This is probably what Rust's internal ASTs look like. But why would you want to input programs as ASTs?

so you can do the transformations (see the rlisp macro section)

Yes, but you could do the same by transforming Rust's ASTs. The only downside is that your input format is different from the format you are transforming. But the upside is that readability is much improved, which matters because code is typically read far more often than it is written.