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Re: How to grok a complicated regex?


From: Tassilo Horn
Subject: Re: How to grok a complicated regex?
Date: Thu, 19 Mar 2015 09:15:54 +0100
User-agent: Gnus/5.130012 (Ma Gnus v0.12) Emacs/25.0.50 (gnu/linux)

Alan Mackenzie <address@hidden> writes:

> I wrote myself the following tool.  It's not production quality, but
> you might find it useful nonetheless.  To use it, Type
>
>      M-: (pp-regexp re-horror).
>
> It displays the regexp at the end of the *scratch* buffer, dropping
> the contents of any \(..\) construct by one line.

Interesting idea, and it helps a bit.  What would be really cool was a
transformation from regexp to rx form.  Oh, and that seems to exist
already (available from Marmalade and MELPA)!

  https://github.com/joddie/pcre2el

Example:

--8<---------------cut here---------------start------------->8---
(rxt-elisp-to-rx 
"\\`\\(?:\\\\[([]\\|\\$+\\)?\\(.*?\\)\\(?:\\\\[])]\\|\\$+\\)?\\'")
;; Evals to...
(seq bos
     (\? (or (seq "\\" (any "[" "("))
             (+ "$")))
     (submatch (*\? nonl))
     (\? (or (seq "\\" (any ")" "]"))
             (+ "$")))
     eos)
--8<---------------cut here---------------end--------------->8---

Bye,
Tassilo



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