Lua: Small embeddable scripting language with co-routines

As in all engineering pursuits, choosing between a compiled language and an interpreted language means measuring the pros and cons of each in context, weighing the trade-offs, and accepting compromises.

An introduction to  Lua programming can be found in the book:

Programming in Lua
by Roberto Ierusalimschy
Lua.org, third edition, January 2013
ISBN 859037985X (also available as e-book)

This book is now in the third edition covering Lua 5.2. The first edition which cover Lua 5.0 is available online; it is still largely relevant. 

Martin Streicher wrote a good intro for IBM Developer Works (Embeddable scripting with Lua): 

Lua offers high-level abstraction without losing touch with the hardware

Level: Introductory

Martin Streicher ([email protected]), Editor-in-Chief, Linux Magazine

28 Apr 2006

Compiled programming languages and scripting languages each have unique advantages, but what if you could use both to create rich applications? Lua is an embeddable scripting language that is small, fast, and very powerful. Before you create yet another configuration file or resource format (and yet another parser to accompany it), try Lua.

The Lua programming language is a small scripting language specifically designed to be embedded in other programs. Lua's C API allows exceptionally clean and simple code both to call Lua from C, and to call C from Lua. This allows developers who want a convenient runtime scripting language to easily implement the basic API elements needed by the scripting language, then use Lua code from their applications. This article introduces the Lua language as a possible tool for simplifying common development tasks, and discusses some of the reasons to embed a scripting language in the first place.

While interpreted programming languages such as Perl, Python, PHP, and Ruby are increasingly favored for Web applications -- and have long been preferred for automating system administration tasks -- compiled programming languages such as C and C++ are still necessary. The performance of compiled programming languages remains unmatched (exceeded only by the performance of hand-tuned assembly), and certain software -- including operating systems and device drivers -- can only be implemented efficiently using compiled code. Indeed, whenever software and hardware need to mesh seamlessly, programmers instinctively reach for a C compiler: C is primitive enough to get "close to the bare metal" -- that is, to capture the idiosyncrasies of a piece of hardware -- yet expressive enough to offer some high-level programming constructs, such as structures, loops, named variables, and scope.

However, scripting languages have distinct advantages, too. For example, after a language's interpreter is successfully ported to a platform, the vast majority of scripts written in that language run on the new platform unchanged -- free of dependencies such as system-specific function libraries. (Think of the many DLL files of the Microsoft® Windows® operating system or the many libcs of UNIX® and Linux®.) Additionally, scripting languages typically offer higher-level programming constructs and convenience operations, which programmers claim boost productivity and agility. Moreover, programmers working in an interpreted language can work faster, because the compilation and link steps are unnecessary. The "code, build, link, run" cycle of C and its ilk is reduced to a hastened "script, run."

Lua novelties

Like every scripting language, Lua has its own peculiarities:

• Lua types. In Lua, values have types, but variables are dynamically typed. The nil, boolean, number, and string types work as you might expect.
  • Nil is the type of the special value nil and is used to represent the absence of a value.
  • Boolean is the type of the constants true and false. (Nil also represents false, and any non-nil value represents true.)
  • All numbers in Lua are doubles (but you can easily build code to realize other numeric types).
  • A string is an immutable array of characters. (Hence, to append to a string, you must make a copy of it.)
• The table, function, and thread types are all references. Each can be assigned to a variable, passed as an argument, or returned from a function. For instance, here's an example of storing a function:
  

  -- example of an anonymous function
  -- returned as a value
  -- see http://www.tecgraf.puc-rio.br/~lhf/ftp/doc/hopl.pdf
  function add(x)
    return function (y) return (x + y) end
  end
  f = add(2)
  print(type(f), f(10))
  function  12
  

   
• Lua threads. A thread is a co-routine created by calling the built-in function coroutine.create(f), where f is a Lua function. Threads do not start when created; instead, a co-routine is started after the fact, using coroutine.resume(t), where t is a thread. Every co-routine must occasionally yield the processor to other co-routines using coroutine.yield().
• Assignment statements. Lua allows multiple assignments, and expressions are evaluated first and are then assigned. For example, the statements:
  

  i = 3
  a = {1, 3, 5, 7, 9}
  i, a[i], a[i+1], b = i+1, a[i+1], a[i]
  print (i, a[3], a[4], b, I)
  

  
  produce 4 7 5 nil nil. If the list of variables is larger than the list of values, excess variables are assigned nil; hence, b is nil. If there are more values than variables, extra values are simply discarded. In Lua, variable names are case-sensitive, explaining why I is nil.
• Chunks. A chunk is any sequence of Lua statements. A chunk can be stored in a file or in a string in a Lua program. Each chunk is executed as the body of an anonymous function. Therefore, a chunk can define local variables and return values.
• More cool stuff. Lua has a mark-and-sweep garbage collector. As of Lua 5.1, the garbage collector works incrementally. Lua has full lexical closures (like Scheme and unlike Python). And Lua has reliable tail call semantics (again, like Scheme and unlike Python).

