GNU bug report logs - #34852
26.1; seq-intersection ignores nil as element

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Message #56 received at 34852 <at> debbugs.gnu.org (full text, mbox):

From: "Miguel V. S. Frasson" <mvsfrasson <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Michael Heerdegen <michael_heerdegen <at> web.de>,
 "Basil L. Contovounesios" <contovob <at> tcd.ie>,
 Nicolas Petton <nicolas <at> petton.fr>, 34852 <at> debbugs.gnu.org
Subject: Re: bug#34852: 26.1; seq-intersection ignores nil as element
Date: Thu, 14 Mar 2019 16:08:36 -0300

Hi

In any case, of another implementation for seq-intersection or not, I
think that the solution from Stefan should be implemented anyway
because

* it makes seq-contains provide a useful return value when ELT=nil, so
it is a good exception; If ELT=nil, seq-contains currently returns nil
anyway;

* it makes seq-contains become a real predicate function, making it more useful;

* since seq-contains has been used as predicate before, it is
unpredictable which code uses it out of official repositories, so this
fix potentially fixes other code.

Cheers

Miguel


Em qui, 14 de mar de 2019 às 10:34, Stefan Monnier
<monnier <at> iro.umontreal.ca> escreveu:
>
> Yet another approach might be to make an exception in seq-contains if
> the returned element is nil (and return something else in that case).
> E.g.
>
>     diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
>     index 4a811d7895..d2398eb588 100644
>     --- a/lisp/emacs-lisp/seq.el
>     +++ b/lisp/emacs-lisp/seq.el
>     @@ -360,7 +360,7 @@ seq-sort-by
>      Equality is defined by TESTFN if non-nil or by `equal' if nil."
>        (seq-some (lambda (e)
>                    (when (funcall (or testfn #'equal) elt e)
>     -                e))
>     +                (or e t)))
>                  sequence))
>
>      (cl-defgeneric seq-set-equal-p (sequence1 sequence2 &optional testfn)
>
>
> -- Stefan



-- 
Miguel Vinicius Santini Frasson
mvsfrasson <at> gmail.com

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