在这个判断函数中这个接收语句fullfil的目的是什么？

Question

我最近开始从 https://learnyousomeerlang.com 学习 Erlang 在本章errors and processes 中，我了解了程序的作用以及它是如何执行的，但是我无法弄清楚在判断函数中接收语句的目的是什么，何时以及如何调用它？

据我了解，如果元组模式与 Pid 和 atom 匹配，它会返回一个 atom。我将如何发送消息以接收内部法官？

  start_critic() ->
  spawn(?MODULE, critic, []).

judge(Pid, Band, Album) ->
  Pid ! {self(), {Band, Album}},
  receive 
    {Pid, Criticism} -> Criticism
  after 2000 ->
    timeout
  end.

critic() ->
  receive
    {From, {"Rage Against the Turing Machine", "Unit Testify"}} ->
      From ! {self(), "They are great!"};
    {From, {"System of a Downtime", "Memoize"}} ->
      From ! {self(), "They're not Johnny Crash but they're good."};
    {From, {"Johnny Crash", "The Token Ring of Fire"}} ->
      From ! {self(), "Simply incredible."};
    {From, {_Band, _Album}} ->
      From ! {self(), "They are terrible!"}
  end,
  critic().

输出

c(linkmon).
{ok,linkmon}

Critic = linkmon:start_critic().
<0.109.0>

linkmon:judge(Critic, "Genesis", "The Lambda Lies Down on Broadway").
"They are terrible!"

linkmon:judge(Critic, "Genesis", "A trick of the Tail Recursion").
"They are terrible!"

linkmon:judge(Critic, "Johnny Crash", "The Token Ring of Fire").
"Simply incredible."

Answer 1

Pid ! ... 行向评论家发送消息。然后，critic 将通过From ! ... 行之一发送响应。 judge 函数中的 receive 等待所述响应，然后简单地返回响应中包含的字符串。