GNU bug report logs - #81361
[PATCH] Add bind-or* form to cond*

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Package: emacs; Reported by: zach shaftel <zach@HIDDEN>; Keywords: patch; Done: Sean Whitton <spwhitton@HIDDEN>; Maintainer for emacs is bug-gnu-emacs@HIDDEN.

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Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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[[[ To any NSA and FBI agents reading my email: please consider    ]]]
[[[ whether defending the US Constitution against all enemies,     ]]]
[[[ foreign or domestic, requires you to follow Snowden's example. ]]]

I am still waiting to see a clear self-contained description of what
bind-or* _does_.  Other people seem to be having a discussion of this,
and making some decisions, which I can't make sense of because I dont
know what bind-or* is _meant_ to do!

Would someone who understands the intended meaning PLEASE
tell me now what that meaning is?  And give me a chance to
comment on it before you make a decision about it?

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

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From: Sean Whitton <spwhitton@HIDDEN>
To: zach shaftel <zach@HIDDEN>
Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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zach shaftel [07/Jul  7:50pm -04] wrote:
> Sean Whitton <spwhitton@HIDDEN> writes:
>
>>> That said, this patch also implements bind-and* without the need for
>>> throw/catch. Is there interest in integrating that into the existing
>>> bind-and* implementation, or is it not worth rocking the boat?
>>
>> Yes, thanks.  Can you make it a standalone patch?  It's probably best to
>> change the code inline instead of adding a helper, but you could add a
>> helper if that doesn't work out well.
>>
>> Please CC Philip Kaludercic on your reply.  Philip worked on trying to
>> avoid throw/catch previously but didn't think there was a good way to do
>> it, so he'll probably want to take a look.
>
> Done, see bug#81374. I CCed you, Philip and Richard.
>
> You can close this one now.

Doing so.  Btw, use X-debbugs-cc not Cc when writing to bug-gnu-emacs@.

-- 
Sean Whitton
Notification sent to zach shaftel <zach@HIDDEN>:
bug acknowledged by developer. Full text available.
Reply sent to Sean Whitton <spwhitton@HIDDEN>:
You have taken responsibility. Full text available.

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In-Reply-To: <87jyr8r7mt.fsf@HIDDEN> (message from zach shaftel on Mon, 06
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Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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[[[ To any NSA and FBI agents reading my email: please consider    ]]]
[[[ whether defending the US Constitution against all enemies,     ]]]
[[[ foreign or domestic, requires you to follow Snowden's example. ]]]

Thanks for showing us the code in both forms.  To understand the uses
of bind-or* I would need to see clear documentation of that construct,
so I am waiting to see your documentation.

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

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Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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Sean Whitton <spwhitton@HIDDEN> writes:

>> That said, this patch also implements bind-and* without the need for
>> throw/catch. Is there interest in integrating that into the existing
>> bind-and* implementation, or is it not worth rocking the boat?
>
> Yes, thanks.  Can you make it a standalone patch?  It's probably best to
> change the code inline instead of adding a helper, but you could add a
> helper if that doesn't work out well.
>
> Please CC Philip Kaludercic on your reply.  Philip worked on trying to
> avoid throw/catch previously but didn't think there was a good way to do
> it, so he'll probably want to take a look.

Done, see bug#81374. I CCed you, Philip and Richard.

You can close this one now.

- Zach
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

Message received at 81361 <at> debbugs.gnu.org:


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From: Sean Whitton <spwhitton@HIDDEN>
To: zach shaftel <zach@HIDDEN>
Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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zach shaftel [06/Jul  4:53pm -04] wrote:
>> I'm unsure about this.  I'm concerned about readability.
>>
>> - feels unnatural, because normally there is a positive association
>>   between a set of bindings and the clause body
>
> This I understand, and I've been trying to think of other possible names
> or forms of the construct that might feel more natural. bind-or* is for
> symmetry with bind-and*. One format that makes more intuitive sense to my
> mind is
> (not (bind* ...))
> but I may be alone in that intuition.
>
>>
>> - it breaks the rule that a set of bindings is scoped over all remaining
>>   clauses if and only if the bindings clause has no body.
>
> bind* does not obey this, its bindings are established around both its body
> and all remaining clauses.

