I do not understand how do you hook to an Erlang application since it does not return the Pid .
Consider for example the snippet below.I am starting a Pid which receives messages to process.However my application behaviour does not return anything. How do i hook to the Pid i am interested in when using application behaviour ?

.app

{
  application,simple_app,
  [
    {description,"something"},
    {mod,{simple_app,[]}},
    {modules,[proc]}
  ]
}

app

-module(simple_app).

-behaviour(application).

-export([start/2, stop/1]).

start(_StartType, _StartArgs) ->
    proc:start().

stop(_State) ->
    ok.

module

-module(proc).
-export([start/0]).

start()->
    Pid=spawn_link(?MODULE,loop,[]),
    {ok,Pid}.

loop()->
    receive 
        {From,Message}-> From !  {ok,Message},
                         loop();
        _ ->loop()
    end.

P.S I am trying to understand how do i get the root Pid to further use it to issue commands ? In my case i need the Pid of the proc:start module.If my root was a supervisor , i would need the Pid of the supervisor.The application does not return a Pid ? How do i hook to it ? The question thus is when starting the application wouldn't i need a Pid returned by it to then be able to issue commands against?