On 20-09-2022 09:23, Andrew Whatson wrote:
>           => (lambda (binding)
> -             (let ((val (frame-local-ref frame (binding-slot binding)
> -                                         (binding-representation binding))))
> +             (let* ((slot (binding-slot binding))
> +                    ;; HACK: Avoid out-of-range from frame-local-ref.
> +                    ;; Some frames have bindings beyond nlocals.  That
> +                    ;; is probably a bug somewhere else, but at least
> +                    ;; this workaround allows them to be printed.
> +                    (val (if (< slot nlocals)
> +                             (frame-local-ref frame slot
> +                                              (binding-representation binding))
> +                             ;; else #<unspecified > +                             )))

I propose to add a link to the bug report in the comments, for future 
reference.  Also, there is an interest in returning zero values in such 
cases: <https://www.mail-archive.com/bug-guile@gnu.org/msg07927.html> 
(that patch didn't work out, but the sentiment is still there).

As such, I recommend being explicit:

(if [...]
     [...]
     *unspecified*)

Greetings,
Maxime.