Add basic lua List module (#4099)

The List module is automatically loaded, but not assigned to a global
variable. It can be included in filters by calling `List = require
'List'`.

Lists of blocks, lists of inlines, and lists of classes are now given
`List` as a metatable, making working with them more convenient. E.g.,
it is now possible to concatenate lists of inlines using Lua's
concatenation operator `..` (requires at least one of the operants to
have `List` as a metatable):

    function Emph (emph)
      local s = {pandoc.Space(), pandoc.Str 'emphasized'}
      return pandoc.Span(emph.content .. s)
    end

Closes: #4081

1 files changed, 110 insertions, 0 deletions

diff --git a/data/List.lua b/data/List.lua
new file mode 100644
index 000000000..344292772
--- /dev/null
+++ b/data/List.lua
@@ -0,0 +1,110 @@
+--[[
+List.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 = "0.1.0"
+}
+
+------------------------------------------------------------------------
+-- Metatable for lists
+-- @type List
+local List = {}
+
+function List:new (o)
+  o = o or {}
+  setmetatable(o, self)
+  self.__index = self
+  return o
+end
+
+function List:__call (o)
+  return self:new(o)
+end
+
+--- Concatenates two lists.
+function List:__concat (list)
+  local res = List.clone(self)
+  List.extend(res, list)
+  return res
+end
+
+--- Returns a (shallow) copy of the list.
+function List:clone ()
+  local lst = setmetatable({}, getmetatable(self))
+  List.extend(lst, self)
+  return lst
+end
+
+--- Appends the given list to the end of this list.
+function List:includes (needle)
+  for i = 1, #self do
+    if self[i] == needle then
+      return true
+    end
+  end
+  return false
+end
+
+--- Returns the value and index of the first occurrence of the given item.
+-- @param needle item to search for
+-- @return first item equal to the needle, or nil if no such item exists.
+-- @return index of that element
+function List:find (needle, init)
+  return List.find_if(self, function(x) return x == needle end, init)
+end
+
+--- Returns the value and index of the first element for which test returns true.
+-- @param test the test function
+-- @param init index at which the search is started
+-- @return first item for which `test` succeeds, or nil if no such item exists.
+-- @return index of that element
+function List:find_if (test, init)
+  init = (init == nil and 1) or (init < 0 and #self - init) or init
+  for i = init, #self do
+    if test(self[i], i) then
+      return self[i], i
+    end
+  end
+  return nil
+end
+
+--- Add the given list to the end of this list.
+-- @param list list to appended
+function List:extend (list)
+  for i = 1, #list do
+    self[#self + 1] = list[i]
+  end
+end
+
+-- Returns a copy of the current list by applying the given function to all
+-- elements.
+function List:map (fn)
+  local res = setmetatable({}, getmetatable(self))
+  for i = 1, #self do
+    res[i] = fn(self[i])
+  end
+  return res
+end
+
+return List