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diff --git a/source3/lua-5.1.4/doc/manual.html b/source3/lua-5.1.4/doc/manual.html deleted file mode 100644 index 118d9059ff..0000000000 --- a/source3/lua-5.1.4/doc/manual.html +++ /dev/null @@ -1,8800 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> -<html> - -<head> -<title>Lua 5.1 Reference Manual</title> -<link rel="stylesheet" type="text/css" href="lua.css"> -<link rel="stylesheet" type="text/css" href="manual.css"> -<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1"> -</head> - -<body> - -<hr> -<h1> -<a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a> -Lua 5.1 Reference Manual -</h1> - -by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes -<p> -<small> -Copyright © 2006-2008 Lua.org, PUC-Rio. -Freely available under the terms of the -<a href="http://www.lua.org/license.html#5">Lua license</a>. -</small> -<hr> -<p> - -<a href="contents.html#contents">contents</A> -· -<a href="contents.html#index">index</A> - -<!-- ====================================================================== --> -<p> - -<!-- $Id: manual.of,v 1.48 2008/08/18 15:24:20 roberto Exp $ --> - - - - -<h1>1 - <a name="1">Introduction</a></h1> - -<p> -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 <em>clean</em> C -(that is, in the common subset of ANSI C and C++). - - -<p> -Being an extension language, Lua has no notion of a "main" program: -it only works <em>embedded</em> in a host client, -called the <em>embedding program</em> or simply the <em>host</em>. -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 <code>lua</code>, -which uses the Lua library to offer a complete, stand-alone Lua interpreter. - - -<p> -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, <code>www.lua.org</code>. - - -<p> -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, <em>Programming in Lua (Second Edition)</em>. - - - -<h1>2 - <a name="2">The Language</a></h1> - -<p> -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. - - -<p> -The language constructs will be explained using the usual extended BNF notation, -in which -{<em>a</em>} means 0 or more <em>a</em>'s, and -[<em>a</em>] means an optional <em>a</em>. -Non-terminals are shown like non-terminal, -keywords are shown like <b>kword</b>, -and other terminal symbols are shown like `<b>=</b>´. -The complete syntax of Lua can be found in <a href="#8">§8</a> -at the end of this manual. - - - -<h2>2.1 - <a name="2.1">Lexical Conventions</a></h2> - -<p> -<em>Names</em> -(also called <em>identifiers</em>) -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. - - -<p> -The following <em>keywords</em> are reserved -and cannot be used as names: - - -<pre> - and break do else elseif - end false for function if - in local nil not or - repeat return then true until while -</pre> - -<p> -Lua is a case-sensitive language: -<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> -are two different, valid names. -As a convention, names starting with an underscore followed by -uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>) -are reserved for internal global variables used by Lua. - - -<p> -The following strings denote other tokens: - -<pre> - + - * / % ^ # - == ~= <= >= < > = - ( ) { } [ ] - ; : , . .. ... -</pre> - -<p> -<em>Literal strings</em> -can be delimited by matching single or double quotes, -and can contain the following C-like escape sequences: -'<code>\a</code>' (bell), -'<code>\b</code>' (backspace), -'<code>\f</code>' (form feed), -'<code>\n</code>' (newline), -'<code>\r</code>' (carriage return), -'<code>\t</code>' (horizontal tab), -'<code>\v</code>' (vertical tab), -'<code>\\</code>' (backslash), -'<code>\"</code>' (quotation mark [double quote]), -and '<code>\'</code>' (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 <code>\<em>ddd</em></code>, -where <em>ddd</em> 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 '<code>\0</code>'. - - -<p> -Literal strings can also be defined using a long format -enclosed by <em>long brackets</em>. -We define an <em>opening long bracket of level <em>n</em></em> as an opening -square bracket followed by <em>n</em> equal signs followed by another -opening square bracket. -So, an opening long bracket of level 0 is written as <code>[[</code>, -an opening long bracket of level 1 is written as <code>[=[</code>, -and so on. -A <em>closing long bracket</em> is defined similarly; -for instance, a closing long bracket of level 4 is written as <code>]====]</code>. -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. - - -<p> -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 '<code>a</code>' is coded as 97, -newline is coded as 10, and '<code>1</code>' is coded as 49), -the five literal strings below denote the same string: - -<pre> - a = 'alo\n123"' - a = "alo\n123\"" - a = '\97lo\10\04923"' - a = [[alo - 123"]] - a = [==[ - alo - 123"]==] -</pre> - -<p> -A <em>numerical constant</em> can be written with an optional decimal part -and an optional decimal exponent. -Lua also accepts integer hexadecimal constants, -by prefixing them with <code>0x</code>. -Examples of valid numerical constants are - -<pre> - 3 3.0 3.1416 314.16e-2 0.31416E1 0xff 0x56 -</pre> - -<p> -A <em>comment</em> starts with a double hyphen (<code>--</code>) -anywhere outside a string. -If the text immediately after <code>--</code> is not an opening long bracket, -the comment is a <em>short comment</em>, -which runs until the end of the line. -Otherwise, it is a <em>long comment</em>, -which runs until the corresponding closing long bracket. -Long comments are frequently used to disable code temporarily. - - - - - -<h2>2.2 - <a name="2.2">Values and Types</a></h2> - -<p> -Lua is a <em>dynamically typed language</em>. -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. - - -<p> -All values in Lua are <em>first-class values</em>. -This means that all values can be stored in variables, -passed as arguments to other functions, and returned as results. - - -<p> -There are eight basic types in Lua: -<em>nil</em>, <em>boolean</em>, <em>number</em>, -<em>string</em>, <em>function</em>, <em>userdata</em>, -<em>thread</em>, and <em>table</em>. -<em>Nil</em> is the type of the value <b>nil</b>, -whose main property is to be different from any other value; -it usually represents the absence of a useful value. -<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>. -Both <b>nil</b> and <b>false</b> make a condition false; -any other value makes it true. -<em>Number</em> 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 <code>luaconf.h</code>.) -<em>String</em> represents arrays of characters. - -Lua is 8-bit clean: -strings can contain any 8-bit character, -including embedded zeros ('<code>\0</code>') (see <a href="#2.1">§2.1</a>). - - -<p> -Lua can call (and manipulate) functions written in Lua and -functions written in C -(see <a href="#2.5.8">§2.5.8</a>). - - -<p> -The type <em>userdata</em> 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 <em>metatables</em>, -the programmer can define operations for userdata values -(see <a href="#2.8">§2.8</a>). -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. - - -<p> -The type <em>thread</em> represents independent threads of execution -and it is used to implement coroutines (see <a href="#2.11">§2.11</a>). -Do not confuse Lua threads with operating-system threads. -Lua supports coroutines on all systems, -even those that do not support threads. - - -<p> -The type <em>table</em> implements associative arrays, -that is, arrays that can be indexed not only with numbers, -but with any value (except <b>nil</b>). -Tables can be <em>heterogeneous</em>; -that is, they can contain values of all types (except <b>nil</b>). -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 <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. -There are several convenient ways to create tables in Lua -(see <a href="#2.5.7">§2.5.7</a>). - - -<p> -Like indices, -the value of a table field can be of any type (except <b>nil</b>). -In particular, -because functions are first-class values, -table fields can contain functions. -Thus tables can also carry <em>methods</em> (see <a href="#2.5.9">§2.5.9</a>). - - -<p> -Tables, functions, threads, and (full) userdata values are <em>objects</em>: -variables do not actually <em>contain</em> these values, -only <em>references</em> to them. -Assignment, parameter passing, and function returns -always manipulate references to such values; -these operations do not imply any kind of copy. - - -<p> -The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type -of a given value. - - - -<h3>2.2.1 - <a name="2.2.1">Coercion</a></h3> - -<p> -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 <code>format</code> function from the string library -(see <a href="#pdf-string.format"><code>string.format</code></a>). - - - - - - - -<h2>2.3 - <a name="2.3">Variables</a></h2> - -<p> -Variables are places that store values. - -There are three kinds of variables in Lua: -global variables, local variables, and table fields. - - -<p> -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): - -<pre> - var ::= Name -</pre><p> -Name denotes identifiers, as defined in <a href="#2.1">§2.1</a>. - - -<p> -Any variable is assumed to be global unless explicitly declared -as a local (see <a href="#2.4.7">§2.4.7</a>). -Local variables are <em>lexically scoped</em>: -local variables can be freely accessed by functions -defined inside their scope (see <a href="#2.6">§2.6</a>). - - -<p> -Before the first assignment to a variable, its value is <b>nil</b>. - - -<p> -Square brackets are used to index a table: - -<pre> - var ::= prefixexp `<b>[</b>´ exp `<b>]</b>´ -</pre><p> -The meaning of accesses to global variables -and table fields can be changed via metatables. -An access to an indexed variable <code>t[i]</code> is equivalent to -a call <code>gettable_event(t,i)</code>. -(See <a href="#2.8">§2.8</a> for a complete description of the -<code>gettable_event</code> function. -This function is not defined or callable in Lua. -We use it here only for explanatory purposes.) - - -<p> -The syntax <code>var.Name</code> is just syntactic sugar for -<code>var["Name"]</code>: - -<pre> - var ::= prefixexp `<b>.