Introduction

If you need to render a format not already handled by pandoc, or you want to change how pandoc renders a format, you can create a custom writer using the Lua language. Pandoc has a built-in Lua interpreter, so you needn’t install any additional software to do this.

A custom writer is a Lua file that defines how to render the document. Two styles of custom writers are supported: classic custom writers must define rendering functions for each AST element. New style writers, available since pandoc 2.17.2, must define just a single function Writer, which gets passed the document and writer options, and then does all rendering.

Classic style

A writer using the classic style defines rendering functions for each element of the pandoc AST.

For example,

function Para(s)
  return "<paragraph>" .. s .. "</paragraph>"
end

The best way to go about creating a classic custom writer is to modify the example that comes with pandoc. To get the example, you can do

pandoc --print-default-data-file sample.lua > sample.lua

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Introduction

If you need to parse a format not already handled by pandoc, you can create a custom reader using the Lua language. Pandoc has a built-in Lua interpreter, so you needn’t install any additional software to do this.

A custom reader is a Lua file that defines a function called Reader, which takes two arguments:

• the raw input to be parsed, as a list of sources
• optionally, a table of reader options, e.g. { columns = 62, standalone = true }.

The Reader function should return a Pandoc AST. This can be created using functions in the pandoc module, which is automatically in scope. (Indeed, all of the utility functions that are available for Lua filters are available in custom readers, too.)

Each source item corresponds to a file or stream passed to pandoc containing its text and name. E.g., if a single file input.txt is passed to pandoc, then the list of sources will contain just a single element s, where s.name == 'input.txt' and s.text contains the file contents as a string.

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Getting the code

Pandoc has a publicly accessible git repository on GitHub: https://github.com/jgm/pandoc. To get a local copy of the source:

git clone https://github.com/jgm/pandoc

The source for the main pandoc program is app/pandoc.hs. The source for the pandoc library is in src/, the source for the tests is in test/, and the source for the benchmarks is in benchmark/.

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