Hello minh, Wednesday, September 3, 2008, 2:09:38 PM, you wrote:
> I'd like to write a data structure to be used inside the IO monad. > The structure has some handles of type Maybe (IORef a), > i.e. IORef are pointers and the Maybe is like null pointers. i've not used this but overall it seems like a correct way to emulate NULL. the whole question is that you probably still think C if you need NULL pointers at all :) > readHandle :: Maybe (IORef a) -> IO (Maybe a) > Are there any related functions in the standard libraries ? readHandle = maybe (return Nothing) (fmap Just . readIORef) or you can add your own primitive: liftNULL op = maybe (return Nothing) (fmap Just . op) readHandle = liftNULL readIORef -- Best regards, Bulat mailto:[EMAIL PROTECTED] _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
