Reactive Banana：备用按钮事件

Question

我第一次尝试使用 Reactive Banana (WX) 在五个按钮顶部显示 "Pressed button One"、"Pressed button Two" 等文本：

{-# LANGUAGE ScopedTypeVariables #-}

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

data Buttons = One | Two | Three | Four | Five deriving (Show)

main :: IO ()
main = start $ do
  f      <- frame [text := “Five Buttons“]
  bone   <- button f [text := “One”]
  btwo   <- button f [text := “Two”]
  bthree <- button f [text := “Three”]
  bfour  <- button f [text := “Four”]
  bfive  <- button f [text := “Five”]
  out    <- staticText f []

  set f [layout := margin 10 $
          column 5 [row 5 [widget bone, widget btwo, widget bthree, widget bfour, widget bfive],
                    grid 5 5 [[label “Output:” , widget out]
                              ]]]

  let networkDescription :: forall t. Frameworks t => Moment t ()
      networkDescription = do
        eone   <- event0 bone   command
        etwo   <- event0 btwo   command
        ethree <- event0 bthree command
        efour  <- event0 bfour  command
        efive  <- event0 bfive  command

        let
          somethinghere::Behaviour t Buttons
          somethinghere = ....
        sink out [text :== "Pressed button " ++ show <$> somethinghere]

  network <- compile networkDescription    
  actuate network

代码只是主要框架。我目前无法做的是填写 somethinghere 方法。如前所述，如果按下按钮 "One"，那么 somethinghere 应该 return 引用 Buttons ADT 数据 One 等等。我尝试使用 accumB and unionWith，但我认为我的机制不正确。有帮助吗？

Answer 1

我相信你想要这样的东西：

let eChangeSelection :: Event t Buttons
    eChangeSelection = unions
        [ One <$ eone
        , Two <$ etwo
        , Three <$ ethree
        , Four <$ efour
        , Five <$ efive
        ]

    -- Your `somethinghere`:
    bSelection :: Behavior t Buttons
    bSelection = stepper One eChangeSelection

bSelection 表示当前选中的按钮，eChangeSelection 是对其的更新流。 unions 合并了五个事件流，(<$) 用适当的值标记每个单独的流。请注意，我随意选择 One 作为初始选择值；您可能更喜欢做一些不同的事情（例如，使用 Behavior t (Maybe Buttons) 这样就可以不选择按钮）。

Reactive Banana：备用按钮事件

Reactive Banana: Alternate buttons events

haskell

wxwidgets

frp

reactive-banana