But if there are some beautiful arithmetics that do not use something like state, I won't say no to them.
-----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: haskell-cafe@haskell.org 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. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
