haskell-reference.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.18 script
import Control.Concurrent (threadDelay)
import Control.Concurrent.Async (replicateConcurrently_)
import Control.Monad (unless)
import Data.IORef
import System.Random (randomIO)

main :: IO ()
main = do
  ref <- newIORef (0 :: Int)
  secret $ do
    x <- randomIO
    writeIORef ref x
    threadDelay 1000
    y <- readIORef ref
    unless (x == y) $ error "failure!"
  putStrLn "All good!"

secret :: IO () -> IO ()
secret = replicateConcurrently_ 1000