primes-concurrent.hs

module Main where

import Control.Concurrent.Chan
import Control.Concurrent

-- A sieve that receives numbers from "inChan", filters
-- out the factors of "prime" and sends the results
-- out through "outChan".
sieve inChan outChan prime = do
    print prime
    ns <- getChanContents inChan
    writeList2Chan outChan [n | n <- ns, n `mod` prime /= 0]

main = do
    ch <- newChan
    -- Start piping all numbers through the sieve chain.
    forkIO (writeList2Chan ch [2..])
    setupSieves ch
  where
    setupSieves ch = do
        next <- newChan
        p <- readChan ch
        -- Create a new sieve for each prime number found.
        forkIO (sieve ch next p)
        setupSieves next