import Control.Monad.Reader

data Connection = Connection
data Builder = Builder

data Context = Context { connection :: Connection, builder :: Builder }

no_action :: Connection -> Builder -> Int -> IO Int
no_action _ _ i = return (i + 1)


type CBIO b = ReaderT Context IO b

liftCBIO :: (Connection -> Builder -> a -> IO b) -> (a -> CBIO b)
liftCBIO f v = do
	context <- ask
	liftIO (f (connection context) (builder context) v)

cbio_no_action = liftCBIO no_action

runWithInIO = flip runReaderT


main = do
	i <- runWithInIO (Context Connection Builder) $ do
		a <- cbio_no_action 20
		liftIO $ putStrLn "Halfway through!"
		b <- cbio_no_action 30
		return (a + b)
	putStrLn $ show i