haskell - `wreq` Get/Post 带异常处理

Question

我正在使用 wreq 进行一些 http 调用并希望捕获任何异常并返回 Either类型。我尝试了类似的方法，但无法弄清楚如何操作调用，以便它进行类型检查。

 -- exhaustive pattern match omitted here
 safeGetUrl :: URL -> Maybe Login -> Maybe Password -> IO (Either String (Response LBS.ByteString))
 safeGetUrl url (Just login) (Just pass) = do
     let def  = defaults
         opts = def & auth ?~ basicAuth (BS.pack login) (BS.pack pass)
     r <- getWith opts url  `E.catch` handler
     return $ Right r

   where
     handler :: HttpException -> Either String (Response LBS.ByteString)
     handler (StatusCodeException s _ _) = do
          return $ Left $ LBS.unpack (s ^. statusMessage)

我粘贴了下面的类型错误，但我知道上面的代码将无法编译。问题是r <- getWith opts url E.catch handler 。第一部分返回IO (Res...但异常处理程序返回 Either.. 。我尝试添加提升 getWith..进入Either但这也没有进行类型检查。

Couldn't match type ‘Either String (Response LBS.ByteString)’
                 with ‘IO (Response LBS.ByteString)’
  Expected type: HttpException -> IO (Response LBS.ByteString)
    Actual type: HttpException
                 -> Either String (Response LBS.ByteString)
  In the second argument of ‘catch’, namely ‘handler’
  In a stmt of a 'do' block: r <- getWith opts url `catch` handler

有没有办法捕获此异常并返回 IO Either类型？

Answer 1

自从 @jozefg 回答以来，API 发生了一些变化，并且答案不再编译。

这是可编译的更新版本:

import qualified Control.Exception     as E
import           Control.Lens
import qualified Data.ByteString.Char8 as BSC
import qualified Data.ByteString.Lazy  as LBS
import           Network.HTTP.Client
import           Network.Wreq          as NW

type URL = String

type Login = String

type Password = String

safeGetUrl ::
     URL
  -> Maybe Login
  -> Maybe Password
  -> IO (Either String (Response LBS.ByteString))
safeGetUrl url (Just login) (Just pass) = do
  let def = defaults
      opts = def & auth ?~ basicAuth (BSC.pack login) (BSC.pack pass)
  (Right <$> getWith opts url) `E.catch` handler
  where
    handler :: HttpException -> IO (Either String (Response LBS.ByteString))
    handler (HttpExceptionRequest _ (StatusCodeException r _)) =
      return $ Left $ BSC.unpack (r ^. NW.responseStatus . statusMessage)