create a filter using a regular expression to highlight duplicate
words in a line
reddit / emacs

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cute-pengui · 2022-04-30 09:34

I would like to create a filter using a regular expression to
highlight duplicate words in a line. I use the highlight package,
which allows me to use regex to highlight certain words. Any ideas of
what regex I could use for this purpose?

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jsled · 2022-04-30 10:55

Classical regular expressions are not expressive enough to do this …
they're not "stateful" in the way you need.

You need "lookaround", which is in the class of "extended regexp";
emacs does not support it natively.

If you have a specific, enumerated wordlist, you could construct a
regex that uses lookaround to match each word separately … and as you
can generally refer to existing-matched groups, something like…

    (foo|bar|baz|quux|…).+(?=\1)


If you have an arbitrary word-list, you could do something like …

    ([a-zA-Z]{3,6}).*(?=\1)

But that's going to match all sorts of silly things.

You're probably looking to say something more like…

    \b([a-ZA-Z]+)\b.+(?=\1)

… to match any "word-boundry"-delimited sequence of characters that
shows up later in the string.

Note at the bottom of [emacswiki.org/[…]/RegularExpression](https://ww
w.emacswiki.org/emacs/RegularExpression) that with python available,
you can use [visual-regexp-steroids](https://github.com/benma/visual-
regexp-steroids.el/) to get access to sufficiently-expressive regexp.

It's not clear to me if the python regexp lib can be used by
highlight, tho.

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cute-pengui · 2022-04-30 13:14

Thank you so much for your detailed answer. I am going to test this
solution and will revert to you.

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brwendel · 2022-04-30 20:13

https://github.com/ioah86/repetition\_error\_finder

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cute-pengui · 2022-05-02 06:51

Thanks to your direction, I got it to work. Many thanks,