Hello, I know there is a special mailing list for reactive, but I got no answers when sending to it. Also, maybe my problem is not totally reactive-centered, it concerns integration of an object speed to obtain its position with FRP. As a newbie with reactive, I'm trying to make a simple example, namely a pong. But I'm stuck with the paddle animation. Here is a how I proceed : A paddle: data Paddle = Paddle { paddleCol :: Double, paddleCenter :: Behavior Double } The paddle moves along a column, so only it's Y coordinate changes. paddleCenter is the Y coordinate of its center. This is how I create a paddle: data Direction = PaddleUp | PaddleDown | PaddleStill deriving (Eq, Show) newPaddle :: Behavior Direction -> Double -> Paddle newPaddle direction column = let position = fmap ((initY ^+^)) $ integral *beat* $ fmap ((speed *) . factor) direction factor PaddleUp = -1 factor PaddleDown = 1 factor _ = 0 speed = 50 -- pixels per second initY = 400 -- suppose we have a 800x600 window: paddle is right at the middle *beat = atTimes [0, 0.01..]* in Paddle column position Basically, a paddle is driven by a behavior which tells him to go up, down or to stand still. My problem is with the tuning of the beat, a ticker event which is used for the integration. How do I have to think ? - My speed is in pixels/second, so it has to tick every second? (atTime [0, 1..]) - My app will run at 60fps, so it has to tick 60 times per second? (atTime [0, 1/60..]) The main program (I'm not using any graphics library, just getting keys ('u' for up, 'd' for down) and displaying the current paddle pos) makeKeyboardEvent = do hSetBuffering stdin NoBuffering hSetBuffering stdout NoBuffering (buttonPressedSink, event) <- makeEvent =<< makeClock forkIO . forever $ getChar >>= buttonPressedSink return event main = do keyEvt <- makeKeyboardEvent let dirEvt = fmap key2dir keyEvt paddle = newPaddle (stepper PaddleStill dirEvt) 50 adaptE $ fmap print $ snapshot_ (paddleCenter paddle) $ atTimes [0, 0.01..] key2dir k = maybe PaddleStill snd $ find (($ k) . fst) [((== 'u'), PaddleUp), ((== 'd'), PaddleDown)] When I launch the program, I hit 'u' or 'd' and I see the position increase/decrease. If the beat ticks every second, I see the position being increased by 50 every second, which is normal, but it's a too low refresh rate for an app that is to run at 60fps. But when I set my beat to tick every 60 times per second, the position is well updated, but I clearly see that the display dramatically slows down after a few seconds of execution. Too heavy rate for integrate? That's why I'm asking: how should I use integrate?