Oh, I had meant to include `{.closure.}`. Oops. Fixed.A stack (of something) is fundamentally required for general non-linear/tree cases. TCO can only help your linear cases (partly why I call them "easy"). Good trees have well bounded depth, but yeah, wildly unbalanced ones can cause trouble for **any** impl, recursive or not. A non-recursive one may minimize the per-stack entry storage a bit better, though.
