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Question

我正在努力撰写Servant的Servant和Handler：

Handler
为了回答一条路线，我必须使用Monad，这是class Monad p => Persist p where
  data Configuration p :: *
  runPersistance       :: Configuration p -> p a -> IO a
  initPersistence      :: p ()
  newKind              :: Kind -> p NewKindStatus
  -- ...

kind :: P.Persist p => KindUid -> KindBody -> p (Handler ())
kind (KindUid uid) (KindBody actions) = undefined

subject :: P.Persist p => KindUid -> SubjectUid -> EventData -> p (Handler EventUid)
subject kind subject body = undefined

event = post :<|> get
where post :: P.Persist p => KindUid -> SubjectUid -> Action -> EventData -> p (Handler EventUid)
        post kind subject action body = undefined
        get :: P.Persist p => KindUid -> SubjectUid -> p (Handler [Event])
        get kind subject = undefined

server :: P.Persist p => p (Server HermesAPI)
server = do
    k <- kind
    s <- subject
    e <- event
    return $ k :<|> s :<|> e

app :: P.Persist p => p (Application)
app = serve hermesAPI server
在做P.Persist。

我没有找到一种方法来编译Monad：

IO
由于server已经是/app/Main.hs:55:3: error:
    • Couldn't match type ‘KindUid
                        -> SubjectUid -> p0 (Handler [Event])’
                    with ‘(KindUid
                            -> SubjectUid -> Action -> EventData -> Handler EventUid)
                        :<|> (KindUid -> SubjectUid -> Handler [Event])’
    Expected type: p (Server HermesAPI)
        Actual type: p ((KindUid -> KindBody -> Handler ())
                        :<|> ((KindUid -> SubjectUid -> EventData -> Handler EventUid)
                            :<|> (KindUid -> SubjectUid -> p0 (Handler [Event]))))
    • In a stmt of a 'do' block: k <- kind
    In the expression:
        do k <- kind
        s <- subject
        e <- event
        return $ k :<|> s :<|> e
    In an equation for ‘server’:
        server
            = do k <- kind
                s <- subject
                e <- event
                ....
   |
55 |   k <- kind
   |   ^^^^^^^^^

app/Main.hs:55:8: error:
    • Couldn't match type ‘KindBody’ with ‘KindUid’
    Expected type: p (KindUid -> KindBody -> Handler ())
        Actual type: KindUid -> KindBody -> KindBody -> Handler ()
    • In a stmt of a 'do' block: k <- kind
    In the expression:
        do k <- kind
        s <- subject
        e <- event
        return $ k :<|> s :<|> e
    In an equation for ‘server’:
        server
            = do k <- kind
                s <- subject
                e <- event
                ....
   |
55 |   k <- kind
   |        ^^^^
，所以我被困住了。如何编写Handler和我的newtype以便在Servant中运行它？

编辑：

我感谢[[Mark Seemann

迈出了一步，抬起Handler以利用Monad：Handler

前往：

ServerT

谢谢。

我正在努力编写Servant的Handler和Monad：class Monad p =>坚持p其中数据配置p :: * runPersistance ::配置p-> pa-> IO a initPersistence ...

Answer 1