विकिपीडिया:Lua

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v t e

Lua is a programming language that is now available, via the Scribunto MediaWiki extension, on the English Wikipedia. Lua code can now be embedded into wiki templates by employing the "{{#invoke:}}" functionality of the Scribunto MediaWiki extension.

The Lua source code is stored in pages called modules (e.g., Module:Bananas). These individual modules are then invoked (by "{{#invoke:}}") on template pages (e.g., Module:Bananas/doc uses the code {{#invoke:Bananas|hello}} to print the text "Hello, world!").

Example modules

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Module:Bananas: The simplest possible script, providing a single function with no arguments.
Module:BananasArgs: Demonstrates how to access and use parameters.

Request a script

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Visit Wikipedia:Lua requests to request help in writing a Lua script to perform a specific task on Wikipedia or another Wikimedia Foundation project.

History

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Sordid history. {{qif}}, ParserFunctions, Lua extension, wiki scripting language debated (JavaScript v. Lua), mw:Extension:WikiScripts, Tim writes Scribunto with initial support for Lua.

Discussed for years, Lua was installed in 2012 for testing on test2.wikipedia.org, with open invitation to all editors to experiment with developing Lua modules. Lua was installed on the English Wikipedia in February 2013, after testing on mediawiki.org and Wikimedia test wikis.

About Lua

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See also Brad Jorsch's short presentation for a basic example of how to convert a wikitext template into a Lua module (PDF).

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 script can be kept simple, for easy understanding, Lua allows complex structures including tables, dynamic functions, and associative arrays where index subscripts 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 an example of Lua source code for a hello world function contained in Module:HelloWorld:

-- All Lua modules on Wikipedia must begin by defining a variable that will hold their
-- externally accessible functions. They can have any name and may also hold data.
my_object = {};

-- Add a function to the variable. These are callable in Wikipedia via the #invoke command.
-- "frame" will contain the data that Wikipedia sends this function when it is called. 
my_object.hello = function( frame ) 

    -- Declare a local variable and assign data to it.
    local str = "Hello World!"  

    -- Quit this function and send the information in "str" back to Wikipedia.
    -- The "print" function is not allowed, so all output is accomplished via 
    -- returning strings in this fashion.
    return str    

-- End the function.
end

-- All modules end by returning the variable containing its functions to Wikipedia.
return my_object

-- We can now use this module by calling {{#invoke: HelloWorld | hello }}.
-- The #invoke command begins with the module's name, in this case "HelloWorld",
-- then takes the name of one of its functions as an argument, in this case "hello".

A sample of Lua is highlighted by tag "<source lang="lua">...</source>" 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, see mw:Extension:Scribunto/Lua reference manual.

Unit testing

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A unit testing framework for Lua scripts on Wikipedia is available at Module:UnitTests. It allows you to execute your script on a given set of inputs and verify that the expected outputs are produced. Unit tests are especially useful for rapidly detecting regressions, where modifications to a script introduce new problems.

By convention, unit tests for a module like Module:Bananas are placed in Module:Bananas/testcases, and are executed on Module talk:Bananas/testcases with e.g. {{#invoke: Bananas/testcases | run_tests}}. Test methods must begin with "test". A simple example from Module:Bananas/testcases is below.

-- Unit tests for [[Module:Bananas]]. Click talk page to run tests.
local p = require('Module:UnitTests')
 
function p:test_hello()
    self:preprocess_equals('{{#invoke:Bananas | hello}}', 'Hello, world!')
end
 
return p

For a list of all modules using unit tests, see Special:Whatlinkshere/Module:UnitTests.

Wikipedia-specific features

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Overall: Lua can only get input as text strings passed to the {{#invoke:}} and what can be fetched via frame:expandTemplate, frame:preprocess, and the like. Lua on Wikipedia can only output wikitext not including pre-save transforms or transclusions and other {{...}} constructs. 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 mw:Extension:Scribunto/Lua reference manual#Differences from standard Lua).

Lua input limitations

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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 Wikipedia. This does not include graphics files (not even .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 category, nor the contents of Special: pages.

Wikitext

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Transcluded Wikipedia 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 of the type [[Wikipedia:Help|]] won't work if returned as output - they need to be written explicitly as [[Wikipedia:Help|Help]]. Other pre-save transforms, such as replacing ~~~~ with signatures, will also fail to be processed. Template transclusions, parser function calls, and variable substitutions (i.e. anything with a {{...}}) will not be processed, nor will tags such as <ref> or <nowiki>.

Labeling converted templates

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Please place the {{lua}} template on the documentation subpage of all templates that use Lua. It will help to better communicate Lua usage and template conversions. It looks like this:

Error: no modules specified