Lua 5.0 Reference Manual
Last revised on November 25, 2003
Lua
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Lua 5.0 Reference Manual
Roberto Ierusalimschy Luiz Henrique de Figueiredo Waldemar Celes lua@tecgraf.puc-rio.br Tecgraf — Computer Science Department — PUC-Rio
PUC-RioInf.MCC14/03 Abril 2003
Abstract
Lua is a powerful, light-weight programming language designed for extending applications. Lua is also frequently used as a general-purpose, stand-alone language. Lua combines simple procedural syntax (similar to Pascal) with powerful data description constructs based on associative arrays and extensible semantics. Lua is dynamically typed, interpreted from opcodes, and has automatic memory management with garbage collection, making it ideal for configuration, scripting, and rapid prototyping.
This document describes version 5.0 of the Lua programming language and the Application
Program Interface (API) that allows interaction between Lua programs and their host C programs.
Resumo
Lua ´e uma linguagem de programa¸c˜ao poderosa e leve, projetada para estender aplica¸c˜oes.
Lua tamb´em ´e frequentemente usada como uma linguagem de prop´osito geral. Lua combina programa¸c˜ao procedural (com sintaxe semelhante `a de Pascal) com poderosas constru¸c˜oes para descri¸c˜ao de dados, baseadas em tabelas associativas e semˆantica extens´ıvel. Lua ´e tipada dinamicamente, interpretada a partir de opcodes, e tem gerenciamento autom´atico de mem´oria com coleta de lixo. Essas caracter´ısticas fazem de Lua uma linguagem ideal para configura¸c˜ao, automa¸c˜ao (scripting) e prototipagem r´apida.
Este documento descreve a vers˜ao 5.0 da linguagem de programa¸c˜ao Lua e a Interface de
Programa¸c˜ao (API) que permite a intera¸c˜ao entre programas Lua e programas C hospedeiros. i ii
Contents
1 Introduction 1
2 The Language 1
2.1 Lexical Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.2 Values and Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2.1 Coercion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4.1 Chunks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4.2 Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4.3 Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4.4 Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.5 For Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.6 Function Calls as Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.4.7 Local Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5.1 Arithmetic Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5.2 Relational Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.5.3 Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.5.4 Concatenation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5.5 Precedence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5.6 Table Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5.7 Function Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.5.8 Function Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.6 Visibility Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.7 Error Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.8 Metatables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.9 Garbage Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.9.1 Garbage-Collection Metamethods . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.9.2 Weak Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.10 Coroutines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3 The Application Program Interface 22
3.1 States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 The Stack and Indices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 Stack Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4 Querying the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.5 Getting Values from the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.6 Pushing Values onto the Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.7 Controlling Garbage Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.8 Userdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.9 Metatables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.10 Loading Lua Chunks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.11 Manipulating Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.12 Manipulating Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.13 Using Tables as Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 iii 3.14 Calling Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.15 Protected Calls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.16 Defining C Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.17 Defining C Closures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.18 Registry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.19 Error Handling in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.20 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4 The Debug Interface 35
4.1 Stack and Function Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.2 Manipulating Local Variables and Upvalues . . . . . . . . . . . . . . . . . . . . . . . 36
4.3 Hooks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5 Standard Libraries 38
5.1 Basic Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.2 Coroutine Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
5.3 String Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.4 Table Manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.5 Mathematical Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
5.6 Input and Output Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.7 Operating System Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.8 The Reflexive Debug Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6 Lua Stand-alone 57
Incompatibilities with Previous Versions 58
The Complete Syntax of Lua 60
Index 61 iv 1 Introduction
Lua is an extension programming language designed to support general procedural programming with data description facilities. It also offers good support for object-oriented programming, functional programming, and data-driven programming. Lua is intended to be used as a powerful, light-weight configuration language for any program that needs one. Lua is implemented as a library, written in clean C (that is, in the common subset of ANSI C and C++).
Being an extension language, Lua has no notion of a “main” program: it only works embedded in a host client, called the embedding program or simply the host. This host program can invoke functions to execute a piece of Lua code, can write and read Lua variables, and can register
C functions to be called by Lua code. Through the use of C functions, Lua can be augmented to cope with a wide range of different domains, thus creating customized programming languages sharing a syntactical framework.
The Lua distribution includes a stand-alone embedding program, lua, that uses the Lua library to offer a complete Lua interpreter.
Lua is free software, and is provided as usual with no guarantees, as stated in its copyright notice.
The implementation described in this manual is available at Lua’s official web site, www.lua.org.
Like any other reference manual, this document is dry in places. For a discussion of the decisions behind the design of Lua, see the papers below, which are available at Lua’s web site.
• R. Ierusalimschy, L. H. de Figueiredo, and W. Celes. Lua—an extensible extension language.
Software: Practice & Experience 26 #6 (1996) 635–652.
• L. H. de Figueiredo, R. Ierusalimschy, and W. Celes. The design and implementation of a language for extending applications. Proceedings of XXI Brazilian Seminar on Software and
Hardware (1994) 273–283.
• L. H. de Figueiredo, R. Ierusalimschy, and W. Celes. Lua: an extensible embedded language.
Dr. Dobb’s Journal 21 #12 (Dec 1996) 26–33.
• R. Ierusalimschy, L. H. de Figueiredo, and W. Celes. The evolution of an extension language: a history of Lua, Proceedings of V Brazilian Symposium on Programming Languages (2001)
B-14–B-28.
Lua means “moon” in Portuguese and is pronounced LOO-ah.
2 The Language
This section describes the lexis, the syntax, and the semantics of Lua. In other words, this section describes which tokens are valid, how they can be combined, and what their combinations mean.
The language constructs will be explained using the usual extended BNF, in which { a } means 0 or more a’s, and [ a ] means an optional a. Non-terminals are shown in italics, keywords are shown in bold, and other terminal symbols are shown in typewriter font, enclosed in single quotes.
2.1 Lexical Conventions
Identifiers in Lua can be any string of letters, digits, and underscores, not beginning with a digit.
This coincides with the definition of identifiers in most languages. (The definition of letter depends on the current locale: any character considered alphabetic by the current locale can be used in an identifier.) The following keywords are reserved and cannot be used as identifiers:
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and break do else elseif end false for function if in local nil not or repeat return then true until while
Lua is a case-sensitive language: and is a reserved word, but And and AND are two different, valid identifiers. As a convention, identifiers starting with an underscore followed by uppercase letters
(such as _VERSION) are reserved for internal variables used by Lua.
The following strings denote other tokens:
+ - * / ^ =
~= = < > ==
( ) { } [ ]
; : , . .. ...
Literal strings can be delimited by matching single or double quotes, and can contain the following C-like escape sequences:
\a — bell
\b — backspace
\f — form feed
\n — newline
\r — carriage return
\t — horizontal tab
\v — vertical tab
\\ — backslash
\" — quotation mark
\’ — apostrophe
\[ — left square bracket
\] — right square bracket
Moreover, a ‘\newline’ (that is, a backslash followed by a real newline) results in a newline in the string. A character in a string may also be specified by its numerical value using the escape sequence ‘\ddd’, where ddd is a sequence of up to three decimal digits. Strings in Lua may contain any 8-bit value, including embedded zeros, which can be specified as ‘\0’.
Literal strings can also be delimited by matching double square brackets [[ . . . ]]. Literals in this bracketed form may run for several lines, may contain nested [[ . . . ]] pairs, and do not interpret any escape sequences. For convenience, when the opening ‘[[’ is immediately followed by a newline, the newline is not included in the string. As an example, in a system using ASCII
(in which ‘a’ is coded as 97, newline is coded as 10, and ‘1’ is coded as 49), the four literals below denote the same string:
(1) "alo\n123\""
(2) ’\97lo\10\04923"’
(3) [[alo
123"]]
(4) [[ alo 123"]]
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Numerical constants may be written with an optional decimal part and an optional decimal exponent. Examples of valid numerical constants are
3 3.0 3.1416 314.16e-2 0.31416E1
Comments start anywhere outside a string with a double hyphen (--). If the text immediately after -- is different from [[, the comment is a short comment, which runs until the end of the line.
Otherwise, it is a long comment, which runs until the corresponding ]]. Long comments may run for several lines and may contain nested [[ . . . ]] pairs.
For convenience, the first line of a chunk is skipped if it starts with #. This facility allows the use of Lua as a script interpreter in Unix systems (see §6).
2.2 Values and Types
Lua is a dynamically typed language. That means that variables do not have types; only values do.
There are no type definitions in the language. All values carry their own type.
There are eight basic types in Lua: nil , boolean, number, string, function, userdata, thread, and table. Nil is the type of the value nil, whose main property is to be different from any other value; usually it represents the absence of a useful value. Boolean is the type of the values false and true. In Lua, both nil and false make a condition false; any other value makes it true. Number represents real (double-precision floating-point) numbers. (It is easy to build Lua interpreters that use other internal representations for numbers, such as single-precision float or long integers.)
String represents arrays of characters. Lua is 8-bit clean: Strings may contain any 8-bit character, including embedded zeros (’\0’) (see §2.1).
Functions are first-class values in Lua. That means that functions can be stored in variables, passed as arguments to other functions, and returned as results. Lua can call (and manipulate) functions written in Lua and functions written in C (see §2.5.7).
The type userdata is provided to allow arbitrary C data to be stored in Lua variables. This type corresponds to a block of raw memory and has no pre-defined operations in Lua, except assignment and identity test. However, by using metatables, the programmer can define operations for userdata values (see §2.8). Userdata values cannot be created or modified in Lua, only through the C API.
This guarantees the integrity of data owned by the host program.
The type thread represents independent threads of execution and it is used to implement coroutines.
The type table implements associative arrays, that is, arrays that can be indexed not only with numbers, but with any value (except nil). Moreover, tables can be heterogeneous, that is, they can contain values of all types (except nil). Tables are the sole data structuring mechanism in Lua; they may be used to represent ordinary arrays, symbol tables, sets, records, graphs, trees, etc. To represent records, Lua uses the field name as an index. The language supports this representation by providing a.name as syntactic sugar for a["name"]. There are several convenient ways to create tables in Lua (see §2.5.6).
Like indices, the value of a table field can be of any type (except nil). In particular, because functions are first class values, table fields may contain functions. Thus tables may also carry methods (see §2.5.8).
Tables, functions, and userdata values are objects: variables do not actually contain these values, only references to them. Assignment, parameter passing, and function returns always manipulate references to such values; these operations do not imply any kind of copy.
The library function type returns a string describing the type of a given value (see §5.1).
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2.2.1 Coercion
Lua provides automatic conversion between string and number values at run time. Any arithmetic operation applied to a string tries to convert that string to a number, following the usual rules.
Conversely, whenever a number is used where a string is expected, the number is converted to a string, in a reasonable format. For complete control of how numbers are converted to strings, use the format function from the string library (see §5.3).
2.3 Variables
Variables are places that store values. There are three kinds of variables in Lua: global variables, local variables, and table fields.
A single name can denote a global variable or a local variable (or a formal parameter of a function, which is a particular form of local variable): var ! Name
Variables are assumed to be global unless explicitly declared local (see §2.4.7). Local variables are lexically scoped: Local variables can be freely accessed by functions defined inside their scope
(see §2.6).
Before the first assignment to a variable, its value is nil.
Square brackets are used to index a table: var ! prefixexp ‘[’ exp ‘]’
The first expression (prefixexp)should result in a table value; the second expression (exp) identifies a specific entry inside that table. The expression denoting the table to be indexed has a restricted syntax; see §2.5 for details.
The syntax var.NAME is just syntactic sugar for var["NAME"]: var ! prefixexp ‘.’ Name
The meaning of accesses to global variables and table fields can be changed via metatables. An access to an indexed variable t[i] is equivalent to a call gettable_event(t,i). (See §2.8 for a complete description of the gettable_event function. This function is not defined or callable in
Lua. We use it here only for explanatory purposes.)
All global variables live as fields in ordinary Lua tables, called environment tables or simply environments. Functions written in C and exported to Lua (C functions) all share a common global environment. Each function written in Lua (a Lua function) has its own reference to an environment, so that all global variables in that function will refer to that environment table.
When a function is created, it inherits the environment from the function that created it. To change or get the environment table of a Lua function, you call setfenv or getfenv (see §5.1).
An access to a global variable x is equivalent to _env.x, which in turn is equivalent to gettable_event(_env, "x") where _env is the environment of the running function. (The _env variable is not defined in Lua.
We use it here only for explanatory purposes.)
2.4 Statements
Lua supports an almost conventional set of statements, similar to those in Pascal or C. This set includes assignment, control structures, procedure calls, table constructors, and variable declarations.
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2.4.1 Chunks
The unit of execution of Lua is called a chunk. A chunk is simply a sequence of statements, which are executed sequentially. Each statement can be optionally followed by a semicolon: chunk ! { stat [ ‘;’ ] }
Lua handles a chunk as the body of an anonymous function (see §2.5.8). As such, chunks can define local variables and return values.
A chunk may be stored in a file or in a string inside the host program. When a chunk is executed, first it is pre-compiled into opcodes for a virtual machine, and then the compiled code is executed by an interpreter for the virtual machine.
Chunks may also be pre-compiled into binary form; see program luac for details. Programs in source and compiled forms are interchangeable; Lua automatically detects the file type and acts accordingly. 2.4.2 Blocks
A block is a list of statements; syntactically, a block is equal to a chunk: block ! chunk
A block may be explicitly delimited to produce a single statement: stat ! do block end
Explicit blocks are useful to control the scope of variable declarations. Explicit blocks are also sometimes used to add a return or break statement in the middle of another block (see §2.4.4).
