defp deps do
  [
    {:pubsub, "~> 1.0"}
  ]
end

defmodule Client do
  def start(client_name) do
    spawn(fn -> loop(client_name) end)
  end
  def loop(name) do
    receive do
      message ->
        IO.puts "#{name} received `#{message}`"
        loop(name)
    end
  end
end

iex(1)> {topic1, topic2} = {:erlang, :elixir}
{:erlang, :elixir}
iex(2)> {:ok, pid} = PubSub.start_link()
{:ok, #PID<0.99.0>}
iex(3)> {pid1, pid2, pid3} =
...(3)> {
...(3)> Client.start("John"),
...(3)> Client.start("Nick"),
...(3)> Client.start("Tim")
...(3)> }
{#PID<0.106.0>, #PID<0.107.0>, #PID<0.108.0>}
iex(4)> PubSub.subscribe(pid1, topic1)
:ok
iex(5)> PubSub.subscribe(pid2, topic1)
:ok
iex(6)> PubSub.subscribe(pid3, topic2)
:ok
iex(7)> PubSub.publish(topic1, "#{topic1} is great!")
"Nick received `erlang is great!`"
"John received `erlang is great!`"
:ok
iex(8)> PubSub.publish(topic2, "#{topic2} is so cool, dude")
"Tim received `elixir is so cool, dude`"
:ok