使用Network.Wreq從Response中提取responseStatus

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"

這使

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

當我尋找

:type response ^. responseStatus

在ghci

response ^. responseStatus :: Status

我是Haskell的新手。

Answer 1

正如上面的評論所指出的，在使用更復雜的庫之前學習Haskell可能是一個好主意。 如前所述，您的代碼中有類型不匹配。 response不是您想像的值，而是單子。 如果要獲取響應的狀態碼，可以嘗試以下操作：

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

請注意，所有操作都在IO monad內部完成，這是Haskell處理IO副作用的方式。