Good point, though we would be introducing a clause type that's
inconsistent in the extent of its bindings.  For all the other types,
the extent of the bindings is always determined just by the shape of the
code, not any values at runtime, which aids readability.

>> The second one seems serious to me.
>>
>> If it's a single binding, then
>>
>>     ((bind* (var val)))
>>     ((not var) ELSE ...)
>>
>> is significantly preferable, I think.
>>
>> So the question is whether it is worth it for multiple bindings.
>>
>> I'd like to see more examples.  Looking at the one you've provided so
>> far, the nested cond that pushes a value and then returns nil seems like
>> rather complex control flow that might not exemplify best practices.
>
> What do you mean exactly? Is
> (or (intern-soft text gaudy-cl--package)
>     (ignore (push text gaudy-cl--unrecognized-symbols)))
> preferable (which it is to me) or is something else about it
> problematic?

I don't think it's great for conditions on whether a block of code is
going to get executed to have anything but the simplest side-effects,
basically.

> Looking over my other uses of bind-or*, most of them are single binding
> cases. So on review, I agree with the readability concern and don't
> think bind-or* would be a good addition after all.

Okay cool, glad my feedback was useful.

> That said, this patch also implements bind-and* without the need for
> throw/catch. Is there interest in integrating that into the existing
> bind-and* implementation, or is it not worth rocking the boat?

Yes, thanks.  Can you make it a standalone patch?  It's probably best to
change the code inline instead of adding a helper, but you could add a
helper if that doesn't work out well.

Please CC Philip Kaludercic on your reply.  Philip worked on trying to
avoid throw/catch previously but didn't think there was a good way to do
it, so he'll probably want to take a look.

-- 
Sean Whitton
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

Message received at 81361 <at> debbugs.gnu.org:


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From: zach shaftel <zach@HIDDEN>
To: Sean Whitton <spwhitton@HIDDEN>
Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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Sean Whitton <spwhitton@HIDDEN> writes:

