[nbadg]

I'm not familiar enough with the innards of other languages to make any definitive comments on it, but I will say that the challenge is in combining a high-level language with late-binding closures with memoization. I'm not aware of a strategy for that which is always intuitive for every program you write; I think it's just a language design combination that has a very high probability of developing "gotchas" no matter what you do.

Also, on a related note, I really love late binding and memoization, so I'm definitely biased on the side of "I understand why the language designers made this decision, and though the ramifications bother me a little bit, I much prefer this way".

On a third note (because hey, why not), with type hints being a thing now, maybe it would be worth considering a default eval hint. It could default to current behavior, and therefore retain backwards compatibility, but you could add syntax to declare defaults as new variables. That might be a smart compromise.