path: root/data/pandoc.lua

--[[
pandoc.lua

Copyright © 2017 Albert Krewinkel

Permission to use, copy, modify, and/or distribute this software for any purpose
with or without fee is hereby granted, provided that the above copyright notice
and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
THIS SOFTWARE.
]]

---
-- Lua functions for pandoc scripts.
--
-- @author Albert Krewinkel
-- @copyright © 2017 Albert Krewinkel
-- @license MIT
local M = {
  _VERSION = "0.3.0"
}

------------------------------------------------------------------------
-- The base class for pandoc's AST elements.
-- @type Element
-- @local
local Element = {}

--- Create a new element subtype
-- @local
function Element:make_subtype(o)
  o = o or {}
  setmetatable(o, self)
  self.__index = self
  return o
end

--- Create a new element given its tag and arguments
-- @local
function Element:new(tag, ...)
  local element = { t = tag }
  local content = {...}
  -- special case for unary constructors
  if #content == 1 then
    element.c = content[1]
  -- Don't set 'c' field if no further arguments were given. This is important
  -- for nullary constructors like `Space` and `HorizontalRule`.
  elseif #content > 0 then
    element.c = content
  end
  setmetatable(element, self)
  self.__index = self
  return element
end

--- Create a new constructor
-- @local
-- @param tag Tag used to identify the constructor
-- @param fn Function to be called when constructing a new element
-- @param accessors names to use as accessors for numerical fields
-- @return function that constructs a new element
function Element:create_constructor(tag, fn, accessors)
  local constr = self:make_subtype({tag = tag, getters = {}, setters = {}})

  -- Add accessors to the metatable
  if type(accessors) == "string" then
    constr.getters[accessors] = function(elem)
      return elem.c
    end
    constr.setters[accessors] = function(elem, v)
      elem.c = v
    end
  else
    for i = 1, #(accessors or {}) do
      if type(accessors[i]) == "string" then
        constr.getters[accessors[i]] = function(elem)
          return elem.c[i]
        end
        constr.setters[accessors[i]] = function(elem, v)
          elem.c[i] = v
        end
      else -- only two levels of nesting are supported
        for k, v in ipairs(accessors[i]) do
          constr.getters[v] = function(elem)
            return elem.c[i][k]
          end
          constr.setters[v] = function(elem, v)
            elem.c[i][k] = v
          end
        end
      end
    end
  end

  function constr:new(...)
    local obj = fn(...)
    setmetatable(obj, self)
    self.__index = function(t, k)
      if getmetatable(t).getters[k] then
        return getmetatable(t).getters[k](t)
      elseif k == "t" then
        return getmetatable(t)["tag"]
      else
        return getmetatable(t)[k]
      end
    end
    self.__newindex = function(t, k, v)
      if getmetatable(t).setters[k] then
        getmetatable(t).setters[k](t, v)
      else
        rawset(t, k, v)
      end
    end
    return obj
  end
  self.constructor = self.constructor or {}
  self.constructor[tag] = constr
  return constr
end

--- Calls the constructor, creating a new element.
-- @local
function Element.__call(t, ...)
  return t:new(...)
end

------------------------------------------------------------------------
--- Pandoc Document
-- @section document

--- A complete pandoc document
-- @function Pandoc
-- @tparam      {Block,...} blocks      document content
-- @tparam[opt] Meta        meta        document meta data
function M.Pandoc(blocks, meta)
  meta = meta or {}
  return {
    ["blocks"] = blocks,
    ["meta"] = meta,
    ["pandoc-api-version"] = {1,17,0,5},
  }
end

-- DEPRECATED synonym:
M.Doc = M.Pandoc

------------------------------------------------------------------------
-- MetaValue
-- @section MetaValue
M.MetaValue = Element:make_subtype{}
M.MetaValue.__call = function(t, ...)
  return t:new(...)
end
--- Meta blocks
-- @function MetaBlocks
-- @tparam {Block,...} blocks blocks

--- Meta inlines
-- @function MetaInlines
-- @tparam {Inline,...} inlines inlines

--- Meta list
-- @function MetaList
-- @tparam {MetaValue,...} meta_values list of meta values

