On Thursday, April 15, 2021 at 4:20:32 PM UTC+2 Angel Joaniquet wrote:

The lua split function is this

```lua
function split(str,pat)
   local tbl = {}
   str:gsub(pat, function(x) tbl[#tbl+1]=x end)
   return tbl
end
```

El jueves, 15 de abril de 2021 a las 16:08:23 UTC+2, Angel Joaniquet escribió:

I'm trying to make a filter to transform some features of org-mode to GitLab-markdown (not supported by Pandoc out of the box), in particular, the math blocks.

The filter should work when transforming to `markdown`, but instead of giving the markdown format for the math blocks (enclosed by `$$...$$`), it should write the blocks as

    ``` math
    a + b = c
    ```

The preces I have now is

In org-mode, the math blocks are simply the latex code:

```
\begin{equation}
a + b = c
\end{equation}
```

this is parsed as a pandoc AST `RawBlock` with format `latex`. I then remove the first (`\begin{equation}`) an last line (`\end{equation}`), and construct a pandoc `CodeBlock` with atrributes `{"math"}`, so the `CodeBlock` object displays in AST as

```
CodeBlock ("",["math"],[]) "a + b = c\n"
```

and then I let Pandoc create the markdown document, and the written result is

    ``` {.math}
    a + b = c
    ```

**The question:**
I want the bare `math`, not `{.math}` written, without the use of CLI options.

I am aware that this can be done setting the Writer extension `fenced_code_attributes` to false (eg. `$pandoc -w markdown-fenced_code_attributes ...`), but I would much prefer this done inside the filter.

Or is it possible to set the extensions inside the filter?

Here is my atempted lua-filter:

``` lua
function RawBlock(rb)
   if rb.format == "latex" then
      local text = rb.text
      split_text = split(text, "[^\n]*")
      if split_text[1] == '\\begin{equation}' and split_text[#split_text-1] == '\\end{equation}' then
         table.remove(split_text, #split_text-1)
         table.remove(split_text, 1)
         text = table.concat(split_text, "\n")
         local cb = pandoc.CodeBlock()
         cb.attr = {"",{"math"}}
         cb.text = text
         return cb
      end
   end
end
```

Kind regards,

Angel