Server.hs

{-# LANGUAGE OverloadedStrings #-}
import Network.Wai
import Network.HTTP.Types
import Network.Wai.Handler.Warp (run)
--
import Control.Concurrent (threadDelay)
import Data.Atomics.Counter --(newCounter, incrCounter)

app :: AtomicCounter -> Application
app counter _ respond = do
    --putStrLn "I've done some IO here"
    print =<< incrCounter 1 counter
    threadDelay 1000000
    incrCounter (-1) counter
    respond $ responseLBS
        status200
        [("Content-Type", "text/plain")]
        "Hello, Web!"

main :: IO ()
main = do
    counter <- newCounter 0
    putStrLn $ "http://localhost:8080/"
    run 8080 (app counter)