GNU bug report logs - #58068
pretty-print corrupts data modified by set-cdr!

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: slbtty <shenlebantongying <at> gmail.com>
To: bug-guile <at> gnu.org
Subject: pretty-print corrupts data modified by set-cdr!
Date: Sat, 24 Sep 2022 18:09:45 -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)

I am not sure about the set-cdr! and quote usage. However, i runned
the same code in other schemes, mit, chicken, racket/r6rs, gambit, and
they all yield tl as (1 2 3).

(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.

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