Pablo Fernandez

I like Erlang and I like gen_servers, I end up coding a lot of stuff as gen_servers and I like behaviors in generally. I even wrote some myself. I haven’t used Erlang for a while. I’ve been playing with it in the last couple of days, hopefully I’ll announce something soon.

I ended up creating my own gen_servers template to get started. It’s a very verbose one and I’m putting it here more for me to know where it is that anything else; but, maybe it’s of use for someone else:

-module(module).
-compile(export_all).

-behaviour(gen_server).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

%% Public API

start() ->
  gen_server:start({local, ?MODULE}, ?MODULE, [], []).

stop(Module) ->
  gen_server:call(Module, stop).

stop() ->
  stop(?MODULE).

state(Module) ->
  gen_server:call(Module, state).

state() ->
  state(?MODULE).

%% Server implementation, a.k.a.: callbacks

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


handle_call(stop, _From, State) ->
  say("stopping by ~p, state was ~p.", [_From, State]),
  {stop, normal, stopped, State};

handle_call(state, _From, State) ->
  say("~p is asking for the state.", [_From]),
  {reply, State, State};

handle_call(_Request, _From, State) ->
  say("call ~p, ~p, ~p.", [_Request, _From, State]),
  {reply, ok, State}.


handle_cast(_Msg, State) ->
  say("cast ~p, ~p.", [_Msg, State]),
  {noreply, State}.


handle_info(_Info, State) ->
  say("info ~p, ~p.", [_Info, State]),
  {noreply, State}.


terminate(_Reason, _State) ->
  say("terminate ~p, ~p", [_Reason, _State]),
  ok.


code_change(_OldVsn, State, _Extra) ->
  say("code_change ~p, ~p, ~p", [_OldVsn, State, _Extra]),
  {ok, State}.

%% Some helper methods.

say(Format) ->
  say(Format, []).
say(Format, Data) ->
  io:format("~p:~p: ~s~n", [?MODULE, self(), io_lib:format(Format, Data)]).

Update 2010-01-04: I keep changing the actual contents of the template as I’m coding a little Erlang app. I’ve recently added, among other things, a call to get the state of the process, useful for debugging.