Thanks for the answer, especially the thoughts on self-hosted compilers. I'd always found myself vaguely unsatisfied with them as an outsider trying to understand them, so it's very useful to hear similar sentiments from someone who actually has experience building them.
BTW, I followed the instructions to run it and was pleasantly surprised by how painless it was.
I actually worried that it wasn't painless enough, and that I should have waited for the web repl to be done before submitting.
These long strings contain the compiled macros. They are only there for debugging. They belong in comments instead of strings, but I didn't think of it at that time.