反应性香蕉节流事件

Question

我想在反应香蕉中实施某种类型的事件限制.它应该起作用,如果从最后一个通过的事件到达少于delta秒,则不通过事件.如果它没有通过那么它被存储并在从最后一个被触发的事件开始的delta秒之后被触发.

下面是一个程序,用于为带有时间戳的数字列表实现此功能.是否有可能将其转化为反应性香蕉？

此外,在反应性香蕉中,如何在其他事件进入后x秒发射事件？

module Main where

import Data.List

-- 1 second throtling
-- logic is to never output a value before 1 second has passed since last value was outputed.

main :: IO()
main = print $ test [ (0.0, 1.0), (1.1, 2.0), (1.5,3.0), (1.7,4.0),  (2.2, 5.0)  ]
--should output  [ (0.0, 1.0), (1.1, 2.0), (2.1,4.0), (3.1, 5.0) ]

test :: [(Double,Double)] -> [(Double,Double)]
test list = g v (concat xs)
       where
               (v, xs) = mapAccumL f (-50,Nothing) list
               g (t, Just x) ys = ys ++ [ (t+1,x) ]
               g _ ys  = ys
               f (lasttime, Just holdvalue) (t,x) = if t > (lasttime+1) then
                               if t > (lasttime + 2) then
                                       ( (t, Nothing), [ (lasttime+1,holdvalue), (t,x)] )
                               else ( (lasttime+1, Just x) , [ (lasttime+1,holdvalue) ] )
                       else        
                               ( (lasttime, Just x), [] )
               f (lasttime, Nothing) (t,x) = if t > (lasttime+1) then
                        ( (t,Nothing) , [ (t, x ) ] ) 
                        else ( (lasttime, Just x), [] )

Answer 1

好的，我设法实现了我在问题中描述的内容。我不太高兴需要 IO 来通过重新启动来控制计时器。我想知道是否有可能有一个带有签名throttle::Event ta -> Int -> Event ta ...的油门

ps：我对 Haskell 很陌生，所以代码可能会更紧凑或更优雅。

{-----------------------------------------------------------------------------

------------------------------------------------------------------------------}
{-# LANGUAGE ScopedTypeVariables #-} -- allows "forall t. NetworkDescription t"

import Graphics.UI.WX hiding (Event)
import Reactive.Banana
import Reactive.Banana.WX
import Data.Time

{-----------------------------------------------------------------------------
    Main
------------------------------------------------------------------------------}

data ThrottledValue a = FireStoredValue a | FireNowAndStartTimer a| HoldIt a | Stopped deriving Show
data ThrottledEvent a = TimerEvent | RealEvent a deriving Show

main = start $ do
    f   <- frame [text := "Countercesss"]
    sl1  <- hslider f False 0 100 []
    sl2  <- hslider f False 0 100 []
    set f [ layout := column 0 [widget sl1, widget sl2] ]
    t <- timer f []
    set t [ enabled := False ] 
    let networkDescription :: forall t. NetworkDescription t ()
        networkDescription = do
        slEv <- event0 sl1 command
        tick <- event0 t command 
        slB <- behavior sl1 selection
        let (throttledEv, reactimates) = throttle (slB <@ slEv) tick t 100
        reactimates
        reactimate $ fmap (\x ->  set sl2 [selection := x]) throttledEv       
    net <- compile networkDescription
    actuate net            

throttle::Event t a -> Event t () -> Timer -> Int -> (Event t a, NetworkDescription t () )    
throttle ev tick timer dt = (throttledEv, reactimates)
        where   
                all = union (fmap (\x-> RealEvent x) ev) (fmap (\x -> TimerEvent) tick)
                result = accumE Stopped $ fmap h all
                        where
                        h (RealEvent x) Stopped = FireNowAndStartTimer x
                        h TimerEvent Stopped = Stopped
                        h (RealEvent x) (FireNowAndStartTimer _) = HoldIt x
                        h TimerEvent (FireNowAndStartTimer _) = Stopped
                        h (RealEvent x) (HoldIt _) = HoldIt x
                        h (TimerEvent) (HoldIt y) = FireStoredValue y
                        h (RealEvent x) (FireStoredValue _) = HoldIt x
                        h (TimerEvent) (FireStoredValue _) = Stopped          
                start (FireStoredValue a) = Just $ resetTimer timer dt
                start (FireNowAndStartTimer a) = Just $ resetTimer timer dt
                start _ = Nothing  
                stop Stopped = Just $ stopTimer timer
                stop _ = Nothing  
                reactimates = do
                        reactimate $ filterJust $ fmap stop result   
                        reactimate $ filterJust $ fmap start result
                filterFired (FireStoredValue a) = Just a
                filterFired (FireNowAndStartTimer a) = Just a
                filterFired _ = Nothing
                throttledEv = filterJust $ fmap filterFired result                 

startTimer t dt = set t [ enabled := True, interval := dt ]
stopTimer t = set t [ enabled := False ]
resetTimer t dt = stopTimer t >> startTimer t dt