Minimal Warp webserver example

Here’s a minimal Hello World application using Warp 3.0+. Run it, then navigate to http://localhost:3000. This example will show Hello world.

In order to keep this example minimal, URL paths are not handled at all (the same content is delivered for any path). For a slightly longer example incorporating URL path handling, see the Haskell Wiki

{-# LANGUAGE OverloadedStrings #-}

import Network.Wai (responseLBS, Application)
import Network.Wai.Handler.Warp (run)
import Network.HTTP.Types (status200)
import Network.HTTP.Types.Header (hContentType)

main = do
  let port = 3000
  putStrLn $ "Listening on port " <> show port
  run port app

app :: Application
app _req f =
  f $ responseLBS status200 [(hContentType, "text/plain")] "Hello world!"