Yes, that's it, State.
Thanks.
-----邮件原件-----
发件人: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 代表 Achim Schneider
发送时间: 2008年6月16日 12:01
收件人: [email protected]
主题: [Haskell-cafe] Re: How to do this in FP way?
"Magicloud Magiclouds" <[EMAIL PROTECTED]> wrote:
> static int old;
> int diff (int now) { /* this would be called once a second */
> int ret = now - old;
> old = now;
> return ret;
> }
>
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State -> IdleCallback
idle state = do
t0 <- get $ t state
t1 <- get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) <- get $ ballPos state
(bvx, bvy) <- get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.
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