servant-examples/tutorial/T5.hs · servant

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1{-# LANGUAGE DataKinds #-}

2{-# LANGUAGE TypeFamilies #-}

3{-# LANGUAGE DeriveGeneric #-}

4{-# LANGUAGE TypeOperators #-}

5{-# LANGUAGE OverloadedStrings #-}

6module T5 where

8import Control.Monad.IO.Class

9import Control.Monad.Trans.Either

10import Data.Aeson

11import GHC.Generics

12import Network.Wai

13import Servant

14import System.Directory

16type IOAPI = "myfile.txt" :> Get '[JSON] FileContent

18ioAPI :: Proxy IOAPI

19ioAPI = Proxy

21newtype FileContent = FileContent

22 { content :: String }

23 deriving Generic

25instance ToJSON FileContent

27server :: Server IOAPI

28server = do

29 exists <- liftIO (doesFileExist "myfile.txt")

30 if exists

31 then liftIO (readFile "myfile.txt") >>= return . FileContent

32 else left custom404Err

34 where custom404Err = err404 { errBody = "myfile.txt just isn't there, please leave this server alone." }

36app :: Application

37app = serve ioAPI server