CODEWITHSUNDEEP
luapandocquarto
Thierry
Thierry

Reputation: 18487

Use Lua filter to set pandoc template variable

My goal is to input different text in the template based on a single variable in the yaml. Below is a minimal attempt, but I can't get it to work. I'm looking for a Lua filter that set the variable $selected$ based on the value of $switch$. In practice, I'll set several template variables based on that variable. The idea is to have one more generic template instead of many templates with relative few differences.

pandoc index.md --to html --from markdown --output index.html --template template.html --lua-filter=filter.lua

file index.md

---
title: "test"
switch: "a"
---
Some text

file template.html

<html>
  <title>$title$</title>
  <body>
    <h1>$selected$</h1>
    <h2>$switch$</h2>
    $body$
  </body>
</html>

file filter.lua

local function choose(info)
  local result
  if (info == "a")
  then
    result = "first choise"
  else
    result = "alternative"
  end
  return result
end

return {
  {
    Meta = function(meta)
      meta.title, meta.selected = choose(meta.switch)
      return meta
    end
  }
}

desired output

<html>
  <title>test</title>
<body>
  <h1>first choise</h1>
  <h2>a</h2>
  <p>Some text</p>
</body>
</html>

the result I get

<html>
  <title>alternative</title>
<body>
  <h1></h1>
  <h2>a</h2>
  <p>Some text</p>
</body>
</html>

Upvotes: 4

Views: 650

Answers (1)

tarleb
tarleb

Reputation: 22609

The issue here is that metadata values look like strings, but can be of some other type. Here, they are Inlines, as can be checked with this filter:

function Meta (meta)
  print(pandoc.utils.type(meta.switch))
end

The easiest solution is to convert the value to a string with pandoc.utils.stringify:

    Meta = function(meta)
      meta.selected = choose(pandoc.utils.stringify(meta.switch))
      return meta
    end

The filter should work as expected now.

Upvotes: 3

Related Questions