2.4.3 Assignment
Lua allows multiple assignment. Therefore, the syntax for assignment defines a list of variables on the left side and a list of expressions on the right side. The elements in both lists are separated by commas: stat ! varlist1 ‘=’ explist1 varlist1 ! var { ‘,’ var } explist1 ! exp { ‘,’ exp }
Expressions are discussed in §2.5.
Before the assignment, the list of values is adjusted to the length of the list of variables. If there are more values than needed, the excess values are thrown away. If there are fewer values than needed, the list is extended with as many nil’s as needed. If the list of expressions ends with a function call, then all values returned by that function call enter in the list of values, before the adjustment (except when the call is enclosed in parentheses; see §2.5).
The assignment statement first evaluates all its expressions and only then are the assignments performed. Thus the code i = 3 i, a[i] = i+1, 20 sets a[3] to 20, without affecting a[4] because the i in a[i] is evaluated (to 3) before it is assigned 4. Similarly, the line x, y = y, x
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exchanges the values of x and y.
The meaning of assignments to global variables and table fields can be changed via metatables.
An assignment to an indexed variable t[i] = val is equivalent to settable_event(t,i,val).
(See §2.8 for a complete description of the settable_event function. This function is not defined or callable in Lua. We use it here only for explanatory purposes.)
An assignment to a global variable x = val is equivalent to the assignment _env.x = val, which in turn is equivalent to settable_event(_env, "x", val) where _env is the environment of the running function. (The _env variable is not defined in Lua.
We use it here only for explanatory purposes.)
2.4.4 Control Structures
The control structures if, while, and repeat have the usual meaning and familiar syntax: stat ! while exp do block end stat ! repeat block until exp stat ! if exp then block { elseif exp then block } [ else block ] end
Lua also has a for statement, in two flavors (see §2.4.5).
The condition expression exp of a control structure may return any value. Both false and nil are considered false. All values different from nil and false are considered true (in particular, the number 0 and the empty string are also true).
The return statement is used to return values from a function or from a chunk. Functions and chunks may return more than one value, so the syntax for the return statement is stat ! return [ explist1 ]
The break statement can be used to terminate the execution of a while, repeat, or for loop, skipping to the next statement after the loop: stat ! break
A break ends the innermost enclosing loop.
For syntactic reasons, return and break statements can only be written as the last statement of a block. If it is really necessary to return or break in the middle of a block, then an explicit inner block can be used, as in the idioms ‘do return end’ and ‘do break end’, because now return and break are the last statements in their (inner) blocks. In practice, those idioms are only used during debugging.
2.4.5 For Statement
The for statement has two forms: one numeric and one generic.
The numeric for loop repeats a block of code while a control variable runs through an arithmetic progression. It has the following syntax: stat ! for Name ‘=’ exp ‘,’ exp [ ‘,’ exp ] do block end
The block is repeated for name starting at the value of the first exp, until it passes the second exp by steps of the third exp. More precisely, a for statement like for var = e1, e2, e3 do block end
6
is equivalent to the code: do local var, _limit, _step = tonumber(e1), tonumber(e2), tonumber(e3) if not (var and _limit and _step) then error() end while (_step>0 and var =
These operators always result in false or true.
Equality (==) first compares the type of its operands. If the types are different, then the result is false. Otherwise, the values of the operands are compared. Numbers and strings are compared in the usual way. Objects (tables, userdata, threads, and functions) are compared by reference:
Two objects are considered equal only if they are the same object. Every time you create a new object (a table, userdata, or function), this new object is different from any previously existing object. You can change the way that Lua compares tables and userdata using the “eq” metamethod
(see §2.8).
The conversion rules of §2.2.1 do not apply to equality comparisons. Thus, "0"==0 evaluates to false, and t[0] and t["0"] denote different entries in a table.
The operator ~= is exactly the negation of equality (==).
The order operators work as follows. If both arguments are numbers, then they are compared as such. Otherwise, if both arguments are strings, then their values are compared according to the current locale. Otherwise, Lua tries to call the “lt” or the “le” metamethod (see §2.8).
2.5.3 Logical Operators
The logical operators in Lua are and or not
Like the control structures (see §2.4.4), all logical operators consider both false and nil as false and anything else as true.
The operator not always return false or true.
The conjunction operator and returns its first argument if this value is false or nil; otherwise, and returns its second argument. The disjunction operator or returns its first argument if this value is different from nil and false; otherwise, or returns its second argument. Both and and or use short-cut evaluation, that is, the second operand is evaluated only if necessary. For example,
10 or error() -> 10 nil or "a" -> "a" nil and 10 -> nil false and error() -> false false and nil -> false false or nil -> nil
10 and 20 -> 20
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2.5.4 Concatenation
The string concatenation operator in Lua is denoted by two dots (‘..’). If both operands are strings or numbers, then they are converted to strings according to the rules mentioned in §2.2.1.
Otherwise, the “concat” metamethod is called (see §2.8).
2.5.5 Precedence
Operator precedence in Lua follows the table below, from lower to higher priority: or and
< > = ~= ==
..
+ -
* / not - (unary)
^
You can use parentheses to change the precedences in an expression. The concatenation (‘..’) and exponentiation (‘^’) operators are right associative. All other binary operators are left associative.
2.5.6 Table Constructors
Table constructors are expressions that create tables. Every time a constructor is evaluated, a new table is created. Constructors can be used to create empty tables, or to create a table and initialize some of its fields. The general syntax for constructors is tableconstructor ! ‘{’ [ fieldlist ] ‘}’ fieldlist ! field { fieldsep field } [ fieldsep ] field ! ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp fieldsep ! ‘,’ | ‘;’
Each field of the form [exp1] = exp2 adds to the new table an entry with key exp1 and value exp2. A field of the form name = exp is equivalent to ["name"] = exp. Finally, fields of the form exp are equivalent to [i] = exp, where i are consecutive numerical integers, starting with 1.
Fields in the other formats do not affect this counting. For example, a = {[f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45} is equivalent to do local temp = {} temp[f(1)] = g temp[1] = "x" -- 1st exp temp[2] = "y" -- 2nd exp temp.x = 1 -- temp["x"] = 1 temp[3] = f(x) -- 3rd exp temp[30] = 23 temp[4] = 45 -- 4th exp a = temp end 10
If the last field in the list has the form exp and the expression is a function call, then all values returned by the call enter the list consecutively (see §2.5.7). To avoid this, enclose the function call in parentheses (see §2.5).
The field list may have an optional trailing separator, as a convenience for machine-generated code. 2.5.7 Function Calls
A function call in Lua has the following syntax: functioncall ! prefixexp args
In a function call, first prefixexp and args are evaluated. If the value of prefixexp has type function, then that function is called with the given arguments. Otherwise, its “call” metamethod is called, having as first parameter the value of prefixexp, followed by the original call arguments (see §2.8).
The form functioncall ! prefixexp ‘:’ Name args can be used to call “methods”. A call v:name(...) is syntactic sugar for v.name(v,...), except that v is evaluated only once.
Arguments have the following syntax: args ! ‘(’ [ explist1 ] ‘)’ args ! tableconstructor args ! Literal
All argument expressions are evaluated before the call. A call of the form f{...} is syntactic sugar for f({...}), that is, the argument list is a single new table. A call of the form f’...’ (or f"..." or f[[...]]) is syntactic sugar for f(’...’), that is, the argument list is a single literal string.
Because a function can return any number of results (see §2.4.4), the number of results must be adjusted before they are used. If the function is called as a statement (see §2.4.6), then its return list is adjusted to zero elements, thus discarding all returned values. If the function is called inside another expression or in the middle of a list of expressions, then its return list is adjusted to one element, thus discarding all returned values except the first one. If the function is called as the last element of a list of expressions, then no adjustment is made (unless the call is enclosed in parentheses). Here are some examples: f() -- adjusted to 0 results g(f(), x) -- f() is adjusted to 1 result g(x, f()) -- g gets x plus all values returned by f() a,b,c = f(), x -- f() is adjusted to 1 result (and c gets nil) a,b,c = x, f() -- f() is adjusted to 2 results a,b,c = f() -- f() is adjusted to 3 results return f() -- returns all values returned by f() return x,y,f() -- returns x, y, and all values returned by f()
{f()} -- creates a list with all values returned by f()
{f(), nil} -- f() is adjusted to 1 result
If you enclose a function call in parentheses, then it is adjusted to return exactly one value: return x,y,(f()) -- returns x, y, and the first value from f()
{(f())} -- creates a table with exactly one element
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As an exception to the free-format syntax of Lua, you cannot put a line break before the ‘(’ in a function call. That restriction avoids some ambiguities in the language. If you write a = f
(g).x(a)
Lua would read that as a = f(g).x(a). So, if you want two statements, you must add a semi-colon between them. If you actually want to call f, you must remove the line break before (g).
A call of the form return functioncall is called a tail call . Lua implements proper tail calls
(or proper tail recursion): In a tail call, the called function reuses the stack entry of the calling function. Therefore, there is no limit on the number of nested tail calls that a program can execute.
However, a tail call erases any debug information about the calling function. Note that a tail call only happens with a particular syntax, where the return has one single function call as argument; this syntax makes the calling function returns exactly the returns of the called function. So, all the following examples are not tails calls: return (f(x)) -- results adjusted to 1 return 2 * f(x) return x, f(x) -- additional results f(x); return -- results discarded return x or f(x) -- results adjusted to 1
2.5.8 Function Definitions
The syntax for function definition is function ! function funcbody funcbody ! ‘(’ [ parlist1 ] ‘)’ block end
The following syntactic sugar simplifies function definitions: stat ! function funcname funcbody stat ! local function Name funcbody funcname ! Name { ‘.’ Name } [ ‘:’ Name ]
The statement function f () ... end translates to f = function () ... end
The statement function t.a.b.c.f () ... end translates to
t.a.b.c.f = function () ... end
The statement local function f () ... end translates to
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local f; f = function () ... end
A function definition is an executable expression, whose value has type function. When Lua pre-compiles a chunk, all its function bodies are pre-compiled too. Then, whenever Lua executes the function definition, the function is instantiated (or closed). This function instance (or closure) is the final value of the expression. Different instances of the same function may refer to different external local variables and may have different environment tables.
Parameters act as local variables that are initialized with the argument values: parlist1 ! namelist [ ‘,’ ‘...’ ] parlist1 ! ‘...’
When a function is called, the list of arguments is adjusted to the length of the list of parameters, unless the function is a variadic or vararg function, which is indicated by three dots (‘...’) at the end of its parameter list. A vararg function does not adjust its argument list; instead, it collects all extra arguments into an implicit parameter, called arg. The value of arg is a table, with a field n that holds the number of extra arguments and with the extra arguments at positions 1, 2, . . . , n.
As an example, consider the following definitions: function f(a, b) end function g(a, b, ...) end function r() return 1,2,3 end
Then, we have the following mapping from arguments to parameters:
CALL PARAMETERS f(3) a=3, b=nil f(3, 4) a=3, b=4 f(3, 4, 5) a=3, b=4 f(r(), 10) a=1, b=10 f(r()) a=1, b=2 g(3) a=3, b=nil, arg={n=0} g(3, 4) a=3, b=4, arg={n=0} g(3, 4, 5, 8) a=3, b=4, arg={5, 8; n=2} g(5, r()) a=5, b=1, arg={2, 3; n=2}
Results are returned using the return statement (see §2.4.4). If control reaches the end of a function without encountering a return statement, then the function returns with no results.
The colon syntax is used for defining methods, that is, functions that have an implicit extra parameter self. Thus, the statement function t.a.b.c:f (...) ... end is syntactic sugar for
t.a.b.c.f = function (self, ...) ... end
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2.6 Visibility Rules
Lua is a lexically scoped language. The scope of variables begins at the first statement after their declaration and lasts until the end of the innermost block that includes the declaration. For instance: x = 10 -- global variable do -- new block local x = x -- new ‘x’, with value 10 print(x) --> 10 x = x+1 do -- another block local x = x+1 -- another ‘x’ print(x) --> 12 end print(x) --> 11 end print(x) --> 10 (the global one)
Notice that, in a declaration like local x = x, the new x being declared is not in scope yet, and so the second x refers to the outside variable.
Because of the lexical scoping rules, local variables can be freely accessed by functions defined inside their scope. For instance: local counter = 0 function inc (x) counter = counter + x return counter end A local variable used by an inner function is called an upvalue, or external local variable, inside the inner function.
Notice that each execution of a local statement defines new local variables. Consider the following example: a = {} local x = 20 for i=1,10 do local y = 0 a[i] = function () y=y+1; return x+y end end The loop creates ten closures (that is, ten instances of the anonymous function). Each of these closures uses a different y variable, while all of them share the same x.
2.7 Error Handling
Because Lua is an extension language, all Lua actions start from C code in the host program calling a function from the Lua library (see §3.15). Whenever an error occurs during Lua compilation or execution, control returns to C, which can take appropriate measures (such as print an error message). 14
Lua code can explicitly generate an error by calling the error function (see §5.1). If you need to catch errors in Lua, you can use the pcall function (see §5.1).
2.8 Metatables
Every table and userdata object in Lua may have a metatable. This metatable is an ordinary Lua table that defines the behavior of the original table and userdata under certain special operations.
You can change several aspects of the behavior of an object by setting specific fields in its metatable.
For instance, when an object is the operand of an addition, Lua checks for a function in the field
"__add" in its metatable. If it finds one, Lua calls that function to perform the addition.
We call the keys in a metatable events and the values metamethods. In the previous example, the event is "add" and the metamethod is the function that performs the addition.
You can query and change the metatable of an object through the set/getmetatable functions
(see §5.1).
