From b8147afcc5bfbeb5fad62e4f68f1b88fc6c60d96 Mon Sep 17 00:00:00 2001 From: sanine Date: Thu, 18 Aug 2022 20:52:26 -0500 Subject: add lua-5.1.5 files --- libs/lua-5.1.5/doc/manual.html | 8804 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 8804 insertions(+) create mode 100644 libs/lua-5.1.5/doc/manual.html (limited to 'libs/lua-5.1.5/doc/manual.html') diff --git a/libs/lua-5.1.5/doc/manual.html b/libs/lua-5.1.5/doc/manual.html new file mode 100644 index 0000000..4e41683 --- /dev/null +++ b/libs/lua-5.1.5/doc/manual.html @@ -0,0 +1,8804 @@ + + + + +Lua 5.1 Reference Manual + + + + + + + +
+

+ +Lua 5.1 Reference Manual +

+ +by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes +

+ +Copyright © 2006–2012 Lua.org, PUC-Rio. +Freely available under the terms of the +Lua license. + +

+

+ +contents +· +index +· +other versions + + +

+ + + + + + +

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 +scripting 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 sample host program called lua, +which uses the Lua library to offer a complete, stand-alone Lua interpreter. + + +

+Lua is free software, +and is provided as usual with no guarantees, +as stated in its license. +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 technical papers available at Lua's web site. +For a detailed introduction to programming in Lua, +see Roberto's book, Programming in Lua (Second Edition). + + + +

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 notation, +in which +{a} means 0 or more a's, and +[a] means an optional a. +Non-terminals are shown like non-terminal, +keywords are shown like kword, +and other terminal symbols are shown like `=´. +The complete syntax of Lua can be found in §8 +at the end of this manual. + + + +

2.1 - Lexical Conventions

+ +

+Names +(also called identifiers) +in Lua can be any string of letters, +digits, and underscores, +not beginning with a digit. +This coincides with the definition of names 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.) +Identifiers are used to name variables and table fields. + + +

+The following keywords are reserved +and cannot be used as names: + + +

+     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 names. +As a convention, names starting with an underscore followed by +uppercase letters (such as _VERSION) +are reserved for internal global 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 [double quote]), +and '\'' (apostrophe [single quote]). +Moreover, a backslash followed by a real newline +results in a newline in the string. +A character in a string can also be specified by its numerical value +using the escape sequence \ddd, +where ddd is a sequence of up to three decimal digits. +(Note that if a numerical escape is to be followed by a digit, +it must be expressed using exactly three digits.) +Strings in Lua can contain any 8-bit value, including embedded zeros, +which can be specified as '\0'. + + +

+Literal strings can also be defined using a long format +enclosed by long brackets. +We define an opening long bracket of level n as an opening +square bracket followed by n equal signs followed by another +opening square bracket. +So, an opening long bracket of level 0 is written as [[, +an opening long bracket of level 1 is written as [=[, +and so on. +A closing long bracket is defined similarly; +for instance, a closing long bracket of level 4 is written as ]====]. +A long string starts with an opening long bracket of any level and +ends at the first closing long bracket of the same level. +Literals in this bracketed form can run for several lines, +do not interpret any escape sequences, +and ignore long brackets of any other level. +They can contain anything except a closing bracket of the proper level. + + +

+For convenience, +when the opening long bracket 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 five literal strings below denote the same string: + +

+     a = 'alo\n123"'
+     a = "alo\n123\""
+     a = '\97lo\10\04923"'
+     a = [[alo
+     123"]]
+     a = [==[
+     alo
+     123"]==]
+
+ +

+A numerical constant can be written with an optional decimal part +and an optional decimal exponent. +Lua also accepts integer hexadecimal constants, +by prefixing them with 0x. +Examples of valid numerical constants are + +

+     3   3.0   3.1416   314.16e-2   0.31416E1   0xff   0x56
+
+ +

+A comment starts with a double hyphen (--) +anywhere outside a string. +If the text immediately after -- is not an opening long bracket, +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 closing long bracket. +Long comments are frequently used to disable code temporarily. + + + + + +

2.2 - Values and Types

+ +

+Lua is a dynamically typed language. +This means that +variables do not have types; only values do. +There are no type definitions in the language. +All values carry their own type. + + +

+All values in Lua are first-class values. +This means that all values can be stored in variables, +passed as arguments to other functions, and returned as results. + + +

+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; +it usually represents the absence of a useful value. +Boolean is the type of the values false and true. +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; +see file luaconf.h.) +String represents arrays of characters. + +Lua is 8-bit clean: +strings can contain any 8-bit character, +including embedded zeros ('\0') (see §2.1). + + +

+Lua can call (and manipulate) functions written in Lua and +functions written in C +(see §2.5.8). + + +

+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 (see §2.11). +Do not confuse Lua threads with operating-system threads. +Lua supports coroutines on all systems, +even those that do not support threads. + + +

+The type table implements associative arrays, +that is, arrays that can be indexed not only with numbers, +but with any value (except nil). +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 can 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 §2.5.7). + + +

+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 can contain functions. +Thus tables can also carry methods (see §2.5.9). + + +

+Tables, functions, threads, and (full) 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. + + + +

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 +this string to a number, following the usual conversion 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 over how numbers are converted to strings, +use the format function from the string library +(see string.format). + + + + + + + +

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 function's formal parameter, +which is a particular kind of local variable): + +

+	var ::= Name
+

+Name denotes identifiers, as defined in §2.1. + + +

+Any variable is assumed to be global unless explicitly declared +as a 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 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.) + + +

+The syntax var.Name is just syntactic sugar for +var["Name"]: + +

+	var ::= prefixexp `.´ Name
+
+ +

+All global variables live as fields in ordinary Lua tables, +called environment tables or simply +environments (see §2.9). +Each function has its own reference to an environment, +so that all global variables in this function +will refer to this environment table. +When a function is created, +it inherits the environment from the function that created it. +To get the environment table of a Lua function, +you call getfenv. +To replace it, +you call setfenv. +(You can only manipulate the environment of C functions +through the debug library; (see §5.9).) + + +

+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. +(See §2.8 for a complete description of the +gettable_event function. +This function is not defined or callable in Lua. +Similarly, the _env variable is not defined in Lua. +We use them 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 +assignments, control structures, function calls, +and variable declarations. + + + +

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 [`;´]}
+

+There are no empty statements and thus ';;' is not legal. + + +

+Lua handles a chunk as the body of an anonymous function +with a variable number of arguments +(see §2.5.9). +As such, chunks can define local variables, +receive arguments, and return values. + + +

+A chunk can be stored in a file or in a string inside the host program. +To execute a chunk, +Lua first pre-compiles the chunk into instructions for a virtual machine, +and then it executes the compiled code +with an interpreter for the virtual machine. + + +

+Chunks can 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 the same as a chunk: + +

+	block ::= chunk
+
+ +

+A block can 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 assignments. +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 ::= varlist `=´ explist
+	varlist ::= var {`,´ var}
+	explist ::= 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 call enter 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
+

+exchanges the values of x and y, +and + +

+     x, y, z = y, z, x
+

+cyclically permutes the values of x, y, and z. + + +

+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 of a +control structure can 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). + + +

+In the repeat–until loop, +the inner block does not end at the until keyword, +but only after the condition. +So, the condition can refer to local variables +declared inside the loop block. + + +

+The return statement is used to return values +from a function or a chunk (which is just a function). + +Functions and chunks can return more than one value, +and so the syntax for the return statement is + +

+	stat ::= return [explist]
+
+ +

+The break statement is 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. + + +

+The 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. + + + + + +

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 v = e1, e2, e3 do block end
+

+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 <= limit) or (step <= 0 and var >= limit) do
+         local v = var
+         block
+         var = var + step
+       end
+     end
+

+Note the following: + +

+ +

+The generic for statement works over functions, +called iterators. +On each iteration, the iterator function is called to produce a new value, +stopping when this new value is nil. +The generic for loop has the following syntax: + +

+	stat ::= for namelist in explist do block end
+	namelist ::= Name {`,´ Name}
+

+A for statement like + +

+     for var_1, ···, var_n in explist do block end
+

+is equivalent to the code: + +

+     do
+       local f, s, var = explist
+       while true do
+         local var_1, ···, var_n = f(s, var)
+         var = var_1
+         if var == nil then break end
+         block
+       end
+     end
+

+Note the following: + +

+ + + + +

2.4.6 - Function Calls as Statements

+To allow possible side-effects, +function calls can be executed as statements: + +

+	stat ::= functioncall
+

+In this case, all returned values are thrown away. +Function calls are explained in §2.5.8. + + + + + +

2.4.7 - Local Declarations

+Local variables can be declared anywhere inside a block. +The declaration can include an initial assignment: + +

+	stat ::= local namelist [`=´ explist]
+

+If present, an initial assignment has the same semantics +of a multiple assignment (see §2.4.3). +Otherwise, all variables are initialized with nil. + + +

+A chunk is also a block (see §2.4.1), +and so local variables can be declared in a chunk outside any explicit block. +The scope of such local variables extends until the end of the chunk. + + +

+The visibility rules for local variables are explained in §2.6. + + + + + + + +

2.5 - Expressions

+ +

+The basic expressions in Lua are the following: + +

+	exp ::= prefixexp
+	exp ::= nil | false | true
+	exp ::= Number
+	exp ::= String
+	exp ::= function
+	exp ::= tableconstructor
+	exp ::= `...´
+	exp ::= exp binop exp
+	exp ::= unop exp
+	prefixexp ::= var | functioncall | `(´ exp `)´
+
+ +

+Numbers and literal strings are explained in §2.1; +variables are explained in §2.3; +function definitions are explained in §2.5.9; +function calls are explained in §2.5.8; +table constructors are explained in §2.5.7. +Vararg expressions, +denoted by three dots ('...'), can only be used when +directly inside a vararg function; +they are explained in §2.5.9. + + +

+Binary operators comprise arithmetic operators (see §2.5.1), +relational operators (see §2.5.2), logical operators (see §2.5.3), +and the concatenation operator (see §2.5.4). +Unary operators comprise the unary minus (see §2.5.1), +the unary not (see §2.5.3), +and the unary length operator (see §2.5.5). + + +

+Both function calls and vararg expressions can result in multiple values. +If an expression is used as a statement +(only possible for function calls (see §2.4.6)), +then its return list is adjusted to zero elements, +thus discarding all returned values. +If an expression is used as the last (or the only) element +of a list of expressions, +then no adjustment is made +(unless the call is enclosed in parentheses). +In all other contexts, +Lua adjusts the result list to one element, +discarding all values except the first one. + + +

+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 results from f()
+     a,b,c = f(), x     -- f() is adjusted to 1 result (c gets nil)
+     a,b = ...          -- a gets the first vararg parameter, b gets
+                        -- the second (both a and b can get nil if there
+                        -- is no corresponding vararg parameter)
+     
+     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 results from f()
+     return ...         -- returns all received vararg parameters
+     return x,y,f()     -- returns x, y, and all results from f()
+     {f()}              -- creates a list with all results from f()
+     {...}              -- creates a list with all vararg parameters
+     {f(), nil}         -- f() is adjusted to 1 result
+
+ +

+Any expression enclosed in parentheses always results in only one value. +Thus, +(f(x,y,z)) is always a single value, +even if f returns several values. +(The value of (f(x,y,z)) is the first value returned by f +or nil if f does not return any values.) + + + +

2.5.1 - Arithmetic Operators

+Lua supports the usual arithmetic operators: +the binary + (addition), +- (subtraction), * (multiplication), +/ (division), % (modulo), and ^ (exponentiation); +and unary - (negation). +If the operands are numbers, or strings that can be converted to +numbers (see §2.2.1), +then all operations have the usual meaning. +Exponentiation works for any exponent. +For instance, x^(-0.5) computes the inverse of the square root of x. +Modulo is defined as + +

+     a % b == a - math.floor(a/b)*b
+

+That is, it is the remainder of a division that rounds +the quotient towards minus infinity. + + + + + +

2.5.2 - Relational Operators

+The relational operators in Lua are + +

+     ==    ~=    <     >     <=    >=
+

+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, thread, or function), +this new object is different from any previously existing object. + + +

+You can change the way that Lua compares tables and userdata +by 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). +A comparison a > b is translated to b < a +and a >= b is translated to b <= a. + + + + + +

2.5.3 - Logical Operators

+The logical operators in Lua are +and, or, and 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 negation operator not always returns 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. +Here are some examples: + +

+     10 or 20            --> 10
+     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
+

+(In this manual, +--> indicates the result of the preceding expression.) + + + + + +

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 - The Length Operator

+ +

+The length operator is denoted by the unary operator #. +The length of a string is its number of bytes +(that is, the usual meaning of string length when each +character is one byte). + + +

+The length of a table t is defined to be any +integer index n +such that t[n] is not nil and t[n+1] is nil; +moreover, if t[1] is nil, n can be zero. +For a regular array, with non-nil values from 1 to a given n, +its length is exactly that n, +the index of its last value. +If the array has "holes" +(that is, nil values between other non-nil values), +then #t can be any of the indices that +directly precedes a nil value +(that is, it may consider any such nil value as the end of +the array). + + + + + +

2.5.6 - Precedence

+Operator precedence in Lua follows the table below, +from lower to higher priority: + +

+     or
+     and
+     <     >     <=    >=    ~=    ==
+     ..
+     +     -
+     *     /     %
+     not   #     - (unary)
+     ^
+

+As usual, +you can use parentheses to change the precedences of an expression. +The concatenation ('..') and exponentiation ('^') +operators are right associative. +All other binary operators are left associative. + + + + + +

2.5.7 - Table Constructors

+Table constructors are expressions that create tables. +Every time a constructor is evaluated, a new table is created. +A constructor can be used to create an empty table +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 t = {}
+       t[f(1)] = g
+       t[1] = "x"         -- 1st exp
+       t[2] = "y"         -- 2nd exp
+       t.x = 1            -- t["x"] = 1
+       t[3] = f(x)        -- 3rd exp
+       t[30] = 23
+       t[4] = 45          -- 4th exp
+       a = t
+     end
+
+ +