</b>´ Name -</pre> - -<p> -All global variables live as fields in ordinary Lua tables, -called <em>environment tables</em> or simply -<em>environments</em> (see <a href="#2.9">§2.9</a>). -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 <a href="#pdf-getfenv"><code>getfenv</code></a>. -To replace it, -you call <a href="#pdf-setfenv"><code>setfenv</code></a>. -(You can only manipulate the environment of C functions -through the debug library; (see <a href="#5.9">§5.9</a>).) - - -<p> -An access to a global variable <code>x</code> -is equivalent to <code>_env.x</code>, -which in turn is equivalent to - -<pre> - gettable_event(_env, "x") -</pre><p> -where <code>_env</code> is the environment of the running function. -(See <a href="#2.8">§2.8</a> for a complete description of the -<code>gettable_event</code> function. -This function is not defined or callable in Lua. -Similarly, the <code>_env</code> variable is not defined in Lua. -We use them here only for explanatory purposes.) - - - - - -<h2>2.4 - <a name="2.4">Statements</a></h2> - -<p> -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. - - - -<h3>2.4.1 - <a name="2.4.1">Chunks</a></h3> - -<p> -The unit of execution of Lua is called a <em>chunk</em>. -A chunk is simply a sequence of statements, -which are executed sequentially. -Each statement can be optionally followed by a semicolon: - -<pre> - chunk ::= {stat [`<b>;</b>´]} -</pre><p> -There are no empty statements and thus '<code>;;</code>' is not legal. - - -<p> -Lua handles a chunk as the body of an anonymous function -with a variable number of arguments -(see <a href="#2.5.9">§2.5.9</a>). -As such, chunks can define local variables, -receive arguments, and return values. - - -<p> -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. - - -<p> -Chunks can also be pre-compiled into binary form; -see program <code>luac</code> for details. -Programs in source and compiled forms are interchangeable; -Lua automatically detects the file type and acts accordingly. - - - - - - -<h3>2.4.2 - <a name="2.4.2">Blocks</a></h3><p> -A block is a list of statements; -syntactically, a block is the same as a chunk: - -<pre> - block ::= chunk -</pre> - -<p> -A block can be explicitly delimited to produce a single statement: - -<pre> - stat ::= <b>do</b> block <b>end</b> -</pre><p> -Explicit blocks are useful -to control the scope of variable declarations. -Explicit blocks are also sometimes used to -add a <b>return</b> or <b>break</b> statement in the middle -of another block (see <a href="#2.4.4">§2.4.4</a>). - - - - - -<h3>2.4.3 - <a name="2.4.3">Assignment</a></h3> - -<p> -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: - -<pre> - stat ::= varlist `<b>=</b>´ explist - varlist ::= var {`<b>,</b>´ var} - explist ::= exp {`<b>,</b>´ exp} -</pre><p> -Expressions are discussed in <a href="#2.5">§2.5</a>. - - -<p> -Before the assignment, -the list of values is <em>adjusted</em> 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 <b>nil</b>'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 <a href="#2.5">§2.5</a>). - - -<p> -The assignment statement first evaluates all its expressions -and only then are the assignments performed. -Thus the code - -<pre> - i = 3 - i, a[i] = i+1, 20 -</pre><p> -sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> -because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) -before it is assigned 4. -Similarly, the line - -<pre> - x, y = y, x -</pre><p> -exchanges the values of <code>x</code> and <code>y</code>, -and - -<pre> - x, y, z = y, z, x -</pre><p> -cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. - - -<p> -The meaning of assignments to global variables -and table fields can be changed via metatables. -An assignment to an indexed variable <code>t[i] = val</code> is equivalent to -<code>settable_event(t,i,val)</code>. -(See <a href="#2.8">§2.8</a> for a complete description of the -<code>settable_event</code> function. -This function is not defined or callable in Lua. -We use it here only for explanatory purposes.) - - -<p> -An assignment to a global variable <code>x = val</code> -is equivalent to the assignment -<code>_env.x = val</code>, -which in turn is equivalent to - -<pre> - settable_event(_env, "x", val) -</pre><p> -where <code>_env</code> is the environment of the running function. -(The <code>_env</code> variable is not defined in Lua. -We use it here only for explanatory purposes.) - - - - - -<h3>2.4.4 - <a name="2.4.4">Control Structures</a></h3><p> -The control structures -<b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and -familiar syntax: - - - - -<pre> - stat ::= <b>while</b> exp <b>do</b> block <b>end</b> - stat ::= <b>repeat</b> block <b>until</b> exp - stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> -</pre><p> -Lua also has a <b>for</b> statement, in two flavors (see <a href="#2.4.5">§2.4.5</a>). - - -<p> -The condition expression of a -control structure can return any value. -Both <b>false</b> and <b>nil</b> are considered false. -All values different from <b>nil</b> and <b>false</b> are considered true -(in particular, the number 0 and the empty string are also true). - - -<p> -In the <b>repeat</b>–<b>until</b> loop, -the inner block does not end at the <b>until</b> keyword, -but only after the condition. -So, the condition can refer to local variables -declared inside the loop block. - - -<p> -The <b>return</b> 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 <b>return</b> statement is - -<pre> - stat ::= <b>return</b> [explist] -</pre> - -<p> -The <b>break</b> statement is used to terminate the execution of a -<b>while</b>, <b>repeat</b>, or <b>for</b> loop, -skipping to the next statement after the loop: - - -<pre> - stat ::= <b>break</b> -</pre><p> -A <b>break</b> ends the innermost enclosing loop. - - -<p> -The <b>return</b> and <b>break</b> -statements can only be written as the <em>last</em> statement of a block. -If it is really necessary to <b>return</b> or <b>break</b> in the -middle of a block, -then an explicit inner block can be used, -as in the idioms -<code>do return end</code> and <code>do break end</code>, -because now <b>return</b> and <b>break</b> are the last statements in -their (inner) blocks. - - - - - -<h3>2.4.5 - <a name="2.4.5">For Statement</a></h3> - -<p> - -The <b>for</b> statement has two forms: -one numeric and one generic. - - -<p> -The numeric <b>for</b> loop repeats a block of code while a -control variable runs through an arithmetic progression. -It has the following syntax: - -<pre> - stat ::= <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> -</pre><p> -The <em>block</em> is repeated for <em>name</em> starting at the value of -the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the -third <em>exp</em>. -More precisely, a <b>for</b> statement like - -<pre> - for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end -</pre><p> -is equivalent to the code: - -<pre> - do - local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>) - if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end - while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do - local v = <em>var</em> - <em>block</em> - <em>var</em> = <em>var</em> + <em>step</em> - end - end -</pre><p> -Note the following: - -<ul> - -<li> -All three control expressions are evaluated only once, -before the loop starts. -They must all result in numbers. -</li> - -<li> -<code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. -The names shown here are for explanatory purposes only. -</li> - -<li> -If the third expression (the step) is absent, -then a step of 1 is used. -</li> - -<li> -You can use <b>break</b> to exit a <b>for</b> loop. -</li> - -<li> -The loop variable <code>v</code> is local to the loop; -you cannot use its value after the <b>for</b> ends or is broken. -If you need this value, -assign it to another variable before breaking or exiting the loop. -</li> - -</ul> - -<p> -The generic <b>for</b> statement works over functions, -called <em>iterators</em>. -On each iteration, the iterator function is called to produce a new value, -stopping when this new value is <b>nil</b>. -The generic <b>for</b> loop has the following syntax: - -<pre> - stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> - namelist ::= Name {`<b>,</b>´ Name} -</pre><p> -A <b>for</b> statement like - -<pre> - for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end -</pre><p> -is equivalent to the code: - -<pre> - do - local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> - while true do - local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) - <em>var</em> = <em>var_1</em> - if <em>var</em> == nil then break end - <em>block</em> - end - end -</pre><p> -Note the following: - -<ul> - -<li> -<code><em>explist</em></code> is evaluated only once. -Its results are an <em>iterator</em> function, -a <em>state</em>, -and an initial value for the first <em>iterator variable</em>. -</li> - -<li> -<code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables. -The names are here for explanatory purposes only. -</li> - -<li> -You can use <b>break</b> to exit a <b>for</b> loop. -</li> - -<li> -The loop variables <code><em>var_i</em></code> are local to the loop; -you cannot use their values after the <b>for</b> ends. -If you need these values, -then assign them to other variables before breaking or exiting the loop. -</li> - -</ul> - - - - -<h3>2.4.6 - <a name="2.4.6">Function Calls as Statements</a></h3><p> -To allow possible side-effects, -function calls can be executed as statements: - -<pre> - stat ::= functioncall -</pre><p> -In this case, all returned values are thrown away. -Function calls are explained in <a href="#2.5.8">§2.5.8</a>. - - - - - -<h3>2.4.7 - <a name="2.4.7">Local Declarations</a></h3><p> -Local variables can be declared anywhere inside a block. -The declaration can include an initial assignment: - -<pre> - stat ::= <b>local</b> namelist [`<b>=</b>´ explist] -</pre><p> -If present, an initial assignment has the same semantics -of a multiple assignment (see <a href="#2.4.3">§2.4.3</a>). -Otherwise, all variables are initialized with <b>nil</b>. - - -<p> -A chunk is also a block (see <a href="#2.4.1">§2.4.1</a>), -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. - - -<p> -The visibility rules for local variables are explained in <a href="#2.6">§2.6</a>. - - - - - - - -<h2>2.5 - <a name="2.5">Expressions</a></h2> - -<p> -The basic expressions in Lua are the following: - -<pre> - exp ::= prefixexp - exp ::= <b>nil</b> | <b>false</b> | <b>true</b> - exp ::= Number - exp ::= String - exp ::= function - exp ::= tableconstructor - exp ::= `<b>...