Eric Wong
I'm relatively new to haskell and due to my strong imperative background, it's really a pain to learn haskell. But I'm really indulged in it. :)
Now I think I understand the basics of Haskell very well, such as the type system and monad. And for those data-flow kind of applications, I can easily structure the problem in a functional way and sketch out an intuitive picture of the computation. But for simulation kind-of problems, in which I think OO really fits the best, what's the haskell way to structure such problems? I once thought maybe I can use the State monad to simulate objects. But it's really hard for me to implement, because I think State monad is used to simulate a global shared state, is it right?
Then what's the best way to simulate private states or just instead how to solve simulation problems such as a physical engine using the haskell way?
A state monad is used to encode a stateful computation. Whether its state is global or not really only depends on how long the computation lives. Here is how you can use one to maintain a list of objects: computation :: State [Object] Result computation = do objs0 <- get (result, objs1) <- doSomethingWith objs0 put objs1 return result This is really just a convenient encoding of: computation :: [Object] -> (Result, [Object]) Whether that [Object] state is global really only depends on where you use evalState, execState or runState and how long the computation takes. I often do something like this, which you can regard as global 'state' (or rather a global environment): type AppIO = ReaderT AppConfig IO myApp :: AppIO () myApp = ... main :: IO () main = getAppConfig >>= evalStateT myApp Greets, Ertugrul. -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://blog.ertes.de/