Example of Symmetric Concurrency Combinators from Parallel concurrent programming in Haskell

symetricConcurrency.hs

#!/usr/bin/env stack
{-
 stack
--resolver lts-17.13 runghc

--package http-conduit
--package async
-}
--
--
import Control.Concurrent
import Control.Concurrent.STM
import Control.Concurrent.Async
import Control.Exception
import qualified Data.ByteString.Lazy as LB
import Network.HTTP.Conduit
import Text.Printf

url1, url2 :: String
(url1, url2) = ("http://www.wikipedia.org/wiki/Shovel" , "http://www.wikipedia.org/wiki/Spade")

main :: IO ()
main  = do
  (r1, r2) <- concurrently(simpleHttp url1) (simpleHttp url2)
  print (LB.length r1, LB.length r2)