</b>´ - exp ::= exp binop exp - exp ::= unop exp - prefixexp ::= var | functioncall | `<b>(</b>´ exp `<b>)</b>´ -</pre> - -<p> -Numbers and literal strings are explained in <a href="#2.1">§2.1</a>; -variables are explained in <a href="#2.3">§2.3</a>; -function definitions are explained in <a href="#2.5.9">§2.5.9</a>; -function calls are explained in <a href="#2.5.8">§2.5.8</a>; -table constructors are explained in <a href="#2.5.7">§2.5.7</a>. -Vararg expressions, -denoted by three dots ('<code>...</code>'), can only be used when -directly inside a vararg function; -they are explained in <a href="#2.5.9">§2.5.9</a>. - - -<p> -Binary operators comprise arithmetic operators (see <a href="#2.5.1">§2.5.1</a>), -relational operators (see <a href="#2.5.2">§2.5.2</a>), logical operators (see <a href="#2.5.3">§2.5.3</a>), -and the concatenation operator (see <a href="#2.5.4">§2.5.4</a>). -Unary operators comprise the unary minus (see <a href="#2.5.1">§2.5.1</a>), -the unary <b>not</b> (see <a href="#2.5.3">§2.5.3</a>), -and the unary <em>length operator</em> (see <a href="#2.5.5">§2.5.5</a>). - - -<p> -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 <a href="#2.4.6">§2.4.6</a>)), -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. - - -<p> -Here are some examples: - -<pre> - 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 -</pre> - -<p> -Any expression enclosed in parentheses always results in only one value. -Thus, -<code>(f(x,y,z))</code> is always a single value, -even if <code>f</code> returns several values. -(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> -or <b>nil</b> if <code>f</code> does not return any values.) - - - -<h3>2.5.1 - <a name="2.5.1">Arithmetic Operators</a></h3><p> -Lua supports the usual arithmetic operators: -the binary <code>+</code> (addition), -<code>-</code> (subtraction), <code>*</code> (multiplication), -<code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation); -and unary <code>-</code> (negation). -If the operands are numbers, or strings that can be converted to -numbers (see <a href="#2.2.1">§2.2.1</a>), -then all operations have the usual meaning. -Exponentiation works for any exponent. -For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>. -Modulo is defined as - -<pre> - a % b == a - math.floor(a/b)*b -</pre><p> -That is, it is the remainder of a division that rounds -the quotient towards minus infinity. - - - - - -<h3>2.5.2 - <a name="2.5.2">Relational Operators</a></h3><p> -The relational operators in Lua are - -<pre> - == ~= < > <= >= -</pre><p> -These operators always result in <b>false</b> or <b>true</b>. - - -<p> -Equality (<code>==</code>) first compares the type of its operands. -If the types are different, then the result is <b>false</b>. -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 <em>reference</em>: -two objects are considered equal only if they are the <em>same</em> object. -Every time you create a new object -(a table, userdata, thread, or function), -this new object is different from any previously existing object. - - -<p> -You can change the way that Lua compares tables and userdata -by using the "eq" metamethod (see <a href="#2.8">§2.8</a>). - - -<p> -The conversion rules of <a href="#2.2.1">§2.2.1</a> -<em>do not</em> apply to equality comparisons. -Thus, <code>"0"==0</code> evaluates to <b>false</b>, -and <code>t[0]</code> and <code>t["0"]</code> denote different -entries in a table. - - -<p> -The operator <code>~=</code> is exactly the negation of equality (<code>==</code>). - - -<p> -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 <a href="#2.8">§2.8</a>). -A comparison <code>a > b</code> is translated to <code>b < a</code> -and <code>a >= b</code> is translated to <code>b <= a</code>. - - - - - -<h3>2.5.3 - <a name="2.5.3">Logical Operators</a></h3><p> -The logical operators in Lua are -<b>and</b>, <b>or</b>, and <b>not</b>. -Like the control structures (see <a href="#2.4.4">§2.4.4</a>), -all logical operators consider both <b>false</b> and <b>nil</b> as false -and anything else as true. - - -<p> -The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>. -The conjunction operator <b>and</b> returns its first argument -if this value is <b>false</b> or <b>nil</b>; -otherwise, <b>and</b> returns its second argument. -The disjunction operator <b>or</b> returns its first argument -if this value is different from <b>nil</b> and <b>false</b>; -otherwise, <b>or</b> returns its second argument. -Both <b>and</b> and <b>or</b> use short-cut evaluation; -that is, -the second operand is evaluated only if necessary. -Here are some examples: - -<pre> - 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 -</pre><p> -(In this manual, -<code>--></code> indicates the result of the preceding expression.) - - - - - -<h3>2.5.4 - <a name="2.5.4">Concatenation</a></h3><p> -The string concatenation operator in Lua is -denoted by two dots ('<code>..</code>'). -If both operands are strings or numbers, then they are converted to -strings according to the rules mentioned in <a href="#2.2.1">§2.2.1</a>. -Otherwise, the "concat" metamethod is called (see <a href="#2.8">§2.8</a>). - - - - - -<h3>2.5.5 - <a name="2.5.5">The Length Operator</a></h3> - -<p> -The length operator is denoted by the unary operator <code>#</code>. -The length of a string is its number of bytes -(that is, the usual meaning of string length when each -character is one byte). - - -<p> -The length of a table <code>t</code> is defined to be any -integer index <code>n</code> -such that <code>t[n]</code> is not <b>nil</b> and <code>t[n+1]</code> is <b>nil</b>; -moreover, if <code>t[1]</code> is <b>nil</b>, <code>n</code> can be zero. -For a regular array, with non-nil values from 1 to a given <code>n</code>, -its length is exactly that <code>n</code>, -the index of its last value. -If the array has "holes" -(that is, <b>nil</b> values between other non-nil values), -then <code>#t</code> can be any of the indices that -directly precedes a <b>nil</b> value -(that is, it may consider any such <b>nil</b> value as the end of -the array). - - - - - -<h3>2.5.6 - <a name="2.5.6">Precedence</a></h3><p> -Operator precedence in Lua follows the table below, -from lower to higher priority: - -<pre> - or - and - < > <= >= ~= == - .. - + - - * / % - not # - (unary) - ^ -</pre><p> -As usual, -you can use parentheses to change the precedences of an expression. -The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>') -operators are right associative. -All other binary operators are left associative. - - - - - -<h3>2.5.7 - <a name="2.5.7">Table Constructors</a></h3><p> -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 - -<pre> - tableconstructor ::= `<b>{</b>´ [fieldlist] `<b>}</b>´ - fieldlist ::= field {fieldsep field} [fieldsep] - field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp - fieldsep ::= `<b>,</b>´ | `<b>;</b>´ -</pre> - -<p> -Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry -with key <code>exp1</code> and value <code>exp2</code>. -A field of the form <code>name = exp</code> is equivalent to -<code>["name"] = exp</code>. -Finally, fields of the form <code>exp</code> are equivalent to -<code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers, -starting with 1. -Fields in the other formats do not affect this counting. -For example, - -<pre> - a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 } -</pre><p> -is equivalent to - -<pre> - 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 -</pre> - -<p> -If the last field in the list has the form <code>exp</code> -and the expression is a function call or a vararg expression, -then all values returned by this expression enter the list consecutively -(see <a href="#2.5.8">§2.5.8</a>). -To avoid this, -enclose the function call or the vararg expression -in parentheses (see <a href="#2.5">§2.5</a>). - - -<p> -The field list can have an optional trailing separator, -as a convenience for machine-generated code. - - - - - -<h3>2.5.8 - <a name="2.5.8">Function Calls</a></h3><p> -A function call in Lua has the following syntax: - -<pre> - functioncall ::= prefixexp args -</pre><p> -In a function call, -first prefixexp and args are evaluated. -If the value of prefixexp has type <em>function</em>, -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 <a href="#2.8">§2.8</a>). - - -<p> -The form - -<pre> - functioncall ::= prefixexp `<b>:</b>´ Name args -</pre><p> -can be used to call "methods". -A call <code>v:name(<em>args</em>)</code> -is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, -except that <code>v</code> is evaluated only once. - - -<p> -Arguments have the following syntax: - -<pre> - args ::= `<b>(</b>´ [explist] `<b>)</b>´ - args ::= tableconstructor - args ::= String -</pre><p> -All argument expressions are evaluated before the call. -A call of the form <code>f{<em>fields</em>}</code> is -syntactic sugar for <code>f({<em>fields</em>})</code>; -that is, the argument list is a single new table. -A call of the form <code>f'<em>string</em>'</code> -(or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>) -is syntactic sugar for <code>f('<em>string</em>')</code>; -that is, the argument list is a single literal string. - - -<p> -As an exception to the free-format syntax of Lua, -you cannot put a line break before the '<code>(</code>' in a function call. -This restriction avoids some ambiguities in the language. -If you write - -<pre> - a = f - (g).x(a) -</pre><p> -Lua would see that as a single statement, <code>a = f(g).x(a)</code>. -So, if you want two statements, you must add a semi-colon between them. -If you actually want to call <code>f</code>, -you must remove the line break before <code>(g)</code>. - - -<p> -A call of the form <code>return</code> <em>functioncall</em> is called -a <em>tail call</em>. -Lua implements <em>proper tail calls</em> -(or <em>proper tail recursion</em>): -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 <b>return</b> 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: - -<pre> - 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 -</pre> - - - - -<h3>2.5.9 - <a name="2.5.9">Function Definitions</a></h3> - -<p> -The syntax for function definition is - -<pre> - function ::= <b>function</b> funcbody - funcbody ::= `<b>(</b>´ [parlist] `<b>)</b>´ block <b>end</b> -</pre> - -<p> -The following syntactic sugar simplifies function definitions: - -<pre> - stat ::= <b>function</b> funcname funcbody - stat ::= <b>local</b> <b>function</b> Name funcbody - funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name] -</pre><p> -The statement - -<pre> - function f () <em>body</em> end -</pre><p> -translates to - -<pre> - f = function () <em>body</em> end -</pre><p> -The statement - -<pre> - function t.a.b.c.f () <em>body</em> end -</pre><p> -translates to - -<pre> - t.a.b.c.f = function () <em>body</em> end -</pre><p> -The statement - -<pre> - local function f () <em>body</em> end -</pre><p> -translates to - -<pre> - local f; f = function () <em>body</em> end -</pre><p> -<em>not</em> to - -<pre> - local f = function () <em>body</em> end -</pre><p> -(This only makes a difference when the body of the function -contains references to <code>f</code>.) - - -<p> -A function definition is an executable expression, -whose value has type <em>function</em>. -When Lua pre-compiles a chunk, -all its function bodies are pre-compiled too. -Then, whenever Lua executes the function definition, -the function is <em>instantiated</em> (or <em>closed</em>). -This function instance (or <em>closure</em>) -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. - - -<p> -Parameters act as local variables that are -initialized with the argument values: - -<pre> - parlist ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ -</pre><p> -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 <em>vararg function</em>, -which is -indicated by three dots ('<code>...