Re: regexp repacement, how to present replacement to user?

[Paul Pogonyshev <pogonyshev@gmx.net>]

Juri Linkov wrote:
> >>      (while (re-search-forward from nil t)
> >>         (if y-or-n-p (format "Replace %s with %s "
> >>                        (match-string 0)
> >>                           (save-match-data
> >>                             (replace-match to nil nil (match-string 0)
> >>                              (prog1 nil
> >>                                (set-match-data
> >>                                  (mapcar
> >>                                    (lambda(x)(if (numberp x)
> >>                                                    (- x (match-beginning 0))
> >>                                                    x)))
> >>                                  (match-data t)))
> >
> > Thanks, but shouldn't this be a function somewhere?  I mean, it's
> > not like random peope are going to easily write such code.
> 
> `query-replace-regexp' already highlights the text matched by
> `from-regexp' in the source buffer, so the user can see the text to
> replace.  And the result of the replacement is also displayed in the
> prompt in the expanded form, so the user sees the resulting string
> before replacing it in the buffer.
> 
> The only thing I don't understand why the result of evaluating \,
> expressions is displayed in the prompt, but the result of back references
> is not.  I mean why, for instance,
> 
> C-M-% \(a\|b\) RET \,\1  \1 RET
> 
> displays
> 
> Query replacing \(a\|b\) with a \1:
> 
> but not
> 
> Query replacing \(a\|b\) with a a:

That is exactly what I'm asking for.  How to present user with expanded
string, without those \N.

In my case I want to scan a buffer for like 20 predefined regexps with
as well predefined replacements, meant only to somehow "standardize"
text.  User is not expected to edit replacement at all, he is expected
only to decide whether to replace, or to skip this case completely (e.g.
because it is a false match, regexps cannot cover all cases in a real
human-language text).

So, I want something like this:

	Replace 12,345.67 with 12 345,67 (Russian number format)?

The user doesn't need to see regexp or its replacement with back-
references.  He should see the text and proposed replacement and just
decide if it is OK, or not.  He is not interested how this particular
occurence was found, with a regexp or not, much less with which
regexp in particular.

> > Besides, what if Emacs regexps are slightly improved with more features,
> > like named groups or whatnot?
> 
> Recently Stefan improved Emacs regexps with numbered groups where a number
> can be explicitly assigned to a regexp group.

That's why I think this (replacement expansion with back-references) must
be a function inside Emacs and not written in a package.  For instance,
code (outside Emacs) written before wouldn't know about this enhancement
by Stefan.  Code written now cannot know in advance about possible future
enhancement.  But if one uses a Emacs function, he can expect that if his
code runs in e.g. Emacs 30, standard function will handle whatever regexp
syntax might evolve to by Emacs 30.

Paul