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bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil.
From: |
Alan Mackenzie |
Subject: |
bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil. |
Date: |
Sat, 18 Mar 2023 08:29:02 +0000 |
Hello, Philip.
On Sat, Mar 18, 2023 at 07:41:14 +0000, Philip Kaludercic wrote:
> Ruijie Yu <ruijie@netyu.xyz> writes:
> > Notice the distinction between these two snippets:
> > (let ((lst-1 '#1=(a #1#)))
> > (list lst-1 (proper-list-p lst-1)))
> > ;; => ((a #1) 2)
> > (let ((lst-2 '#1=(a . #1#)))
> > (list lst-2 (proper-list-p lst-2)))
> > ;; => ((a . #0) nil)
> Doesn't this point resolve the issue?
No, it doesn't. A circular list is defined (Elisp manual page "Lists
and Cons Cells") as one where "some cons cell’s CDR could point to one
of the previous cons cells in the list". A proper list (page
"List-related Predicates") is one which is neither dotted nor circular.
The list #1=(a . #1#) is clearly circular. proper-list-p should return
nil for it.
The purpose of proper-list-p is surely to find out in advance whether an
algorithm one wishes to run on a list can proceed without taking special
precautions for dottedness or circularity. proper-list-p fails here.
> Shouldn't the bug report be closed?
Only once it's been fixed.
> --
> Philip Kaludercic
--
Alan Mackenzie (Nuremberg, Germany).
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Alan Mackenzie, 2023/03/07
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Ruijie Yu, 2023/03/07
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Philip Kaludercic, 2023/03/18
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil.,
Alan Mackenzie <=
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Philip Kaludercic, 2023/03/18
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Ruijie Yu, 2023/03/31
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Philip Kaludercic, 2023/03/31
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Ruijie Yu, 2023/03/31
- bug#62037: (proper-list-p '#1=(a #1#)) => 2. It should return nil., Eli Zaretskii, 2023/03/31