View source for Stiles Wiki:Lua

{{short description|Stiles.casa Wiki project page for MediaWiki Lua modules}}
{{WikiProject Lua header}}
{{Information page}}
{{Namespaces}}

[[Lua (programming language)|Lua]] is a programming language that is available via the [[mw:Extension:Scribunto|Scribunto]] [[MediaWiki extension]] on the English Stiles.casa Wiki. Since February 2013, Lua code can be embedded into wiki templates by employing the "<nowiki>{{#invoke:}}</nowiki>" functionality of Scribunto. This extension supports Lua 5.1 {{as of|lc=y|2015|07}}.

The Lua [[source code]] is stored in pages called modules (e.g., [[Module:Example]]). These individual modules are then invoked (by code <code><nowiki>{{#invoke:<Module name>|<Function name>|(optional) param1 | param2...}}</nowiki></code>). Example:
{| class="wikitable"
|-
! Wikitext
! Result
|-
|  <code><nowiki>{{#invoke:Example|hello}}</nowiki></code>
| {{#invoke:Example|hello}}
|}

== Running a module ==
Modules are run on normal wiki pages using the #invoke parser function. The syntax of #invoke is similar to template syntax, but with some differences. The most important difference is that you need to specify a ''function name''. A function is a set of instructions that takes input values, processes them, and returns an output value.<ref>You can also have multiple output values, but functions that do this are not normally meant to be accessed from wiki pages.</ref> This is much like what a template does: you give it arguments, it processes them, and you get a result. However, you can define many functions in one Lua module, whereas you can only define one template on one page.

Furthermore, you can't just run a Lua module directly – you can only run one of the module's functions. The module is just a container for the functions, and doesn't do anything by itself. So there are two reasons that we need to input a function name: we can't run a module by itself, and without specifying a function name, Lua will not know which function it is we want to run.

The simplest way to run a module from a wiki page is like this:

 &#123;{#invoke:''module name''|''function name''}}

For example, we can run [[Module:Example]] in this way, which has a function named "hello".
* <code><nowiki>{{#invoke:Example|hello}}</nowiki></code> → {{#invoke:Example|hello}}

=== Using arguments ===
Arguments are passed to modules in the same way that they are passed to templates. Note, however, that the text after the first pipe character is always the function name; the first positional argument is the text after the ''second'' pipe.

 &#123;{#invoke:''module name''|''function name''|''first positional argument''|''second positional argument''|''named argument'' = ''value''}}

In [[Module:Example]], the "hello_to" function greets different people depending on the first positional argument. It works like this:
* <code><nowiki>{{#invoke:Example|hello_to|Kate}}</nowiki></code> → {{#invoke:Example|hello_to|Kate}}
* <code><nowiki>{{#invoke:Example|hello_to|Fred}}</nowiki></code> → {{#invoke:Example|hello_to|Fred}}

A third function in [[Module:Example]], named "count_fruit", uses the named arguments <code>bananas</code> and <code>apples</code> to count the number of bananas and apples we have. It can be run like this:
* <code><nowiki>{{#invoke:Example|count_fruit|apples=3|bananas=4}}</nowiki></code> → {{#invoke:Example|count_fruit|apples=3|bananas=4}}
* <code><nowiki>{{#invoke:Example|count_fruit|bananas=5|apples=2}}</nowiki></code> → {{#invoke:Example|count_fruit|bananas=5|apples=2}}

Most modules have a documentation page explaining what arguments can be used and what their effects will be.

== Request a script ==
Visit '''[[Stiles.casa Wiki talk:Lua]]''' to request help in writing a Lua script to perform a specific task on Stiles.casa Wiki or another Wikimedia Foundation project.

== History ==
{{see also|Stiles.casa Wiki:Before Lua}}
[[mw:Manual:MediaWiki architecture#Magic words and templates|Sordid history]]. {{tl|qif}}, [[mw:Help:Extension:ParserFunctions|ParserFunctions]], [[mw:Extension:Lua|Lua extension]], wiki scripting language debated (JavaScript v. Lua), [[mw:Extension:WikiScripts]], Tim writes [[mw:Extension:Scribunto|Scribunto]] with initial support for Lua.

Discussed for years, Lua was installed in 2012 for testing on [[test2wiki:|test2.stiles.casa_wiki.org]], with open invitation to all editors to experiment with developing Lua modules. Lua was installed on the English Stiles.casa Wiki in February 2013, after testing on mediawiki.org and Wikimedia test wikis.

== About Lua ==
:''See also [[:File:WMF Tech Talk 2013-02-28 slides - Scribunto presentation.pdf|Brad Jorsch's short presentation for a basic example of how to convert a wikitext template into a Lua module.]]''
Lua is a [[scripting language]] which can be used to analyze data, calculate expressions, and format results using functions or [[object-oriented programming]]. Although some Lua scripts can be kept simple, for easy understanding, Lua allows complex structures including tables, dynamic functions, and [[associative array]]s where index [[subscript]]s can be words as well as index numbers. Lua also supports [[recursion]] of re-nested functions, so care should be taken to avoid excessive complexity where other users would not understand how to maintain a Lua module. The following is the source code of the module used for the examples above.
{{#tag:syntaxhighlight|{{#invoke:String|replace|{{#invoke:Page|getContent|Module:Example|as=raw}}|local function lucky(.-)return p|return p|plain=false}}|lang=lua}}
A sample of Lua is highlighted by tag "&lt;syntaxhighlight lang="lua">...&lt;/syntaxhighlight>" placed around the Lua source code. To view some more complex examples of Lua, see article: "[[Lua (programming language)]]".