A metatable may control how an object behaves in arithmetic operations, order comparisons, concatenation, and indexing. A metatable can also define a function to be called when a userdata is garbage collected. For each of those operations Lua associates a specific key called an event.
When Lua performs one of those operations over a table or a userdata, it checks whether that object has a metatable with the corresponding event. If so, the value associated with that key (the metamethod) controls how Lua will perform the operation.
Metatables control the operations listed next. Each operation is identified by its corresponding name. The key for each operation is a string with its name prefixed by two underscores; for instance, the key for operation “add” is the string "__add". The semantics of these operations is better explained by a Lua function describing how the interpreter executes that operation.
The code shown here in Lua is only illustrative; the real behavior is hard coded in the interpreter and it is much more efficient than this simulation. All functions used in these descriptions (rawget, tonumber, etc.) are described in §5.1. In particular, to retrieve the metamethod of a given object, we use the expression metatable(obj)[event] This should be read as rawget(metatable(obj) or {}, event)
That is, the access to a metamethod does not invoke other metamethods, and the access to objects with no metatables does not fail (it simply results in nil).
“add”: the + operation.
The function getbinhandler below defines how Lua chooses a handler for a binary operation.
First, Lua tries the first operand. If its type does not define a handler for the operation, then Lua tries the second operand. function getbinhandler (op1, op2, event) return metatable(op1)[event] or metatable(op2)[event] end Using that function, the behavior of the op1 + op2 is
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function add_event (op1, op2) local o1, o2 = tonumber(op1), tonumber(op2) if o1 and o2 then -- both operands are numeric? return o1 + o2 -- ‘+’ here is the primitive ‘add’ else -- at least one of the operands is not numeric local h = getbinhandler(op1, op2, "__add") if h then
-- call the handler with both operands return h(op1, op2) else -- no handler available: default behavior error("...") end end end
“sub”: the - operation. Behavior similar to the “add” operation.
“mul”: the * operation. Behavior similar to the “add” operation.
“div”: the / operation. Behavior similar to the “add” operation.
“pow”: the ^ (exponentiation) operation. function pow_event (op1, op2) local o1, o2 = tonumber(op1), tonumber(op2) if o1 and o2 then -- both operands are numeric? return __pow(o1, o2) -- call global ‘__pow’ else -- at least one of the operands is not numeric local h = getbinhandler(op1, op2, "__pow") if h then
-- call the handler with both operands return h(op1, op2) else -- no handler available: default behavior error("...") end end end
“unm”: the unary - operation. function unm_event (op) local o = tonumber(op) if o then -- operand is numeric? return -o -- ‘-’ here is the primitive ‘unm’ else -- the operand is not numeric.
-- Try to get a handler from the operand local h = metatable(op).__unm if h then
-- call the handler with the operand and nil return h(op, nil)
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else -- no handler available: default behavior error("...") end end end
“concat”: the .. (concatenation) operation. function concat_event (op1, op2) if (type(op1) == "string" or type(op1) == "number") and
(type(op2) == "string" or type(op2) == "number") then return op1 .. op2 -- primitive string concatenation else local h = getbinhandler(op1, op2, "__concat") if h then return h(op1, op2) else error("...") end end end “eq”: the == operation. The function getcomphandler defines how Lua chooses a metamethod for comparison operators. A metamethod only is selected when both objects being compared have the same type and the same metamethod for the selected operation. function getcomphandler (op1, op2, event) if type(op1) ~= type(op2) then return nil end local mm1 = metatable(op1)[event] local mm2 = metatable(op2)[event] if mm1 == mm2 then return mm1 else return nil end end The “eq” event is defined as follows: function eq_event (op1, op2) if type(op1) ~= type(op2) then -- different types? return false -- different objects end if op1 == op2 then -- primitive equal? return true -- objects are equal end -- try metamethod local h = getcomphandler(op1, op2, "__eq") if h then return h(op1, op2) else return false
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end end a ~= b is equivalent to not (a == b).
“lt”: the < operation. function lt_event (op1, op2) if type(op1) == "number" and type(op2) == "number" then return op1 < op2 -- numeric comparison elseif type(op1) == "string" and type(op2) == "string" then return op1 < op2 -- lexicographic comparison else local h = getcomphandler(op1, op2, "__lt") if h then return h(op1, op2) else error("..."); end end end a > b is equivalent to b < a.
“le”: the 30 40 20 30* lua_settop(L, -3) --> 30 40* lua_settop(L, 6) --> 30 40 nil nil nil nil*
3.4 Querying the Stack
To check the type of a stack element, the following functions are available: int lua_type (lua_State *L, int index); int lua_isnil (lua_State *L, int index); int lua_isboolean (lua_State *L, int index); int lua_isnumber (lua_State *L, int index); int lua_isstring (lua_State *L, int index); int lua_istable (lua_State *L, int index); int lua_isfunction (lua_State *L, int index); int lua_iscfunction (lua_State *L, int index); int lua_isuserdata (lua_State *L, int index); int lua_islightuserdata (lua_State *L, int index);
These functions can be called with any acceptable index.
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lua_type returns the type of a value in the stack, or LUA_TNONE for a non-valid index (that is, if that stack position is “empty”). The types returned by lua_type are coded by the following constants defined in lua.h: LUA_TNIL, LUA_TNUMBER, LUA_TBOOLEAN, LUA_TSTRING, LUA_TTABLE,
LUA_TFUNCTION, LUA_TUSERDATA, LUA_TTHREAD, LUA_TLIGHTUSERDATA. The following function translates these constants to strings: const char *lua_typename (lua_State *L, int type);
The lua_is* functions return 1 if the object is compatible with the given type, and 0 otherwise. lua_isboolean is an exception to this rule: It succeeds only for boolean values (otherwise it would be useless, as any value has a boolean value). They always return 0 for a non-valid index. lua_isnumber accepts numbers and numerical strings; lua_isstring accepts strings and numbers (see §2.2.1); lua_isfunction accepts both Lua functions and C functions; and lua_isuserdata accepts both full and light userdata. To distinguish between Lua functions and C functions, you can use lua_iscfunction. To distinguish between full and light userdata, you can use lua_islightuserdata. To distinguish between numbers and numerical strings, you can use lua_type.
The API also contains functions to compare two values in the stack: int lua_equal (lua_State *L, int index1, int index2); int lua_rawequal (lua_State *L, int index1, int index2); int lua_lessthan (lua_State *L, int index1, int index2); lua_equal and lua_lessthan are equivalent to their counterparts in Lua (see §2.5.2). lua_rawequal compares the values for primitive equality, without metamethods. These functions return 0 (false) if any of the indices are non-valid.
3.5 Getting Values from the Stack
To translate a value in the stack to a specific C type, you can use the following conversion functions: int lua_toboolean (lua_State *L, int index); lua_Number lua_tonumber (lua_State *L, int index); const char *lua_tostring (lua_State *L, int index); size_t lua_strlen (lua_State *L, int index); lua_CFunction lua_tocfunction (lua_State *L, int index); void *lua_touserdata (lua_State *L, int index); lua_State *lua_tothread (lua_State *L, int index); void *lua_topointer (lua_State *L, int index);
These functions can be called with any acceptable index. When called with a non-valid index, they act as if the given value had an incorrect type. lua_toboolean converts the Lua value at the given index to a C “boolean” value (0 or 1). Like all tests in Lua, lua_toboolean returns 1 for any Lua value different from false and nil; otherwise it returns 0. It also returns 0 when called with a non-valid index. (If you want to accept only real boolean values, use lua_isboolean to test the type of the value.) lua_tonumber converts the Lua value at the given index to a number (by default, lua_Number is double). The Lua value must be a number or a string convertible to number (see §2.2.1); otherwise, lua_tonumber returns 0.
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lua_tostring converts the Lua value at the given index to a string (const char*). The Lua value must be a string or a number; otherwise, the function returns NULL. If the value is a number, then lua_tostring also changes the actual value in the stack to a string. (This change confuses lua_next when lua_tostring is applied to keys.) lua_tostring returns a fully aligned pointer to a string inside the Lua state. This string always has a zero (’\0’) after its last character (as in C), but may contain other zeros in its body. If you do not know whether a string may contain zeros, you can use lua_strlen to get its actual length. Because Lua has garbage collection, there is no guarantee that the pointer returned by lua_tostring will be valid after the corresponding value is removed from the stack. If you need the string after the current function returns, then you should duplicate it or put it into the registry (see §3.18). lua_tocfunction converts a value in the stack to a C function. This value must be a C function; otherwise, lua_tocfunction returns NULL. The type lua_CFunction is explained in §3.16. lua_tothread converts a value in the stack to a Lua thread (represented as lua_State *).
This value must be a thread; otherwise, lua_tothread returns NULL. lua_topointer converts a value in the stack to a generic C pointer (void *). The value may be a userdata, a table, a thread, or a function; otherwise, lua_topointer returns NULL. Lua ensures that different objects of the same type return different pointers. There is no direct way to convert the pointer back to its original value. Typically this function is used for debug information. lua_touserdata is explained in §3.8.
3.6 Pushing Values onto the Stack
The API has the following functions to push C values onto the stack: void lua_pushboolean (lua_State *L, int b); void lua_pushnumber (lua_State *L, lua_Number n); void lua_pushlstring (lua_State *L, const char *s, size_t len); void lua_pushstring (lua_State *L, const char *s); void lua_pushnil (lua_State *L); void lua_pushcfunction (lua_State *L, lua_CFunction f); void lua_pushlightuserdata (lua_State *L, void *p);
These functions receive a C value, convert it to a corresponding Lua value, and push the result onto the stack. In particular, lua_pushlstring and lua_pushstring make an internal copy of the given string. lua_pushstring can only be used to push proper C strings (that is, strings that end with a zero and do not contain embedded zeros); otherwise, you should use the more general lua_pushlstring, which accepts an explicit size.
You can also push “formatted” strings: const char *lua_pushfstring (lua_State *L, const char *fmt, ...); const char *lua_pushvfstring (lua_State *L, const char *fmt, va_list argp);
These functions push onto the stack a formatted string and return a pointer to that string. They are similar to sprintf and vsprintf, but with some important differences:
• You do not have to allocate the space for the result: The result is a Lua string and Lua takes care of memory allocation (and deallocation, through garbage collection).
• The conversion specifiers are quite restricted. There are no flags, widths, or precisions. The conversion specifiers can be simply ‘%%’ (inserts a ‘%’ in the string), ‘%s’ (inserts a zeroterminated string, with no size restrictions), ‘%f’ (inserts a lua_Number), ‘%d’ (inserts an int), and ‘%c’ (inserts an int as a character).
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The function void lua_concat (lua_State *L, int n); concatenates the n values at the top of the stack, pops them, and leaves the result at the top. If n is 1, the result is that single string (that is, the function does nothing); if n is 0, the result is the empty string. Concatenation is done following the usual semantics of Lua (see §2.5.4).
3.7 Controlling Garbage Collection
Lua uses two numbers to control its garbage collection: the count and the threshold (see §2.9). The first counts the amount of memory in use by Lua; when the count reaches the threshold, Lua runs its garbage collector. After the collection, the count is updated and the threshold is set to twice the count value.
You can access the current values of these two numbers through the following functions: int lua_getgccount (lua_State *L); int lua_getgcthreshold (lua_State *L);
Both return their respective values in Kbytes. You can change the threshold value with void lua_setgcthreshold (lua_State *L, int newthreshold);
Again, the newthreshold value is given in Kbytes. When you call this function, Lua sets the new threshold and checks it against the byte counter. If the new threshold is less than the byte counter, then Lua immediately runs the garbage collector. In particular lua_setgcthreshold(L,0) forces a garbage collection. After the collection, a new threshold is set according to the previous rule.
3.8 Userdata
Userdata represents C values in Lua. Lua supports two types of userdata: full userdata and light userdata. A full userdata represents a block of memory. It is an object (like a table): You must create it, it can have its own metatable, and you can detect when it is being collected. A full userdata is only equal to itself (under raw equality).
A light userdata represents a pointer. It is a value (like a number): You do not create it, it has no metatables, it is not collected (as it was never created). A light userdata is equal to “any” light userdata with the same C address.
In Lua code, there is no way to test whether a userdata is full or light; both have type userdata.
In C code, lua_type returns LUA_TUSERDATA for full userdata, and LUA_TLIGHTUSERDATA for light userdata. You can create a new full userdata with the following function: void *lua_newuserdata (lua_State *L, size_t size);
This function allocates a new block of memory with the given size, pushes on the stack a new userdata with the block address, and returns this address.
To push a light userdata into the stack you use lua_pushlightuserdata (see §3.6). lua_touserdata (see §3.5) retrieves the value of a userdata. When applied on a full userdata, it returns the address of its block; when applied on a light userdata, it returns its pointer; when applied on a non-userdata value, it returns NULL.
When Lua collects a full userdata, it calls the userdata’s gc metamethod, if any, and then it frees the userdata’s corresponding memory.
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3.9 Metatables
The following functions allow you to manipulate the metatables of an object: int lua_getmetatable (lua_State *L, int index); int lua_setmetatable (lua_State *L, int index); lua_getmetatable pushes on the stack the metatable of a given object. If the index is not valid, or if the object does not have a metatable, lua_getmetatable returns 0 and pushes nothing on the stack. lua_setmetatable pops a table from the stack and sets it as the new metatable for the given object. lua_setmetatable returns 0 when it cannot set the metatable of the given object (that is, when the object is neither a userdata nor a table); even then it pops the table from the stack.
