servant/servant-examples/tutorial/T5.hs

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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
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{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
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module T5 where
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import Control.Monad.IO.Class
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import Control.Monad.Trans.Except
import Data.Aeson
import GHC.Generics
import Network.Wai
import Servant
import System.Directory
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type IOAPI = "myfile.txt" :> Get '[JSON] FileContent
ioAPI :: Proxy IOAPI
ioAPI = Proxy
newtype FileContent = FileContent
{ content :: String }
deriving Generic
instance ToJSON FileContent
server :: Server IOAPI
server = do
exists <- liftIO (doesFileExist "myfile.txt")
if exists
then liftIO (readFile "myfile.txt") >>= return . FileContent
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else throwE custom404Err
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where custom404Err = err404 { errBody = "myfile.txt just isn't there, please leave this server alone." }
app :: Application
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app = serve ioAPI EmptyConfig server