GNU bug report logs - #26440
seq-mapn fails with circular sequence

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: "Phillip Lord" <phillip.lord <at> russet.org.uk>
Subject: bug#26440: closed (Re: bug#26440: seq-mapn fails with circular
 sequence)
Date: Tue, 01 Aug 2017 18:41:02 +0000

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Your bug report

#26440: seq-mapn fails with circular sequence

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 26440 <at> debbugs.gnu.org.

-- 
26440: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=26440
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Nicolas Petton <nicolas <at> petton.fr>
To: Phillip Lord <phillip.lord <at> russet.org.uk>
Cc: 26440-done <at> debbugs.gnu.org, 26440 <at> debbugs.gnu.org
Subject: Re: bug#26440: seq-mapn fails with circular sequence
Date: Tue, 01 Aug 2017 20:40:20 +0200

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Nicolas Petton <nicolas <at> petton.fr> writes:

Hi Phillip,

> This is using seq.el from trunk:
>
>   (defvar l '(a c d))
>   (setq l (nconc l l))
>   (seq-mapn #'cons l '(1)) ;; ((a . 1))


I'm closing this issue, but feel free to reopen it if you can reproduce
the problem with master.

Cheers,
Nico

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From: "Phillip Lord" <phillip.lord <at> russet.org.uk>
To: bug-gnu-emacs <at> gnu.org
Subject: seq-mapn fails with circular sequence
Date: Tue, 11 Apr 2017 08:12:40 -0000

On Emacs-25 circular structures cause seq-mapn not to terminate
although the documentation suggest that they should.

Consider:

    (defvar l '(a c d))
    (setq l (nconc l l))
    (seq-mapn #'cons l '(1))

This should return '((a . 1)) but actually does not terminate.

The problem is caused by call to seq-into which includes:

    (append sequence nil)

The problem does exist on trunk which does this instead:

    (if (listp sequence)
        sequence
      (append sequence nil)))

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