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{{Short description|Lightweight programming language}}
{{
{{Use dmy dates|date=February 2021}}{{Infobox programming language
| name
| logo
| logo size = 140px
| screenshot = Excerpt of Coordinates module in Lua.png
| screenshot_size = 250px
| screenshot caption = Screenshot of Lua code from a [[WP:Lua|Wikipedia Lua module]] using the [[MediaWiki]] [[mw:Extension:Scribunto|Scribunto]] extension
| paradigm = [[Multi-paradigm]]: [[Scripting language|scripting]], [[Imperative programming|imperative]] ([[Procedural programming|procedural]], [[Prototype-based programming|prototype-based]], [[Object-oriented programming|object-oriented]]), [[Functional programming|functional]], [[Metaprogramming|meta]], [[Reflective programming|reflective]]
| year = {{Start date and age|1993|df=yes}}
| designer = [[Roberto Ierusalimschy]]<br/>Waldemar Celes<br/>Luiz Henrique de Figueiredo
| developer =
| latest release version = {{wikidata|property|reference|edit |Q207316 |P348}}
| latest release date = {{start date and age|{{wikidata|qualifier|Q207316|P348|P577}}}}
| latest preview version =
| latest preview date =
| typing = [[Dynamic typing|Dynamic]], [[Strong and weak typing|strong]], [[Duck typing|duck]]
| implementations = [//www.lua.org/download.html Lua], [[LuaJIT]], [//github.com/luavela/luavela LuaVela],
[https://www.moonsharp.org/ MoonSharp],
| programming language = [[ANSI C]]
| dialects = [https://www.nongnu.org/gsl-shell/ GSL Shell], [https://luau.org Lua''u'']
| influenced by = [[C++]], [[CLU (programming language)|CLU]], [[Modula]], [[Scheme (programming language)|Scheme]], [[SNOBOL]]
| influenced = [[GameMonkey Script|GameMonkey]],<!--2003--> [[Io (programming language)|Io]],<!--2002--> [[JavaScript]]{{Citation needed|date=November 2022}}, [[Julia (programming language)|Julia]],<!--2006--> [[Red (programming language)|Red]], [[Ring (programming language)|Ring]],<ref name="The Ring programming language and other languages">{{cite web |url=https://ring-lang.sourceforge.net/doc1.6/introduction.html#ring-and-other-languages |title=The Ring programming language and other languages |author=Ring Team |date=5 December 2017 |work=ring-lang.net |access-date=5 December 2017 |archive-date=25 December 2018 |archive-url=https://web.archive.org/web/20181225175312/http://ring-lang.sourceforge.net/doc1.6/introduction.html#ring-and-other-languages |url-status=dead}}</ref> [[Ruby (programming language)|Ruby]],{{Citation needed|date=November 2022}} [[Squirrel (programming language)|Squirrel]],<!--2011--> [[C--]], [[Roblox Studio|Luau]],
| operating system = [[Cross-platform software|Cross-platform]]
| license = [[MIT License|MIT]]
| website = {{url|https://lua.org/}}
| file ext = <code>.lua</code>
| wikibooks =
}}
'''Lua''' {{Noexcerpt|({{IPAc-en|ˈ|l|uː|ə}} {{Respell|LOO|ə}}; from {{Langx|pt|[[wikt:lua#Portuguese|lua]]}} {{IPA|pt|ˈlu(w)ɐ|}} meaning ''[[moon]]'')}} is a [[Lightweight programming language|lightweight]], [[High-level programming language|high-level]], [[multi-paradigm programming language|multi-paradigm]] [[programming language]] designed mainly for [[Scripting language|embedded use]] in applications.<ref name="luaspe">{{cite journal|last1=Ierusalimschy|first1=Roberto|last2=de Figueiredo|first2=Luiz Henrique|last3=Filho|first3=Waldemar Celes|title=Lua—An Extensible Extension Language|journal=Software: Practice and Experience|date=June 1996|volume=26|issue=6|pages=635–652|doi=10.1002/(SICI)1097-024X(199606)26:6<635::AID-SPE26>3.0.CO;2-P|s2cid=61066194 |url=https://www.lua.org/spe.html|access-date=24 October 2015|url-access=subscription}}</ref> Lua is [[cross-platform software]], since the [[Interpreter (computing)|interpreter]] of [[Compiler|compiled]] [[bytecode]] is written in [[ANSI C]],<ref name=luaabout>{{cite web |url=https://www.lua.org/about.html#why |title=About Lua |publisher=Lua.org |access-date=2011-08-11}}</ref> and Lua has a relatively simple C application programming interface ([[API]]) to embed it into applications.<ref>{{cite magazine |last1=Takhteyev |first1=Yuri |date=21 April 2013 |url=https://www.foreignaffairs.com/articles/139332/yuri-takhteyev/from-brazil-to-wikipedia?page=2 |title=From Brazil to Wikipedia |magazine=[[Foreign Affairs]] |access-date=25 April 2013}}</ref>
Lua originated in 1993 as a language for extending [[application software|software applications]] to meet the increasing demand for customization at the time. It provided the basic facilities of most [[procedural programming]] languages, but more complicated or [[___domain-specific language|___domain-specific]] features were not included; rather, it included mechanisms for extending the language, allowing programmers to implement such features. As Lua was intended to be a general embeddable extension language, the designers of Lua focused on improving its [[Profiling (computer programming)|speed]], [[Porting|portability]], extensibility and ease-of-use in development.
== History ==
Lua was created in 1993 by [[Roberto Ierusalimschy]], Luiz Henrique de Figueiredo, and Waldemar Celes, members of the Computer Graphics Technology Group ([[Tecgraf]]) at the [[Pontifical Catholic University of Rio de Janeiro]], in [[Brazil]].
