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* "The starting list count" ?????
@ 2022-01-03 17:49 Alan Mackenzie
  2022-01-03 18:00 ` Robin Tarsiger
                   ` (2 more replies)
  0 siblings, 3 replies; 19+ messages in thread
From: Alan Mackenzie @ 2022-01-03 17:49 UTC (permalink / raw)
  To: emacs-devel

Hello, Emacs.

I'm trying to make sense of the form whose printed syntax is

    (1 . #1)

which arises in the Emacs test suite file seq-tests.el.  I'm having
difficulty.

The Elisp manual page "Special Read Syntax" says about it:

   `#N'
       When printing circular structures, this construct is used to
       represent where the structure loops back onto itself, and `N' is
       the starting list count:

            (let ((a (list 1)))
              (setcdr a a))
            => (1 . #0)

..  What does this mean, please?  What does "is the starting list count"
mean?  There is only one "list", so what is the "list count"?

Clearly the N in #N is counting something, but what?  What is the
meaning of

    (1 . #1)

?  What is it about the description in the manual which is so perplexing
me?

Help!

-- 
Alan Mackenzie (Nuremberg, Germany).



^ permalink raw reply	[flat|nested] 19+ messages in thread

end of thread, other threads:[~2022-01-04  0:43 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-01-03 17:49 "The starting list count" ????? Alan Mackenzie
2022-01-03 18:00 ` Robin Tarsiger
2022-01-03 18:33   ` Andreas Schwab
2022-01-03 18:59     ` Robin Tarsiger
2022-01-03 19:24       ` Andreas Schwab
2022-01-03 19:36       ` Eli Zaretskii
2022-01-03 18:54   ` Alan Mackenzie
2022-01-03 19:26     ` Andreas Schwab
2022-01-03 18:05 ` Stefan Monnier
2022-01-03 19:21   ` Alan Mackenzie
2022-01-03 19:50     ` Andreas Schwab
2022-01-03 19:55       ` Alan Mackenzie
2022-01-03 20:38     ` Stefan Monnier
2022-01-03 20:58       ` Stefan Monnier
2022-01-03 21:03       ` Alan Mackenzie
2022-01-03 21:15         ` Stefan Monnier
2022-01-03 21:33           ` Alan Mackenzie
2022-01-04  0:43             ` Stefan Monnier
2022-01-03 18:13 ` Andreas Schwab

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