Find more examples of Lua code in Programming in Lua and in the Lua-users wiki (for links, see the Resources section below).

Mixing the best of both worlds

But what if you could enjoy the best of both worlds: close to bare metal performance and high-level, powerful abstractions? Better yet, what if you could optimize algorithms and functions that are processor intensive and system dependent as well as separate logic that's system independent and highly susceptible to changes in requirements?

Balancing the need for high-performance code and high-level programming is the purview of Lua, an embeddable scripting language. Applications that include Lua are a combination of compiled code and Lua scripts. Compiled code can drop to the metal when necessary, yet can call Lua scripts to manipulate complex data. And because the Lua scripts are separate from the compiled code, you readily and separately revise the scripts. With Lua, the development cycle is more akin to "Code, Build, Run, Script, Script, Script...".

For example, the Lua Web site "Uses" page (see Resources) lists several mass-market computer games, including World of Warcraft and (the home console version of arcade classic) Defender, that integrate Lua to run everything from the user interface to the artificial intelligence of foes. Other applications of Lua include an extension mechanism for the popular Linux software update tool apt-rpm and the control of the "Crazy Ivan" Robocup 2000 champion. Many of the testimonials on that page laud Lua's small size and excellent performance.

Getting started with Lua

Lua version 5.0.2 was the current version at the time of this writing, although version 5.1 was released recently. You can download Lua as source code from lua.org, and you can find a variety of pre-built binaries at the Lua-users wiki (see Resources for links). The entire Lua 5.0.2 core, including the standard libraries and the Lua compiler, is less than 200KB in size.

If you use Debian Linux, you can install Lua 5.0 quickly and easily by running this command:

# apt-get install lua50

as the superuser. All the examples shown here were run on Debian Linux "Sarge" using Lua 5.0.2 and the 2.4.27-2-686 Linux kernel.

After you've installed Lua on your system, give the stand-alone Lua interpreter a try. (All Lua applications must be embedded in a host application. The interpreter is simply a special kind of host, useful for development and debugging.) Create a file called factorial.lua, and enter the lines:

-- defines a factorial function
function fact (n)
  if n == 0 then
    return 1
  else
    return n * fact(n-1)
  end
end

print("enter a number:")
a = io.read("*number")
print(fact(a))

The code in factorial.lua -- more specifically, any sequence of Lua statements -- is called a chunk, as described in the Lua novelties section above. To execute the chunk you just created, run the command lua factorial.lua:

$ lua factorial.lua
enter a number:
10
3628800
 



 

Or, as in other interpreted languages, you can add a "shebang" (#!) line at the top of the script, make the script executable, and then run the file as a stand-alone command:

$ (echo '#! /usr/bin/lua'; cat factorial.lua) > factorial 
$ chmod u+x factorial
$ ./factorial
enter a number:
4
24

The Lua language

Lua has many of the conveniences found in a modern scripting language: scope, control structures, iterators, and a host of standard libraries for processing strings, emitting and collecting data, and performing mathematical operations. A complete description of the Lua language is in the Lua 5.0 Reference Manual (see Resources).

In Lua, only values have a type, but variables are dynamically typed. There are eight fundamental types (of values) in Lua: nil, boolean, number, string, function, thread, table, and userdata. The first six types are largely self-descriptive (see the Lua novelties section above for the exceptions); the last two need some explanation.

Lua tables

Tables are the catch-all data structure in Lua. Indeed, tables are the only data structure in Lua. You can use a table as an array, a dictionary (also called a hash or an associative array), a tree, a record, and so on.

Unlike other programming languages, the contents of a Lua table need not be homogeneous: The table can include any combination of types and can contain a mix of array-like elements and dictionary-like elements. Moreover, any Lua value -- including a function or another table -- can serve as a dictionary element key.

