module Main where

import System.Random
import Control.Monad.State

type RandomMonad a = State StdGen a

randomRState :: Random a => (a, a) -> RandomMonad a
randomRState rt = get >>= (\(a, g) -> put g >> return a) . randomR rt

randomBool :: RandomMonad Bool
randomBool = randomRState (False,True)

unfoldM :: Monad m => (a -> m a) -> (a -> Bool) -> a -> m [a]
unfoldM f s a = do
  v <- f a
  if s v
    then return []
    else liftM (v :) (unfoldM f s v)

whiteout :: Char -> RandomMonad Char
whiteout c = do
  r <- randomBool
  if r
    then return c
    else return ' '

blank :: String -> Bool
blank = all (== ' ')

disintegrate :: String -> RandomMonad [String]
disintegrate = unfoldM (mapM whiteout) blank

main :: IO ()
main = do
  r <- getStdGen
  i <- getLine
  mapM_ putStrLn $ evalState (disintegrate i) r