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我第一次尝试使用 Reactive Banana (WX) 在五个按钮之上显示诸如“按下按钮一”、“按下按钮二”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

代码只是主要骨架。我目前无法做的是填充somethinghere方法。如前所述，如果例如按下按钮“One”，somethinghere则应返回参考ButtonsADT 数据One等。我试过了accumB，unionWith但我认为我没有得到正确的机制。有什么帮助吗？

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1 回答 1

3

I believe you want something like:

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 represents the currently selected button, and eChangeSelection is the stream of updates to it. unions merges the five event streams, and (<$) tags each individual stream with the appropriate value. Note that I arbitrarily picked One as the initial selection value; you might prefer doing something different (e.g. using a Behavior t (Maybe Buttons) so that it is possible to not have a button selected).

于 2015-09-01T00:30:31.320 回答