+If the last field in the list has the form exp +and the expression is a function call or a vararg expression, +then all values returned by this expression enter the list consecutively +(see §2.5.8). +To avoid this, +enclose the function call or the vararg expression +in parentheses (see §2.5). + + +

+The field list can have an optional trailing separator, +as a convenience for machine-generated code. + + + + + +

2.5.8 - 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 this function is called +with the given arguments. +Otherwise, the prefixexp "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(args) +is syntactic sugar for v.name(v,args), +except that v is evaluated only once. + + +

+Arguments have the following syntax: + +

+	args ::= `(´ [explist] `)´
+	args ::= tableconstructor
+	args ::= String
+

+All argument expressions are evaluated before the call. +A call of the form f{fields} is +syntactic sugar for f({fields}); +that is, the argument list is a single new table. +A call of the form f'string' +(or f"string" or f[[string]]) +is syntactic sugar for f('string'); +that is, the argument list is a single literal string. + + +

+As an exception to the free-format syntax of Lua, +you cannot put a line break before the '(' in a function call. +This restriction avoids some ambiguities in the language. +If you write + +

+     a = f
+     (g).x(a)
+

+Lua would see that as a single statement, 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 return exactly +the returns of the called function. +So, none of the following examples are tail 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
+
+ + + + +

2.5.9 - Function Definitions

+ +

+The syntax for function definition is + +

+	function ::= function funcbody
+	funcbody ::= `(´ [parlist] `)´ 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 () body end
+

+translates to + +

+     f = function () body end
+

+The statement + +

+     function t.a.b.c.f () body end
+

+translates to + +

+     t.a.b.c.f = function () body end
+

+The statement + +

+     local function f () body end
+

+translates to + +

+     local f; f = function () body end
+

+not to + +

+     local f = function () body end
+

+(This only makes a difference when the body of the function +contains references to f.) + + +

+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 +can refer to different external local variables +and can have different environment tables. + + +

+Parameters act as local variables that are +initialized with the argument values: + +

+	parlist ::= namelist [`,´ `...´] | `...´
+

+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 and supplies them +to the function through a vararg expression, +which is also written as three dots. +The value of this expression is a list of all actual extra arguments, +similar to a function with multiple results. +If a vararg expression is used inside another expression +or in the middle of a list of expressions, +then its return list is adjusted to one element. +If the expression is used as the last element of a list of expressions, +then no adjustment is made +(unless that last expression is enclosed in parentheses). + + +

+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 and +to the vararg expression: + +

+     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, ... -->  (nothing)
+     g(3, 4)          a=3, b=4,   ... -->  (nothing)
+     g(3, 4, 5, 8)    a=3, b=4,   ... -->  5  8
+     g(5, r())        a=5, b=1,   ... -->  2  3
+
+ +

+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 (params) body end
+

+is syntactic sugar for + +

+     t.a.b.c.f = function (self, params) body end
+
+ + + + + + +

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. +Consider the following example: + +

+     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. +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 embedded extension language, +all Lua actions start from C code in the host program +calling a function from the Lua library (see lua_pcall). +Whenever an error occurs during Lua compilation or execution, +control returns to C, +which can take appropriate measures +(such as printing an error message). + + +

+Lua code can explicitly generate an error by calling the +error function. +If you need to catch errors in Lua, +you can use the pcall function. + + + + + +

2.8 - Metatables

+ +

+Every value in Lua can have a metatable. +This metatable is an ordinary Lua table +that defines the behavior of the original value +under certain special operations. +You can change several aspects of the behavior +of operations over a value by setting specific fields in its metatable. +For instance, when a non-numeric value is the operand of an addition, +Lua checks for a function in the field "__add" in its metatable. +If it finds one, +Lua calls this 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 the metatable of any value +through the getmetatable function. + + +

+You can replace the metatable of tables +through the setmetatable +function. +You cannot change the metatable of other types from Lua +(except by using the debug library); +you must use the C API for that. + + +

+Tables and full userdata have individual metatables +(although multiple tables and userdata can share their metatables). +Values of all other types share one single metatable per type; +that is, there is one single metatable for all numbers, +one for all strings, etc. + + +

+A metatable controls how an object behaves in arithmetic operations, +order comparisons, concatenation, length operation, and indexing. +A metatable also can define a function to be called when a userdata +is garbage collected. +For each of these operations Lua associates a specific key +called an event. +When Lua performs one of these operations over a value, +it checks whether this value 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 the 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(getmetatable(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). + + + +

+ + + + +

2.9 - Environments

+ +

+Besides metatables, +objects of types thread, function, and userdata +have another table associated with them, +called their environment. +Like metatables, environments are regular tables and +multiple objects can share the same environment. + + +

+Threads are created sharing the environment of the creating thread. +Userdata and C functions are created sharing the environment +of the creating C function. +Non-nested Lua functions +(created by loadfile, loadstring or load) +are created sharing the environment of the creating thread. +Nested Lua functions are created sharing the environment of +the creating Lua function. + + +

+Environments associated with userdata have no meaning for Lua. +It is only a convenience feature for programmers to associate a table to +a userdata. + + +

+Environments associated with threads are called +global environments. +They are used as the default environment for threads and +non-nested Lua functions created by the thread +and can be directly accessed by C code (see §3.3). + + +

+The environment associated with a C function can be directly +accessed by C code (see §3.3). +It is used as the default environment for other C functions +and userdata created by the function. + + +

+Environments associated with Lua functions are used to resolve +all accesses to global variables within the function (see §2.3). +They are used as the default environment for nested Lua functions +created by the function. + + +

+You can change the environment of a Lua function or the +running thread by calling setfenv. +You can get the environment of a Lua function or the running thread +by calling getfenv. +To manipulate the environment of other objects +(userdata, C functions, other threads) you must +use the C API. + + + + + +

2.10 - Garbage Collection

+ +

+Lua performs automatic memory management. +This means that +you have to worry neither about allocating memory for new objects +nor about freeing it when the objects are no longer needed. +Lua manages memory automatically by running +a garbage collector from time to time +to collect all dead objects +(that is, objects that are no longer accessible from Lua). +All memory used by Lua is subject to automatic management: +tables, userdata, functions, threads, strings, etc. + + +

+Lua implements an incremental mark-and-sweep collector. +It uses two numbers to control its garbage-collection cycles: +the garbage-collector pause and +the garbage-collector step multiplier. +Both use percentage points as units +(so that a value of 100 means an internal value of 1). + + +

+The garbage-collector pause +controls how long the collector waits before starting a new cycle. +Larger values make the collector less aggressive. +Values smaller than 100 mean the collector will not wait to +start a new cycle. +A value of 200 means that the collector waits for the total memory in use +to double before starting a new cycle. + + +

+The step multiplier +controls the relative speed of the collector relative to +memory allocation. +Larger values make the collector more aggressive but also increase +the size of each incremental step. +Values smaller than 100 make the collector too slow and +can result in the collector never finishing a cycle. +The default, 200, means that the collector runs at "twice" +the speed of memory allocation. + + +

+You can change these numbers by calling lua_gc in C +or collectgarbage in Lua. +With these functions you can also control +the collector directly (e.g., stop and restart it). + + + +

2.10.1 - Garbage-Collection Metamethods

+ +

+Using the C API, +you can set garbage-collector metamethods for userdata (see §2.8). +These metamethods are also called finalizers. +Finalizers allow you to coordinate Lua's garbage collection +with external resource management +(such as closing files, network or database connections, +or freeing your own memory). + + +

+Garbage userdata with a field __gc in their metatables are not +collected immediately by the garbage collector. +Instead, Lua puts them in a list. +After the collection, +Lua does the equivalent of the following function +for each userdata in that list: + +

+     function gc_event (udata)
+       local h = metatable(udata).__gc
+       if h then
+         h(udata)
+       end
+     end
+
+ +

+At the end of each garbage-collection cycle, +the finalizers for userdata are called in reverse +order of their creation, +among those collected in that cycle. +That is, the first finalizer to be called is the one associated +with the userdata created last in the program. +The userdata itself is freed only in the next garbage-collection cycle. + + + + + +

2.10.2 - Weak Tables

+ +

+A weak table is a table whose elements are +weak references. +A weak reference is ignored by the garbage collector. +In other words, +if the only references to an object are weak references, +then the garbage collector will collect this object. + + +

+A weak table can have weak keys, weak values, or both. +A table with weak keys allows the collection of its keys, +but prevents the collection of its values. +A table with both weak keys and weak values allows the collection of +both keys and values. +In any case, if either the key or the value is collected, +the whole pair is removed from the table. +The weakness of a table is controlled by the +__mode field of its metatable. +If the __mode field is a string containing the character 'k', +the keys in the table are weak. +If __mode contains 'v', +the values in the table are weak. + + +

+After you use a table as a metatable, +you should not change the value of its __mode field. +Otherwise, the weak behavior of the tables controlled by this +metatable is undefined. + + + + + + + +

2.11 - Coroutines

+ +

+Lua supports coroutines, +also called collaborative multithreading. +A coroutine in Lua represents an independent thread of execution. +Unlike threads in multithread systems, however, +a coroutine only suspends its execution by explicitly calling +a yield function. + + +

+You create a coroutine with a call to coroutine.create. +Its sole argument is a function +that is the main function of the coroutine. +The create function only creates a new coroutine and +returns a handle to it (an object of type thread); +it does not start the coroutine execution. + + +

+When you first call coroutine.resume, +passing as its first argument +a thread returned by coroutine.create, +the coroutine starts its execution, +at the first line of its main function. +Extra arguments passed to coroutine.resume are passed on +to the coroutine main function. +After the coroutine starts running, +it runs until it terminates or yields. + + +

+A coroutine can terminate its execution in two ways: +normally, when its main function returns +(explicitly or implicitly, after the last instruction); +and abnormally, if there is an unprotected error. +In the first case, coroutine.resume returns true, +plus any values returned by the coroutine main function. +In case of errors, coroutine.resume returns false +plus an error message. + + +

+A coroutine yields by calling coroutine.yield. +When a coroutine yields, +the corresponding coroutine.resume returns immediately, +even if the yield happens inside nested function calls +(that is, not in the main function, +but in a function directly or indirectly called by the main function). +In the case of a yield, coroutine.resume also returns true, +plus any values passed to coroutine.yield. +The next time you resume the same coroutine, +it continues its execution from the point where it yielded, +with the call to coroutine.yield returning any extra +arguments passed to coroutine.resume. + + +

+Like coroutine.create, +the coroutine.wrap function also creates a coroutine, +but instead of returning the coroutine itself, +it returns a function that, when called, resumes the coroutine. +Any arguments passed to this function +go as extra arguments to coroutine.resume. +coroutine.wrap returns all the values returned by coroutine.resume, +except the first one (the boolean error code). +Unlike coroutine.resume, +coroutine.wrap does not catch errors; +any error is propagated to the caller. + + +

+As an example, +consider the following code: + +

+     function foo (a)
+       print("foo", a)
+       return coroutine.yield(2*a)
+     end
+     
+     co = coroutine.create(function (a,b)
+           print("co-body", a, b)
+           local r = foo(a+1)
+           print("co-body", r)
+           local r, s = coroutine.yield(a+b, a-b)
+           print("co-body", r, s)
+           return b, "end"
+     end)
+            
+     print("main", coroutine.resume(co, 1, 10))
+     print("main", coroutine.resume(co, "r"))
+     print("main", coroutine.resume(co, "x", "y"))
+     print("main", coroutine.resume(co, "x", "y"))
+

+When you run it, it produces the following output: + +

+     co-body 1       10
+     foo     2
+     
+     main    true    4
+     co-body r
+     main    true    11      -9
+     co-body x       y
+     main    true    10      end
+     main    false   cannot resume dead coroutine
+
+ + + + +

3 - The Application Program Interface

+ +

+ +This section describes the C API for Lua, that is, +the set of C functions available to the host program to communicate +with Lua. +All API functions and related types and constants +are declared in the header file lua.h. + + +

+Even when we use the term "function", +any facility in the API may be provided as a macro instead. +All such macros use each of their arguments exactly once +(except for the first argument, which is always a Lua state), +and so do not generate any hidden side-effects. + + +

+As in most C libraries, +the Lua API functions do not check their arguments for validity or consistency. +However, you can change this behavior by compiling Lua +with a proper definition for the macro luai_apicheck, +in file luaconf.h. + + + +

3.1 - The Stack

+ +

+Lua uses a virtual stack to pass values to and from C. +Each element in this stack represents a Lua value +(nil, number, string, etc.). + + +

+Whenever Lua calls C, the called function gets a new stack, +which is independent of previous stacks and of stacks of +C functions that are still active. +This stack initially contains any arguments to the C function +and it is where the C function pushes its results +to be returned to the caller (see lua_CFunction). + + +

+For convenience, +most query operations in the API do not follow a strict stack discipline. +Instead, they can refer to any element in the stack +by using an index: +A positive index represents an absolute stack position +(starting at 1); +a negative index represents an offset relative to the top of the stack. +More specifically, if the stack has n elements, +then index 1 represents the first element +(that is, the element that was pushed onto the stack first) +and +index n represents the last element; +index -1 also represents the last element +(that is, the element at the top) +and index -n represents the first element. +We say that an index is valid +if it lies between 1 and the stack top +(that is, if 1 ≤ abs(index) ≤ top). + + + + + + +

3.2 - Stack Size

+ +

+When you interact with Lua API, +you are responsible for ensuring consistency. +In particular, +you are responsible for controlling stack overflow. +You can use the function lua_checkstack +to grow the stack size. + + +

+Whenever Lua calls C, +it ensures that at least LUA_MINSTACK stack positions are available. +LUA_MINSTACK is defined as 20, +so that usually you do not have to worry about stack space +unless your code has loops pushing elements onto the stack. + + +

+Most query functions accept as indices any value inside the +available stack space, that is, indices up to the maximum stack size +you have set through lua_checkstack. +Such indices are called acceptable indices. +More formally, we define an acceptable index +as follows: + +

+     (index < 0 && abs(index) <= top) ||
+     (index > 0 && index <= stackspace)
+

