Question

{-# LANGUAGE OverloadedStrings #-}
import Network.Wreq
import Data.ByteString.Lazy
import Control.Lens

totalResponse :: IO (Response ByteString)
totalResponse =  response

status :: Status
status =  response ^. responseStatus

response = get "url"

给出了

getRequest.hs:10:23: error:
    • Couldn't match type ‘Response body0’
                     with ‘IO (Response ByteString)’
      Expected type: Getting Status (IO (Response ByteString)) Status
        Actual type: (Status -> Const Status Status)
                     -> Response body0 -> Const Status (Response body0)
    • In the second argument of ‘(^.)’, namely ‘responseStatus’
      In the expression: response ^. responseStatus
      In an equation for ‘status’: status = response ^. responseStatus

当我寻找

:type response ^. responseStatus

在ghci中给出了

response ^. responseStatus :: Status

我对Haskell来说是全新的。

Answer 1

正如上面的评论指出的那样，在使用更复杂的库之前学习Haskell可能是个好主意。如上所述，您的代码中存在类型不匹配。 response不是你想象的那个值，而是一个monad。如果您想获得回复的状态代码，可以试试这个：

status :: IO Status
status = do
  resp <- get "url" -- This is how the value returned by get is obtained.
  return (resp ^. responseStatus)

请注意，一切都在IO monad中完成，这是Haskell处理IO副作用的方式。

使用Network.Wreq从Response中提取responseStatus

1 个答案: