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Subject: |
24.3.50; ring.el: Subtle issue with duplicate "value" entries |
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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 address@hidden
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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