Three Dollar Quill

I started specifying and implementing what's required to incrementally detect nullable rules. One hurdle is that I'm informally writing this out in a mostly imperative style, but I'm implementing it all functionally, and sometimes the gaps between the two approaches get... wide.

Complaining about this was enough of an impetus to try and get the implementation right before I could manage to explain what the issues were, so this is probably close to done, but there are still various bits of bookkeeping to handle.

I can't handle them right now, because it's late. Let's see what I'm up for tomorrow...

Good night.