</code>') 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 <em>vararg expression</em>, -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). - - -<p> -As an example, consider the following definitions: - -<pre> - function f(a, b) end - function g(a, b, ...) end - function r() return 1,2,3 end -</pre><p> -Then, we have the following mapping from arguments to parameters and -to the vararg expression: - -<pre> - 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 -</pre> - -<p> -Results are returned using the <b>return</b> statement (see <a href="#2.4.4">§2.4.4</a>). -If control reaches the end of a function -without encountering a <b>return</b> statement, -then the function returns with no results. - - -<p> -The <em>colon</em> syntax -is used for defining <em>methods</em>, -that is, functions that have an implicit extra parameter <code>self</code>. -Thus, the statement - -<pre> - function t.a.b.c:f (<em>params</em>) <em>body</em> end -</pre><p> -is syntactic sugar for - -<pre> - t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end -</pre> - - - - - - -<h2>2.6 - <a name="2.6">Visibility Rules</a></h2> - -<p> - -Lua is a lexically scoped language. -The scope of variables begins at the first statement <em>after</em> -their declaration and lasts until the end of the innermost block that -includes the declaration. -Consider the following example: - -<pre> - 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) -</pre> - -<p> -Notice that, in a declaration like <code>local x = x</code>, -the new <code>x</code> being declared is not in scope yet, -and so the second <code>x</code> refers to the outside variable. - - -<p> -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 <em>upvalue</em>, or <em>external local variable</em>, -inside the inner function. - - -<p> -Notice that each execution of a <b>local</b> statement -defines new local variables. -Consider the following example: - -<pre> - a = {} - local x = 20 - for i=1,10 do - local y = 0 - a[i] = function () y=y+1; return x+y end - end -</pre><p> -The loop creates ten closures -(that is, ten instances of the anonymous function). -Each of these closures uses a different <code>y</code> variable, -while all of them share the same <code>x</code>. - - - - - -<h2>2.7 - <a name="2.7">Error Handling</a></h2> - -<p> -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 <a href="#lua_pcall"><code>lua_pcall</code></a>). -Whenever an error occurs during Lua compilation or execution, -control returns to C, -which can take appropriate measures -(such as printing an error message). - - -<p> -Lua code can explicitly generate an error by calling the -<a href="#pdf-error"><code>error</code></a> function. -If you need to catch errors in Lua, -you can use the <a href="#pdf-pcall"><code>pcall</code></a> function. - - - - - -<h2>2.8 - <a name="2.8">Metatables</a></h2> - -<p> -Every value in Lua can have a <em>metatable</em>. -This <em>metatable</em> 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 <code>"__add"</code> in its metatable. -If it finds one, -Lua calls this function to perform the addition. - - -<p> -We call the keys in a metatable <em>events</em> -and the values <em>metamethods</em>. -In the previous example, the event is <code>"add"</code> -and the metamethod is the function that performs the addition. - - -<p> -You can query the metatable of any value -through the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. - - -<p> -You can replace the metatable of tables -through the <a href="#pdf-setmetatable"><code>setmetatable</code></a> -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. - - -<p> -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. - - -<p> -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 <em>event</em>. -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. - - -<p> -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, '<code>__</code>'; -for instance, the key for operation "add" is the -string <code>"__add"</code>. -The semantics of these operations is better explained by a Lua function -describing how the interpreter executes the operation. - - -<p> -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 -(<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.) -are described in <a href="#5.1">§5.1</a>. -In particular, to retrieve the metamethod of a given object, -we use the expression - -<pre> - metatable(obj)[event] -</pre><p> -This should be read as - -<pre> - rawget(getmetatable(obj) or {}, event) -</pre><p> - -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 <b>nil</b>). - - - -<ul> - -<li><b>"add":</b> -the <code>+</code> operation. - - - -<p> -The function <code>getbinhandler</code> below defines how Lua chooses a handler -for a binary operation. -First, Lua tries the first operand. -If its type does not define a handler for the operation, -then Lua tries the second operand. - -<pre> - function getbinhandler (op1, op2, event) - return metatable(op1)[event] or metatable(op2)[event] - end -</pre><p> -By using this function, -the behavior of the <code>op1 + op2</code> is - -<pre> - function add_event (op1, op2) - local o1, o2 = tonumber(op1), tonumber(op2) - if o1 and o2 then -- both operands are numeric? - return o1 + o2 -- '+' here is the primitive 'add' - else -- at least one of the operands is not numeric - local h = getbinhandler(op1, op2, "__add") - if h then - -- call the handler with both operands - return (h(op1, op2)) - else -- no handler available: default behavior - error(···) - end - end - end -</pre><p> -</li> - -<li><b>"sub":</b> -the <code>-</code> operation. - -Behavior similar to the "add" operation. -</li> - -<li><b>"mul":</b> -the <code>*</code> operation. - -Behavior similar to the "add" operation. -</li> - -<li><b>"div":</b> -the <code>/</code> operation. - -Behavior similar to the "add" operation. -</li> - -<li><b>"mod":</b> -the <code>%</code> operation. - -Behavior similar to the "add" operation, -with the operation -<code>o1 - floor(o1/o2)*o2</code> as the primitive operation. -</li> - -<li><b>"pow":</b> -the <code>^</code> (exponentiation) operation. - -Behavior similar to the "add" operation, -with the function <code>pow</code> (from the C math library) -as the primitive operation. -</li> - -<li><b>"unm":</b> -the unary <code>-</code> operation. - - -<pre> - function unm_event (op) - local o = tonumber(op) - if o then -- operand is numeric? - return -o -- '-' here is the primitive 'unm' - else -- the operand is not numeric. - -- Try to get a handler from the operand - local h = metatable(op).__unm - if h then - -- call the handler with the operand - return (h(op)) - else -- no handler available: default behavior - error(···) - end - end - end -</pre><p> -</li> - -<li><b>"concat":</b> -the <code>..</code> (concatenation) operation. - - -<pre> - function concat_event (op1, op2) - if (type(op1) == "string" or type(op1) == "number") and - (type(op2) == "string" or type(op2) == "number") then - return op1 .. op2 -- primitive string concatenation - else - local h = getbinhandler(op1, op2, "__concat") - if h then - return (h(op1, op2)) - else - error(···) - end - end - end -</pre><p> -</li> - -<li><b>"len":</b> -the <code>#</code> operation. - - -<pre> - function len_event (op) - if type(op) == "string" then - return strlen(op) -- primitive string length - elseif type(op) == "table" then - return #op -- primitive table length - else - local h = metatable(op).__len - if h then - -- call the handler with the operand - return (h(op)) - else -- no handler available: default behavior - error(···) - end - end - end -</pre><p> -See <a href="#2.5.5">§2.5.5</a> for a description of the length of a table. -</li> - -<li><b>"eq":</b> -the <code>==</code> operation. - -The function <code>getcomphandler</code> defines how Lua chooses a metamethod -for comparison operators. -A metamethod only is selected when both objects -being compared have the same type -and the same metamethod for the selected operation. - -<pre> - function getcomphandler (op1, op2, event) - if type(op1) ~= type(op2) then return nil end - local mm1 = metatable(op1)[event] - local mm2 = metatable(op2)[event] - if mm1 == mm2 then return mm1 else return nil end - end -</pre><p> -The "eq" event is defined as follows: - -<pre> - function eq_event (op1, op2) - if type(op1) ~= type(op2) then -- different types? - return false -- different objects - end - if op1 == op2 then -- primitive equal? - return true -- objects are equal - end - -- try metamethod - local h = getcomphandler(op1, op2, "__eq") - if h then - return (h(op1, op2)) - else - return false - end - end -</pre><p> -<code>a ~= b</code> is equivalent to <code>not (a == b)</code>. -</li> - -<li><b>"lt":</b> -the <code><</code> operation. - - -<pre> - function lt_event (op1, op2) - if type(op1) == "number" and type(op2) == "number" then - return op1 < op2 -- numeric comparison - elseif type(op1) == "string" and type(op2) == "string" then - return op1 < op2 -- lexicographic comparison - else - local h = getcomphandler(op1, op2, "__lt") - if h then - return (h(op1, op2)) - else - error(···) - end - end - end -</pre><p> -<code>a > b</code> is equivalent to <code>b < a</code>. -</li> - -<li><b>"le":</b> -the <code><=</code> operation. - - -<pre> - function le_event (op1, op2) - if type(op1) == "number" and type(op2) == "number" then - return op1 <= op2 -- numeric comparison - elseif type(op1) == "string" and type(op2) == "string" then - return op1 <= op2 -- lexicographic comparison - else - local h = getcomphandler(op1, op2, "__le") - if h then - return (h(op1, op2)) - else - h = getcomphandler(op1, op2, "__lt") - if h then - return not h(op2, op1) - else - error(···) - end - end - end - end -</pre><p> -<code>a >= b</code> is equivalent to <code>b <= a</code>. -Note that, in the absence of a "le" metamethod, -Lua tries the "lt", assuming that <code>a <= b</code> is -equivalent to <code>not (b < a)</code>. -</li> - -<li><b>"index":</b> -The indexing access <code>table[key]</code>. - - -<pre> - function gettable_event (table, key) - local h - if type(table) == "table" then - local v = rawget(table, key) - if v ~= nil then return v end - h = metatable(table).