bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

Hi,

I have this string expression in latex-mode:

$K(U_1, V_1, x_1; t_2, x_2)$

If the pointer is located on the opened "(" and I run "forward-sexp" it 
works and the
pointer goes after the closed ")".

But if, again, the pointer is located on the opened "(" and I evaluate
"(sexp-at-point)" it returns nil.

If I remove the ";" symbol from the expression it works and returns the 
sexp-at-point:

$K(U_1, V_1, x_1 t_2, x_2)$

Is it a bug?

Best regards,

Gabriele


In GNU Emacs 29.4 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
cairo version 1.16.0) of 2024-06-24 built on lcy02-amd64-050
Repository revision: 176061eb965cf945e7627ce87bb16ec5a03f8a4d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.6 LTS

Configured using:
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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Jeremy Bryant via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Gabriele Nicolardi <gabriele@medialab.sissa.it> writes:

> Hi,
>
> I have this string expression in latex-mode:
>
> $K(U_1, V_1, x_1; t_2, x_2)$
>
> If the pointer is located on the opened "(" and I run "forward-sexp"
> it works and the
> pointer goes after the closed ")".
>
> But if, again, the pointer is located on the opened "(" and I evaluate
> "(sexp-at-point)" it returns nil.
>
> If I remove the ";" symbol from the expression it works and returns
> the sexp-at-point:
>
> $K(U_1, V_1, x_1 t_2, x_2)$
>
> Is it a bug?
>
> Best regards,
>
> Gabriele
>
>
> In GNU Emacs 29.4 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
> cairo version 1.16.0) of 2024-06-24 built on lcy02-amd64-050
> Repository revision: 176061eb965cf945e7627ce87bb16ec5a03f8a4d
> Repository branch: master
> Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
> System Description: Ubuntu 20.04.6 LTS
>

> Important settings:
> value of $LANG: it_IT.UTF-8
> locale-coding-system: utf-8-unix
>
> Major mode: LaTeX

This suggests you are using the major mode from AUCTeX, rather than the
built-in latex-mode?  Is this right?

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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Il 25/06/24 23:52, Jeremy Bryant ha scritto:
>> Important settings:
>> value of $LANG: it_IT.UTF-8
>> locale-coding-system: utf-8-unix
>>
>> Major mode: LaTeX
> This suggests you are using the major mode from AUCTeX, rather than the
> built-in latex-mode?  Is this right?
No, I'm using the built-in latex-mode. AUCTeX is not installed on my 
machine.

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains "; "

[Eli Zaretskii]

> Date: Tue, 25 Jun 2024 19:53:59 +0200
> From: Gabriele Nicolardi <gabriele@medialab.sissa.it>
> 
> I have this string expression in latex-mode:
> 
> $K(U_1, V_1, x_1; t_2, x_2)$
> 
> If the pointer is located on the opened "(" and I run "forward-sexp" it 
> works and the
> pointer goes after the closed ")".
> 
> But if, again, the pointer is located on the opened "(" and I evaluate
> "(sexp-at-point)" it returns nil.
> 
> If I remove the ";" symbol from the expression it works and returns the 
> sexp-at-point:
> 
> $K(U_1, V_1, x_1 t_2, x_2)$
> 
> Is it a bug?

I don't think it's a bug.  forward-sexp moves across balanced
expressions, so it is not specific to Lisp.  By contrast,
sexp-at-point is specific to Lisp and Lisp-like syntax, and so it uses
the buffer's syntax.  Which is why ';' affects the result.

Adding Stefan in case he has comments for this.

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>> $K(U_1, V_1, x_1; t_2, x_2)$
>> 
>> If the pointer is located on the opened "(" and I run "forward-sexp" it 
>> works and the
>> pointer goes after the closed ")".
>> 
>> But if, again, the pointer is located on the opened "(" and I evaluate
>> "(sexp-at-point)" it returns nil.
>> 
>> If I remove the ";" symbol from the expression it works and returns the 
>> sexp-at-point:
>> 
>> $K(U_1, V_1, x_1 t_2, x_2)$
>> 
>> Is it a bug?
>
> I don't think it's a bug.  forward-sexp moves across balanced
> expressions, so it is not specific to Lisp.  By contrast,
> sexp-at-point is specific to Lisp and Lisp-like syntax, and so it uses
> the buffer's syntax.  Which is why ';' affects the result.
>
> Adding Stefan in case he has comments for this.

