Re: Parenthesis matching should consider the kind of parenthesis during pair-search

[Alan Mackenzie <acm@muc.de>]

Hello, Géza

On Mon, Feb 12, 2024 at 14:10:06 +0100, Herman, Géza wrote:

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

> >> What do you think, shouldn't Emacs consider the kind of parenthesis
> >> when during searching for a pair? (in other words, it should ignore
> >> all other kinds of parentheses when it searches for a pair)

> > No, I don't think that.  ;-)  A lot of the time (?most of the time),
> > we want Emacs to point out paren mismatch errors, and that
> > alternative way of scanning parens would prevent this.

> The only gain with the current way is that Emacs will point out 
> the mismatch (considering my Makefile example), if the cursor is 
> on the opening '('.  With my suggested method, it's not the 
> mismatch which would be shown, but the pair of '(' would (which is 
> actually a correct behavior in this case, the pair of '(' is 
> indeed the ')' ).

OK, I don't agree with some of the things you're saying, but why don't
you implement your idea so that we can try it out?

> All the other interactions would be the same.

That's a bold thing to say, indeed!

> If you put the cursor on the '}', Emacs would still show that it 
> is a paren without a pair, just like now (but instead of saying 
> that its "pair" is the '(', it wouldn't show anything, because '}' 
> doesn't have a pair.

What if earlier on in the file there were a

    ({)

?  Should your new way of matching find that {?  Or would the enclosing
( and ) prevent this being a match?  If so, what are the exact criteria?

> Why is it a desired thing that Emacs should show some mismatching 
> paren if the cursor is on a completely unrelated paren?

Emacs doesn't have the facilities to determine that the mismatching
paren is "completely unrelated".  It's fairly likely to be a typo.  For
example, on some keyboard layouts (including British English), ] and }
are on the same key.  It's easy to mistype } as ] and not notice right
away.  The show-paren-mode mismatch facility helps notice it sooner.

But, as I say, the best way to go from here would be to implement your
new matching scheme and then we can try it out.  I can think of some
uses for it, for example for commands like `occur' on M-s o, where a
regexp gets entered into the minibuffer.  Regexps frequently have
unmatched parens.

-- 
Alan Mackenzie (Nuremberg, Germany).