__index - if h == nil then return nil end - else - h = metatable(table).__index - if h == nil then - error(···) - end - end - if type(h) == "function" then - return (h(table, key)) -- call the handler - else return h[key] -- or repeat operation on it - end - end -</pre><p> -</li> - -<li><b>"newindex":</b> -The indexing assignment <code>table[key] = value</code>. - - -<pre> - function settable_event (table, key, value) - local h - if type(table) == "table" then - local v = rawget(table, key) - if v ~= nil then rawset(table, key, value); return end - h = metatable(table).__newindex - if h == nil then rawset(table, key, value); return end - else - h = metatable(table).__newindex - if h == nil then - error(···) - end - end - if type(h) == "function" then - h(table, key,value) -- call the handler - else h[key] = value -- or repeat operation on it - end - end -</pre><p> -</li> - -<li><b>"call":</b> -called when Lua calls a value. - - -<pre> - function function_event (func, ...) - if type(func) == "function" then - return func(...) -- primitive call - else - local h = metatable(func).__call - if h then - return h(func, ...) - else - error(···) - end - end - end -</pre><p> -</li> - -</ul> - - - - -<h2>2.9 - <a name="2.9">Environments</a></h2> - -<p> -Besides metatables, -objects of types thread, function, and userdata -have another table associated with them, -called their <em>environment</em>. -Like metatables, environments are regular tables and -multiple objects can share the same environment. - - -<p> -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 <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>) -are created sharing the environment of the creating thread. -Nested Lua functions are created sharing the environment of -the creating Lua function. - - -<p> -Environments associated with userdata have no meaning for Lua. -It is only a convenience feature for programmers to associate a table to -a userdata. - - -<p> -Environments associated with threads are called -<em>global environments</em>. -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 <a href="#3.3">§3.3</a>). - - -<p> -The environment associated with a C function can be directly -accessed by C code (see <a href="#3.3">§3.3</a>). -It is used as the default environment for other C functions -and userdata created by the function. - - -<p> -Environments associated with Lua functions are used to resolve -all accesses to global variables within the function (see <a href="#2.3">§2.3</a>). -They are used as the default environment for nested Lua functions -created by the function. - - -<p> -You can change the environment of a Lua function or the -running thread by calling <a href="#pdf-setfenv"><code>setfenv</code></a>. -You can get the environment of a Lua function or the running thread -by calling <a href="#pdf-getfenv"><code>getfenv</code></a>. -To manipulate the environment of other objects -(userdata, C functions, other threads) you must -use the C API. - - - - - -<h2>2.10 - <a name="2.10">Garbage Collection</a></h2> - -<p> -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 <em>garbage collector</em> from time to time -to collect all <em>dead objects</em> -(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. - - -<p> -Lua implements an incremental mark-and-sweep collector. -It uses two numbers to control its garbage-collection cycles: -the <em>garbage-collector pause</em> and -the <em>garbage-collector step multiplier</em>. -Both use percentage points as units -(so that a value of 100 means an internal value of 1). - - -<p> -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. - - -<p> -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. - - -<p> -You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C -or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. -With these functions you can also control -the collector directly (e.g., stop and restart it). - - - -<h3>2.10.1 - <a name="2.10.1">Garbage-Collection Metamethods</a></h3> - -<p> -Using the C API, -you can set garbage-collector metamethods for userdata (see <a href="#2.8">§2.8</a>). -These metamethods are also called <em>finalizers</em>. -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). - - -<p> -Garbage userdata with a field <code>__gc</code> 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: - -<pre> - function gc_event (udata) - local h = metatable(udata).__gc - if h then - h(udata) - end - end -</pre> - -<p> -At the end of each garbage-collection cycle, -the finalizers for userdata are called in <em>reverse</em> -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. - - - - - -<h3>2.10.2 - <a name="2.10.2">Weak Tables</a></h3> - -<p> -A <em>weak table</em> is a table whose elements are -<em>weak references</em>. -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. - - -<p> -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 -<code>__mode</code> field of its metatable. -If the <code>__mode</code> field is a string containing the character '<code>k</code>', -the keys in the table are weak. -If <code>__mode</code> contains '<code>v</code>', -the values in the table are weak. - - -<p> -After you use a table as a metatable, -you should not change the value of its <code>__mode</code> field. -Otherwise, the weak behavior of the tables controlled by this -metatable is undefined. - - - - - - - -<h2>2.11 - <a name="2.11">Coroutines</a></h2> - -<p> -Lua supports coroutines, -also called <em>collaborative multithreading</em>. -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. - - -<p> -You create a coroutine with a call to <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>. -Its sole argument is a function -that is the main function of the coroutine. -The <code>create</code> function only creates a new coroutine and -returns a handle to it (an object of type <em>thread</em>); -it does not start the coroutine execution. - - -<p> -When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, -passing as its first argument -a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, -the coroutine starts its execution, -at the first line of its main function. -Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on -to the coroutine main function. -After the coroutine starts running, -it runs until it terminates or <em>yields</em>. - - -<p> -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, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>, -plus any values returned by the coroutine main function. -In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b> -plus an error message. - - -<p> -A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. -When a coroutine yields, -the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> 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, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>, -plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. -The next time you resume the same coroutine, -it continues its execution from the point where it yielded, -with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra -arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. - - -<p> -Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, -the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> 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 <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. -<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, -except the first one (the boolean error code). -Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, -<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors; -any error is propagated to the caller. - - -<p> -As an example, -consider the following code: - -<pre> - 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")) -</pre><p> -When you run it, it produces the following output: - -<pre> - 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 -</pre> - - - - -<h1>3 - <a name="3">The Application Program Interface</a></h1> - -<p> - -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 <a name="pdf-lua.h"><code>lua.h</code></a>. - - -<p> -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. - - -<p> -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 <a name="pdf-luai_apicheck"><code>luai_apicheck</code></a>, -in file <code>luaconf.h</code>. - - - -<h2>3.1 - <a name="3.1">The Stack</a></h2> - -<p> -Lua uses a <em>virtual stack</em> to pass values to and from C. -Each element in this stack represents a Lua value -(<b>nil</b>, number, string, etc.). - - -<p> -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 <a href="#lua_CFunction"><code>lua_CFunction</code></a>). - - -<p> -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 <em>index</em>: -A positive index represents an <em>absolute</em> stack position -(starting at 1); -a negative index represents an <em>offset</em> relative to the top of the stack. -More specifically, if the stack has <em>n</em> elements, -then index 1 represents the first element -(that is, the element that was pushed onto the stack first) -and -index <em>n</em> represents the last element; -index -1 also represents the last element -(that is, the element at the top) -and index <em>-n</em> represents the first element. -We say that an index is <em>valid</em> -if it lies between 1 and the stack top -(that is, if <code>1 ≤ abs(index) ≤ top</code>). - - - - - - -<h2>3.2 - <a name="3.2">Stack Size</a></h2> - -<p> -When you interact with Lua API, -you are responsible for ensuring consistency. -In particular, -<em>you are responsible for controlling stack overflow</em>. -You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a> -to grow the stack