Haskell 在gtk2hs中的事件处理程序之间切换

我想这样做：

handlerOn = do
  cid <- canvas `on` buttonPressEvent $ tryEvent do
    signalDisconnect cid
    handlerOff
  putStrLn "handlerOn"

handlerOff = do
  cid <- canvas `on` buttonPressEvent $ tryEvent do
    signalDisconnect cid
    handlerOn
  putStrLn "handlerOff"

handlerOn=do
cidGHC支持

或者自己管理处理程序

do ...
    h <- newIORef undefined
    let handlerOn = do
            ...
            writeIORef h handlerOff
        handlerOff = do
            ...
            writeIORef h handlerOn
    writeIORef h handlerOn
    canvas `on` buttonPressEvent $ tryEvent =<< readIORef h

做。。。
h谢谢！我正在使用第一个选项，至少对我来说，我必须添加括号，如：rec{cid…handlerOff}中所示，这样它才能工作。
handlerOff = do
  mfix $ \cid -> canvas `on` buttonPressEvent $ tryEvent do
    signalDisconnect cid
    handlerOn
  putStrLn "handlerOff"

do ...
    h <- newIORef undefined
    let handlerOn = do
            ...
            writeIORef h handlerOff
        handlerOff = do
            ...
            writeIORef h handlerOn
    writeIORef h handlerOn
    canvas `on` buttonPressEvent $ tryEvent =<< readIORef h

do ...
    ms <- newIORef False
    canvas `on` buttonPressEvent $ tryEvent do
        s <- readIORef ms
        if s
            then ...
            else ...