+Note that 0 is never an acceptable index. + + + + + +

3.3 - Pseudo-Indices

+ +

+Unless otherwise noted, +any function that accepts valid indices can also be called with +pseudo-indices, +which represent some Lua values that are accessible to C code +but which are not in the stack. +Pseudo-indices are used to access the thread environment, +the function environment, +the registry, +and the upvalues of a C function (see §3.4). + + +

+The thread environment (where global variables live) is +always at pseudo-index LUA_GLOBALSINDEX. +The environment of the running C function is always +at pseudo-index LUA_ENVIRONINDEX. + + +

+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_getfield(L, LUA_GLOBALSINDEX, varname);
+
+ + + + +

3.4 - C Closures

+ +

+When a C function is created, +it is possible to associate some values with it, +thus creating a C closure; +these values are called upvalues and are +accessible to the function whenever it is called +(see lua_pushcclosure). + + +

+Whenever a C function is called, +its upvalues are located at specific pseudo-indices. +These pseudo-indices are produced by the macro +lua_upvalueindex. +The first value associated with a function is at position +lua_upvalueindex(1), and so on. +Any access to lua_upvalueindex(n), +where n is greater than the number of upvalues of the +current function (but not greater than 256), +produces an acceptable (but invalid) index. + + + + + +

3.5 - Registry

+ +

+Lua provides a registry, +a pre-defined table that can be used by any C code to +store whatever Lua value it needs to store. +This table is always located at pseudo-index +LUA_REGISTRYINDEX. +Any C library can store data into this table, +but it should take care to choose keys different from those used +by other libraries, to avoid collisions. +Typically, you should use as key a string containing your library name +or a light userdata with the address of a C object in your code. + + +

+The integer keys in the registry are used by the reference mechanism, +implemented by the auxiliary library, +and therefore should not be used for other purposes. + + + + + +

3.6 - Error Handling in C

+ +

+Internally, Lua uses the C longjmp facility to handle errors. +(You can also choose to use exceptions if you use C++; +see file luaconf.h.) +When Lua faces any error +(such as memory allocation errors, type errors, syntax errors, +and runtime errors) +it raises an error; +that is, it does a long jump. +A protected environment uses setjmp +to set a recover point; +any error jumps to the most recent active recover point. + + +

+Most functions in the API can throw an error, +for instance due to a memory allocation error. +The documentation for each function indicates whether +it can throw errors. + + +

+Inside a C function you can throw an error by calling lua_error. + + + + + +

3.7 - Functions and Types

+ +

+Here we list all functions and types from the C API in +alphabetical order. +Each function has an indicator like this: +[-o, +p, x] + + +

+The first field, o, +is how many elements the function pops from the stack. +The second field, p, +is how many elements the function pushes onto the stack. +(Any function always pushes its results after popping its arguments.) +A field in the form x|y means the function can push (or pop) +x or y elements, +depending on the situation; +an interrogation mark '?' means that +we cannot know how many elements the function pops/pushes +by looking only at its arguments +(e.g., they may depend on what is on the stack). +The third field, x, +tells whether the function may throw errors: +'-' means the function never throws any error; +'m' means the function may throw an error +only due to not enough memory; +'e' means the function may throw other kinds of errors; +'v' means the function may throw an error on purpose. + + + +

lua_Alloc

+
typedef void * (*lua_Alloc) (void *ud,
+                             void *ptr,
+                             size_t osize,
+                             size_t nsize);
+ +

+The type of the memory-allocation function used by Lua states. +The allocator function must provide a +functionality similar to realloc, +but not exactly the same. +Its arguments are +ud, an opaque pointer passed to lua_newstate; +ptr, a pointer to the block being allocated/reallocated/freed; +osize, the original size of the block; +nsize, the new size of the block. +ptr is NULL if and only if osize is zero. +When nsize is zero, the allocator must return NULL; +if osize is not zero, +it should free the block pointed to by ptr. +When nsize is not zero, the allocator returns NULL +if and only if it cannot fill the request. +When nsize is not zero and osize is zero, +the allocator should behave like malloc. +When nsize and osize are not zero, +the allocator behaves like realloc. +Lua assumes that the allocator never fails when +osize >= nsize. + + +

+Here is a simple implementation for the allocator function. +It is used in the auxiliary library by luaL_newstate. + +

+     static void *l_alloc (void *ud, void *ptr, size_t osize,
+                                                size_t nsize) {
+       (void)ud;  (void)osize;  /* not used */
+       if (nsize == 0) {
+         free(ptr);
+         return NULL;
+       }
+       else
+         return realloc(ptr, nsize);
+     }
+

+This code assumes +that free(NULL) has no effect and that +realloc(NULL, size) is equivalent to malloc(size). +ANSI C ensures both behaviors. + + + + + +

lua_atpanic

+[-0, +0, -] +

lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);
+ +

+Sets a new panic function and returns the old one. + + +

+If an error happens outside any protected environment, +Lua calls a panic function +and then calls exit(EXIT_FAILURE), +thus exiting the host application. +Your panic function can avoid this exit by +never returning (e.g., doing a long jump). + + +

+The panic function can access the error message at the top of the stack. + + + + + +

lua_call

+[-(nargs + 1), +nresults, e] +

void lua_call (lua_State *L, int nargs, int nresults);
+ +

+Calls a function. + + +

+To call a function you must use 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 you call lua_call; +nargs is the number of arguments that you pushed onto the stack. +All arguments and the function value are popped from the stack +when the function is called. +The function results are pushed onto the stack when the function returns. +The number of results is adjusted to nresults, +unless nresults is LUA_MULTRET. +In this 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 of the stack. + + +

+Any error inside the called function is propagated upwards +(with a longjmp). + + +

+The following example shows how the host program can do the +equivalent to this Lua code: + +

+     a = f("how", t.x, 14)
+

+Here it is in C: + +

+     lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */
+     lua_pushstring(L, "how");                        /* 1st argument */
+     lua_getfield(L, LUA_GLOBALSINDEX, "t");   /* table to be indexed */
+     lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
+     lua_remove(L, -2);                  /* remove 't' from the stack */
+     lua_pushinteger(L, 14);                          /* 3rd argument */
+     lua_call(L, 3, 1);     /* call 'f' with 3 arguments and 1 result */
+     lua_setfield(L, LUA_GLOBALSINDEX, "a");        /* set global 'a' */
+

+Note that the code above is "balanced": +at its end, the stack is back to its original configuration. +This is considered good programming practice. + + + + + +

lua_CFunction

+
typedef int (*lua_CFunction) (lua_State *L);
+ +

+Type for C functions. + + +

+In order to communicate properly with Lua, +a C function must use 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, +lua_gettop(L) returns the number of arguments received by the function. +The first argument (if any) is at index 1 +and its last argument is at index lua_gettop(L). +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 +discarded 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 <= n; i++) {
+         if (!lua_isnumber(L, i)) {
+           lua_pushstring(L, "incorrect argument");
+           lua_error(L);
+         }
+         sum += lua_tonumber(L, i);
+       }
+       lua_pushnumber(L, sum/n);        /* first result */
+       lua_pushnumber(L, sum);         /* second result */
+       return 2;                   /* number of results */
+     }
+
+ + + + +

lua_checkstack

+[-0, +0, m] +

int lua_checkstack (lua_State *L, int extra);
+ +

+Ensures that there are at least extra free stack slots in the stack. +It returns false if it cannot grow the stack to that size. +This function never shrinks the stack; +if the stack is already larger than the new size, +it is left unchanged. + + + + + +

lua_close

+[-0, +0, -] +

void lua_close (lua_State *L);
+ +

+Destroys all objects in the given Lua state +(calling the corresponding garbage-collection metamethods, if any) +and frees all dynamic memory used by this state. +On several platforms, you may not need to call this function, +because all resources are naturally released when the host program ends. +On the other hand, long-running programs, +such as a daemon or a web server, +might need to release states as soon as they are not needed, +to avoid growing too large. + + + + + +

lua_concat

+[-n, +1, e] +

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 the single value on the stack +(that is, the function does nothing); +if n is 0, the result is the empty string. +Concatenation is performed following the usual semantics of Lua +(see §2.5.4). + + + + + +

lua_cpcall

+[-0, +(0|1), -] +

int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);
+ +

+Calls the C function func in protected mode. +func starts with only one element in its stack, +a light userdata containing ud. +In case of errors, +lua_cpcall returns the same error codes as lua_pcall, +plus the error object on the top of the stack; +otherwise, it returns zero, and does not change the stack. +All values returned by func are discarded. + + + + + +

lua_createtable

+[-0, +1, m] +

void lua_createtable (lua_State *L, int narr, int nrec);
+ +

+Creates a new empty table and pushes it onto the stack. +The new table has space pre-allocated +for narr array elements and nrec non-array elements. +This pre-allocation is useful when you know exactly how many elements +the table will have. +Otherwise you can use the function lua_newtable. + + + + + +

lua_dump

+[-0, +0, m] +

int lua_dump (lua_State *L, lua_Writer writer, void *data);
+ +

+Dumps a function as a binary chunk. +Receives a Lua function on the top of the stack +and produces a binary chunk that, +if loaded again, +results in a function equivalent to the one dumped. +As it produces parts of the chunk, +lua_dump calls function writer (see lua_Writer) +with the given data +to write them. + + +

+The value returned is the error code returned by the last +call to the writer; +0 means no errors. + + +

+This function does not pop the Lua function from the stack. + + + + + +

lua_equal

+[-0, +0, e] +

int lua_equal (lua_State *L, int index1, int index2);
+ +

+Returns 1 if the two values in acceptable indices index1 and +index2 are equal, +following the semantics of the Lua == operator +(that is, may call metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices is non valid. + + + + + +

lua_error

+[-1, +0, v] +

int lua_error (lua_State *L);
+ +

+Generates a Lua error. +The error message (which can actually be a Lua value of any type) +must be on the stack top. +This function does a long jump, +and therefore never returns. +(see luaL_error). + + + + + +

lua_gc

+[-0, +0, e] +

int lua_gc (lua_State *L, int what, int data);
+ +

+Controls the garbage collector. + + +

+This function performs several tasks, +according to the value of the parameter what: + +

+ + + + +

lua_getallocf

+[-0, +0, -] +

lua_Alloc lua_getallocf (lua_State *L, void **ud);
+ +

+Returns the memory-allocation function of a given state. +If ud is not NULL, Lua stores in *ud the +opaque pointer passed to lua_newstate. + + + + + +

lua_getfenv

+[-0, +1, -] +

void lua_getfenv (lua_State *L, int index);
+ +

+Pushes onto the stack the environment table of +the value at the given index. + + + + + +

lua_getfield

+[-0, +1, e] +

void lua_getfield (lua_State *L, int index, const char *k);
+ +

+Pushes onto the stack the value t[k], +where t is the value at the given valid index. +As in Lua, this function may trigger a metamethod +for the "index" event (see §2.8). + + + + + +

lua_getglobal

+[-0, +1, e] +

void lua_getglobal (lua_State *L, const char *name);
+ +

+Pushes onto the stack the value of the global name. +It is defined as a macro: + +

+     #define lua_getglobal(L,s)  lua_getfield(L, LUA_GLOBALSINDEX, s)
+
+ + + + +

lua_getmetatable

+[-0, +(0|1), -] +

int lua_getmetatable (lua_State *L, int index);
+ +

+Pushes onto the stack the metatable of the value at the given +acceptable index. +If the index is not valid, +or if the value does not have a metatable, +the function returns 0 and pushes nothing on the stack. + + + + + +

lua_gettable

+[-1, +1, e] +

void lua_gettable (lua_State *L, int index);
+ +

+Pushes onto the stack the value t[k], +where t is the value at the given valid index +and k is the value at the top of the stack. + + +

+This function pops the key from the stack +(putting the resulting value in its place). +As in Lua, this function may trigger a metamethod +for the "index" event (see §2.8). + + + + + +

lua_gettop

+[-0, +0, -] +

int lua_gettop (lua_State *L);
+ +

+Returns the index of the top element in the stack. +Because indices start at 1, +this result is equal to the number of elements in the stack +(and so 0 means an empty stack). + + + + + +

lua_insert

+[-1, +1, -] +

void lua_insert (lua_State *L, int index);
+ +

+Moves the top element into the given valid index, +shifting up the elements above this index to open space. +Cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +

lua_Integer

+
typedef ptrdiff_t lua_Integer;
+ +

+The type used by the Lua API to represent integral values. + + +

+By default it is a ptrdiff_t, +which is usually the largest signed integral type the machine handles +"comfortably". + + + + + +

lua_isboolean

+[-0, +0, -] +

int lua_isboolean (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index has type boolean, +and 0 otherwise. + + + + + +

lua_iscfunction

+[-0, +0, -] +

int lua_iscfunction (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a C function, +and 0 otherwise. + + + + + +

lua_isfunction

+[-0, +0, -] +

int lua_isfunction (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a function +(either C or Lua), and 0 otherwise. + + + + + +

lua_islightuserdata

+[-0, +0, -] +

int lua_islightuserdata (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a light userdata, +and 0 otherwise. + + + + + +

lua_isnil

+[-0, +0, -] +

int lua_isnil (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is nil, +and 0 otherwise. + + + + + +

lua_isnone

+[-0, +0, -] +

int lua_isnone (lua_State *L, int index);
+ +

+Returns 1 if the given acceptable index is not valid +(that is, it refers to an element outside the current stack), +and 0 otherwise. + + + + + +

lua_isnoneornil

+[-0, +0, -] +

int lua_isnoneornil (lua_State *L, int index);
+ +

+Returns 1 if the given acceptable index is not valid +(that is, it refers to an element outside the current stack) +or if the value at this index is nil, +and 0 otherwise. + + + + + +

lua_isnumber

+[-0, +0, -] +

int lua_isnumber (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a number +or a string convertible to a number, +and 0 otherwise. + + + + + +

lua_isstring

+[-0, +0, -] +

int lua_isstring (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a string +or a number (which is always convertible to a string), +and 0 otherwise. + + + + + +

lua_istable

+[-0, +0, -] +

int lua_istable (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a table, +and 0 otherwise. + + + + + +

lua_isthread

+[-0, +0, -] +

int lua_isthread (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a thread, +and 0 otherwise. + + + + + +

lua_isuserdata

+[-0, +0, -] +

int lua_isuserdata (lua_State *L, int index);
+ +

+Returns 1 if the value at the given acceptable index is a userdata +(either full or light), and 0 otherwise. + + + + + +

lua_lessthan

+[-0, +0, e] +

int lua_lessthan (lua_State *L, int index1, int index2);
+ +

+Returns 1 if the value at acceptable index index1 is smaller +than the value at acceptable index index2, +following the semantics of the Lua < operator +(that is, may call metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices is non valid. + + + + + +

lua_load

+[-0, +1, -] +

int lua_load (lua_State *L,
+              lua_Reader reader,
+              void *data,
+              const char *chunkname);
+ +

