Corrected Sample code from https://code.tutsplus.com/articles/what-is-genserver-and-why-should-you-care--cms-29143

processes_sample.ex

# code from: https://code.tutsplus.com/articles/what-is-genserver-and-why-should-you-care--cms-29143

defmodule MathServer do
  def start do
    spawn &listen/0
  end
 
  defp listen do
    receive do
      {:sqrt, caller, arg} -> send(caller, {:result, do_sqrt(arg)})
      _ -> IO.puts :stderr, "Not implemented."
    end
    listen()
  end

  def sqrt(server, arg) do
    send(server, {:sqrt, self(), arg})
  end

  defp do_sqrt(arg) do
    :math.sqrt(arg)
  end

  def grab_result do
    receive do
      {:result, result} -> result
      after 5000 -> IO.puts :stderr, "Timeout"
    end
  end

end


math_server = MathServer.start
MathServer.sqrt(math_server, 3)
MathServer.grab_result |> IO.puts