behaviors_3.ex

defmodule Tracer do

  # ...

  defmacro __using__(_opts) do
    quote do
      import Kernel, except: [def: 2]
      import Tracer, only: [def: 2]
    end
  end
end

defmodule Calculator do
  use Tracer

  def puts_sum_three(a, b, c), do: IO.puts a + b + c
end

Calculator.puts_sum_three(1, 2, 3)