Concurrent prime number sieve

main.pony

// Finds prime numbers up to the value of the first argument or 100.
// Terribly inefficient but fun.
// Source: http://www.cs.dartmouth.edu/~doug/sieve/sieve.pdf

actor Main
  let max: I32
  let sink: Prime

  new create(env: Env) =>
    max = try env.args(1)?.i32()? else 100 end
    let n: I32 = 2
    sink = Prime(env, n)

    send(n)

  be send(n: I32) =>
    if n < max then
      sink.filter(n)
      send(n + 1)
    end

actor Prime
  let p: I32
  var sink: (Prime | None)
  let env: Env

  new create(env': Env, p': I32) =>
    p = p'
    sink = None
    env = env'

    env.out.print(p.string())

  be filter(n : I32) =>
    if (n % p) != 0 then
      match sink
      | None => sink = Prime(env, n)
      | let q: Prime => q.filter(n)
      end
    end