I'm trying to simulate a bouncing ball with the Yampa-Framework: Given an initial x-position, height and velocity, the ball should bounce according to gravity rules. The signal function takes a "Tip-Event" as input, the idea being "when the ball is tipped, it's speed should double".
The ball bounces nicely, but every time there is a tipping event, the function goes in to an endless loop. I figured I probably need to add a delay (dSwitch, pre, notYet?), but I do not know how. Any help would be appreciated!
{-# LANGUAGE Arrows #-}
module Ball where
import FRP.Yampa
type Position = Double
type Velocity = Double
type Height = Double
data Ball = Ball {
height :: Height,
width :: Position,
vel :: Velocity
} deriving (Show)
type Tip = Event ()
fly :: Position -> (Height, Velocity) -> SF Tip (Ball, Event (Height,Velocity))
fly w0 (h0, v0) = proc tipEvent -> do
let tip = (tipEvent == Event ())
v <- (v0+) ^<< integral -< -10.0
h <- (h0+) ^<< integral -< v
returnA -< (Ball h w0 v,
if h < 0 then Event (0,(-v*0.6))
else if tip then Event (h, (v*2))
else NoEvent)
bounce w (h,v) = switch (fly w (h,v)) (bounce w)
runBounce w (h,v) = embed (bounce 10 (100.0, 10.0)) (deltaEncode 0.1 [NoEvent, NoEvent, NoEvent, Event (), NoEvent])
EDIT: I managed to avoid the endless loop by feeding back a flag when a tip occurred, but that still does not feel like the right way to do it...
fly :: Position -> (Height, Velocity, Bool) -> SF Tip (Ball, Event (Height,Velocity,Bool))
fly w0 (h0, v0, alreadyTipped) = proc tipEvent -> do
let tip = tipEvent == Event () && (not alreadyTipped)
v <- (v0+) ^<< integral -< -10.0
h <- (h0+) ^<< integral -< v
returnA -< (Ball h w0 v,
if h < 0 then Event (0,(-v*0.6), False)
else if tip then Event (h, (v*2), True)
else NoEvent)
bounce w (h,v,alreadyTipped) = switch (fly w (h,v,alreadyTipped)) (bounce w)