+-- | Like 'runIO', but in the event of an exception that causes an exit,
+-- we don't shut down the system cleanly, we just exit. This is
+-- useful in some cases, because the safe exit version will give other
+-- threads a chance to clean up first, which might shut down the
+-- system in a different way. For example, try
+--
+-- main = forkIO (runIO (exitWith (ExitFailure 1))) >> threadDelay 10000
+--
+-- This will sometimes exit with "interrupted" and code 0, because the
+-- main thread is given a chance to shut down when the child thread calls
+-- safeExit. There is a race to shut down between the main and child threads.
+--
+runIOFastExit :: IO a -> IO a
+runIOFastExit main = catchException main topHandlerFastExit
+ -- NB. this is used by the testsuite driver
+