Umm superficially you could say it is anything. The reality is it IS Scheme. (define (foo bar) (format "hi ~a" bar)) works just fine. As will any of the Scheme code, as it's merely syntactic sugar, (import :std/sugar) that you are confusing with a whole new language.

Look at things like:

    (define lst '(4 5 6))
    (set! (car lst) 3)
    (display (car lst))

    ;; 3

That's a pretty serious semantic departure. It's at least as different from RnRS as Racket, which insists it is not Scheme.

I was requesting valid scheme that did not work properly. Given the https://ecraven.github.io/r7rs-benchmarks/ shows Gerbil passing more tests than many other implementations, it seems hard to call it a "non-scheme".

There's an SRFI for generalised set! that lots of implementations (Racket, Guile, Chicken, etc) support: https://srfi.schemers.org/srfi-17/srfi-17.html

Neat. Learn something new every day.

It's not in widespread use though.