To explore tables, start the Lua interpreter and type the lines shown in bold in Listing 1.

$ lua
> -- create an empty table and add some elements
> t1 = {}
> t1[1] = "moustache"
> t1[2] = 3
> t1["brothers"] = true

> -- more commonly, create the table and define elements
> all at once
> t2 = {[1] = "groucho", [3] = "chico", [5] = "harpo"}
> t3 = {[t1[1]] = t2[1], accent = t2[3], horn = t2[5]}
> t4 = {}
> t4[t3] = "the marx brothers"
> t5 = {characters = t2, marks = t3}
> t6 = {["a night at the opera"] = "classic"}

> -- make a reference and a string
> i = t3
> s = "a night at the opera"

> -- indices can be any Lua value
> print(t1[1], t4[t3], t6[s])
moustache   the marx brothers classic

> -- the phrase table.string is the same as table["string"]
> print(t3.horn, t3["horn"])
harpo   harpo

> -- indices can also be "multi-dimensional"
> print (t5["marks"]["horn"], t5.marks.horn)
harpo   harpo

> -- i points to the same table as t3
> = t4[i]
the marx brothers

> -- non-existent indices return nil values
> print(t1[2], t2[2], t5.films)
nil     nil     nil

>  -- even a function can be a key 
> t = {}
> function t.add(i,j)
>> return(i+j)
>> end
> print(t.add(1,2))
3
> print(t['add'](1,2))
3
>  -- and another variation of a function as a key 
> t = {}
> function v(x)
>> print(x)
>> end
> t[v] = "The Big Store"
> for key,value in t do key(value) end
The Big Store

> table.foreachi(t1, print)
1 moustache
2 3

Others, such as table.foreach(), iterate over an entire table:

> table.foreach(t2,print)
1       groucho
3       chico
5       harpo
> table.foreach(t1,print)
1       moustache
2       3
brothers        true

While some iterators are optimized for integer indices, all simply process (key, value) pairs.

For fun, create a table, t, with elements {2, 4, 6, language="Lua", version="5", 8, 10, 12, web="www.lua.org"}, and run table.foreach(t, print) and table.foreachi(t, print).

Userdata

Because Lua is intended to be embedded in a host application written in a language such as C or C++ and is intended to cooperate with the host application, data must be shared between the C environment and Lua. As the Lua 5.0 Reference Manual says, the userdata type allows "arbitrary C data to be stored in Lua variables." You can think of userdata as an array of bytes -- bytes that might represent a pointer, a structure, or a file in the host application.

The contents of userdata originates with C, so it cannot be modified in Lua. Of course, because the userdata originates in C, there are no pre-defined operations for userdata in Lua. However, you can create operations that operate on userdata using another Lua mechanism, called metatables.

Metatables

Because tables and userdata are so flexible, Lua permits you to overload operations for objects of either type. (You cannot overload the six other types.) A metatable is a (normal) Lua table that maps standard operations to custom functions that you provide. The keys of the metatable are called events; the values (in other words, the functions) are called metamethods.

The functions setmetatable() and getmetatable() modify and query an object's metatable, respectively. Each table and userdata object can have its own metatable.

For example, one event is __add, for addition. Can you deduce what this chunk does?

-- Overload the add operation
-- to do string concatenation
--
mt = {}

function String(string)
  return setmetatable({value = string or ''}, mt)
end

-- The first operand is a String table
-- The second operand is a string
-- .. is the Lua concatenate operator
--
function mt.__add(a, b)
  return String(a.value..b)
end

s = String('Hello')
print((s + ' There ' + ' World!').value )

This chunk emits the following text:

Hello There World!

__index is another event. The metamethod for __index is called whenever a key doesn't exist in a table. Here's an example that "memoizes," or remembers, the value of a function:

-- code courtesy of Rici Lake, [email protected]
function Memoize(func, t)
  return setmetatable(
     t or {},
    {__index =
      function(t, k)
        local v = func(k);
        t[k] = v;
        return v;
        end
    }
  )
end

COLORS = {"red", "blue", "green", "yellow", "black"}
color = Memoize(
  function(node)
    return COLORS[math.random(1, table.getn(COLORS))]
    end
)

Put the code into the Lua interpreter, and then type print(color[1], color[2], color[1]). You should see something like blue black blue.