> zach shaftel via "Bug reports for GNU Emacs, the Swiss army knife of text
> editors" [06/Jul 1:48am -04] wrote:
>> Sure. I'm not sure the best format to share it so I'll just include the
>> code inline. Here is the original expression:
>>
>> (if-let* ((head (gaudy-cl--head node))
>>           (child (gaudy-cl--unwrap head qdepth))
>>           (_ (string= (treesit-node-type child) "interned_symbol"))
>>           (operator (let ((text (gaudy-cl--node-text child)))
>>                       (cond
>>                         ((intern-soft text gaudy-cl--package))
>>                         (t (push text gaudy-cl--unrecognized-symbols)
>>                            nil))))
>>           (real-sym (symbol-function operator)))
>>     (if-let* ((local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
>>         (progn
>>           (gaudy-cl-reference-local child local)
>>           (gaudy-cl-do-nodes (:following arg head)
>>             (gaudy-cl-walk arg)))
>>       (let ((ftype (get real-sym :definition))
>>             (handler (symbol-function real-sym)))
>>         (pcase ftype
>>           (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
>>           (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
>>           (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator)))
>>         (cond*
>>           (handler (funcall handler head))
>>           ((or (plusp qdepth) (eq ftype :function))
>>            (gaudy-cl-do-nodes (:following child head)
>>              (gaudy-cl--walk child nil qdepth)))
>>           ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
>>                       (body-pos (get real-sym :body)))
>>            (gaudy-cl--walk-body
>>             (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))))
>>   (when (plusp qdepth)
>>     (gaudy-cl-do-nodes (:siblings child head)
>>       (gaudy-cl--walk child nil qdepth))))
>>
>> Here is the cond* form with bind-or*:
>>
>> (cond*
>>   ((bind-or* (head (gaudy-cl--head node))) nil) ;empty list, who cares
>>   ((bind-or* (child (gaudy-cl--unwrap head qdepth))
>>              (_ (string= (treesit-node-type child) "interned_symbol"))
>>              (operator (let ((text (gaudy-cl--node-text child)))
>>                          (cond
>>                            ((intern-soft text gaudy-cl--package))
>>                            (t (push text gaudy-cl--unrecognized-symbols)
>>                               nil))))
>>              (real-sym (symbol-function operator)))
>>    (when (plusp qdepth)
>>      (gaudy-cl-do-nodes (:siblings child head)
>>        (gaudy-cl--walk child nil qdepth))))
>>   ((bind-and* (local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
>>    (gaudy-cl-reference-local child local)
>>    (gaudy-cl-do-nodes (:following arg head)
>>      (gaudy-cl-walk arg)))
>>   ((bind* (ftype (get real-sym :definition))))
>>   (t (pcase ftype
>>        (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
>>        (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
>>        (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator))))
>>   ((bind-and* (handler (symbol-function real-sym)))
>>    (funcall handler head))
>>   ((or (plusp qdepth) (eq ftype :function))
>>    (gaudy-cl-do-nodes (:following child head)
>>      (gaudy-cl--walk child nil qdepth)))
>>   ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
>>               (body-pos (get real-sym :body)))
>>    (gaudy-cl--walk-body (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))
>>
>> In the case of a single binding, bind-or* is roughly equivalent to
>>
>> (cond* ((bind* (var val)))
>>        ((not var) ELSE...)
>>        ...)
>>
>> but when there are multiple bindings, you get the if-let* behavior of
>> short circuiting evaluation on the first nil value. And with bind-or*,
>> VAR would not be in scope around ELSE.
>>
>> I'd be happy to show more examples. After converting a few other
>> expressions in the same package, I actually ended up using bind-or*
>> slightly more than bind-and*, which surprised me.
>
> I'm unsure about this.  I'm concerned about readability.
>
> - feels unnatural, because normally there is a positive association
>   between a set of bindings and the clause body

This I understand, and I've been trying to think of other possible names
or forms of the construct that might feel more natural. bind-or* is for
symmetry with bind-and*. One format that makes more intuitive sense to my
mind is
(not (bind* ...))
but I may be alone in that intuition.

>
> - it breaks the rule that a set of bindings is scoped over all remaining
>   clauses if and only if the bindings clause has no body.

bind* does not obey this, its bindings are established around both its body
and all remaining clauses.

> The second one seems serious to me.
>
> If it's a single binding, then
>
>     ((bind* (var val)))
>     ((not var) ELSE ...)
>
> is significantly preferable, I think.
>
> So the question is whether it is worth it for multiple bindings.
>
> I'd like to see more examples.  Looking at the one you've provided so
> far, the nested cond that pushes a value and then returns nil seems like
> rather complex control flow that might not exemplify best practices.

What do you mean exactly? Is
(or (intern-soft text gaudy-cl--package)
    (ignore (push text gaudy-cl--unrecognized-symbols)))
preferable (which it is to me) or is something else about it
problematic?

Looking over my other uses of bind-or*, most of them are single binding
cases. So on review, I agree with the readability concern and don't
think bind-or* would be a good addition after all.

That said, this patch also implements bind-and* without the need for
throw/catch. Is there interest in integrating that into the existing
bind-and* implementation, or is it not worth rocking the boat?