size. - - -<p> -Whenever Lua calls C, -it ensures that at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> stack positions are available. -<code>LUA_MINSTACK</code> 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. - - -<p> -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 <a href="#lua_checkstack"><code>lua_checkstack</code></a>. -Such indices are called <em>acceptable indices</em>. -More formally, we define an <em>acceptable index</em> -as follows: - -<pre> - (index < 0 && abs(index) <= top) || - (index > 0 && index <= stackspace) -</pre><p> -Note that 0 is never an acceptable index. - - - - - -<h2>3.3 - <a name="3.3">Pseudo-Indices</a></h2> - -<p> -Unless otherwise noted, -any function that accepts valid indices can also be called with -<em>pseudo-indices</em>, -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 <a href="#3.4">§3.4</a>). - - -<p> -The thread environment (where global variables live) is -always at pseudo-index <a name="pdf-LUA_GLOBALSINDEX"><code>LUA_GLOBALSINDEX</code></a>. -The environment of the running C function is always -at pseudo-index <a name="pdf-LUA_ENVIRONINDEX"><code>LUA_ENVIRONINDEX</code></a>. - - -<p> -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 - -<pre> - lua_getfield(L, LUA_GLOBALSINDEX, varname); -</pre> - - - - -<h2>3.4 - <a name="3.4">C Closures</a></h2> - -<p> -When a C function is created, -it is possible to associate some values with it, -thus creating a <em>C closure</em>; -these values are called <em>upvalues</em> and are -accessible to the function whenever it is called -(see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>). - - -<p> -Whenever a C function is called, -its upvalues are located at specific pseudo-indices. -These pseudo-indices are produced by the macro -<a name="lua_upvalueindex"><code>lua_upvalueindex</code></a>. -The first value associated with a function is at position -<code>lua_upvalueindex(1)</code>, and so on. -Any access to <code>lua_upvalueindex(<em>n</em>)</code>, -where <em>n</em> is greater than the number of upvalues of the -current function (but not greater than 256), -produces an acceptable (but invalid) index. - - - - - -<h2>3.5 - <a name="3.5">Registry</a></h2> - -<p> -Lua provides a <em>registry</em>, -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 -<a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>. -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. - - -<p> -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. - - - - - -<h2>3.6 - <a name="3.6">Error Handling in C</a></h2> - -<p> -Internally, Lua uses the C <code>longjmp</code> facility to handle errors. -(You can also choose to use exceptions if you use C++; -see file <code>luaconf.h</code>.) -When Lua faces any error -(such as memory allocation errors, type errors, syntax errors, -and runtime errors) -it <em>raises</em> an error; -that is, it does a long jump. -A <em>protected environment</em> uses <code>setjmp</code> -to set a recover point; -any error jumps to the most recent active recover point. - - -<p> -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. - - -<p> -Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>. - - - - - -<h2>3.7 - <a name="3.7">Functions and Types</a></h2> - -<p> -Here we list all functions and types from the C API in -alphabetical order. -Each function has an indicator like this: -<span class="apii">[-o, +p, <em>x</em>]</span> - - -<p> -The first field, <code>o</code>, -is how many elements the function pops from the stack. -The second field, <code>p</code>, -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 <code>x|y</code> means the function can push (or pop) -<code>x</code> or <code>y</code> elements, -depending on the situation; -an interrogation mark '<code>?</code>' 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, <code>x</code>, -tells whether the function may throw errors: -'<code>-</code>' means the function never throws any error; -'<code>m</code>' means the function may throw an error -only due to not enough memory; -'<code>e</code>' means the function may throw other kinds of errors; -'<code>v</code>' means the function may throw an error on purpose. - - - -<hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3> -<pre>typedef void * (*lua_Alloc) (void *ud, - void *ptr, - size_t osize, - size_t nsize);</pre> - -<p> -The type of the memory-allocation function used by Lua states. -The allocator function must provide a -functionality similar to <code>realloc</code>, -but not exactly the same. -Its arguments are -<code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>; -<code>ptr</code>, a pointer to the block being allocated/reallocated/freed; -<code>osize</code>, the original size of the block; -<code>nsize</code>, the new size of the block. -<code>ptr</code> is <code>NULL</code> if and only if <code>osize</code> is zero. -When <code>nsize</code> is zero, the allocator must return <code>NULL</code>; -if <code>osize</code> is not zero, -it should free the block pointed to by <code>ptr</code>. -When <code>nsize</code> is not zero, the allocator returns <code>NULL</code> -if and only if it cannot fill the request. -When <code>nsize</code> is not zero and <code>osize</code> is zero, -the allocator should behave like <code>malloc</code>. -When <code>nsize</code> and <code>osize</code> are not zero, -the allocator behaves like <code>realloc</code>. -Lua assumes that the allocator never fails when -<code>osize >= nsize</code>. - - -<p> -Here is a simple implementation for the allocator function. -It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>. - -<pre> - 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); - } -</pre><p> -This code assumes -that <code>free(NULL)</code> has no effect and that -<code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>. -ANSI C ensures both behaviors. - - - - - -<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> - -<p> -Sets a new panic function and returns the old one. - - -<p> -If an error happens outside any protected environment, -Lua calls a <em>panic function</em> -and then calls <code>exit(EXIT_FAILURE)</code>, -thus exiting the host application. -Your panic function can avoid this exit by -never returning (e.g., doing a long jump). - - -<p> -The panic function can access the error message at the top of the stack. - - - - - -<hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> -<span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> -<pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> - -<p> -Calls a function. - - -<p> -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 <a href="#lua_call"><code>lua_call</code></a>; -<code>nargs</code> 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 <code>nresults</code>, -unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. -In this case, <em>all</em> 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. - - -<p> -Any error inside the called function is propagated upwards -(with a <code>longjmp</code>). - - -<p> -The following example shows how the host program can do the -equivalent to this Lua code: - -<pre> - a = f("how", t.x, 14) -</pre><p> -Here it is in C: - -<pre> - 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' */ -</pre><p> -Note that the code above is "balanced": -at its end, the stack is back to its original configuration. -This is considered good programming practice. - - - - - -<hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3> -<pre>typedef int (*lua_CFunction) (lua_State *L);</pre> - -<p> -Type for C functions. - - -<p> -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, -<code>lua_gettop(L)</code> 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 <code>lua_gettop(L)</code>. -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. - - -<p> -As an example, the following function receives a variable number -of numerical arguments and returns their average and sum: - -<pre> - 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 */ - } -</pre> - - - - -<hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>int lua_checkstack (lua_State *L, int extra);</pre> - -<p> -Ensures that there are at least <code>extra</code> 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. - - - - - -<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>void lua_close (lua_State *L);</pre> - -<p> -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. - - - - - -<hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> -<span class="apii">[-n, +1, <em>e</em>]</span> -<pre>void lua_concat (lua_State *L, int n);</pre> - -<p> -Concatenates the <code>n</code> values at the top of the stack, -pops them, and leaves the result at the top. -If <code>n</code> is 1, the result is the single value on the stack -(that is, the function does nothing); -if <code>n</code> is 0, the result is the empty string. -Concatenation is performed following the usual semantics of Lua -(see <a href="#2.5.4">§2.5.4</a>). - - - - - -<hr><h3><a name="lua_cpcall"><code>lua_cpcall</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>-</em>]</span> -<pre>int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);</pre> - -<p> -Calls the C function <code>func</code> in protected mode. -<code>func</code> starts with only one element in its stack, -a light userdata containing <code>ud</code>. -In case of errors, -<a href="#lua_cpcall"><code>lua_cpcall</code></a> returns the same error codes as <a href="#lua_pcall"><code>lua_pcall</code></a>, -plus the error object on the top of the stack; -otherwise, it returns zero, and does not change the stack. -All values returned by <code>func</code> are discarded. - - - - - -<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> - -<p> -Creates a new empty table and pushes it onto the stack. -The new table has space pre-allocated -for <code>narr</code> array elements and <code>nrec</code> 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 <a href="#lua_newtable"><code>lua_newtable</code></a>. - - - - - -<hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre> - -<p> -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, -<a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>) -with the given <code>data</code> -to write them. - - -<p> -The value returned is the error code returned by the last -call to the writer; -0 means no errors. - - -<p> -This function does not pop the Lua function from the stack. - - - - - -<hr><h3><a name="lua_equal"><code>lua_equal</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>int lua_equal (lua_State *L, int