3.10 Loading Lua Chunks
You can load a Lua chunk with lua_load: typedef const char * (*lua_Chunkreader)
(lua_State *L, void *data, size_t *size); int lua_load (lua_State *L, lua_Chunkreader reader, void *data, const char *chunkname);
The return values of lua_load are:
• 0 — no errors;
• LUA_ERRSYNTAX — syntax error during pre-compilation.
• LUA_ERRMEM — memory allocation error.
If there are no errors, lua_load pushes the compiled chunk as a Lua function on top of the stack.
Otherwise, it pushes an error message. lua_load automatically detects whether the chunk is text or binary, and loads it accordingly
(see program luac). lua_load uses a user-supplied reader function to read the chunk. Every time it needs another piece of the chunk, lua_load calls the reader, passing along its data parameter. The reader must return a pointer to a block of memory with a new piece of the chunk and set size to the block size.
To signal the end of the chunk, the reader returns NULL. The reader function may return pieces of any size greater than zero.
In the current implementation, the reader function cannot call any Lua function; to ensure that, it always receives NULL as the Lua state.
The chunkname is used for error messages and debug information (see §4).
See the auxiliary library (lauxlib.c) for examples of how to use lua_load and for some readyto- use functions to load chunks from files and strings.
3.11 Manipulating Tables
Tables are created by calling the function void lua_newtable (lua_State *L);
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This function creates a new, empty table and pushes it onto the stack.
To read a value from a table that resides somewhere in the stack, call void lua_gettable (lua_State *L, int index); where index points to the table. lua_gettable pops a key from the stack and returns (on the stack) the contents of the table at that key. The table is left where it was in the stack. As in Lua, this function may trigger a metamethod for the “index” event (see §2.8). To get the real value of any table key, without invoking any metamethod, use the raw version: void lua_rawget (lua_State *L, int index);
To store a value into a table that resides somewhere in the stack, you push the key and then the value onto the stack, and call void lua_settable (lua_State *L, int index); where index points to the table. lua_settable pops from the stack both the key and the value.
The table is left where it was in the stack. As in Lua, this operation may trigger a metamethod for the “settable” or “newindex” events. To set the real value of any table index, without invoking any metamethod, use the raw version: void lua_rawset (lua_State *L, int index);
You can traverse a table with the function int lua_next (lua_State *L, int index); where index points to the table to be traversed. The function pops a key from the stack, and pushes a key-value pair from the table (the “next” pair after the given key). If there are no more elements, then lua_next returns 0 (and pushes nothing). Use a nil key to signal the start of a traversal. A typical traversal looks like this:
/* table is in the stack at index ‘t’ */ lua_pushnil(L); /* first key */ while (lua_next(L, t) != 0) {
/* ‘key’ is at index -2 and ‘value’ at index -1 */ printf("%s - %s\n", lua_typename(L, lua_type(L, -2)), lua_typename(L, lua_type(L, -1))); lua_pop(L, 1); /* removes ‘value’; keeps ‘key’ for next iteration */
}
While traversing a table, do not call lua_tostring directly on a key, unless you know that the key is actually a string. Recall that lua_tostring changes the value at the given index; this confuses the next call to lua_next.
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3.12 Manipulating Environments
All global variables are kept in ordinary Lua tables, called environments. The initial environment is called the global environment. This table is always at pseudo-index LUA_GLOBALSINDEX.
To access and change the value of global variables, you can use regular table operations over an environment table. For instance, to access the value of a global variable, do lua_pushstring(L, varname); lua_gettable(L, LUA_GLOBALSINDEX);
You can change the global environment of a Lua thread using lua_replace.
The following functions get and set the environment of Lua functions: void lua_getfenv (lua_State *L, int index); int lua_setfenv (lua_State *L, int index); lua_getfenv pushes on the stack the environment table of the function at index index in the stack.
If the function is a C function, lua_getfenv pushes the global environment. lua_setfenv pops a table from the stack and sets it as the new environment for the function at index index in the stack. If the object at the given index is not a Lua function, lua_setfenv returns 0.
3.13 Using Tables as Arrays
The API has functions that help to use Lua tables as arrays, that is, tables indexed by numbers only: void lua_rawgeti (lua_State *L, int index, int n); void lua_rawseti (lua_State *L, int index, int n); lua_rawgeti pushes the value of the n-th element of the table at stack position index. lua_rawseti sets the value of the n-th element of the table at stack position index to the value at the top of the stack, removing this value from the stack.
3.14 Calling Functions
Functions defined in Lua and C functions registered in Lua can be called from the host program.
This is done using the following protocol: First, the function to be called is pushed onto the stack; then, the arguments to the function are pushed in direct order, that is, the first argument is pushed first. Finally, the function is called using void lua_call (lua_State *L, int nargs, int nresults); nargs is the number of arguments that you pushed onto the stack. All arguments and the function value are popped from the stack, and the function results are pushed. The number of results are adjusted to nresults, unless nresults is LUA_MULTRET. In that case, all results from the function are pushed. Lua takes care that the returned values fit into the stack space. The function results are pushed onto the stack in direct order (the first result is pushed first), so that after the call the last result is on the top.
The following example shows how the host program may do the equivalent to this Lua code: a = f("how", t.x, 14)
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Here it is in C: lua_pushstring(L, "t"); lua_gettable(L, LUA_GLOBALSINDEX); /* global ‘t’ (for later use) */ lua_pushstring(L, "a"); /* var name */ lua_pushstring(L, "f"); /* function name */ lua_gettable(L, LUA_GLOBALSINDEX); /* function to be called */ lua_pushstring(L, "how"); /* 1st argument */ lua_pushstring(L, "x"); /* push the string "x" */ lua_gettable(L, -5); /* push result of t.x (2nd arg) */ lua_pushnumber(L, 14); /* 3rd argument */ lua_call(L, 3, 1); /* call function with 3 arguments and 1 result */ lua_settable(L, LUA_GLOBALSINDEX); /* set global variable ‘a’ */ lua_pop(L, 1); /* remove ‘t’ from the stack */
Note that the code above is “balanced”: at its end, the stack is back to its original configuration.
This is considered good programming practice.
(We did this example using only the raw functions provided by Lua’s API, to show all the details. Usually programmers define and use several macros and auxiliary functions that provide higher level access to Lua. See the source code of the standard libraries for examples.)
3.15 Protected Calls
When you call a function with lua_call, any error inside the called function is propagated upwards
(with a longjmp). If you need to handle errors, then you should use lua_pcall: int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);
Both nargs and nresults have the same meaning as in lua_call. If there are no errors during the call, lua_pcall behaves exactly like lua_call. However, if there is any error, lua_pcall catches it, pushes a single value at the stack (the error message), and returns an error code. Like lua_call, lua_pcall always removes the function and its arguments from the stack.
If errfunc is 0, then the error message returned is exactly the original error message. Otherwise, errfunc gives the stack index for an error handler function. (In the current implementation, that index cannot be a pseudo-index.) In case of runtime errors, that function will be called with the error message and its return value will be the message returned by lua_pcall.
Typically, the error handler function is used to add more debug information to the error message, such as a stack traceback. Such information cannot be gathered after the return of lua_pcall, since by then the stack has unwound.
The lua_pcall function returns 0 in case of success or one of the following error codes (defined in lua.h):
• LUA_ERRRUN — a runtime error.
• LUA_ERRMEM — memory allocation error. For such errors, Lua does not call the error handler function. • LUA_ERRERR — error while running the error handler function.
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3.16 Defining C Functions
Lua can be extended with functions written in C. These functions must be of type lua_CFunction, which is defined as typedef int (*lua_CFunction) (lua_State *L);
A C function receives a Lua state and returns an integer, the number of values it wants to return to Lua.
In order to communicate properly with Lua, a C function must follow the following protocol, which defines the way parameters and results are passed: A C function receives its arguments from
Lua in its stack in direct order (the first argument is pushed first). So, when the function starts, its first argument (if any) is at index 1. To return values to Lua, a C function just pushes them onto the stack, in direct order (the first result is pushed first), and returns the number of results. Any other value in the stack below the results will be properly discharged by Lua. Like a Lua function, a C function called by Lua can also return many results.
As an example, the following function receives a variable number of numerical arguments and returns their average and sum: static int foo (lua_State *L) { int n = lua_gettop(L); /* number of arguments */ lua_Number sum = 0; int i; for (i = 1; i ’. For instance, to know in which line a function f was defined, you can write lua_Debug ar; lua_pushstring(L, "f"); lua_gettable(L, LUA_GLOBALSINDEX); /* get global ‘f’ */ lua_getinfo(L, ">S", &ar); printf("%d\n", ar.linedefined);
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The fields of lua_Debug have the following meaning: source If the function was defined in a string, then source is that string. If the function was defined in a file, then source starts with a ‘@’ followed by the file name. short_src A “printable” version of source, to be used in error messages. linedefined the line number where the definition of the function starts. what the string "Lua" if this is a Lua function, "C" if this is a C function, "main" if this is the main part of a chunk, and "tail" if this was a function that did a tail call. In the latter case, Lua has no other information about this function. currentline the current line where the given function is executing. When no line information is available, currentline is set to −1. name a reasonable name for the given function. Because functions in Lua are first class values, they do not have a fixed name: Some functions may be the value of multiple global variables, while others may be stored only in a table field. The lua_getinfo function checks how the function was called or whether it is the value of a global variable to find a suitable name. If it cannot find a name, then name is set to NULL. namewhat Explains the name field. The value of namewhat can be "global", "local", "method",
"field", or "" (the empty string), according to how the function was called. (Lua uses the empty string when no other option seems to apply.) nups The number of upvalues of the function.
4.2 Manipulating Local Variables and Upvalues
For the manipulation of local variables and upvalues, the debug interface uses indices: The first parameter or local variable has index 1, and so on, until the last active local variable. Upvalues have no particular order, as they are active through the whole function.
The following functions allow the manipulation of the local variables of a given activation record: const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n); const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);
The parameter ar must be a valid activation record that was filled by a previous call to lua_getstack or given as argument to a hook (see §4.3). lua_getlocal gets the index n of a local variable, pushes the variable’s value onto the stack, and returns its name. lua_setlocal assigns the value at the top of the stack to the variable and returns its name. Both functions return NULL when the index is greater than the number of active local variables.
The following functions allow the manipulation of the upvalues of a given function (unlike local variables, the upvalues of a function are accessible even when the function is not active): const char *lua_getupvalue (lua_State *L, int funcindex, int n); const char *lua_setupvalue (lua_State *L, int funcindex, int n);
These functions operate both on Lua functions and on C functions. (For Lua functions, upvalues are the external local variables that the function uses, and that consequently are included in its closure.) funcindex points to a function in the stack. lua_getpuvalue gets the index n of an upvalue, pushes the upvalue’s value onto the stack, and returns its name. lua_setupvalue assigns the value at the top of the stack to the upvalue and returns its name. Both functions return NULL when the index is greater than the number of upvalues. For C functions, these functions use the empty string "" as a name for all upvalues.
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As an example, the following function lists the names of all local variables and upvalues for a function at a given level of the stack: int listvars (lua_State *L, int level) { lua_Debug ar; int i; const char *name; if (lua_getstack(L, level, &ar) == 0) return 0; /* failure: no such level in the stack */ i = 1; while ((name = lua_getlocal(L, &ar, i++)) != NULL) { printf("local %d %s\n", i-1, name); lua_pop(L, 1); /* remove variable value */
}
lua_getinfo(L, "f", &ar); /* retrieves function */ i = 1; while ((name = lua_getpuvalue(L, -1, i++)) != NULL) { printf("upvalue %d %s\n", i-1, name); lua_pop(L, 1); /* remove upvalue value */
}
return 1;
}
4.3 Hooks
Lua offers a mechanism of hooks, which are user-defined C functions that are called during the program execution. A hook may be called in four different events: a call event, when Lua calls a function; a return event, when Lua returns from a function; a line event, when Lua starts executing a new line of code; and a count event, which happens every “count” instructions. Lua identifies these events with the following constants: LUA_HOOKCALL, LUA_HOOKRET (or LUA_HOOKTAILRET, see below), LUA_HOOKLINE, and LUA_HOOKCOUNT.
A hook has type lua_Hook, defined as follows: typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);
You can set the hook with the following function: int lua_sethook (lua_State *L, lua_Hook func, int mask, int count); func is the hook. mask specifies on which events the hook will be called: It is formed by a disjunction of the constants LUA_MASKCALL, LUA_MASKRET, LUA_MASKLINE, and LUA_MASKCOUNT.
The count argument is only meaningful when the mask includes LUA_MASKCOUNT. For each event, the hook is called as explained below:
The call hook is called when the interpreter calls a function. The hook is called just after
Lua enters the new function.
The return hook is called when the interpreter returns from a function. The hook is called just before Lua leaves the function.
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The line hook is called when the interpreter is about to start the execution of a new line of code, or when it jumps back in the code (even to the same line). (This event only happens while Lua is executing a Lua function.)
The count hook is called after the interpreter executes every count instructions. (This event only happens while Lua is executing a Lua function.)
A hook is disabled by setting mask to zero.
You can get the current hook, the current mask, and the current count with the next functions: lua_Hook lua_gethook (lua_State *L); int lua_gethookmask (lua_State *L); int lua_gethookcount (lua_State *L);
Whenever a hook is called, its ar argument has its field event set to the specific event that triggered the hook. Moreover, for line events, the field currentline is also set. To get the value of any other field in ar, the hook must call lua_getinfo. For return events, event may be
LUA_HOOKRET, the normal value, or LUA_HOOKTAILRET. In the latter case, Lua is simulating a return from a function that did a tail call; in this case, it is useless to call lua_getinfo.
While Lua is running a hook, it disables other calls to hooks. Therefore, if a hook calls back
Lua to execute a function or a chunk, that execution occurs without any calls to hooks.
