An example of the actor pattern in Elixir.

actor_tutorial.exs

@moduledoc """
This file showcases how the actor pattern works in elixir by using send/receive
to pass messages and spawn to create a separate state for an actor.

    import ActorTutorial

Create a tally actor and send a message

    tally = start_tally()
    send tally, {:add, 5}
    send tally, {:add, 3}
    send tally, {:query, self()}

By sending a message to `self()` we send a message to our own inbox. It can be
received with the blocking `receive` keyword:

    receive do message -> IO.puts(message)

We can also start another process that can be responsible for printing out the
messages:

    listener = start_listener()
    send tally, {:query, listener}
    send tally, {:add, 300}
    send tally, {query, listener}
"""
defmodule ActorTutorial do
  def start_tally do
    spawn_link fn ->
      tally(0)
    end
  end

  def start_listener do
    spawn_link fn ->
      listener_display()
    end
  end

  defp tally(current) do
    receive do
      {:add, addition} -> tally(current + addition)
      {:query, to_inform} ->
        send(to_inform, current)
        tally(current)
      _else -> tally(current)
    end
  end

  defp listener_display() do
    receive do
      a ->
        IO.puts(a)
        listener_display()
    end
  end
end