Amazon web services 用镜头捕捉多个异常

我使用

Lens

和

Amazonka

来处理错误，但我很难处理错误：

doSignup e p = (AWS.send $ AWS.signUp "secret" e p)
    $> Right ()
    & catching_ AWS._UsernameExistsException (return $ Left AlreadyExistingEmail)
    & catching_ AWS._InvalidPasswordException (return $ Left WeakPassword)
    & catching  AWS._SertviceError (return . UnknownSignUpError)

data SignUpError where
  AlreadyExistingEmail ::                          SignUpError
  NotAnEmail           ::                          SignUpError
  WeakPassword         ::                          SignUpError
  UnknownSignUpError   :: forall a. Show a => a -> SignUpError

我努力保持一致的捕获行为，当抛出

\u用户名existsexception

时，我得到了一个

左弱密码

它变得更奇怪，因为当我删除
WeakPassword
行时，它就工作了

虽然我得到了正确的错误（只保留最后一行）：

我曾尝试使用
捕捉
，但
处理程序
需要
可打印
镜头，但事实并非如此

我怎样才能有一种“类似模式匹配”的方法来处理异常？提前感谢。
事实上，使用了
控件.Lens.catching
而不是
Network.AWS.Prelude.catching
，这扰乱了异常处理。
这似乎非常令人惊讶。能否显示引发异常的代码？也许你没有得到你认为的例外。
       expected: Right ()
        but got: Left UnknownSignUpError ServiceError' {_serviceAbbrev = Abbrev "CognitoIdentityProvider", _serviceStatus = Status {statusCode = 400, statusMessage = "Bad Request"}, _serviceHeaders = [("Date","Tue, 06 Oct 2020 05:38:56 GMT"),("Content-Type","application/x-amz-json-1.1"),("Content-Length","96"),("Connection","keep-alive"),("x-amzn-RequestId","b09210a3-41ed-46ee-af4f-46db58b98695"),("x-amzn-ErrorType","UsernameExistsException:"),("x-amzn-ErrorMessage","An account with the given email already exists.")], _serviceCode = ErrorCode "UsernameExists", _serviceMessage = Just (ErrorMessage "An account with the given email already exists."), _serviceRequestId = Just (RequestId "b09210a3-41ed-46ee-af4f-46db58b98695")}