- Zach
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

Message received at 81361 <at> debbugs.gnu.org:


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From: Sean Whitton <spwhitton@HIDDEN>
To: zach shaftel <zach@HIDDEN>, rms@HIDDEN
Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
In-Reply-To: <87jyr8r7mt.fsf@HIDDEN>
References: <87se5yqini.fsf@HIDDEN> <E1wgawU-004X6A-3q@HIDDEN>
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zach shaftel via "Bug reports for GNU Emacs, the Swiss army knife of text editors" [06/Jul  1:48am -04] wrote:
> Sure. I'm not sure the best format to share it so I'll just include the
> code inline. Here is the original expression:
>
> (if-let* ((head (gaudy-cl--head node))
>           (child (gaudy-cl--unwrap head qdepth))
>           (_ (string= (treesit-node-type child) "interned_symbol"))
>           (operator (let ((text (gaudy-cl--node-text child)))
>                       (cond
>                         ((intern-soft text gaudy-cl--package))
>                         (t (push text gaudy-cl--unrecognized-symbols)
>                            nil))))
>           (real-sym (symbol-function operator)))
>     (if-let* ((local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
>         (progn
>           (gaudy-cl-reference-local child local)
>           (gaudy-cl-do-nodes (:following arg head)
>             (gaudy-cl-walk arg)))
>       (let ((ftype (get real-sym :definition))
>             (handler (symbol-function real-sym)))
>         (pcase ftype
>           (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
>           (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
>           (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator)))
>         (cond*
>           (handler (funcall handler head))
>           ((or (plusp qdepth) (eq ftype :function))
>            (gaudy-cl-do-nodes (:following child head)
>              (gaudy-cl--walk child nil qdepth)))
>           ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
>                       (body-pos (get real-sym :body)))
>            (gaudy-cl--walk-body
>             (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))))
>   (when (plusp qdepth)
>     (gaudy-cl-do-nodes (:siblings child head)
>       (gaudy-cl--walk child nil qdepth))))
>
> Here is the cond* form with bind-or*:
>
> (cond*
>   ((bind-or* (head (gaudy-cl--head node))) nil) ;empty list, who cares
>   ((bind-or* (child (gaudy-cl--unwrap head qdepth))
>              (_ (string= (treesit-node-type child) "interned_symbol"))
>              (operator (let ((text (gaudy-cl--node-text child)))
>                          (cond
>                            ((intern-soft text gaudy-cl--package))
>                            (t (push text gaudy-cl--unrecognized-symbols)
>                               nil))))
>              (real-sym (symbol-function operator)))
>    (when (plusp qdepth)
>      (gaudy-cl-do-nodes (:siblings child head)
>        (gaudy-cl--walk child nil qdepth))))
>   ((bind-and* (local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
>    (gaudy-cl-reference-local child local)
>    (gaudy-cl-do-nodes (:following arg head)
>      (gaudy-cl-walk arg)))
>   ((bind* (ftype (get real-sym :definition))))
>   (t (pcase ftype
>        (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
>        (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
>        (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator))))
>   ((bind-and* (handler (symbol-function real-sym)))
>    (funcall handler head))
>   ((or (plusp qdepth) (eq ftype :function))
>    (gaudy-cl-do-nodes (:following child head)
>      (gaudy-cl--walk child nil qdepth)))
>   ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
>               (body-pos (get real-sym :body)))
>    (gaudy-cl--walk-body (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))
>
> In the case of a single binding, bind-or* is roughly equivalent to
>
> (cond* ((bind* (var val)))
>        ((not var) ELSE...)
>        ...)
>
> but when there are multiple bindings, you get the if-let* behavior of
> short circuiting evaluation on the first nil value. And with bind-or*,
> VAR would not be in scope around ELSE.
>
> I'd be happy to show more examples. After converting a few other
> expressions in the same package, I actually ended up using bind-or*
> slightly more than bind-and*, which surprised me.

I'm unsure about this.  I'm concerned about readability.

- feels unnatural, because normally there is a positive association
  between a set of bindings and the clause body

- it breaks the rule that a set of bindings is scoped over all remaining
  clauses if and only if the bindings clause has no body.

The second one seems serious to me.

If it's a single binding, then

    ((bind* (var val)))
    ((not var) ELSE ...)

is significantly preferable, I think.

So the question is whether it is worth it for multiple bindings.

I'd like to see more examples.  Looking at the one you've provided so
far, the nested cond that pushes a value and then returns nil seems like
rather complex control flow that might not exemplify best practices.

