cps.hs

import Data.Void
import Control.Monad.Trans.Cont

type Program = Cont Context Void

data Status = Failure | Success deriving Show
data Context = Read (String -> Context) | Write String Context | Exit Status

readline :: Cont Context String
readline = cont Read

writeline :: String -> Cont Context ()
writeline str = cont $ \f -> Write str (f ())

exit :: Status -> Cont Context Void
exit status = cont $ \_ -> Exit status

program :: Program
program = readline >>= writeline >> exit Success

kernel :: Cont Context Void -> IO ()
kernel p = parse (fromvoid p) where 
	fromvoid p = runCont p absurd
	parse next = case next of
		Read f -> parse (f "lol")
		Write s c -> parse c
		Exit s -> print s

main = kernel program