From 1977 until 1992, Brazil had a policy of strong [[trade barrier]]s (called a market reserve) for [[computer hardware]] and [[software]], believing that Brazil could and should produce its own hardware and software. In that climate, Tecgraf's clients could not afford, either politically or financially, to buy customized software from abroad; under the market reserve, clients would have to go through a complex bureaucratic process to prove their needs couldn't be met by Brazilian companies. Those reasons led Tecgraf to implement the basic tools it needed from scratch.<ref name=hopl2007>{{cite book |last1=Ierusalimschy |first1=R. |author1-link=Roberto Ierusalimschy |last2=Figueiredo |first2=L. H. |last3=Celes |first3=W. |year=2007 |title=Proceedings of the third ACM SIGPLAN conference on History of programming languages |contribution=The evolution of Lua |contribution-url=https://www.lua.org/doc/hopl.pdf |doi=10.1145/1238844.1238846 |url=https://www.acm.org/sigs/sigplan/hopl |pages=2–1–2–26 |isbn=978-1-59593-766-7 |s2cid=475143}}</ref><!-- More sources about the Brazilian market reserve are needed, as it helps further prove how it affected the development of the Lua language.-->
Lua's predecessors were the data-description and configuration languages Simple Object Language (SOL) and Data-Entry Language (DEL).<ref name="luahist2001">{{cite web|url=https://www.lua.org/history.html|title=The evolution of an extension language: a history of Lua|year=2001|access-date=2008-12-18}}
<!-- {{cite journal |last1=Ierusalimschy |first1=R. |author1-link=Roberto Ierusalimschy |last2=Figueiredo |first2=L. H. |last3=Celes |first3=W. |year=2001 |contribution=The evolution of an extension language: a history of Lua |contribution-url=https://www.lua.org/history.html |title=Proceedings of V Brazilian Symposium on Programming Languages |pages=B–14–B–28}} --></ref> They had been independently developed at Tecgraf in 1992–1993 to add some flexibility into two different projects (both were interactive graphical programs for engineering applications at [[Petrobras]] company). There was a lack of any flow-control structures in SOL and DEL, and Petrobras felt a growing need to add full programming power to them.
In ''The Evolution of Lua'', the language's authors wrote:<ref name=hopl2007/>
{{Blockquote|In 1993, the only real contender was [[Tcl]], which had been explicitly designed to be embedded into applications. However, Tcl had unfamiliar syntax, did not offer good support for data description, and ran only on Unix platforms. We did not consider [[Lisp (programming language)|LISP]] or [[Scheme (programming language)|Scheme]] because of their unfriendly syntax. [[Python (programming language)|Python]] was still in its infancy. In the free, do-it-yourself atmosphere that then reigned in Tecgraf, it was quite natural that we should try to develop our own scripting language ... Because many potential users of the language were not professional programmers, the language should avoid cryptic syntax and semantics. The implementation of the new language should be highly portable, because Tecgraf's clients had a very diverse collection of computer platforms. Finally, since we expected that other Tecgraf products would also need to embed a scripting language, the new language should follow the example of SOL and be provided as a library with a C API.}}
Lua 1.0 was designed in such a way that its object constructors, being then slightly different from the current light and flexible style, incorporated the data-description syntax of SOL (hence the name Lua: ''Sol'' meaning "Sun" in Portuguese, and ''Lua'' meaning "Moon"). Lua [[Syntax (programming languages)|syntax]] for control structures was mostly borrowed from [[Modula]] (<code>if</code>, <code>while</code>, <code>repeat</code>/<code>until</code>), but also had taken influence from [[CLU (programming language)|CLU]] (multiple assignments and multiple returns from function calls, as a simpler alternative to [[Call by reference|reference parameters]] or explicit [[pointer (computer programming)|pointers]]), [[C++]] ("neat idea of allowing a [[local variable]] to be declared only where we need it"<ref name=hopl2007/>), [[SNOBOL]] and [[AWK]] ([[associative array]]s). In an article published in ''[[Dr. Dobb's Journal]]'', Lua's creators also state that LISP and Scheme with their single, ubiquitous data-structure mechanism (the [[List (abstract data type)|list]]) were a major influence on their decision to develop the table as the primary data structure of Lua.<ref name=ddj96>{{cite news |last1=Figueiredo |first1=L. H. |last2=Ierusalimschy |first2=R. |last3=Celes |first3=W. |date=December 1996 |title=Lua: an Extensible Embedded Language. A few metamechanisms replace a host of features |magazine=Dr. Dobb's Journal |volume=21 |issue=12 |pages=26–33 |url=https://www.lua.org/ddj.html}}</ref>
Lua [[semantics]] have been increasingly influenced by Scheme over time,<ref name=hopl2007/> especially with the introduction of [[anonymous function]]s and full [[Scope (computer science)#Lexical scope vs. dynamic scope|lexical scoping]]. Several features were added in new Lua versions.
Versions of Lua prior to version 5.0 were released under a license similar to the [[BSD licenses|BSD license]]. From version 5.0 onwards, Lua has been licensed under the [[MIT License]]. Both are [[permissive free software licences]] and are almost identical.
== Features ==
Lua is commonly described as a
In general, Lua strives to provide simple, flexible [[metaprogramming|meta-features]] that can be extended as needed, rather than supply a feature-set specific to one programming paradigm. As a result, the base language is [[
Lua implements a small set of advanced features such as [[first-class function]]s, [[Garbage collection (computer science)|garbage collection]], [[Closure (computer science)|closures]], proper [[Tail recursion|tail calls]], [[Type conversion|coercion]] (automatic conversion between string and number values at run time), [[coroutine]]s (cooperative multitasking) and [[Dynamic loading|dynamic module loading]].
=== Syntax ===
The classic [["Hello, World!" program]] can be written as follows, with or without parentheses:<ref>{{cite web |url=https://www.lua.org/pil/1.html |title=Programming in Lua : 1}}</ref>{{efn|[[Syntactic sugar]], a table construct or literal string following an identifier is a valid function call.<ref>{{cite web |url=https://www.lua.org/manual/5.0/manual.html#2.5.7 |title=Lua 5.0 Reference Manual, 2.5.7, Function Calls}}</ref>}}
<syntaxhighlight lang="lua">
print("Hello, World!")
</syntaxhighlight>
<syntaxhighlight lang="lua">
print "Hello, World!"
</syntaxhighlight>
The declaration of a variable, without a value.
<syntaxhighlight lang="lua">
local variable
</syntaxhighlight>
The declaration of a variable with a value of 10.
<syntaxhighlight lang="lua">
local students = 10
</syntaxhighlight>
A [[Comment (computer programming)|comment]] in Lua starts with a double-hyphen and runs to the end of the line, similar to [[Ada (programming language)|Ada]], [[Eiffel (programming language)|Eiffel]], [[Haskell]], [[SQL]] and [[VHDL]]. Multi-line strings and comments are marked with double square brackets.