5 Standard Libraries
The standard libraries provide useful functions that are implemented directly through the C API.
Some of these functions provide essential services to the language (e.g., type and getmetatable); others provide access to “outside” services (e.g., I/O); and others could be implemented in Lua itself, but are quite useful or have critical performance to deserve an implementation in C (e.g., sort). All libraries are implemented through the official C API and are provided as separate C modules.
Currently, Lua has the following standard libraries:
• basic library;
• string manipulation;
• table manipulation;
• mathematical functions (sin, log, etc.);
• input and output;
• operating system facilities;
• debug facilities.
Except for the basic library, each library provides all its functions as fields of a global table or as methods of its objects.
To have access to these libraries, the C host program must first call the functions luaopen_base
(for the basic library), luaopen_string (for the string library), luaopen_table (for the table library), luaopen_math (for the mathematical library), luaopen_io (for the I/O and the Operating
System libraries), and luaopen_debug (for the debug library). These functions are declared in lualib.h. 38
5.1 Basic Functions
The basic library provides some core functions to Lua. If you do not include this library in your application, you should check carefully whether you need to provide some alternative implementation for some of its facilities.
• assert (v [, message])
Issues an error when the value of its argument v is nil or false; otherwise, returns this value. message is an error message; when absent, it defaults to “assertion failed!”
• collectgarbage ([limit])
Sets the garbage-collection threshold to the given limit (in Kbytes) and checks it against the byte counter. If the new threshold is smaller than the byte counter, then Lua immediately runs the garbage collector (see §2.9). If limit is absent, it defaults to zero (thus forcing a garbage-collection cycle). • dofile (filename)
Opens the named file and executes its contents as a Lua chunk. When called without arguments, dofile executes the contents of the standard input (stdin). Returns any value returned by the chunk. In case of errors, dofile propagates the error to its caller (that is, it does not run in protected mode).
• error (message [, level])
Terminates the last protected function called and returns message as the error message. Function error never returns.
The level argument specifies where the error message points the error. With level 1 (the default), the error position is where the error function was called. Level 2 points the error to where the function that called error was called; and so on.
• _G
A global variable (not a function) that holds the global environment (that is, _G._G = _G). Lua itself does not use this variable; changing its value does not affect any environment. (Use setfenv to change environments.)
• getfenv (f)
Returns the current environment in use by the function. f can be a Lua function or a number, which specifies the function at that stack level: Level 1 is the function calling getfenv. If the given function is not a Lua function, or if f is 0, getfenv returns the global environment. The default for f is 1.
If the environment has a "__fenv" field, returns the associated value, instead of the environment.
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• getmetatable (object)
If the object does not have a metatable, returns nil. Otherwise, if the object’s metatable has a
"__metatable" field, returns the associated value. Otherwise, returns the metatable of the given object. • gcinfo ()
Returns two results: the number of Kbytes of dynamic memory that Lua is using and the current garbage collector threshold (also in Kbytes).
• ipairs (t)
Returns an iterator function, the table t, and 0, so that the construction for i,v in ipairs(t) do ... end will iterate over the pairs (1,t[1]), (2,t[2]), . . . , up to the first integer key with a nil value in the table.
• loadfile (filename)
Loads a file as a Lua chunk (without running it). If there are no errors, returns the compiled chunk as a function; otherwise, returns nil plus the error message. The environment of the returned function is the global environment.
• loadlib (libname, funcname)
Links the program with the dynamic C library libname. Inside this library, looks for a function funcname and returns this function as a C function. libname must be the complete file name of the C library, including any eventual path and extension. This function is not supported by ANSI C. As such, it is only available on some platforms
(Windows, Linux, Solaris, BSD, plus other Unix systems that support the dlfcn standard).
• loadstring (string [, chunkname])
Loads a string as a Lua chunk (without running it). If there are no errors, returns the compiled chunk as a function; otherwise, returns nil plus the error message. The environment of the returned function is the global environment.
The optional parameter chunkname is the name to be used in error messages and debug information.
To load and run a given string, use the idiom assert(loadstring(s))() 40
• next (table [, index])
Allows a program to traverse all fields of a table. Its first argument is a table and its second argument is an index in this table. next returns the next index of the table and the value associated with the index. When called with nil as its second argument, next returns the first index of the table and its associated value. When called with the last index, or with nil in an empty table, next returns nil. If the second argument is absent, then it is interpreted as nil.
Lua has no declaration of fields; There is no difference between a field not present in a table or a field with value nil. Therefore, next only considers fields with non-nil values. The order in which the indices are enumerated is not specified, even for numeric indices. (To traverse a table in numeric order, use a numerical for or the ipairs function.)
The behavior of next is undefined if, during the traversal, you assign any value to a non-existent field in the table.
• pairs (t)
Returns the next function and the table t (plus a nil), so that the construction for k,v in pairs(t) do ... end will iterate over all key–value pairs of table t.
• pcall (f, arg1, arg2, ...)
Calls function f with the given arguments in protected mode. That means that any error inside f is not propagated; instead, pcall catches the error and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In such case, pcall also returns all results from the call, after this first result. In case of any error, pcall returns false plus the error message.
• print (e1, e2, ...)
Receives any number of arguments, and prints their values in stdout, using the tostring function to convert them to strings. This function is not intended for formatted output, but only as a quick way to show a value, typically for debugging. For formatted output, use format (see §5.3).
• rawequal (v1, v2)
Checks whether v1 is equal to v2, without invoking any metamethod. Returns a boolean.
• rawget (table, index)
Gets the real value of table[index], without invoking any metamethod. table must be a table; index is any value different from nil.
• rawset (table, index, value)
Sets the real value of table[index] to value, without invoking any metamethod. table must be a table, index is any value different from nil, and value is any Lua value.
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• require (packagename)
Loads the given package. The function starts by looking into the table _LOADED to determine whether packagename is already loaded. If it is, then require returns the value that the package returned when it was first loaded. Otherwise, it searches a path looking for a file to load.
If the global variable LUA_PATH is a string, this string is the path. Otherwise, require tries the environment variable LUA_PATH. As a last resort, it uses the predefined path "?;?.lua".
The path is a sequence of templates separated by semicolons. For each template, require will change each interrogation mark in the template to packagename, and then will try to load the resulting file name. So, for instance, if the path is
"./?.lua;./?.lc;/usr/local/?/?.lua;/lasttry"
a require "mod" will try to load the files ./mod.lua, ./mod.lc, /usr/local/mod/mod.lua, and
/lasttry, in that order.
The function stops the search as soon as it can load a file, and then it runs the file. After that, it associates, in table _LOADED, the package name with the value that the package returned, and returns that value. If the package returns nil (or no value), require converts this value to true.
If the package returns false, require also returns false. However, as the mark in table _LOADED is false, any new attempt to reload the file will happen as if the package was not loaded (that is, the package will be loaded again).
If there is any error loading or running the file, or if it cannot find any file in the path, then require signals an error.
While running a file, require defines the global variable _REQUIREDNAME with the package name. The package being loaded always runs within the global environment.
• setfenv (f, table)
Sets the current environment to be used by the given function. f can be a Lua function or a number, which specifies the function at that stack level: Level 1 is the function calling setfenv.
As a special case, when f is 0 setfenv changes the global environment of the running thread.
If the original environment has a "__fenv" field, setfenv raises an error.
• setmetatable (table, metatable)
Sets the metatable for the given table. (You cannot change the metatable of a userdata from Lua.)
If metatable is nil, removes the metatable of the given table. If the original metatable has a
"__metatable" field, raises an error.
• tonumber (e [, base])
Tries to convert its argument to a number. If the argument is already a number or a string convertible to a number, then tonumber returns that number; otherwise, it returns nil.
An optional argument specifies the base to interpret the numeral. The base may be any integer between 2 and 36, inclusive. In bases above 10, the letter ‘A’ (in either upper or lower case) represents 10, ‘B’ represents 11, and so forth, with ‘Z’ representing 35. In base 10 (the default), the number may have a decimal part, as well as an optional exponent part (see §2.2.1). In other bases, only unsigned integers are accepted.
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• tostring (e)
Receives an argument of any type and converts it to a string in a reasonable format. For complete control of how numbers are converted, use format (see §5.3).
If the metatable of e has a "__tostring" field, tostring calls the corresponding value with e as argument, and uses the result of the call as its result.
• type (v)
Returns the type of its only argument, coded as a string. The possible results of this function are "nil" (a string, not the value nil), "number", "string", "boolean, "table", "function",
"thread", and "userdata".
• unpack (list)
Returns all elements from the given list. This function is equivalent to return list[1], list[2], ..., list[n] except that the above code can be written only for a fixed n. The number n is the size of the list, as defined for the table.getn function.
• _VERSION
A global variable (not a function) that holds a string containing the current interpreter version.
The current content of this string is "Lua 5.0".
• xpcall (f, err)
This function is similar to pcall, except that you can set a new error handler. xpcall calls function f in protected mode, using err as the error handler. Any error inside f is not propagated; instead, xpcall catches the error, calls the err function with the original error object, and returns a status code. Its first result is the status code (a boolean), which is true if the call succeeds without errors. In such case, xpcall also returns all results from the call, after this first result. In case of any error, xpcall returns false plus the result from err.
5.2 Coroutine Manipulation
The operations related to coroutines comprise a sub-library of the basic library and come inside the table coroutine. See §2.10 for a general description of coroutines.
• coroutine.create (f)
Creates a new coroutine, with body f. f must be a Lua function. Returns this new coroutine, an object with type "thread".
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• coroutine.resume (co, val1, ...)
Starts or continues the execution of coroutine co. The first time you resume a coroutine, it starts running its body. The arguments val1, . . . go as the arguments to the body function. If the coroutine has yielded, resume restarts it; the arguments val1, . . . go as the results from the yield.
If the coroutine runs without any errors, resume returns true plus any values passed to yield
(if the coroutine yields) or any values returned by the body function (if the coroutine terminates).
If there is any error, resume returns false plus the error message.
• coroutine.status (co)
Returns the status of coroutine co, as a string: "running", if the coroutine is running (that is, it called status); "suspended", if the coroutine is suspended in a call to yield, or if it has not started running yet; and "dead" if the coroutine has finished its body function, or if it has stopped with an error.
• coroutine.wrap (f)
Creates a new coroutine, with body f. f must be a Lua function. Returns a function that resumes the coroutine each time it is called. Any arguments passed to the function behave as the extra arguments to resume. Returns the same values returned by resume, except the first boolean. In case of error, propagates the error.
• coroutine.yield (val1, ...)
Suspends the execution of the calling coroutine. The coroutine cannot be running neither a C function, nor a metamethod, nor an iterator. Any arguments to yield go as extra results to resume. 5.3 String Manipulation
This library provides generic functions for string manipulation, such as finding and extracting substrings, and pattern matching. When indexing a string in Lua, the first character is at position 1
(not at 0, as in C). Indices are allowed to be negative and are interpreted as indexing backwards, from the end of the string. Thus, the last character is at position −1, and so on.
The string library provides all its functions inside the table string.
• string.byte (s [, i])
Returns the internal numerical code of the i-th character of s, or nil if the index is out of range.
If i is absent, then it is assumed to be 1. i may be negative.
Note that numerical codes are not necessarily portable across platforms.
• string.char (i1, i2, ...)
Receives 0 or more integers. Returns a string with length equal to the number of arguments, in which each character has the internal numerical code equal to its correspondent argument.
Note that numerical codes are not necessarily portable across platforms.
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• string.dump (function)
Returns a binary representation of the given function, so that a later loadstring on that string returns a copy of the function. function must be a Lua function without upvalues.
• string.find (s, pattern [, init [, plain]])
Looks for the first match of pattern in the string s. If it finds one, then find returns the indices of s where this occurrence starts and ends; otherwise, it returns nil. If the pattern specifies captures
(see string.gsub below), the captured strings are returned as extra results. A third, optional numerical argument init specifies where to start the search; its default value is 1 and may be negative. A value of true as a fourth, optional argument plain turns off the pattern matching facilities, so the function does a plain “find substring” operation, with no characters in pattern being considered “magic”. Note that if plain is given, then init must be given too.
• string.len (s)
Receives a string and returns its length. The empty string "" has length 0. Embedded zeros are counted, so "a\000b\000c" has length 5.
• string.lower (s)
Receives a string and returns a copy of that string with all uppercase letters changed to lowercase.
All other characters are left unchanged. The definition of what is an uppercase letter depends on the current locale.
• string.rep (s, n)
Returns a string that is the concatenation of n copies of the string s.
• string.sub (s, i [, j])
Returns the substring of s that starts at i and continues until j; i and j may be negative. If j is absent, then it is assumed to be equal to −1 (which is the same as the string length). In particular, the call string.sub(s,1,j) returns a prefix of s with length j, and string.sub(s, -i) returns a suffix of s with length i.
• string.upper (s)
Receives a string and returns a copy of that string with all lowercase letters changed to uppercase.
All other characters are left unchanged. The definition of what is a lowercase letter depends on the current locale.
• string.format (formatstring, e1, e2, ...)
Returns a formatted version of its variable number of arguments following the description given in its first argument (which must be a string). The format string follows the same rules as the printf family of standard C functions. The only differences are that the options/modifiers *, l, L, n, p, and h are not supported, and there is an extra option, q. The q option formats a string in a form suitable to be safely read back by the Lua interpreter: The string is written between double quotes,
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and all double quotes, newlines, and backslashes in the string are correctly escaped when written.
