GNU bug report logs - #63671
Add function to test equality of hash tables

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

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: bug-gnu-emacs <at> gnu.org
Subject: Add function to test equality of hash tables
Date: Tue, 23 May 2023 12:32:08 -0700

Hello!

Would y'all be open to adding something like this?

(defun hash-equal (hash1 hash2)
  "Return non-nil when the contents of HASH1 and HASH2 are equal.
Table values are compared using `equal' unless they are both hash
tables themselves, in which case `hash-equal' is used.
Does not compare equality predicates."
  (and (= (hash-table-count hash1)
          (hash-table-count hash2))
       (catch 'flag (maphash (lambda (key hash1-value)
                               (let ((hash2-value (gethash key hash2)))
                                 (or (if (and (hash-table-p hash1-value)
                                              (hash-table-p hash2-value))
                                         (hash-equal hash1-value hash2-value)
                                       (equal hash1-value hash2-value))
                                     (throw 'flag nil))))
                             hash1)
              t)))

Rudimentary test:

(let ((hash1 (make-hash-table))
      (hash2 (make-hash-table))
      (hash3 (make-hash-table))
      (hash4 (make-hash-table)))
  (puthash 'foo "foo" hash1)
  (puthash 'foo "foo" hash2)
  (puthash 'bar "foo" hash3)
  (puthash 'bar "foo" hash4)
  (puthash 'baz hash3 hash1)
  (puthash 'baz hash4 hash2)
  (hash-equal hash1 hash2))

We could use hash-table-test to compare predicates, perhaps
dependent on the presence of a 'compare-tests flag?

Best,

Joseph

Message #8 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Joseph Turner <joseph <at> breatheoutbreathe.in>
Cc: 63671 <at> debbugs.gnu.org
Subject: bug#63671: Add function to test equality of hash tables
Date: Wed, 24 May 2023 11:27:41 +0200

Thank you, but this seems a bit too specific to your own requirements -- maybe you can keep that procedure locally where you need it? The standard library must be generally useful with clear semantics.

Message #11 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Wed, 24 May 2023 10:27:13 -0700

Mattias Engdegård <mattias.engdegard <at> gmail.com> writes:

> Thank you, but this seems a bit too specific to your own requirements
> -- maybe you can keep that procedure locally where you need it?

It's no problem to keep the procedure local.

> The standard library must be generally useful with clear semantics.

Would extending `equal' to handle hash tables be generally useful?

Joseph

Message #14 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Ihor Radchenko <yantar92 <at> posteo.net>
To: Joseph Turner <joseph <at> breatheoutbreathe.in>
Cc: Mattias Engdegård <mattias.engdegard <at> gmail.com>,
 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Wed, 24 May 2023 20:01:01 +0000

Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs <at> gnu.org> writes:

>> The standard library must be generally useful with clear semantics.
>
> Would extending `equal' to handle hash tables be generally useful?

See https://yhetil.org/emacs-devel/871qvz4kdw.fsf <at> localhost/

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>

Message #17 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Joseph Turner <joseph <at> breatheoutbreathe.in>
Cc: 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Wed, 24 May 2023 22:34:11 +0200

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

24 maj 2023 kl. 19.27 skrev Joseph Turner <joseph <at> breatheoutbreathe.in>:

> Would extending `equal' to handle hash tables be generally useful?

It would, but doing so would be very risky at this point since it would change long-standing semantics.

We could make an augmented version of `equal` but what we really want is one that works for user-defined types (see Ihor's reference to a previous discussion).

Anyway, here's an old patch I had lying around, in case we decide that we do need a shoddy equality predicate for hash tables only.

[hash-table-equal-p.diff (application/octet-stream, attachment)]

Message #20 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>
Cc: yantar92 <at> posteo.net, 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Wed, 24 May 2023 19:44:29 -0700

Mattias Engdegård <mattias.engdegard <at> gmail.com> writes:

> 24 maj 2023 kl. 19.27 skrev Joseph Turner <joseph <at> breatheoutbreathe.in>:
>
>> Would extending `equal' to handle hash tables be generally useful?
>
> It would, but doing so would be very risky at this point since it would change long-standing semantics.
>
> We could make an augmented version of `equal` but what we really want is one that works for user-defined types (see Ihor's reference to a previous discussion).
>
> Anyway, here's an old patch I had lying around, in case we decide that we do need a shoddy equality predicate for hash tables only.

Thank you for the references, Ihor and Mattias! Since this is a
duplicate of Ihor's thread, my report should probably be closed.

How do I close this report?

Joseph

Message #23 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Ihor Radchenko <yantar92 <at> posteo.net>
To: Joseph Turner <joseph <at> breatheoutbreathe.in>
Cc: Mattias Engdegård <mattias.engdegard <at> gmail.com>,
 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Thu, 25 May 2023 06:31:52 +0000

Joseph Turner <joseph <at> breatheoutbreathe.in> writes:

> Thank you for the references, Ihor and Mattias! Since this is a
> duplicate of Ihor's thread, my report should probably be closed.

If we are serious about adding this feature, lets not close this report.
My email was on emacs-devel, and it is thus less visible compared to
something being tracked on debbugs.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>

Message #26 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: Ihor Radchenko <yantar92 <at> posteo.net>
Cc: Mattias Engdegård <mattias.engdegard <at> gmail.com>,
 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Thu, 25 May 2023 00:22:50 -0700

Ihor Radchenko <yantar92 <at> posteo.net> writes:

> If we are serious about adding this feature, lets not close this report.
> My email was on emacs-devel, and it is thus less visible compared to
> something being tracked on debbugs.

I would be happy to see this feature added to Emacs! Unfortunately, I
won't be of much help right now since I have no C experience.

Message #29 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Joseph Turner <joseph <at> breatheoutbreathe.in>
To: Ihor Radchenko <yantar92 <at> posteo.net>
Cc: Mattias Engdegård <mattias.engdegard <at> gmail.com>,
 63671 <at> debbugs.gnu.org
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Thu, 25 May 2023 00:22:50 -0700

Ihor Radchenko <yantar92 <at> posteo.net> writes:

> If we are serious about adding this feature, lets not close this report.
> My email was on emacs-devel, and it is thus less visible compared to
> something being tracked on debbugs.

I would be happy to see this feature added to Emacs! Unfortunately, I
won't be of much help right now since I have no C experience.

Message #32 received at 63671 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Ihor Radchenko <yantar92 <at> posteo.net>
Cc: 63671 <at> debbugs.gnu.org, Joseph Turner <joseph <at> breatheoutbreathe.in>
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Thu, 25 May 2023 10:18:03 +0200

25 maj 2023 kl. 08.31 skrev Ihor Radchenko <yantar92 <at> posteo.net>:

> If we are serious about adding this feature, lets not close this report.

I for one am not, at least not now.

Message #39 received at 63671-done <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Mattias Engdegård <mattias.engdegard <at> gmail.com>, 
 Ihor Radchenko <yantar92 <at> posteo.net>
Cc: 63671-done <at> debbugs.gnu.org, Joseph Turner <joseph <at> breatheoutbreathe.in>
Subject: Re: bug#63671: Add function to test equality of hash tables
Date: Mon, 11 Sep 2023 11:39:04 -0700

Mattias Engdegård <mattias.engdegard <at> gmail.com> writes:

> 25 maj 2023 kl. 08.31 skrev Ihor Radchenko <yantar92 <at> posteo.net>:
>
>> If we are serious about adding this feature, lets not close this report.
>
> I for one am not, at least not now.

Let's close this for now then.

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