haskell - 如何在 ScottyM 中运行 IO

Question

我Scotty用来写一个小的网络应用程序。我需要IO在ScottyM类型内运行。

有几个困难：

首先，我不能自动派生类型同义词MonadIO以便运行liftIO：

type ScottyM = ScottyT Text IO 

其次，我不知道如何从中派生 ScottyT MonadIO：

newtype ScottyT e m a

Constructors
ScottyT  

    runS :: State (ScottyState e m) a 

我有哪些选择？

谢谢

Answer 1

您是否有必要在内部ScottyM而不是在开始之前运行 IO scotty？

{-# LANGUAGE OverloadedStrings #-}

import Web.Scotty

import Data.Monoid (mconcat)

main = do
    print "Hello world!" -- Or your IO action of choice
    scotty 3000 $
        get "/:word" $ do
            beam <- param "word"
        html $ mconcat ["<h1>Scotty, ", beam, " me up!</h1>"]

另一种选择是滥用notFound并next在 IO 中运行ActionM，这更直接：

{-# LANGUAGE OverloadedStrings #-}

import Web.Scotty

import Control.Monad.Trans.Class (lift)
import Data.Monoid (mconcat)

main = scotty 3000 $ do
    notFound $ do
        lift $ print "Hello world!" -- Or some other IO action
        next
    get "/:word" $ do
        beam <- param "word"
        html $ mconcat ["<h1>Scotty, ", beam, " me up!</h1>"]