gistfile1.txt

http://www.slideshare.net/sleepy_yoshi/erlang-1 を見る

c(normal).

Pid = normal:start_stack().

normal:get_stack(Pid).

normal:push(Pid, hoge).

normal:get_stack(Pid).

normal:push(Pid, hoge2).

normal:get_stack(Pid).

normal:pop(Pid).

normal:get_stack(Pid).

get_stackあたりに
    io:format("new logging !~n"),
とでも追加して、
c(normal).

その後、

normal:get_stack(Pid).

プログラムは変更したが状態が失われていない！！

結構面倒くさそうなところが多いとは思いますが、OTPフレームワークというやつを使うとこのあたりが非常に分かりやすく書き換えられる

c(otp_test).

{ok, Pid2} = otp_test:start_stack().

otp_test:get_stack(Pid2).

otp_test:push(Pid2, hoge).

otp_test:get_stack(Pid2).

otp_test:pop(Pid2).

normal.erl

-module(normal).
-export([start_stack/0, stack/1, get_stack/1, push/2, pop/1]).

start_stack() ->
    spawn(?MODULE, stack, [[]]).

get_stack(Pid) ->
    io:format("new logging !~n"),
    Pid ! {all, self()},
    receive
        Item -> Item
    end.

push(Pid, Item) ->
    Pid ! {push, Item}.

pop(Pid) ->
    Pid ! {pop, self()},
    receive
        Item -> Item
    end.

stack(Stack) ->
    receive
        {push, Item} -> 
            stack([Item|Stack]);
        {pop, From} ->
            [Item|After] = Stack,
            From ! Item,
            stack(After);
        {all, From} ->
            From ! Stack,
            stack(Stack)
    end.

otp_test.erl

-module(otp_test).
-behaviour(gen_server).
-export([start_stack/0, get_stack/1, push/2, pop/1]).
-export([init/1, handle_call/3, handle_cast/2, code_change/3, terminate/2, handle_info/2]).

start_stack() ->
    gen_server:start_link(?MODULE, [], []).

get_stack(Pid) ->
    gen_server:call(Pid, all).

push(Pid, Item) ->
    gen_server:cast(Pid, {push, Item}).

pop(Pid) ->
    gen_server:call(Pid, pop).

init(_Args) ->
    {ok, []}.

handle_cast({push, Item}, Stack) ->
    {noreply, [Item|Stack]}.

handle_call(pop, _From, Stack) ->
    [Item|After] = Stack,
    {reply, Item, After};
handle_call(all, _From, Stack) ->
    {reply, Stack, Stack}.

code_change(_, _, _) ->
    ok.

handle_info(Msg, State) ->
    io:format("Unexpected message: ~p~n",[Msg]),
    {noreply, State}.

terminate(_, _) ->
    ok.

otp_test.ex

defmodule OtpTest do
  @behaviour :gen_server
  def start_stack() do
      :gen_server.start_link(__MODULE__, [], [])
  end

  def get_stack(pid) do
      :gen_server.call(pid, :all)
  end

  def push(pid, item) do
      :gen_server.cast(pid, {:push, item})
  end

  def pop(pid) ->
      :gen_server.call(pid, :pop)
  end

  def init(_Args) do
      {:ok, []}
  end

  def handle_cast({:push, item}, stack) do
      {:noreply, [item|stack]}
  end

  def handle_call(:pop, _from, stack) do
      [ item | after ] = stack
      {:reply, item, after}
  end
  def handle_call(all, _from, stack) do
      {:reply, stack, stack}
  end

  def code_change(_, _, _) do
      :ok
  end

  def handle_info(msg, state) do
      :io.format("Unexpected message: ~p~n",[msg])
      {:noreply, state}.
  end

  def terminate(_, _) do
      ok
  end

end