last'' :: [a] -> a
last'' xs
    | null xs   = undefined
    | otherwise = xs !! (n-1)
    where n = length xs

-- Problem 2
-- Find the last but one element of a list. 
last'' :: [a] -> a
last'' xs
    | null xs   = undefined
    | otherwise = xs !! (n-1)
    where n = length xs

-- Problem 2
-- Find the last but one element of a list. 
last'' xs
    | null xs   = undefined
    | otherwise = xs !! (n-1)
    where n = length xs

-- Problem 2
-- Find the last but one element of a list. 