> so yes, we may need to remember where we've been. (At this point
> someone will inevitably point out a helpful invariant that is obvious
> in hindsight. This is just my cunning attempt at making that happen.)

No helpful invariant that makes it trivial, but if we keep pushing the
same idea that we rely on the assumption that we just have
a syntactically nested loop nest, then we can handle that as in the
patch below.

I.e. keep the idea I proposed of keeping track of a beg..end region
that's already been handled.  But now we really do have to maintain both
ends (before, I only had `done` which kept track of the end of the
region), and just "restart" when we jump back to a point before the
"done" region.


        Stefan