Re: Proposed extension of show-paren-mode: Highlight parens when point is in L or R margin.

[Alan Mackenzie <acm@muc.de>]

Hello, Stefan.

On Wed, Oct 15, 2014 at 10:43:21PM -0400, Stefan Monnier wrote:
> >             foo = /* */ bar; /* comment */
> > PPPPPPPPPPPP                PPPPPPPPPPPPPP
> >             CCCCCCCCCCCCCCCC

> I don't understand why you'd want to consider the inside of the /*
> comment */ as part of the periphery.  This increases
> ambiguity/complexity of the behavior since there might be parentheses
> inside the comment (and then there's the case of nested comments).

The parens inside the comment would still get shown as they do
currently.  I think my thinking was that some paren pair near point
should be shown "most of the time", but this would get annoying when
point is inside the core.

But yes, I've not taken nested comments into account.  Maybe it would be
better just to count whitespace (not comments) as being in the periphery.
If handling for nested comments were added, things would be beginning to
get out of hand.

How about the following model:

            foo = /* */ bar; /* comment */
PPPPPPPPPPPP                              P
            CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

?

[ ... ]

> >> This would make it clear that the behavior is unchanged when
> >> show-paren-when-point-in-periphery is nil, and also makes it clear what
> >> is the effect of setting show-paren-when-point-in-periphery to non-nil.
> > That's neat.  But it wouldn't be quite the same.  It would be a quite
> > restricted version of what I'm proposing: e.g. point in the LH periphery
> > wouldn't then trigger a paren at "end of core",

> I don't understand which case you're referring to.  Can you give an
> example of such a "point in the LH periphery; paren at end of core"?

(defface show-paren-mismatch
  '((((class color)) (:foreground "white" :background "purple"))
    (t (:inverse-video t)))
  "Face used for a mismatching paren."
  :group 'paren-showing-faces)   <-------- paren
^
|
point

> > nor even a close paren at "beginning of core" (which happens a little
> > in lisp, a lot in C).

> So you also want to highlight the matching opening paren in the case

>    <point>   }

Yes.

> ?  If so, I guess we should also do it in cases such as:

>    foo(blabla<point>);

Hmmm.   Maybe.  But this whole idea was meant just to be a simple
extension.

> > Incidentally, I think `show-paren-highlight-openparen', which is a defvar
> > really ought to be a customisable variable.

> That's probably a leftover/oversight from before defcustom existed.

I'll make it a defcustom, then.

> > Maybe `show-paren-data-function' should be, too.

> Why?  It was introduced for the benefit of smie.el, so it's typically
> set buffer-locally by major-modes, which makes it a poor fit for
> a defcustom.

OK.

So, to sum up, I'll remove comments from the definition of "periphery",
and make that variable a defcustom.  I don't think you need to see
another amended patch.

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).