haskell_train.hs

replicate' :: Int -> a -> [a]
replicate' n x 
  | n <= 0 = []
  | otherwise = x : replicate' (n-1) x


zip' :: [a] -> [b] -> [(a, b)]
zip' [] _ = []
zip' _ [] = []
zip' (x:xs) (y:ys) = (x, y) : zip' xs ys

zip'' :: [a] -> [b] -> [(a, b)]
zip'' = zipWith (,)


elem' :: (Eq a) => a -> [a] -> Bool
elem' _ [] = False
elem' x (y:ys) = x == y || elem' x ys

zipWith' :: (a -> b -> c) -> [a] -> [b] -> [c]
zipWith' _ [] _ = []
zipWith' _ _ [] = []
zipWith' f (x:xs) (y:ys) = f x y : zipWith' f xs ys