+Loads a Lua chunk. +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. +The return values of lua_load are: + +

+ +

+This function only loads a chunk; +it does not run it. + + +

+lua_load automatically detects whether the chunk is text or binary, +and loads it accordingly (see program luac). + + +

+The lua_load function uses a user-supplied reader function +to read the chunk (see lua_Reader). +The data argument is an opaque value passed to the reader function. + + +

+The chunkname argument gives a name to the chunk, +which is used for error messages and in debug information (see §3.8). + + + + + +

lua_newstate

+[-0, +0, -] +

lua_State *lua_newstate (lua_Alloc f, void *ud);
+ +

+Creates a new, independent state. +Returns NULL if cannot create the state +(due to lack of memory). +The argument f is the allocator function; +Lua does all memory allocation for this state through this function. +The second argument, ud, is an opaque pointer that Lua +simply passes to the allocator in every call. + + + + + +

lua_newtable

+[-0, +1, m] +

void lua_newtable (lua_State *L);
+ +

+Creates a new empty table and pushes it onto the stack. +It is equivalent to lua_createtable(L, 0, 0). + + + + + +

lua_newthread

+[-0, +1, m] +

lua_State *lua_newthread (lua_State *L);
+ +

+Creates a new thread, pushes it on the stack, +and returns a pointer to a lua_State that represents this new thread. +The new state returned by this function shares with the original state +all global objects (such as tables), +but has an independent execution stack. + + +

+There is no explicit function to close or to destroy a thread. +Threads are subject to garbage collection, +like any Lua object. + + + + + +

lua_newuserdata

+[-0, +1, m] +

void *lua_newuserdata (lua_State *L, size_t size);
+ +

+This function allocates a new block of memory with the given size, +pushes onto the stack a new full userdata with the block address, +and returns this address. + + +

+Userdata represent C values in Lua. +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). + + +

+When Lua collects a full userdata with a gc metamethod, +Lua calls the metamethod and marks the userdata as finalized. +When this userdata is collected again then +Lua frees its corresponding memory. + + + + + +

lua_next

+[-1, +(2|0), e] +

int lua_next (lua_State *L, int index);
+ +

+Pops a key from the stack, +and pushes a key-value pair from the table at the given index +(the "next" pair after the given key). +If there are no more elements in the table, +then lua_next returns 0 (and pushes nothing). + + +

+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) {
+       /* uses 'key' (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)));
+       /* removes 'value'; keeps 'key' for next iteration */
+       lua_pop(L, 1);
+     }
+
+ +

+While traversing a table, +do not call lua_tolstring directly on a key, +unless you know that the key is actually a string. +Recall that lua_tolstring changes +the value at the given index; +this confuses the next call to lua_next. + + + + + +

lua_Number

+
typedef double lua_Number;
+ +

+The type of numbers in Lua. +By default, it is double, but that can be changed in luaconf.h. + + +

+Through the configuration file you can change +Lua to operate with another type for numbers (e.g., float or long). + + + + + +

lua_objlen

+[-0, +0, -] +

size_t lua_objlen (lua_State *L, int index);
+ +

+Returns the "length" of the value at the given acceptable index: +for strings, this is the string length; +for tables, this is the result of the length operator ('#'); +for userdata, this is the size of the block of memory allocated +for the userdata; +for other values, it is 0. + + + + + +

lua_pcall

+[-(nargs + 1), +(nresults|1), -] +

int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);
+ +

+Calls a function in protected mode. + + +

+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 on 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 on the stack +is exactly the original error message. +Otherwise, errfunc is the stack index of an +error handler function. +(In the current implementation, this index cannot be a pseudo-index.) +In case of runtime errors, +this function will be called with the error message +and its return value will be the message returned on the stack 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_pop

+[-n, +0, -] +

void lua_pop (lua_State *L, int n);
+ +

+Pops n elements from the stack. + + + + + +

lua_pushboolean

+[-0, +1, -] +

void lua_pushboolean (lua_State *L, int b);
+ +

+Pushes a boolean value with value b onto the stack. + + + + + +

lua_pushcclosure

+[-n, +1, m] +

void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);
+ +

+Pushes a new C closure onto the stack. + + +

+When a C function is created, +it is possible to associate some values with it, +thus creating a C closure (see §3.4); +these values are then accessible to the function whenever it is called. +To associate values with a C function, +first these values should be pushed onto the stack +(when there are multiple values, the first value is pushed first). +Then lua_pushcclosure +is called to create and push the C function onto the stack, +with the argument n telling how many values should be +associated with the function. +lua_pushcclosure also pops these values from the stack. + + +

+The maximum value for n is 255. + + + + + +

lua_pushcfunction

+[-0, +1, m] +

void lua_pushcfunction (lua_State *L, lua_CFunction f);
+ +

+Pushes a C function onto the stack. +This function receives a pointer to a C function +and pushes onto the stack a Lua value of type function that, +when called, invokes the corresponding C function. + + +

+Any function to be registered in Lua must +follow the correct protocol to receive its parameters +and return its results (see lua_CFunction). + + +

+lua_pushcfunction is defined as a macro: + +

+     #define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)
+
+ + + + +

lua_pushfstring

+[-0, +1, m] +

const char *lua_pushfstring (lua_State *L, const char *fmt, ...);
+ +

+Pushes onto the stack a formatted string +and returns a pointer to this string. +It is similar to the C function sprintf, +but has some important differences: + +

+ + + + +

lua_pushinteger

+[-0, +1, -] +

void lua_pushinteger (lua_State *L, lua_Integer n);
+ +

+Pushes a number with value n onto the stack. + + + + + +

lua_pushlightuserdata

+[-0, +1, -] +

void lua_pushlightuserdata (lua_State *L, void *p);
+ +

+Pushes a light userdata onto the stack. + + +

+Userdata represent C values in Lua. +A light userdata represents a pointer. +It is a value (like a number): +you do not create it, it has no individual metatable, +and it is not collected (as it was never created). +A light userdata is equal to "any" +light userdata with the same C address. + + + + + +

lua_pushliteral

+[-0, +1, m] +

void lua_pushliteral (lua_State *L, const char *s);
+ +

+This macro is equivalent to lua_pushlstring, +but can be used only when s is a literal string. +In these cases, it automatically provides the string length. + + + + + +

lua_pushlstring

+[-0, +1, m] +

void lua_pushlstring (lua_State *L, const char *s, size_t len);
+ +

+Pushes the string pointed to by s with size len +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at s can be freed or reused immediately after +the function returns. +The string can contain embedded zeros. + + + + + +

lua_pushnil

+[-0, +1, -] +

void lua_pushnil (lua_State *L);
+ +

+Pushes a nil value onto the stack. + + + + + +

lua_pushnumber

+[-0, +1, -] +

void lua_pushnumber (lua_State *L, lua_Number n);
+ +

+Pushes a number with value n onto the stack. + + + + + +

lua_pushstring

+[-0, +1, m] +

void lua_pushstring (lua_State *L, const char *s);
+ +

+Pushes the zero-terminated string pointed to by s +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at s can be freed or reused immediately after +the function returns. +The string cannot contain embedded zeros; +it is assumed to end at the first zero. + + + + + +

lua_pushthread

+[-0, +1, -] +

int lua_pushthread (lua_State *L);
+ +

+Pushes the thread represented by L onto the stack. +Returns 1 if this thread is the main thread of its state. + + + + + +

lua_pushvalue

+[-0, +1, -] +

void lua_pushvalue (lua_State *L, int index);
+ +

+Pushes a copy of the element at the given valid index +onto the stack. + + + + + +

lua_pushvfstring

+[-0, +1, m] +

const char *lua_pushvfstring (lua_State *L,
+                              const char *fmt,
+                              va_list argp);
+ +

+Equivalent to lua_pushfstring, except that it receives a va_list +instead of a variable number of arguments. + + + + + +

lua_rawequal

+[-0, +0, -] +

int lua_rawequal (lua_State *L, int index1, int index2);
+ +

+Returns 1 if the two values in acceptable indices index1 and +index2 are primitively equal +(that is, without calling metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices are non valid. + + + + + +

lua_rawget

+[-1, +1, -] +

void lua_rawget (lua_State *L, int index);
+ +

+Similar to lua_gettable, but does a raw access +(i.e., without metamethods). + + + + + +

lua_rawgeti

+[-0, +1, -] +

void lua_rawgeti (lua_State *L, int index, int n);
+ +

+Pushes onto the stack the value t[n], +where t is the value at the given valid index. +The access is raw; +that is, it does not invoke metamethods. + + + + + +

lua_rawset

+[-2, +0, m] +

void lua_rawset (lua_State *L, int index);
+ +

+Similar to lua_settable, but does a raw assignment +(i.e., without metamethods). + + + + + +

lua_rawseti

+[-1, +0, m] +

void lua_rawseti (lua_State *L, int index, int n);
+ +

+Does the equivalent of t[n] = v, +where t is the value at the given valid index +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +The assignment is raw; +that is, it does not invoke metamethods. + + + + + +

lua_Reader

+
typedef const char * (*lua_Reader) (lua_State *L,
+                                    void *data,
+                                    size_t *size);
+ +

+The reader function used by lua_load. +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. +The block must exist until the reader function is called again. +To signal the end of the chunk, +the reader must return NULL or set size to zero. +The reader function may return pieces of any size greater than zero. + + + + + +

lua_register

+[-0, +0, e] +

void lua_register (lua_State *L,
+                   const char *name,
+                   lua_CFunction f);
+ +

+Sets the C function f as the new value of global name. +It is defined as a macro: + +

+     #define lua_register(L,n,f) \
+            (lua_pushcfunction(L, f), lua_setglobal(L, n))
+
+ + + + +

lua_remove

+[-1, +0, -] +

void lua_remove (lua_State *L, int index);
+ +

+Removes the element at the given valid index, +shifting down the elements above this index to fill the gap. +Cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +

lua_replace

+[-1, +0, -] +

void lua_replace (lua_State *L, int index);
+ +

+Moves the top element into the given position (and pops it), +without shifting any element +(therefore replacing the value at the given position). + + + + + +

lua_resume

+[-?, +?, -] +

int lua_resume (lua_State *L, int narg);
+ +

+Starts and resumes a coroutine in a given thread. + + +

+To start a coroutine, you first create a new thread +(see lua_newthread); +then you push onto its stack the main function plus any arguments; +then you call lua_resume, +with narg being the number of arguments. +This call returns when the coroutine suspends or finishes its execution. +When it returns, the stack contains all values passed to lua_yield, +or all values returned by the body function. +lua_resume returns +LUA_YIELD if the coroutine yields, +0 if the coroutine finishes its execution +without errors, +or an error code in case of errors (see lua_pcall). +In case of errors, +the stack is not unwound, +so you can use the debug API over it. +The error message is on the top of the stack. +To restart a coroutine, you put on its stack only the values to +be passed as results from yield, +and then call lua_resume. + + + + + +

lua_setallocf

+[-0, +0, -] +

void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);
+ +

+Changes the allocator function of a given state to f +with user data ud. + + + + + +

lua_setfenv

+[-1, +0, -] +

int lua_setfenv (lua_State *L, int index);
+ +

+Pops a table from the stack and sets it as +the new environment for the value at the given index. +If the value at the given index is +neither a function nor a thread nor a userdata, +lua_setfenv returns 0. +Otherwise it returns 1. + + + + + +

lua_setfield

+[-1, +0, e] +

void lua_setfield (lua_State *L, int index, const char *k);
+ +

+Does the equivalent to t[k] = v, +where t is the value at the given valid index +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see §2.8). + + + + + +

lua_setglobal

+[-1, +0, e] +

void lua_setglobal (lua_State *L, const char *name);
+ +

+Pops a value from the stack and +sets it as the new value of global name. +It is defined as a macro: + +

+     #define lua_setglobal(L,s)   lua_setfield(L, LUA_GLOBALSINDEX, s)
+
+ + + + +

lua_setmetatable

+[-1, +0, -] +

int lua_setmetatable (lua_State *L, int index);
+ +

+Pops a table from the stack and +sets it as the new metatable for the value at the given +acceptable index. + + + + + +

lua_settable

+[-2, +0, e] +

void lua_settable (lua_State *L, int index);
+ +

+Does the equivalent to t[k] = v, +where t is the value at the given valid index, +v is the value at the top of the stack, +and k is the value just below the top. + + +

+This function pops both the key and the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see §2.8). + + + + + +

lua_settop

+[-?, +?, -] +

void lua_settop (lua_State *L, int index);
+ +

+Accepts any acceptable index, or 0, +and sets the stack top to this index. +If the new top is larger than the old one, +then the new elements are filled with nil. +If index is 0, then all stack elements are removed. + + + + + +

lua_State

+
typedef struct lua_State lua_State;
+ +

+Opaque structure that keeps the whole state of a Lua interpreter. +The Lua library is fully reentrant: +it has no global variables. +All information about a state is kept in this structure. + + +

+A pointer to this state must be passed as the first argument to +every function in the library, except to lua_newstate, +which creates a Lua state from scratch. + + + + + +

lua_status

+[-0, +0, -] +

int lua_status (lua_State *L);
+ +

+Returns the status of the thread L. + + +

+The status can be 0 for a normal thread, +an error code if the thread finished its execution with an error, +or LUA_YIELD if the thread is suspended. + + + + + +

lua_toboolean

+[-0, +0, -] +

int lua_toboolean (lua_State *L, int index);
+ +

+Converts the Lua value at the given acceptable 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 actual boolean values, +use lua_isboolean to test the value's type.) + + + + + +

lua_tocfunction

+[-0, +0, -] +

lua_CFunction lua_tocfunction (lua_State *L, int index);
+ +

+Converts a value at the given acceptable index to a C function. +That value must be a C function; +otherwise, returns NULL. + + + + + +

lua_tointeger

+[-0, +0, -] +

lua_Integer lua_tointeger (lua_State *L, int index);
+ +

+Converts the Lua value at the given acceptable index +to the signed integral type lua_Integer. +The Lua value must be a number or a string convertible to a number +(see §2.2.1); +otherwise, lua_tointeger returns 0. + + +

