author

date

title

Albert Krewinkel

John MacFarlane

January 10, 2020

Pandoc Lua Filters

Introduction

Pandoc has long supported filters, which allow the pandoc abstract syntax tree (AST) to be manipulated between the parsing and the writing phase. Traditional pandoc filters accept a JSON representation of the pandoc AST and produce an altered JSON representation of the AST. They may be written in any programming language, and invoked from pandoc using the --filter option.

Although traditional filters are very flexible, they have a couple of disadvantages. First, there is some overhead in writing JSON to stdout and reading it from stdin (twice, once on each side of the filter). Second, whether a filter will work will depend on details of the user's environment. A filter may require an interpreter for a certain programming language to be available, as well as a library for manipulating the pandoc AST in JSON form. One cannot simply provide a filter that can be used by anyone who has a certain version of the pandoc executable.

Starting with version 2.0, pandoc makes it possible to write filters in Lua without any external dependencies at all. A Lua interpreter (version 5.3) and a Lua library for creating pandoc filters is built into the pandoc executable. Pandoc data types are marshaled to Lua directly, avoiding the overhead of writing JSON to stdout and reading it from stdin.

Here is an example of a Lua filter that converts strong emphasis to small caps:

return {
  {
    Strong = function (elem)
      return pandoc.SmallCaps(elem.c)
    end,
  }
}

or equivalently,

function Strong(elem)
  return pandoc.SmallCaps(elem.c)
end

This says: walk the AST, and when you find a Strong element, replace it with a SmallCaps element with the same content.

To run it, save it in a file, say smallcaps.lua, and invoke pandoc with --lua-filter=smallcaps.lua.

Here's a quick performance comparison, converting the pandoc manual (MANUAL.txt) to HTML, with versions of the same JSON filter written in compiled Haskell (smallcaps) and interpreted Python (smallcaps.py):

Command Time

pandoc 1.01s pandoc --filter ./smallcaps 1.36s pandoc --filter ./smallcaps.py 1.40s pandoc --lua-filter ./smallcaps.lua 1.03s

As you can see, the Lua filter avoids the substantial overhead associated with marshaling to and from JSON over a pipe.

Lua filter structure

Lua filters are tables with element names as keys and values consisting of functions acting on those elements.

Filters are expected to be put into separate files and are passed via the --lua-filter command-line argument. For example, if a filter is defined in a file current-date.lua, then it would be applied like this:

pandoc --lua-filter=current-date.lua -f markdown MANUAL.txt

The --lua-filter option may be supplied multiple times. Pandoc applies all filters (including JSON filters specified via --filter and Lua filters specified via --lua-filter) in the order they appear on the command line.

Pandoc expects each Lua file to return a list of filters. The filters in that list are called sequentially, each on the result of the previous filter. If there is no value returned by the filter script, then pandoc will try to generate a single filter by collecting all top-level functions whose names correspond to those of pandoc elements (e.g., Str, Para, Meta, or Pandoc). (That is why the two examples above are equivalent.)

For each filter, the document is traversed and each element subjected to the filter. Elements for which the filter contains an entry (i.e. a function of the same name) are passed to Lua element filtering function. In other words, filter entries will be called for each corresponding element in the document, getting the respective element as input.

The return of a filter function must one of the following:

nil: this means that the object should remain unchanged.
a pandoc object: this must be of the same type as the input and will replace the original object.
a list of pandoc objects: these will replace the original object; the list is merged with the neighbors of the original objects (spliced into the list the original object belongs to); returning an empty list deletes the object.

The function's output must result in an element of the same type as the input. This means a filter function acting on an inline element must return either nil, an inline, or a list of inlines, and a function filtering a block element must return one of nil, a block, or a list of block elements. Pandoc will throw an error if this condition is violated.

If there is no function matching the element's node type, then the filtering system will look for a more general fallback function. Two fallback functions are supported, Inline and Block. Each matches elements of the respective type.

Elements without matching functions are left untouched.

See module documentation for a list of pandoc elements.

Filters on element sequences

For some filtering tasks, it is necessary to know the order in which elements occur in the document. It is not enough then to inspect a single element at a time.

There are two special function names, which can be used to define filters on lists of blocks or lists of inlines.

[Inlines (inlines)]{#inlines-filter} : If present in a filter, this function will be called on all lists of inline elements, like the content of a Para (paragraph) block, or the description of an Image. The inlines argument passed to the function will be a List of Inlines for each call.

[Blocks (blocks)]{#blocks-filter} : If present in a filter, this function will be called on all lists of block elements, like the content of a MetaBlocks meta element block, on each item of a list, and the main content of the Pandoc document. The blocks argument passed to the function will be a List of Blocks for each call.

These filter functions are special in that the result must either be nil, in which case the list is left unchanged, or must be a list of the correct type, i.e., the same type as the input argument. Single elements are not allowed as return values, as a single element in this context usually hints at a bug.

See "Remove spaces before normal citations" for an example.

This functionality has been added in pandoc 2.9.2.

Execution Order

Element filter functions within a filter set are called in a fixed order, skipping any which are not present:

functions for Inline elements,
the Inlines filter function,
functions for Block elements ,
the Blocks filter function,
the Meta filter function, and last
the Pandoc filter function.

It is still possible to force a different order by explicitly returning multiple filter sets. For example, if the filter for Meta is to be run before that for Str, one can write

-- ... filter definitions ...

return {
  { Meta = Meta },  -- (1)
  { Str = Str }     -- (2)
}

Filter sets are applied in the order in which they are returned. All functions in set (1) are thus run before those in (2), causing the filter function for Meta to be run before the filtering of Str elements is started.

Global variables

Pandoc passes additional data to Lua filters by setting global variables.

FORMAT : The global FORMAT is set to the format of the pandoc writer being used (html5, latex, etc.), so the behavior of a filter can be made conditional on the eventual output format.

PANDOC_READER_OPTIONS : Table of the options which were provided to the parser.

PANDOC_VERSION : Contains the pandoc version as a Version object which behaves like a numerically indexed table, most significant number first. E.g., for pandoc 2.7.3, the value of the variable is equivalent to a table {2, 7, 3}. Use tostring(PANDOC_VERSION) to produce a version string. This variable is also set in custom writers.

PANDOC_API_VERSION : Contains the version of the pandoc-types API against which pandoc was compiled. It is given as a numerically indexed table, most significant number first. E.g., if pandoc was compiled against pandoc-types 1.17.3, then the value of the variable will behave like the table {1, 17, 3}. Use tostring(PANDOC_API_VERSION) to produce a version string. This variable is also set in custom writers.

PANDOC_SCRIPT_FILE : The name used to involve the filter. This value can be used to find files relative to the script file. This variable is also set in custom writers.

PANDOC_STATE : The state shared by all readers and writers. It is used by pandoc to collect and pass information. The value of this variable is of type CommonState and is read-only.

Pandoc Module

The pandoc Lua module is loaded into the filter's Lua environment and provides a set of functions and constants to make creation and manipulation of elements easier. The global variable pandoc is bound to the module and should generally not be overwritten for this reason.

Two major functionalities are provided by the module: element creator functions and access to some of pandoc's main functionalities.

Element creation

Element creator functions like Str, Para, and Pandoc are designed to allow easy creation of new elements that are simple to use and can be read back from the Lua environment. Internally, pandoc uses these functions to create the Lua objects which are passed to element filter functions. This means that elements created via this module will behave exactly as those elements accessible through the filter function parameter.

Exposed pandoc functionality

Some pandoc functions have been made available in Lua:

walk_block and walk_inline allow filters to be applied inside specific block or inline elements;
read allows filters to parse strings into pandoc documents;
pipe runs an external command with input from and output to strings;
the pandoc.mediabag module allows access to the "mediabag," which stores binary content such as images that may be included in the final document;
the pandoc.utils module contains various utility functions.

Lua interpreter initialization

Initialization of pandoc's Lua interpreter can be controlled by placing a file init.lua in pandoc's data directory. A common use-case would be to load additional modules, or even to alter default modules.

The following snippet is an example of code that might be useful when added to init.lua. The snippet adds all Unicode-aware functions defined in the text module to the default string module, prefixed with the string uc_.

for name, fn in pairs(require 'text') do
  string['uc_' .. name] = fn
end

This makes it possible to apply these functions on strings using colon syntax (mystring:uc_upper()).

