testfunc = do r <- newSTRef ('x',0) foo r bar r (c,n) <- readSTRef r return n
Yeap, I could do it like this myself :) The whole problem is with passing the 'r' as a parameter, which is
Hi, precisly
what I'm trying to avoid. I think I already understood how to use this monad. Its pretty different from the monad state I was expecting, and as far as I can see, to be used in distinct situations. If I understand you correctly, you want global mutable variables, right? This is, I believe, only possible using IORef's and unsafePerformIO. Something like this: | xRef :: IORef Int | xRef = unsafePerformIO $ | newIORef 0 | update_x :: IO () | update_x = do | x <- readIORef xRef | writeIORef xRef (x+1) (Sorry for formatting, I'm using Outlook now :-)
Of course this is not very functional, nice, safe or robust under compiler transformations (there probably should be a NOINLINE pragma there somewhere) Another option is to use implicit variables here. I haven't tested this approach yet, maybe somebody else on the list has? You don't need to pass the reference around, but if you're fond of explicitly giving types for top-level entities (as I am) you're stuck putting it in all type signatures affected (context-ellipsis would come in handy here!!) Cheers, Jan