+If the number is not an integer, +it is truncated in some non-specified way. + + + + + +

lua_tolstring

+[-0, +0, m] +

const char *lua_tolstring (lua_State *L, int index, size_t *len);
+ +

+Converts the Lua value at the given acceptable index to a C string. +If len is not NULL, +it also sets *len with the string length. +The Lua value must be a string or a number; +otherwise, the function returns NULL. +If the value is a number, +then lua_tolstring also +changes the actual value in the stack to a string. +(This change confuses lua_next +when lua_tolstring is applied to keys during a table traversal.) + + +

+lua_tolstring 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 can contain other zeros in its body. +Because Lua has garbage collection, +there is no guarantee that the pointer returned by lua_tolstring +will be valid after the corresponding value is removed from the stack. + + + + + +

lua_tonumber

+[-0, +0, -] +

lua_Number lua_tonumber (lua_State *L, int index);
+ +

+Converts the Lua value at the given acceptable index +to the C type lua_Number (see lua_Number). +The Lua value must be a number or a string convertible to a number +(see §2.2.1); +otherwise, lua_tonumber returns 0. + + + + + +

lua_topointer

+[-0, +0, -] +

const void *lua_topointer (lua_State *L, int index);
+ +

+Converts the value at the given acceptable index to a generic +C pointer (void*). +The value can be a userdata, a table, a thread, or a function; +otherwise, lua_topointer returns NULL. +Different objects will give different pointers. +There is no way to convert the pointer back to its original value. + + +

+Typically this function is used only for debug information. + + + + + +

lua_tostring

+[-0, +0, m] +

const char *lua_tostring (lua_State *L, int index);
+ +

+Equivalent to lua_tolstring with len equal to NULL. + + + + + +

lua_tothread

+[-0, +0, -] +

lua_State *lua_tothread (lua_State *L, int index);
+ +

+Converts the value at the given acceptable index to a Lua thread +(represented as lua_State*). +This value must be a thread; +otherwise, the function returns NULL. + + + + + +

lua_touserdata

+[-0, +0, -] +

void *lua_touserdata (lua_State *L, int index);
+ +

+If the value at the given acceptable index is a full userdata, +returns its block address. +If the value is a light userdata, +returns its pointer. +Otherwise, returns NULL. + + + + + +

lua_type

+[-0, +0, -] +

int lua_type (lua_State *L, int index);
+ +

+Returns the type of the value in the given acceptable index, +or LUA_TNONE for a non-valid index +(that is, an index to an "empty" stack position). +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, +and +LUA_TLIGHTUSERDATA. + + + + + +

lua_typename

+[-0, +0, -] +

const char *lua_typename  (lua_State *L, int tp);
+ +

+Returns the name of the type encoded by the value tp, +which must be one the values returned by lua_type. + + + + + +

lua_Writer

+
typedef int (*lua_Writer) (lua_State *L,
+                           const void* p,
+                           size_t sz,
+                           void* ud);
+ +

+The type of the writer function used by lua_dump. +Every time it produces another piece of chunk, +lua_dump calls the writer, +passing along the buffer to be written (p), +its size (sz), +and the data parameter supplied to lua_dump. + + +

+The writer returns an error code: +0 means no errors; +any other value means an error and stops lua_dump from +calling the writer again. + + + + + +

lua_xmove

+[-?, +?, -] +

void lua_xmove (lua_State *from, lua_State *to, int n);
+ +

+Exchange values between different threads of the same global state. + + +

+This function pops n values from the stack from, +and pushes them onto the stack to. + + + + + +

lua_yield

+[-?, +?, -] +

int lua_yield  (lua_State *L, int nresults);
+ +

+Yields a coroutine. + + +

+This function should only be called as the +return expression of a C function, as follows: + +

+     return lua_yield (L, nresults);
+

+When a C function calls lua_yield in that way, +the running coroutine suspends its execution, +and the call to lua_resume that started this coroutine returns. +The parameter nresults is the number of values from the stack +that are passed as results to lua_resume. + + + + + + + +

3.8 - The Debug Interface

+ +

+Lua has no built-in debugging facilities. +Instead, it offers a special interface +by means of functions and hooks. +This interface allows the construction of different +kinds of debuggers, profilers, and other tools +that need "inside information" from the interpreter. + + + +

lua_Debug

+
typedef struct lua_Debug {
+  int event;
+  const char *name;           /* (n) */
+  const char *namewhat;       /* (n) */
+  const char *what;           /* (S) */
+  const char *source;         /* (S) */
+  int currentline;            /* (l) */
+  int nups;                   /* (u) number of upvalues */
+  int linedefined;            /* (S) */
+  int lastlinedefined;        /* (S) */
+  char short_src[LUA_IDSIZE]; /* (S) */
+  /* private part */
+  other fields
+} lua_Debug;
+ +

+A structure used to carry different pieces of +information about an active function. +lua_getstack fills only the private part +of this structure, for later use. +To fill the other fields of lua_Debug with useful information, +call lua_getinfo. + + +

+The fields of lua_Debug have the following meaning: + +

+ + + + +

lua_gethook

+[-0, +0, -] +

lua_Hook lua_gethook (lua_State *L);
+ +

+Returns the current hook function. + + + + + +

lua_gethookcount

+[-0, +0, -] +

int lua_gethookcount (lua_State *L);
+ +

+Returns the current hook count. + + + + + +

lua_gethookmask

+[-0, +0, -] +

int lua_gethookmask (lua_State *L);
+ +

+Returns the current hook mask. + + + + + +

lua_getinfo

+[-(0|1), +(0|1|2), m] +

int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);
+ +

+Returns information about a specific function or function invocation. + + +

+To get information about a function invocation, +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 lua_Hook). + + +

+To get information about a function you push it onto the stack +and start the what string with the character '>'. +(In that case, +lua_getinfo pops the function in the top of the stack.) +For instance, to know in which line a function f was defined, +you can write the following code: + +

+     lua_Debug ar;
+     lua_getfield(L, LUA_GLOBALSINDEX, "f");  /* get global 'f' */
+     lua_getinfo(L, ">S", &ar);
+     printf("%d\n", ar.linedefined);
+
+ +

+Each character in the string what +selects some fields of the structure ar to be filled or +a value to be pushed on the stack: + +

+ +

+This function returns 0 on error +(for instance, an invalid option in what). + + + + + +

lua_getlocal

+[-0, +(0|1), -] +

const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);
+ +

+Gets information about a local variable of a given activation record. +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 lua_Hook). +The index n selects which local variable to inspect +(1 is the first parameter or active local variable, and so on, +until the last active local variable). +lua_getlocal pushes the variable's value onto the stack +and returns its name. + + +

+Variable names starting with '(' (open parentheses) +represent internal variables +(loop control variables, temporaries, and C function locals). + + +

+Returns NULL (and pushes nothing) +when the index is greater than +the number of active local variables. + + + + + +

lua_getstack

+[-0, +0, -] +

int lua_getstack (lua_State *L, int level, lua_Debug *ar);
+ +

+Get information about the interpreter runtime stack. + + +

+This function fills parts of a lua_Debug structure with +an identification of the activation record +of the function executing at a given level. +Level 0 is the current running function, +whereas level n+1 is the function that has called level n. +When there are no errors, lua_getstack returns 1; +when called with a level greater than the stack depth, +it returns 0. + + + + + +

lua_getupvalue

+[-0, +(0|1), -] +

const char *lua_getupvalue (lua_State *L, int funcindex, int n);
+ +

+Gets information about a closure's upvalue. +(For Lua functions, +upvalues are the external local variables that the function uses, +and that are consequently included in its closure.) +lua_getupvalue gets the index n of an upvalue, +pushes the upvalue's value onto the stack, +and returns its name. +funcindex points to the closure in the stack. +(Upvalues have no particular order, +as they are active through the whole function. +So, they are numbered in an arbitrary order.) + + +

+Returns NULL (and pushes nothing) +when the index is greater than the number of upvalues. +For C functions, this function uses the empty string "" +as a name for all upvalues. + + + + + +

lua_Hook

+
typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);
+ +

+Type for debugging hook functions. + + +

+Whenever a hook is called, its ar argument has its field +event set to the specific event that triggered the hook. +Lua identifies these events with the following constants: +LUA_HOOKCALL, LUA_HOOKRET, +LUA_HOOKTAILRET, LUA_HOOKLINE, +and LUA_HOOKCOUNT. +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 can 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, +this execution occurs without any calls to hooks. + + + + + +

lua_sethook

+[-0, +0, -] +

int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);
+ +

+Sets the debugging hook function. + + +

+Argument f is the hook function. +mask specifies on which events the hook will be called: +it is formed by a bitwise or 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: + +

+ +

+A hook is disabled by setting mask to zero. + + + + + +

lua_setlocal

+[-(0|1), +0, -] +

const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);
+ +

+Sets the value of a local variable of a given activation record. +Parameters ar and n are as in lua_getlocal +(see lua_getlocal). +lua_setlocal assigns the value at the top of the stack +to the variable and returns its name. +It also pops the value from the stack. + + +

+Returns NULL (and pops nothing) +when the index is greater than +the number of active local variables. + + + + + +

lua_setupvalue

+[-(0|1), +0, -] +

const char *lua_setupvalue (lua_State *L, int funcindex, int n);
+ +

+Sets the value of a closure's upvalue. +It assigns the value at the top of the stack +to the upvalue and returns its name. +It also pops the value from the stack. +Parameters funcindex and n are as in the lua_getupvalue +(see lua_getupvalue). + + +

+Returns NULL (and pops nothing) +when the index is greater than the number of upvalues. + + + + + + + +

4 - The Auxiliary Library

+ +

+ +The auxiliary library provides several convenient functions +to interface C with Lua. +While the basic API provides the primitive functions for all +interactions between C and Lua, +the auxiliary library provides higher-level functions for some +common tasks. + + +

+All functions from the auxiliary library +are defined in header file lauxlib.h and +have a prefix luaL_. + + +

+All functions in the auxiliary library are built on +top of the basic API, +and so they provide nothing that cannot be done with this API. + + +

+Several functions in the auxiliary library are used to +check C function arguments. +Their names are always luaL_check* or luaL_opt*. +All of these functions throw an error if the check is not satisfied. +Because the error message is formatted for arguments +(e.g., "bad argument #1"), +you should not use these functions for other stack values. + + + +

4.1 - Functions and Types

+ +

+Here we list all functions and types from the auxiliary library +in alphabetical order. + + + +

luaL_addchar

+[-0, +0, m] +

void luaL_addchar (luaL_Buffer *B, char c);
+ +

+Adds the character c to the buffer B +(see luaL_Buffer). + + + + + +

luaL_addlstring

+[-0, +0, m] +

void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);
+ +

+Adds the string pointed to by s with length l to +the buffer B +(see luaL_Buffer). +The string may contain embedded zeros. + + + + + +

luaL_addsize

+[-0, +0, m] +

void luaL_addsize (luaL_Buffer *B, size_t n);
+ +

+Adds to the buffer B (see luaL_Buffer) +a string of length n previously copied to the +buffer area (see luaL_prepbuffer). + + + + + +

luaL_addstring

+[-0, +0, m] +

void luaL_addstring (luaL_Buffer *B, const char *s);
+ +

+Adds the zero-terminated string pointed to by s +to the buffer B +(see luaL_Buffer). +The string may not contain embedded zeros. + + + + + +

luaL_addvalue

+[-1, +0, m] +

void luaL_addvalue (luaL_Buffer *B);
+ +

+Adds the value at the top of the stack +to the buffer B +(see luaL_Buffer). +Pops the value. + + +

+This is the only function on string buffers that can (and must) +be called with an extra element on the stack, +which is the value to be added to the buffer. + + + + + +

luaL_argcheck

+[-0, +0, v] +

void luaL_argcheck (lua_State *L,
+                    int cond,
+                    int narg,
+                    const char *extramsg);
+ +

+Checks whether cond is true. +If not, raises an error with the following message, +where func is retrieved from the call stack: + +

+     bad argument #<narg> to <func> (<extramsg>)
+
+ + + + +

luaL_argerror

+[-0, +0, v] +

int luaL_argerror (lua_State *L, int narg, const char *extramsg);
+ +

+Raises an error with the following message, +where func is retrieved from the call stack: + +

+     bad argument #<narg> to <func> (<extramsg>)
+
+ +

+This function never returns, +but it is an idiom to use it in C functions +as return luaL_argerror(args). + + + + + +

luaL_Buffer

+
typedef struct luaL_Buffer luaL_Buffer;
+ +

+Type for a string buffer. + + +

+A string buffer allows C code to build Lua strings piecemeal. +Its pattern of use is as follows: + +