AFAICT, `sexp-at-point` correctly finds the parenthesized thingy, but it
is asked to return the Lisp object it represents rather than a string,
so it `read`s, which inevitably obeys the ELisp syntax.

IOW, I suspect you want (thing-at-point 'sexp) rather than
(sexp-at-point).


        Stefan

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

Il 26/06/24 15:46, Stefan Monnier ha scritto:
>>> $K(U_1, V_1, x_1; t_2, x_2)$
>>>
>>> If the pointer is located on the opened "(" and I run "forward-sexp" it
>>> works and the
>>> pointer goes after the closed ")".
>>>
>>> But if, again, the pointer is located on the opened "(" and I evaluate
>>> "(sexp-at-point)" it returns nil.
>>>
>>> If I remove the ";" symbol from the expression it works and returns the
>>> sexp-at-point:
>>>
>>> $K(U_1, V_1, x_1 t_2, x_2)$
>>>
>>> Is it a bug?
>> I don't think it's a bug.  forward-sexp moves across balanced
>> expressions, so it is not specific to Lisp.  By contrast,
>> sexp-at-point is specific to Lisp and Lisp-like syntax, and so it uses
>> the buffer's syntax.  Which is why ';' affects the result.
>>
>> Adding Stefan in case he has comments for this.
> AFAICT, `sexp-at-point` correctly finds the parenthesized thingy, but it
> is asked to return the Lisp object it represents rather than a string,
> so it `read`s, which inevitably obeys the ELisp syntax.
>
> IOW, I suspect you want (thing-at-point 'sexp) rather than
> (sexp-at-point).
>
>
>          Stefan
I need to test if a parenthesis in LaTeX (latex-mode) starts a balanced 
expression.

sexp-at-point: Return the sexp at point, or nil if none is found.

This is not possible with (thing-at-point 'sexp) because it does no return nil in the case, e.g.:

$K(U_1, V_1, x_1 t_2, x_2$

Gabriele

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

 From the previous responses, I have understood that the sexp-at-point 
function is not suitable for my purpose.
However, I suggest updating the documentation because the explanations 
you provided are not trivial, and the similarity in names with other 
functions (forward-sexp, etc.) creates misunderstandings.

Lastly, I would like to point out an issue on Stack Exchange:

https://emacs.stackexchange.com/q/81603/15606

where I asked for help with a function that fits my needs.

Thank you!

Gabriele

Il 26/06/24 15:46, Stefan Monnier ha scritto:
>>> $K(U_1, V_1, x_1; t_2, x_2)$
>>>
>>> If the pointer is located on the opened "(" and I run "forward-sexp" it
>>> works and the
>>> pointer goes after the closed ")".
>>>
>>> But if, again, the pointer is located on the opened "(" and I evaluate
>>> "(sexp-at-point)" it returns nil.
>>>
>>> If I remove the ";" symbol from the expression it works and returns the
>>> sexp-at-point:
>>>
>>> $K(U_1, V_1, x_1 t_2, x_2)$
>>>
>>> Is it a bug?
>> I don't think it's a bug.  forward-sexp moves across balanced
>> expressions, so it is not specific to Lisp.  By contrast,
>> sexp-at-point is specific to Lisp and Lisp-like syntax, and so it uses
>> the buffer's syntax.  Which is why ';' affects the result.
>>
>> Adding Stefan in case he has comments for this.
> AFAICT, `sexp-at-point` correctly finds the parenthesized thingy, but it
> is asked to return the Lisp object it represents rather than a string,
> so it `read`s, which inevitably obeys the ELisp syntax.
>
> IOW, I suspect you want (thing-at-point 'sexp) rather than
> (sexp-at-point).
>
>
>          Stefan
>

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> I need to test if a parenthesis in LaTeX (latex-mode) starts
> a balanced expression.

You mentioned `forward-sexp` which should do the trick, so what made you
try `sexp-at-point`?

> sexp-at-point: Return the sexp at point, or nil if none is found.
>
> This is not possible with (thing-at-point 'sexp) because it does no return nil in the case, e.g.:
>
> $K(U_1, V_1, x_1; t_2, x_2$

The "<foo>-at-point" functions (by the very nature of the concept of
"foo at point") are DWIMish functions.
They're usually not appropriate for use from ELisp code unless that
ELisp code itself wants to be DWIMish.


        Stefan

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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Il 26/06/24 22:11, Stefan Monnier ha scritto:
>> I need to test if a parenthesis in LaTeX (latex-mode) starts
>> a balanced expression.
> You mentioned `forward-sexp` which should do the trick, so what made you
> try `sexp-at-point`?
Because `forward-sexp` does not return nil if the parenthesis does not 
start a balanced expression.

