bookdown-equations, Convert LaTeX equation labels to bookdown compatible labels

The filter modifies the internal document representation to bookdown specified labelling/numbering system. Hence it will work with documentation formats using bookdown.

Plain pandoc

License

This pandoc Lua filter is published under the MIT license, see file LICENSE for details.

Example

input.tex

\documentclass[a4paper,12pt]{article} % The document class with options
\usepackage[T1]{fontenc}
\author{Abhi-1U}
\title{Using bookdown equations Lua filter}
% A comment in the preamble
\begin{document}
\begin{equation}\label{eq:emc.2}
    e = m c^2
\end{equation}
This is a new equation \ref{eq:emc.2}
\end{document}

output.md

---
author:
- Abhi-1U
title: Using bookdown equations Lua filter
---

$$\label{eq:emc.2}
    e = m c^2 (\#eq:emc-2)$$ This is a new equation \@ref(eq:emc-2)

Code

--- bookdown-equation.lua - A Pandoc Lua filter for Converting LaTeX equation
--- labels to Bookdown Style equation labels in MathJax environment.
--- pandoc generated sample : $$\label{eq:EB} LE = R_n - G - H$$
--- filter generated equation : $$\label{eq:EB} LE = R_n - G - H (\#eq:EB)$$
--- Copyright: © 2021-2022 Abhishek Ulayil
--- License: MIT – see LICENSE for details

-- Makes sure users know if their pandoc version is too old for this
-- filter.
PANDOC_VERSION:must_be_at_least '2.9'


-- table to store all equation labels
equation_labels = {}

--[[
Converts LaTeX label to bookdown label format in the Math element
--]]
function Math(el)
    if el.text:match('label') then
        local text = pandoc.utils.stringify(el.text)
        s, e, l =string.find(text,"\\label{(.-)}")
        table.insert(equation_labels,l)
        -- Bookdown does not support period in equations hence substituting them as hyphen
        l = string.gsub(l, "%.", "-")
        el.text = text .. [[ (\#]] .. l .. [[)]]
    else
        --pass
    end
    return(el)
end

--[[
Converts Links to equations to modified format
--]]
function Link(el)
    local is_bkdwn = false
    for _,label in pairs(equation_labels) do
        if ("#"..label) == el.target then
            local link_text = el.target
            -- Bookdown does not support period in equations hence substituting them as hyphen
            link_text = string.gsub(link_text, "%.", "-")
            label = string.gsub(label, "%.", "-")
            el.target = link_text
            --bookdown type reference constructor
            bkdwn = [[\@ref(]] .. label .. [[)]]
            is_bkdwn = true
            break
        end
    end
    if is_bkdwn then
        return pandoc.RawInline('markdown', bkdwn)
    else
        return(el)
    end
end