This code, given a key, node, looks up the color for the node. If it doesn't exist, the code permanently assigns node a new, randomly chosen color. Otherwise, the node's assigned color is returned. In the former case, the __index metamethod is executed once to assign a color. The latter case is a simple and fast hash lookup.

The Lua language offers many other powerful features, and all of them are well documented. But in case you ever run into trouble or want to talk to a wizard, head over to the Lua Users Chat Room IRC Channel (see Resources) for some very enthusiastic support.

Embed and extend

Beyond Lua's simple syntax and powerful table structure, Lua's real power is evident when mixing it with a host language. As has been intimated, Lua scripts can extend the host language's own capabilities. But the reciprocal is true as well: The host language can simultaneously extend Lua. C functions can call Lua functions and vice versa, for example.

At the heart of the symbiotic relationship between Lua and its host language is a virtual stack. The virtual stack -- like a real stack -- is a last in-first out (LIFO) data structure that temporarily stores function arguments and function results. To make a call from Lua to its host language and vice versa, the caller pushes values onto the stack and calls the target function; the callee pops the arguments (verifying the type and value of each argument, of course), processes the data, and pushes the result on the stack. When control returns to the caller, the caller extracts the return values from the stack.

Virtually all the C application program interface (API) for Lua operations operate through the stack. The stack can hold any Lua value; however, the type of the value must be known to the caller and callee, and specific functions push and pop each type from the stack (such as lua_pushnil() and lua_pushnumber().

Listing 2 shows a simple C program (taken from Chapter 24 of the Programming in Lua book cited in Resources) that implements a minimal but functional Lua interpreter.

 1 #include <stdio.h>
 2 #include <lua.h>
 3 #include <lauxlib.h>
 4 #include <lualib.h>
 5
 6 int main (void) {
 7   char buff[256];
 8   int error;
 9   lua_State *L = lua_open();   /* opens Lua */
10   luaopen_base(L);             /* opens the basic library */
11   luaopen_table(L);            /* opens the table library */
12   luaopen_io(L);               /* opens the I/O library */
13   luaopen_string(L);           /* opens the string lib. */
14   luaopen_math(L);             /* opens the math lib. */
15
16   while (fgets(buff, sizeof(buff), stdin) != NULL) {
17     error = luaL_loadbuffer(L, buff, strlen(buff), "line") ||
18             lua_pcall(L, 0, 0, 0);
19     if (error) {
20       fprintf(stderr, "%s", lua_tostring(L, -1));
21       lua_pop(L, 1);  /* pop error message from the stack */
22     }
23   }
24
25   lua_close(L);
26   return 0;
27 }

Lines 2 through 4 include the Lua standard functions, several convenience functions that are used in all Lua libraries, and functions to open libraries, respectively. Line 9 creates a Lua state. All states are initially empty; you add libraries of functions to the state using luaopen_...(), as shown in Lines 10 through 14.

Line 17 and luaL_loadbuffer() take the input from stdin as a chunk and compile it, placing the chunk on the virtual stack. Line 18 pops the chunk from the stack and executes it. If an error occurs during execution, a Lua string is pushed on the stack. Line 20 accesses the top of the stack (the top of the stack has an index of -1) as a Lua string, prints the message, and then removes the value from the stack.

Using the C API, your application can also "reach" into the Lua state to extract information. This snippet grabs two global variables from the Lua state:

..
if (luaL_loadfile(L, filename) || lua_pcall(L, 0, 0, 0))
  error(L, "cannot run configuration file: %s", lua_tostring(L, -1));

lua_getglobal(L, "width");
lua_getglobal(L, "height");
..
width = (int) lua_tonumber(L, -2);
height = (int) lua_tonumber(L, -1);
..

Again, notice that the stack enables the transfer. Calling any Lua function from C is similar to this code:

• Grab the function using lua_getglobal(),
• push arguments, make a lua_pcall(),
• and then process the results.

If a Lua function returns n values, the first value is at location -n in the stack, and the last value is at position -1.

The inverse -- calling a C function from Lua -- is similar. If your operating system supports dynamic loading, Lua can load and call functions on demand. (In operating systems where static loading is a necessity, extending the Lua engine to call a C function requires you to rebuild Lua.)

Lua is out of this world

Lua is an incredibly easy language to pick up, but its simple syntax disguises its power: The language supports objects (which are similar to Perl's), metatables make its table type quite malleable, and the C API allows great integration and extension between scripts and the host language. Lua has been hosted in the C, C++, C#, Java™, and Python languages.

