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amming language the article is about the lua programming language itself for its use in wikipedia see wikipedia lua lua paradigm multi paradigm scripting imperative procedural prototype based object oriented functional meta reflective designed by roberto ierusalimschy waldemar celes luiz henrique de figueiredo first appeared 1993 29 years ago 1993 stable release 5 4 4 1 26 january 2022 10 months ago 26 january 2022 typing discipline dynamic weak duck implementation language ansi c os cross platform license mit license filename extensions lua website www lua org major implementations lua luajit luavela moonsharp luvit luart luau dialects metalua idle gsl shell influenced by c clu modula scheme snobol influenced gamemonkey io javascript citation needed julia minid red ring 2 ruby citation needed squirrel moonscript c lua ˈ l uː ə loo ə from portuguese lua ˈlu w ɐ meaning moon is a lightweight high level multi paradigm programming language designed primarily for embedded use in applications 3 lua is cross platform since the interpreter of compiled bytecode is written in ansi c 4 and lua has a relatively simple c api to embed it into applications 5 lua originated in 1993 as a language for extending 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 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 speed portability extensibility and ease of use in development contents 1 history 2 features 2 1 syntax 2 2 control flow 2 3 functions 2 4 tables 2 5 metatables 2 6 object oriented programming 2 6 1 inheritance 3 implementation 4 c api 4 1 modules 5 applications 6 derived languages 6 1 languages that compile to lua 6 2 dialects 7 see also 8 references 9 further reading 10 external links history edit 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 barriers called a market reserve for computer hardware and software in that atmosphere tecgraf s clients could not afford either politically or financially to buy customized software from abroad those reasons led tecgraf to implement the basic tools it needed from scratch 6 lua s predecessors were the data description configuration languages sol simple object language and del data entry language 7 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 6 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 or scheme because of their unfriendly syntax 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 for control structures was mostly borrowed from modula if while repeat until but also had taken influence from clu multiple assignments and multiple returns from function calls as a simpler alternative to reference parameters or explicit pointers c neat idea of allowing a local variable to be declared only where we need it 6 snobol and awk associative arrays 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 were a major influence on their decision to develop the table as the primary data structure of lua 8 lua semantics have been increasingly influenced by scheme over time 6 especially with the introduction of anonymous functions and full 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 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 edit wikibooks has a book on the topic of lua programming lua is commonly described as a multi paradigm language providing a small set of general features that can be extended to fit different problem types lua does not contain explicit support for inheritance but allows it to be implemented with metatables similarly lua allows programmers to implement namespaces classes and other related features using its single table implementation first class functions allow the employment of many techniques from functional programming and full lexical scoping allows fine grained information hiding to enforce the principle of least privilege in general lua strives to provide simple flexible 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 light the full reference interpreter is only about 247 kb compiled 4 and easily adaptable to a broad range of applications a dynamically typed language intended for use as an extension language or scripting language lua is compact enough to fit on a variety of host platforms it supports only a small number of atomic data structures such as boolean values numbers double precision floating point and 64 bit integers by default and strings typical data structures such as arrays sets lists and records can be represented using lua s single native data structure the table which is essentially a heterogeneous associative array lua implements a small set of advanced features such as first class functions garbage collection closures proper tail calls coercion automatic conversion between string and number values at run time coroutines cooperative multitasking and dynamic module loading syntax edit the classic hello world program can be written as follows 9 print hello world or as print hello world a comment in lua starts with a double hyphen and runs to the end of the line similar to ada eiffel haskell sql and vhdl multi line strings and comments are adorned with double square brackets the factorial function is implemented as a function in this example function factorial n local x 1 for i 2 n do x x i end return x end control flow edit lua has one type of conditional test if then end with optional else and elseif then execution control constructs the generic if then end statement requires all three keywords if condition then statement body end the else keyword may be added with an accompanying statement block to control execution when the if condition evaluates to false if condition then statement body else statement body end execution may also be controlled according to multiple conditions using the elseif then keywords if condition then statement body elseif condition then statement body else optional optional default statement body end lua has four types of conditional loops the while loop the repeat loop similar to a do while loop the numeric for loop and the generic for loop 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 the generic for loop for key value in pairs _g do print key value end would iterate over the table _g using the standard iterator function pairs until it returns nil loops can also be nested put inside of another loop 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 functions edit lua s treatment of functions as first class values is shown in the following example where the print function s behavior is modified 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 the new one has only one argument oldprint s foo and bar or s end end any future calls to print will now be routed through the new function and because of lua s lexical scoping the old print function will only be accessible by the new modified print lua also supports closures as demonstrated below function addto x return a new function that adds x to the argument return function y when we refer to the variable x which is outside the current scope and whose lifetime would be shorter than that of this anonymous function lua creates a closure return x y end end fourplus addto 4 print fourplus 3 prints 7 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 a new closure for the variable x is created every time addto is called so that each new anonymous function returned will always access its own x parameter the closure is managed by lua s garbage collector just like any other object tables edit tables are the most important data structures and by design the only built in composite data type in lua and are the foundation of all user created types they are associative arrays with addition of automatic numeric key and special syntax a table is a collection of key and data pairs where the data is referenced by key in other words it is a hashed heterogeneous associative array tables are created using the constructor syntax a_table creates a new empty table tables are always passed by reference see call by sharing a key index can be any value except nil and nan including functions a_table x 10 creates a new table with one entry mapping x to the number 10 print a_table x prints the value associated with the string key in this case 10 b_table a_table b_table x 20 the value in the table has been changed to 20 print b_table x prints 20 print a_table x also prints 20 because a_table and b_table both refer to the same table a table is often used as structure or record by using strings as keys because such use is very common lua features a special syntax for accessing such fields 10 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 by using a table to store related functions it can act as a namespace point point new function x y return x x y y return x x y y end point set_x function point x point x x point x x end tables are automatically assigned a numerical key enabling them to be used as an array data type the first automatic index is 1 rather than 0 as it is for many other programming languages though an explicit index of 0 is allowed a numeric key 1 is distinct from a string key 1 array a b c d indices are assigned automatically print array 2 prints b automatic indexing in lua starts at 1 print array prints 4 is the length operator for tables and strings array 0 z zero is a legal index print array still prints 4 as lua arrays are 1 based the length of a table t is defined to be any integer index n such that t n is not nil and t n 1 is nil moreover if t 1 is nil n can be zero for a regular array with non nil values from 1 to a given n its length is exactly that n the index of its last value if the array has holes that is nil values between other non nil values then t can be any of the indices that directly precedes a nil value that is it may consider any such nil value as the end of the array 11 exampletable 1 2 3 4 5 6 7 8 print exampletable 1 3 prints 3 print exampletable 2 4 prints 8 a table can be an array of objects 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 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 12 metatables edit extensible semantics is a key feature of lua and the metatable concept allows powerful customization of tables the following example demonstrates an infinite table for any n fibs n will give the n th fibonacci number using dynamic programming and memoization 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 object oriented programming edit although lua does not have a built in concept of classes object oriented programming can be emulated using functions and tables an object is formed by putting methods and fields in a table inheritance both single and multiple can be implemented with metatables delegating nonexistent methods and fields to a parent object there is no such concept as class with these techniques rather prototypes are used similar to self or javascript new objects are created either with a factory method that constructs new objects from scratch or by cloning an existing object creating a basic vector object local vector local vectormeta __index vector function vector new x y z the constructor return setmetatable x x y y z z vectormeta end function vector magnitude self another method 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 here setmetatable tells lua to look for an element in the vector table if it is not present in the vec table vec magnitude which is equivalent to vec magnitude first looks in the vec table for the magnitude ele...