使用响应香蕉中的数据设置自定义事件答案

【问题标题】：Setup custom Events with data in reactive-banana使用响应香蕉中的数据设置自定义事件
【发布时间】：2022-08-24 13:06:22
【问题描述】：

我有一个从reactive-banana repo 中获取的样本。这使用gloss。但是当我处理事件时，我有自己的数据事件。这些事件不一定是 UI 事件。所以我期待 FRP 可以帮助我编写自定义事件。因此，例如，一个列表可能会改变，而改变的数据在一个事件中，而应用程序的另一部分使用改变的数据。我初步的 Haskell 知识并没有帮助我使用reactive-banana 实现这一目标，但我确实遇到了something similar。

如何使用我自己的事件，如makeTickEvent 并触发它们？它可以保存数据吗？

{-# LANGUAGE ScopedTypeVariables #-}

module Main where
import Control.Monad (when)
import Data.Maybe (isJust, fromJust)
import Data.List (nub)
import System.Random
import System.IO
import Debug.Trace
import Data.IORef
import Reactive.Banana as R
import Reactive.Banana.Frameworks as R

import Graphics.Gloss
import Graphics.Gloss.Data.Extent
import Graphics.Gloss.Interface.Pure.Game
import Graphics.Gloss.Data.Picture

main :: IO()
main = do
    sources <- makeSources
    network <- compile $ networkDescription sources
    actuate network
    eventLoop sources
    display windowDisplay white drawBoard

windowDisplay :: Display
windowDisplay = InWindow \"Window\" (200, 200) (10, 10)

makeTickEvent :: MomentIO (R.Event ())
makeTickEvent = do
  (etick, tick) <- newEvent
  
  tid <- liftIO  $ do
    tick ()

  pure etick

drawBoard :: Picture
drawBoard =
  Pictures $ [ translate x y $ rectangleWire 90 90| x<-[0,90..180], y<-[0,90..180] ] 


makeSources =  newAddHandler


type EventSource a = (AddHandler a, a -> IO ())



addHandler :: EventSource a -> AddHandler a
addHandler = fst

eventLoop :: (EventSource ())  -> IO ()
eventLoop (displayvalueevent)  =
  fire displayvalueevent ()

fire :: EventSource a -> a -> IO ()
fire = snd


networkDescription :: (EventSource ()) -> MomentIO ()
networkDescription ( displayvalueevent )= do
  -- Obtain events 
  displayvalue <- fromAddHandler (addHandler displayvalueevent)
  reactimate $ putStrLn . showValue <$> displayvalue
 
showValue value = \"Value is \" ++ show value

这是来自文档。

plainChanges :: Behavior a -> MomentIO (Event a)
plainChanges b = do
    (e, handle) <- newEvent
    eb <- changes b
    reactimate\' $ (fmap handle) <$> eb
    return e

这会创建一个可以触发的新事件吗？

我发现很难理解你在问什么，但你是否在寻找fromAddHandler？
我正在寻找一种使用封装数据声明新事件的方法，例如 \'makeTickEvent\'。并解雇他们。我无法理解 \'newEvent\' 的工作原理。我认为。

标签： haskell frp reactive-banana

【解决方案1】：

我现在已经设法让这段代码工作了。触发事件并在初始光泽窗口中呈现新帧。似乎可以触发自定义事件。但我不确定在事件中封装数据。

makeNewEvent :: MomentIO (Reactive.Banana.Event ())
makeNewEvent = do
  (enew, new) <- newEvent
  
  tid <- liftIO  $ do
    putStrLn "Fire new Event" 
    new ()

  return enew

以下代码回答了一些问题。如果我有更多详细信息，我可以稍后进行编辑。这仍然是非常基本的，因为我正在学习 reactive-banana 和“haskell”

------------------------------------------------------------------------------}
{-# LANGUAGE ScopedTypeVariables #-}

module Main where
import Data.IORef
import Data.Bool (bool)
import Data.IORef (newIORef, readIORef, writeIORef)
import Graphics.Gloss hiding (pictures)
import Reactive.Banana
import Reactive.Banana.Frameworks
import Graphics.Gloss.Interface.IO.Game( Event(..) )
import Graphics.Gloss.Interface.IO.Game( MouseButton(..) )
import Graphics.Gloss.Interface.IO.Game( KeyState( Down ) )
import Graphics.Gloss.Interface.IO.Game
import qualified Graphics.Gloss.Interface.IO.Game as Gloss (Event, playIO)


main = do

   picRef ← newIORef blank
   (eventHandler, event) ← newAddHandler

   sources <- makeSources
   network <- compile $ networkDescriptor picRef sources
   actuate network
   eventLoop sources

   Gloss.playIO
    (InWindow "Functional Reactive" (320, 240) (800, 200))
    white
    30
    ()
    (\() -> readIORef picRef)
    (\ ev   _ → quit ev >> () <$ event ev)
    (\_ () -> pure ())
  where
    quit (EventKey (Char 's' )
                          _ _ _) = reactToKeyPress
    quit  _ = return ()

reactToKeyPress :: IO ()
reactToKeyPress = putStrLn "Key Pressed"



drawBoard :: Picture
drawBoard =
   Pictures $ [ color violet $ translate x y $ rectangleWire 90 90| x<-[0,90..180], y<-[0,90..180] ] 


makeSources =  newAddHandler


type EventSource a = (AddHandler a, a -> IO ())



addHandler :: EventSource a -> AddHandler a
addHandler = fst

eventLoop :: EventSource ()  -> IO ()
eventLoop ( displayvalueevent)  =
  fire displayvalueevent ()

fire :: EventSource a -> a -> IO ()
fire = snd



networkDescriptor :: IORef Picture -> EventSource() -> MomentIO ()
networkDescriptor lastFrame  displayGlossEvent = do
  glossEvent <- fromAddHandler (addHandler displayGlossEvent )
  reactimate $ putStrLn . showValue <$> glossEvent

  picture <- liftMoment (handleKeys displayGlossEvent )
  changes picture >>= reactimate' . fmap (fmap (writeIORef lastFrame))
  valueBLater picture >>= liftIO . writeIORef lastFrame




showValue value = "Value is " ++ show value

handleKeys :: EventSource ()  -> Moment (Behavior Picture)
handleKeys glossEvent = do


  let picture = drawBoard
  return $ pure picture

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