Question

使用：

mailHandler = do 
  name  <- param "name"
  email <- param "email"
  renderSendMail $ forwardMail name email

main = scotty 3000 $ post "/mail" mailHandler

我收到以下类型错误：

    Couldn't match type `IO'
                  with `Web.Scotty.Internal.Types.ActionT T.Text IO'
    Expected type: Web.Scotty.Internal.Types.ActionT T.Text IO ()
      Actual type: IO ()
    In a stmt of a 'do' block: renderSendMail $ forwardMail name email
    In the expression:
      do { name <- param "name";
           email <- param "email";
           renderSendMail $ forwardMail name email }
    In an equation for `mailHandler':
        mailHandler
          = do { name <- param "name";
                 email <- param "email";
                 renderSendMail $ forwardMail name email }
Failed to install server-0.0.1
cabal: Error: some packages failed to install:
server-0.0.1 failed during the building phase. The exception was:
ExitFailure 1

花了几个小时后，我仍然没有看到如何解决这个问题。如果我使用Scotty内部的函数，没问题，但如果我想在外部处理任何东西，我会得到上面的错误。如何通过此Web.Scotty.Internal.Types.ActionT T.Text IO ()

Answer 1

Web.Scotty.Internal.Types.ActionT T.Text IO ()是 monad转换器超过IO。这些通常会实现MonadIO类，以便您可以使用liftIO函数（来自Control.Monad.IO.Class，如果尚未导入）来“提升”IO行为进入他们：

liftIO . renderSendMail $ forwardMail name email

Scotty post类型不会产生影响

1 个答案: