Maybe inside IO Monad / MaybeT example

gistfile1.hs

import Control.Monad             (guard)
import Control.Monad.Trans.Maybe (MaybeT(..), runMaybeT)
import Control.Monad.Error

import Data.Char

readBoth :: IO (Maybe String)
readBoth = runMaybeT $ do a <- funA2
  	          funB2 a
	      
funA2 :: MaybeT IO String
funA2 = MaybeT funA

funB2 :: String -> MaybeT IO String
funB2 = MaybeT . funB

funA :: IO (Maybe String)
funA = do putStrLn "What is your name?"
	  name <- getLine
          guard $ not (null name)
	  return $ Just name

funB :: String -> IO (Maybe String)
funB name = do putStrLn ("hello, " ++ name)
	       putStrLn "how old are you?"
               age <- getLine
               guard (all isDigit age)
	       return $ Just age