Capturing in Servant

servant_sample_04.hs

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

import Control.Exception as E

import Servant
import Control.Monad.IO.Class   -- liftIO
import Network.Wai.Handler.Warp -- run 

type FileRead04 = "file" :> Capture "filename" String :> Get '[PlainText] String 

myAPI04 :: Proxy FileRead04 
myAPI04 = Proxy

app04 :: Application
app04 = serve myAPI04 server04

server04 :: Server FileRead04
server04 = \x -> do 
  -- liftIO (putStrLn x)
  ret <- liftIO (readF x)
  case ret of
    Left  e -> throwError err404 {errBody="file error"}
    Right s -> return s

readF :: String -> IO (Either SomeException String) 
readF x = E.try (readFile x) 

main04 :: IO ()
main04 = run 8080 app04