My favorite elixir program

.iex.exs

# based on Joe Armstrong's blog post, 'My favorite erlang program'
# http://joearms.github.io/2013/11/21/My-favorite-erlang-program.html

defmodule Server do
  def universal_server() do
    receive do
      {:become, f} ->
        apply(f, [])
    end
  end

  def factorial_server() do
    receive do
      {from, n} ->
        send(from, factorial(n))
        factorial_server()
    end
  end

  def factorial(0), do: 1
  def factorial(n), do: n * factorial(n - 1)
end

pid = spawn(&Server.universal_server/0)

send(pid, {:become, &Server.factorial_server/0})

send(pid, {self, 50})

receive do
  x -> x
end