import Control.Monad.State
import Data.List

get_length :: String -> IO Int

get_length name = 
    do contents <- readFile name
       return (length (lines contents))

update_best_with :: (String, Int) -> StateT (String, Int) IO ()

update_best_with (current_name, current_count) =
    do (best_name, best_count) <- get
       if current_count > best_count 
	  then put (current_name, current_count)
	  else return ()

do_next :: String -> StateT (String, Int) IO ()

do_next name = 
    do count <- get_length name
       update_best_with (name, count)

longest_file :: [String] -> IO (String, Int)

longest_file names =
    execStateT (sequence_ (map do_next names)) ("none", 0)

main = do (name, count) <- longest_file ["/etc/hostname", "/etc/ntp.conf", "/etc/timezone"]
	  putStrLn ("Longest file is " ++ name ++ " which is " ++ show count ++ " lines long")