Debugging Lua filters

It is possible to use a debugging interface to halt execution and step through a Lua filter line by line as it is run inside Pandoc. This is accomplished using the remote-debugging interface of the package mobdebug. Although mobdebug can be run from the terminal, it is more useful run within the donation-ware Lua editor and IDE, ZeroBrane. ZeroBrane offers a REPL console and UI to step-through and view all variables and state.

If you already have Lua 5.3 installed, you can add mobdebug and its dependency luasocket using luarocks, which should then be available on the path. ZeroBrane also includes both of these in its package, so if you don't want to install Lua separately, you should add/modify your LUA_PATH and LUA_CPATH to include the correct locations; see detailed instructions here.

Examples

The following filters are presented as examples. A repository of useful Lua filters (which may also serve as good examples) is available at https://github.com/pandoc/lua-filters.

Macro substitution

The following filter converts the string {{helloworld}} into emphasized text "Hello, World".

return {
  {
    Str = function (elem)
      if elem.text == "{{helloworld}}" then
        return pandoc.Emph {pandoc.Str "Hello, World"}
      else
        return elem
      end
    end,
  }
}

Center images in LaTeX and HTML output

For LaTeX, wrap an image in LaTeX snippets which cause the image to be centered horizontally. In HTML, the image element's style attribute is used to achieve centering.

-- Filter images with this function if the target format is LaTeX.
if FORMAT:match 'latex' then
  function Image (elem)
    -- Surround all images with image-centering raw LaTeX.
    return {
      pandoc.RawInline('latex', '\\hfill\\break{\\centering'),
      elem,
      pandoc.RawInline('latex', '\\par}')
    }
  end
end

-- Filter images with this function if the target format is HTML
if FORMAT:match 'html' then
  function Image (elem)
    -- Use CSS style to center image
    elem.attributes.style = 'margin:auto; display: block;'
    return elem
  end
end

Setting the date in the metadata

This filter sets the date in the document's metadata to the current date, if a date isn't already set:

function Meta(m)
  if m.date == nil then
    m.date = os.date("%B %e, %Y")
    return m
  end
end

Remove spaces before citations

This filter removes all spaces preceding an "author-in-text" citation. In Markdown, author-in-text citations (e.g., @citekey), must be preceded by a space. If these spaces are undesired, they must be removed with a filter.

local function is_space_before_author_in_text(spc, cite)
  return spc and spc.t == 'Space'
    and cite and cite.t == 'Cite'
    -- there must be only a single citation, and it must have
    -- mode 'AuthorInText'
    and #cite.citations == 1
    and cite.citations[1].mode == 'AuthorInText'
end

function Inlines (inlines)
  -- Go from end to start to avoid problems with shifting indices.
  for i = #inlines-1, 1, -1 do
    if is_space_before_author_in_text(inlines[i], inlines[i+1]) then
      inlines:remove(i)
    end
  end
  return inlines
end

Replacing placeholders with their metadata value

Lua filter functions are run in the order

Inlines → Blocks → Meta → Pandoc.

Passing information from a higher level (e.g., metadata) to a lower level (e.g., inlines) is still possible by using two filters living in the same file:

local vars = {}

function get_vars (meta)
  for k, v in pairs(meta) do
    if type(v) == 'table' and v.t == 'MetaInlines' then
      vars["%" .. k .. "%"] = {table.unpack(v)}
    end
  end
end

function replace (el)
  if vars[el.text] then
    return pandoc.Span(vars[el.text])
  else
    return el
  end
end

return {{Meta = get_vars}, {Str = replace}}

If the contents of file occupations.md is

---
name: Samuel Q. Smith
occupation: Professor of Phrenology
---

Name

:   %name%

Occupation

:   %occupation%

then running pandoc --lua-filter=meta-vars.lua occupations.md will output:

<dl>
<dt>Name</dt>
<dd><p><span>Samuel Q. Smith</span></p>
</dd>
<dt>Occupation</dt>
<dd><p><span>Professor of Phrenology</span></p>
</dd>
</dl>

Modifying pandoc's `MANUAL.txt` for man pages

This is the filter we use when converting MANUAL.txt to man pages. It converts level-1 headers to uppercase (using walk_block to transform inline elements inside headers), removes footnotes, and replaces links with regular text.

-- we use preloaded text to get a UTF-8 aware 'upper' function
local text = require('text')

function Header(el)
    if el.level == 1 then
      return pandoc.walk_block(el, {
        Str = function(el)
            return pandoc.Str(text.upper(el.text))
        end })
    end
end

function Link(el)
    return el.content
end

function Note(el)
    return {}
end

Creating a handout from a paper

This filter extracts all the numbered examples, section headers, block quotes, and figures from a document, in addition to any divs with class handout. (Note that only blocks at the "outer level" are included; this ignores blocks inside nested constructs, like list items.)

-- creates a handout from an article, using its headings,
-- blockquotes, numbered examples, figures, and any
-- Divs with class "handout"

function Pandoc(doc)
    local hblocks = {}
    for i,el in pairs(doc.blocks) do
        if (el.t == "Div" and el.classes[1] == "handout") or
           (el.t == "BlockQuote") or
           (el.t == "OrderedList" and el.style == "Example") or
           (el.t == "Para" and #el.c == 1 and el.c[1].t == "Image") or
           (el.t == "Header") then
           table.insert(hblocks, el)
        end
    end
    return pandoc.Pandoc(hblocks, doc.meta)
end

Counting words in a document

This filter counts the words in the body of a document (omitting metadata like titles and abstracts), including words in code. It should be more accurate than wc -w run directly on a Markdown document, since the latter will count markup characters, like the # in front of an ATX header, or tags in HTML documents, as words. To run it, pandoc --lua-filter wordcount.lua myfile.md.

-- counts words in a document

words = 0

wordcount = {
  Str = function(el)
    -- we don't count a word if it's entirely punctuation:
    if el.text:match("%P") then
        words = words + 1
    end
  end,

  Code = function(el)
    _,n = el.text:gsub("%S+","")
    words = words + n
  end,

  CodeBlock = function(el)
    _,n = el.text:gsub("%S+","")
    words = words + n
  end
}

function Pandoc(el)
    -- skip metadata, just count body:
    pandoc.walk_block(pandoc.Div(el.blocks), wordcount)
    print(words .. " words in body")
    os.exit(0)
end

Converting ABC code to music notation

This filter replaces code blocks with class abc with images created by running their contents through abcm2ps and ImageMagick's convert. (For more on ABC notation, see https://abcnotation.com.)

Images are added to the mediabag. For output to binary formats, pandoc will use images in the mediabag. For textual formats, use --extract-media to specify a directory where the files in the mediabag will be written, or (for HTML only) use --self-contained.

-- Pandoc filter to process code blocks with class "abc" containing
-- ABC notation into images.
--
-- * Assumes that abcm2ps and ImageMagick's convert are in the path.
-- * For textual output formats, use --extract-media=abc-images
-- * For HTML formats, you may alternatively use --self-contained

local filetypes = { html = {"png", "image/png"}
                  , latex = {"pdf", "application/pdf"}
                  }
local filetype = filetypes[FORMAT][1] or "png"
local mimetype = filetypes[FORMAT][2] or "image/png"

local function abc2eps(abc, filetype)
    local eps = pandoc.pipe("abcm2ps", {"-q", "-O", "-", "-"}, abc)
    local final = pandoc.pipe("convert", {"-", filetype .. ":-"}, eps)
    return final
end

function CodeBlock(block)
    if block.classes[1] == "abc" then
        local img = abc2eps(block.text, filetype)
        local fname = pandoc.sha1(img) .. "." .. filetype
        pandoc.mediabag.insert(fname, mimetype, img)
        return pandoc.Para{ pandoc.Image({pandoc.Str("abc tune")}, fname) }
    end
end

Building images with TikZ

This filter converts raw LaTeX TikZ environments into images. It works with both PDF and HTML output. The TikZ code is compiled to an image using pdflatex, and the image is converted from pdf to svg format using pdf2svg, so both of these must be in the system path. Converted images are cached in the working directory and given filenames based on a hash of the source, so that they need not be regenerated each time the document is built. (A more sophisticated version of this might put these in a special cache directory.)