--- Meta map
-- @function MetaMap
-- @tparam table key_value_map a string-indexed map of meta values
M.meta_value_types = {
  "MetaBlocks",
  "MetaInlines",
  "MetaList",
  "MetaMap",
}
for i = 1, #M.meta_value_types do
  M[M.meta_value_types[i]] = M.MetaValue:create_constructor(
    M.meta_value_types[i],
    function(content)
      return content
    end
  )
end

--- Creates string to be used in meta data.
-- Does nothing, lua strings are meta strings.
-- @function MetaString
-- @tparam string str string value
function M.MetaString(str)
  return str
end

--- Creates boolean to be used in meta data.
-- Does nothing, lua booleans are meta booleans.
-- @function MetaBool
-- @tparam boolean bool boolean value
function M.MetaBool(bool)
  return bool
end

------------------------------------------------------------------------
-- Blocks
-- @section Block

--- Block elements
M.Block = Element:make_subtype{}
M.Block.__call = function (t, ...)
  return t:new(...)
end

--- Creates a block quote element
-- @function BlockQuote
-- @tparam      {Block,...} content     block content
-- @treturn     Block                   block quote element
M.BlockQuote = M.Block:create_constructor(
  "BlockQuote",
  function(content) return {c = content} end,
  "content"
)

--- Creates a bullet (i.e. unordered) list.
-- @function BulletList
-- @tparam      {{Block,...},...} content     list of items
-- @treturn     Block block quote element
M.BulletList = M.Block:create_constructor(
  "BulletList",
  function(content) return {c = content} end,
  "content"
)

--- Creates a code block element
-- @function CodeBlock
-- @tparam      string      text        code string
-- @tparam[opt] Attr        attr element attributes
-- @treturn     Block                   code block element
M.CodeBlock = M.Block:create_constructor(
  "CodeBlock",
  function(text, attr) return {c = {attr or M.Attr(), text}} end,
  {{"identifier", "classes", "attributes"}, "text"}
)

--- Creates a definition list, containing terms and their explanation.
-- @function DefinitionList
-- @tparam      {{{Inline,...},{Block,...}},...} content     list of items
-- @treturn     Block block quote element
M.DefinitionList = M.Block:create_constructor(
  "DefinitionList",
  function(content) return {c = content} end,
  "content"
)

--- Creates a div element
-- @function Div
-- @tparam      {Block,...} content     block content
-- @tparam[opt] Attr        attr  element attributes
-- @treturn     Block                   code block element
M.Div = M.Block:create_constructor(
  "Div",
  function(content, attr)
    return {c = {attr or M.Attr(), content}}
  end,
  {{"identifier", "classes", "attributes"}, "content"}
)

--- Creates a block quote element.
-- @function Header
-- @tparam      int          level       header level
-- @tparam      {Inline,...} content     inline content
-- @tparam[opt] Attr         attr element attributes
-- @treturn     Block                    header element
M.Header = M.Block:create_constructor(
  "Header",
  function(level, content, attr)
    return {c = {level, attr or M.Attr(), content}}
  end,
  {"level", {"identifier", "classes", "attributes"}, "content"}
)

--- Creates a horizontal rule.
-- @function HorizontalRule
-- @treturn     Block                   horizontal rule
M.HorizontalRule = M.Block:create_constructor(
  "HorizontalRule",
  function() return {} end
)

--- Creates a line block element.
-- @function LineBlock
-- @tparam      {{Inline,...},...} content    inline content
-- @treturn     Block                   block quote element
M.LineBlock = M.Block:create_constructor(
  "LineBlock",
  function(content) return {c = content} end,
  "content"
)

--- Creates a null element.
-- @function Null
-- @treturn     Block                   null element
M.Null = M.Block:create_constructor(
  "Null",
  function() return {} end
)

--- Creates an ordered list.
-- @function OrderedList
-- @tparam      {{Block,...},...} items list items
-- @param[opt]  listAttributes list parameters
-- @treturn     Block
M.OrderedList = M.Block:create_constructor(
  "OrderedList",
  function(items, listAttributes)
    listAttributes = listAttributes or {1, M.DefaultStyle, M.DefaultDelim}
    return {c = {listAttributes, items}}
  end,
  {{"start", "style", "delimiter"}, "content"}
)

