[mananaysiempre]

It is really remarkably sucky to process trees without algebraic datatypes and full pattern matching. Most of your options for that are ML progeny, and the rest are mostly Lisps with a pattern-matching macro. While it’s definitely possible to implement, say, unification in C, I wouldn’t want to—and I happen to actually like C.

Given the task is to bootstrap Rust, a Rust subset is a reasonable and pragmatic choice if not literally the only one (Mes, a Lisp, could also work and is already part of the bootstrappable ecosystem).