Programming Elixir 1.3

Putting It Together—Tracing Method Calls

Let’s work through a larger example. We want to write a module called Tracer. If we use Tracer in another module, entry and exit tracing will be added to any subsequently defined function. For example, given the following:

use/tracer.ex

defmodule Test do
  use Tracer
  def puts_sum_three(a,b,c), do: IO.inspect(a+b+c)
  def add_list(list),        do: Enum.reduce(list, 0, &(&1+&2))
end

Test.puts_sum_three(1,2,3)
Test.add_list([5,6,7,8])

we’d get this output:

==> call    puts_sum_three(1, 2, 3)
6
<== returns 6
==> call    add_list([5,6,7,8])
<== returns 26

My approach to writing this kind of code is to start by exploring what we have to work with, and then to generalize. The goal is to metaprogram ...