struct_and_protocol.ex

defprotocol Simple.StreamReader do
  def read_line(stream)
end

defmodule Simple.Socket do
  defstruct socket: nil
end

defimpl Simple.StreamReader, for: Simple.Socket do
  def read_line(simple_socket) do
    :gen_tcp.recv simple_socket.socket, 0
  end
end

defmodule Simple.Client do
  def start(socket) do
    spawn Simple.Client, :loop, [socket]
  end
  
  def loop(socket) do
    parser = Simple.Parser.start self, %Simple.Socket{socket: socket}
    loop socket, parser
  end
  
  defp loop(socket, parser) do
    receive do
      {^parser, :add} -> IO.puts("got add"); loop(socket, parser)
      {^parser, :remove} -> IO.puts("got remove"); loop(socket, parser)
    end
  end
end

defmodule Simple.Parser do
  def start(client, stream) do
    spawn Simple.Parser, :loop, [client, stream]
  end
  
  def loop(client, stream) do
    case Simple.StreamReader.read_line(stream) ->
      val ->
        cond do
          String.starts_with?(val, "add") -> send client, {self(), :add}
          String.starts_with?(val, "remove") -> send client, {self(), :remove}
          true -> :void
        end
    end
    loop client, stream
  end
end