> lines' :: String -> [String]
> lines' [] = []
> lines' (x:xs) = f x (lines' xs)

> f :: Char -> [String] -> [String]
> f '\n' xss = "" : xss
> f x [] = [[x]]
> f x (ys:yss) = (x:ys) : yss

> main = interact (unlines . lines')