is_prime := n -> {
  0.1.sleep // wow, what an inefficient algorithm, oh no
  d := 1
  loop {
    &d = (d, 1).sum
    if d.lt(n) {
      if n.modulo(d).eq(0) (false)
    } else (true)
  }
}

find_primes := start_at -> {
  () -> (loop {
    out := if start_at.is_prime (start_at)
    &start_at = (start_at, 1).sum
    out
  })
}

primes_count := 0

background_thread := {() ->
  2.find_primes.take(20).map(p -> { &primes_count = (primes_count, 1).sum, p }).as_list
}.thread

// Show status to the user while the background thread works
loop {
  0.2.sleep
  (" Found ", primes_count, " primes...\r").concat.print
  if background_thread.thread_finished (())
}

("\nPrimes: ", background_thread.thread_await).concat.println