If we syntax-highlight (withs ...) this way, since it expands into several (fn ...) forms it'll give a different color to each of its variables. But that's assuming we're able to perform some amount of macroexpansion frequently enough to be useful as the programmer edits, and it also assumes we can relate the original syntax to the transformed version returned by the macro.
It would be interesting to see a macro system tailor-made for purposes like these. Some hygienic macro systems might already apply, but I wonder what the options are here. I think Reactive Demand Programming would be an effective ingredient for this kind of incremental program visualization, but that's not a complete plan on its own.
Fun fact: if you used boxes, it would be really easy to associate the "withs" form with its expanded form, since the boxes would be the same.
The Nulan IDE already incrementally macroexpands as you're typing, and syntax-highlights boxes different colors depending on their scope. So this would be fairly trivial to add in.
