At 2002-11-18 11:05, Sven Panne wrote:

...

global :: a -> IORef a global a = unsafePerformIO (newIORef a)

This is useful, you can do this with it:

ref = global Nothing

convert :: a -> IO b convert a = do writeIORef ref (Just a) Just b <- readIORef ref return b

This particular "flexibility" provided by unsafePerformIO is actually documented... http://www.haskell.org/ghc/docs/latest/html/base/System.IO.Unsafe.html#u nsafePerformIO Cheers, Simon