[project @ 2000-10-02 11:06:19 by simonmar]

[project @ 2000-10-02 11:06:19 by simonmar]
- move readMVar and swapMVar from PrelConc to concurrent

- add the following exception-safe MVar operations:

	withMVar    :: MVar a -> (a -> IO b) -> IO b
	modifyMVar  :: MVar a -> (a -> IO (a,b)) -> IO b
	modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()

- re-implement readMVar and swapMVar in an exception-safe way.

- re-implement the Chan operations using withMVar et al.