I wrote up some rust low-level bindings for guile [1]. The problem is that Guile liberally uses setjmp/longjmp, which breaks rust destructors. It might be possible to fix this by wrapping every call the way rlua does [2], but I'm not familiar enough with Guile to know.

1: https://github.com/ysimonson/guile-sys

2: https://github.com/amethyst/rlua/issues/21

Or Chicken Scheme, or Gambit Scheme, which can be used standalone, embedded, or as glue with their great C interop.

I love seeing Scheme(or Lisp) implementations, they are kind of a Rosetta Stone of programming languages. We can study them and learn the target languages.

They seldom become implementations in widespread usage on their own, though.