import System.Exit
import Control.Monad
import Control.Monad.Free

data TeletypeF next = Say String next | Ask (String -> next) | Stop

instance Functor TeletypeF where
	fmap f (Say msg next) = Say msg (f next)
	fmap f (Ask k) = Ask (f . k)
	fmap _ Stop = Stop

type Teletype = Free TeletypeF

example :: Teletype ()
example = Free $ Say "What is your name?" $ Free $ Ask $ \name ->
	if (length name >= 10) then Pure ()
	else Free $ Say ("Hello, " ++ name ++ "!") (Pure ())

runIO :: Teletype a -> IO a
runIO (Pure r) = return r
runIO (Free (Say msg t)) = print msg >> runIO t
runIO (Free (Ask f)) = getLine >>= runIO . f
runIO (Free Stop) = exitSuccess

main = runIO example