Re: prettify-symbols-mode to handle "\alpha-\beta" ...

[Christopher Dimech]

We should find the best way to do this rather than a hack
that is likely to be rejected by emacs-devel.  pretty-symbols 
is a good candidate for this because it is intended for use
with general programming modes.  Texinfo has today evolved
like a programming language with its support for plain-tex
and commands for mathjax.  

Whilst texinfo.el takes care of texinfo commands, it completely
disregards the use of tex constructs and the focus on displaying
mathematical expressions within texinfo.   


---------------------
Christopher Dimech
General Administrator - Naiad Informatics - GNU Project (Geocomputation)
- Geophysical Simulation
- Geological Subsurface Mapping
- Disaster Preparedness and Mitigation
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- Free Software Advocacy


> Sent: Thursday, February 04, 2021 at 4:04 PM
> From: "Stefan Monnier" <monnier@iro.umontreal.ca>
> To: "Óscar Fuentes" <ofv@wanadoo.es>
> Cc: emacs-devel@gnu.org
> Subject: Re: prettify-symbols-mode to handle "\alpha-\beta" ...
>
> > Supporting what you want would require either changing what texinfo
> > considers a symbol or changing prettify-symbols-mode to work on
> > something else instead of symbols.
> 
> The second can be done without changing the code of
> `prettify-symbols-mode`: you want to change
> `prettify-symbols-compose-predicate` which contains the function that decides
> whether a given occurrence should be prettified or not.
> 
> E.g. the default is the function `prettify-symbols-default-compose-p`
> defined as follows:
> 
>     (defun prettify-symbols-default-compose-p (start end _match)
>       "Return true iff the symbol MATCH should be composed.
>     The symbol starts at position START and ends at position END.
>     This is the default for `prettify-symbols-compose-predicate'
>     which is suitable for most programming languages such as C or Lisp."
>       ;; Check that the chars should really be composed into a symbol.
>       (let* ((syntaxes-beg (if (memq (char-syntax (char-after start)) '(?w 
> ?_))
>                                '(?w ?_) '(?. ?\\)))
>              (syntaxes-end (if (memq (char-syntax (char-before end)) '(?w ?_))
>                                '(?w ?_) '(?. ?\\))))
>         (not (or (memq (char-syntax (or (char-before start) ?\s)) 
> syntaxes-beg)
>                  (memq (char-syntax (or (char-after end) ?\s)) syntaxes-end)
>                  (nth 8 (syntax-ppss))))))
> 
> You'd presumably want to then define your own such function which does
> pretty much the same except that it doesn't accept the syntax `_`:
> 
>     (defun texinf-prettify-symbols-compose-p (start end _match)
>       ;; We know the matches all start with a backslash and end with
>       ;; a word-element.
>       (not (or (memq (char-before start) '(?\\))
>                (memq (char-syntax (or (char-after end) ?\s)) '(?w))
>                (nth 8 (syntax-ppss)))))
> 
> 
> -- Stefan
> 
> 
>