-- 
Sean Whitton
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

Message received at 81361 <at> debbugs.gnu.org:


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From: zach shaftel <zach@HIDDEN>
To: rms@HIDDEN
Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
In-Reply-To: <E1wgawU-004X6A-3q@HIDDEN>
References: <87se5yqini.fsf@HIDDEN> <E1wgawU-004X6A-3q@HIDDEN>
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Richard Stallman <rms@HIDDEN> writes:

> [[[ To any NSA and FBI agents reading my email: please consider    ]]]
> [[[ whether defending the US Constitution against all enemies,     ]]]
> [[[ foreign or domestic, requires you to follow Snowden's example. ]]]
>
> Looking at this, I don't understand what it concretely means.
>
>   > +@code{(bind-or* @var{bindings}@dots{})} is like @code{bind-and*}, but
>   > +the bindings are established only around the @emph{following}
>   > +clauses.
>
> Would you please write the documentation of bind-or* in self-contained form,
> one which is easier to understand because it avoids being terse?

Rereading it now I agree, the current patch's documentation is
lackluster. I'll clarify it and submit an updated patch.

> Also, could you show this example, in both the original form
> and the modified form, so we can see the improvement?
>
>    With
>   > this I was able to convert a mess of nested if-let*/let*/cond forms into
>   > a single cond* form, which is very satisfying.

Sure. I'm not sure the best format to share it so I'll just include the
code inline. Here is the original expression:

(if-let* ((head (gaudy-cl--head node))
          (child (gaudy-cl--unwrap head qdepth))
          (_ (string= (treesit-node-type child) "interned_symbol"))
          (operator (let ((text (gaudy-cl--node-text child)))
                      (cond
                        ((intern-soft text gaudy-cl--package))
                        (t (push text gaudy-cl--unrecognized-symbols)
                           nil))))
          (real-sym (symbol-function operator)))
    (if-let* ((local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
        (progn
          (gaudy-cl-reference-local child local)
          (gaudy-cl-do-nodes (:following arg head)
            (gaudy-cl-walk arg)))
      (let ((ftype (get real-sym :definition))
            (handler (symbol-function real-sym)))
        (pcase ftype
          (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
          (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
          (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator)))
        (cond*
          (handler (funcall handler head))
          ((or (plusp qdepth) (eq ftype :function))
           (gaudy-cl-do-nodes (:following child head)
             (gaudy-cl--walk child nil qdepth)))
          ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
                      (body-pos (get real-sym :body)))
           (gaudy-cl--walk-body
            (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))))
  (when (plusp qdepth)
    (gaudy-cl-do-nodes (:siblings child head)
      (gaudy-cl--walk child nil qdepth))))

Here is the cond* form with bind-or*:

(cond*
  ((bind-or* (head (gaudy-cl--head node))) nil) ;empty list, who cares
  ((bind-or* (child (gaudy-cl--unwrap head qdepth))
             (_ (string= (treesit-node-type child) "interned_symbol"))
             (operator (let ((text (gaudy-cl--node-text child)))
                         (cond
                           ((intern-soft text gaudy-cl--package))
                           (t (push text gaudy-cl--unrecognized-symbols)
                              nil))))
             (real-sym (symbol-function operator)))
   (when (plusp qdepth)
     (gaudy-cl-do-nodes (:siblings child head)
       (gaudy-cl--walk child nil qdepth))))
  ((bind-and* (local (assq real-sym (cddr (assq :functions gaudy-cl-locals)))))
   (gaudy-cl-reference-local child local)
   (gaudy-cl-do-nodes (:following arg head)
     (gaudy-cl-walk arg)))
  ((bind* (ftype (get real-sym :definition))))
  (t (pcase ftype
       (:function (gaudy-cl-fontify-node child 'font-lock-function-call-face))
       (:macro    (gaudy-cl-fontify-node child 'gaudy-cl-macro))
       (:special  (gaudy-cl-fontify-node child 'gaudy-cl-special-operator))))
  ((bind-and* (handler (symbol-function real-sym)))
   (funcall handler head))
  ((or (plusp qdepth) (eq ftype :function))
   (gaudy-cl-do-nodes (:following child head)
     (gaudy-cl--walk child nil qdepth)))
  ((bind-and* (_ gaudy-cl-guess-spec-from-lambda-list)
              (body-pos (get real-sym :body)))
   (gaudy-cl--walk-body (gaudy-cl--nth-sexp-sibling (1+ body-pos) child))))

