The Interceptor library allows you to intercept function calls, as you can see in the Interceptor module documentation.

This module allows you to intercept your functions using @intercept true “annotations”, instead of having to use the Interceptor.intercept/1 macro.

This is how you can use the Interceptor.Annotated module on the example Intercepted module (defined on the Interceptor module documentation):

defmodule Intercepted do
  use Interceptor.Annotated

  @intercept true
  def abc(x), do: "Got #{inspect(x)}"

  # the following function can't be intercepted
  # because it doesn't have the `@intercept true` annotation
  def not_intercepted(f, g, h), do: f+g+h
end

This way of intercepting the Intercepted.abc/1 function is equivalent to the one using the Interceptor.intercept/1 macro described on the Interceptor module documentation. Please check it for more information on how to configure this library.