Re: Lua filter to change macro for figure caption md -> latex

[Julien Dutant <julien.dutant-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Lua filters only change Pandoc's AST representation of your document, i.e. 
before it is then converted to LaTeX. A Raw block filter will not act on 
Pandoc's LaTeX output, but only on Raw LaTeX blocks that are in the 
markdown itself.

A Pandoc solution would be to write a custom Lua *writer* 
<https://pandoc.org/custom-writers.html>. The writer would use pandoc.write 
to generate Pandoc's own LaTeX output (body only) and modify it with 
regular expressions or Lua patterns. To replace just a command name this is 
fairly easy, though longer than the third solution below.

A LaTeX solution is to redefine \caption as \sidecaption:
\renewcommand{\caption}{\sidecaption} 

You can keep this enclosed in groups ({...}) to ensure that the 
redefinition only applies locally.

A hybrid Pandoc/LaTeX solution is a Lua filter that insert LaTeX code to 
redefine \caption around figures:

``` lua
if FORMAT:match 'latex' then
    function Figure (elem) return { 
        pandoc.RawBlock('latex','{\\renewcommand{\\caption}{\\subcaption}'
), 
         elem, 
         pandoc.RawBlock('latex','}') 
       } 
   end 
end

```

This replaces any 'Figure' block element by a list (succession) of three 
raw LaTeX blocks. The output should look like:
{\renewcommand{\caption}{\subcaption} 
... Pandoc's LaTeX for the figure ... 
} 

Reposted from 
https://stackoverflow.com/questions/77504584/pandoc-md-latex-write-lua-filter-to-change-latex-macro-used-for-caption/77607636#77607636

On Monday, November 20, 2023 at 7:06:57 AM UTC+11 lukeflo wrote:

> Hi everybody,
>
> I have written a custom latex `.cls' file to establish a typesetting
> workflow for the scientific journals of my research institute. The texts
> should be written in Markdown and then be processed with `pandoc' to
> LaTeX.
>
> I already have an elaborated pandoc template to produce the LaTeX
> preambel etc. So far its working great.
>
> But for the figures I need the caption from the Markdown file to be set
> with `\sidecaption' instead of `\caption' in LaTeX, as well as with an
> optional argument (short-caption) for the image attribution in the list
> of figures.
>
> To get the latter working I use the following template from a GitHub
> discussion in the [pandoc repo]:
>
> ┌────
> │ PANDOC_VERSION:must_be_at_least '3.1'
> │
> │ if FORMAT:match 'latex' then
> │   function Figure(f)
> │     local short = f.content[1].content[1].attributes['short-caption']
> │     if short and not f.caption.short then
> │       f.caption.short = pandoc.Inlines(short)
> │     end
> │     return f
> │   end
> │ end
> └────
>
> That works without any flaws.
>
> But now I need to figure out how to change the LaTeX macro used for the
> caption. The older [approach of pre pandoc version 3.0 posted] by tarleb
> is really intuitive and I could have easily adapted it to my needs. But
> since pandoc 3.0 there is the new [/complex figures/] approach and, so
> far, I couldn't figure out how to change the LaTeX macro used for the
> captions with this new behaviour.
>
> I tried something like that (Adapted from [here]:
>
> ┌────
> │ if FORMAT:match 'latex' then
> │   function RawBlock (raw)
> │     local caption = raw.text:match('\\caption')
> │     if caption then
> │        raw:gsub('\\caption', '\\sidecaption')
> │     end
> │     return raw
> │   end
> │ end
> └────
>
> But nothing happened.
>
> The main challenge for me are my more-or-less non-existing lua skills. I
> just never had to use it for my daily tasks. I thought about using `awk'
> or `sed' to edit the `.tex' file itself using a regex-substitution, but
> that should remain an absolute stopgap, since it makes the whole
> workflow less portable.
>
> Thus, I'm hoping for a hint/a solution in form of a pandoc-lua script
> which 1. helps me to achieve the goal, and 2. improve my understanding
> of lua and the /complex figures/ approach for similar future tasks.
>
> I appreciate any tipp!
>
> Best,
> Lukeflo
>
> This question is also posted on StackOverFlow: 
> https://stackoverflow.com/q/77504584/19647155
>
> [pandoc repo]
> <https://github.com/jgm/pandoc/issues/7915#issuecomment-1427113349>
>
> [approach of pre pandoc version 3.0 posted]
> <https://github.com/jgm/pandoc/issues/7915#issuecomment-1039370851>
>
> [/complex figures/] <https://github.com/jgm/pandoc/releases?page=2>
>
> [here] <https://stackoverflow.com/a/71296595/19647155>
>

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