server.exs

require Logger

defmodule Playground do
  def accept(port) do
    {:ok, socket} = :gen_tcp.listen(port, [:binary, packet: :line,
      active: false, reuseaddr: true])
    Logger.info "Accepting connections on port #{port}"
    loop_acceptor(socket)
  end

  def loop_acceptor(socket) do
    {:ok, client} = :gen_tcp.accept(socket)
    serve(client)
    loop_acceptor(socket)
  end

  def serve(socket) do
    socket
    |> read_line
    |> write_line(socket)

    serve(socket)
  end

  def read_line(socket) do
    {:ok, data} = :gen_tcp.recv(socket, 0)
    data
  end

  def write_line(line, socket) do
    :gen_tcp.send(socket, line)
  end
end

port = (System.argv |> List.first) || "8787"

port
|> Integer.parse
|> elem(0)
|> Playground.accept