我是Haskell和Yesod的新手,我正在尝试使用该Control.Concurrent.Async模块来做异步.(代码基于:https://hackage.haskell.org/package/async-2.1.1/docs/Control-Concurrent-Async.html#v : withAsync)
quizWidget = do
--Get first question
withAsync (showQuizItem 1 1 ) $ \qi -> do
withAsync (showScoreboard) $ \sb -> do
quizItem <- wait (qi)
scoreboard <- wait (sb)
toWidget $(hamletFile "hamlet/quiz.hamlet")
但是这会产生以下错误:
"使用'toWidget'时没有(MonadWidget IO)的实例".
所以问题是我做错了什么？