On Mon, Dec 03, 2007 at 08:47:48PM -0600, David McBride wrote:
I am still in the early stages learning haskell, which is my first foray into functional programming. Well there's no better way to learn than to write something, so I started writing a game.
Mostly the thing looks good so far, far better than the C version did. However, my problem is that code like the following is showing up more often and it is becoming unwieldy.
gameLoop :: World -> IO () gameLoop w = do drawScreen w
action <- processInput
let (result, w') = processAction action w
case result of MoveOutOfBounds -> putStrLn "Sorry you can't move in that direction." MoveBadTerrain a -> case a of Wall -> putStrLn "You walk into a wall." Tree -> putStrLn "There is a tree in the way." otherwise -> putStrLn "You can't move there." otherwise -> return ()
let w'' = w' { window = updateWindowLocation (window w') (location $ player w')}
unless (action == Quit) (gameLoop w'')
Where world contains the entire game's state and so I end up with w's with multiple apostrophes at the end. But at the same time I can't really break these functions apart easily. This is error prone and seems pointless.
I have been reading about control.monad.state and I have seen that I could run execstate over this and use modify but only if each function took a world and returned a world. That seems really limiting. I'm not even sure if this is what I should be looking at.
I am probably just stuck in an imperative mindset, but I have no idea what to try to get rid of the mess and it is only going to get worse over time. Any suggestions on what I can do about it?
I'd recommend using StateT World IO. You can always run other functions using 'lift'; for instance lift can be :: IO () -> StateT World IO (). Stefan