behaviors_4.ex

defmodule Tracer do
  defmacro def(definition, do: expression) do
    {name, _, args} = definition
    quote do
      Kernel.def(unquote(definition)) do
        IO.puts "==> call:   #{unquote(name)} (#{unquote(args)})"
        result = unquote(content)
        IO.puts "<== result: #{result}"
        result
      end
    end
  end
end