Simple filter to run a text string through an R function

[harrelfe]

Description

I would like to have a simple filter that allows me to process text strings with a user-specified function. For example I'd like

This is {=xx a string of text that is arbitrarily long but is one line}.

to result in

`r xx("a string of text that is arbitrarily long but is one line")`.

Is this possible and can anyone provide a simple how-to? The = delimiter before the function name can be anything that doesn't conflict with existing filters.

[mcanouil]

Could you explain a bit more your use case and/or your goal with such filter?
I don't understand what this adds to the inline R call, i.e., `{r} f(arg)` (it's not shorter, nor simpler and it would hide the computing language used).

It feels more complicated and I am not even sure you can do that because, this would require the computation to happen after this filter.

[harrelfe]

Thanks for responding. I'd like to use simple functions to process a number of simple markups, with R handling logic for the output format of html vs docx. The goal is to not use all the quote marks needed by a regular inline call, e.g., the call is not as simple as you wrote but is instead r f("arg"). The double quotes get in the way of the visual flow, and it would be good to not have to use backticks. I know this is minor cosmetics but I'd like to use this if it's not hard to implement. I can do a lot of markups with divs but I'm needing multiple different markups within a paragraph.

Occasionally I'll also use a function to send output to a different destination than the current report flow.

[mcanouil]

See:

• https://pandoc.org/lua-filters.html
• https://quarto.org/docs/extensions/lua.html
• https://quarto.org/docs/prerelease/1.4/lua_changes.html#more-precise-targeting-of-ast-processing-phases
• https://quarto.org/docs/extensions/lua-api.html

If feels way more complicated that it needs to be and only for a "quotes issue".
See below an example, showing that it won't work as the earlier is pre AST not pre-computations (I might be missing something, but don't think so).

---
title: "Quarto Playground"
format: html
filters:
  - at: pre-ast
    path: filter.lua
engine: knitr
---

This is a playground for Quarto.

This is `a string of text that is arbitrarily long but is one line`{=xx}.

`{r} 1+1`

function RawInline(raw)
  if raw.format == "xx" then
    return pandoc.Code("{r} identity('" .. raw.text .. "')")
  end
end

[harrelfe]

Thanks very much! I defer to your expertise. I didn't realize the computation order issue.

[cscheid]

Yes, Lua filters run after the execution engines. We have (long-term) plans to add a pre-engine Pandoc pass, but that will not happen for at least a year.