Before you create yet another configuration file or resource format (and yet another parser to accompany it), try Lua. The Lua language -- like its community -- is robust, inventive, and ready to help.

History

Some of its closest relatives include Icon for its design and Python for its ease of use by non-programmers. 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.[1]

Lua has been used in many applications, both commercial and non-commercial. See the Applications section for a detailed list. Lua has been used to program homebrew applications for the PlayStation Portable and the Nintendo DS.

Features

In general, Lua strives to provide 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 - in fact, the full reference interpreter is only about 150kB compiled - and easily adaptable to a broad range of applications.

Lua is a dynamically typed language intended for use as an extension or scripting language, and 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 by default), and strings. Typical data structures such as arrays, sets, hash tables, lists, and records can be represented using Lua's single native data structure, the table, which is essentially a heterogeneous map.

Lua has no built-in support for namespaces and object-oriented programming. Instead, metatable and metamethods are used to extend the language to support both programming paradigms in an elegant and straight-forward manner.

Lua implements a small set of advanced features such as higher-order functions, garbage collection, first-class functions, closures, proper tail calls, coercion (automatic conversion between string and number values at run time), coroutines (cooperative multitasking) and dynamic module loading.

By including only a minimum set of data types, Lua attempts to strike a balance between power and size.

Example code

print "Hello, World!" The factorial is an example of a recursive function:

function factorial(n) if n == 0 then return 1 end return n * factorial(n - 1) -- A comment in Lua starts with a double-hyphen end -- and runs to the end of the line

Lua's treatment of functions as first class variables is shown in the following example, where the print function's behavior is modified:

do local oldprint = print -- Store current print function as old print print = function(s) -- Redefine print function if s == "foo" then oldprint("bar") else oldprint(s) end end end

Any future calls to "print" will now be routed through the new function, and thanks to 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 makeaddfunc(x) -- Return a new function that adds x to the argument return function(y) -- When we refer to the variable x, which is outside of the current -- scope and whose lifetime is shorter than that of this anonymous -- function, Lua creates a closure. return x + y end end plustwo = makeaddfunc(2) print(plustwo(5)) -- Prints 7

A new closure for the variable x is created every time makeaddfunc is called, so that the anonymous function returned will always access its own x parameter. The closure is managed by Lua's garbage collector, just like any other object.

Extensible semantics is a key feature of Lua, and the "metatable" concept allows Lua's tables to be customized in powerful and unique ways. The following example demonstrates an "infinite" table. For any n, fibs[n] will give the nth Fibonacci number using dynamic programming.

fibs = { 1, 1 } -- Initial values for fibs[1] and fibs[2]. setmetatable(fibs, { -- Give fibs some magic behavior. __index = function(name, n) -- Call this function if fibs[n] does not exist. name[n] = name[n - 1] + name[n - 2] -- Calculate and memoize fibs[n]. return name[n] end })

Tables

The table is a collection of key and data pairs (known also as hashed heterogeneous associative array), where the data is referenced by key. The key (index) can be of any data type except nil. An integer key of 1 is considered distinct from a string key of "1".

Tables are created using the {} constructor syntax: a_table = {} -- Creates a new, empty table

Tables are always passed by reference: a_table = {x = 10} -- Creates a new table, with one associated entry. The string x mapping to the number 10. print(a_table["x"]) -- Prints the value associated with the string key, in this case 10. b_table = a_table a_table["x"] = 20 -- The value in the table is been changed to 20. print(a_table["x"]) -- Prints 20. print(b_table["x"]) -- Prints 20, because a_table and b_table both refer to the same table.

Table as structure

Table as array

A simple array of strings: 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.

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 print(array[2].y) -- Prints 40

Object-oriented programming

There is no such concept as "class" with these techniques, rather "prototypes" are used as in Self programming language or Javascript. New objects are created either with a factory method (that constructs new objects from scratch) or by cloning an existing object.

Lua provides some syntactic sugar to facilitate object orientation. To declare member functions inside a prototype table, you can use function table:func(args), which is equivalent to function table.func(self, args). Calling class methods also makes use of the colon: object:func(args) is equivalent to object.func(object, args).