Gabriele

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

>>> I need to test if a parenthesis in LaTeX (latex-mode) starts
>>> a balanced expression.
>> You mentioned `forward-sexp` which should do the trick, so what made you
>> try `sexp-at-point`?
> Because `forward-sexp` does not return nil if the parenthesis does not start
> a balanced expression.

There is no function that does just what you want; you need to make them
do what you want.  E.g.

    (save-excursion
      (condition-case nil
          (progn (forward-sexp 1) t)
        (scan-error nil)))

Note that "test if a parenthesis in LaTeX (latex-mode) starts a balanced
expression" is a kind of weird request, because it will only return nil
if there's a missing close-paren but not if there are too many
close-parens, i.e. it only detects one half of the imbalances.


        Stefan

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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Il 26/06/24 22:25, Stefan Monnier ha scritto:
> Note that "test if a parenthesis in LaTeX (latex-mode) starts a balanced
> expression" is a kind of weird request, because it will only return nil
> if there's a missing close-paren but not if there are too many
> close-parens, i.e. it only detects one half of the imbalances.
>
>
>          Stefan
For my purposes it is enough.

I need to write a function to interactively resize mathematical 
parentheses based on their content, such as "\left( ... \right)". So 
far, I have successfully used `sexp-at-point`, but this function does 
not recognize balanced expressions that contain ";" and only works with 
"(" and "[" but not with < etc..

The `forward-sexp` function does not necessarily give an error if the 
parenthesis does not start a balanced expression. E.g.

$( x + y ]$

here "(" does not start a balanced expression but `forward-sexp` does 
not return an error.

Gabriele

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> The `forward-sexp` function does not necessarily give an error if the
> parenthesis does not start a balanced expression. E.g.
>
> $( x + y ]$

Yup.  Most of the functions that are meant to be used to parse code
while it's being edited don't check validity.  Basically they try to
find "what is the meaning of this text" rather than "does this text have
meaning".  That's on purpose, because it makes them more usable even
when the text is not 100% valid.

`read` (which parses an ELisp s-exp and is used in `sexp-at-point` to
try and turn the string "( x + y ]" (found by `forward-sexp) into a Lisp
value) is one of the rare exceptions because that one is not meant to
parse text as you type it but rather to parse text in order to process
it (typically, to execute it).

But it obeys the ELisp syntax rather than the LaTeX syntax.

> here "(" does not start a balanced expression but `forward-sexp` does not
> return an error.

I don't think there's code in Emacs which does what you want, so if you
really need to check proper pairing you're going to have to write the code.


        Stefan

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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> I don't think there's code in Emacs which does what you want, so if you
> really need to check proper pairing you're going to have to write the code.
>
>
>          Stefan
Thank you very much!

Gabriele

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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> I don't think there's code in Emacs which does what you want, so if you
> really need to check proper pairing you're going to have to write the code.
>
>
>          Stefan
FYI. NickD offers me this code 
https://emacs.stackexchange.com/a/81604/15606:

|(defun ndk/paren-match-p () (let ((mismatch (nth 4 
(show-paren--default)))) (not mismatch))) It seems working. Gabriele |

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> |(defun ndk/paren-match-p () (let ((mismatch (nth 4 (show-paren--default))))
>  (not mismatch))) It seems working. Gabriele |

AFAIK It only checks the outside pair of parens.
E.g. it won't detect the problem in

    ((a + b])


- Stefan

bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Gabriele Nicolardi]

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>> |(defun ndk/paren-match-p () (let ((mismatch (nth 4 (show-paren--default))))
>>   (not mismatch))) It seems working. Gabriele |
> AFAIK It only checks the outside pair of parens.
> E.g. it won't detect the problem in
>
>      ((a + b])
>
>
> - Stefan
it is good for me because it cover the case, e.g.:

B=((1,3)∪(2,5])

Gabriele

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bug#71777: 29.4; sexp-at-point in latex-mode when sexp contains ";"

[Eli Zaretskii]

> Date: Thu, 27 Jun 2024 08:01:13 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>, 71777@debbugs.gnu.org
> From: Gabriele Nicolardi <gabriele@medialab.sissa.it>
> 
> it is good for me because it cover the case, e.g.:
> 
> B=((1,3)∪(2,5])

Thanks, I've now made clear in the doc string that sexp-at-point is
for returning Lisp objects, and I'm therefore closing this bug.