<
-- Single line comment
--[[
Multi-line comment
--]]
</syntaxhighlight>
{{anchor|Factorial example}}The [[factorial]] function is implemented in this example:<!-- referred to elsewhere in this article -->
<syntaxhighlight lang="lua">
function factorial(n)
for i = 2, n do
x = x * i
end
return x
end
</syntaxhighlight>
=== Control flow ===
Lua has one type of [[Conditional (computer programming)|conditional]] test: <code>[[Conditional_(computer_programming)#If–then(–else)|if then end]]</code> with optional <code>else</code> and <code>elseif then</code> execution control constructs.
The generic <code>if then end</code> statement requires all three keywords:
<syntaxhighlight lang="lua">
if condition then
--statement body
end
</syntaxhighlight>
An example of an <code>if</code> statement
<syntaxhighlight lang="lua">
if x ~= 10 then
print(x)
end
</syntaxhighlight>
The <code>else</code> keyword may be added with an accompanying statement block to control execution when the <code>if</code> condition evaluates to <code>false</code>:
<syntaxhighlight lang="lua">
if condition then
--statement body
else
--statement body
end
</syntaxhighlight>
An example of an <code>if else</code> statement
<syntaxhighlight lang="lua">
if x == 10 then
print(10)
else
print(x)
end
</syntaxhighlight>
Execution may also be controlled according to multiple conditions using the <code>elseif then</code> keywords:
<syntaxhighlight lang="lua">
if condition then
--statement body
elseif condition then
--statement body
else -- optional
--optional default statement body
end
</syntaxhighlight>
An example of an <code>if elseif else</code> statement
<syntaxhighlight lang="lua">
if x == y then
print("x = y")
elseif x == z then
print("x = z")
else -- optional
print("x does not equal any other variable")
end
</syntaxhighlight>
Lua has four types of conditional loops: the [[while loop|<code>while</code> loop]], the <code>repeat</code> loop (similar to a [[do while loop|<code>do while</code> loop]]), the numeric [[for loop|<code>for</code> loop]] and the generic <code>for</code> loop.
<syntaxhighlight lang="lua">
--condition = true
while condition do
--statements
end
repeat
--statements
until condition
for i = first, last, delta do --delta may be negative, allowing the for loop to count down or up
--statements
--example: print(i)
end
</syntaxhighlight>
This generic <code>for</code> loop would iterate over the table <code>_G</code> using the standard iterator function <code>pairs</code>, until it returns <code>nil</code>:
<syntaxhighlight lang="lua">
for key, value in pairs(_G) do
print(key, value)
end
</syntaxhighlight>
Loops can also be [[Nesting (programming)|nested]] (put inside of another loop).
<syntaxhighlight lang="lua">
local grid = {
{ 11, 12, 13 },
{ 21, 22, 23 },
{ 31, 32, 33 }
}
for y, row in pairs(grid) do
for x, value in pairs(row) do
print(x, y, value)
end
end
</syntaxhighlight>
=== Functions ===
Lua's treatment of functions as [[first-class function|first-class]] values is shown in the following example, where the print function's behavior is modified:
<syntaxhighlight lang="lua">
do
local oldprint = print
-- Store current print function as oldprint function print(s)
--[[ Redefine print function. The usual print function can still be used
through oldprint
oldprint(s == "foo" and "bar" or s)
end
end
</syntaxhighlight>
Any future calls to
Lua also supports [[Closure (computer
<
function
-- Return a new function that adds x to the argument
return function(y)
--[[ When we refer to the variable x, which is outside
return x + y
end
end
fourplus = addto(4)
print(
--This can also be achieved by calling the function in the following way:
print(addto(4)(3))
--[[ This is because we are calling the returned function from 'addto(4)' with the argument '3' directly.
This also helps to reduce data cost and up performance if being called iteratively.]]
</syntaxhighlight>
A new closure for the variable <code>x</code> is created every time <code>addto</code> is called, so that each new anonymous function returned will always access its own <code>x</code> parameter. The closure is managed by Lua's garbage collector, just like any other object.
=== Tables ===
Tables are the most important data
A table is a set of key and data pairs, where the data is referenced by key; in other words, it is a [[hash table|hashed]] heterogeneous associative array.
Tables are created using the <code>{}</code> constructor syntax.
<syntaxhighlight lang="lua">
a_table = {} -- Creates a new, empty table
</syntaxhighlight>
Tables are always passed by reference (see [[Call by sharing]]).
A key (index) can be any value except <code>nil</code> and [[NaN]], including functions.
<syntaxhighlight lang="lua">
a_table = {x = 10} -- Creates a new table, with one entry mapping "x" to the number 10.
print(a_table["x"])
b_table = a_table
print(
print(a_table["x"]) --
</syntaxhighlight>
A table is often used as [[object composition|structure]] (or [[Record (computer science)|record]]) by using [[string (computer science)|strings]] as keys. Because such use is very common, Lua features a special syntax for accessing such fields.<ref>{{cite web|url=https://www.lua.org/manual/5.1/manual.html#2.3|title=Lua 5.1 Reference Manual|access-date=2014-02-27|year=2014}}</ref>
<syntaxhighlight lang="lua">
point = { x = 10, y = 20 } -- Create new table
print(point["x"]) -- Prints 10
print(point.x) -- Has exactly the same meaning as line above. The easier-to-read dot notation is just syntactic sugar.
</syntaxhighlight>
By using a table to store related functions, it can act as a namespace.
<syntaxhighlight lang="lua">
Point = {}
return {x = x, y = y} -- return {["x"] = x, ["y"] = y}
end
Point.set_x = function
point.x = x -- point["x"] = x;
end
</syntaxhighlight>
A numeric key <code>1</code> is distinct from a string key <code>"1"</code>.
<syntaxhighlight lang="lua">
array = { "a", "b", "c", "d" } -- Indices are assigned automatically.
print(array[2]) -- Prints "b". Automatic indexing in Lua starts at 1.
Line 166 ⟶ 287:
array[0] = "z" -- Zero is a legal index.
print(#array) -- Still prints 4, as Lua arrays are 1-based.