+ +

+During its normal operation, +a string buffer uses a variable number of stack slots. +So, while using a buffer, you cannot assume that you know where +the top of the stack is. +You can use the stack between successive calls to buffer operations +as long as that use is balanced; +that is, +when you call a buffer operation, +the stack is at the same level +it was immediately after the previous buffer operation. +(The only exception to this rule is luaL_addvalue.) +After calling luaL_pushresult the stack is back to its +level when the buffer was initialized, +plus the final string on its top. + + + + + +

luaL_buffinit

+[-0, +0, -] +

void luaL_buffinit (lua_State *L, luaL_Buffer *B);
+ +

+Initializes a buffer B. +This function does not allocate any space; +the buffer must be declared as a variable +(see luaL_Buffer). + + + + + +

luaL_callmeta

+[-0, +(0|1), e] +

int luaL_callmeta (lua_State *L, int obj, const char *e);
+ +

+Calls a metamethod. + + +

+If the object at index obj has a metatable and this +metatable has a field e, +this function calls this field and passes the object as its only argument. +In this case this function returns 1 and pushes onto the +stack the value returned by the call. +If there is no metatable or no metamethod, +this function returns 0 (without pushing any value on the stack). + + + + + +

luaL_checkany

+[-0, +0, v] +

void luaL_checkany (lua_State *L, int narg);
+ +

+Checks whether the function has an argument +of any type (including nil) at position narg. + + + + + +

luaL_checkint

+[-0, +0, v] +

int luaL_checkint (lua_State *L, int narg);
+ +

+Checks whether the function argument narg is a number +and returns this number cast to an int. + + + + + +

luaL_checkinteger

+[-0, +0, v] +

lua_Integer luaL_checkinteger (lua_State *L, int narg);
+ +

+Checks whether the function argument narg is a number +and returns this number cast to a lua_Integer. + + + + + +

luaL_checklong

+[-0, +0, v] +

long luaL_checklong (lua_State *L, int narg);
+ +

+Checks whether the function argument narg is a number +and returns this number cast to a long. + + + + + +

luaL_checklstring

+[-0, +0, v] +

const char *luaL_checklstring (lua_State *L, int narg, size_t *l);
+ +

+Checks whether the function argument narg is a string +and returns this string; +if l is not NULL fills *l +with the string's length. + + +

+This function uses lua_tolstring to get its result, +so all conversions and caveats of that function apply here. + + + + + +

luaL_checknumber

+[-0, +0, v] +

lua_Number luaL_checknumber (lua_State *L, int narg);
+ +

+Checks whether the function argument narg is a number +and returns this number. + + + + + +

luaL_checkoption

+[-0, +0, v] +

int luaL_checkoption (lua_State *L,
+                      int narg,
+                      const char *def,
+                      const char *const lst[]);
+ +

+Checks whether the function argument narg is a string and +searches for this string in the array lst +(which must be NULL-terminated). +Returns the index in the array where the string was found. +Raises an error if the argument is not a string or +if the string cannot be found. + + +

+If def is not NULL, +the function uses def as a default value when +there is no argument narg or if this argument is nil. + + +

+This is a useful function for mapping strings to C enums. +(The usual convention in Lua libraries is +to use strings instead of numbers to select options.) + + + + + +

luaL_checkstack

+[-0, +0, v] +

void luaL_checkstack (lua_State *L, int sz, const char *msg);
+ +

+Grows the stack size to top + sz elements, +raising an error if the stack cannot grow to that size. +msg is an additional text to go into the error message. + + + + + +

luaL_checkstring

+[-0, +0, v] +

const char *luaL_checkstring (lua_State *L, int narg);
+ +

+Checks whether the function argument narg is a string +and returns this string. + + +

+This function uses lua_tolstring to get its result, +so all conversions and caveats of that function apply here. + + + + + +

luaL_checktype

+[-0, +0, v] +

void luaL_checktype (lua_State *L, int narg, int t);
+ +

+Checks whether the function argument narg has type t. +See lua_type for the encoding of types for t. + + + + + +

luaL_checkudata

+[-0, +0, v] +

void *luaL_checkudata (lua_State *L, int narg, const char *tname);
+ +

+Checks whether the function argument narg is a userdata +of the type tname (see luaL_newmetatable). + + + + + +

luaL_dofile

+[-0, +?, m] +

int luaL_dofile (lua_State *L, const char *filename);
+ +

+Loads and runs the given file. +It is defined as the following macro: + +

+     (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
+

+It returns 0 if there are no errors +or 1 in case of errors. + + + + + +

luaL_dostring

+[-0, +?, m] +

int luaL_dostring (lua_State *L, const char *str);
+ +

+Loads and runs the given string. +It is defined as the following macro: + +

+     (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
+

+It returns 0 if there are no errors +or 1 in case of errors. + + + + + +

luaL_error

+[-0, +0, v] +

int luaL_error (lua_State *L, const char *fmt, ...);
+ +

+Raises an error. +The error message format is given by fmt +plus any extra arguments, +following the same rules of lua_pushfstring. +It also adds at the beginning of the message the file name and +the line number where the error occurred, +if this information is available. + + +

+This function never returns, +but it is an idiom to use it in C functions +as return luaL_error(args). + + + + + +

luaL_getmetafield

+[-0, +(0|1), m] +

int luaL_getmetafield (lua_State *L, int obj, const char *e);
+ +

+Pushes onto the stack the field e from the metatable +of the object at index obj. +If the object does not have a metatable, +or if the metatable does not have this field, +returns 0 and pushes nothing. + + + + + +

luaL_getmetatable

+[-0, +1, -] +

void luaL_getmetatable (lua_State *L, const char *tname);
+ +

+Pushes onto the stack the metatable associated with name tname +in the registry (see luaL_newmetatable). + + + + + +

luaL_gsub

+[-0, +1, m] +

const char *luaL_gsub (lua_State *L,
+                       const char *s,
+                       const char *p,
+                       const char *r);
+ +

+Creates a copy of string s by replacing +any occurrence of the string p +with the string r. +Pushes the resulting string on the stack and returns it. + + + + + +

luaL_loadbuffer

+[-0, +1, m] +

int luaL_loadbuffer (lua_State *L,
+                     const char *buff,
+                     size_t sz,
+                     const char *name);
+ +

+Loads a buffer as a Lua chunk. +This function uses lua_load to load the chunk in the +buffer pointed to by buff with size sz. + + +

+This function returns the same results as lua_load. +name is the chunk name, +used for debug information and error messages. + + + + + +

luaL_loadfile

+[-0, +1, m] +

int luaL_loadfile (lua_State *L, const char *filename);
+ +

+Loads a file as a Lua chunk. +This function uses lua_load to load the chunk in the file +named filename. +If filename is NULL, +then it loads from the standard input. +The first line in the file is ignored if it starts with a #. + + +

+This function returns the same results as lua_load, +but it has an extra error code LUA_ERRFILE +if it cannot open/read the file. + + +

+As lua_load, this function only loads the chunk; +it does not run it. + + + + + +

luaL_loadstring

+[-0, +1, m] +

int luaL_loadstring (lua_State *L, const char *s);
+ +

+Loads a string as a Lua chunk. +This function uses lua_load to load the chunk in +the zero-terminated string s. + + +

+This function returns the same results as lua_load. + + +

+Also as lua_load, this function only loads the chunk; +it does not run it. + + + + + +

luaL_newmetatable

+[-0, +1, m] +

int luaL_newmetatable (lua_State *L, const char *tname);
+ +

+If the registry already has the key tname, +returns 0. +Otherwise, +creates a new table to be used as a metatable for userdata, +adds it to the registry with key tname, +and returns 1. + + +

+In both cases pushes onto the stack the final value associated +with tname in the registry. + + + + + +

luaL_newstate

+[-0, +0, -] +

lua_State *luaL_newstate (void);
+ +

+Creates a new Lua state. +It calls lua_newstate with an +allocator based on the standard C realloc function +and then sets a panic function (see lua_atpanic) that prints +an error message to the standard error output in case of fatal +errors. + + +

+Returns the new state, +or NULL if there is a memory allocation error. + + + + + +

luaL_openlibs

+[-0, +0, m] +

void luaL_openlibs (lua_State *L);
+ +

+Opens all standard Lua libraries into the given state. + + + + + +

luaL_optint

+[-0, +0, v] +

int luaL_optint (lua_State *L, int narg, int d);
+ +

+If the function argument narg is a number, +returns this number cast to an int. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

luaL_optinteger

+[-0, +0, v] +

lua_Integer luaL_optinteger (lua_State *L,
+                             int narg,
+                             lua_Integer d);
+ +

+If the function argument narg is a number, +returns this number cast to a lua_Integer. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

luaL_optlong

+[-0, +0, v] +

long luaL_optlong (lua_State *L, int narg, long d);
+ +

+If the function argument narg is a number, +returns this number cast to a long. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

luaL_optlstring

+[-0, +0, v] +

const char *luaL_optlstring (lua_State *L,
+                             int narg,
+                             const char *d,
+                             size_t *l);
+ +

+If the function argument narg is a string, +returns this string. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + +

+If l is not NULL, +fills the position *l with the results's length. + + + + + +

luaL_optnumber

+[-0, +0, v] +

lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);
+ +

+If the function argument narg is a number, +returns this number. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

luaL_optstring

+[-0, +0, v] +

const char *luaL_optstring (lua_State *L,
+                            int narg,
+                            const char *d);
+ +

+If the function argument narg is a string, +returns this string. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

luaL_prepbuffer

+[-0, +0, -] +

char *luaL_prepbuffer (luaL_Buffer *B);
+ +

+Returns an address to a space of size LUAL_BUFFERSIZE +where you can copy a string to be added to buffer B +(see luaL_Buffer). +After copying the string into this space you must call +luaL_addsize with the size of the string to actually add +it to the buffer. + + + + + +

luaL_pushresult

+[-?, +1, m] +

void luaL_pushresult (luaL_Buffer *B);
+ +

+Finishes the use of buffer B leaving the final string on +the top of the stack. + + + + + +

luaL_ref

+[-1, +0, m] +

int luaL_ref (lua_State *L, int t);
+ +

+Creates and returns a reference, +in the table at index t, +for the object at the top of the stack (and pops the object). + + +

+A reference is a unique integer key. +As long as you do not manually add integer keys into table t, +luaL_ref ensures the uniqueness of the key it returns. +You can retrieve an object referred by reference r +by calling lua_rawgeti(L, t, r). +Function luaL_unref frees a reference and its associated object. + + +

+If the object at the top of the stack is nil, +luaL_ref returns the constant LUA_REFNIL. +The constant LUA_NOREF is guaranteed to be different +from any reference returned by luaL_ref. + + + + + +

luaL_Reg

+
typedef struct luaL_Reg {
+  const char *name;
+  lua_CFunction func;
+} luaL_Reg;
+ +

+Type for arrays of functions to be registered by +luaL_register. +name is the function name and func is a pointer to +the function. +Any array of luaL_Reg must end with an sentinel entry +in which both name and func are NULL. + + + + + +

luaL_register

+[-(0|1), +1, m] +

void luaL_register (lua_State *L,
+                    const char *libname,
+                    const luaL_Reg *l);
+ +

+Opens a library. + + +

+When called with libname equal to NULL, +it simply registers all functions in the list l +(see luaL_Reg) into the table on the top of the stack. + + +

+When called with a non-null libname, +luaL_register creates a new table t, +sets it as the value of the global variable libname, +sets it as the value of package.loaded[libname], +and registers on it all functions in the list l. +If there is a table in package.loaded[libname] or in +variable libname, +reuses this table instead of creating a new one. + + +

+In any case the function leaves the table +on the top of the stack. + + + + + +

luaL_typename

+[-0, +0, -] +

const char *luaL_typename (lua_State *L, int index);
+ +

+Returns the name of the type of the value at the given index. + + + + + +

luaL_typerror

+[-0, +0, v] +

int luaL_typerror (lua_State *L, int narg, const char *tname);
+ +

+Generates an error with a message like the following: + +

+     location: bad argument narg to 'func' (tname expected, got rt)
+

+where location is produced by luaL_where, +func is the name of the current function, +and rt is the type name of the actual argument. + + + + + +

luaL_unref

+[-0, +0, -] +

void luaL_unref (lua_State *L, int t, int ref);
+ +

+Releases reference ref from the table at index t +(see luaL_ref). +The entry is removed from the table, +so that the referred object can be collected. +The reference ref is also freed to be used again. + + +

+If ref is LUA_NOREF or LUA_REFNIL, +luaL_unref does nothing. + + + + + +

luaL_where

+[-0, +1, m] +

void luaL_where (lua_State *L, int lvl);
+ +

+Pushes onto the stack a string identifying the current position +of the control at level lvl in the call stack. +Typically this string has the following format: + +

+     chunkname:currentline:
+

+Level 0 is the running function, +level 1 is the function that called the running function, +etc. + + +

+This function is used to build a prefix for error messages. + + + + + + + +

5 - Standard Libraries

+ +

+The standard Lua 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 requirements that +deserve an implementation in C (e.g., table.sort). + + +

+All libraries are implemented through the official C API +and are provided as separate C modules. +Currently, Lua has the following standard libraries: + +

+Except for the basic and package libraries, +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 should call the luaL_openlibs function, +which opens all standard libraries. +Alternatively, +it can open them individually by calling +luaopen_base (for the basic library), +luaopen_package (for the package 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 library), +luaopen_os (for the Operating System library), +and luaopen_debug (for the debug library). +These functions are declared in lualib.h +and should not be called directly: +you must call them like any other Lua C function, +e.g., by using lua_call. + + + +

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 +implementations for some of its facilities. + + +

+

assert (v [, message])

+Issues an error when +the value of its argument v is false (i.e., nil or false); +otherwise, returns all its arguments. +message is an error message; +when absent, it defaults to "assertion failed!" + + + + +

+

collectgarbage ([opt [, arg]])

+ + +

+This function is a generic interface to the garbage collector. +It performs different functions according to its first argument, opt: + +

+ + + +

+

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 all values returned by the chunk. +In case of errors, dofile propagates the error +to its caller (that is, dofile 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. + + +

+Usually, error adds some information about the error position +at the beginning of the message. +The level argument specifies how to get the error position. +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. +Passing a level 0 avoids the addition of error position information +to the message. + + + + +

+

_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, +nor vice-versa. +(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 +that 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. + + + + +

+

getmetatable (object)

+ + +

+If 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. + + + + +

+

ipairs (t)

+ + +

+Returns three values: an iterator function, the table t, and 0, +so that the construction + +

+     for i,v in ipairs(t) do body end
+

+will iterate over the pairs (1,t[1]), (2,t[2]), ···, +up to the first integer key absent from the table. + + + + +

+

load (func [, chunkname])

+ + +

+Loads a chunk using function func to get its pieces. +Each call to func must return a string that concatenates +with previous results. +A return of an empty string, nil, or no value signals the end of the chunk. + + +

+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. + + +

+chunkname is used as the chunk name for error messages +and debug information. +When absent, +it defaults to "=(load)". + + + + +

+

loadfile ([filename])

