#ifdef __HUGS__
import Hugs.ConcBase ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
tryTakeMVar, tryPutMVar, isEmptyMVar,
- readMVar, swapMVar,
)
-import Hugs.Exception ( throwIO )
#endif
#ifdef __GLASGOW_HASKELL__
import Prelude
import Control.Exception as Exception
-#ifdef __HUGS__
--- This is as close as Hugs gets to providing throw
-throw :: Exception -> IO a
-throw = throwIO
-#endif
-
-#ifdef __GLASGOW_HASKELL__
{-|
This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
from the 'MVar', puts it back, and also returns it.
-- |Swap the contents of an 'MVar' for a new value.
swapMVar :: MVar a -> a -> IO a
-swapMVar mvar new = modifyMVar mvar (\old -> return (new,old))
-#endif
+swapMVar mvar new =
+ block $ do
+ old <- takeMVar mvar
+ putMVar mvar new
+ return old
{-|
'withMVar' is a safe wrapper for operating on the contents of an