Re: modern regexes in emacs

["Mattias Engdegård" <mattiase@acm.org>]

17 feb. 2019 kl. 21.47 skrev Stefan Monnier <monnier@iro.umontreal.ca>:
> 
> Other than isearch, most other commands should (ideally) read their
> regexps interactively with `read-regexp`, so it should be easy for
> a third party package to advise `read-regexp` so it accepts the PCRE
> syntax (or the RX syntax, ...) and then converts it to Emacs's
> own syntax.  Shouldn't break any package at all.

Like this?

(defun backslash-mod-regexp (re)
  "Invert the backslash requirements for |(){} in RE."
  (with-temp-buffer
    (insert re)
    (goto-char (point-min))
    (while (re-search-forward
	    (rx (or (seq "["
			 (opt "^")
			 (opt "]")
			 (* (not (any "]")))
			 "]")
		    (seq "\\" (or (group (any "|(){}"))
				  (seq (any "sScC") anything)
				  anything))
		    (group (any "|(){}"))))
	    nil t)
      (cond
       ((match-beginning 1) (replace-match "\\1"))
       ((match-beginning 2) (replace-match "\\\\\\&"))))
    (buffer-string)))

(defadvice read-regexp (after read-regexp-backslash-mod last activate)
  (when (stringp ad-return-value)
    (setq ad-return-value (backslash-mod-regexp ad-return-value))))

Of course it won't help with commands that display previously entered regexps, which users naturally want to see in the form entered, not converted. However, that should not matter functionally.