tjay.dreaming:
Thanks for the demo. I don't actually understand what's going on yet, but your code doesn't really use a global variable, does it? From what I can understand, the main function is passing the State to the other functions.
Right, via the monad. The monad does all the threading.
I think I was careless about mixing "IO functions" and normal functions. Now that I think about it, my "global variable" really should only be available to IO functions, so the following should be just fine:
---------------------------------------------------------- module Global where
import Data.IORef
theGlobalVariable = newIORef []
testIt = do ref <- theGlobalVariable original <- readIORef ref print original writeIORef ref [1,2,3] new <- readIORef ref print new ----------------------------------------------------------
I've got a lot to learn about Haskell...
Now, if you wanted to pass that ref to other functions, you'd have to thread it explicitly -- unless you store it in a state monad :) i.e. do ref <- theGlobalVariable ... .. f ref ... f r = do ... .. g r ... I kind of jumped ahead that step, and went straight to the implicitly threaded version. -- Don