</syntaxhighlight>
The length of a table <code>t</code> is defined to be any integer index <code>n</code> such that <code>t[n]</code> is not <code>nil</code> and <code>t[n+1]</code> is <code>nil</code>; moreover, if <code>t[1]</code> is <code>nil</code>, <code>n</code> can be zero. For a regular array, with non-nil values from 1 to a given <code>n</code>, its length is exactly that <code>n</code>, the index of its last value. If the array has "holes" (that is, nil values between other non-nil values), then <code>#t</code> can be any of the indices that directly precedes a <code>nil</code> value (that is, it may consider any such nil value as the end of the array).<ref>{{cite web|url=https://www.lua.org/manual/5.1/manual.html#2.5.5|title=Lua 5.1 Reference Manual|access-date=2012-10-16|year=2012}}</ref>
<syntaxhighlight lang="lua">
ExampleTable =
{
{1, 2, 3, 4},
{5, 6, 7, 8}
}
print(ExampleTable[1][3]) -- Prints "3"
print(ExampleTable[2][4]) -- Prints "8"
</syntaxhighlight>
A table can be an array of objects.
<syntaxhighlight lang="lua">
function Point(x, y) -- "Point" object constructor
return { x = x, y = y } -- Creates and returns a new object (table)
end
array = { Point(10, 20), Point(30, 40), Point(50, 60) } -- Creates array of points
-- array = { { x = 10, y = 20 }, { x = 30, y = 40 }, { x = 50, y = 60 } };
print(array[2].y) -- Prints 40
</syntaxhighlight>
Using a hash map to emulate an array is normally slower than using an actual array; however, Lua tables are optimized for use as arrays to help avoid this issue.<ref name=lobject_h_array>{{cite web|url=https://www.lua.org/source/5.1/lobject.h.html#array|title=Lua 5.1 Source Code|access-date=2011-03-24|year=2006}}</ref><!-- I'd like to find a message on the mailing list from one of the developers, but I can't. However, source code is a reasonably trustworthy reference. -->
=== Metatables ===
Extensible semantics is a key feature of Lua, and the metatable allows powerful customization of tables. The following example demonstrates an "infinite" table. For any <code>n</code>, <code>fibs[n]</code> will give the <code>n</code>-th [[Fibonacci number]] using [[dynamic programming]] and [[memoization]].
<syntaxhighlight lang="lua">
fibs = { 1, 1 } -- Initial values for fibs[1] and fibs[2].
setmetatable(fibs, {
__index = function(values, n) --[[__index is a function predefined by Lua,
it is called if key "n" does not exist.]]
values[n] = values[n - 1] + values[n - 2] -- Calculate and memoize fibs[n].
return values[n]
end
})
</syntaxhighlight>
=== Object-oriented programming ===
Although Lua does not have a built-in concept of [[class (computer science)|classes]],
There is no such concept as
Creating a basic [[Vector (geometry)|vector]] object:
<syntaxhighlight lang="lua">
local Vector = {}
local VectorMeta = { __index = Vector}
function Vector.new(x, y, z) -- The constructor
return setmetatable({x = x, y = y, z = z}, VectorMeta)
end
return math.sqrt(self.x^2 + self.y^2 + self.z^2)
end
local vec = Vector.new(0, 1, 0) -- Create a vector
print(vec.magnitude(vec)) -- Call a method (output: 1)
print(vec.x) -- Access a member variable (output: 0)
</syntaxhighlight>
Here, {{code |lang=lua|setmetatable}} tells Lua to look for an element in the {{code |lang=lua|Vector}} table if it is not present in the {{code |lang=lua|vec}} table. {{code |lang=lua|vec.magnitude}}, which is equivalent to {{code |lang=lua|vec["magnitude"]}}, first looks in the {{code |lang=lua|vec}} table for the {{code |lang=lua|magnitude}} element. The {{code |lang=lua|vec}} table does not have a {{code |lang=lua|magnitude}} element, but its metatable delegates to the {{code |lang=lua|Vector}} table for the {{code |lang=lua|magnitude}} element when it's not found in the {{code |lang=lua|vec}} table.
Lua provides some [[syntactic sugar]] to facilitate object orientation. To declare [[Method (computer science)|member functions]] inside a prototype table, one can use {{code |lang=lua |function table:func(args)}}, which is equivalent to {{code |lang=lua |function table.func(self, args)}}. Calling class methods also makes use of the colon: {{code |lang=lua |object:func(args)}} is equivalent to {{code |lang=lua |object.func(object, args)}}.
That in mind, here is a corresponding class with {{code|lang=lua|:}} syntactic sugar:
<syntaxhighlight lang="lua">
local Vector = {}
Vector.__index = Vector
function Vector:new(x, y, z) -- The constructor
-- Since the function definition uses a colon,
-- its first argument is "self" which refers
-- to "Vector"
return setmetatable({x = x, y = y, z = z}, self)
end
function Vector:magnitude() -- Another method
-- Reference the implicit object using self
return math.sqrt(self.x
end
local vec = Vector:new(0, 1, 0) -- Create a vector
print(vec:magnitude()) -- Call a method (output: 1)
print(vec.x) -- Access a member variable (output: 0)
</syntaxhighlight>
==== Inheritance ====
Lua supports using metatables to give Lua class inheritance.<ref>{{cite book|title=Programming in Lua, 4th Edition|page=165|author=Roberto Ierusalimschy}}</ref> In this example, we allow vectors to have their values multiplied by a constant in a derived class.
