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bug#24982: 24.5; way to let Elisp reader ignore unreadable #(...) constr
From: |
Drew Adams |
Subject: |
bug#24982: 24.5; way to let Elisp reader ignore unreadable #(...) constructs |
Date: |
Sat, 22 Aug 2020 15:44:02 -0700 (PDT) |
You bring up a few things. I'll comment only about
commenting. ;-)
> I couldn't quite remember whether the Common Lisp #| |# was balanced,
> but it is, which is nice. That is, you can write
> #| foo #| bar |# zot |#
> and the first |# doesn't end the first #|.
Yes, CL block commenting is fully nestable and unnestable.
(IMO, that's really the point/advantage of block commenting.)
> I'm not an expert on the Emacs Lisp reader, but poking at it at bit, it
> seems like adding support for #| |# should be trivial: It's just a new
> comment syntax, really, so we just have to count #|'s and discard the
> input.
Possibly; dunno.
[Aside: I think it would be great if Elisp had reader
macros - give Lisp programs control over the Lisp reader.]
> So ... What's the use case? Well, I think it's handy
> when developing. If I'm in the middle of a function
> (foo)
> (bar)
> (and-here-i'm-adding-some-new-stuff-that's-not-finished
> ...
> )
> (zot)
>
> and I'm testing stuff, and I decide to take out the stuff I'm
> writing... Emacs doesn't really handle that well. I usually end up
> deleting the sexp, and hoping that the kill ring is big enough to hold
> it until I need it again, or slapping a (when nil ...) around it, which
> is unsatisfactory, because that changes the indentation.
>
> Just being able to do:
> (foo)
> (bar)
> #|
> (and-here-i'm-adding-some-new-stuff-that's-not-finished
> ...
> )
> |#
> (zot)
>
> would be nice. And then the stuff I'm working on doesn't even have to
> be syntactically correct.
Yes. Well, we do have such a feature, but we don't have
it by just inserting paired delimiters.
We have it with `comment-region' (and similar). How so?
Plain `C-u' UNcomments/unnests a given comment level.
One difference, besides the paired-delimiter one (but
which follows from it), is that you can't do it with
the same effect in-line.
Another is that because a single `;' comments to eol,
syntactically there's no essential difference among
`;', `;;', `;;;', etc. And yet the commenting and
UNcommenting of `comment-region' give you the
additional control of how many `;' to work with.
E.g., you can "uncomment" by N `;', which may uncomment
some code and leave other code commented (which had M>N
`;'). But that's also what makes `comment-region' and
its `C-u' give you block-commenting behavior.
That's how I use `comment-region' - for block commenting
and uncommenting - unnesting a block of commented code.
And it's why I use `M-;' (`comment-dwim') ONLY for a
comment after a line of code. I don't use it to comment
the region as a block comment. Its behavior when the
region consists only of comments is different from its
region behavior otherwise. And I don't want that.
___
Actually, instead of `comment-region' for block commenting
I use this, which is the same except it comments/uncomments
whole lines.
(defun comment-region-lines (beg end &optional arg)
(interactive "*r\nP")
(when (> beg end) (setq beg (prog1 end (setq end beg))))
(let ((bol (save-excursion
(goto-char beg)
(line-beginning-position)))
(eol (save-excursion
(goto-char end)
(if (bolp) (point) (line-end-position)))))
(comment-region bol eol arg)))