Define a function at compile-time

Questions & Help Questions
1

I have a module for which I want to create a function rule_ids/0 at compile time. The code collects the rule ids at compile time from the first argument of all clauses of the function condition/3 using the AST.
It does not work because the variable rule_ids_ defined at compile time is not accessible when defining the function with def rule_ids(), do: rule_ids_.
How could I proceed to get it working? Should I use a macro somewhere?

defmodule Rules do

  # Collect the rule ids at compile time
  {_ast, rule_ids_} = File.read!(__ENV__.file)
    |> Code.string_to_quoted()
    |> Macro.traverse([],
      fn
        {:def, _, [{:condition, _, [rule_id, {:v, _, nil}, {:site, _, nil}]} | _]} = x, acc -> {x, [rule_id | acc]}
        other, acc -> {other, acc}
      end,
      fn other, acc -> {other, acc} end
    )

  # How could I use rule_ids_ here?
  def rule_ids(), do: rule_ids_

  def condition(rule_id, v, site)

  def condition(1018, v, site) do
    v[site][7018] < 50 && v[site][7019] < 50 && v[site][7020] < 50
  end

  def condition(1017, v, site) do
    v[site][7027] > 42
  end

  # ...

end