--- Creates a para element.
-- @function Para
-- @tparam      {Inline,...} content    inline content
-- @treturn     Block                   block quote element
M.Para = M.Block:create_constructor(
  "Para",
  function(content) return {c = content} end,
  "content"
)

--- Creates a plain element.
-- @function Plain
-- @tparam      {Inline,...} content    inline content
-- @treturn     Block                   block quote element
M.Plain = M.Block:create_constructor(
  "Plain",
  function(content) return {c = content} end,
  "content"
)

--- Creates a raw content block of the specified format.
-- @function RawBlock
-- @tparam      string      format      format of content
-- @tparam      string      text        string content
-- @treturn     Block                   block quote element
M.RawBlock = M.Block:create_constructor(
  "RawBlock",
  function(format, text) return {c = {format, text}} end,
  {"format", "text"}
)

--- Creates a table element.
-- @function Table
-- @tparam      {Inline,...} caption    table caption
-- @tparam      {AlignDefault|AlignLeft|AlignRight|AlignCenter,...} aligns alignments
-- @tparam      {int,...}    widths     column widths
-- @tparam      {Block,...}  headers    header row
-- @tparam      {{Block,...}} rows      table rows
-- @treturn     Block                   block quote element
M.Table = M.Block:create_constructor(
  "Table",
  function(caption, aligns, widths, headers, rows)
    return {c = {caption, aligns, widths, headers, rows}}
  end,
  {"caption", "aligns", "widths", "headers", "rows"}
)


------------------------------------------------------------------------
-- Inline
-- @section Inline

--- Inline element class
M.Inline = Element:make_subtype{}
M.Inline.__call = function (t, ...)
  return t:new(...)
end

--- Creates a Cite inline element
-- @function Cite
-- @tparam {Inline,...}   content       List of inlines
-- @tparam {Citation,...} citations     List of citations
-- @treturn Inline citations element
M.Cite = M.Inline:create_constructor(
  "Cite",
  function(content, citations) return {c = {citations, content}} end,
  {"citations", "content"}
)

--- Creates a Code inline element
-- @function Code
-- @tparam      string      text        brief image description
-- @tparam[opt] Attr        attr  additional attributes
-- @treturn Inline code element
M.Code = M.Inline:create_constructor(
  "Code",
  function(text, attr) return {c = {attr or M.Attr(), text}} end,
  {{"identifier", "classes", "attributes"}, "text"}
)

--- Creates an inline element representing emphasised text.
-- @function Emph
-- @tparam      {Inline,..} content     inline content
-- @treturn Inline emphasis element
M.Emph = M.Inline:create_constructor(
  "Emph",
  function(content) return {c = content} end,
  "content"
)

--- Creates a Image inline element
-- @function Image
-- @tparam      {Inline,..} caption     text used to describe the image
-- @tparam      string      src         path to the image file
-- @tparam[opt] string      title       brief image description
-- @tparam[opt] Attr        attr additional attributes
-- @treturn Inline image element
M.Image = M.Inline:create_constructor(
  "Image",
  function(caption, src, title, attr)
    title = title or ""
    attr = attr or M.Attr()
    return {c = {attr, caption, {src, title}}}
  end,
  {{"identifier", "classes", "attributes"}, "caption", {"src", "title"}}
)

--- Create a LineBreak inline element
-- @function LineBreak
-- @treturn Inline linebreak element
M.LineBreak = M.Inline:create_constructor(
  "LineBreak",
  function() return {} end
)

--- Creates a link inline element, usually a hyperlink.
-- @function Link
-- @tparam      {Inline,..} content     text for this link
-- @tparam      string      target      the link target
-- @tparam[opt] string      title       brief link description
-- @tparam[opt] Attr        attr additional attributes
-- @treturn Inline image element
M.Link = M.Inline:create_constructor(
  "Link",
  function(content, target, title, attr)
    title = title or ""
    attr = attr or M.Attr()
    return {c = {attr, content, {target, title}}}
  end,
  {{"identifier", "classes", "attributes"}, "content", {"target", "title"}}
)