local system = require 'pandoc.system'

local tikz_doc_template = [[
\documentclass{standalone}
\usepackage{xcolor}
\usepackage{tikz}
\begin{document}
\nopagecolor
%s
\end{document}
]]

local function tikz2image(src, filetype, outfile)
  system.with_temporary_directory('tikz2image', function (tmpdir)
    system.with_working_directory(tmpdir, function()
      local f = io.open('tikz.tex', 'w')
      f:write(tikz_doc_template:format(src))
      f:close()
      os.execute('pdflatex tikz.tex')
      if filetype == 'pdf' then
        os.rename('tikz.pdf', outfile)
      else
        os.execute('pdf2svg tikz.pdf ' .. outfile)
      end
    end)
  end)
end

extension_for = {
  html = 'svg',
  html4 = 'svg',
  html5 = 'svg',
  latex = 'pdf',
  beamer = 'pdf' }

local function file_exists(name)
  local f = io.open(name, 'r')
  if f ~= nil then
    io.close(f)
    return true
  else
    return false
  end
end

local function starts_with(start, str)
  return str:sub(1, #start) == start
end


function RawBlock(el)
  if starts_with('\\begin{tikzpicture}', el.text) then
    local filetype = extension_for[FORMAT] or 'svg'
    local fname = system.get_working_directory() .. '/' ..
        pandoc.sha1(el.text) .. '.' .. filetype
    if not file_exists(fname) then
      tikz2image(el.text, filetype, fname)
    end
    return pandoc.Para({pandoc.Image({}, fname)})
  else
   return el
  end
end

Example of use:

pandoc --lua-filter tikz.lua -s -o cycle.html <<EOF
Here is a diagram of the cycle:

\begin{tikzpicture}

\def \n {5}
\def \radius {3cm}
\def \margin {8} % margin in angles, depends on the radius

\foreach \s in {1,...,\n}
{
  \node[draw, circle] at ({360/\n * (\s - 1)}:\radius) {$\s$};
  \draw[->, >=latex] ({360/\n * (\s - 1)+\margin}:\radius)
    arc ({360/\n * (\s - 1)+\margin}:{360/\n * (\s)-\margin}:\radius);
}
\end{tikzpicture}
EOF

Lua type reference

This section describes the types of objects available to Lua filters. See the pandoc module for functions to create these objects.

Shared Properties

`clone`

clone ()

All instances of the types listed here, with the exception of read-only objects, can be cloned via the clone() method.

Usage:

local emph = pandoc.Emph {pandoc.Str 'important'}
local cloned_emph = emph:clone()  -- note the colon

Pandoc {#type-pandoc}

Pandoc document

Values of this type can be created with the pandoc.Pandoc constructor. Object equality is determined via pandoc.utils.equals.

blocks : document content (List of Blocks)

meta : document meta information (Meta object)

Meta {#type-meta}

Meta information on a document; string-indexed collection of MetaValues.

Values of this type can be created with the pandoc.Meta constructor. Object equality is determined via pandoc.utils.equals.

MetaValue {#type-metavalue}

Document meta information items.

Object equality is determined via pandoc.utils.equals.

MetaBlocks {#type-metablocks}

A list of blocks usable as meta value (List of Blocks).

Fields:

tag, t : the literal MetaBlocks (string)

MetaBool {#type-metabool}

Alias for Lua boolean, i.e. the values true and false.

MetaInlines {#type-metainlines}

List of inlines used in metadata (List of Inlines)

Values of this type can be created with the pandoc.MetaInlines constructor.

Fields:

tag, t : the literal MetaInlines (string)

MetaList {#type-metalist}

A list of other metadata values (List of MetaValues).

Values of this type can be created with the pandoc.MetaList constructor.

Fields:

tag, t : the literal MetaList (string)

All methods available for Lists can be used on this type as well.

MetaMap {#type-metamap}

A string-indexed map of meta-values. (table).

Values of this type can be created with the pandoc.MetaMap constructor.

Fields:

tag, t : the literal MetaMap (string)

Note: The fields will be shadowed if the map contains a field with the same name as those listed.

MetaString {#type-metastring}

Plain Lua string value (string).

Block {#type-block}

Object equality is determined via pandoc.utils.equals.

BlockQuote {#type-blockquote}

A block quote element.

Values of this type can be created with the pandoc.BlockQuote constructor.

Fields:

content: : block content (List of Blocks)

tag, t : the literal BlockQuote (string)

BulletList {#type-bulletlist}

A bullet list.

Values of this type can be created with the pandoc.BulletList constructor.

Fields:

content : list items (List of List of Blocks)

tag, t : the literal BulletList (string)

CodeBlock {#type-codeblock}

Block of code.

Values of this type can be created with the pandoc.CodeBlock constructor.

Fields:

text : code string (string)

attr : element attributes (Attr)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal CodeBlock (string)

DefinitionList {#type-definitionlist}

Definition list, containing terms and their explanation.

Values of this type can be created with the pandoc.DefinitionList constructor.

Fields:

content : list of items

tag, t : the literal DefinitionList (string)

Div {#type-div}

Generic block container with attributes.

Values of this type can be created with the pandoc.Div constructor.

Fields:

content : block content (List of Blocks)

attr : element attributes (Attr)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Div (string)

Header {#type-header}

Creates a header element.

Values of this type can be created with the pandoc.Header constructor.

Fields:

level : header level (integer)

content : inline content (List of Inlines)

attr : element attributes (Attr)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Header (string)

HorizontalRule {#type-horizontalrule}

A horizontal rule.

Values of this type can be created with the pandoc.HorizontalRule constructor.

Fields:

tag, t : the literal HorizontalRule (string)

LineBlock {#type-lineblock}

A line block, i.e. a list of lines, each separated from the next by a newline.

Values of this type can be created with the pandoc.LineBlock constructor.

Fields:

content : inline content

tag, t : the literal LineBlock (string)

Null {#type-null}

A null element; this element never produces any output in the target format.

Values of this type can be created with the pandoc.Null constructor.

tag, t : the literal Null (string)

OrderedList {#type-orderedlist}

An ordered list.

Values of this type can be created with the pandoc.OrderedList constructor.

Fields:

content : list items (List of List of Blocks)

listAttributes : list parameters (ListAttributes)

start : alias for listAttributes.start (integer)

style : alias for listAttributes.style (string)

delimiter : alias for listAttributes.delimiter (string)

tag, t : the literal OrderedList (string)

Para {#type-para}

A paragraph.

Values of this type can be created with the pandoc.Para constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Para (string)

Plain {#type-plain}

Plain text, not a paragraph.

Values of this type can be created with the pandoc.Plain constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Plain (string)

RawBlock {#type-rawblock}

Raw content of a specified format.

Values of this type can be created with the pandoc.RawBlock constructor.

Fields:

format : format of content (string)

text : raw content (string)

tag, t : the literal RawBlock (string)

Table {#type-table}

A table.

Values of this type can be created with the pandoc.Table constructor.

Fields:

attr : table attributes (Attr)

caption : table caption (Caption)

colspecs : column specifications, i.e., alignments and widths (List of ColSpecs)

head : table head (TableHead)

bodies : table bodies (List of TableBodys)

foot : table foot (TableFoot)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Table (string)

A [table cell]{#type-table-cell} is a list of blocks.

Alignment{#type-alignment} is a string value indicating the horizontal alignment of a table column. AlignLeft, AlignRight, and AlignCenter leads cell content to be left-aligned, right-aligned, and centered, respectively. The default alignment is AlignDefault (often equivalent to centered).

Inline {#type-inline}

Object equality is determined via pandoc.utils.equals.

Cite {#type-cite}

Citation.

Values of this type can be created with the pandoc.Cite constructor.

Fields:

content : (List of Inlines)

citations : citation entries (List of Citations)

tag, t : the literal Cite (string)

Code {#type-code}

Inline code

Values of this type can be created with the pandoc.Code constructor.

Fields:

text : code string (string)

attr : attributes (Attr)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Code (string)

Emph {#type-emph}

Emphasized text

Values of this type can be created with the pandoc.Emph constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Emph (string)

Image {#type-image}

Image: alt text (list of inlines), target

Values of this type can be created with the pandoc.Image constructor.

