Can we add a delete-match function to subr(-x).el?

Can we add a delete-match function to subr(-x).el?

[Paul W. Rankin]

Hello Emacizens,

I frequently forget that Emacs doesn't include a delete-match function
to be called after (re-)search-forward or the like.

Can we add something like the following to subr(-x).el?

    (defun delete-match (&optional subexp)
      "Delete text matched by last search.

    Optional argument SUBEXP specifies the subexpression to delete,
    or delete the entire match."
      (when (consp (match-data))
        (unless group (setq subexp 0))
        (delete-region (match-beginning subexp) (match-end subexp))))

Re: Can we add a delete-match function to subr(-x).el?

[Stefan Kangas]

Paul W. Rankin <hello@paulwrankin.com> writes:

> I frequently forget that Emacs doesn't include a delete-match function
> to be called after (re-)search-forward or the like.
>
> Can we add something like the following to subr(-x).el?
>
>     (defun delete-match (&optional subexp)
>       "Delete text matched by last search.
>
>     Optional argument SUBEXP specifies the subexpression to delete,
>     or delete the entire match."
>       (when (consp (match-data))
>         (unless group (setq subexp 0))
>         (delete-region (match-beginning subexp) (match-end subexp))))

I think adding that would be convenient.

You have a typo in the code btw, should say:
    (unless subexp (setq subexp 0))

Best regards,
Stefan Kangas

Re: Can we add a delete-match function to subr(-x).el?

[Paul W. Rankin]

On Sat, Jan 25 2020, Stefan Kangas wrote:
>
> You have a typo in the code btw, should say:
>     (unless subexp (setq subexp 0))

Whoops, thanks! I'd been using this in my init for a while with "group"
and too quickly made the change for Emaconsistency.

    (defun delete-match (&optional subexp)
      "Delete text matched by last search.

    Optional argument SUBEXP specifies the subexpression to delete,
    or delete the entire match."
      (when (consp (match-data))
        (unless subexp (setq subexp 0))
        (delete-region (match-beginning subexp) (match-end subexp))))

Re: Can we add a delete-match function to subr(-x).el?

[Stefan Monnier]

>       (when (consp (match-data))

This allocates N cons cells just to test if there's something and in
practice there's basically *always* something (the match data keeps
info about the last successful match, so even if your last match was
a failure, `match-data` won't be nil]).


        Stefan

Re: Can we add a delete-match function to subr(-x).el?

[Paul W. Rankin]

On Sun, Jan 26 2020, Stefan Monnier wrote:
>>       (when (consp (match-data))
>
> This allocates N cons cells just to test if there's something and in
> practice there's basically *always* something (the match data keeps
> info about the last successful match, so even if your last match was
> a failure, `match-data` won't be nil]).

I figured this was a waste, just wanted it to look more thorough.

Would this be better as a macro?

    (defmacro delete-match (&optional subexp)
      "Delete text matched by last search.

    Optional argument SUBEXP specifies the subexpression to delete,
    or delete the entire match."
      (list 'unless subexp (list 'setq subexp 0))
      (list 'delete-region (list 'match-beginning subexp)
                           (list 'match-end subexp)))

I like this because of this:

    (macroexpand-all
     '(while (re-search-forward "foo\\(ba[rz]\\)" nil t)
        (delete-match 1)))

    => (while (re-search-forward "foo\\(ba[rz]\\)" nil t)
         (delete-region (match-beginning 1) (match-end 1)))