> I think latest Guile version supports r7rs now (or most of it). I'm
> not a Guile user so I can't really confirm.

Guile 3 supports R7RS:

$ docker run -it weinholt/guile:3.0 guile --r7rs
GNU Guile 3.0.0
Copyright (C) 1995-2020 Free Software Foundation, Inc.

[...]
xxxxxx@(guile-user)> (define-library (example) (import (scheme base))
(begin (define (hello) "Hello world")))
xxxxxx@(example)> (hello)
$1 = "Hello world"
xxxxxx@(example)>