GNU bug report logs - #22765
Missing interfaces for syntax of characters in buffers.

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

From: Alan Mackenzie <acm <at> muc.de>
To: bug-gnu-emacs <at> gnu.org
Subject: Missing interfaces for syntax of characters in buffers.
Date: Mon, 22 Feb 2016 11:12:12 +0000

Hello, Emacs.

In all versions of Emacs to date, we are missing an interface to return
the syntax of a character in a buffer in a "nice" form.  By a "nice"
form, I mean the characters ?\ , ?., ?w, ?\(, ?\), etc., which programs
should be able to use.

We have `char-syntax', but that takes no account of syntax-table text
properties which might be on a buffer position, and so shouldn't really
be used any more in buffers.  There are still around 160 uses of
`char-syntax' in our sources.

We have `syntax-after', but this returns a raw syntax descriptor (like
(4 . 41)), and we have no means of extracting ?\( from this.

I propose adding the two functions `syntax-class-to-char' which would
convert 4 to ?\(, and `char-syntax-after', which would return ?\(
directly, given a buffer position with such a character under it.

This would greatly aid in the conversion of these old `char-syntax'
calls.

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #8 received at 22765 <at> debbugs.gnu.org (full text, mbox):

From: npostavs <at> users.sourceforge.net
To: Alan Mackenzie <acm <at> muc.de>
Cc: 22765 <at> debbugs.gnu.org
Subject: Re: bug#22765: Missing interfaces for syntax of characters in buffers.
Date: Wed, 05 Apr 2017 20:43:44 -0400

Alan Mackenzie <acm <at> muc.de> writes:

> We have `char-syntax', but that takes no account of syntax-table text
> properties which might be on a buffer position, and so shouldn't really
> be used any more in buffers.  There are still around 160 uses of
> `char-syntax' in our sources.

I'm afraid I added another one in my recent `indent-sexp' changes.  We
should at least add a warning about this to the docstring.

> We have `syntax-after', but this returns a raw syntax descriptor (like
> (4 . 41)), and we have no means of extracting ?\( from this.
>
> I propose adding the two functions `syntax-class-to-char' which would
> convert 4 to ?\(, and `char-syntax-after', which would return ?\(
> directly, given a buffer position with such a character under it.

We do have string-to-syntax which can be used to convert in the other
direction, although code using it would end up a bit more verbose.

    (eq (char-syntax-after POS) ?\()
vs
    (eq (syntax-class (syntax-after POS)) (car (string-to-syntax "(")))

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