<syntaxhighlight lang="lua">
local Vector = {}
Vector.__index = Vector
-- Here, self refers to whatever class's "new"
-- method we call. In a derived class, self will
-- be the derived class; in the Vector class, self
-- will be Vector
return setmetatable({x = x, y = y, z = z}, self)
end
function Vector:magnitude() -- Another method
-- Reference the implicit object using self
return math.sqrt(self.x^2 + self.y^2 + self.z^2)
end
-- Example of class inheritance
local VectorMult = {}
VectorMult.__index = VectorMult
setmetatable(VectorMult, Vector) -- Make VectorMult a child of Vector
function VectorMult:multiply(value)
self.x = self.x * value
self.y = self.y * value
self.z = self.z * value
return self
end
local vec = VectorMult:new(0, 1, 0) -- Create a vector
print(vec:magnitude()) -- Call a method (output: 1)
print(vec.y) -- Access a member variable (output: 1)
vec:multiply(2) -- Multiply all components of vector by 2
print(vec.y) -- Access member again (output: 2)
</syntaxhighlight>
Lua also supports [[multiple inheritance]]; {{code|language=lua|__index}} can either be a function or a table.<ref>{{Cite web|title=Programming in Lua : 16.3|url=https://www.lua.org/pil/16.3.html|access-date=2021-09-16|website=Lua}}</ref> [[Operator overloading]] can also be done; Lua metatables can have elements such as {{code|language=lua|__add}}, {{code|language=lua|__sub}} and so on.<ref>{{Cite web|title= Metamethods Tutorial|url=http://lua-users.org/wiki/MetamethodsTutorial|access-date=2021-09-16|website=lua-users wiki |url-status=dead |archive-url=https://web.archive.org/web/20210916182214/http://lua-users.org/wiki/MetamethodsTutorial |archive-date=September 16, 2021}}</ref>
== Implementation ==
Lua programs are not [[Interpreter (computing)|interpreted]] directly from the textual Lua file, but are [[Compiler|compiled]] into bytecode, which is then run on the Lua [[virtual machine]] (VM). The compiling process is typically invisible to the user and is performed during [[Run time (program lifecycle phase)|run-time]], especially when a [[just-in-time compilation]] (JIT) compiler is used, but it can be done offline to increase loading performance or reduce the memory footprint of the host environment by leaving out the compiler. Lua bytecode can also be produced and executed from within Lua, using the <code>dump</code> function from the string library and the <code>load/loadstring/loadfile</code> functions. Lua version 5.3.4 is implemented in approximately 24,000 lines of C code.<ref name="luaspe"/><ref name="luaabout"/>
Like most CPUs, and unlike most virtual machines (which are [[Stack machine|stack-based]]), the Lua VM is [[Register machine|register-based]], and therefore more closely resembles most hardware design. The register architecture both avoids excessive copying of values, and reduces the total number of instructions per function. The virtual machine of Lua 5 is one of the first register-based pure VMs to have a wide use.<ref name=lua5impl>{{cite journal |last1=Ierusalimschy |first1=R. |last2=Figueiredo |first2=L. H. |last3=Celes |first3=W. |year=2005 |title=The implementation of Lua 5.0 |journal=J. Of Universal Comp. Sci. |volume=11 |issue=7 |pages=1159–1176 |url=http://www.jucs.org/jucs_11_7/the_implementation_of_lua/jucs_11_7_1159_1176_defigueiredo.html |doi=10.3217/jucs-011-07-1159 |doi-access=free}}</ref> [[Parrot virtual machine|Parrot]] and [[Android (operating system)|Android]]'s [[Dalvik (software)|Dalvik]] are two other well-known register-based VMs. PCScheme's VM was also register-based.<ref>{{cite book |last1=Texas Instruments |year=1990 |title=PC Scheme: Users Guide and Language Reference Manual, Trade Edition |publisher=MIP Press |isbn=0-262-70040-9}}</ref>
This example is the bytecode listing of the factorial function defined [[#Factorial example|above]] (as shown by the <code>luac</code> 5.1 compiler):<ref name=luavm51instr>{{cite web |last1=Man |first1=Kein-Hong |year=2006 |title=A No-Frills Introduction to Lua 5.1 VM Instructions |url=https://talk.pokitto.com/uploads/default/original/2X/7/716c67a0b5b1636cbc4dc1fec232ca2536cb74d1.pdf}}</ref><!-- See earlier revisions for now-dead original and archive.org snapshots of this link, in case it moves again. It is CC-BY-NC-SA so it can be rehosted if needed. -->
function <factorial.lua:1,7> (9 instructions, 36 bytes at 0x8063c60)
1 param, 6 slots, 0 upvalues, 6 locals, 2 constants, 0 functions
1 [2] LOADK 1 -1 ; 1
2 [3] LOADK 2 -2 ; 2
3 [3] MOVE 3 0
4 [3] LOADK 4 -1 ; 1
5 [3] FORPREP 2 1 ; to 7
6 [4] MUL 1 1 5
7 [3] FORLOOP 2 -2 ; to 6
8 [6] RETURN 1 2
9 [7] RETURN 0 1
Lua is intended to be embedded into other applications, and provides a [[C (programming language)|C]] [[Application Programming Interface|API]] for this purpose. The API is divided into two parts: the Lua core and the Lua auxiliary library.<ref name="luarefman">{{cite web |url=https://www.lua.org/manual/5.2/ |title=Lua 5.2 Reference Manual |publisher=Lua.org |access-date=2012-10-23}}</ref> The Lua API's design eliminates the need for manual [[reference counting]] (management) in C code, unlike [[Python (programming language)|Python]]'s API. The API, like the language, is minimalist. Advanced functions are provided by the auxiliary library, which consists largely of [[preprocessor]] [[Macro (computer science)|macros]] which assist with complex table operations.
The Lua C API is [[Stack (data structure)|stack]] based. Lua provides functions to push and pop most simple C data types (integers, floats, etc.) to and from the stack, and functions to manipulate tables through the stack. The Lua stack is somewhat different from a traditional stack; the stack can be indexed directly, for example. Negative indices indicate offsets from the top of the stack. For example, −1<!-- not a hyphen --> is the top (most recently pushed value), while positive indices indicate offsets from the bottom (oldest value). [[Marshalling (computer science)|Marshalling]] data between C and Lua functions is also done using the stack. To call a Lua function, arguments are pushed onto the stack, and then the <code>lua_call</code> is used to call the actual function. When writing a C function to be directly called from Lua, the arguments are read from the stack.
Here is an example of calling a Lua function from C:
<syntaxhighlight lang="c">
#include <stdio.h>
#include <lua.h> // Lua main library (lua_*)
#include <lauxlib.h> // Lua auxiliary library (luaL_*)
int main(void)
{
// create a Lua state
lua_State *L = luaL_newstate();
// load and execute a string
if (luaL_dostring(L, "function foo (x,y) return x+y end")) {
lua_close(L);
return -1;
}
// push value of global "foo" (the function defined above)
// to the stack, followed by integers 5 and 3
lua_getglobal(L, "foo");
lua_pushinteger(L, 5);
lua_pushinteger(L, 3);
lua_call(L, 2, 1); // call a function with two arguments and one return value
printf("Result: %d\n", lua_tointeger(L, -1)); // print integer value of item at stack top
lua_pop(L, 1); // return stack to original state
lua_close(L); // close Lua state
return 0;
}
</syntaxhighlight>
Running this example gives:
<syntaxhighlight lang="console">
$ cc -o example example.c -llua
$ ./example
Result: 8
</syntaxhighlight>
The C API also provides some special tables, located at various "pseudo-indices" in the Lua stack. At <code>LUA_GLOBALSINDEX</code> prior to Lua 5.2<ref name="Changes in the API, Lua 5.2 manual">{{cite book |first1=Roberto |last1=Ierusalimschy |first2=Luiz Henrique |last2=de Figueiredo |first3=Waldemar |last3=Celes |date=2011–2013 |url=https://www.lua.org/manual/5.2/manual.html#8.3 |title=Changes in the API |work=Lua 5.2 Reference Manual |publisher=Lua.org |access-date=2014-05-09}}</ref> is the globals table, <code>_G</code> from within Lua, which is the main [[namespace]]. There is also a registry located at <code>LUA_REGISTRYINDEX</code> where C programs can store Lua values for later retrieval.
