Without much knowledge at all, I'd agree with the conclusion that "block-accepting methods for enumerator types would seem to be equally risky". It sounds to me

Without much knowledge at all, I'd agree with the conclusion that "block-accepting methods for enumerator types would seem to be equally risky". It sounds to me like having non-pure functions that can terminate at any point. And that sounds like asking for trouble in your code. I like my safeties in languages though.