我正在尝试使用Scotty来构建一个非常简单的API。我想扩展Scotty monads,使我的路由处理器操作能够访问不变的环境。我相信这样做的方法是将一个Reader
monad添加到堆栈。现在我只想通过一些Text
数据。我如何将读者monad添加到Scotty的monad中?
type BrandyScottyM = ScottyT TL.Text (ReaderT T.Text IO)
type BrandyActionM = ActionT TL.Text (ReaderT T.Text IO)
https://github.com/stu-smith/Brandy/blob/0838a63537d7e396ac82d58d460c6529349303d3/src/Core.hs
所以我的第一个问题是,这是正确的做法:
我如下扩展斯科蒂单子?
我已经成功地更改了我的路由处理程序的类型,但我无法解决如何使用此堆栈来启动Scotty。我已经尝试以下操作:
runScotty :: Port -> Text -> BrandyScottyM() -> IO()
runScotty port file = T.scottyT port ((\f -> runReader f file)) id
https://github.com/stu-smith/Brandy/blob/0838a63537d7e396ac82d58d460c6529349303d3/src/Main.hs
但我得到的错误:
Couldn't match type `IO' with `Data.Functor.Identity.Identity'
Expected type: Reader Text (IO a)
Actual type: ReaderT Text IO a
In the first argument of `runReader', namely `f'
In the expression: runReader f file
In the second argument of `T.scottyT', namely
`((\ f -> runReader f file))'
/home/stu/git/Brandy/src/Main.hs: line 36, column 65:
Couldn't match type `ReaderT Text IO Network.Wai.Internal.Response'
with `IO Network.Wai.Internal.Response'
Expected type: ReaderT Text IO Network.Wai.Internal.Response
-> IO Network.Wai.Internal.Response
Actual type: ReaderT Text IO Network.Wai.Internal.Response
-> ReaderT Text IO Network.Wai.Internal.Response
In the third argument of `T.scottyT', namely `id'
In the expression: T.scottyT port ((\ f -> runReader f file)) id
In an equation for `runScotty':
runScotty port file = T.scottyT port ((\ f -> runReader f file)) id
所以我的第二个问题是,我该如何推出斯科蒂用不同的单子栈?这是我第一次尝试使用monad变形金刚,并且我似乎无望地迷路了。
啊哈太棒了,让我在正确的路线。我还必须在应用程序和操作级别都创建'Reader',所以最终的调用是:''.scottyT port(\'runReaderT \'file)(\'runReaderT \'file)' – stusmith