Add exercises.hs

week4/exercises.hs

@@ -0,0 +1,13 @@
+fun :: Num a => (a -> a) -> (a -> Bool) -> [a] -> [a]
+fun f p xs = map f (filter p xs)
+
+map' :: (a -> b) -> [a] -> [b]
+map' f xs = foldr ((:).f) [] xs
+
+filter' :: (a -> Bool) -> [a] -> [a]
+filter' p xs = foldr (\x xs -> if (p x) then x:xs else xs) [] xs
+
+altMap :: (a -> b) -> (a -> b) -> [a] -> [b]
+altMap fa fb xs = map
+    (\(x, val) -> if x then fa val else fb val)
+    (zip [x `mod` 2 == 1 | x <- [0..((length xs) - 1)]] xs)