Define a function at compile-time

[lkuty]

@LostKobrakai

You can use @on_definition on a module (say A) to have it call a macro or function elsewhere (Say on B) whenever a function or macro is defined on the module. With a macro being provided you can then pull information from those definitions and store them in an arbitrary module attribute of A.

I’ve put @on_definition {Hooks, :rule_ids} in module Rules but in the other module called Hooks I cannot see how I can accumulate the ids and make use of them in the rule_ids/6 function.

defmodule Hooks do
  Module.register_attribute(__MODULE__, :rule_ids, accumulate: true, persist: false)

  def rule_ids(_env, :def, :condition, [rule_id | _], _guards, _body)
  when is_integer(rule_id)
  do
    IO.puts rule_id
  end
  def rule_ids(_env, _kind, _name, _args, _guards, _body), do: nil
end