--- Creates a Math element, either inline or displayed.
-- @function Math
-- @tparam      "InlineMath"|"DisplayMath" mathtype rendering specifier
-- @tparam      string      text        Math content
-- @treturn     Inline                  Math element
M.Math = M.Inline:create_constructor(
  "Math",
  function(mathtype, text)
    return {c = {mathtype, text}}
  end,
  {"mathtype", "text"}
)
--- Creates a DisplayMath element (DEPRECATED).
-- @function DisplayMath
-- @tparam      string      text        Math content
-- @treturn     Inline                  Math element
M.DisplayMath = M.Inline:create_constructor(
  "DisplayMath",
  function(text) return M.Math("DisplayMath", text) end,
  {"mathtype", "text"}
)
--- Creates an InlineMath inline element (DEPRECATED).
-- @function InlineMath
-- @tparam      string      text        Math content
-- @treturn     Inline                  Math element
M.InlineMath = M.Inline:create_constructor(
  "InlineMath",
  function(text) return M.Math("InlineMath", text) end,
  {"mathtype", "text"}
)

--- Creates a Note inline element
-- @function Note
-- @tparam      {Block,...} content     footnote block content
M.Note = M.Inline:create_constructor(
  "Note",
  function(content) return {c = content} end,
  "content"
)

--- Creates a Quoted inline element given the quote type and quoted content.
-- @function Quoted
-- @tparam      "DoubleQuote"|"SingleQuote" quotetype type of quotes to be used
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  quoted element
M.Quoted = M.Inline:create_constructor(
  "Quoted",
  function(quotetype, content) return {c = {quotetype, content}} end,
  {"quotetype", "content"}
)
--- Creates a single-quoted inline element (DEPRECATED).
-- @function SingleQuoted
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  quoted element
-- @see Quoted
M.SingleQuoted = M.Inline:create_constructor(
  "SingleQuoted",
  function(content) return M.Quoted(M.SingleQuote, content) end,
  {"quotetype", "content"}
)
--- Creates a single-quoted inline element (DEPRECATED).
-- @function DoubleQuoted
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  quoted element
-- @see Quoted
M.DoubleQuoted = M.Inline:create_constructor(
  "DoubleQuoted",
  function(content) return M.Quoted("DoubleQuote", content) end,
  {"quotetype", "content"}
)

--- Creates a RawInline inline element
-- @function RawInline
-- @tparam      string      format      format of the contents
-- @tparam      string      text        string content
-- @treturn     Inline                  raw inline element
M.RawInline = M.Inline:create_constructor(
  "RawInline",
  function(format, text) return {c = {format, text}} end,
  {"format", "text"}
)

--- Creates text rendered in small caps
-- @function SmallCaps
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  smallcaps element
M.SmallCaps = M.Inline:create_constructor(
  "SmallCaps",
  function(content) return {c = content} end,
  "content"
)

--- Creates a SoftBreak inline element.
-- @function SoftBreak
-- @treturn     Inline                  softbreak element
M.SoftBreak = M.Inline:create_constructor(
  "SoftBreak",
  function() return {} end
)

--- Create a Space inline element
-- @function Space
-- @treturn Inline space element
M.Space = M.Inline:create_constructor(
  "Space",
  function() return {} end
)

--- Creates a Span inline element
-- @function Span
-- @tparam      {Inline,..} content     inline content
-- @tparam[opt] Attr        attr  additional attributes
-- @treturn Inline span element
M.Span = M.Inline:create_constructor(
  "Span",
  function(content, attr) return {c = {attr or M.Attr(), content}} end,
  {{"identifier", "classes", "attributes"}, "content"}
)

--- Creates a Str inline element
-- @function Str
-- @tparam      string      text        content
-- @treturn     Inline                  string element
M.Str = M.Inline:create_constructor(
  "Str",
  function(text) return {c = text} end,
  "text"
)

--- Creates text which is striked out.
-- @function Strikeout
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  strikeout element
M.Strikeout = M.Inline:create_constructor(
  "Strikeout",
  function(content) return {c = content} end,
  "content"
)

--- Creates a Strong element, whose text is usually displayed in a bold font.
-- @function Strong
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  strong element
M.Strong = M.Inline:create_constructor(
  "Strong",
  function(content) return {c = content} end,
  "content"
)

--- Creates a Subscript inline element
-- @function Subscript
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  subscript element
M.Subscript = M.Inline:create_constructor(
  "Subscript",
  function(content) return {c = content} end,
  "content"
)