+ + +

+Similar to load, +but gets the chunk from file filename +or from the standard input, +if no file name is given. + + + + +

+

loadstring (string [, chunkname])

+ + +

+Similar to load, +but gets the chunk from the given string. + + +

+To load and run a given string, use the idiom + +

+     assert(loadstring(s))()
+
+ +

+When absent, +chunkname defaults to the given string. + + + + +

+

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 its associated value. +When called with nil as its second argument, +next returns an initial index +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. +In particular, +you can use next(t) to check whether a table is empty. + + +

+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. +You may however modify existing fields. +In particular, you may clear existing fields. + + + + +

+

pairs (t)

+ + +

+Returns three values: the next function, the table t, and nil, +so that the construction + +

+     for k,v in pairs(t) do body end
+

+will iterate over all key–value pairs of table t. + + +

+See function next for the caveats of modifying +the table during its traversal. + + + + +

+

pcall (f, arg1, ···)

+ + +

+Calls function f with +the given arguments in protected mode. +This 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 (···)

+Receives any number of arguments, +and prints their values to stdout, +using the tostring function to convert them to strings. +print is not intended for formatted output, +but only as a quick way to show a value, +typically for debugging. +For formatted output, use string.format. + + + + +

+

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 may be any value. + + + + +

+

rawset (table, index, value)

+Sets the real value of table[index] to value, +without invoking any metamethod. +table must be a table, +index any value different from nil, +and value any Lua value. + + +

+This function returns table. + + + + +

+

select (index, ···)

+ + +

+If index is a number, +returns all arguments after argument number index. +Otherwise, index must be the string "#", +and select returns the total number of extra arguments it received. + + + + +

+

setfenv (f, table)

+ + +

+Sets the environment to be used by the given function. +f can be a Lua function or a number +that specifies the function at that stack level: +Level 1 is the function calling setfenv. +setfenv returns the given function. + + +

+As a special case, when f is 0 setfenv changes +the environment of the running thread. +In this case, setfenv returns no values. + + + + +

+

setmetatable (table, metatable)

+ + +

+Sets the metatable for the given table. +(You cannot change the metatable of other types from Lua, only from C.) +If metatable is nil, +removes the metatable of the given table. +If the original metatable has a "__metatable" field, +raises an error. + + +

+This function returns table. + + + + +

+

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 this 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 can have a decimal part, +as well as an optional exponent part (see §2.1). +In other bases, only unsigned integers are accepted. + + + + +

+

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 string.format. + + +

+If the metatable of e has a "__tostring" field, +then 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 [, i [, j]])

+Returns the elements from the given table. +This function is equivalent to + +
+     return list[i], list[i+1], ···, list[j]
+

+except that the above code can be written only for a fixed number +of elements. +By default, i is 1 and j is the length of the list, +as defined by the length operator (see §2.5.5). + + + + +

+

_VERSION

+A global variable (not a function) that +holds a string containing the current interpreter version. +The current contents of this variable is "Lua 5.1". + + + + +

+

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 this 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 §2.11 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". + + + + +

+

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 values val1, ··· are passed +as the arguments to the body function. +If the coroutine has yielded, +resume restarts it; +the values val1, ··· are passed +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.running ()

+ + +

+Returns the running coroutine, +or nil when called by the main thread. + + + + +

+

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; +"normal" if the coroutine is active but not running +(that is, it has resumed another coroutine); +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 (···)

+ + +

+Suspends the execution of the calling coroutine. +The coroutine cannot be running a C function, +a metamethod, or an iterator. +Any arguments to yield are passed as extra results to resume. + + + + + + + +

5.3 - Modules

+ +

+The package library provides basic +facilities for loading and building modules in Lua. +It exports two of its functions directly in the global environment: +require and module. +Everything else is exported in a table package. + + +

+

module (name [, ···])

+ + +

+Creates a module. +If there is a table in package.loaded[name], +this table is the module. +Otherwise, if there is a global table t with the given name, +this table is the module. +Otherwise creates a new table t and +sets it as the value of the global name and +the value of package.loaded[name]. +This function also initializes t._NAME with the given name, +t._M with the module (t itself), +and t._PACKAGE with the package name +(the full module name minus last component; see below). +Finally, module sets t as the new environment +of the current function and the new value of package.loaded[name], +so that require returns t. + + +

+If name is a compound name +(that is, one with components separated by dots), +module creates (or reuses, if they already exist) +tables for each component. +For instance, if name is a.b.c, +then module stores the module table in field c of +field b of global a. + + +

+This function can receive optional options after +the module name, +where each option is a function to be applied over the module. + + + + +

+

require (modname)

+ + +

+Loads the given module. +The function starts by looking into the package.loaded table +to determine whether modname is already loaded. +If it is, then require returns the value stored +at package.loaded[modname]. +Otherwise, it tries to find a loader for the module. + + +

+To find a loader, +require is guided by the package.loaders array. +By changing this array, +we can change how require looks for a module. +The following explanation is based on the default configuration +for package.loaders. + + +

+First require queries package.preload[modname]. +If it has a value, +this value (which should be a function) is the loader. +Otherwise require searches for a Lua loader using the +path stored in package.path. +If that also fails, it searches for a C loader using the +path stored in package.cpath. +If that also fails, +it tries an all-in-one loader (see package.loaders). + + +

+Once a loader is found, +require calls the loader with a single argument, modname. +If the loader returns any value, +require assigns the returned value to package.loaded[modname]. +If the loader returns no value and +has not assigned any value to package.loaded[modname], +then require assigns true to this entry. +In any case, require returns the +final value of package.loaded[modname]. + + +

+If there is any error loading or running the module, +or if it cannot find any loader for the module, +then require signals an error. + + + + +

+

package.cpath

+ + +

+The path used by require to search for a C loader. + + +

+Lua initializes the C path package.cpath in the same way +it initializes the Lua path package.path, +using the environment variable LUA_CPATH +or a default path defined in luaconf.h. + + + + +

+ +

package.loaded

+ + +

+A table used by require to control which +modules are already loaded. +When you require a module modname and +package.loaded[modname] is not false, +require simply returns the value stored there. + + + + +

+

package.loaders

+ + +

+A table used by require to control how to load modules. + + +

+Each entry in this table is a searcher function. +When looking for a module, +require calls each of these searchers in ascending order, +with the module name (the argument given to require) as its +sole parameter. +The function can return another function (the module loader) +or a string explaining why it did not find that module +(or nil if it has nothing to say). +Lua initializes this table with four functions. + + +

+The first searcher simply looks for a loader in the +package.preload table. + + +

+The second searcher looks for a loader as a Lua library, +using the path stored at package.path. +A path is a sequence of templates separated by semicolons. +For each template, +the searcher will change each interrogation +mark in the template by filename, +which is the module name with each dot replaced by a +"directory separator" (such as "/" in Unix); +then it will try to open the resulting file name. +So, for instance, if the Lua path is the string + +

+     "./?.lua;./?.lc;/usr/local/?/init.lua"
+

+the search for a Lua file for module foo +will try to open the files +./foo.lua, ./foo.lc, and +/usr/local/foo/init.lua, in that order. + + +

+The third searcher looks for a loader as a C library, +using the path given by the variable package.cpath. +For instance, +if the C path is the string + +

+     "./?.so;./?.dll;/usr/local/?/init.so"
+

+the searcher for module foo +will try to open the files ./foo.so, ./foo.dll, +and /usr/local/foo/init.so, in that order. +Once it finds a C library, +this searcher first uses a dynamic link facility to link the +application with the library. +Then it tries to find a C function inside the library to +be used as the loader. +The name of this C function is the string "luaopen_" +concatenated with a copy of the module name where each dot +is replaced by an underscore. +Moreover, if the module name has a hyphen, +its prefix up to (and including) the first hyphen is removed. +For instance, if the module name is a.v1-b.c, +the function name will be luaopen_b_c. + + +

+The fourth searcher tries an all-in-one loader. +It searches the C path for a library for +the root name of the given module. +For instance, when requiring a.b.c, +it will search for a C library for a. +If found, it looks into it for an open function for +the submodule; +in our example, that would be luaopen_a_b_c. +With this facility, a package can pack several C submodules +into one single library, +with each submodule keeping its original open function. + + + + +

+

package.loadlib (libname, funcname)

+ + +

+Dynamically links the host program with the C library libname. +Inside this library, looks for a function funcname +and returns this function as a C function. +(So, funcname must follow the protocol (see lua_CFunction)). + + +

+This is a low-level function. +It completely bypasses the package and module system. +Unlike require, +it does not perform any path searching and +does not automatically adds extensions. +libname must be the complete file name of the C library, +including if necessary a path and extension. +funcname must be the exact name exported by the C library +(which may depend on the C compiler and linker used). + + +

+This function is not supported by ANSI C. +As such, it is only available on some platforms +(Windows, Linux, Mac OS X, Solaris, BSD, +plus other Unix systems that support the dlfcn standard). + + + + +

+

package.path

+ + +

+The path used by require to search for a Lua loader. + + +

+At start-up, Lua initializes this variable with +the value of the environment variable LUA_PATH or +with a default path defined in luaconf.h, +if the environment variable is not defined. +Any ";;" in the value of the environment variable +is replaced by the default path. + + + + +

+

package.preload

+ + +

+A table to store loaders for specific modules +(see require). + + + + +

+

package.seeall (module)

+ + +

+Sets a metatable for module with +its __index field referring to the global environment, +so that this module inherits values +from the global environment. +To be used as an option to function module. + + + + + + + +

5.4 - 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. +It also sets a metatable for strings +where the __index field points to the string table. +Therefore, you can use the string functions in object-oriented style. +For instance, string.byte(s, i) +can be written as s:byte(i). + + +

+The string library assumes one-byte character encodings. + + +

+

string.byte (s [, i [, j]])

+Returns the internal numerical codes of the characters s[i], +s[i+1], ···, s[j]. +The default value for i is 1; +the default value for j is i. + + +

+Note that numerical codes are not necessarily portable across platforms. + + + + +

+

string.char (···)

+Receives zero 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 corresponding argument. + + +

+Note that numerical codes are not necessarily portable across platforms. + + + + +

+

string.dump (function)

+ + +

+Returns a string containing a binary representation of the given function, +so that a later loadstring on this 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 a match, then find returns the indices of s +where this occurrence starts and ends; +otherwise, it returns nil. +A third, optional numerical argument init specifies +where to start the search; +its default value is 1 and can 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 as well. + + +

+If the pattern has captures, +then in a successful match +the captured values are also returned, +after the two indices. + + + + +

+

string.format (formatstring, ···)

+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 that 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, +and all double quotes, newlines, embedded zeros, +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. + + +

+This function does not accept string values +containing embedded zeros, +except as arguments to the q option. + + + + +

+

string.gmatch (s, pattern)

+Returns an iterator function that, +each time it is called, +returns the next captures from pattern over string s. +If pattern 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.gmatch(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.gmatch(s, "(%w+)=(%w+)") do
+       t[k] = v
+     end
+
+ +

+For this function, a '^' at the start of a pattern does not +work as an anchor, as this would prevent the iteration. + + + + +

+

string.gsub (s, pattern, repl [, n])

+Returns a copy of s +in which all (or the first n, if given) +occurrences of the pattern have been +replaced by a replacement string specified by repl, +which can be a string, a table, or a function. +gsub also returns, as its second value, +the total number of matches that occurred. + + +

+If repl is a string, then its value is used for replacement. +The character % works as an escape character: +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). +The sequence %0 stands for the whole match. +The sequence %% stands for a single %. + + +

+If repl is a table, then the table is queried for every match, +using the first capture as the key; +if the pattern specifies no captures, +then the whole match is used as the key. + + +

+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 the table query or by the function call +is a string or a number, +then it is used as the replacement string; +otherwise, if it is false or nil, +then there is no replacement +(that is, the original match is kept in the string). + + +

+Here are some examples: + +

+     x = string.gsub("hello world", "(%w+)", "%1 %1")
+     --> x="hello hello world world"
+     
+     x = string.gsub("hello world", "%w+", "%0 %0", 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="5.1"}
+     x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
+     --> x="lua-5.1.tar.gz"
+
+ + + +

+

string.len (s)

+Receives a string and returns its length. +The empty string "" has length 0. +Embedded zeros are counted, +so "a\000bc\000" has length 5. + + + + +

+

string.lower (s)

+Receives a string and returns a copy of this string with all +uppercase letters changed to lowercase. +All other characters are left unchanged. +The definition of what an uppercase letter is depends on the current locale. + + + + +

+

string.match (s, pattern [, init])

+Looks for the first match of +pattern in the string s. +If it finds one, then match returns +the captures from the pattern; +otherwise it returns nil. +If pattern specifies no captures, +then the whole match is returned. +A third, optional numerical argument init specifies +where to start the search; +its default value is 1 and can be negative. + + + + +

+

string.rep (s, n)

+Returns a string that is the concatenation of n copies of +the string s. + + + + +

+

string.reverse (s)

+Returns a string that is the string s reversed. + + + + +

+

string.sub (s, i [, j])

+Returns the substring of s that +starts at i and continues until j; +i and j can 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 this string with all +lowercase letters changed to uppercase. +All other characters are left unchanged. +The definition of what a lowercase letter is depends on the current locale. + + + +

5.4.1 - Patterns

+ + +

Character Class:

+A character class is used to represent a set of characters. +The following combinations are allowed in describing a character class: + +

+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. + + + + + +

Pattern Item:

+A pattern item can be + +

+ + + + +

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 can 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. + + +

+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. + + + + + + + + + + + +

5.5 - 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 these functions, when we talk about the "length" of a table +we mean the result of the length operator. + + +

+

table.concat (table [, sep [, i [, j]]])

+Given an array where all elements are strings or numbers, +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 length of the table. +If i is greater than j, returns the empty string. + + + + +

+

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 length of the table (see §2.5.5), +so that a call table.insert(t,x) inserts x at the end +of table t. + + + + +

+

table.maxn (table)

+ + +

+Returns the largest positive numerical index of the given table, +or zero if the table has no positive numerical indices. +(To do its job this function does a linear traversal of +the whole table.) + + + + +

