pad.hs

import Control.Applicative (liftA2)
import Data.Foldable
import Data.Tuple.Homogenous
import Graphics.Gloss.Interface.Pure.Game

import Debug.Trace

main = play
    (InWindow "Deriv II" (500,500) (100,100))
    black
    120
    ((0, pure 0, pure $ pure 0) :: (Float, Tuple2 Float, Tuple9 (Tuple2 Float)))
    (\w@(time,point,history) ->  traceShow w $ fold $ do
                divisor <- Tuple2(time,time*time)
                (coeff,clr) <- coefficients
                let deriv = fmap (/divisor) (foldr (liftA2 (+)) (pure 0) $ do
                    hist <- history
                    co <- coeff
                    return $ fmap (co*) hist)
                return $ color clr $ Line [untuple2 point, untuple2 $ (+) <$> point <*> deriv]
                )
    (\e w@(t,p,h) -> case e of
        EventMotion p' -> (t,Tuple2 p',h)
        _ -> w
        )
    (\t (_,p,h) -> (t, p, cons p h))

coefficients = tuple2
    (negate <$> (tuple9 (-761/280) (8) (-14) (56/3) (-35/2) (56/5) (-14/3) (8/7) (-1/8)                          ), green)
    (           (tuple9 (29531/5040) (-962/35) (621/10) (-4006/45) (691/8) (-282/5) (2143/90) (206/35) (363/560) ), red  )

cons x (Tuple9 (x0,x1,x2,x3,x4,x5,x6,x7,x8)) = tuple9 x x0 x1 x2 x3 x4 x5 x6 x7