For instance, the call string.format(’%q’, ’a string with "quotes" and \n new line’) will produce the string:
"a string with \"quotes\" and \ new line"
The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number as argument, whereas q and s expect a string. The * modifier can be simulated by building the appropriate format string.
For example, "%*g" can be simulated with "%"..width.."g".
String values to be formatted with %s cannot contain embedded zeros.
• string.gfind (s, pat)
Returns an iterator function that, each time it is called, returns the next captures from pattern pat over string s.
If pat specifies no captures, then the whole match is produced in each call.
As an example, the following loop s = "hello world from Lua" for w in string.gfind(s, "%a+") do print(w) end will iterate over all the words from string s, printing one per line. The next example collects all pairs key=value from the given string into a table: t = {} s = "from=world, to=Lua" for k, v in string.gfind(s, "(%w+)=(%w+)") do t[k] = v end • string.gsub (s, pat, repl [, n])
Returns a copy of s in which all occurrences of the pattern pat have been replaced by a replacement string specified by repl. gsub also returns, as a second value, the total number of substitutions made. If repl is a string, then its value is used for replacement. Any sequence in repl of the form %n, with n between 1 and 9, stands for the value of the n-th captured substring (see below).
If repl is a function, then this function is called every time a match occurs, with all captured substrings passed as arguments, in order; if the pattern specifies no captures, then the whole match is passed as a sole argument. If the value returned by this function is a string, then it is used as the replacement string; otherwise, the replacement string is the empty string.
The optional last parameter n limits the maximum number of substitutions to occur. For instance, when n is 1 only the first occurrence of pat is replaced.
Here are some examples:
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x = string.gsub("hello world", "(%w+)", "%1 %1")
--> x="hello hello world world" x = string.gsub("hello world", "(%w+)", "%1 %1", 1)
--> x="hello hello world" x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
--> x="world hello Lua from" x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
--> x="home = /home/roberto, user = roberto" x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s) return loadstring(s)() end) --> x="4+5 = 9" local t = {name="lua", version="5.0"} x = string.gsub("$name_$version.tar.gz", "%$(%w+)", function (v) return t[v] end) --> x="lua_5.0.tar.gz"
Patterns
Character Class: A character class is used to represent a set of characters. The following combinations are allowed in describing a character class: x (where x is not one of the magic characters ^$()%.[]*+-?) — represents the character x itself. . — (a dot) represents all characters.
%a — represents all letters.
%c — represents all control characters.
%d — represents all digits.
%l — represents all lowercase letters.
%p — represents all punctuation characters.
%s — represents all space characters.
%u — represents all uppercase letters.
%w — represents all alphanumeric characters.
%x — represents all hexadecimal digits.
%z — represents the character with representation 0.
%x (where x is any non-alphanumeric character) — represents the character x . This is the standard way to escape the magic characters. Any punctuation character (even the non magic) can be preceded by a ‘%’ when used to represent itself in a pattern.
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[set] — represents the class which is the union of all characters in set. A range of characters may be specified by separating the end characters of the range with a ‘-’. All classes
%x described above may also be used as components in set. All other characters in set represent themselves. For example, [%w_] (or [_%w]) represents all alphanumeric characters plus the underscore, [0-7] represents the octal digits, and [0-7%l%-] represents the octal digits plus the lowercase letters plus the ‘-’ character.
The interaction between ranges and classes is not defined. Therefore, patterns like [%a-z] or [a-%%] have no meaning.
[^set] — represents the complement of set, where set is interpreted as above.
For all classes represented by single letters (%a, %c, etc.), the corresponding uppercase letter represents the complement of the class. For instance, %S represents all non-space characters.
The definitions of letter, space, and other character groups depend on the current locale. In particular, the class [a-z] may not be equivalent to %l. The second form should be preferred for portability. Pattern Item: A pattern item may be
• a single character class, which matches any single character in the class;
• a single character class followed by ‘*’, which matches 0 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
• a single character class followed by ‘+’, which matches 1 or more repetitions of characters in the class. These repetition items will always match the longest possible sequence;
• a single character class followed by ‘-’, which also matches 0 or more repetitions of characters in the class. Unlike ‘*’, these repetition items will always match the shortest possible sequence;
• a single character class followed by ‘?’, which matches 0 or 1 occurrence of a character in the class; • %n, for n between 1 and 9; such item matches a substring equal to the n-th captured string
(see below);
• %bxy, where x and y are two distinct characters; such item matches strings that start with x , end with y, and where the x and y are balanced. This means that, if one reads the string from left to right, counting +1 for an x and −1 for a y, the ending y is the first y where the count reaches 0. For instance, the item %b() matches expressions with balanced parentheses.
Pattern: A pattern is a sequence of pattern items. A ‘^’ at the beginning of a pattern anchors the match at the beginning of the subject string. A ‘$’ at the end of a pattern anchors the match at the end of the subject string. At other positions, ‘^’ and ‘$’ have no special meaning and represent themselves. Captures: A pattern may contain sub-patterns enclosed in parentheses; they describe captures.
When a match succeeds, the substrings of the subject string that match captures are stored (captured) for future use. Captures are numbered according to their left parentheses. For instance, in the pattern "(a*(.)%w(%s*))", the part of the string matching "a*(.)%w(%s*)" is stored as the first capture (and therefore has number 1); the character matching . is captured with number 2, and the part matching %s* has number 3.
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As a special case, the empty capture () captures the current string position (a number). For instance, if we apply the pattern "()aa()" on the string "flaaap", there will be two captures: 3 and 5.
A pattern cannot contain embedded zeros. Use %z instead.
5.4 Table Manipulation
This library provides generic functions for table manipulation. It provides all its functions inside the table table.
Most functions in the table library assume that the table represents an array or a list. For those functions, an important concept is the size of the array. There are three ways to specify that size:
• the field "n" — When the table has a field "n" with a numerical value, that value is assumed as its size.
• setn — You can call the table.setn function to explicitly set the size of a table.
• implicit size — Otherwise, the size of the object is one less the first integer index with a nil value. For more details, see the descriptions of the table.getn and table.setn functions.
• table.concat (table [, sep [, i [, j]]])
Returns table[i]..sep..table[i+1] ... sep..table[j]. The default value for sep is the empty string, the default for i is 1, and the default for j is the size of the table. If i is greater than j, returns the empty string.
• table.foreach (table, f)
Executes the given f over all elements of table. For each element, f is called with the index and respective value as arguments. If f returns a non-nil value, then the loop is broken, and this value is returned as the final value of foreach.
See the next function for extra information about table traversals.
• table.foreachi (table, f)
Executes the given f over the numerical indices of table. For each index, f is called with the index and respective value as arguments. Indices are visited in sequential order, from 1 to n, where n is the size of the table (see §5.4). If f returns a non-nil value, then the loop is broken and this value is returned as the result of foreachi.
• table.getn (table)
Returns the size of a table, when seen as a list. If the table has an n field with a numeric value, this value is the size of the table. Otherwise, if there was a previous call to table.setn over this table, the respective value is returned. Otherwise, the size is one less the first integer index with a nil value.
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• table.sort (table [, comp])
Sorts table elements in a given order, in-place, from table[1] to table[n], where n is the size of the table (see §5.4). If comp is given, then it must be a function that receives two table elements, and returns true when the first is less than the second (so that not comp(a[i+1],a[i]) will be true after the sort). If comp is not given, then the standard Lua operator < is used instead.
The sort algorithm is not stable, that is, elements considered equal by the given order may have their relative positions changed by the sort.
• table.insert (table, [pos,] value)
Inserts element value at position pos in table, shifting up other elements to open space, if necessary.
The default value for pos is n+1, where n is the size of the table (see §5.4), so that a call table.insert(t,x) inserts x at the end of table t. This function also updates the size of the table by calling table.setn(table, n+1).
• table.remove (table [, pos])
Removes from table the element at position pos, shifting down other elements to close the space, if necessary. Returns the value of the removed element. The default value for pos is n, where n is the size of the table (see §5.4), so that a call table.remove(t) removes the last element of table
t. This function also updates the size of the table by calling table.setn(table, n-1).
• table.setn (table, n)
Updates the size of a table. If the table has a field "n" with a numerical value, that value is changed to the given n. Otherwise, it updates an internal state so that subsequent calls to table.getn(table) return n.
5.5 Mathematical Functions
This library is an interface to most of the functions of the standard C math library. (Some have slightly different names.) It provides all its functions inside the table math. In addition, it registers the global __pow for the binary exponentiation operator ^, so that x^y returns xy. The library provides the following functions: math.abs math.acos math.asin math.atan math.atan2 math.ceil math.cos math.deg math.exp math.floor math.log math.log10 math.max math.min math.mod math.pow math.rad math.sin math.sqrt math.tan math.frexp math.ldexp math.random math.randomseed plus a variable math.pi. Most of them are only interfaces to the corresponding functions in the
C library. All trigonometric functions work in radians (previous versions of Lua used degrees). The functions math.deg and math.rad convert between radians and degrees.
The function math.max returns the maximum value of its numeric arguments. Similarly, math.min computes the minimum. Both can be used with 1, 2, or more arguments.
The functions math.random and math.randomseed are interfaces to the simple random generator functions rand and srand that are provided by ANSI C. (No guarantees can be given for their statistical properties.) When called without arguments, math.random returns a pseudo-random
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real number in the range [0, 1). When called with a number n, math.random returns a pseudorandom integer in the range [1, n]. When called with two arguments, l and u, math.random returns a pseudo-random integer in the range [l, u]. The math.randomseed function sets a “seed” for the pseudo-random generator: Equal seeds produce equal sequences of numbers.
5.6 Input and Output Facilities
The I/O library provides two different styles for file manipulation. The first one uses implicit file descriptors, that is, there are operations to set a default input file and a default output file, and all input/output operations are over those default files. The second style uses explicit file descriptors.
When using implicit file descriptors, all operations are supplied by table io. When using explicit file descriptors, the operation io.open returns a file descriptor and then all operations are supplied as methods by the file descriptor.
The table io also provides three predefined file descriptors with their usual meanings from C: io.stdin, io.stdout, and io.stderr.
A file handle is a userdata containing the file stream (FILE*), with a distinctive metatable created by the I/O library.
Unless otherwise stated, all I/O functions return nil on failure (plus an error message as a second result) and some value different from nil on success.
• io.close ([file])
Equivalent to file:close(). Without a file, closes the default output file.
• io.flush ()
Equivalent to file:flush over the default output file.
• io.input ([file])
When called with a file name, it opens the named file (in text mode), and sets its handle as the default input file. When called with a file handle, it simply sets that file handle as the default input file. When called without parameters, it returns the current default input file.
In case of errors this function raises the error, instead of returning an error code.
• io.lines ([filename])
Opens the given file name in read mode and returns an iterator function that, each time it is called, returns a new line from the file. Therefore, the construction for line in io.lines(filename) do ... end will iterate over all lines of the file. When the iterator function detects the end of file, it returns nil (to finish the loop) and automatically closes the file.
The call io.lines() (without a file name) is equivalent to io.input():lines(), that is, it iterates over the lines of the default input file.
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• io.open (filename [, mode])
This function opens a file, in the mode specified in the string mode. It returns a new file handle, or, in case of errors, nil plus an error message.
The mode string can be any of the following:
“r” read mode (the default);
“w” write mode;
“a” append mode;
“r+” update mode, all previous data is preserved;
“w+” update mode, all previous data is erased;
“a+” append update mode, previous data is preserved, writing is only allowed at the end of file. The mode string may also have a b at the end, which is needed in some systems to open the file in binary mode. This string is exactly what is used in the standard C function fopen.
• io.output ([file])
Similar to io.input, but operates over the default output file.
• io.read (format1, ...)
Equivalent to io.input():read.
• io.tmpfile ()
Returns a handle for a temporary file. This file is open in update mode and it is automatically removed when the program ends.
• io.type (obj)
Checks whether obj is a valid file handle. Returns the string "file" if obj is an open file handle,
"closed file" if obj is a closed file handle, and nil if obj is not a file handle.
• io.write (value1, ...)
Equivalent to io.output():write.
• file:close ()
Closes file.
• file:flush ()
Saves any written data to file.
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• file:lines ()
Returns an iterator function that, each time it is called, returns a new line from the file. Therefore, the construction for line in file:lines() do ... end will iterate over all lines of the file. (Unlike io.lines, this function does not close the file when the loop ends.)
• file:read (format1, ...)
Reads the file file, according to the given formats, which specify what to read. For each format, the function returns a string (or a number) with the characters read, or nil if it cannot read data with the specified format. When called without formats, it uses a default format that reads the entire next line (see below).
The available formats are
“*n” reads a number; this is the only format that returns a number instead of a string.
“*a” reads the whole file, starting at the current position. On end of file, it returns the empty string. “*l” reads the next line (skipping the end of line), returning nil on end of file. This is the default format. number reads a string with up to that number of characters, returning nil on end of file. If number is zero, it reads nothing and returns an empty string, or nil on end of file.
• file:seek ([whence] [, offset])
Sets and gets the file position, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence, as follows:
“set” base is position 0 (beginning of the file);
“cur” base is current position;
“end” base is end of file;
In case of success, function seek returns the final file position, measured in bytes from the beginning of the file. If this function fails, it returns nil, plus a string describing the error.
The default value for whence is "cur", and for offset is 0. Therefore, the call file:seek() returns the current file position, without changing it; the call file:seek("set") sets the position to the beginning of the file (and returns 0); and the call file:seek("end") sets the position to the end of the file, and returns its size.
• file:write (value1, ...)
Writes the value of each of its arguments to the filehandle file. The arguments must be strings or numbers. To write other values, use tostring or string.format before write.
5.7 Operating System Facilities
This library is implemented through table os.
