Information:Lua

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Lua is a programming language available through the Scribunto MediaWiki extension on BattleTechWiki.

Lua source code is stored in pages called modules (e.g., the source code for a module named "Example" would be at Module:Example). Individual modules are then invoked, by code {{#invoke:<Module name>|<Function name>|(optional) param1 | param2...}}, for example:

Wikitext	Result
{{#invoke:Example|hello}}	Hello World!

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. 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:

{{#invoke:module name|function name}}

For example, we can run Module:Example in this way, which has a function named "hello".

• {{#invoke:Example|hello}} → Hello World!

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.

{{#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:

• {{#invoke:Example|hello_to|Kate}} → Hello, Kate!
• {{#invoke:Example|hello_to|Fred}} → Hello, Fred!

A third function in Module:Example, named "count_fruit", uses the named arguments bananas and apples to count the number of bananas and apples we have. It can be run like this:

• {{#invoke:Example|count_fruit|apples=3|bananas=4}} → I have 4 bananas and 3 apples
• {{#invoke:Example|count_fruit|bananas=5|apples=2}} → I have 5 bananas and 2 apples

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

About Lua

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 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 the source code of the module used for the examples above.

local p = {};     --All lua modules on Wikipedia must begin by defining a variable 
                    --that will hold their externally accessible functions.
                    --Such variables can have whatever name you want and may 
                    --also contain various data as well as functions.
p.hello = function( frame )     --Add a function to "p".  
                                        --Such functions are callable in Wikipedia
                                        --via the #invoke command.
                                        --"frame" will contain the data that Wikipedia
                                        --sends this function when it runs. 
                                 -- 'Hello' is a name of your choice. The same name needs to be referred to when the module is used.
    
    local str = "Hello World!"  --Declare a local variable and set it equal to
                                --"Hello World!".  
    
    return str    --This tells us to quit this function and send the information in
                  --"str" back to Wikipedia.
    
end  -- end of the function "hello"
function p.hello_to(frame)		-- Add another function
	local name = frame.args[1]  -- To access arguments passed to a module, use `frame.args`
							    -- `frame.args[1]` refers to the first unnamed parameter
							    -- given to the module
	return "Hello, " .. name .. "!"  -- `..` concatenates strings. This will return a customized
									 -- greeting depending on the name given, such as "Hello, Fred!"
end
function p.count_fruit(frame)
	local num_bananas = frame.args.bananas -- Named arguments ({{#invoke:Example|count_fruit|foo=bar}}) are likewise 
	local num_apples = frame.args.apples   -- accessed by indexing `frame.args` by name (`frame.args["bananas"]`, or)
										   -- equivalently `frame.args.bananas`.
	return 'I have ' .. num_bananas .. ' bananas and ' .. num_apples .. ' apples'
										   -- Like above, concatenate a bunch of strings together to produce
										   -- a sentence based on the arguments given.
end

return p    --All modules end by returning the variable containing their functions to Wikipedia.
-- Now we can use this module by calling {{#invoke: Example | hello }},
-- {{#invoke: Example | hello_to | foo }}, or {{#invoke:Example|count_fruit|bananas=5|apples=6}}
-- Note that the first part of the invoke is the name of the Module's wikipage,
-- and the second part is the name of one of the functions attached to the 
-- variable that you returned.

-- The "print" function is not allowed in Wikipedia.  All output is accomplished
-- via strings "returned" to Wikipedia.

A sample of Lua is highlighted by tag <syntaxhighlight lang="lua">...</syntaxhighlight> placed around the Lua source code. To view some more complex examples of Lua, see Wikipedia article: "Lua".

For instructions on how to use Lua within MediaWiki (and hence BattleTechWiki), see mw:Extension:Scribunto/Lua reference manual.

Labeling converted templates

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.

See also

Categories

• Category:Lua language on BattleTechWiki – usage of Lua on Wikipedia
• Category:Modules – top-level category for Lua modules
  • Category:Lua metamodules – modules that aid other Lua modules
• Category:Lua-based templates – groups of Lua-based templates
• Category:Lua-related templates – templates related to the usage of Lua on Wikipedia

Other pages

• 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
• Manual:Coding conventions/Lua – standards to improve the readability of code through consistency
• mw:Extension:Scribunto/Lua reference manual
• Wikipedia:Advanced template coding