elixir_logger.ex

defmodule FunctionLogger do
  defmacro __using__(_) do
    quote do
      import Kernel, except: [def: 2]
      import FunctionLogger
    end
  end

  defmacro def(fun_def, do: block) do
    quote do
      Kernel.def unquote(fun_def) do
        fn -> unquote(block) end.()
        |> FunctionLogger.log
      end
    end
  end

  def log(value) do
    IO.inspect "Return value is #{value}"

    value
  end
end

defmodule Example do
  use FunctionLogger

  def three do
    3
  end

  def four do
    4
  end

  def n(n) do
    n
  end
end

IO.puts Example.n(10)