-- fold the list:
maximum' :: Ord a => [a] -> a
maximum' = foldr1 (\x y ->if x >= y then x else y)
--For the recursive version (no double checking):
maximum'' :: Ord a => [a] -> a
maximum'' [x] = x
maximum'' (x:x':xs) = maximum' ((if x >= x' then x else x'):xs)
-- If you want wards:
maximum'' :: Ord a => [a] -> a
maximum'' [x] = x
maximum'' (x:x':xs) | x >= x' = maximum' (x:xs)
maximum'' (x:x':xs) | otherwise = maximum' (x':xs)