-- From "On embedding a microarchitectural design language within Haskell",
-- "Use and Abuse of unsafePerformIO"

import Data.IORef
import System.IO.Unsafe

-- Resurrects the original ML-reference problem
-- Also see the comments in GHC/IOBase.lhs
cast :: a->b
cast x = let r = unsafePerformIO (newIORef undefined)
             in unsafePerformIO (do {writeIORef r x; readIORef r})

-- cast' :: a -> a
cast' x = unsafePerformIO
          (do 
              r <- newIORef undefined
              writeIORef r x
              readIORef r)