import qualified Data.Vector.Mutable as MV
import Data.IORef
import Control.Monad

test1 n = do
  sum <- newIORef (0 :: Int)
  v <- MV.new (n+1)
  forM_ [0..n] $ \i ->do
    MV.write v i i
  forM_ [0..n] $ \i ->do
    MV.read v i >>= writeIORef sum
  readIORef sum

test2 n = do
  sum <- newIORef (0 :: Int)
  vec <- MV.new (n+1) >>= newIORef
  forM_ [0..n] $ \i ->do
    v <- readIORef vec
    MV.write v i i
  forM_ [0..n] $ \i ->do
    v <- readIORef vec
    MV.read v i >>= writeIORef sum
  readIORef sum

main = do
  test1 1000000 >>= print