On 8 Jan 2008, at 3:38 PM, Achim Schneider wrote:
---$<---
or, while I'm at it
---$<---
moveBall :: State' -> State'
moveBall state = state {ballPos' = (bpx+bvx, bpy+bvy)}
where (bpx, bpy) = ballPos' state
(bvx, bvy) = ballVel' state
idle'' :: StateRef -> IdleCallback
idle'' st = st $~ moveBall
---$<---
With the multiple IORef-Model, moveBall looks like this:
moveBall :: Vec2 -> Vec2 -> Vec2
moveBall (bpx, bpy) (bvx,bvy) = (bpx+bvx, bpy+bvy)
You can use this with the single IORef model, using the lifting function
liftMove :: (Vec2 -> Vec2 -> Vec2) -> IORef State -> IO ()
liftMove move r = withIORef r $ \ st -> st{ballPos = moveBall
(ballPos st) (ballVel st) }
liftMove and moveBall can then be maintained separately; liftMove is
part of your state framework (the outer layer of your program);
moveBall is part of the algorithm specification (the inner layer of
your program).
jcc
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