lukeflo schrieb am Montag, 11. Dezember 2023 um 11:33:21 UTC+1:

So far, I took the markdwon writer example from the pandoc docs to try out the general function of writers. It works and I think that I understand the general usage.

But especially figures (in latex writer and presuambley in general) are relativley complex. Here are two things I tried out so far but always got an error:

``` lua
function Writer (doc, opts)
local filter = {
function Figure (caption, image, attr)
local figcap = '\sidecaption{' .. caption .. '}'
return '\\begin{figure}\n' .. image .. '\n' .. figcap .. '\n' '\\end{figure}\n'
end
}
return pandoc.write(doc:walk(filter), 'latex', opts)
end
```
If I run this writer with my custom template from the CLI using pandoc --template=../custom.template -t test-writer.lua ast-test.txt -o ast-test.tex I get Error running Lua:
test-writer.lua:27: '(' expected near 'Figure'.

Furthermore, I tried running the following code just to understand how those writer work. Here I just wanted to replace {figure} with the starred version {figure*} (not sidecaption):

``` lua
function Writer (doc, opts)
local filter = {
Figure = function (fig)
local tester = '\\begin{figure*}\n' .. fig.content[1].caption[1].attributes[1] .. '\\end{figure*}\n'
return pandoc.RawBlock('latex', tester)
end
}
return pandoc.write(doc:walk(filter), 'latex', opts)
end
```
But also got an error:

Error running Lua:
test-writer.lua:28: attempt to index a nil value (field 'caption')
stack traceback:
[C]: in ?
[C]: in method 'walk'
test-writer.lua:32: in function 'Writer'
stack traceback:
test-writer.lua:32: in function 'Writer'

I'm aware that I might be missing something very basic and maybe even very simple. But I'm kind of getting lost a little bit inside all functions, modules etc. as well as the general framework of such writers.

Thus, any help explaining my errors and maybe suggesting some better code is very appreciated!

The test file in both cases is very simple:

``` markdown
---
title: A title
---

# Headline

Some text

![caption to an image](counter_plot_new_periods.png)
```

Thanks in advance!
lukeflo schrieb am Freitag, 8. Dezember 2023 um 08:35:48 UTC+1:
Hello Julien,

thanks for the reply. Unfortunatley, as mentioned in the stackoverflow post, your suggested LaTeX code won't work.

The \caption macro is very complex in the backend and cannot be copied on the fly via \let, \NewCommandCopy or something similar. Even after doing so with e.g. \NewCommandCopy{\oldcaption}{\caption} and then setting \RenewDocumentCommand{\caption}{o m}{\sidecaption[#1]{#2}} nothing changes and the definition of \caption, checked with \meaning or something similar, stays the same as before (even \DeclareDocumentCommand doesn't work).

In the end, it might be possible to somehow change the \caption macro itself. But the effort might not be worth the result (and its more of a question for TeX.SE).

Using a custom writer for building Latex figures and replace the \caption string inside would be a great solution. I read through the writer manual, but didn't really understand how the AST works and which values have to be used in such a writer. Furthermore, I'm using a a custom Latex template for exporting (based on the default.template.latex) which has to be integrated with such a writer.
Therefore, I really woud appreciate a Lua framework to understand which functions have to be edited etc. to accomplish the substitution.
Best

Julien Dutant schrieb am Dienstag, 5. Dezember 2023 um 17:09:19 UTC+1:

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. 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>