# problematic function
  def foo(x) do
    stuff = get_stuff(x)
    case stuff do
      nil -> false
      _ -> Enum.any?(stuff, fn unit -> x in unit end)
    end
  end

  # below is the source of Enum.any?
  @spec any?(t, (element -> as_boolean(term))) :: boolean
  def any?(enumerable, fun) when is_list(enumerable) do
    predicate_list(enumerable, false, fun)
  end

  def any?(first..last//step, fun) do
    predicate_range(first, last, step, false, fun)
  end

  def any?(enumerable, fun) do
    Enumerable.reduce(enumerable, {:cont, false}, fn entry, _ ->
      if fun.(entry), do: {:halt, true}, else: {:cont, false}
    end)
    |> elem(1)
  end

  defp predicate_list([h | t], initial, fun) do
    if !!fun.(h) == initial do
      predicate_list(t, initial, fun)
    else
      not initial
    end
  end

  defp predicate_list([], initial, _) do
    initial
  end