Re: modern regexes in emacs

[Philippe Vaucher <philippe.vaucher@gmail.com>]

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>
> > Would this even be possible? I can imagine a whole lot of packages
> breaking if the regexp syntax changed, and changing it just for the user
> input in interactive functions looks a bit sketchy.
>
> We could just add a special tag at the beginning of a regexp to indicate
> that it's a pcre regexp; something like this maybe? (re-search-forward
> "\\(?pcre:\\)…[pcre regexp goes here]…").  This form is currently a syntax
> error, so there would be no ambiguity, and we could define a (pcre …) macro
> so that you could write (re-search-forward (pcre "…[pcre regexp goes
> here]…")) instead.  Alternatively, we could use an explicit tag, something
> like (re-search-forward (cons 'pcre "…[pcre regexp goes here]…")).
>
> For interactive functions, I imagine you'd have a defcustom with a
> preferred regexp dialect.
>

I like where this is going, that and Eli's suggestion of a special text
property we have plenty of ways to implement it where it'd play nice with
the existing code.

So far 3 proposals:

   - Regexps are always strings, with "\\(?pcre:\\)" as part of the regexp
      - when the string is displayed you need to scan the beginning to see
      it is a PCRE regex
      - no separation between the regexp and it's kind
   - Regexps are strings (emacs regexps) or conses with their kind as
   symbol with the first argument
      - when the argument is displayed you see immediatly wether it's an
      emacs regexp or one using another engine
      - the regexp is clearly separated from it's kind, probably faciliting
      convertions
      - seems more "open", in the sense we can easily imagine new types
      ('emacs, 'pcre', 'rx, 'sed, 'vim-verymagic, etc)
   - Special text property on the string
      - Not immediatly visible that it is a PCRE regexp
      - Harder to manipulate?

Given this I'm in favor of the 2nd option, but maybe I missed some points.

Philippe

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