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• os.clock ()
Returns an approximation of the amount of CPU time used by the program, in seconds.
• os.date ([format [, time]])
Returns a string or a table containing date and time, formatted according to the given string format. If the time argument is present, this is the time to be formatted (see the os.time function for a description of this value). Otherwise, date formats the current time.
If format starts with ‘!’, then the date is formatted in Coordinated Universal Time. After that optional character, if format is *t, then date returns a table with the following fields: year (four digits), month (1–12), day (1–31), hour (0–23), min (0–59), sec (0–61), wday (weekday, Sunday is 1), yday (day of the year), and isdst (daylight saving flag, a boolean).
If format is not *t, then date returns the date as a string, formatted according with the same rules as the C function strftime.
When called without arguments, date returns a reasonable date and time representation that depends on the host system and on the current locale (that is, os.date() is equivalent to os.date("%c")).
• os.difftime (t2, t1)
Returns the number of seconds from time t1 to time t2. In Posix, Windows, and some other systems, this value is exactly t2−t1.
• os.execute (command)
This function is equivalent to the C function system. It passes command to be executed by an operating system shell. It returns a status code, which is system-dependent.
• os.exit ([code])
Calls the C function exit, with an optional code, to terminate the host program. The default value for code is the success code.
• os.getenv (varname)
Returns the value of the process environment variable varname, or nil if the variable is not defined.
• os.remove (filename)
Deletes the file with the given name. If this function fails, it returns nil, plus a string describing the error.
• os.rename (oldname, newname)
Renames file named oldname to newname. If this function fails, it returns nil, plus a string describing the error.
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• os.setlocale (locale [, category])
Sets the current locale of the program. locale is a string specifying a locale; category is an optional string describing which category to change: "all", "collate", "ctype", "monetary",
"numeric", or "time"; the default category is "all". The function returns the name of the new locale, or nil if the request cannot be honored.
• os.time ([table])
Returns the current time when called without arguments, or a time representing the date and time specified by the given table. This table must have fields year, month, and day, and may have fields hour, min, sec, and isdst (for a description of these fields, see the os.date function).
The returned value is a number, whose meaning depends on your system. In Posix, Windows, and some other systems, this number counts the number of seconds since some given start time
(the “epoch”). In other systems, the meaning is not specified, and the number returned by time can be used only as an argument to date and difftime.
• os.tmpname ()
Returns a string with a file name that can be used for a temporary file. The file must be explicitly opened before its use and removed when no longer needed.
This function is equivalent to the tmpnam C function, and many people (and even some compilers!) advise against its use, because between the time you call this function and the time you open the file, it is possible for another process to create a file with the same name.
5.8 The Reflexive Debug Interface
The debug library provides the functionality of the debug interface to Lua programs. You should exert care when using this library. The functions provided here should be used exclusively for debugging and similar tasks, such as profiling. Please resist the temptation to use them as a usual programming tool: They can be very slow. Moreover, setlocal and getlocal violate the privacy of local variables and therefore can compromise some otherwise secure code.
All functions in this library are provided inside a debug table.
• debug.debug ()
Enters an interactive mode with the user, running each string that the user enters. Using simple commands and other debug facilities, the user can inspect global and local variables, change their values, evaluate expressions, and so on. A line containing only the word cont finishes this function, so that the caller continues its execution.
Note that commands for debug.debug are not lexically nested with any function, so they have no direct access to local variables.
• debug.gethook ()
Returns the current hook settings, as three values: the current hook function, the current hook mask, and the current hook count (as set by the debug.sethook function).
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• debug.getinfo (function [, what])
This function returns a table with information about a function. You can give the function directly, or you can give a number as the value of function, which means the function running at level function of the call stack: Level 0 is the current function (getinfo itself); level 1 is the function that called getinfo; and so on. If function is a number larger than the number of active functions, then getinfo returns nil.
The returned table contains all the fields returned by lua_getinfo, with the string what describing which fields to fill in. The default for what is to get all information available. If present, the option ‘f’ adds a field named func with the function itself.
For instance, the expression debug.getinfo(1,"n").name returns the name of the current function, if a reasonable name can be found, and debug.getinfo(print) returns a table with all available information about the print function.
• debug.getlocal (level, local)
This function returns the name and the value of the local variable with index local of the function at level level of the stack. (The first parameter or local variable has index 1, and so on, until the last active local variable.) The function returns nil if there is no local variable with the given index, and raises an error when called with a level out of range. (You can call debug.getinfo to check whether the level is valid.)
• debug.getupvalue (func, up)
This function returns the name and the value of the upvalue with index up of the function func.
The function returns nil if there is no upvalue with the given index.
• debug.setlocal (level, local, value)
This function assigns the value value to the local variable with index local of the function at level level of the stack. The function returns nil if there is no local variable with the given index, and raises an error when called with a level out of range. (You can call getinfo to check whether the level is valid.)
• debug.setupvalue (func, up, value)
This function assigns the value value to the upvalue with index up of the function func. The function returns nil if there is no upvalue with the given index.
• debug.sethook (hook, mask [, count])
Sets the given function as a hook. The string mask and the number count describe when the hook will be called. The string mask may have the following characters, with the given meaning:
"c" The hook is called every time Lua calls a function;
"r" The hook is called every time Lua returns from a function;
"l" The hook is called every time Lua enters a new line of code.
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With a count different from zero, the hook is called after every count instructions.
When called without arguments, the debug.sethook function turns off the hook.
When the hook is called, its first parameter is always a string describing the event that triggered its call: "call", "return" (or "tail return"), "line", and "count". Moreover, for line events, it also gets as its second parameter the new line number. Inside a hook, you can call getinfo with level 2 to get more information about the running function (level 0 is the getinfo function, and level 1 is the hook function), unless the event is "tail return". In this case, Lua is only simulating the return, and a call to getinfo will return invalid data.
• debug.traceback ([message])
Returns a string with a traceback of the call stack. An optional message string is appended at the beginning of the traceback. This function is typically used with xpcall to produce better error messages. 6 Lua Stand-alone
Although Lua has been designed as an extension language, to be embedded in a host C program, it is also frequently used as a stand-alone language. An interpreter for Lua as a stand-alone language, called simply lua, is provided with the standard distribution. The stand-alone interpreter includes all standard libraries plus the reflexive debug interface. Its usage is: lua [options] [script [args]]
The options are:
- executes stdin as a file;
-e stat executes string stat;
-l file “requires” file;
-i enters interactive mode after running script;
-v prints version information;
-- stop handling options.
After handling its options, lua runs the given script, passing to it the given args. When called without arguments, lua behaves as lua -v -i when stdin is a terminal, and as lua - otherwise.
Before running any argument, the interpreter checks for an environment variable LUA_INIT. If its format is @filename, then lua executes the file. Otherwise, lua executes the string itself.
All options are handled in order, except -i. For instance, an invocation like
$ lua -e’a=1’ -e ’print(a)’ script.lua will first set a to 1, then print a, and finally run the file script.lua. (Here, $ is the shell prompt.
Your prompt may be different.)
Before starting to run the script, lua collects all arguments in the command line in a global table called arg. The script name is stored in index 0, the first argument after the script name goes to index 1, and so on. The field n gets the number of arguments after the script name. Any arguments before the script name (that is, the interpreter name plus the options) go to negative indices. For instance, in the call
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$ lua -la.lua b.lua t1 t2 the interpreter first runs the file a.lua, then creates a table arg = { [-2] = "lua", [-1] = "-la.lua", [0] = "b.lua",
[1] = "t1", [2] = "t2"; n = 2 } and finally runs the file b.lua.
In interactive mode, if you write an incomplete statement, the interpreter waits for its completion.
If the global variable _PROMPT is defined as a string, then its value is used as the prompt.
Therefore, the prompt can be changed directly on the command line:
$ lua -e"_PROMPT=’myprompt> ’" -i
(the outer pair of quotes is for the shell, the inner is for Lua), or in any Lua programs by assigning to _PROMPT. Note the use of -i to enter interactive mode; otherwise, the program would end just after the assignment to _PROMPT.
In Unix systems, Lua scripts can be made into executable programs by using chmod +x and the #! form, as in
#!/usr/local/bin/lua
(Of course, the location of the Lua interpreter may be different in your machine. If lua is in your
PATH, then
#!/usr/bin/env lua is a more portable solution.)
Acknowledgments
The Lua team is grateful to Tecgraf for its continued support to Lua. We thank everyone at Tecgraf, specially the head of the group, Marcelo Gattass. At the risk of omitting several names, we also thank the following individuals for supporting, contributing to, and spreading the word about Lua:
Alan Watson. Andr´e Clinio, Andr´e Costa, Antonio Scuri, Asko Kauppi, Bret Mogilefsky, Cameron
Laird, Carlos Cassino, Carlos Henrique Levy, Claudio Terra, David Jeske, Ed Ferguson, Edgar
Toernig, Erik Hougaard, Jim Mathies, John Belmonte, John Passaniti, John Roll, Jon Erickson,
Jon Kleiser, Mark Ian Barlow, Nick Trout, Noemi Rodriguez, Norman Ramsey, Philippe Lhoste,
Renata Ratton, Renato Borges, Renato Cerqueira, Reuben Thomas, Stephan Herrmann, Steve
Dekorte, Thatcher Ulrich, Tom´as Gorham, Vincent Penquerc’h. Thank you!
Incompatibilities with Previous Versions
Lua 5.0 is a major release. There are several incompatibilities with its previous version, Lua 4.0.
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Incompatibilities with version 4.0
Changes in the Language
• The whole tag-method scheme was replaced by metatables.
• Function calls written between parentheses result in exactly one value.
• A function call as the last expression in a list constructor (like {a,b,f()}) has all its return values inserted in the list.
• The precedence of or is smaller than the precedence of and.
• in, false, and true are reserved words.
• The old construction for k,v in t, where t is a table, is deprecated (although it is still supported). Use for k,v in pairs(t) instead.
• When a literal string of the form [[...]] starts with a newline, this newline is ignored.
• Upvalues in the form %var are obsolete; use external local variables instead.
Changes in the Libraries
• Most library functions now are defined inside tables. There is a compatibility script (compat.lua) that redefine most of them as global names.
• In the math library, angles are expressed in radians. With the compatibility script (compat.lua), functions still work in degrees.
• The call function is deprecated. Use f(unpack(tab)) instead of call(f, tab) for unprotected calls, or the new pcall function for protected calls.
• dofile do not handle errors, but simply propagates them.
• dostring is deprecated. Use loadstring instead.
• The read option *w is obsolete.
• The format option %n$ is obsolete.
Changes in the API
• lua_open does not have a stack size as its argument (stacks are dynamic).
• lua_pushuserdata is deprecated. Use lua_newuserdata or lua_pushlightuserdata instead.
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The Complete Syntax of Lua chunk ! { stat [ ‘;’ ] } block ! chunk stat ! varlist1 ‘=’ explist1
| functioncall
| do block end
| while exp do block end
| repeat block until exp
| if exp then block { elseif exp then block } [ else block ] end
| return [ explist1 ]
| break
| for Name ‘=’ exp ‘,’ exp [ ‘,’ exp ] do block end
| for Name { ‘,’ Name } in explist1 do block end
| function funcname funcbody
| local function Name funcbody
| local namelist [ init ] funcname ! Name { ‘.’ Name } [ ‘:’ Name ] varlist1 ! var { ‘,’ var } var ! Name | prefixexp ‘[’ exp ‘]’ | prefixexp ‘.’ Name namelist ! Name { ‘,’ Name } init ! ‘=’ explist1 explist1 ! { exp ‘,’ } exp exp ! nil | false | true | Number | Literal
| function | prefixexp | tableconstructor | exp binop exp | unop exp prefixexp ! var | functioncall | ‘(’ exp ‘)’ functioncall ! prefixexp args | prefixexp ‘:’ Name args args ! ‘(’ [ explist1 ] ‘)’ | tableconstructor | Literal function ! function funcbody funcbody ! ‘(’ [ parlist1 ] ‘)’ block end parlist1 ! Name { ‘,’ Name } [ ‘,’ ‘...’ ] | ‘...’ tableconstructor ! ‘{’ [ fieldlist ] ‘}’ fieldlist ! field { fieldsep field } [ fieldsep ] field ! ‘[’ exp ‘]’ ‘=’ exp | name ‘=’ exp | exp fieldsep ! ‘,’ | ‘;’ binop ! ‘+’ | ‘-’ | ‘*’ | ‘/’ | ‘^’ | ‘..’