index1, int index2);</pre> - -<p> -Returns 1 if the two values in acceptable indices <code>index1</code> and -<code>index2</code> are equal, -following the semantics of the Lua <code>==</code> operator -(that is, may call metamethods). -Otherwise returns 0. -Also returns 0 if any of the indices is non valid. - - - - - -<hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p> -<span class="apii">[-1, +0, <em>v</em>]</span> -<pre>int lua_error (lua_State *L);</pre> - -<p> -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 <a href="#luaL_error"><code>luaL_error</code></a>). - - - - - -<hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>int lua_gc (lua_State *L, int what, int data);</pre> - -<p> -Controls the garbage collector. - - -<p> -This function performs several tasks, -according to the value of the parameter <code>what</code>: - -<ul> - -<li><b><code>LUA_GCSTOP</code>:</b> -stops the garbage collector. -</li> - -<li><b><code>LUA_GCRESTART</code>:</b> -restarts the garbage collector. -</li> - -<li><b><code>LUA_GCCOLLECT</code>:</b> -performs a full garbage-collection cycle. -</li> - -<li><b><code>LUA_GCCOUNT</code>:</b> -returns the current amount of memory (in Kbytes) in use by Lua. -</li> - -<li><b><code>LUA_GCCOUNTB</code>:</b> -returns the remainder of dividing the current amount of bytes of -memory in use by Lua by 1024. -</li> - -<li><b><code>LUA_GCSTEP</code>:</b> -performs an incremental step of garbage collection. -The step "size" is controlled by <code>data</code> -(larger values mean more steps) in a non-specified way. -If you want to control the step size -you must experimentally tune the value of <code>data</code>. -The function returns 1 if the step finished a -garbage-collection cycle. -</li> - -<li><b><code>LUA_GCSETPAUSE</code>:</b> -sets <code>data</code> as the new value -for the <em>pause</em> of the collector (see <a href="#2.10">§2.10</a>). -The function returns the previous value of the pause. -</li> - -<li><b><code>LUA_GCSETSTEPMUL</code>:</b> -sets <code>data</code> as the new value for the <em>step multiplier</em> of -the collector (see <a href="#2.10">§2.10</a>). -The function returns the previous value of the step multiplier. -</li> - -</ul> - - - - -<hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> - -<p> -Returns the memory-allocation function of a given state. -If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the -opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>. - - - - - -<hr><h3><a name="lua_getfenv"><code>lua_getfenv</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_getfenv (lua_State *L, int index);</pre> - -<p> -Pushes onto the stack the environment table of -the value at the given index. - - - - - -<hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>void lua_getfield (lua_State *L, int index, const char *k);</pre> - -<p> -Pushes onto the stack the value <code>t[k]</code>, -where <code>t</code> is the value at the given valid index. -As in Lua, this function may trigger a metamethod -for the "index" event (see <a href="#2.8">§2.8</a>). - - - - - -<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>void lua_getglobal (lua_State *L, const char *name);</pre> - -<p> -Pushes onto the stack the value of the global <code>name</code>. -It is defined as a macro: - -<pre> - #define lua_getglobal(L,s) lua_getfield(L, LUA_GLOBALSINDEX, s) -</pre> - - - - -<hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>-</em>]</span> -<pre>int lua_getmetatable (lua_State *L, int index);</pre> - -<p> -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. - - - - - -<hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> -<span class="apii">[-1, +1, <em>e</em>]</span> -<pre>void lua_gettable (lua_State *L, int index);</pre> - -<p> -Pushes onto the stack the value <code>t[k]</code>, -where <code>t</code> is the value at the given valid index -and <code>k</code> is the value at the top of the stack. - - -<p> -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 <a href="#2.8">§2.8</a>). - - - - - -<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_gettop (lua_State *L);</pre> - -<p> -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). - - - - - -<hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> -<span class="apii">[-1, +1, <em>-</em>]</span> -<pre>void lua_insert (lua_State *L, int index);</pre> - -<p> -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. - - - - - -<hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3> -<pre>typedef ptrdiff_t lua_Integer;</pre> - -<p> -The type used by the Lua API to represent integral values. - - -<p> -By default it is a <code>ptrdiff_t</code>, -which is usually the largest signed integral type the machine handles -"comfortably". - - - - - -<hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isboolean (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index has type boolean, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_iscfunction (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a C function, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isfunction (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a function -(either C or Lua), and 0 otherwise. - - - - - -<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_islightuserdata (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a light userdata, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isnil (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is <b>nil</b>, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isnone (lua_State *L, int index);</pre> - -<p> -Returns 1 if the given acceptable index is not valid -(that is, it refers to an element outside the current stack), -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isnoneornil (lua_State *L, int index);</pre> - -<p> -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 <b>nil</b>, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isnumber (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a number -or a string convertible to a number, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isstring (lua_State *L, int index);</pre> - -<p> -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. - - - - - -<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_istable (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a table, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isthread (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a thread, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_isuserdata (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given acceptable index is a userdata -(either full or light), and 0 otherwise. - - - - - -<hr><h3><a name="lua_lessthan"><code>lua_lessthan</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>int lua_lessthan (lua_State *L, int index1, int index2);</pre> - -<p> -Returns 1 if the value at acceptable index <code>index1</code> is smaller -than the value at acceptable index <code>index2</code>, -following the semantics of the Lua <code><</code> operator -(that is, may call metamethods). -Otherwise returns 0. -Also returns 0 if any of the indices is non valid. - - - - - -<hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>int lua_load (lua_State *L, - lua_Reader reader, - void *data, - const char *chunkname);</pre> - -<p> -Loads a Lua chunk. -If there are no errors, -<a href="#lua_load"><code>lua_load</code></a> pushes the compiled chunk as a Lua -function on top of the stack. -Otherwise, it pushes an error message. -The return values of <a href="#lua_load"><code>lua_load</code></a> are: - -<ul> - -<li><b>0:</b> no errors;</li> - -<li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>:</b> -syntax error during pre-compilation;</li> - -<li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b> -memory allocation error.</li> - -</ul> - -<p> -This function only loads a chunk; -it does not run it. - - -<p> -<a href="#lua_load"><code>lua_load</code></a> automatically detects whether the chunk is text or binary, -and loads it accordingly (see program <code>luac</code>). - - -<p> -The <a href="#lua_load"><code>lua_load</code></a> function uses a user-supplied <code>reader</code> function -to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>). -The <code>data</code> argument is an opaque value passed to the reader function. - - -<p> -The <code>chunkname</code> argument gives a name to the chunk, -which is used for error messages and in debug information (see <a href="#3.8">§3.8</a>). - - - - - -<hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> - -<p> -Creates a new, independent state. -Returns <code>NULL</code> if cannot create the state -(due to lack of memory). -The argument <code>f</code> is the allocator function; -Lua does all memory allocation for this state through this function. -The second argument, <code>ud</code>, is an opaque pointer that Lua -simply passes to the allocator in every call. - - - - - -<hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_newtable (lua_State *L);</pre> - -<p> -Creates a new empty table and pushes it onto the stack. -It is equivalent to <code>lua_createtable(L, 0, 0)</code>. - - - - - -<hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>lua_State *lua_newthread (lua_State *L);</pre> - -<p> -Creates a new thread, pushes it on the stack, -and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> 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. - - -<p> -There is no explicit function to close or to destroy a thread. -Threads are subject to garbage collection, -like any Lua object. - - - - - -<hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> - -<p> -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. - - -<p> -Userdata represent C values in Lua. -A <em>full userdata</em> 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). - - -<p> -When Lua collects a full userdata with a <code>gc</code> metamethod, -Lua calls the metamethod and marks the userdata as finalized. -When this userdata is collected again then -Lua frees its corresponding memory. - - - - - -<hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> -<span class="apii">[-1, +(2|0), <em>e</em>]</span> -<pre>int lua_next (lua_State *L, int index);</pre> - -<p> -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 <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). - - -<p> -A typical traversal looks like this: - -<pre> - /* 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); - } -</pre> - -<p> -While traversing a table, -do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, -unless