+

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 length of the table, +so that a call table.remove(t) removes the last element +of table t. + + + + +

+

table.sort (table [, comp])

+Sorts table elements in a given order, in-place, +from table[1] to table[n], +where n is the length of the table. +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. + + + + + + + +

5.6 - Mathematical Functions

+ +

+This library is an interface to the standard C math library. +It provides all its functions inside the table math. + + +

+

math.abs (x)

+ + +

+Returns the absolute value of x. + + + + +

+

math.acos (x)

+ + +

+Returns the arc cosine of x (in radians). + + + + +

+

math.asin (x)

+ + +

+Returns the arc sine of x (in radians). + + + + +

+

math.atan (x)

+ + +

+Returns the arc tangent of x (in radians). + + + + +

+

math.atan2 (y, x)

+ + +

+Returns the arc tangent of y/x (in radians), +but uses the signs of both parameters to find the +quadrant of the result. +(It also handles correctly the case of x being zero.) + + + + +

+

math.ceil (x)

+ + +

+Returns the smallest integer larger than or equal to x. + + + + +

+

math.cos (x)

+ + +

+Returns the cosine of x (assumed to be in radians). + + + + +

+

math.cosh (x)

+ + +

+Returns the hyperbolic cosine of x. + + + + +

+

math.deg (x)

+ + +

+Returns the angle x (given in radians) in degrees. + + + + +

+

math.exp (x)

+ + +

+Returns the value ex. + + + + +

+

math.floor (x)

+ + +

+Returns the largest integer smaller than or equal to x. + + + + +

+

math.fmod (x, y)

+ + +

+Returns the remainder of the division of x by y +that rounds the quotient towards zero. + + + + +

+

math.frexp (x)

+ + +

+Returns m and e such that x = m2e, +e is an integer and the absolute value of m is +in the range [0.5, 1) +(or zero when x is zero). + + + + +

+

math.huge

+ + +

+The value HUGE_VAL, +a value larger than or equal to any other numerical value. + + + + +

+

math.ldexp (m, e)

+ + +

+Returns m2e (e should be an integer). + + + + +

+

math.log (x)

+ + +

+Returns the natural logarithm of x. + + + + +

+

math.log10 (x)

+ + +

+Returns the base-10 logarithm of x. + + + + +

+

math.max (x, ···)

+ + +

+Returns the maximum value among its arguments. + + + + +

+

math.min (x, ···)

+ + +

+Returns the minimum value among its arguments. + + + + +

+

math.modf (x)

+ + +

+Returns two numbers, +the integral part of x and the fractional part of x. + + + + +

+

math.pi

+ + +

+The value of pi. + + + + +

+

math.pow (x, y)

+ + +

+Returns xy. +(You can also use the expression x^y to compute this value.) + + + + +

+

math.rad (x)

+ + +

+Returns the angle x (given in degrees) in radians. + + + + +

+

math.random ([m [, n]])

+ + +

+This function is an interface to the simple +pseudo-random generator function rand provided by ANSI C. +(No guarantees can be given for its statistical properties.) + + +

+When called without arguments, +returns a uniform pseudo-random real number +in the range [0,1). +When called with an integer number m, +math.random returns +a uniform pseudo-random integer in the range [1, m]. +When called with two integer numbers m and n, +math.random returns a uniform pseudo-random +integer in the range [m, n]. + + + + +

+

math.randomseed (x)

+ + +

+Sets x as the "seed" +for the pseudo-random generator: +equal seeds produce equal sequences of numbers. + + + + +

+

math.sin (x)

+ + +

+Returns the sine of x (assumed to be in radians). + + + + +

+

math.sinh (x)

+ + +

+Returns the hyperbolic sine of x. + + + + +

+

math.sqrt (x)

+ + +

+Returns the square root of x. +(You can also use the expression x^0.5 to compute this value.) + + + + +

+

math.tan (x)

+ + +

+Returns the tangent of x (assumed to be in radians). + + + + +

+

math.tanh (x)

+ + +

+Returns the hyperbolic tangent of x. + + + + + + + +

5.7 - 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 these 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 of 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. +The I/O library never closes these files. + + +

+Unless otherwise stated, +all I/O functions return nil on failure +(plus an error message as a second result and +a system-dependent error code as a third 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 this 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 body 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() (with no file name) is equivalent +to io.input():lines(); +that is, it iterates over the lines of the default input file. +In this case it does not close the file when the loop ends. + + + + +

+

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: + +

+The mode string can 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.popen (prog [, mode])

+ + +

+Starts program prog in a separated process and returns +a file handle that you can use to read data from this program +(if mode is "r", the default) +or to write data to this program +(if mode is "w"). + + +

+This function is system dependent and is not available +on all platforms. + + + + +

+

io.read (···)

+ + +

+Equivalent to io.input():read. + + + + +

+

io.tmpfile ()

+ + +

+Returns a handle for a temporary file. +This file is opened 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, +or nil if obj is not a file handle. + + + + +

+

io.write (···)

+ + +

+Equivalent to io.output():write. + + + + +

+

file:close ()

+ + +

+Closes file. +Note that files are automatically closed when +their handles are garbage collected, +but that takes an unpredictable amount of time to happen. + + + + +

+

file:flush ()

+ + +

+Saves any written data to file. + + + + +

+

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 body 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 (···)

+ + +

+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 + +

+ + + +

+

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: + +

+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:setvbuf (mode [, size])

+ + +

+Sets the buffering mode for an output file. +There are three available modes: + +

+For the last two cases, size +specifies the size of the buffer, in bytes. +The default is an appropriate size. + + + + +

+

file:write (···)

+ + +

+Writes the value of each of its arguments to +the file. +The arguments must be strings or numbers. +To write other values, +use tostring or string.format before write. + + + + + + + +

5.8 - Operating System Facilities

+ +

+This library is implemented through table os. + + +

+

os.clock ()

+ + +

+Returns an approximation of the amount in seconds of CPU time +used by the program. + + + + +

+

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 this optional character, +if format is the string "*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 to 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. +If command is absent, then it returns nonzero if a shell is available +and zero otherwise. + + + + +

+

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 or directory with the given name. +Directories must be empty to be removed. +If this function fails, it returns nil, +plus a string describing the error. + + + + +

+

os.rename (oldname, newname)

+ + +

+Renames file or directory named oldname to newname. +If this function fails, it returns nil, +plus a string describing the error. + + + + +

+

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. + + +

+If locale is the empty string, +the current locale is set to an implementation-defined native locale. +If locale is the string "C", +the current locale is set to the standard C locale. + + +

+When called with nil as the first argument, +this function only returns the name of the current locale +for the given category. + + + + +

+

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 explicitly removed when no longer needed. + + +

+On some systems (POSIX), +this function also creates a file with that name, +to avoid security risks. +(Someone else might create the file with wrong permissions +in the time between getting the name and creating the file.) +You still have to open the file to use it +and to remove it (even if you do not use it). + + +

+When possible, +you may prefer to use io.tmpfile, +which automatically removes the file when the program ends. + + + + + + + +

5.9 - The Debug Library

+ +

+This 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, several of these functions +violate some assumptions about Lua code +(e.g., that variables local to a function +cannot be accessed from outside or +that userdata metatables cannot be changed by Lua code) +and therefore can compromise otherwise secure code. + + +

+All functions in this library are provided +inside the debug table. +All functions that operate over a thread +have an optional first argument which is the +thread to operate over. +The default is always the current thread. + + +

+

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 +within any function, and so have no direct access to local variables. + + + + +

+

debug.getfenv (o)

+Returns the environment of object o. + + + + +

+

debug.gethook ([thread])

+ + +

+Returns the current hook settings of the thread, as three values: +the current hook function, the current hook mask, +and the current hook count +(as set by the debug.sethook function). + + + + +

+

debug.getinfo ([thread,] function [, what])

+ + +

+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 +of the given thread: +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 can contain 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, +except the table of valid lines. +If present, +the option 'f' +adds a field named func with the function itself. +If present, +the option 'L' +adds a field named activelines with the table of +valid lines. + + +

+For instance, the expression debug.getinfo(1,"n").name returns +a table with a name for the current function, +if a reasonable name can be found, +and the expression debug.getinfo(print) +returns a table with all available information +about the print function. + + + + +

+

debug.getlocal ([thread,] 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.) + + +

+Variable names starting with '(' (open parentheses) +represent internal variables +(loop control variables, temporaries, and C function locals). + + + + +

+

debug.getmetatable (object)

+ + +

+Returns the metatable of the given object +or nil if it does not have a metatable. + + + + +

+

debug.getregistry ()

+ + +

+Returns the registry table (see §3.5). + + + + +

+

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.setfenv (object, table)

+ + +

+Sets the environment of the given object to the given table. +Returns object. + + + + +

+

debug.sethook ([thread,] 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: + +

+With a count different from zero, +the hook is called after every count instructions. + + +

+When called without arguments, +debug.sethook turns off the hook. + + +

+When the hook is called, its first parameter is a string +describing the event that has triggered its call: +"call", "return" (or "tail return", +when simulating a return from a tail call), +"line", and "count". +For line events, +the hook also gets the new line number as its second parameter. +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.setlocal ([thread,] 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.) +Otherwise, it returns the name of the local variable. + + + + +

+

debug.setmetatable (object, table)

+ + +

+Sets the metatable for the given object to the given table +(which can be nil). + + + + +

+

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. +Otherwise, it returns the name of the upvalue. + + + + +

+

debug.traceback ([thread,] [message [, level]])

+ + +

+Returns a string with a traceback of the call stack. +An optional message string is appended +at the beginning of the traceback. +An optional level number tells at which level +to start the traceback +(default is 1, the function calling traceback). + + + + + + + +

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, including the debug library. +Its usage is: + +

+     lua [options] [script [args]]
+

+The options are: + +

+After handling its options, lua runs the given script, +passing to it the given args as string arguments. +When called without arguments, +lua behaves as lua -v -i +when the standard input (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 the value of a (which is '1'), +and finally run the file script.lua with no arguments. +(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 at index 0, +the first argument after the script name goes to index 1, +and so on. +Any arguments before the script name +(that is, the interpreter name plus the options) +go to negative indices. +For instance, in the call + +

+     $ lua -la b.lua t1 t2
+

+the interpreter first runs the file a.lua, +then creates a table + +

+     arg = { [-2] = "lua", [-1] = "-la",
+             [0] = "b.lua",
+             [1] = "t1", [2] = "t2" }
+

+and finally runs the file b.lua. +The script is called with arg[1], arg[2], ··· +as arguments; +it can also access these arguments with the vararg expression '...'. + + +

+In interactive mode, +if you write an incomplete statement, +the interpreter waits for its completion +by issuing a different prompt. + + +

+If the global variable _PROMPT contains a string, +then its value is used as the prompt. +Similarly, if the global variable _PROMPT2 contains a string, +its value is used as the secondary prompt +(issued during incomplete statements). +Therefore, both prompts can be changed directly on the command line +or in any Lua programs by assigning to _PROMPT. +See the next example: + +

+     $ lua -e"_PROMPT='myprompt> '" -i
+

+(The outer pair of quotes is for the shell, +the inner pair is for Lua.) +Note the use of -i to enter interactive mode; +otherwise, +the program would just end silently +right after the assignment to _PROMPT. + + +

+To allow the use of Lua as a +script interpreter in Unix systems, +the stand-alone interpreter skips +the first line of a chunk if it starts with #. +Therefore, 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.) + + + +

7 - Incompatibilities with the Previous Version

+ +

+Here we list the incompatibilities that you may find when moving a program +from Lua 5.0 to Lua 5.1. +You can avoid most of the incompatibilities compiling Lua with +appropriate options (see file luaconf.h). +However, +all these compatibility options will be removed in the next version of Lua. + + + +

7.1 - Changes in the Language

+ + + + + +

7.2 - Changes in the Libraries

+ + + + + +

7.3 - Changes in the API

+ + + + + +

8 - The Complete Syntax of Lua

+ +

+Here is the complete syntax of Lua in extended BNF. +(It does not describe operator precedences.) + + + + +

+
+	chunk ::= {stat [`;´]} [laststat [`;´]]
+
+	block ::= chunk
+
+	stat ::=  varlist `=´ explist | 
+		 functioncall | 
+		 do block end | 
+		 while exp do block end | 
+		 repeat block until exp | 
+		 if exp then block {elseif exp then block} [else block] end | 
+		 for Name `=´ exp `,´ exp [`,´ exp] do block end | 
+		 for namelist in explist do block end | 
+		 function funcname funcbody | 
+		 local function Name funcbody | 
+		 local namelist [`=´ explist] 
+
+	laststat ::= return [explist] | break
+
+	funcname ::= Name {`.´ Name} [`:´ Name]
+
+	varlist ::= var {`,´ var}
+
+	var ::=  Name | prefixexp `[´ exp `]´ | prefixexp `.´ Name 
+
+	namelist ::= Name {`,´ Name}
+
+	explist ::= {exp `,´} exp
+
+	exp ::=  nil | false | true | Number | String | `...´ | function | 
+		 prefixexp | tableconstructor | exp binop exp | unop exp 
+
+	prefixexp ::= var | functioncall | `(´ exp `)´
+
+	functioncall ::=  prefixexp args | prefixexp `:´ Name args 
+
+	args ::=  `(´ [explist] `)´ | tableconstructor | String 
+
+	function ::= function funcbody
+
+	funcbody ::= `(´ [parlist] `)´ block end
+
+	parlist ::= namelist [`,´ `...´] | `...´
+
+	tableconstructor ::= `{´ [fieldlist] `}´
+
+	fieldlist ::= field {fieldsep field} [fieldsep]
+
+	field ::= `[´ exp `]´ `=´ exp | Name `=´ exp | exp
+
+	fieldsep ::= `,´ | `;´
+
+	binop ::= `+´ | `-´ | `*´ | `/´ | `^´ | `%´ | `..´ | 
+		 `<´ | `<=´ | `>´ | `>=´ | `==´ | `~=´ | 
+		 and | or
+
+	unop ::= `-´ | not | `#´
+
+
+ +

+ + + + + + + +

+ +Last update: +Mon Feb 13 18:54:19 BRST 2012 + + + + + -- cgit v1.2.1