Fields:

attr : attributes (Attr)

caption : text used to describe the image (List of Inlines)

src : path to the image file (string)

title : brief image description

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Image (string)

LineBreak {#type-linebreak}

Hard line break

Values of this type can be created with the pandoc.LineBreak constructor.

Fields:

tag, t : the literal LineBreak (string)

Link {#type-link}

Hyperlink: alt text (list of inlines), target

Values of this type can be created with the pandoc.Link constructor.

Fields:

attr : attributes (Attr)

content : text for this link (List of Inlines)

target : the link target (string)

title : brief link description

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Link (string)

Math {#type-math}

TeX math (literal)

Values of this type can be created with the pandoc.Math constructor.

Fields:

mathtype : specifier determining whether the math content should be shown inline (InlineMath) or on a separate line (DisplayMath) (string)

text : math content (string)

tag, t : the literal Math (string)

Note {#type-note}

Footnote or endnote

Values of this type can be created with the pandoc.Note constructor.

Fields:

content : (List of Blocks)

tag, t : the literal Note (string)

Quoted {#type-quoted}

Quoted text

Values of this type can be created with the pandoc.Quoted constructor.

Fields:

quotetype : type of quotes to be used; one of SingleQuote or DoubleQuote (string)

content : quoted text (List of Inlines)

tag, t : the literal Quoted (string)

RawInline {#type-rawinline}

Raw inline

Values of this type can be created with the pandoc.RawInline constructor.

Fields:

format : the format of the content (string)

text : raw content (string)

tag, t : the literal RawInline (string)

SmallCaps {#type-smallcaps}

Small caps text

Values of this type can be created with the pandoc.SmallCaps constructor.

Fields:

content : (List of Inlines)

tag, t : the literal SmallCaps (string)

SoftBreak {#type-softbreak}

Soft line break

Values of this type can be created with the pandoc.SoftBreak constructor.

Fields:

tag, t : the literal SoftBreak (string)

Space {#type-space}

Inter-word space

Values of this type can be created with the pandoc.Space constructor.

Fields:

tag, t : the literal Space (string)

Span {#type-span}

Generic inline container with attributes

Values of this type can be created with the pandoc.Span constructor.

Fields:

attr : attributes (Attr)

content : wrapped content (List of Inlines)

identifier : alias for attr.identifier (string)

classes : alias for attr.classes (List of strings)

attributes : alias for attr.attributes (Attributes)

tag, t : the literal Span (string)

Str {#type-str}

Text

Values of this type can be created with the pandoc.Str constructor.

Fields:

text : content (string)

tag, t : the literal Str (string)

Strikeout {#type-strikeout}

Strikeout text

Values of this type can be created with the pandoc.Strikeout constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Strikeout (string)

Strong {#type-strong}

Strongly emphasized text

Values of this type can be created with the pandoc.Strong constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Strong (string)

Subscript {#type-subscript}

Subscripted text

Values of this type can be created with the pandoc.Subscript constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Subscript (string)

Superscript {#type-superscript}

Superscripted text

Values of this type can be created with the pandoc.Superscript constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Superscript (string)

Underline {#type-underline}

Underlined text

Values of this type can be created with the pandoc.Underline constructor.

Fields:

content : inline content (List of Inlines)

tag, t : the literal Underline (string)

Element components

Attr {#type-attr}

A set of element attributes. Values of this type can be created with the pandoc.Attr constructor. For convenience, it is usually not necessary to construct the value directly if it is part of an element, and it is sufficient to pass an HTML-like table. E.g., to create a span with identifier "text" and classes "a" and "b", one can write:

local span = pandoc.Span('text', {id = 'text', class = 'a b'})

This also works when using the attr setter:

local span = pandoc.Span 'text'
span.attr = {id = 'text', class = 'a b', other_attribute = '1'}

Object equality is determined via pandoc.utils.equals.

Fields:

identifier : element identifier (string)

classes : element classes (List of strings)

attributes : collection of key/value pairs (Attributes)

Attributes {#type-attributes}

List of key/value pairs. Values can be accessed by using keys as indices to the list table.

Caption {#type-caption}

The caption of a table, with an optional short caption.

Fields:

long : long caption (list of Blocks)

short : short caption (list of Inlines)

Cell {#type-cell}

A table cell.

Fields:

attr : cell attributes

alignment : individual cell alignment (Alignment).

contents : cell contents (list of Blocks).

col_span : number of columns occupied by the cell; the height of the cell (integer).

row_span : number of rows occupied by the cell; the height of the cell (integer).

Citation {#type-citation}

Single citation entry

Values of this type can be created with the pandoc.Citation constructor.

Object equality is determined via pandoc.utils.equals.

Fields:

id : citation identifier, e.g., a bibtex key (string)

mode : citation mode, one of AuthorInText, SuppressAuthor, or NormalCitation (string)

prefix : citation prefix (List of Inlines)

suffix : citation suffix (List of Inlines)

note_num : note number (integer)

hash : hash (integer)

ColSpec {#type-colspec}

Column alignment and width specification for a single table column.

This is a pair with the following components:

cell alignment (Alignment).
table column width, as a fraction of the total table width (number).

ListAttributes {#type-listattributes}

List attributes

Values of this type can be created with the pandoc.ListAttributes constructor.

Object equality is determined via pandoc.utils.equals.

Fields:

start : number of the first list item (integer)

style : style used for list numbers; possible values are DefaultStyle, Example, Decimal, LowerRoman, UpperRoman, LowerAlpha, and UpperAlpha (string)

delimiter : delimiter of list numbers; one of DefaultDelim, Period, OneParen, and TwoParens (string)

Row {#type-row}

A table row.

Tuple fields:

row attributes
row cells (list of Cells)

TableBody {#type-tablebody}

A body of a table, with an intermediate head and the specified number of row header columns.

Fields:

attr : table body attributes (Attr)

body : table body rows (list of Rows)

head : intermediate head (list of Rows)

row_head_columns : number of columns taken up by the row head of each row of a TableBody. The row body takes up the remaining columns.

TableFoot {#type-tablefoot}

The foot of a table.

This is a pair with the following components:

attributes
foot rows (Rows)

TableHead {#type-tablehead}

The head of a table.

This is a pair with the following components:

attributes
head rows (Rows)

ReaderOptions {#type-readeroptions}

Pandoc reader options

Fields:

abbreviations : set of known abbreviations (set of strings)

columns : number of columns in terminal (integer)

default_image_extension : default extension for images (string)

extensions : string representation of the syntax extensions bit field (string)

indented_code_classes : default classes for indented code blocks (list of strings)

standalone : whether the input was a standalone document with header (boolean)

strip_comments : HTML comments are stripped instead of parsed as raw HTML (boolean)

tab_stop : width (i.e. equivalent number of spaces) of tab stops (integer)

track_changes : track changes setting for docx; one of AcceptChanges, RejectChanges, and AllChanges (string)

CommonState {#type-commonstate}

The state used by pandoc to collect information and make it available to readers and writers.

Fields:

input_files : List of input files from command line (List of strings)

output_file : Output file from command line (string or nil)

log : A list of log messages in reverse order (List of LogMessages)

request_headers : Headers to add for HTTP requests; table with header names as keys and header contents as value (table)

resource_path : Path to search for resources like included images (List of strings)

source_url : Absolute URL or directory of first source file (string or nil)

user_data_dir : Directory to search for data files (string or nil)

trace : Whether tracing messages are issued (boolean)

verbosity : Verbosity level; one of INFO, WARNING, ERROR (string)

List {#type-list}

A list is any Lua table with integer indices. Indices start at one, so if alist = {'value'} then alist[1] == 'value'.

Lists, when part of an element, or when generated during marshaling, are made instances of the pandoc.List type for convenience. The pandoc.List type is defined in the pandoc.List module. See there for available methods.

Values of this type can be created with the pandoc.List constructor, turning a normal Lua table into a List.

LogMessage {#type-logmessage}

A pandoc log message. Objects have no fields, but can be converted to a string via tostring.

SimpleTable {#type-simpletable}

A simple table is a table structure which resembles the old (pre pandoc 2.10) Table type. Bi-directional conversion from and to Tables is possible with the pandoc.utils.to_simple_table and pandoc.utils.from_simple_table function, respectively. Instances of this type can also be created directly with the pandoc.SimpleTable constructor.