Creating a basic vector object:

Vector = { } -- Create a table to hold the class methods function Vector:new(x, y, z) -- The constructor function object = { x = x, y = y, z = z } setmetatable(object, { -- Overload the index event so that fields not present within the object are -- looked up in the prototype Vector table __index = Vector }) return object end function Vector:mag() -- Declare another member function, to determine the magnitude of the vector -- Reference the implicit object using self return math.sqrt(self.x * self.x + self.y * self.y + self.z * self.z) end local vec = Vector:new(0, 1, 0) -- Create a vector print(vec:mag()) -- Call a member function using ":" print(vec.x) -- Access a member variable using "."

Internals

This example is the bytecode listing of the factorial function described above (in Lua 5.1.1):

function <factorial.lua:1,6> (10 instructions, 40 bytes at 003D5818) 1 param, 3 slots, 0 upvalues, 1 local, 3 constants, 0 functions 1 [2] EQ 0 0 -1 ; - 0 2 [2] JMP 2 ; to 5 3 [3] LOADK 1 -2 ; 1 4 [3] RETURN 1 2 5 [5] GETGLOBAL 1 -3 ; factorial 6 [5] SUB 2 0 -2 ; - 1 7 [5] CALL 1 2 2 8 [5] MUL 1 0 1 9 [5] RETURN 1 2 10 [6] RETURN 0 1

There is also a free, third-party just-in-time compiler for the latest version (5.1) of Lua, called LuaJIT. It's very small (under 32kB of additional code) and can often improve the performance of a Lua program significantly. [2]

C API

The Lua API is fairly straightforward because its unique design eliminates the need for manual reference management in C code, unlike Python's API. The API, like the language, is minimalistic. Advanced functionality is provided by the auxiliary library, which consists largely of preprocessor macros which make complex table operations more palatable.

The Lua Stack

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 lua_call is used to call the actual function. When writing a C function to be directly called from Lua, the arguments are popped from the stack.

Special Tables

Extension Modules

NEWS CONTENTS

• 20151207 : Scripted window actions on Ubuntu with Devilspie 2 ( Scripted window actions on Ubuntu with Devilspie 2, Dec 07, 2015 )

Old News ;-)

[Dec 07, 2015] Scripted window actions on Ubuntu with Devilspie 2

On this page
•What is LUA?
•Installation.
•Config and Scripting. •Sample Scripts.
•Sript Commands.

•Links

Devilspie2 is a program that detects windows as they are created, and performs scripted actions on them. The scripts are written in LUA, allowing a great deal of customization. This tutorial will show you the installation of Devilspie 2 on Ubuntu 14.04 and give you a introduction into Devilspie scripting.

What is LUA?

Lua is a powerful, fast, lightweight, embeddable scripting language. Lua combines simple procedural syntax with powerful data description constructs based on associative arrays and extensible semantics. Lua is dynamically typed, runs by interpreting bytecode for a register-based virtual machine, and has automatic memory management with incremental garbage collection, making it ideal for configuration, scripting, and rapid prototyping.

For futher infomation visit: http://www.lua.org/

Embed Lua for scriptable apps

The Lua programming language is a small scripting language specifically designed to be embedded in other programs. Lua&apos;s C API allows exceptionally clean and simple code both to call Lua from C, and to call C from Lua. This allows developers who want a convenient runtime scripting language to easily implement the basic API elements needed by the scripting language, then use Lua code from their applications. This article introduces the Lua language as a possible tool for simplifying common development tasks, and discusses some of the reasons to embed a scripting language in the first place.

Recommended Links

The Programming Language Lua

• The Reference manual for Lua 5.0 describes the entire Lua language.
• The book Programming in Lua by Roberto Ierusalimschy (Roberto Ierusalimschy, 2003) is an invaluable resource for learning how to code effectively in Lua.
• Consult the library of Lua tutorials, in the Lua-users wiki, to use a particular feature of Lua.
• See a list of projects that use Lua.

Lua (programming language) - Wikipedia, the free encyclopedia

• Lua.org - official site.
• lua-users.org - community website for and by users (and authors) of Lua.
• A Look at Lua - Overview of the language in Linux Journal.
• Introducing Lua - ONLamp.com.
• An Introduction to Lua - GameDev.net.
• Embeddable scripting with Lua - IBM developerWorks.
• Interview with Roberto Ierusalimschy on Lua - Computerworld.

