Converting a Span element to a BulletList in a Pandoc Lua Extension: A Step-by-Step Guide

Are you tired of manually formatting your documents to get that perfect bullet list? Look no further! In this article, we’ll dive into the world of Pandoc Lua extensions and explore how to convert a Span element to a BulletList that works seamlessly for both PDF and HTML outputs. Buckle up, and let’s get started!

What is Pandoc?

Pandoc is a powerful, open-source tool that converts files from one markup format to another. It’s like a Swiss Army knife for document formatting. With Pandoc, you can turn your Markdown files into beautiful PDFs, HTMLs, and even eBooks. But what makes Pandoc truly special is its ability to be extended using Lua scripts.

What is a Pandoc Lua Extension?

A Pandoc Lua extension is a script that allows you to customize Pandoc’s behavior. You can think of it as a plugin that extends Pandoc’s capabilities. With a Lua extension, you can manipulate the document’s AST (Abstract Syntax Tree) to achieve custom formatting, add new features, or even fix pesky formatting issues.

Converting a Span Element to a BulletList: The Problem

When working with Pandoc, you might encounter situations where you need to convert a Span element to a BulletList. Perhaps you’re working with a document that uses inline formatting, and you want to turn those inline elements into a neat bullet list. Sounds simple, right? But, what if you want this conversion to work for both PDF and HTML outputs?

That’s where things get tricky. By default, Pandoc doesn’t provide an out-of-the-box solution for this specific use case. Fear not, dear reader! We’ll create a custom Lua extension to tackle this problem head-on.

Step 1: Create a New Lua Extension

First, you’ll need to create a new Lua file. Name it anything you like, but for the sake of this example, let’s call it `span-to-bullet-list.lua`. Open your favorite text editor, and create a new file with that name.

touch span-to-bullet-list.lua

In this file, we’ll define our Lua extension.

Step 2: Define the Extension

Inside the `span-to-bullet-list.lua` file, add the following code:

function SpanToBulletList(block)
  if block.t == 'Span' then
    local bullet_list = pandoc.BulletList()
    for _, elem in ipairs(block.content) do
      table.insert(bullet_list, elem)
    end
    return bullet_list
  end
end

This code defines a function `SpanToBulletList` that takes a block element as an argument. If the block element is a Span (`block.t == ‘Span’`), it creates a new BulletList and appends each element from the Span’s content to the list. Finally, it returns the newly created BulletList.

Step 3: Register the Extension

To register our extension, we need to add the following code:

function Pandoc(filter)
  if filter.format == 'html' or filter.format == 'pdf' then
    return {{ SpanToBulletList }}
  end
end

This code registers our `SpanToBulletList` function as a filter for both HTML and PDF formats. When Pandoc processes a document in either of these formats, it will apply our custom filter.

Step 4: Use the Extension in Your Pandoc Conversion

Now that we have our Lua extension, let’s use it in a Pandoc conversion! Create a new Markdown file, `example.md`, and add the following content:

This is a test document.

This will become a bullet list

Next, run the following Pandoc command:

pandoc -f markdown -t html --lua-filter=span-to-bullet-list.lua example.md -o output.html

This will generate an HTML file, `output.html`, with the Span element converted to a BulletList.

Step 5: Verify the Output

Open the generated `output.html` file, and you should see the following HTML code:

<ul>
  <li>This will become a bullet list</li>
</ul>

Success! Our Lua extension has successfully converted the Span element to a BulletList for HTML output. But what about PDF output?

Step 6: Verify PDF Output

Let’s generate a PDF file using the same Lua extension. Run the following Pandoc command:

pandoc -f markdown -t latex --lua-filter=span-to-bullet-list.lua example.md -o output.pdf

This will generate a PDF file, `output.pdf`, with the Span element converted to a BulletList.

Open the PDF file, and you should see a nicely formatted bullet list:

•	This will become a bullet list

Wow, we did it! Our Lua extension now converts Span elements to BulletLists for both HTML and PDF outputs.

Conclusion

In this article, we’ve explored the world of Pandoc Lua extensions and learned how to convert a Span element to a BulletList that works seamlessly for both PDF and HTML outputs. With this knowledge, you can create custom formats, automate document processing, and even tackle complex formatting issues.

Remember, the power of Pandoc Lua extensions lies in their flexibility and customizability. Don’t be afraid to experiment, and who knows, you might just create the next game-changing Pandoc extension!

Happy formatting, and see you in the next article!

• Download the complete Lua extension file: span-to-bullet-list.lua
• Explore more Pandoc Lua extensions: Pandoc Lua Filters

Frequently Asked Questions

Are you tired of wrestling with pandoc Lua extensions to get that perfect formatting for your HTML and PDF outputs? Worry no more! Here are some frequently asked questions about converting a span element to a bullet list in a pandoc Lua extension that works for both PDF and HTML.