GNU bug report logs - #14568
24.3.50; ring.el: Subtle issue with duplicate "value" entries

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Jambunathan K <kjambunathan <at> gmail.com>
Subject: bug#14568: closed (Re: bug#14568: 24.3.50; ring.el: Subtle issue
 with duplicate "value" entries)
Date: Fri, 15 Nov 2013 04:59:02 +0000

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Your bug report

#14568: 24.3.50; ring.el: Subtle issue with duplicate "value" entries

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 14568 <at> debbugs.gnu.org.

-- 
14568: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14568
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Jambunathan K <kjambunathan <at> gmail.com>
To: 14568-done <at> debbugs.gnu.org
Subject: Re: bug#14568: 24.3.50;
 ring.el: Subtle issue with duplicate "value" entries
Date: Fri, 15 Nov 2013 10:27:59 +0530

OP here.  Closed.

[Message part 3 (message/rfc822, inline)]

From: Jambunathan K <kjambunathan <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50; ring.el: Subtle issue with duplicate "value" entries
Date: Thu, 06 Jun 2013 22:54:40 +0530

`search-mark-ring' is a variable that I have in my private library.
This is a ring that is created using ring.el and is used to store
markers.

M-: search-mark-ring

(0 5 .
   [
    #<marker at 4503 in textprop.c> 
	     #<marker at 109654 in editfns.c> 
	     #<marker at 16866 in lisp.h> 
	     #<marker at 109654 in editfns.c> 
	     #<marker at 16863 in lisp.h> nil nil nil nil nil nil nil
   nil nil nil nil])

M-: search-mark-ring-current

#<marker at 16863 in lisp.h>

M-: (setq search-mark-ring-current (ring-next search-mark-ring
search-mark-ring-current))

When the last form is repeatedly evaluated, you will see that there is
no way I can hit the oldest marker - the one at 4503 - in the ring.
This is because there are duplicate entries in 109654.

Possible solutions:

1. `ring-member' should use `eq' instead of `equal'.
2. `ring-insert' should check for duplicate entries before insertion.

I would prefer solution (1).  

ring.el is probably one of the oldest libraries and so (1) may break
existing behaviours.  Possible bugfix.

1. Augment the structure and allow for a predicate.

2. Check if the ring is a ring of markers and use `eq' instead of
`equal'.

ps: It is a requirement that ring be robust in presence of duplicate
entries.


In GNU Emacs 24.3.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2013-06-06 on debian-6.05
Bzr revision: 112866 acm <at> muc.de-20130605205709-0cwqswy801vgkyx8
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
Important settings:
  value of $LANG: en_IN
  locale-coding-system: iso-latin-1-unix
  default enable-multibyte-characters: t

Major mode: Emacs-Lisp

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