{-# OPTIONS -fglasgow-exts #-}
-- By Jesse Tov (ccs.neu.edu!tov), November 2007
-- This is a DRAFT.  Later versions at http://www.ccs.neu.edu/home/tov/.
module CMLChan (
  CMLChan, newCMLChan, writeCMLChan, readCMLChan,
) where

import Data.Typeable
import Control.Concurrent.MVar

newtype CMLChan a = CC (MVar (MVar a))
  deriving Typeable

newCMLChan = newEmptyMVar >>= return . CC

writeCMLChan (CC cc) v = do
  mv <- takeMVar cc
  putMVar mv v

readCMLChan (CC cc) = do
  mv <- newEmptyMVar
  putMVar cc mv
  takeMVar mv

tryWriteCMLChan (CC cc) v = do
  mv <- tryTakeMVar cc
  case mv of
    Just mv -> putMVar mv v >> return True
    Nothing -> return False