Re: [prettify-symbols-mode] Two consecutive matches don't work?

[Robert Pluim]

>>>>> On Wed, 18 May 2022 14:56:53 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> Feedback-ID: ie15541ac:Fastmail
    >> Date: Wed, 18 May 2022 11:32:07 +0200
    >> From: Joost <joostkremers@fastmail.fm>
    >> 
    >> I'm dealing with some `.xml` files that contain data which uses the
    >> sequence `<<!` as some sort of operator. Because it's XML, the
    >> LESS-THAN sign needs to be encoded as `&lt;`, yielding `&lt;&lt;!`.
    >> 
    >> So I thought this would be the ideal use case for
    >> `prettify-symbols-mode`. I added `("&lt;" . ?<)` to
    >> `prettify-symbols-alist` and activated the mode.
    >> 
    >> Unfortunately, only the first `&lt;` in each sequence is
    >> prettified. This seems to be due to the fact that the second `&lt;`
    >> is followed by the exclamation mark: if I insert a space in between,
    >> prettification works.
    >> 
    >> Is there any way to remedy this?

    Eli> prettify-symbols-mode is not general-purpose enough, its defaults are
    Eli> tailored to prettifying keywords of programming languages, not just
    Eli> any arbitrary strings of characters.

Yes, it by default does a lot of stuff based on the syntax tables of
the buffer.

    Eli> I think you will need to tailor prettify-symbols-default-compose-p or
    Eli> roll your own predicate and bind prettify-symbols-compose-predicate to
    Eli> that predicate, if you want to support such sequences.

(setq prettify-symbols-alist '(("&lt;" . "<"))
      prettify-symbols-compose-predicate
      (lambda (s e m)
        (string-match-p "&lt;" m)))

seems to do the trick.

You could even generalize it to:

(setq prettify-symbols-alist '(("&lt;" . "<"))
      prettify-symbols-compose-predicate
      (lambda (s e m)
        t))

:-)

Robert
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