=== Modules ===
Besides standard library (core) modules it is possible to write extensions using the Lua API. Extension modules are [[Library (computing)#Dynamic linking|shared objects]] which can be used to extend the functions of the interpreter by providing native facilities to Lua scripts. Lua scripts may load extension modules using <code>require</code>,<ref name="luarefman"/> just like modules written in Lua itself, or with <code>package.loadlib</code>.<ref>{{Cite web |title=Lua 5.4 Reference Manual |url=https://www.lua.org/manual/5.4/manual.html#pdf-package.loadlib |first1=Roberto |last1=Ierusalimschy |first2=Luiz Henrique |last2=de Figueiredo |first3=Waldemar |last3=Celes |access-date=2022-06-01 |website=Lua}}</ref> When a C library is loaded via {{ml-lua|foo}} Lua will look for the function <code>luaopen_foo</code> and call it, which acts as any C function callable from Lua and generally returns a table filled with methods. A growing set of modules termed ''rocks'' are available through a [[package management system]] named [[LuaRocks]],<ref>{{cite web |url=https://luarocks.org/ |title=LuaRocks |publisher=luarocks.org |access-date=2009-05-24}}</ref> in the spirit of [[CPAN]], [[RubyGems]] and [[Python eggs]]. Prewritten Lua [[Language binding|bindings]] exist for most popular programming languages, including other scripting languages.<ref>{{cite web |url=http://lua-users.org/wiki/BindingCodeToLua |title=Binding Code To Lua |publisher=Lua-users wiki |access-date=2009-05-24 |url-status=dead |archive-url=https://web.archive.org/web/20090727080345/http://lua-users.org/wiki/BindingCodeToLua |archive-date= Jul 27, 2009}}</ref> For C++, there are a number of template-based approaches and some automatic binding generators.
== Applications ==
{{main|List of applications using Lua}}
In [[video game development]], Lua is widely used as a [[scripting language]], mainly due to its perceived ease of embedding, fast execution, and short [[learning curve]].<ref>{{cite web|url=https://stackoverflow.com/questions/38338/why-is-lua-considered-a-game-language |title=Why is Lua considered a game language? |website=Stack Overflow |access-date=2017-04-22 |url-status=dead |archive-url=https://web.archive.org/web/20130820131611/http://stackoverflow.com/questions/38338/why-is-lua-considered-a-game-language |archive-date=20 August 2013}}</ref> Notable games which use Lua include ''[[Roblox]]'',<ref>{{Cite web|title=Why Lua''u''?|url=https://luau-lang.org/why.html|access-date=2022-03-23|website=Luau|language=en-US}}</ref> ''[[Garry's Mod]]'', '' [[World of Warcraft]]'', ''[[Payday 2]]'', ''[[Phantasy Star Online 2]]'', ''[[Dota 2]]'', ''[[Crysis (video game)|Crysis]]'',<ref>{{cite web |url=https://crymp.net/thread?id=347 |title=Introduction to Crysis server-side modding |access-date=23 March 2022}}</ref> and many others. Some games that do not natively support Lua programming or scripting have this function added by mods, as ComputerCraft does for ''[[Minecraft]]''. Similarly, Lua API libraries, like Discordia, are used for platforms that do not natively support Lua.<ref>{{Cite web|title=Discordia API|url=https://github.com/SinisterRectus/Discordia|access-date=2025-07-02|language=en-US}}</ref> Lua is used in an open-source 2-dimensional game engine called LOVE2D.<ref>{{Cite web|title=LOVE2D Game Engine|url=https://love2d.org/|access-date=2025-07-02|language=en-US|archive-date=5 March 2025|archive-url=https://web.archive.org/web/20250305202646/https://love2d.org/|url-status=dead}}</ref> Also, Lua is used in non-video game software, such as [[Adobe Lightroom]], [[Moho (software)|Moho]], [[iClone]], [[Aerospike (database)|Aerospike]], and some system software in [[FreeBSD]] and [[NetBSD]], and used as a template scripting language on [[MediaWiki]] using the Scribunto extension.<ref>{{Cite web|title=Lua Functions|url=https://wow.gamepedia.com/Lua_functions|access-date=2021-03-01|website=wow.gamepedia.com|language=en-US}}</ref>
In 2003, a poll conducted by GameDev.net showed that Lua was the most popular scripting language for game programming.<ref>{{cite web|url=https://gamedev.net/gdpolls/viewpoll.asp?ID=163 |title=Poll Results |access-date=2017-04-22 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20031207171619/http://gamedev.net/gdpolls/viewpoll.asp?ID=163 |archive-date=7 December 2003}}</ref> On 12 January 2012, Lua was announced as a winner of the Front Line Award 2011 from the magazine ''[[Game Developer (magazine)|Game Developer]]'' in the category Programming Tools.<ref>{{cite web|url=http://www.gdmag.com/blog/2012/01/front-line-award-winners.php |title=Front Line Award Winners Announced |access-date=2017-04-22 |url-status=dead |archive-url=https://web.archive.org/web/20130615013638/http://www.gdmag.com/blog/2012/01/front-line-award-winners.php |archive-date=15 June 2013}}</ref>
Many non-game applications also use Lua for extensibility, such as [[LuaTeX]], an implementation of the [[TeX]] type-setting language; [[Redis]], a [[key-value database]]; [[ScyllaDB]], a [[wide-column store]], [[Neovim]], a text editor; [[Nginx]], a [[web server]]; [[Wireshark]], a network packet analyzer; Disordia, a [[Discord]] API library; and [[Pure Data]], a visual audio programming language (through the pdlua extension).
