module Data.IORef(
  IORef,
  newIORef,
  readIORef,
  writeIORef,
  modifyIORef,
  ) where
import Prelude()              -- do not import Prelude
import Primitives
import Data.Eq

-- An IORef is represented as an IOArray with a single element.
newtype IORef a = R (IOArray a)

instance forall a . Eq (IORef a) where
  R x == R y  =  primArrEQ x y

newIORef :: forall a . a -> IO (IORef a)
newIORef a = primArrAlloc 1 a `primBind` \ p -> primReturn (R p)

readIORef :: forall a . IORef a -> IO a
readIORef (R p) = primArrRead p 0

writeIORef :: forall a . IORef a -> a -> IO ()
writeIORef (R p) a = primArrWrite p 0 a

modifyIORef :: forall a . IORef a -> (a -> a) -> IO ()
modifyIORef (R p) f = primArrRead p 0 `primBind` \ a -> primArrWrite p 0 (f a)