Re: Ugly regexps

[Stefan Monnier]

>> (defun ere (re)
>>    "Convert an ERE-style regexp RE to an Emacs-style regexp."
>>    (let ((pos 0)
>>          (last 0)
>>          (chunks '()))
>>      (while (string-match "\\\\.\\|[{}()|]" re pos)
>>        (let ((beg (match-beginning 0))
>>              (end (match-end 0)))
>>          (when (subregexp-context-p re beg)
>>            (cond
>>             ;; A normal paren: add a backslash.
>>             ((= (1+ beg) end)
>>              (push (substring re last beg) chunks) (setq last beg)
>>              (push "\\" chunks))
>>             ;; A grouping paren: skip the backslash.
>>             ((memq (aref re (1+ beg)) '(?\( ?\) ?\{ ?\} ?\|))
>>              (push (substring re last beg) chunks)
>>              (setq last (1+ beg)))))
>>          (setq pos end)))
>>      (mapconcat #'identity (nreverse (cons (substring re last) chunks)) "")))
>
> See also xref--regexp-to-extended, my last attempt at RE->ERE conversion,
> though woefully lacking in tests.

Oh, thanks for the pointer.

> Its goal was to move in the other direction, but (unless I'm missing
> something about the syntax differences) this function is reversible.

Indeed it is,


        Stefan