--- Creates a Superscript inline element
-- @function Superscript
-- @tparam      {Inline,..} content     inline content
-- @treturn     Inline                  strong element
M.Superscript = M.Inline:create_constructor(
  "Superscript",
  function(content) return {c = content} end,
  "content"
)


------------------------------------------------------------------------
-- Helpers
-- @section helpers

-- Find a value pair in a list.
-- @function find
-- @tparam table list to be searched
-- @param needle element to search for
-- @param[opt] key when non-nil, compare on this field of each list element
local function find (alist, needle, key)
  local test
  if key then
    test = function(x) return x[key] == needle end
  else
    test = function(x) return x == needle end
  end
  for i, k in ipairs(alist) do
    if test(k) then
      return i, k
    end
  end
  return nil
end

-- Lookup a value in an associative list
-- @function lookup
-- @tparam {{key, value},...} alist associative list
-- @param key key for which the associated value is to be looked up
local function lookup(alist, key)
  return (select(2, find(alist, key, 1)) or {})[2]
end

--- Return an iterator which returns key-value pairs of an associative list.
-- @function apairs
-- @tparam {{key, value},...} alist associative list
local apairs = function (alist)
  local i = 1
  local cur
  function nxt ()
    cur = rawget(alist, i)
    if cur then
      i = i + 1
      return cur[1], cur[2]
    end
    return nil
  end
  return nxt, nil, nil
end

-- AttributeList, a metatable to allow table-like access to attribute lists
-- represented by associative lists.
local AttributeList = {
  __index = function (t, k)
    if type(k) == "number" then
      return rawget(t, k)
    else
      return lookup(t, k)
    end
  end,

  __newindex = function (t, k, v)
    local idx, cur = find(t, k, 1)
    if v == nil then
      table.remove(t, idx)
    elseif cur then
      cur[2] = v
    elseif type(k) == "number" then
      rawset(t, k, v)
    else
      rawset(t, #t + 1, {k, v})
    end
  end,

  __pairs = apairs
}

-- convert a table to an associative list. The order of key-value pairs in the
-- alist is undefined. The table should either contain no numeric keys or
-- already be an associative list.
-- @tparam table associative list or table without numeric keys.
-- @treturn table associative list
local to_alist = function (tbl)
  if #tbl ~= 0 or next(tbl) == nil then
    -- probably already an alist
    return tbl
  end
  local alist = {}
  local i = 1
  for k, v in pairs(tbl) do
    alist[i] = {k, v}
    i = i + 1
  end
  return alist
end

-- Attr
M.Attr = {}
M.Attr._field_names = {identifier = 1, classes = 2, attributes = 3}
--- Create a new set of attributes (Attr).
-- @function Attr
-- @tparam[opt] string       identifier element identifier
-- @tparam[opt] {string,...} classes    element classes
-- @tparam[opt] table        attributes table containing string keys and values
-- @return element attributes
M.Attr.__call = function(t, identifier, classes, attributes)
  identifier = identifier or ''
  classes = classes or {}
  attributes = setmetatable(to_alist(attributes or {}), AttributeList)
  local attr = {identifier, classes, attributes}
  setmetatable(attr, t)
  return attr
end
M.Attr.__index = function(t, k)
  return rawget(t, k) or
    rawget(t, M.Attr._field_names[k]) or
    rawget(getmetatable(t), k)
end
M.Attr.__newindex = function(t, k, v)
  if M.Attr._field_names[k] then
    rawset(t, M.Attr._field_names[k], v)
  else
    rawset(t, k, v)
  end
end
setmetatable(M.Attr, M.Attr)


--- Creates a single citation.
-- @function Citation
-- @tparam      string       id       citation identifier (like a bibtex key)
-- @tparam      AuthorInText|SuppressAuthor|NormalCitation mode citation mode
-- @tparam[opt] {Inline,...} prefix   citation prefix
-- @tparam[opt] {Inline,...} suffix   citation suffix
-- @tparam[opt] int          note_num note number
-- @tparam[opt] int          hash  hash number
M.Citation = function(id, mode, prefix, suffix, note_num, hash)
  prefix = prefix or {}
  suffix = suffix or {}
  note_num = note_num or 0
  hash = hash or 0
  return {
    citationId = id,
    citationPrefix = prefix,
    citationSuffix = suffix,
    citationMode = mode,
    citationNoteNum = note_num,
    citationHash = hash,
  }
end