Fields:

caption: : List of Inlines

aligns: : column alignments (List of Alignments)

widths: : column widths; a (List of numbers)

headers: : table header row (List of lists of Blocks)

rows: : table rows (List of rows, where a row is a list of lists of Blocks)

Version {#type-version}

A version object. This represents a software version like "2.7.3". The object behaves like a numerically indexed table, i.e., if version represents the version 2.7.3, then

version[1] == 2
version[2] == 7
version[3] == 3
#version == 3   -- length

Comparisons are performed element-wise, i.e.

Version '1.12' > Version '1.9'

Values of this type can be created with the pandoc.types.Version constructor.

`must_be_at_least`

must_be_at_least(actual, expected [, error_message])

Raise an error message if the actual version is older than the expected version; does nothing if actual is equal to or newer than the expected version.

Parameters:

actual : actual version specifier (Version)

expected : minimum expected version (Version)

error_message : optional error message template. The string is used as format string, with the expected and actual versions as arguments. Defaults to "expected version %s or newer, got %s".

Usage:

PANDOC_VERSION:must_be_at_least '2.7.3'
PANDOC_API_VERSION:must_be_at_least(
  '1.17.4',
  'pandoc-types is too old: expected version %s, got %s'
)

Module text

UTF-8 aware text manipulation functions, implemented in Haskell. The module is made available as part of the pandoc module via pandoc.text. The text module can also be loaded explicitly:

-- uppercase all regular text in a document:
text = require 'text'
function Str (s)
  s.text = text.upper(s.text)
  return s
end

lower {#text.lower}

lower (s)

Returns a copy of a UTF-8 string, converted to lowercase.

upper {#text.upper}

upper (s)

Returns a copy of a UTF-8 string, converted to uppercase.

reverse {#text.reverse}

reverse (s)

Returns a copy of a UTF-8 string, with characters reversed.

len {#text.len}

len (s)

Returns the length of a UTF-8 string.

sub {#text.sub}

sub (s)

Returns a substring of a UTF-8 string, using Lua's string indexing rules.

Module pandoc

Lua functions for pandoc scripts; includes constructors for document tree elements, functions to parse text in a given format, and functions to filter and modify a subtree.

Pandoc

[Pandoc (blocks[, meta])]{#pandoc.pandoc}

: A complete pandoc document

Parameters:

`blocks`:
:   document content

`meta`:
:   document meta data

Returns: [Pandoc] object

MetaValue

[MetaBlocks (blocks)]{#pandoc.metablocks}

: Meta blocks

Parameters:

`blocks`:
:   blocks

Returns: [MetaBlocks] object

[MetaInlines (inlines)]{#pandoc.metainlines}

: Meta inlines

Parameters:

`inlines`:
:   inlines

Returns: [MetaInlines] object

[MetaList (meta_values)]{#pandoc.metalist}

: Meta list

Parameters:

`meta_values`:
:   list of meta values

Returns: [MetaList] object

[MetaMap (key_value_map)]{#pandoc.metamap}

: Meta map

Parameters:

`key_value_map`:
:   a string-indexed map of meta values

Returns: [MetaMap] object

[MetaString (str)]{#pandoc.metastring}

: Creates string to be used in meta data.

Parameters:

`str`:
:   string value

Returns: [MetaString] object

[MetaBool (bool)]{#pandoc.metabool}

: Creates boolean to be used in meta data.

Parameters:

`bool`:
:   boolean value

Returns: [MetaBool] object

Blocks

[BlockQuote (content)]{#pandoc.blockquote}

: Creates a block quote element

Parameters:

`content`:
:   block content

Returns: [BlockQuote] object

[BulletList (items)]{#pandoc.bulletlist}

: Creates a bullet list.

Parameters:

`items`:
:   list items

Returns: [BulletList] object

[CodeBlock (text[, attr])]{#pandoc.codeblock}

: Creates a code block element

Parameters:

`text`:
:   code string

`attr`:
:   element attributes

Returns: [CodeBlock] object

[DefinitionList (content)]{#pandoc.definitionlist}

: Creates a definition list, containing terms and their explanation.

Parameters:

`content`:
:   list of items

Returns: [DefinitionList] object

[Div (content[, attr])]{#pandoc.div}

: Creates a div element

Parameters:

`content`:
:   block content

`attr`:
:   element attributes

Returns: [Div] object

[Header (level, content[, attr])]{#pandoc.header}

: Creates a header element.

Parameters:

`level`:
:   header level

`content`:
:   inline content

`attr`:
:   element attributes

Returns: [Header] object

[HorizontalRule ()]{#pandoc.horizontalrule}

: Creates a horizontal rule.

Returns: [HorizontalRule] object

[LineBlock (content)]{#pandoc.lineblock}

: Creates a line block element.

Parameters:

`content`:
:   inline content

Returns: [LineBlock] object

[Null ()]{#pandoc.null}

: Creates a null element.

Returns: [Null] object

[OrderedList (items[, listAttributes])]{#pandoc.orderedlist}

: Creates an ordered list.

Parameters:

`items`:
:   list items

`listAttributes`:
:   list parameters

Returns: [OrderedList](#type-orderedlist) object

[Para (content)]{#pandoc.para}

: Creates a para element.

Parameters:

`content`:
:   inline content

Returns: [Para](#type-para) object

[Plain (content)]{#pandoc.plain}

: Creates a plain element.

Parameters:

`content`:
:   inline content

Returns: [Plain](#type-plain) object

[RawBlock (format, text)]{#pandoc.rawblock}

: Creates a raw content block of the specified format.

Parameters:

`format`:
:   format of content

`text`:
:   string content

Returns: [RawBlock](#type-rawblock) object

[Table (caption, colspecs, head, bodies, foot[, attr])]{#pandoc.table}

: Creates a table element.

Parameters:

`caption`:
:   table [caption](#type-caption)

`colspecs`:
:   column alignments and widths (list of [ColSpec](#type-colspec)s)

`head`:
:   [table head](#type-tablehead)

`bodies`:
:   [table bodies](#type-tablebody)

`foot`:
:   [table foot](#type-tablefoot)

`attr`:
:   element attributes

Returns: [Table](#type-table) object

Inline

[Cite (content, citations)]{#pandoc.cite}

: Creates a Cite inline element

Parameters:

`content`:
:   List of inlines

`citations`:
:   List of citations

Returns: [Cite](#type-cite) object

[Code (text[, attr])]{#pandoc.code}

: Creates a Code inline element

Parameters:

`text`:
:   code string

`attr`:
:   additional attributes

Returns: [Code](#type-code) object

[Emph (content)]{#pandoc.emph}

: Creates an inline element representing emphasized text.

Parameters:

`content`:
:   inline content

Returns: [Emph](#type-emph) object

[Image (caption, src[, title[, attr]])]{#pandoc.image}

: Creates a Image inline element

Parameters:

`caption`:
:   text used to describe the image

`src`:
:   path to the image file

`title`:
:   brief image description

`attr`:
:   additional attributes

Returns: [Image](#type-image) object

[LineBreak ()]{#pandoc.linebreak}

: Create a LineBreak inline element

Returns: [LineBreak](#type-linebreak) object

[Link (content, target[, title[, attr]])]{#pandoc.link}

: Creates a link inline element, usually a hyperlink.

Parameters:

`content`:
:   text for this link

`target`:
:   the link target

`title`:
:   brief link description

`attr`:
:   additional attributes

Returns: [Link](#type-link) object

[Math (mathtype, text)]{#pandoc.math}

: Creates a Math element, either inline or displayed.

Parameters:

`mathtype`:
:   rendering specifier

`text`:
:   Math content

Returns: [Math](#type-math) object

[DisplayMath (text)]{#pandoc.displaymath}

: Creates a math element of type "DisplayMath" (DEPRECATED).

Parameters:

`text`:
:   Math content

Returns: [Math](#type-math) object

[InlineMath (text)]{#pandoc.inlinemath}

: Creates a math element of type "InlineMath" (DEPRECATED).

Parameters:

`text`:
:   Math content

Returns: [Math](#type-math) object

[Note (content)]{#pandoc.note}

: Creates a Note inline element

Parameters:

`content`:
:   footnote block content

Returns: [Note](#type-note) object

[Quoted (quotetype, content)]{#pandoc.quoted}

: Creates a Quoted inline element given the quote type and quoted content.

