    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.HGL.Internals.Utilities
    -- Copyright   :  (c) Alastair Reid, 1999-2003
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  internal
    -- Portability :  non-portable (requires concurrency)
    --
    -- A simple graphics library.
    --
    -----------------------------------------------------------------------------

    -- #hide
    module Graphics.HGL.Internals.Utilities(
    	bracket, bracket_,
    	safeTry,
    	Exception,
            modMVar, modMVar_
    	) where

    import qualified Control.Exception as E (bracket, try, IOException, tryJust)
    import Control.Concurrent( MVar, takeMVar, putMVar )

    bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
    bracket = E.bracket

    -- Not exactly the same type as GHC's bracket_
    bracket_ :: IO a -> (a -> IO b) -> IO c -> IO c
    bracket_ left right m = bracket left right (const m)

    type Exception = E.IOException
    safeTry :: IO a -> IO (Either Exception a)
    safeTry = E.try

    ----------------------------------------------------------------
    -- Utilities
    ----------------------------------------------------------------

    modMVar :: MVar a -> (a -> a) -> IO a
    modMVar mv f = do
      x <- takeMVar mv
      putMVar mv (f x)
      return x

    modMVar_ :: MVar a -> (a -> a) -> IO ()
    modMVar_ mv f = do
      x <- takeMVar mv
      putMVar mv (f x)