defmodule Calculator do
  def start do
    spawn(fn -> loop(0) end)
  end

  defp loop(cur_val) do
    result = receive do
      {:value, sender_id} -> send(sender_id, {:result, cur_val})

      {:add, val1, val2} -> cur_val + val1 + val2
    end
    loop(result)
  end

  def get_result(receiver_id) do
    send(receiver_id, {:value, self()})
    receive do
      {:result, result} -> result
    end
  end

  def add(receiver_id, val1, val2) do
    send(receiver_id, {:add, val1, val2})
    get_result(receiver_id)
  end
end