaximumBy' m (y:ys)
+            | f y m == GT = myMaximumBy' y ys
+            | otherwise = myMaximumBy' m ys
+
+-- 9
+myMinimumBy :: (a -> a -> Ordering)
+            -> [a] -> a
+myMinimumBy f (x:xs) = myMinimumBy' x xs
+    where myMinimumBy' m [] = m
+          myMinimumBy' m (y:ys)
+            | f y m == LT = myMinimumBy' y ys
+            | otherwise = myMinimumBy' m ys
+
+-- 10
+myMaximum :: (Ord a) => [a] -> a
+myMaximum = myMaximumBy compare
+
+myMinimum :: (Ord a) => [a] -> a
+myMinimum = myMinimumBy compare