DailyProgrammer Challenge #209e Solution (The Button can be pressed but once...)

c209e.hs

import Control.Monad
import Data.Char
import Data.List
import Data.Ord
import System.IO

type Time = Double
type User = (String, Time)

readUser :: String -> User
readUser s = (userName, read $ dropWhile (not . isDigit) time)
       where (userName, time) = break (== ':') s

readUsers :: [User] -> Int -> IO [User]
readUsers users 0 = return $ sortBy (comparing snd) $ users
readUsers users n = getLine >>= \user -> readUsers (readUser user : users) (n - 1)

timeUser :: Time -> User -> (Time, User)
timeUser time (userName, absoluteTime) = (absoluteTime, (userName, 60.0 + time - absoluteTime))

main = do numUsers <- getLine
          users <- readUsers [] $ read numUsers
          putStr
            $ unlines
            $ map (\(userName, time) -> userName ++ ": " ++ (show $ floor time)) $ snd
            $ mapAccumL timeUser 0.0
            $ users