plp/haskell/haskell4.hs

module Haskell4 where

import Control.Applicative
import Control.Monad

exmon :: (Monad m, Num r) => m r -> m r -> m r 
exmon m1 m2 = do x <- m1
                 y <- m2
                 return $ x-y

main = exmon (do putStr "?> "
                 x <- getLine;
                 return (read x :: Int))
             (return 10)