Demonstrate use of forM_ in the example.

hs/ImperativeProgramming.hs

import Data.Maybe (fromJust)
import qualified Data.Map as M
import Control.Monad (liftM)
import Control.Monad (liftM, forM_)
import Control.Applicative ((<$>), (<*>))
example = do
    "x" .= 3
    "x" .+= 4
    "y" .= (-1)
    "z" .= 0
    forM_ [1..10] $ \n ->
        "z" .-= n
    "x" .+ "y"
data Imperative a b = Imperative (M.Map String a -> (M.Map String a, b))