== Derived languages ==
===Languages that compile to Lua===
* MoonScript is a [[Dynamic programming language|dynamic]], [[Whitespace character|whitespace]]-sensitive [[scripting language]] inspired by [[CoffeeScript]], which is compiled into Lua. This means that instead of using <code>do</code> and <code>end</code> (or <code>{</code> and <code>}</code>) to delimit sections of code it uses [[Line break (computing)|line breaks]] and [[indentation style]].<ref>{{Cite web|title=Language Guide - MoonScript 0.5.0|url=https://moonscript.org/reference/|access-date=2020-09-25|website=moonscript.org}}</ref><ref>{{Cite web|last=leaf|title=leafo/moonscript|website=[[GitHub]] |date=2020-09-23|url=https://github.com/leafo/moonscript|access-date=2020-09-25}}</ref><ref name=":1">{{cite web |url=https://andregarzia.com/2020/06/languages-that-compile-to-lua.html |title=Languages that compile to Lua |website=AndreGarzia.com |last1=Garzia |first1=Andre Alves |access-date= 25 September 2020}}</ref> A notable use of MoonScript is the video game distribution website [[Itch.io]].
* [[Haxe]] supports compiling to some Lua targets, including Lua 5.1-5.3 and [[LuaJIT]] 2.0 and 2.1.
* Fennel, a Lisp dialect that targets Lua.<ref name=":1"/>
* Urn, a [[Lisp (programming language)|Lisp]] dialect built on Lua.<ref>{{Cite web|title=Urn: A Lisp implementation for Lua {{!}} Urn|url=https://urn-lang.com/|access-date=2021-01-12|website=urn-lang.com}}</ref>
* Amulet, an [[ML (programming language)|ML]]-like [[functional programming]] language, which compiler emits Lua files.<ref>{{Cite web|title=Amulet ML|url=https://amulet.works/|access-date=2021-01-12|website=amulet.works|language=en-US}}</ref>
* LunarML, Standard ML compiler that produces Lua/JavaScript<ref>{{Cite web|title=LunarML, Standard ML compiler that produces Lua/JavaScript|website=[[GitHub]] |url=https://github.com/minoki/LunarML}}</ref>
=== Dialects ===
* [[LuaJIT]], a just-in-time compiler of Lua 5.1.<ref>{{cite web |title=LuaJIT |url=https://luajit.org/luajit.html |website=LuaJIT}}</ref><ref>{{cite web |title=Extensions |url=https://luajit.org/extensions.html |website=LuaJIT}}</ref>
* [[Roblox#Roblox Studio and game design|Luau]] developed by [[Roblox Corporation]], a derivative of and backwards-compatible with Lua 5.1 with [[gradual typing]], additional features, and a focus on performance.<ref>{{Cite web |title=Why Luau? |url=https://luau-lang.org/why |access-date=2024-08-03 |website=Luau |language=en |quote=All of these motivated us to start reshaping Lua 5.1 that we started from into a new, derivative language that we call Luau. Our focus is on making the language more performant and feature-rich, and make it easier to write robust code through a combination of linting and type checking using a gradual type system.}}</ref> Luau has improved sandboxing to allow for running untrusted code in embedded applications.<ref>{{Cite web |title=Sandboxing |url=https://luau.org/sandbox |access-date=2025-03-27 |website=Luau |language=en}}</ref>
* Ravi, a JIT-enabled Lua 5.3 language with optional static typing. JIT is guided by type information.<ref>{{cite web |title=Ravi Programming Language |url=http://ravilang.github.io/ |website=GitHub}}</ref>
* Shine, a fork of [[LuaJIT]] with many extensions, including a module system and a macro system.<ref>{{cite web |last1=Hundt |first1=Richard |title=richardhundt/shine |website=[[GitHub]] |url=https://github.com/richardhundt/shine |date=2021-04-22}}</ref>
* Glua, a modified version embedded into the game [[Garry's Mod]] as its scripting language.<ref>{{cite web |title=Garry's Mod Wiki |url=https://wiki.facepunch.com/gmod/ |website=wiki.facepunch.com}}</ref>
* Teal, a [[Type system#Static type checking|statically typed]] Lua dialect written in Lua.<ref>{{cite web |title=teal-language/tl |date=2024-12-23 |url=https://github.com/teal-language/tl |access-date=2024-12-23 |website=Teal language}}</ref>
* [[PICO-8]], a "fantasy video game console", uses a subset of Lua known as PICO-8 Lua.
* Pluto, a superset of Lua 5.4 offering enhanced syntax, libraries, and better developer experience, all while staying compatible with regular Lua.<ref>{{cite web|title=What is Pluto?|url=https://pluto-lang.org/docs/Introduction|access-date=2025-06-27|website=Pluto}}</ref>
In addition, the Lua users community provides some ''power patches'' on top of the reference C implementation.<ref>{{cite web |title=Lua Power Patches |url=http://lua-users.org/wiki/LuaPowerPatches |website=lua-users.org |access-date=18 May 2021 |archive-date=18 May 2021 |archive-url=https://web.archive.org/web/20210518114041/http://lua-users.org/wiki/LuaPowerPatches |url-status=dead}}</ref>
== See also ==
* [[Comparison of programming languages]]
== Notes ==
{{Notelist}}
== References ==
{{Reflist}}
== Further reading ==
* {{cite book |last1=Ierusalimschy |first1=R. |title=Programming in Lua |edition=3rd |year=2013 |publisher=Lua.org |isbn=978-85-903798-5-0 |url=https://www.lua.org/pil/}} (The 1st ed. is available [https://www.lua.org/pil/contents.html online].)
