shift_complexity.ex

defmodule Hub do
  defmacro on_match(pattern, do: on_match, after: on_after) do
    on_match = quote do
      term -> Hub.match term, unquote(pattern), do: unquote(on_match)
    end

    quote do
      receive(do: unquote(on_match), after: unquote(on_after))
    end
  end

  # Dummy macro
  defmacro match(_term, _pattern, do: block) do
    block
  end

  # Dummy subscribe
  def subscribe(pid) do
    IO.puts "Subscribed to #{pid}"
  end
end

defmodule Subscriber do
  require Hub

  def subscribe do
    Hub.subscribe :hub

    Hub.on_match %{foo: foo} when foo < 5 do
      # Do the job
    after
      1_000 -> IO.puts "timed out!"
    end
  end
end

Subscriber.subscribe