example of state monad

gistfile1.hs

module Main where 

import Control.Monad.State

type IntState = State Int

inc :: IntState ()
-- inc = get >>= put . (+1)
inc = do 
	v <- get 
	put (v + 1)

twice :: IntState ()
twice = modify ( * 2) 

calculate = do 
	twice 
	inc 
	twice