Parameters:

`quotetype`:
:   type of quotes to be used

`content`:
:   inline content

Returns: [Quoted](#type-quoted) object

[SingleQuoted (content)]{#pandoc.singlequoted}

: Creates a single-quoted inline element (DEPRECATED).

Parameters:

`content`:
:   inline content

Returns: [Quoted](#type-quoted)

[DoubleQuoted (content)]{#pandoc.doublequoted}

: Creates a single-quoted inline element (DEPRECATED).

Parameters:

`content`:
:   inline content

Returns: [Quoted](#type-quoted)

[RawInline (format, text)]{#pandoc.rawinline}

: Creates a raw inline element

Parameters:

`format`:
:   format of the contents

`text`:
:   string content

Returns: [RawInline](#type-rawinline) object

[SmallCaps (content)]{#pandoc.smallcaps}

: Creates text rendered in small caps

Parameters:

`content`:
:   inline content

Returns: [SmallCaps](#type-smallcaps) object

[SoftBreak ()]{#pandoc.softbreak}

: Creates a SoftBreak inline element.

Returns: [SoftBreak](#type-softbreak) object

[Space ()]{#pandoc.space}

: Create a Space inline element

Returns: [Space](#type-space) object

[Span (content[, attr])]{#pandoc.span}

: Creates a Span inline element

Parameters:

`content`:
:   inline content

`attr`:
:   additional attributes

Returns: [Span](#type-span) object

[Str (text)]{#pandoc.str}

: Creates a Str inline element

Parameters:

`text`:
:   content

Returns: [Str](#type-str) object

[Strikeout (content)]{#pandoc.strikeout}

: Creates text which is struck out.

Parameters:

`content`:
:   inline content

Returns: [Strikeout](#type-strikeout) object

[Strong (content)]{#pandoc.strong}

: Creates a Strong element, whose text is usually displayed in a bold font.

Parameters:

`content`:
:   inline content

Returns: [Strong](#type-strong) object

[Subscript (content)]{#pandoc.subscript}

: Creates a Subscript inline element

Parameters:

`content`:
:   inline content

Returns: [Subscript](#type-subscript) object

[Superscript (content)]{#pandoc.superscript}

: Creates a Superscript inline element

Parameters:

`content`:
:   inline content

Returns: [Superscript](#type-superscript) object

[Underline (content)]{#pandoc.underline}

: Creates an Underline inline element

Parameters:

`content`:
:   inline content

Returns: [Underline](#type-underline) object

Element components

[Attr ([identifier[, classes[, attributes]]])]{#pandoc.attr}

: Create a new set of attributes (Attr).

Parameters:

`identifier`:
:   element identifier

`classes`:
:   element classes

`attributes`:
:   table containing string keys and values

Returns: [Attr](#type-attr) object

[Citation (id, mode[, prefix[, suffix[, note_num[, hash]]]])]{#pandoc.citation}

: Creates a single citation.

Parameters:

`id`:
:   citation identifier (like a bibtex key)

`mode`:
:   citation mode

`prefix`:
:   citation prefix

`suffix`:
:   citation suffix

`note_num`:
:   note number

`hash`:
:   hash number

Returns: [Citation](#type-citation) object

[ListAttributes ([start[, style[, delimiter]]])]{#pandoc.listattributes}

: Creates a set of list attributes.

Parameters:

`start`:
:   number of the first list item

`style`:
:   style used for list numbering

`delimiter`:
:   delimiter of list numbers

Returns: [ListAttributes](#type-listattributes) object

Legacy types

[SimpleTable (caption, aligns, widths, headers, rows)]{#pandoc.simpletable}

: Creates a simple table resembling the old (pre pandoc 2.10) table type.

Parameters:

`caption`:
:   [List] of [Inlines]

`aligns`:
:   column alignments ([List] of [Alignments](#type-alignment))

`widths`:
:   column widths; a  ([List] of numbers)

`headers`:
:   table header row ([List] of lists of [Blocks])

`rows`:
:   table rows ([List] of rows, where a row is a list of lists
    of [Blocks])

Returns: [SimpleTable] object

Usage:

    local caption = "Overview"
    local aligns = {pandoc.AlignDefault, pandoc.AlignDefault}
    local widths = {0, 0} -- let pandoc determine col widths
    local headers = {{pandoc.Plain({pandoc.Str "Language"})},
                     {pandoc.Plain({pandoc.Str "Typing"})}}
    local rows = {
      {{pandoc.Plain "Haskell"}, {pandoc.Plain "static"}},
      {{pandoc.Plain "Lua"}, {pandoc.Plain "Dynamic"}},
    }
    simple_table = pandoc.SimpleTable(
      caption,
      aligns,
      widths,
      headers,
      rows
    )

Constants

[AuthorInText]{#pandoc.authorintext}

: Author name is mentioned in the text.

See also: [Citation](#type-citation)

[SuppressAuthor]{#pandoc.suppressauthor}

: Author name is suppressed.

See also: [Citation](#type-citation)

[NormalCitation]{#pandoc.normalcitation}

: Default citation style is used.

See also: [Citation](#type-citation)

[AlignLeft]{#pandoc.alignleft}

: Table cells aligned left.

See also: [Table](#type-alignment)

[AlignRight]{#pandoc.alignright}

: Table cells right-aligned.

See also: [Table](#type-alignment)

[AlignCenter]{#pandoc.aligncenter}

: Table cell content is centered.

See also: [Table](#type-alignment)

[AlignDefault]{#pandoc.aligndefault}

: Table cells are alignment is unaltered.

See also: [Table](#type-alignment)

[DefaultDelim]{#pandoc.defaultdelim}

: Default list number delimiters are used.

See also: [ListAttributes](#type-listattributes)

[Period]{#pandoc.period}

: List numbers are delimited by a period.

See also: [ListAttributes](#type-listattributes)

[OneParen]{#pandoc.oneparen}

: List numbers are delimited by a single parenthesis.

See also: [ListAttributes](#type-listattributes)

[TwoParens]{#pandoc.twoparens}

: List numbers are delimited by a double parentheses.

See also: [ListAttributes](#type-listattributes)

[DefaultStyle]{#pandoc.defaultstyle}

: List are numbered in the default style

See also: [ListAttributes](#type-listattributes)

[Example]{#pandoc.example}

: List items are numbered as examples.

See also: [ListAttributes](#type-listattributes)

[Decimal]{#pandoc.decimal}

: List are numbered using decimal integers.

See also: [ListAttributes](#type-listattributes)

[LowerRoman]{#pandoc.lowerroman}

: List are numbered using lower-case roman numerals.

See also: [ListAttributes](#type-listattributes)

[UpperRoman]{#pandoc.upperroman}

: List are numbered using upper-case roman numerals

See also: [ListAttributes](#type-listattributes)

[LowerAlpha]{#pandoc.loweralpha}

: List are numbered using lower-case alphabetic characters.

See also: [ListAttributes](#type-listattributes)

[UpperAlpha]{#pandoc.upperalpha}

: List are numbered using upper-case alphabetic characters.

See also: [ListAttributes](#type-listattributes)

[sha1]{#pandoc.sha1}

: Alias for pandoc.utils.sha1 (DEPRECATED).

Helper functions

pipe {#pandoc.pipe}

pipe (command, args, input)

Runs command with arguments, passing it some input, and returns the output.

Parameters:

command : program to run; the executable will be resolved using default system methods (string).

args : list of arguments to pass to the program (list of strings).

input : data which is piped into the program via stdin (string).

Returns:

Output of command, i.e. data printed to stdout (string)

Raises:

A table containing the keys command, error_code, and output is thrown if the command exits with a non-zero error code.

Usage:

local output = pandoc.pipe("sed", {"-e","s/a/b/"}, "abc")

walk_block {#pandoc.walk_block}

walk_block (element, filter)

Apply a filter inside a block element, walking its contents.

Parameters:

element: : the block element

filter: : a Lua filter (table of functions) to be applied within the block element

Returns: the transformed block element

walk_inline {#pandoc.walk_inline}

walk_inline (element, filter)

Apply a filter inside an inline element, walking its contents.

Parameters:

element: : the inline element

filter: : a Lua filter (table of functions) to be applied within the inline element

Returns: the transformed inline element

read {#pandoc.read}

read (markup[, format])

Parse the given string into a Pandoc document.