In the case of a single binding, bind-or* is roughly equivalent to

(cond* ((bind* (var val)))
       ((not var) ELSE...)
       ...)

but when there are multiple bindings, you get the if-let* behavior of
short circuiting evaluation on the first nil value. And with bind-or*,
VAR would not be in scope around ELSE.

I'd be happy to show more examples. After converting a few other
expressions in the same package, I actually ended up using bind-or*
slightly more than bind-and*, which surprised me.

- Zach
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

Message received at 81361 <at> debbugs.gnu.org:


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From: Richard Stallman <rms@HIDDEN>
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Subject: Re: bug#81361: [PATCH] Add bind-or* form to cond*
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Looking at this, I don't understand what it concretely means.

  > +@code{(bind-or* @var{bindings}@dots{})} is like @code{bind-and*}, but
  > +the bindings are established only around the @emph{following}
  > +clauses.

Would you please write the documentation of bind-or* in self-contained form,
one which is easier to understand because it avoids being terse?

Also, could you show this example, in both the original form
and the modified form, so we can see the improvement?

   With
  > this I was able to convert a mess of nested if-let*/let*/cond forms into
  > a single cond* form, which is very satisfying.

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.

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From: zach shaftel <zach@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Subject: [PATCH] Add bind-or* form to cond*
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--=-=-=
Content-Type: text/plain

This is like bind-and*, but flipped: if the binds are all non-nil,
continue to the next clause; otherwise, run the clause's body. Like
bind-and*, the bindings are only established around the code where all
the values are non-nil.

I found myself wanting this construct just as often as bind-and*. With
this I was able to convert a mess of nested if-let*/let*/cond forms into
a single cond* form, which is very satisfying.

-Zach

In GNU Emacs 32.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.52, cairo version 1.18.4) of 2026-06-26 built on arch-thinkpad
Repository revision: 98f3bfe7e1cbd8bc43fcfd62bf985471aa255e34
Repository branch: master
System Description: Arch Linux

Configured using:
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--=-=-=
Content-Type: text/x-patch
Content-Disposition: attachment;
 filename=0001-Add-bind-or-form-to-cond.patch

From 4335c334abf5118b9d0e73cda61250bd61e8c101 Mon Sep 17 00:00:00 2001
From: Zach Shaftel <zach@HIDDEN>
Date: Sat, 4 Jul 2026 21:56:37 -0400
Subject: [PATCH] Add bind-or* form to cond*

This is effectively the inverse of bind-and*: evaluate the clause's body
if any bindings are nil, otherwise establish the bindings around the
remaining clauses.

* lisp/emacs-lisp/cond-star.el (cond*-convert-bind-conditional): New
helper function to expand both bind-and* and bind-or* clauses.
(cond*-convert-condition): Use cond*-convert-bind-conditional.
(cond*, bind-or*): Document it.

* doc/lispref/control.texi (cond* Macro): Document it.
---
 doc/lispref/control.texi     |  14 +++--
 lisp/emacs-lisp/cond-star.el | 103 ++++++++++++++++++++++++++---------
 2 files changed, 86 insertions(+), 31 deletions(-)

diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi
index d3662f727cc..6226b425f53 100644
--- a/doc/lispref/control.texi
+++ b/doc/lispref/control.texi
@@ -1529,10 +1529,10 @@ cond* Macro
 @defmac cond* &rest clauses
 The @code{cond*} macro is an extended form of the traditional
 @code{cond}.  A @code{cond*} expression contains a series of
-@var{clauses}, each of which can use @code{bind*} or @code{bind-and*} to
-specify binding variables, use @code{match*} or @code{pcase*} to specify
-matching a pattern as a condition, or specify an expression as a
-condition to evaluate as a test.
+@var{clauses}, each of which can use @code{bind*}, @code{bind-and*} or
+@code{bind-or*} to specify binding variables, use @code{match*} or
+@code{pcase*} to specify matching a pattern as a condition, or specify
+an expression as a condition to evaluate as a test.
 
