> unless you literally have written a new type system and compiler
This is entirely possible with plain lisp macros. See https://coalton-lang.github.io
Having that natively available as plain Common Lisp code is a very different thing from your "just read a text block and compile it as rust code!" concept. Or at least, the tool chain gymnastics required to make a C program emit its own source in another language... Why?
Well, I was talking about the fundamental part. Of course you can have more practical implementations, like Scala or rust's macro system, that gives you a proper typed AST.