palindrome
isPalindrome l = undefined

{-
 - Duplicate the elements in list xs, for example "duplicate [1,2,3]" would give the list [1,1,2,2,3,3]
 - Hint: The "
index :: Int -> [Int] -> Int
index k l = let
  helper [] _ = -1
  helper (x:xs) i | x == k = i
                  | otherwise = helper xs (i + 1)
  in helper l 0
index k l = let
  helper [] _ = -1
  helper (x:xs) i | x == k = i
                  | otherwise = helper xs (i + 1)
  in helper l 0