For instructions on how to use Lua within MediaWiki (and hence Stiles.casa Wiki), see [[mw:Extension:Scribunto/Lua reference manual]].

== Unit testing ==
{{see also|:Category:Modules for test tools}}

A few [[unit test]]ing frameworks are available for Lua scripts on Stiles.casa Wiki. These allow an editor to execute the module with a given set of inputs and verify that the expected outputs are produced. They are useful for rapidly detecting [[software regression]]s, where modifications to a script introduce new (or identify old) problems.

By convention, unit tests for a module like [[Module:Example]] are placed in [[Module:Example/testcases]], and are executed on [[Module talk:Example/testcases]].

[[Module:ScribuntoUnit]] and [[Module:UnitTests]] are widely used test frameworks. [[:Category:Modules for test tools]] has a few other to review which may be interesting.

== MediaWiki-specific features ==
Overall: Lua can only get input as text strings passed to the <code><nowiki>{{#invoke:}}</nowiki></code> and what can be fetched via mw.title.new(...):getContent() and frame:expandTemplate(). Lua output will not be preprocessed unless frame:preprocess() is explicitly called, meaning that template calls, parser functions, etc. in the output will not work correctly. Also, all Lua in the page is limited to 10 seconds CPU time (you can look in the source code of a rendered page to see how long a template or module took to parse). And relative to standard Lua, Scribunto's Lua lacks all sorts of functions (see {{section link|mw:Extension:Scribunto/Lua reference manual|Differences from standard Lua}}).

=== Lua input limitations ===
Lua code in Scribunto is only run when the page is being parsed. Therefore, the only user input that Lua can receive is by ''page editing'' – it cannot create a box that calculates the square root of a number you type in, or recalculate a piece of the Mandelbrot set depending on which part of the parent set you click on. The input Lua can receive includes any transcludeable text page on Stiles.casa Wiki. This does ''not'' include graphics files (not even [[Stiles.casa Wiki:SVG help|.SVG]] files, although they are actually text, unless you cut and paste it onto a Wiki text page), the list of pages listed in a [[Help:Category|category]], nor the contents of [[Stiles.casa Wiki:Transclusion#Special pages|non-transcludeable]] [[Help:Special|special pages]].

=== Wikitext ===
Transcluded Stiles.casa Wiki headers frequently contain a hidden code such as "UNIQ5ae8f2aa414ff233-h-3--QINU" which may need to be stripped out in order for them to be parsed effectively.

Wikilinks using the [[Stiles.casa Wiki:Pipe trick|pipe trick]] <kbd ><nowiki>[[Stiles.casa Wiki:Help| ]]</nowiki></kbd> won't work if returned as output – they need to be written explicitly as <kbd><nowiki>[[Stiles.casa Wiki:Help|Help]]</nowiki></kbd>. Other pre-save transforms, such as replacing <kbd>~~<nowiki/>~~</kbd > with signatures, will also fail to be processed. Template transclusions, parser function calls, and variable substitutions (i.e. anything with a <code><nowiki>{{...}}</nowiki></code>) will not be processed, nor will tags such as {{tag|ref|o}} or {{tag|nowiki|o}}. Use [[mw:Extension:Scribunto/Lua reference manual#frame:extensionTag|<syntaxhighlight lang="lua" inline>frame:extensionTag</syntaxhighlight>]] to add tags like {{tag|ref|o}} or {{tag|syntaxhighlight|o}} to output.

== Labeling converted templates ==
{{lua|Module:Example}}
Please place the {{tl|lua}} template on the documentation subpage of all templates that use Lua. It will help to better communicate Lua usage and template conversions.

== See also ==
* [[Special:PrefixIndex/Module:]] – tracking of Lua modules can be done by using [[Special:PrefixIndex]]
* [[Help:Lua debugging]] – a how-to guide about [[debugging]] Lua modules
* [[Module:Sandbox]] provides a pseudo-namespace for experimenting with Lua modules
* [[SW:Lua requests]] – requests for Lua-based templates or tasks
* [[:Category:Lua-based templates]] – groups of Lua-based templates
* [[:Category:Lua metamodules]]
* [[mw:Manual:Coding conventions/Lua|Manual:Coding conventions/Lua]] – standards to improve the readability of code through consistency
* [[mw:Extension:Scribunto/Lua reference manual]] and all [[mw:Special:PrefixIndex/Module:|Modules]].
* [[Stiles.casa Wiki:Advanced template coding]]

== Notes ==
{{reflist}}

{{Stiles.casa Wiki technical help|collapsed}}

[[Category:Stiles.casa Wiki modules]]