Monad Transformers hello world

monadTransHelloWorld.hs

module Main where

import Control.Monad.State
import Control.Monad.Trans
import Control.Monad.Maybe
import Control.Monad.Reader
import Control.Monad.Writer

type X = ReaderT String (WriterT [String] (StateT Int Maybe)) Int

main:: IO()
main = print $ runStateT (runWriterT (runReaderT m1 "hello world")) 0

m1 :: X
m1 = do
	put 32
	(lift.lift.lift) Nothing

m2 :: X
m2 = do
	x <- ask
	put 32
	return 50