| ‘=’ | ‘==’ | ‘~=’
| and | or unop ! ‘-’ | not
60
Index
G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
LOADED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
PROMPT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
REQUIREDNAME . . . . . . . . . . . . . . . . . . . . . . . . . . 42
VERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A
acceptable index . . . . . . . . . . . . . . . . . . . . . . . . 23
“add” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 arg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 arithmetic operators . . . . . . . . . . . . . . . . . . . . . . 8 arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 assert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 associative arrays . . . . . . . . . . . . . . . . . . . . . . . . . 3
B
basic types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 boolean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 break statement . . . . . . . . . . . . . . . . . . . . . . . . . . 6
CC
API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Chunkreader . . . . . . . . . . . . . . . . . . . . . . . . 28 lua call . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 lua CFunction . . . . . . . . . . . . . . . . . . . . . . 32 lua checkstack . . . . . . . . . . . . . . . . . . . . 23 lua close . . . . . . . . . . . . . . . . . . . . . . . . . . 22 lua concat . . . . . . . . . . . . . . . . . . . . . . . . . 27 lua cpcall . . . . . . . . . . . . . . . . . . . . . . . . . 34 lua Debug . . . . . . . . . . . . . . . . . . . . . . . . . . 35 lua equal . . . . . . . . . . . . . . . . . . . . . . . . . . 25
LUA ERRERR . . . . . . . . . . . . . . . . . . . . . . . . . 31
LUA ERRMEM . . . . . . . . . . . . . . . . . . . . . 28, 31 lua error . . . . . . . . . . . . . . . . . . . . . . . . . . 34
LUA ERRRUN . . . . . . . . . . . . . . . . . . . . . . . . . 31
LUA ERRSYNTAX . . . . . . . . . . . . . . . . . . . . . . 28 lua getfenv . . . . . . . . . . . . . . . . . . . . . . . . 30 lua getgccount . . . . . . . . . . . . . . . . . . . . 27 lua getgcthreshold . . . . . . . . . . . . . . . . 27 lua gethook . . . . . . . . . . . . . . . . . . . . . . . . 38 lua gethookcount . . . . . . . . . . . . . . . . . . 38 lua gethookmask . . . . . . . . . . . . . . . . . . . 38 lua getinfo . . . . . . . . . . . . . . . . . . . . . . . . 35 lua getlocal . . . . . . . . . . . . . . . . . . . . . . . 36 lua getmetatable . . . . . . . . . . . . . . . . . . 28 lua getstack . . . . . . . . . . . . . . . . . . . . . . . 35 lua gettable . . . . . . . . . . . . . . . . . . . . . . . 29 lua gettop . . . . . . . . . . . . . . . . . . . . . . . . . 23 lua getupvalue . . . . . . . . . . . . . . . . . . . . 36
LUA GLOBALSINDEX . . . . . . . . . . . . . . . . . . 30 lua Hook . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
LUA HOOKCALL . . . . . . . . . . . . . . . . . . . . . . . 37
LUA HOOKCOUNT . . . . . . . . . . . . . . . . . . . . . . 37
LUA HOOKLINE . . . . . . . . . . . . . . . . . . . . . . . 37
LUA HOOKRET . . . . . . . . . . . . . . . . . . . . . . . . 37
LUA HOOKTAILRET . . . . . . . . . . . . . . . . . . . 37 lua insert . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua isboolean . . . . . . . . . . . . . . . . . . . . . . 24 lua iscfunction . . . . . . . . . . . . . . . . . . . 24 lua isfunction . . . . . . . . . . . . . . . . . . . . 24 lua islightuserdata . . . . . . . . . . . . . . 24 lua isnil . . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua isnumber . . . . . . . . . . . . . . . . . . . . . . . 24 lua isstring . . . . . . . . . . . . . . . . . . . . . . . 24 lua istable . . . . . . . . . . . . . . . . . . . . . . . . 24 lua isuserdata . . . . . . . . . . . . . . . . . . . . 24 lua lessthan . . . . . . . . . . . . . . . . . . . . . . . 25 lua load . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
LUA MASKCALL . . . . . . . . . . . . . . . . . . . . . . . 37
LUA MASKCOUNT . . . . . . . . . . . . . . . . . . . . . . 37
LUA MASKLINE . . . . . . . . . . . . . . . . . . . . . . . 37
LUA MASKRET . . . . . . . . . . . . . . . . . . . . . . . . 37
LUA MINSTACK . . . . . . . . . . . . . . . . . . . . . . . 23
LUA MULTRET . . . . . . . . . . . . . . . . . . . . . . . . 30 lua newtable . . . . . . . . . . . . . . . . . . . . . . . 29 lua newthread . . . . . . . . . . . . . . . . . . . . . . 34 lua newuserdata . . . . . . . . . . . . . . . . . . . 27 lua next . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 lua Number . . . . . . . . . . . . . . . . . . . . . . . . . 25 lua open . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 lua pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua pushboolean . . . . . . . . . . . . . . . . . . . 26 lua pushcclosure . . . . . . . . . . . . . . . . . . 33
61
lua pushcfunction . . . . . . . . . . . . . . . . . 26 lua pushfstring . . . . . . . . . . . . . . . . . . . 26 lua pushlightuserdata . . . . . . . . . . . . 26 lua pushlstring . . . . . . . . . . . . . . . . . . . 26 lua pushnil . . . . . . . . . . . . . . . . . . . . . . . . 26 lua pushnumber . . . . . . . . . . . . . . . . . . . . 26 lua pushstring . . . . . . . . . . . . . . . . . . . . 26 lua pushvalue . . . . . . . . . . . . . . . . . . . . . . 24 lua pushvfstring . . . . . . . . . . . . . . . . . . 26 lua rawequal . . . . . . . . . . . . . . . . . . . . . . . 25 lua rawget . . . . . . . . . . . . . . . . . . . . . . . . . 29 lua rawgeti . . . . . . . . . . . . . . . . . . . . . . . . 30 lua rawset . . . . . . . . . . . . . . . . . . . . . . . . . 29 lua rawseti . . . . . . . . . . . . . . . . . . . . . . . . 30 lua register . . . . . . . . . . . . . . . . . . . . . . . 32
LUA REGISTRYINDEX . . . . . . . . . . . . . . . . . 33 lua remove . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua replace . . . . . . . . . . . . . . . . . . . . . . . . 24 lua resume . . . . . . . . . . . . . . . . . . . . . . . . . 34 lua setfenv . . . . . . . . . . . . . . . . . . . . . . . . 30 lua setgcthreshold . . . . . . . . . . . . . . . . 27 lua sethook . . . . . . . . . . . . . . . . . . . . . . . . 37 lua setlocal . . . . . . . . . . . . . . . . . . . . . . . 36 lua setmetatable . . . . . . . . . . . . . . . . . . 28 lua settable . . . . . . . . . . . . . . . . . . . . . . . 29 lua settop . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua setupvalue . . . . . . . . . . . . . . . . . . . . 36 lua State . . . . . . . . . . . . . . . . . . . . . . . . . . 22 lua strlen . . . . . . . . . . . . . . . . . . . . . . . . . 25 lua toboolean . . . . . . . . . . . . . . . . . . . . . . 25 lua tocfunction . . . . . . . . . . . . . . . . . . . 25 lua tonumber . . . . . . . . . . . . . . . . . . . . . . . 25 lua topointer . . . . . . . . . . . . . . . . . . . . . . 25 lua tostring . . . . . . . . . . . . . . . . . . . . . . . 25 lua tothread . . . . . . . . . . . . . . . . . . . . . . . 25 lua touserdata . . . . . . . . . . . . . . . . . . . . 25 lua type . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 lua typename . . . . . . . . . . . . . . . . . . . . . . . 25 lua upvalueindex . . . . . . . . . . . . . . . . . . 33 lua xmove . . . . . . . . . . . . . . . . . . . . . . . . . . 34 lua yield . . . . . . . . . . . . . . . . . . . . . . . . . . 34 luaopen base . . . . . . . . . . . . . . . . . . . . . . . 38 luaopen debug . . . . . . . . . . . . . . . . . . . . . . 38 luaopen io . . . . . . . . . . . . . . . . . . . . . . . . . 38 luaopen math . . . . . . . . . . . . . . . . . . . . . . . 38 luaopen string . . . . . . . . . . . . . . . . . . . . 38 luaopen table . . . . . . . . . . . . . . . . . . . . . . 38
C closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
“call” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 captures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 character class . . . . . . . . . . . . . . . . . . . . . . . . . . 47 chunk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 collectgarbage . . . . . . . . . . . . . . . . . . . . . . . . 39 comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 concatenation . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
“concatenation” event . . . . . . . . . . . . . . . . . . . 17 condition expression . . . . . . . . . . . . . . . . . . . . . . 6 constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 coroutine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 coroutine.create . . . . . . . . . . . . . . . . . . 21, 43 coroutine.resume . . . . . . . . . . . . . . . . . . 21, 44 coroutine.status . . . . . . . . . . . . . . . . . . . . . . 44 coroutine.wrap . . . . . . . . . . . . . . . . . . . . 21, 44 coroutine.yield . . . . . . . . . . . . . . . . . . . 21, 44
D
debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 debug.debug . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 debug.gethook . . . . . . . . . . . . . . . . . . . . . . . . . 55 debug.getinfo . . . . . . . . . . . . . . . . . . . . . . . . . 56 debug.getlocal . . . . . . . . . . . . . . . . . . . . . . . . 56 debug.getupvalue . . . . . . . . . . . . . . . . . . . . . . 56 debug.sethook . . . . . . . . . . . . . . . . . . . . . . . . . 56 debug.setlocal . . . . . . . . . . . . . . . . . . . . . . . . 56 debug.setupvalue . . . . . . . . . . . . . . . . . . . . . . 56 debug.traceback . . . . . . . . . . . . . . . . . . . . . . . 57
“div” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 dofile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
E
eight-bit clean . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 environment tables . . . . . . . . . . . . . . . . . . . . . . . 4
“eq” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 exponentiation . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
F
file:close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 file:flush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 file:lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 file:read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 file:seek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 file:write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
62
finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 for statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 full userdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 function call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 function definitions . . . . . . . . . . . . . . . . . . . . . . 12
G
garbage collector . . . . . . . . . . . . . . . . . . . . . . . . 20 gcinfo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 getfenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 getmetatable . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 args . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11, 60 binop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 60 chunk . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 60 exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 60 explist1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 60 field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 60 fieldlist . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 60 fieldsep . . . . . . . . . . . . . . . . . . . . . . . . . . 10, 60 funcbody . . . . . . . . . . . . . . . . . . . . . . . . 12, 60 funcname . . . . . . . . . . . . . . . . . . . . . . . 12, 60 function . . . . . . . . . . . . . . . . . . . . . . . . . 12, 60 functioncall . . . . . . . . . . . . . . . . . . . . . 11, 60 init . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 namelist . . . . . . . . . . . . . . . . . . . . . . . . . . 8, 60 parlist1 . . . . . . . . . . . . . . . . . . . . . . . . . . 13, 60 prefixexp . . . . . . . . . . . . . . . . . . . . . . . . . 8, 60 stat . . . . . . . . . . . . . . . . . . . . . . . . 5–8, 12, 60 tableconstructor . . . . . . . . . . . . . . . . . 10, 60 unop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 var . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4, 60 varlist1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 60
I
identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 if-then-else statement . . . . . . . . . . . . . . . . . . . . . 6
“index” event . . . . . . . . . . . . . . . . . . . . . . . . 18, 19 io . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.flush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.open . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51, 52 io.output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 io.read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 io.stderr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.stdin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.stdout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 io.tmpfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 io.type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 io.write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 ipairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
K keywords and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 else . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 elseif . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 false . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 function . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 nil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 true . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
L
lexical scoping . . . . . . . . . . . . . . . . . . . . . . . . . . 14 light userdata . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 literal strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 loadfile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 loadlib . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 loadstring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 local variables . . . . . . . . . . . . . . . . . . . . . . . . . 4, 8 logical operators . . . . . . . . . . . . . . . . . . . . . . . . . . 9
“lt” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 lua stand-alone . . . . . . . . . . . . . . . . . . . . . . . . . . 57
LUA INIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
LUA PATH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 luac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5, 28
63
M math . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.abs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.acos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.asin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.atan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.atan2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.ceil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.cos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.def . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.floor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.frexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.ldexp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.log10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.max . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.min . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.mod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.pi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.pow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.rad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.random . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.randomseed . . . . . . . . . . . . . . . . . . . . . . . 50 math.sin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 math.tan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 metamethod add . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 concatenation . . . . . . . . . . . . . . . . . . . . . . . 17 div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 index . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18, 19 lt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 mul . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 pow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 sub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 unm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 metamethod . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 metamethods . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 metatable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
“mul” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 multiple assignment . . . . . . . . . . . . . . . . . . . . . . 5
N
next . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 nil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 numerical constants . . . . . . . . . . . . . . . . . . . . . . 3
O
operator precedence . . . . . . . . . . . . . . . . . . . . . 10 or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 os . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 os.clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.difftime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.execute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.getenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.rename . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 os.setlocale . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 os.time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 os.tmpname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
P
pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 panic function . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 pattern item . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 pcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
“pow” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 pre-compilation . . . . . . . . . . . . . . . . . . . . . . . . . . 5 print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 proper tail calls . . . . . . . . . . . . . . . . . . . . . . . . . 12 pseudo-indices . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
R
rawequal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 rawget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 rawset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 relational operators . . . . . . . . . . . . . . . . . . . . . . . 9 repeat-until statement . . . . . . . . . . . . . . . . . . . . 6 require . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 reserved words . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 return statement . . . . . . . . . . . . . . . . . . . . . . . . . 6
S
self . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
64
setfenv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 setmetatable . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 short-cut evaluation . . . . . . . . . . . . . . . . . . . . . . 9 stack index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 string . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 string.byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 string.char . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 string.dump . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.find . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.format . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.gsub . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 string.len . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.lower . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.rep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.sub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 string.upper . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
“sub” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
T
table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 table.concat . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 table.foreach . . . . . . . . . . . . . . . . . . . . . . . . . 49 table.foreachi . . . . . . . . . . . . . . . . . . . . . . . . 49 table.getn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 table.insert . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 table.remove . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 table.setn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 table.sort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 tail call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 tonumber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 tostring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
U
“unm” event . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 unpack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 upvalue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 userdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
V valid index .
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23 values and types . . . . . . . . . . . . . . . . . . . . . . . . . . 3 vararg function . . . . . . . . . . . . . . . . . . . . . . . . . . 13 version 4.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
W weak references .
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20
weak table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 while-do statement . . . . . . . . . . . . . . . . . . . . . . . 6
X
xpcall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
65