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Re: rx vs sregex - a "match" to the death

From: Oliver Scholz
Subject: Re: rx vs sregex - a "match" to the death
Date: Mon, 06 Oct 2003 09:25:03 +0200
User-agent: Gnus/5.1002 (Gnus v5.10.2) Emacs/21.3.50 (windows-nt)

Martin Stone Davis <> writes:
> While I was comparing the two functions, I could not find if/how rx
> handles numbered backreferences.  It's done in sregex like this:
> ;;   (sregexq (group (or "Go" "Run"))
> ;;            ", Spot, "
> ;;            (backref 1))             =>  "\\(Go\\|Run\\), Spot, \\1"
> How do you do the same using rx?

Well, you could use (regexp "\\1"), but this is of course not
satisfying. I am not aware of any other way to use backrefs with `rx'.

However, I was not aware that you actually can use backrefs within a
regexp. I tried 

(progn (looking-at "\\w+")
       (forward-char 1)
       (re-search-forward "\\0" nil t))

But that did not lead to the result that you would expect if backrefs
are/were supported within regexps.

Could you provide an example where this is meaningful?

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