 Each clause normally has the form @w{@code{(@var{condition}
 @var{body}@dots{})}}.
@@ -1557,6 +1557,12 @@ cond* Macro
 evaluates to @code{nil}, the expressions for the values of subsequent
 bindings are not evaluated.
 
+@findex bind-or*
+@code{(bind-or* @var{bindings}@dots{})} is like @code{bind-and*}, but
+the bindings are established only around the @emph{following}
+clauses. As a condition, it counts as true if any of the bindings
+evaluate to @code{nil}.
+
 @findex match*
 @findex pcase*
 @code{(match* @var{pattern} @var{datum})} means to match @var{datum}
diff --git a/lisp/emacs-lisp/cond-star.el b/lisp/emacs-lisp/cond-star.el
index ef0af260e89..dd787372b2e 100644
--- a/lisp/emacs-lisp/cond-star.el
+++ b/lisp/emacs-lisp/cond-star.el
@@ -71,6 +71,11 @@ cond*
 `if-let*') for only the the body of the clause.  If any expression
 evaluates to nil, the condition counts as false.
 
+`(bind-or* BINDINGS...)' is the inverse of `bind-and*': if any
+expression in BINDINGS evaluates to nil, the condition counts as true;
+otherwise the bindings are established for only the remaining `cond*'
+clauses.
+
 `(pcase* PATTERN DATUM)' means to match DATUM against the
 pattern PATTERN, using the same pattern syntax as `pcase'.
 The condition counts as true if PATTERN matches DATUM.
@@ -93,7 +98,8 @@ cond*
 conditions."
   (declare
    (debug (&rest ([&or ("bind*" &rest &or symbolp (symbolp &optional form))
-                       ("bind-and*" &rest &or symbolp (symbolp form) (form))
+                       ((&or "bind-and*" "bind-or*")
+                        &rest &or symbolp (symbolp form) (form))
                        ("match*" sexp form)
                        ("pcase*" pcase-PAT form)
                        form]
@@ -186,6 +192,14 @@ bind-and*
   (macroexp-warn-and-return "`bind-and*' used other than as a `cond*' condition"
                             nil 'suspicious))
 
+;;;###autoload
+(defmacro bind-or* (&rest _bindings)
+  "Evaluate BINDINGS like `if-let*'.
+This is not really a Lisp operator; it is meaningful only in the
+CONDITION of a `cond*' clause.  See `cond*' for details."
+  (macroexp-warn-and-return "`bind-or*' used other than as a `cond*' condition"
+                            nil 'suspicious))
+
 ;;;###autoload
 (defmacro pcase* (_pattern _datum)
   "Evaluate PATTERN and DATUM like an element of BINDINGS in `pcase-let'.
@@ -266,6 +280,64 @@ cond*-convert-clause
     (cond*-convert-condition (car-safe clause) (cdr-safe clause) nil
                              rest (cond*-convert rest))))
 