Parameters:

markup: : the markup to be parsed

format: : format specification, defaults to "markdown".

Returns: pandoc document

Usage:

local org_markup = "/emphasis/"  -- Input to be read
local document = pandoc.read(org_markup, "org")
-- Get the first block of the document
local block = document.blocks[1]
-- The inline element in that block is an `Emph`
assert(block.content[1].t == "Emph")

Module pandoc.utils

This module exposes internal pandoc functions and utility functions.

The module is loaded as part of the pandoc module and available as pandoc.utils. In versions up-to and including pandoc 2.6, this module had to be loaded explicitly. Example:

pandoc.utils = require 'pandoc.utils'

Use the above for backwards compatibility.

blocks_to_inlines {#pandoc.utils.blocks_to_inlines}

blocks_to_inlines (blocks[, sep])

Squash a list of blocks into a list of inlines.

Parameters:

blocks: : List of Blocks to be flattened.

sep: : List of Inlines inserted as separator between two consecutive blocks; defaults to { pandoc.Space(), pandoc.Str'¶', pandoc.Space()}.

Returns:

List of Inlines

Usage:

local blocks = {
  pandoc.Para{ pandoc.Str 'Paragraph1' },
  pandoc.Para{ pandoc.Emph 'Paragraph2' }
}
local inlines = pandoc.utils.blocks_to_inlines(blocks)
-- inlines = {
--   pandoc.Str 'Paragraph1',
--   pandoc.Space(), pandoc.Str'¶', pandoc.Space(),
--   pandoc.Emph{ pandoc.Str 'Paragraph2' }
-- }

equals {#pandoc.utils.equals}

equals (element1, element2)

Test equality of AST elements. Elements in Lua are considered equal if and only if the objects obtained by unmarshaling are equal.

Parameters:

element1, element2: : Objects to be compared. Acceptable input types are Pandoc, Meta, MetaValue, Block, Inline, Attr, ListAttributes, and Citation.

Returns:

Whether the two objects represent the same element (boolean)

from_simple_table {#pandoc.utils.from_simple_table}

from_simple_table (table)

Creates a Table block element from a SimpleTable. This is useful for dealing with legacy code which was written for pandoc versions older than 2.10.

Returns:

table block element (Table)

Usage:

local simple = pandoc.SimpleTable(table)
-- modify, using pre pandoc 2.10 methods
simple.caption = pandoc.SmallCaps(simple.caption)
-- create normal table block again
table = pandoc.utils.from_simple_table(simple)

make_sections {#pandoc.utils.make_sections}

make_sections (number_sections, base_level, blocks)

Converts list of Blocks into sections. Divs will be created beginning at each Header and containing following content until the next Header of comparable level. If number_sections is true, a number attribute will be added to each Header containing the section number. If base_level is non-null, Header levels will be reorganized so that there are no gaps, and so that the base level is the level specified.

Returns:

List of Blocks.

Usage:

local blocks = {
  pandoc.Header(2, pandoc.Str 'first'),
  pandoc.Header(2, pandoc.Str 'second'),
}
local newblocks = pandoc.utils.make_sections(true, 1, blocks)

run_json_filter {#pandoc.utils.run_json_filter}

run_json_filter (doc, filter[, args])

Filter the given doc by passing it through the a JSON filter.

Parameters:

doc: : the Pandoc document to filter

filter: : filter to run

args: : list of arguments passed to the filter. Defaults to {FORMAT}.

Returns:

(Pandoc) Filtered document

Usage:

-- Assumes `some_blocks` contains blocks for which a
-- separate literature section is required.
local sub_doc = pandoc.Pandoc(some_blocks, metadata)
sub_doc_with_bib = pandoc.utils.run_json_filter(
  sub_doc,
  'pandoc-citeproc'
)
some_blocks = sub_doc.blocks -- some blocks with bib

normalize_date {#pandoc.utils.normalize_date}

normalize_date (date_string)

Parse a date and convert (if possible) to "YYYY-MM-DD" format. We limit years to the range 1601-9999 (ISO 8601 accepts greater than or equal to 1583, but MS Word only accepts dates starting 1601).

Returns:

A date string, or nil when the conversion failed.

sha1 {#pandoc.utils.sha1}

sha1 (contents)

Returns the SHA1 has of the contents.

Returns:

SHA1 hash of the contents.

Usage:

local fp = pandoc.utils.sha1("foobar")

stringify {#pandoc.utils.stringify}

stringify (element)

Converts the given element (Pandoc, Meta, Block, or Inline) into a string with all formatting removed.

Returns:

A plain string representation of the given element.

Usage:

local inline = pandoc.Emph{pandoc.Str 'Moin'}
-- outputs "Moin"
print(pandoc.utils.stringify(inline))

to_roman_numeral {#pandoc.utils.to_roman_numeral}

to_roman_numeral (integer)

Converts an integer < 4000 to uppercase roman numeral.

Returns:

A roman numeral string.

Usage:

local to_roman_numeral = pandoc.utils.to_roman_numeral
local pandoc_birth_year = to_roman_numeral(2006)
-- pandoc_birth_year == 'MMVI'

to_simple_table {#pandoc.utils.to_simple_table}

to_simple_table (table)

Creates a SimpleTable out of a Table block.

Returns:

a simple table object (SimpleTable)

Usage:

local simple = pandoc.utils.to_simple_table(table)
-- modify, using pre pandoc 2.10 methods
simple.caption = pandoc.SmallCaps(simple.caption)
-- create normal table block again
table = pandoc.utils.from_simple_table(simple)

Module pandoc.mediabag

The pandoc.mediabag module allows accessing pandoc's media storage. The "media bag" is used when pandoc is called with the --extract-media or (for HTML only) --self-contained option.

The module is loaded as part of module pandoc and can either be accessed via the pandoc.mediabag field, or explicitly required, e.g.:

local mb = require 'pandoc.mediabag'

delete {#pandoc.mediabag.delete}

delete (filepath)

Removes a single entry from the media bag.

Parameters:

filepath: : filename of the item to be deleted. The media bag will be left unchanged if no entry with the given filename exists.

empty {#pandoc.mediabag.empty}

empty ()

Clear-out the media bag, deleting all items.

insert {#pandoc.mediabag.insert}

insert (filepath, mime_type, contents)

Adds a new entry to pandoc's media bag.

Parameters:

filepath: : filename and path relative to the output folder.

mime_type: : the file's MIME type

contents: : the binary contents of the file.

Usage:

local fp = "media/hello.txt"
local mt = "text/plain"
local contents = "Hello, World!"
pandoc.mediabag.insert(fp, mt, contents)

items {#pandoc.mediabag.items}

items ()

Returns an iterator triple to be used with Lua's generic for statement. The iterator returns the filepath, MIME type, and content of a media bag item on each invocation. Items are processed one-by-one to avoid excessive memory use.

This function should be used only when full access to all items, including their contents, is required. For all other cases, list should be preferred.

Returns:

The iterator function; must be called with the iterator state and the current iterator value.
Iterator state -- an opaque value to be passed to the iterator function.
Initial iterator value.

Usage:

for fp, mt, contents in pandoc.mediabag.items() do
  -- print(fp, mt, contents)
end

list {#pandoc.mediabag.list}

list ()

Get a summary of the current media bag contents.

Returns: A list of elements summarizing each entry in the media bag. The summary item contains the keys path, type, and length, giving the filepath, MIME type, and length of contents in bytes, respectively.

Usage:

-- calculate the size of the media bag.
local mb_items = pandoc.mediabag.list()
local sum = 0
for i = 1, #mb_items do
    sum = sum + mb_items[i].length
end
print(sum)

lookup {#pandoc.mediabag.lookup}

lookup (filepath)

Lookup a media item in the media bag, and return its MIME type and contents.

Parameters:

filepath: : name of the file to look up.

Returns:

the entry's MIME type, or nil if the file was not found.
contents of the file, or nil if the file was not found.

Usage:

local filename = "media/diagram.png"
local mt, contents = pandoc.mediabag.lookup(filename)

fetch {#pandoc.mediabag.fetch}

fetch (source, base_url)

Fetches the given source from a URL or local file. Returns two values: the contents of the file and the MIME type (or an empty string).

Returns:

the entries MIME type, or nil if the file was not found.
contents of the file, or nil if the file was not found.

