Haskell 捕捉快照处理程序中的HTTPException

在我的一个快照处理程序中，我正在使用HTTP客户端通过HTTP调用外部资源，该客户端可以抛出

HttpException

。在最简单的情况下，我只想捕获错误并在调试时写入std；然而，我很难把这些类型排好

assignCategories' :: String -> [String] -> Handler App (AuthManager App) String
assignCategories' l_id cats  = do
            let baseAttribs = M.fromList [("id",l_id)]                                                            
            let saveQuery = WMSaveObject {baseAttributesSO= baseAttribs ,relatedSO=relatedObjects}

            -- this is the function that can throw an HTTPException            
            -- runWMSave :: WMQueryObj -> Handler App (AuthManager App) String

            saveresponse <- try $ H.runWMSave saveQuery
            return $ case saveresponse of
                Left  e -> show (e :: HttpException)
                Right r -> r

   No instance for (Control.Monad.Catch.MonadCatch
                       (Handler App (AuthManager App)))
      arising from a use of ‘try’
    In the expression: try
    In a stmt of a 'do' block:
      saveresponse <- try $ H.runWMSave saveQuery
    In the expression:
      do { liftIO $ putStrLn l_id;
           let baseAttribs = M.fromList ...;
           let relatedObjects = concatMap makeRelatedRow cats;
           let saveQuery = ...;
           .... }

谢谢，

---

Neil

问题解决了，我使用了MonadCatchIO transformers的

try

，效果很好。

问题解决了，我使用了MonadCatchIO transformers的

try

，效果很好