haskell - 如何提升到Servant服务器类型？

Question

我在使用以下代码时遇到问题:

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}

module API where

import           Data.Text
import           Servant.API
import           Servant
import           Repository 
import           FileOperation
import           Util
import           Config
import qualified Data.Map                   as M
import           Control.Monad.State.Strict (liftIO)
import           Network.Wai.Handler.Warp

type RepositoryAPI = "repository" :> "all" :> Get '[JSON] [Repository] 
                :<|> "all" :> "repository" :> Get '[JSON] [Repository]

server :: Server RepositoryAPI
server = do
  repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
  let repositories = M.elems repositoriesMap in do
    return repositories 

repositoryAPI :: Proxy RepositoryAPI 
repositoryAPI = Proxy

app :: Application
app = serve repositoryAPI server

main :: IO ()
main = run 8081 app

我得到的错误是:

API.hs:22:3: error:
    • Couldn't match type ‘[a0]’ with ‘Handler [Repository]’
      Expected type: Server RepositoryAPI
        Actual type: Handler [Repository] :<|> [a0]
    • In a stmt of a 'do' block:
        repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
      In the expression:
        do repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
           let repositories = ... in do return repositories
      In an equation for ‘server’:
          server
            = do repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
                 let ... in do ...
   |
22 |   repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
   |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

问题是我如何正确提升，以便提升返回仆人服务器类型？

Answer 1

问题与举重无关。真正的问题是你只指定了一个 Handler ，但您的服务器需要两个 Handler s，一个为"repository" :> "all" :> Get '[JSON] [Repository]一个用于 "all" :> "repository" :> Get '[JSON] [Repository] .这是你的第二个骨架(用这个替换你现有的 server):

getRepositoryAll :: Handler [Repository]
getRepositoryAll = do
  repositoriesMap <- liftIO $ loadFromFile repositoryMapFile
  let repositories = M.elems repositoriesMap in do
    return repositories 

getAllRepository :: Handler [Repository]
getAllRepository = undefined -- fill this in

server :: Server RepositoryAPI
server = getRepositoryAll :<|> getAllRepository