module Main (main) where

import Control.Monad (liftM)
import Control.Monad.State (State, runState, evalState, get, put)

main :: IO ()
main = do xs <- readFile "data"
          ys <- readFile "data"
          print (evalState readChunks xs == ys)

---

type FirstMonad = State String

readChunks :: FirstMonad String
readChunks = do xs <- get
                if null xs then return []
                           else do chunk <- case foo xs of
                                                (ys, zs) ->
                                                    do put zs
                                                       return ys
                                   chunks <- readChunks
                                   return (chunk ++ chunks)

---

type SecondMonad = State String

foo :: String -> (String, String)
foo = runState bar

bar :: SecondMonad String
bar = do inp <- get
         case inp of
             [] -> return []
             x:xs -> do put xs
                        liftM (x:) bar