------------------------------------------------------------------------
-- Constants
-- @section constants

--- Author name is mentioned in the text.
-- @see Citation
-- @see Cite
M.AuthorInText = "AuthorInText"

--- Author name is suppressed.
-- @see Citation
-- @see Cite
M.SuppressAuthor = "SuppressAuthor"

--- Default citation style is used.
-- @see Citation
-- @see Cite
M.NormalCitation = "NormalCitation"

--- Table cells aligned left.
-- @see Table
M.AlignLeft = "AlignLeft"

--- Table cells right-aligned.
-- @see Table
M.AlignRight = "AlignRight"

--- Table cell content is centered.
-- @see Table
M.AlignCenter = "AlignCenter"

--- Table cells are alignment is unaltered.
-- @see Table
M.AlignDefault = "AlignDefault"

--- Default list number delimiters are used.
-- @see OrderedList
M.DefaultDelim = "DefaultDelim"

--- List numbers are delimited by a period.
-- @see OrderedList
M.Period = "Period"

--- List numbers are delimited by a single parenthesis.
-- @see OrderedList
M.OneParen = "OneParen"

--- List numbers are delimited by a double parentheses.
-- @see OrderedList
M.TwoParens = "TwoParens"

--- List are numbered in the default style
-- @see OrderedList
M.DefaultStyle = "DefaultStyle"

--- List items are numbered as examples.
-- @see OrderedList
M.Example = "Example"

--- List are numbered using decimal integers.
-- @see OrderedList
M.Decimal = "Decimal"

--- List are numbered using lower-case roman numerals.
-- @see OrderedList
M.LowerRoman = "LowerRoman"

--- List are numbered using upper-case roman numerals
-- @see OrderedList
M.UpperRoman = "UpperRoman"

--- List are numbered using lower-case alphabetic characters.
-- @see OrderedList
M.LowerAlpha = "LowerAlpha"

--- List are numbered using upper-case alphabetic characters.
-- @see OrderedList
M.UpperAlpha = "UpperAlpha"


------------------------------------------------------------------------
-- Helper Functions
-- @section helpers

--- Parse the given string into a Pandoc document.
-- The method used to interpret input is specified by *format*. Acceptable
-- values for this parameter are equal to those that can be given to the
-- `--from` command line option.
-- @tparam      string markup the markup to be parsed
-- @tparam[opt] string format format specification, defaults to "markdown".
-- @treturn Pandoc 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")
function M.read(markup, format)
  format = format or "markdown"
  local pd = pandoc._read(format, markup)
  if type(pd) == "string" then
    error(pd)
  else
    return pd
  end
end

--- Runs command with arguments, passing it some input, and returns the output.
-- @treturn string Output of command.
-- @raise A table containing the keys `command`, `error_code`, and `output` is
-- thrown if the command exits with a non-zero error code.
-- @usage
-- local ec, output = pandoc.pipe("sed", {"-e","s/a/b/"}, "abc")
function M.pipe (command, args, input)
  local ec, output = pandoc._pipe(command, args, input)
  if ec ~= 0 then
    err = setmetatable(
      { command = command, error_code = ec, output = output},
      { __tostring = function(e)
          return "Error running " .. e.command
            .. " (error code " .. e.error_code .. "): "
            .. e.output
        end
      }
    )
    error(err)
  end
  return output
end

--- Use functions defined in the global namespace to create a pandoc filter.
-- All globally defined functions which have names of pandoc elements are
-- collected into a new table.
-- @return A list of filter functions
-- @usage
-- -- within a file defining a pandoc filter:
-- function Str(text)
--   return pandoc.Str(utf8.upper(text))
-- end
--
-- return {pandoc.global_filter()}
-- -- the above is equivallent to
-- -- return {{Str = Str}}
function M.global_filter()
  local res = {}
  function is_filter_function(k)
    return M.Inline.constructor[k] or
      M.Block.constructor[k] or
      k == "Meta" or k == "Doc" or k == "Pandoc" or
      k == "Block" or k == "Inline"
  end
  for k, v in pairs(_G) do
    if is_filter_function(k) then
      res[k] = v
    end
  end
  return res
end

return M