longestWord02.hs

import Text.Regex
import Control.Monad.State

longestWord' :: [String] -> State Int String
longestWord' [x]    = return x
longestWord' (x:xs) = do x' <- longestWord' xs
                         if length x < length x'
                            then do inc 
                                    return x'
                            else return x

inc = modify (+1)

longestWord xs = runState (longestWord' xs) 0

main = print $ longestWord $ splitRegex (mkRegex " ") "The quick brown fox"