GNU bug report logs - #37400
Patch for bug in cl-reduce: function called with no arguments when list is empty

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Adrià Garriga <adria.garriga <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Patch for bug in cl-reduce: function called with no arguments when
 list is empty
Date: Fri, 13 Sep 2019 09:50:39 +0100

[Message part 1 (text/plain, inline)]

Hello Emacs developers,

I found a bug in cl-reduce, which should be reproducible by running the test in the patch. I'm running 26.2 but the bug is also present in master. Please let me know if there are any problems with the patch (including that it is useless :) or if I need to do something else.

Thank you for your hard work maintaining Emacs!

Adrià Garriga-Alonso

[0001-cl-reduce-avoids-calling-the-function-when-list-is-n.patch (application/octet-stream, attachment)]

Message #8 received at 37400 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Adrià Garriga <adria.garriga <at> gmail.com>
Cc: 37400 <at> debbugs.gnu.org
Subject: Re: bug#37400: Patch for bug in cl-reduce: function called with no
 arguments when list is empty
Date: Fri, 13 Sep 2019 11:18:27 -0400

Adrià Garriga <adria.garriga <at> gmail.com> writes:

> +(ert-deftest cl-seq-reduce ()
> +  (let ((bad-add (lambda (x y) (+ x y))))
> +    (should-not (cl-reduce bad-add nil))

Actually, I think it's a docstring bug.  The Common Lisp Hyperspec says:

    If the subsequence is empty and no initial-value is given, then the
    function is called with zero arguments, and reduce returns whatever
    function does. This is the only case where the function is called
    with other than two arguments.

It looks like Emacs' current implementation is correct, but the
docstring doesn't explain it accurately.

https://www.cs.cmu.edu/Groups/AI/html/hyperspec/HyperSpec/Body/fun_reduce.html

Message #11 received at 37400 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: 37400 <at> debbugs.gnu.org,
 Adrià Garriga <adria.garriga <at> gmail.com>
Subject: Re: bug#37400: Patch for bug in cl-reduce: function called with no
 arguments when list is empty
Date: Mon, 07 Oct 2019 06:33:01 +0200

Noam Postavsky <npostavs <at> gmail.com> writes:

> Actually, I think it's a docstring bug.  The Common Lisp Hyperspec says:
>
>     If the subsequence is empty and no initial-value is given, then the
>     function is called with zero arguments, and reduce returns whatever
>     function does. This is the only case where the function is called
>     with other than two arguments.

I've now added a variation of this to the doc string, and I'm closing
this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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