Bindings to Other Languages

• LuaInterface http://luaforge.net/projects/luainterface/ for CLR based languages.
• Tao.Lua http://www.taoframework.com/project/lua for .Net and Mono
• LuaJava http://luaforge.net/projects/luajava for Java.
• Kahlua http://code.google.com/p/kahlua/ for J2ME (CLDC 1.1). This is not a binding, but a reimplementation of the Lua virtual machine.

Applications

Games

• World of Warcraft, a fantasy MMORPG. Lua is used to allow users to customize its user interface.
• Dawn of War, uses Lua throughout the game.
• Far Cry, a first-person shooter. Lua is used to script a substantial chunk of the game logic, manage game objects' (Entity system), configure the HUD and store other configuration information.
• Crysis, a first-person shooter & sequel to Far Cry.
• Company of Heroes, a WW2 RTS. Lua is used for the console, AI, single player scripting, win condition scripting and for storing unit attributes and configuration information.
• Supreme Commander allows you to edit almost all its aspects with Lua.
• Ragnarok Online recently had a Lua implementation, allowing players to fully customize the artificial intelligence of their homunculus to their liking, provided that they have an Alchemist to summon one.
• Garry's Mod and Fortress Forever, mods for Half-Life 2, use Lua scripting for tools and other sorts of things for full customization.
• Grim Fandango and Escape from Monkey Island, both based on the GrimE engine are two of the first games which used Lua for significant purposes.
• Aleph One, a derivative of Bungie's classic first-person shooter series, Marathon. Lua scripts are often used in multiplayer games to display or alter scores, announce killings, and in some instances to create new gametypes.
• Multi Theft Auto, a multi-player modification for the Grand Theft Auto video game series. The recent adaptation for the game Grand Theft Auto San Andreas uses Lua.
• Roblox, a multi-player game that uses Lua in various customizable scripts in the online 'places'.
• Tales of Pirates uses Lua.
• Warhammer Online uses Lua.
• Rail Simulator uses Lua.
• Natural Selection 2 is written almost entirely in Lua.
• Spring supports modification with Lua.
• Open Tibia uses Lua.

Other applications

• Celestia uses Lua to expand its capabilities without recompiling its source code
• Multimedia Fusion Developer 2 has a Lua extension that allows it to run Lua scripts
• Adobe Photoshop Lightroom uses Lua for its user interface
• The window manager Ion uses Lua for customization and extensibility.
• The packet sniffer Wireshark uses Lua for scripting and prototyping.
• The Aegisub subtitles manipulation program uses Lua in its automation module, to generate advanced effects, such as karaoke.
• Intellipool Network Monitor uses Lua for customization and extensibility.
• Lua Player is a port designed to run on Sony Computer Entertainment's PlayStation Portable to allow entry-level programming.
• CMUcam uses Lua for customization and extensibility as part of the CMUcam 3 scripter
• lighttpd uses Lua for its Cache Meta Language, a sophisticated way to describe caching behavior.
• The popular network mapping program nmap uses Lua as the basis for its scripting language, called nse.
• The version control system Monotone uses Lua for scripting hooks.
• eyeon's Fusion compositor uses embedded Lua for internal and external scripts and also plugin prototyping.
• The Snort Intrusion Detection/Prevention System version 3.0 uses Lua for its command line interpreter.
• New versions of SciTE allow Lua to be used to provide additional features.
• Version 2.01 of the profile management software for Logitech's G15 gaming keyboard uses Lua as its scripting language.
• A new extended version of the TeX typesetting system using Lua as its embedded scripting lanuage is currently under development and reached Beta status in August 2007 (LuaTeX).

Books

• Lua 5.1 Reference Manual (online version of paper book) (ISBN 85-903798-3-3)
• Programming in Lua, Second Edition (online first edition) (ISBN 85-903798-2-5)
• Game Development with Lua (ISBN 1-58450-404-8)
• Beginning Lua Programming (ISBN 978-0-470-06917-2)

Trivia

• The historic "SCUMM bar" from the Monkey Island games is renovated and renamed to the "Lua bar" during Escape from Monkey Island, as a reference to the fact that the game was the first in the series to be coded in Lua (previous games used the SCUMM engine).

External links

• Lua Official Site
• Lua mailing list
• Applications that use Lua
• LuaForge
• Lua Player (PSP)
• Plua (Palm (PDA))
• onlamp.com: Introducing Lua
• An Introduction to Lua from GameDev
• Introduction to Lua Programming from Scratch Projects
• Lua Support Forum

Etc

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Classic books:

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Last modified: March 12, 2019