{-# LANGAUGE RankNTypes #-}
import Data.Array.ST
import Data.Array.Unboxed
import Control.Monad.ST

-- 例 1: runSTUArray

-- コンパイル可能 (f $ runSTUArray $ do ..)
testSuccess :: (Int, Int)
testSuccess = bounds $ runSTUArray $ do
      arr <- newArray (0, 10) (0 :: Int)
      return arr

-- コンパイル不能 (f . runSTUArray $ do ..)
testFailure :: (Int, Int)
testFailure = bounds . runSTUArray $ do
      arr <- newArray (0, 10) (0 :: Int)
      return arr

-- 例 2: runST

-- コンパイル可能 (f $ runST $ do ..)
testSuccess2 :: (Int, Int)
testSuccess2 = bounds $ runST $ do
      arr <- newArray (0, 10) (0 :: Int) :: ST s (STUArray s Int Int)
      freeze arr

-- コンパイル不能 (f . runST $ do ..)
testFailure2 :: (Int, Int)
testFailure2 = bounds . runST $ do
      arr <- newArray (0, 10) (0 :: Int) :: ST s (STUArray s Int Int)
      freeze arr

main :: IO ()
main = do
  print $ testFailure