<!--UPDATEME to 5.2: * {{cite book |last1=Ierusalimschy |first1= R. |last2=Figueiredo |first2=L. H. |last3=Celes |first3=W. |year=2006 |title=Lua 5.1 Reference Manual |publisher=Lua.org |isbn= 85-903798-3-3 |url=https://www.lua.org/manual/5.1/}}-->
* {{cite book |last1=Gutschmidt |first1=T. |year=2003 |title=Game Programming with Python, Lua, and Ruby |publisher=Course Technology PTR |isbn=978-1-59200-077-7}}
* {{cite book |last1=Schuytema |first1=P. |last2=Manyen |first2=M. |year=2005 |title=Game Development with Lua |publisher=Charles River Media |isbn=978-1-58450-404-7}}
* {{cite book |last1=Jung |first1=K. |last2=Brown |first2=A. |year=2007 |title=Beginning Lua Programming |publisher=[[Wrox Press]] |isbn=978-0-470-06917-2 |url=https://www.wrox.com/WileyCDA/WroxTitle/productCd-0470069171.html |access-date=7 July 2018 |archive-url=https://web.archive.org/web/20180708015602/https://www.wrox.com/WileyCDA/WroxTitle/productCd-0470069171.html |archive-date=8 July 2018 |url-status=dead}}
* {{cite book |editor-last=Figueiredo |editor-first=L. H. |editor2-last=Celes |editor2-first=W. |editor3-last=Ierusalimschy |editor3-first=R. |title=Lua Programming Gems |publisher=Lua.org |year=2008 |isbn=978-85-903798-4-3 |url=https://www.lua.org/gems/}}
* {{cite book |last1=Takhteyev |first1=Yuri |year=2012 |title=Coding Places: Software Practice in a South American City |publisher=[[The MIT Press]] |isbn=978-0-262-01807-4 |url=https://codingplaces.net/ |archive-url=https://web.archive.org/web/20121102000628/http://codingplaces.net/ |url-status=dead |archive-date=2012-11-02}} Chapters 6 and 7 are dedicated to Lua, while others look at software in Brazil more broadly.
* {{cite book |last=Varma |first=Jayant |title=Learn Lua for iOS Game Development |publisher=[[Apress]] |year=2012 |isbn=978-1-4302-4662-6 |url=https://www.amazon.com/exec/obidos/ASIN/1430246626/lua-docs-20}}
* {{cite web |url=https://www.gamedev.net/page/resources/_/technical/game-programming/an-introduction-to-lua-r1932 |title=An Introduction to Lua |website=GameDev.net |date=29 April 2003 |access-date=3 January 2013 |author=Matheson, Ash |archive-url=https://web.archive.org/web/20121218104442/http://www.gamedev.net/page/resources/_/technical/game-programming/an-introduction-to-lua-r1932 |archive-date=18 December 2012 |url-status=dead}}
* {{cite web|url=http://www.onlamp.com/pub/a/onlamp/2006/02/16/introducing-lua.html|title=Introducing Lua|last=Fieldhouse|first=Keith|date=16 February 2006|work=ONLamp.com|publisher=[[O'Reilly Media]]|access-date=28 February 2006|archive-url=https://web.archive.org/web/20060312124121/http://www.onlamp.com/pub/a/onlamp/2006/02/16/introducing-lua.html|archive-date=12 March 2006|url-status=dead}}
* {{cite web|url=https://www.ibm.com/developerworks/linux/library/l-lua.html|title=Embeddable scripting with Lua|last=Streicher|first=Martin|date=28 April 2006|work=developerWorks|publisher=[[IBM]]|access-date=7 July 2018|archive-date=2 July 2009|archive-url=https://web.archive.org/web/20090702111603/http://www.ibm.com/developerworks/linux/library/l-lua.html|url-status=dead}}
* {{cite journal |last=Quigley|first=Joseph|date=1 June 2007|title=A Look at Lua|journal=[[Linux Journal]]|url=https://www.linuxjournal.com/article/9605}}
* {{cite news|url=https://www.computerworld.com.au/article/260022/a-z_programming_languages_lua/|title=The A-Z of Programming Languages: Lua|last=Hamilton|first=Naomi|date=11 September 2008|work=[[Computerworld]]|publisher=[[International Data Group|IDG]]|access-date=7 July 2018|archive-url=https://web.archive.org/web/20180708020030/https://www.computerworld.com.au/article/260022/a-z_programming_languages_lua/|archive-date=8 July 2018|url-status=dead}} Interview with Roberto Ierusalimschy.
* {{cite journal|title=Passing a Language through the Eye of a Needle|last1=Ierusalimschy|first1=Roberto|last2=de Figueiredo|first2=Luiz Henrique|last3=Celes|first3=Waldemar|date=12 May 2011|journal=[[ACM Queue]]|volume=9|issue=5|pages=20–29|doi=10.1145/1978862.1983083|s2cid=19484689|doi-access=free}} How the embeddability of Lua impacted its design.
* {{cite journal|url=https://cacm.acm.org/magazines/2018/11/232214-a-look-at-the-design-of-lua|title=A Look at the Design of Lua|last1=Ierusalimschy|first1=Roberto|last2=de Figueiredo|first2=Luiz Henrique|last3=Celes|first3=Waldemar|journal=[[Communications of the ACM]]|volume=61|issue=11|pages=114–123|date=November 2018|doi=10.1145/3186277|s2cid=53114923|url-access=subscription}}{{Dead link|date=June 2020 |bot=InternetArchiveBot |fix-attempted=yes}}
* [https://www.lua.org/papers.html Lua papers and theses]
== External links ==
{{Wikibooks|Lua Programming}}
{{Sister project links|display=Lua|b=Lua Programming|v=Lua|wikt=no|q=no|s=no|commons=no}}
* {{Official website}}
* [http://lua-users.org/ Lua Users] {{Webarchive|url=https://web.archive.org/web/20101216084624/http://lua-users.org/ |date=16 December 2010}}, Community
* [https://luaforum.com Lua Forum] {{Webarchive|url=https://web.archive.org/web/20210928172635/https://www.luaforum.com/ |date=28 September 2021}}
* [https://luadist.org LuaDist]
* [https://luarocks.org/ Lua Rocks - Package manager]
* [https://web.archive.org/web/20070202005230/http://luaforge.net/ Projects in Lua]
{{Lua programming language}}
{{FOSS}}
{{Programming languages}}
{{Authority control}}
{{Portal bar|Free and open-source software|Computer programming}}
[[Category:Lua (programming language)| ]]
[[Category:Articles with example C code]]
[[Category:Brazilian inventions]]
[[Category:Cross-platform free software]]
[[Category:Cross-platform software]]
[[Category:Dynamic programming languages]]
[[Category:Dynamically typed programming languages]]
[[Category:Embedded systems]]
[[Category:Free and open source interpreters]]
[[Category:Free computer libraries]]
[[Category:Free software programmed in C]]
[[Category:Object-oriented programming languages]]
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[[Category:Programming languages]]
[[Category:Programming languages created in 1993]]
[[Category:Prototype-based programming languages]]
[[Category:Register-based virtual machines]]
[[Category:Scripting languages]]
[[Category:Software using the MIT license]]
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