+(defun cond*-convert-bind-conditional (condition then else uncondit-clauses)
+  "Convert a `bind-and*' or `bind-or*' cond* clause.
+CONDITION is the `bind-and*' or `bind-or*' form. THEN is an expression
+which is evaluated if the condition is true (all non-nil for
+`bind-and*', any nil for `bind-or*'); ELSE is evaluated if it is
+false. UNCONDIT-CLAUSES are like in `cond*-convert-condition'.
+
+The bindings are only in scope around the value forms in the bindings
+themselves, around UNCONDIT-CLAUSES, and in either the THEN
+expression (for `bind-and*') or the ELSE expression (for `bind-or*')."
+  (let ((is-and (eq (car condition) 'bind-and*))
+        (checks '())
+        (rebinds '())
+        (ignores '())
+        (last t)
+        (uncondit-clauses
+         (and uncondit-clauses (cond*-convert uncondit-clauses))))
+    ;; Since the bindings are not established around the alternative
+    ;; expression, bind them all initially to dummies, while binding the
+    ;; real variables to those dummies around each value form, and then
+    ;; finally bind all the rebinds around the consequent expression.
+    (dolist (bind (cdr condition))
+      (let ((dummy (gensym "value")))
+        (push (list dummy
+                    (list 'and last
+                          (if rebinds
+                              `(let (,@rebinds)
+                                 (ignore ,@ignores) ;Satisfy the compiler
+                                 ,(cadr bind))
+                            (cadr bind))))
+              checks)
+        (unless (eq (car bind) '_)
+          (push (list (car bind) dummy) rebinds)
+          (push (car bind) ignores))
+        (setq last dummy)))
+    (cond ((null rebinds) nil)
+          ((not is-and)
+           (and else (setq else `(let (,@rebinds)
+                                   (ignore ,@ignores)
+                                   ,else)))
+           (and uncondit-clauses (setq uncondit-clauses
+                                       `(let (,@rebinds)
+                                          (ignore ,@ignores)
+                                          ,uncondit-clauses))))
+          (then (setq then `(let (,@rebinds)
+                              (ignore ,@ignores)
+                              ,then)))
+          ;; `bind-and*' as the final clause with no consequent forms
+          ;; behaves like `and-let*'
+          (t (setq then last)))
+    (let ((test (if is-and last `(not ,last))))
+      (macroexp-let* (nreverse checks)
+                     (if uncondit-clauses
+                         `(progn
+                            ,(macroexp-if test then else)
+                            ,uncondit-clauses)
+                       (macroexp-if test then else))))))
+
 (defun cond*-convert-condition (condition true-exps uncondit-clauses rest iffalse)
   "Process the condition part of one cond* clause.
 TRUE-EXPS is a list of Lisp expressions to be executed if this
@@ -332,32 +404,9 @@ cond*-convert-condition
                     (let* ,mod-bindings
                       (when ,init-gensym
                         . ,true-exps)))))))
-          ((eq pat-type 'bind-and*)
-           (let ((checks '()) (last t))
-             (dolist (bind (cdr condition))
-               (push (list (car bind) (list 'and last (cadr bind)))
-                     checks)
-               (when (eq (caar checks) '_)
-                 (setcar (car checks) (make-symbol "s")))
-               (setq last (caar checks)))
-             (cond
-              ;; For explanations on these cases, see "Ordinary
-              ;; Lisp expression is the condition." below.
-              (rest
-               (let ((quit (gensym "quit")))
-                 `(catch ',quit
-                    (let* (,@(nreverse checks))
-                      (if ,last (throw ',quit ,(macroexp-progn true-exps))))
-                    ,iffalse)))
-              (uncondit-clauses
-               `(progn
-                  (let* (,@(nreverse checks))
-                    (if ,last ,(macroexp-progn true-exps)))
-                  ,(cond*-convert uncondit-clauses)))
-              (true-exps
-               `(let* (,@(nreverse checks))
-                  (if ,last ,(macroexp-progn true-exps))))
-              (t last))))
+          ((memq pat-type '(bind-and* bind-or*))
+           (cond*-convert-bind-conditional condition (macroexp-progn true-exps)
+                                           iffalse uncondit-clauses))
           ((eq pat-type 'pcase*)
            (if true-exps
                (progn
-- 
2.54.0


--=-=-=--
Acknowledgement sent to zach shaftel <zach@HIDDEN>:
New bug report received and forwarded. Copy sent to rms@HIDDEN, bug-gnu-emacs@HIDDEN. Full text available.
Report forwarded to rms@HIDDEN, bug-gnu-emacs@HIDDEN:
bug#81361; Package emacs. Full text available.
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