As we briefly hinted at before, we can leverage the GenServer behaviour to implement a process that will provide some kind of service through a well-defined public interface. To do so, one only has to use GenServer in its module and implement the necessary callbacks:
iex> defmodule Calculator do...> use GenServer...>...> def handle_call({:mult5, number}, _from, state) do...> {:reply, number*5, state}...> end...> end{:module, Calculator, <<70, 79, 82, 49, 0, 0, 12, 224, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 1, 138, 0, 0, 0, 42, 17, 69, 108, 105, 120, 105, 114, 46, 67, 97, 108, 99, 117, 108, 97, 116, 111, 114, 8, 95, 95, 105, 110, ...>>, {:handle_call, 3}}iex> {:ok, calc} = GenServer.start_link(Calculator, []) ...
