Concurrent Rainbow 7 个进程相互之间并不通信, 它们只和一个中心通信, 最后 7 个进程都拥有了各自独特的颜色

rainbow.ex

defmodule Rainbow do
  @moduledoc """
  Documentation for Rainbow.
  """

  @colors ~w(赤 橙 黄 绿 青 蓝 紫)

  def start do
    node = spawn(fn ->
      loop([])
    end)
    for _ <- 1..7 do
      spawn(fn -> draw(node, @colors) end)
    end
  end

  def draw(node, [color|colors]) do
    case post(node, color) do
      :ok -> IO.inspect({self(), color})
      :error -> draw(node, colors)
    end
  end

  def post(node, color) do
    send(node, {:color, color, self()})
    receive do
      {:resp, resp} ->
        resp
    end
  end

  defp loop(state) do
    receive do
      {:color, color, pid} ->
        if color in state do
          send(pid, {:resp, :error})
          loop(state)
        else
          send(pid, {:resp, :ok})
          loop([color|state])
        end
    end
  end

end

iex(1)> Rainbow.start
[#PID<0.143.0>, #PID<0.144.0>, #PID<0.145.0>, #PID<0.146.0>, #PID<0.147.0>,
 #PID<0.148.0>, #PID<0.149.0>]
{#PID<0.144.0>, "橙"}
{#PID<0.145.0>, "黄"}
{#PID<0.146.0>, "绿"}
{#PID<0.147.0>, "青"}
{#PID<0.148.0>, "蓝"}
{#PID<0.149.0>, "紫"}
{#PID<0.143.0>, "赤"}