Module:Labelled list hatnote

From Omniversalis
This module provides a handful of functions that make it easy to implement hatnotes that take the form of a label in front of a list of pages, e.g.



Invoking the labelledList() function is enough to implement most such templates:

{{#invoke:Labelled list hatnote|labelledList|Universal label}}


{{#invoke:Labelled list hatnote|labelledList|Singular label|Plural label}}

For example, providing "See also" instead of "Universal label" duplicates the functionality of {{see also}}, while providing "Main article" and "Main articles" instead of "Singular label" and "Plural label" duplicates the (article namespace) functionality of {{main}}.


The preprocessDisplays() function takes a raw list of arguments and combines in any display arguments. For example, {{see also|1|l1=One}} initially has the arguments table {'1', ['l1'] = 'One'}; this table would combine those into the table {'1|One'}. It overrides manual piping (e.g. {{see also|1{{!}}2|l1=One}}{'1|One'}) and compresses sparse arrays if a parameter is skipped or left empty.

local mLabelledList = require('Module:Labelled list hatnote')
local pages = mLabelledList.preprocessDisplays(args)


For modules that need to modify the functionality slightly while still using it, _labelledList() provides some flexibility. It takes three parameters:

  1. A pages list, preferably preprocessed and compressed by preprocessDisplays
  2. A labels table, where the first item is the singular or universal label, and the second either a plural label or a copy of the first.
  3. An options table, preferably containing:
    • a template string with the full title of the template. Defaults to the title of this module.
    • a category string (or nil) as taken by makeWikitextError from Module:Hatnote, to optionally disable error categories
    • a selfref string (or nil) as taken by _hatnote to enable the selfref option
local mLabelledList = require('Module:Labelled list hatnote')
return mLabelledList._labelledList(pages, labels, options)


This module causes templates based on it to produce an error message if no page names are provided as template parameters. Normally, these should lead back to "Errors" sections in the documentation of those templates. However, if those templates use a module with _labelledList() and don't provide a template item in their options table, that error defaults to leading back here. The error can be solved by providing at least one valid page-name parameter to the template in question; the problem in the template can be fixed by providing some value to the template item of the _labelledList() options table.

--                               Labelled list                                --
--                                                                            --
-- This module does the core work of creating a hatnote composed of a list    --
-- prefixed by a colon-terminated label, i.e. "LABEL: [andList of pages]",    --
-- for {{see also}} and similar templates.                                    --

local mHatnote = require('Module:Hatnote')
local mHatlist = require('Module:Hatnote list')
local mArguments --initialize lazily
local yesno --initialize lazily
local p = {}

-- Defaults global to this module
local defaults = {
	label = 'See also', --Final fallback for label argument
	labelForm = '%s: %s',
	prefixes = {'label', 'label ', 'l'},
	template = 'Module:Labelled list hatnote'

-- Localizable message strings
local msg = {
	errorSuffix = '#Errors',
	noInputWarning = 'no page names specified',
	noOutputWarning =
		"'''[[%s]] — no output: none of the target pages exist.'''"

-- Helper function that pre-combines display parameters into page arguments.
-- Also compresses sparse arrays, as a desirable side-effect.
function p.preprocessDisplays (args, prefixes)
	-- Prefixes specify which parameters, in order, to check for display options
	-- They each have numbers auto-appended, e.g. 'label1', 'label 1', & 'l1'
	prefixes = prefixes or defaults.prefixes
	local indices = {}
	local sparsePages = {}
	for k, v in pairs(args) do
		if type(k) == 'number' then
			indices[#indices + 1] = k
			local display
			for i = 1, #prefixes do
				display = args[prefixes[i] .. k]
				if display then break end
			sparsePages[k] = display and
				string.format('%s|%s', string.gsub(v, '|.*$', ''), display) or v
	local pages = {}
	for k, v in ipairs(indices) do pages[#pages + 1] = sparsePages[v] end
	return pages

--Helper function to get a page target from a processed page string
--e.g. "Page|Label" → "Page" or "Target" → "Target"
local function getTarget(pagename)
 	local pipe = string.find(pagename, '|')
	return string.sub(pagename, 0, pipe and pipe - 1 or nil)

-- Produces a labelled pages-list hatnote.
-- The main frame (template definition) takes 1 or 2 arguments, for a singular
-- and (optionally) plural label respectively:
-- * {{#invoke:Labelled list hatnote|labelledList|Singular label|Plural label}}
-- The resulting template takes pagename & label parameters normally.
function p.labelledList (frame)
	mArguments = require('Module:Arguments')
	yesno = require('Module:Yesno')
	local labels = {frame.args[1] or defaults.label}
	labels[2] = frame.args[2] or labels[1]
	labels[3] = frame.args[3] --no defaulting
	labels[4] = frame.args[4] --no defaulting
	local template = frame:getParent():getTitle()
	local args = mArguments.getArgs(frame, {parentOnly = true})
	local pages = p.preprocessDisplays(args)
	local options = {
		category = yesno(args.category),
		extraclasses = frame.args.extraclasses,
		ifexists = yesno(frame.args.ifexists),
		namespace = frame.args.namespace or args.namespace,
		selfref = yesno(frame.args.selfref or args.selfref),
		template = template
	return p._labelledList(pages, labels, options)

function p._labelledList (pages, labels, options)
	if options.ifexists then
		for k = #pages, 1, -1 do --iterate backwards to allow smooth removals
			local v = pages[k]
			local title =, namespace)
			if (v == '') or title == nil or not title.exists then
				table.remove(pages, k)
	labels = labels or {}
	label = (#pages == 1 and labels[1] or labels[2]) or defaults.label
	for k, v in pairs(pages) do 
		if mHatnote.findNamespaceId(v) ~= 0 then
			label =
					#pages == 1 and
					(labels[3] or labels[1] or defaults.label) or
					(labels[4] or labels[2] or defaults.label)
				) or defaults.label
	if #pages == 0 then
		if options.ifexists then
					msg.noOutputWarning, options.template or defaults.template
			return ''
			return mHatnote.makeWikitextError(
				(options.template or defaults.template) .. msg.errorSuffix,
	local text = string.format(
		options.labelForm or defaults.labelForm,
		mHatlist.andList(pages, true)
	local hnOptions = {
		extraclasses = options.extraclasses,
		selfref = options.selfref
	return mHatnote._hatnote(text, hnOptions)

return p