Creol

interface Buffer begin
  with Producer
    op put(x: Int)
  with Consumer
    op get(out x: Int)
end

class BoundedBuffer(max: Int) implements Buffer begin
  var buf: List[Int] := nil
  var n: Int := 0

  with Producer
    op put(x: Int) ==
      await n < max;
      buf := buf |- x;
      n := n + 1

  with Consumer
    op get(out x: Int) ==
      await n > 0;
      x := head(buf);
      buf := tail(buf);
      n := n - 1
end

class Producer(b: Buffer) begin
  var count: Int := 0

  op run ==
    while count < 10 do
      b.put(count);
      count := count + 1
    end
end

class Consumer(b: Buffer) begin
  op run ==
    var x: Int;
    b.get(x);
    !run()
end