Subject: bug#58066: pretty-print will make data modified by set-cdr! to random value

From: slbtty <[email-masked]>
Date: Sat, 24 Sep 2022 06:01:13 -0400

GNU Guile 3.0.8

Using `guile3 < file.scm` to run the code below will makes the result
of tp unpredictable (pointing to very random things)

(use-modules (ice-9 pretty-print))
(define tl '(1 2))
(define tp (cdr tl))
(set-cdr! tp (cons 3 '()))
  (pretty-print tl)
  (pretty-print tp)
---

However, if i use plain old (display tp), the code will out put
expected valve (1 2 3) (3)
(define tl '(1 2))
(define tp (cdr tl))
(set-cdr! tp (cons 3 '()))
  (display tl) (newline)
  (display tp) (newline)

---

Context:

I am using guile3's repl and whenever i access a variable's by typing
its name after (set-cdr!), the result will goes wild.