GNU bug report logs - #7083
Why is `copy-tree's symbol-plist carrying side-effect-free error-free?

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

From: MON KEY <monkey <at> sandpframing.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Why is `copy-tree's symbol-plist carrying side-effect-free error-free?
Date: Wed, 22 Sep 2010 02:31:41 -0400

Why is `copy-tree' side-effect-free error-free?

(symbol-plist 'copy-tree)
=> (side-effect-free error-free)

It (potentially) `nconc's `nreverse's and `aset's the TREE arg recursively.

At revno: 45675 `copy-tree' was moved into subr.el from cl.el

,----
|
| committer: Colin Walters <walters <at> gnu.org>
| timestamp: Sat 2002-06-08 20:48:15 +0000
| message:
|   (copy-list): Moved here from cl.el.
|   (copy-tree): Renamed here from `cl-copy-tree' in cl.el.
|
`----

--
/s_P\

Message #10 received at 7083-done <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: MON KEY <monkey <at> sandpframing.com>
Cc: 7083-done <at> debbugs.gnu.org
Subject: Re: bug#7083: Why is `copy-tree's symbol-plist carrying
	side-effect-free error-free?
Date: Wed, 22 Sep 2010 23:35:56 +0200

MON KEY <monkey <at> sandpframing.com> writes:

> It (potentially) `nconc's `nreverse's and `aset's the TREE arg recursively.

Only the copy.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Message #13 received at 7083 <at> debbugs.gnu.org (full text, mbox):

From: MON KEY <monkey <at> sandpframing.com>
To: Andreas Schwab <schwab <at> linux-m68k.org>
Cc: 7083 <at> debbugs.gnu.org
Subject: Re: bug#7083: Why is `copy-tree's symbol-plist carrying
	side-effect-free error-free?
Date: Thu, 23 Sep 2010 01:23:44 -0400

On Wed, Sep 22, 2010 at 5:35 PM, Andreas Schwab <schwab <at> linux-m68k.org> wrote:
> MON KEY <monkey <at> sandpframing.com> writes:
>
>> It (potentially) `nconc's `nreverse's and `aset's the TREE arg recursively.
>
> Only the copy.
>

Only for the copy of a list.

Why has this bug been marked done?

When copy-tree copies vectors they share structure.

(let ((orig '((a b) (c d) (e f) (g h)))
      new-cp)
  (setq new-cp (copy-tree orig))
  (equal (elt
          (prog1 orig
            (setf (car new-cp) "bubba")) 0)
         '(a b)))
;=> t

(let ((orig [[a b] [c d] [e f] [g h]])
      new-cp)
  (setq new-cp (copy-tree orig))
  (string-equal (aref (prog1 orig
                        (aset new-cp 0 "bubba"))
                      0)
                "bubba"))
;=> t

Shouldn't idx 0 of the orig tree still be [a b]?

If not, it should be documented that when copy-tree copies vectors the
"copy" will share structure just as with `copy-sequence'.

Regardless, simply marking the bug report as done with only a terse 3
word reply is obnoxious and not the least bit helpful for anyone else
referencing this report in the future, esp. as there does appear to be
a bug.


> Andreas.

--
/s_P\

Message #16 received at 7083 <at> debbugs.gnu.org (full text, mbox):

From: MON KEY <monkey <at> sandpframing.com>
To: bug-gnu-emacs <at> gnu.org
Cc: 7083 <at> debbugs.gnu.org, Andreas Schwab <schwab <at> linux-m68k.org>
Subject: `copy-tree' of a vector copy sharing structure.with original
Date: Thu, 23 Sep 2010 01:28:33 -0400

When copy-tree copies vectors the copy shares structure with the original.

This is unlike the behavior of copy-tree on a list of lists:

(let ((orig '((a b) (c d) (e f) (g h)))
      new-cp)
  (setq new-cp (copy-tree orig))
  (equal (elt
          (prog1 orig
            (setf (car new-cp) "bubba")) 0)
         '(a b)))
;=> t

(let ((orig [[a b] [c d] [e f] [g h]])
      new-cp)
  (setq new-cp (copy-tree orig))
  (string-equal (aref (prog1 orig
                        (aset new-cp 0 "bubba"))
                      0)
                "bubba"))
;=> t

Shouldn't idx 0 of the orig tree still be [a b]?

Note This bug _should_ prob. have stayed with Bug7083 but that bug
report was prematurely closed.

--
/s_P\

Message #19 received at 7083 <at> debbugs.gnu.org (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: MON KEY <monkey <at> sandpframing.com>
Cc: 7083 <at> debbugs.gnu.org, 7088-done <at> debbugs.gnu.org
Subject: Re: bug#7088: `copy-tree' of a vector copy sharing structure.with
	original
Date: Thu, 23 Sep 2010 10:47:36 +0200

MON KEY <monkey <at> sandpframing.com> writes:

> When copy-tree copies vectors the copy shares structure with the original.

Works as documented.  A vector is not a cons cell.

If TREE is a cons cell, this recursively copies both its car and its cdr.
             ^^^^^^^^^

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Message #22 received at 7083 <at> debbugs.gnu.org (full text, mbox):

From: David De La Harpe Golden <david <at> harpegolden.net>
To: MON KEY <monkey <at> sandpframing.com>
Cc: 7083 <at> debbugs.gnu.org, 7088 <at> debbugs.gnu.org
Subject: Re: bug#7088: `copy-tree' of a vector copy sharing structure.with
	original
Date: Thu, 23 Sep 2010 21:41:30 +0100

On 23/09/10 06:28, MON KEY wrote:
> (let ((orig [[a b] [c d] [e f] [g h]])
>        new-cp)
>    (setq new-cp (copy-tree orig))

Some people would have at least considered a quick C-h f copy-tree
before filing a bug?

You're missing the VECP arg to emacs lisp copy-tree.

Without that, emacs lisp copy-tree is, much like common lisp copy-tree, 
documented to copy trees of _conses_.   Conses do of course look pretty 
like 2 element vectors, but they are a separate datatype in emacs lisp.

ELISP> (let ((orig [[a b] [c d] [e f] [g h]])
      new-cp)
  (setq new-cp (copy-tree orig t))
  (string-equal (aref (prog1 orig
                        (aset new-cp 0 "bubba"))
                      0)
                "bubba"))
*** Eval error ***  Wrong type argument: stringp, [a b]

Message #25 received at 7083 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: MON KEY <monkey <at> sandpframing.com>
Cc: 7083 <at> debbugs.gnu.org, Andreas Schwab <schwab <at> linux-m68k.org>
Subject: Re: bug#7083: Why is `copy-tree's symbol-plist carrying
	side-effect-free error-free?
Date: Fri, 24 Sep 2010 00:19:47 +0200

> Why has this bug been marked done?
> When copy-tree copies vectors they share structure.

C-h f copy-tree RET documents the second (optional) argument which
affects this behavior.  So it looks perfectly correct, and documented.


        Stefan

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