Main.hs

{-# LANGUAGE ScopedTypeVariables #-}
module Main where

import Control.Concurrent
import Control.Monad

{-
  ghc --make Main.hs
  ./Main
-}

main :: IO ()
main = do
    (inch :: Chan Int) <- (newChan :: IO (Chan Int))
    outch <- newChan
    _ <- forkIO (fwdChan inch outch)
    _ <- forkIO (printChan outch)
    writeChan inch 1
    writeChan inch 2
    threadDelay 3000000

fwdChan :: Chan a -> Chan a -> IO ()
fwdChan inch outch = forever $ do
    x <- readChan inch
    writeChan outch x

printChan :: Show a => Chan a -> IO ()
printChan chan = forever $ do
    x <- readChan chan
    y <- readChan chan
    print x
    print y
-- printChan chan = forever (readChan chan >>= (\x -> readChan >>= (\y -> print x >> print y)))