Usage:

local diagram_url = "https://pandoc.org/diagram.jpg"
local mt, contents = pandoc.mediabag.fetch(diagram_url, ".")

Module pandoc.List

The this module defines pandoc's list type. It comes with useful methods and convenience functions.

Constructor

[pandoc.List([table])]{#pandoc.list}

: Create a new List. If the optional argument table is given, set the metatable of that value to pandoc.List. This is an alias for pandoc.List:new([table]).

Metamethods

[pandoc.List:__concat (list)]{#pandoc.list:__concat}

: Concatenates two lists.

Parameters:

`list`:
:   second list concatenated to the first

Returns: a new list containing all elements from list1 and
list2

Methods

[pandoc.List:clone ()]{#pandoc.list:clone}

: Returns a (shallow) copy of the list.

[pandoc.List:extend (list)]{#pandoc.list:extend}

: Adds the given list to the end of this list.

Parameters:

`list`:
:   list to appended

[pandoc.List:find (needle, init)]{#pandoc.list:find}

: Returns the value and index of the first occurrence of the given item.

Parameters:

`needle`:
:   item to search for

`init`:
:   index at which the search is started

Returns: first item equal to the needle, or nil if no such
item exists.

[pandoc.List:find_if (pred, init)]{#pandoc.list:find_if}

: Returns the value and index of the first element for which the predicate holds true.

Parameters:

`pred`:
:   the predicate function

`init`:
:   index at which the search is started

Returns: first item for which \`test\` succeeds, or nil if
no such item exists.

[pandoc.List:filter (pred)]{#pandoc.list:filter}

: Returns a new list containing all items satisfying a given condition.

Parameters:

`pred`:
:   condition items must satisfy.

Returns: a new list containing all items for which \`test\`
was true.

[pandoc.List:includes (needle, init)]{#pandoc.list:includes}

: Checks if the list has an item equal to the given needle.

Parameters:

`needle`:
:   item to search for

`init`:
:   index at which the search is started

Returns: true if a list item is equal to the needle, false
otherwise

[pandoc.List:insert ([pos], value)]{#pandoc.list:insert}

: Inserts element value at position pos in list, shifting elements to the next-greater index if necessary.

This function is identical to
[`table.insert`](https://www.lua.org/manual/5.3/manual.html#6.6).

Parameters:

`pos`:
:   index of the new value; defaults to length of the list + 1

`value`:
:   value to insert into the list

[pandoc.List:map (fn)]{#pandoc.list:map}

: Returns a copy of the current list by applying the given function to all elements.

Parameters:

`fn`:
:   function which is applied to all list items.

[pandoc.List:new([table])]{#pandoc.list:new}

: Create a new List. If the optional argument table is given, set the metatable of that value to pandoc.List.

Parameters:

`table`:
:   table which should be treatable as a list; defaults to an
    empty table

Returns: the updated input value

[pandoc.List:remove ([pos])]{#pandoc.list:remove}

: Removes the element at position pos, returning the value of the removed element.

 This function is identical to
 [`table.remove`](https://www.lua.org/manual/5.3/manual.html#6.6).

Parameters:

`pos`:
:   position of the list value that will be removed; defaults
    to the index of the last element

Returns: the removed element

[pandoc.List:sort ([comp])]{#pandoc.list:sort}

: Sorts list elements in a given order, in-place. If comp is given, then it must be a function that receives two list elements and returns true when the first element must come before the second in the final order (so that, after the sort, i < j implies not comp(list[j],list[i])). If comp is not given, then the standard Lua operator < is used instead.

Note that the comp function must define a strict partial
order over the elements in the list; that is, it must be
asymmetric and transitive. Otherwise, no valid sort may be
possible.

The sort algorithm is not stable: elements considered equal
by the given order may have their relative positions changed
by the sort.

This function is identical to
[`table.sort`](https://www.lua.org/manual/5.3/manual.html#6.6).

Parameters:

`comp`:
:   Comparison function as described above.

Module pandoc.system

Access to system information and functionality.

Static Fields

arch {#pandoc.system.arch}

The machine architecture on which the program is running.

os {#pandoc.system.os}

The operating system on which the program is running.

Functions

environment {#pandoc.system.environment}

environment ()

Retrieve the entire environment as a string-indexed table.

Returns:

A table mapping environment variables names to their string value (table).

get_working_directory {#pandoc.system.get_working_directory}

get_working_directory ()

Obtain the current working directory as an absolute path.

Returns:

The current working directory (string).

with_environment {#pandoc.system.with_environment}

with_environment (environment, callback)

Run an action within a custom environment. Only the environment variables given by environment will be set, when callback is called. The original environment is restored after this function finishes, even if an error occurs while running the callback action.

Parameters:

environment : Environment variables and their values to be set before running callback. (table with string keys and string values)

callback : Action to execute in the custom environment (function)

Returns:

The result(s) of the call to callback

with_temporary_directory {#pandoc.system.with_temporary_directory}

with_temporary_directory ([parent_dir,] templ, callback)

Create and use a temporary directory inside the given directory. The directory is deleted after the callback returns.

Parameters:

parent_dir : Parent directory to create the directory in (string). If this parameter is omitted, the system's canonical temporary directory is used.

templ : Directory name template (string).

callback : Function which takes the name of the temporary directory as its first argument (function).

Returns:

The result of the call to callback.

with_working_directory {#pandoc.system.with_working_directory}

with_working_directory (directory, callback)

Run an action within a different directory. This function will change the working directory to directory, execute callback, then switch back to the original working directory, even if an error occurs while running the callback action.

Parameters:

directory : Directory in which the given callback should be executed (string)

callback : Action to execute in the given directory (function)

Returns:

The result(s) of the call to callback

Module pandoc.types

Constructors for types which are not part of the pandoc AST.

Version {#pandoc.types.version}

Version (version_specifier)

Creates a Version object.

Parameters:

version_specifier: : Version specifier: this can be a version string like '2.7.3', a list of integers like {2, 7, 3}, a single integer, or a Version.

Returns:

A new Version object.

Files

lua-filters.md

Latest commit

History

lua-filters.md

File metadata and controls

Introduction

Lua filter structure

Filters on element sequences

Execution Order

Global variables

Pandoc Module

Element creation

Exposed pandoc functionality

Lua interpreter initialization

Debugging Lua filters

Examples

Macro substitution

Center images in LaTeX and HTML output

Setting the date in the metadata

Remove spaces before citations

Replacing placeholders with their metadata value

Modifying pandoc's MANUAL.txt for man pages

Creating a handout from a paper

Counting words in a document

Converting ABC code to music notation

Building images with TikZ

Lua type reference

Shared Properties

clone

Pandoc {#type-pandoc}

Meta {#type-meta}

MetaValue {#type-metavalue}

MetaBlocks {#type-metablocks}

MetaBool {#type-metabool}

MetaInlines {#type-metainlines}

MetaList {#type-metalist}

MetaMap {#type-metamap}

MetaString {#type-metastring}

Block {#type-block}

BlockQuote {#type-blockquote}

BulletList {#type-bulletlist}

CodeBlock {#type-codeblock}

DefinitionList {#type-definitionlist}

Div {#type-div}

Header {#type-header}

HorizontalRule {#type-horizontalrule}

LineBlock {#type-lineblock}

Null {#type-null}

OrderedList {#type-orderedlist}

Para {#type-para}

Plain {#type-plain}

RawBlock {#type-rawblock}

Table {#type-table}

Inline {#type-inline}

Cite {#type-cite}

Code {#type-code}

Emph {#type-emph}

Image {#type-image}

LineBreak {#type-linebreak}

Link {#type-link}

Math {#type-math}

Note {#type-note}

Quoted {#type-quoted}

RawInline {#type-rawinline}

SmallCaps {#type-smallcaps}

SoftBreak {#type-softbreak}

Space {#type-space}

Span {#type-span}

Str {#type-str}

Strikeout {#type-strikeout}

Strong {#type-strong}

Subscript {#type-subscript}

Superscript {#type-superscript}

Underline {#type-underline}

Element components

Attr {#type-attr}

Attributes {#type-attributes}

Caption {#type-caption}

Cell {#type-cell}

Modifying pandoc's `MANUAL.txt` for man pages

`clone`

`must_be_at_least`