We (Elixir) would rather define lists on top of non empty lists:

    list(a) = empty_list() or non_empty_list(a)

So you should pass non-empty lists everywhere a list is expected. But you can’t pass a list where a non-empty one is expected.

But overall, you are right: our concern is exactly all of the extra function calls that may now suddenly become necessary (and the tension mentioned in the article). We will review our design decisions as we keep on rolling out the type system!