you know that the key is actually a string. -Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> <em>changes</em> -the value at the given index; -this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. - - - - - -<hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> -<pre>typedef double lua_Number;</pre> - -<p> -The type of numbers in Lua. -By default, it is double, but that can be changed in <code>luaconf.h</code>. - - -<p> -Through the configuration file you can change -Lua to operate with another type for numbers (e.g., float or long). - - - - - -<hr><h3><a name="lua_objlen"><code>lua_objlen</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>size_t lua_objlen (lua_State *L, int index);</pre> - -<p> -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 ('<code>#</code>'); -for userdata, this is the size of the block of memory allocated -for the userdata; -for other values, it is 0. - - - - - -<hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> -<span class="apii">[-(nargs + 1), +(nresults|1), <em>-</em>]</span> -<pre>int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);</pre> - -<p> -Calls a function in protected mode. - - -<p> -Both <code>nargs</code> and <code>nresults</code> have the same meaning as -in <a href="#lua_call"><code>lua_call</code></a>. -If there are no errors during the call, -<a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>. -However, if there is any error, -<a href="#lua_pcall"><code>lua_pcall</code></a> catches it, -pushes a single value on the stack (the error message), -and returns an error code. -Like <a href="#lua_call"><code>lua_call</code></a>, -<a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function -and its arguments from the stack. - - -<p> -If <code>errfunc</code> is 0, -then the error message returned on the stack -is exactly the original error message. -Otherwise, <code>errfunc</code> is the stack index of an -<em>error handler function</em>. -(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 <a href="#lua_pcall"><code>lua_pcall</code></a>. - - -<p> -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 <a href="#lua_pcall"><code>lua_pcall</code></a>, -since by then the stack has unwound. - - -<p> -The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns 0 in case of success -or one of the following error codes -(defined in <code>lua.h</code>): - -<ul> - -<li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>:</b> -a runtime error. -</li> - -<li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b> -memory allocation error. -For such errors, Lua does not call the error handler function. -</li> - -<li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>:</b> -error while running the error handler function. -</li> - -</ul> - - - - -<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> -<span class="apii">[-n, +0, <em>-</em>]</span> -<pre>void lua_pop (lua_State *L, int n);</pre> - -<p> -Pops <code>n</code> elements from the stack. - - - - - -<hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushboolean (lua_State *L, int b);</pre> - -<p> -Pushes a boolean value with value <code>b</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> -<span class="apii">[-n, +1, <em>m</em>]</span> -<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> - -<p> -Pushes a new C closure onto the stack. - - -<p> -When a C function is created, -it is possible to associate some values with it, -thus creating a C closure (see <a href="#3.4">§3.4</a>); -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 <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> -is called to create and push the C function onto the stack, -with the argument <code>n</code> telling how many values should be -associated with the function. -<a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. - - -<p> -The maximum value for <code>n</code> is 255. - - - - - -<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> - -<p> -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 <code>function</code> that, -when called, invokes the corresponding C function. - - -<p> -Any function to be registered in Lua must -follow the correct protocol to receive its parameters -and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). - - -<p> -<code>lua_pushcfunction</code> is defined as a macro: - -<pre> - #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0) -</pre> - - - - -<hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> - -<p> -Pushes onto the stack a formatted string -and returns a pointer to this string. -It is similar to the C function <code>sprintf</code>, -but has some important differences: - -<ul> - -<li> -You do not have to allocate space for the result: -the result is a Lua string and Lua takes care of memory allocation -(and deallocation, through garbage collection). -</li> - -<li> -The conversion specifiers are quite restricted. -There are no flags, widths, or precisions. -The conversion specifiers can only be -'<code>%%</code>' (inserts a '<code>%</code>' in the string), -'<code>%s</code>' (inserts a zero-terminated string, with no size restrictions), -'<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>), -'<code>%p</code>' (inserts a pointer as a hexadecimal numeral), -'<code>%d</code>' (inserts an <code>int</code>), and -'<code>%c</code>' (inserts an <code>int</code> as a character). -</li> - -</ul> - - - - -<hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> - -<p> -Pushes a number with value <code>n</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> - -<p> -Pushes a light userdata onto the stack. - - -<p> -Userdata represent C values in Lua. -A <em>light userdata</em> 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. - - - - - -<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_pushliteral (lua_State *L, const char *s);</pre> - -<p> -This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>, -but can be used only when <code>s</code> is a literal string. -In these cases, it automatically provides the string length. - - - - - -<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_pushlstring (lua_State *L, const char *s, size_t len);</pre> - -<p> -Pushes the string pointed to by <code>s</code> with size <code>len</code> -onto the stack. -Lua makes (or reuses) an internal copy of the given string, -so the memory at <code>s</code> can be freed or reused immediately after -the function returns. -The string can contain embedded zeros. - - - - - -<hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushnil (lua_State *L);</pre> - -<p> -Pushes a nil value onto the stack. - - - - - -<hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> - -<p> -Pushes a number with value <code>n</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_pushstring (lua_State *L, const char *s);</pre> - -<p> -Pushes the zero-terminated string pointed to by <code>s</code> -onto the stack. -Lua makes (or reuses) an internal copy of the given string, -so the memory at <code>s</code> 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. - - - - - -<hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>int lua_pushthread (lua_State *L);</pre> - -<p> -Pushes the thread represented by <code>L</code> onto the stack. -Returns 1 if this thread is the main thread of its state. - - - - - -<hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_pushvalue (lua_State *L, int index);</pre> - -<p> -Pushes a copy of the element at the given valid index -onto the stack. - - - - - -<hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *lua_pushvfstring (lua_State *L, - const char *fmt, - va_list argp);</pre> - -<p> -Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> -instead of a variable number of arguments. - - - - - -<hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> - -<p> -Returns 1 if the two values in acceptable indices <code>index1</code> and -<code>index2</code> are primitively equal -(that is, without calling metamethods). -Otherwise returns 0. -Also returns 0 if any of the indices are non valid. - - - - - -<hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> -<span class="apii">[-1, +1, <em>-</em>]</span> -<pre>void lua_rawget (lua_State *L, int index);</pre> - -<p> -Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access -(i.e., without metamethods). - - - - - -<hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void lua_rawgeti (lua_State *L, int index, int n);</pre> - -<p> -Pushes onto the stack the value <code>t[n]</code>, -where <code>t</code> is the value at the given valid index. -The access is raw; -that is, it does not invoke metamethods. - - - - - -<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p> -<span class="apii">[-2, +0, <em>m</em>]</span> -<pre>void lua_rawset (lua_State *L, int index);</pre> - -<p> -Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment -(i.e., without metamethods). - - - - - -<hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>void lua_rawseti (lua_State *L, int index, int n);</pre> - -<p> -Does the equivalent of <code>t[n] = v</code>, -where <code>t</code> is the value at the given valid index -and <code>v</code> is the value at the top of the stack. - - -<p> -This function pops the value from the stack. -The assignment is raw; -that is, it does not invoke metamethods. - - - - - -<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> -<pre>typedef const char * (*lua_Reader) (lua_State *L, - void *data, - size_t *size);</pre> - -<p> -The reader function used by <a href="#lua_load"><code>lua_load</code></a>. -Every time it needs another piece of the chunk, -<a href="#lua_load"><code>lua_load</code></a> calls the reader, -passing along its <code>data</code> parameter. -The reader must return a pointer to a block of memory -with a new piece of the chunk -and set <code>size</code> 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 <code>NULL</code> or set <code>size</code> to zero. -The reader function may return pieces of any size greater than zero. - - - - - -<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>void lua_register (lua_State *L, - const char *name, - lua_CFunction f);</pre> - -<p> -Sets the C function <code>f</code> as the new value of global <code>name</code>. -It is defined as a macro: - -<pre> - #define lua_register(L,n,f) \ - (lua_pushcfunction(L, f), lua_setglobal(L, n)) -</pre> - - - - -<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> -<span class="apii">[-1, +0, <em>-</em>]</span> -<pre>void lua_remove (lua_State *L, int index);</pre> - -<p> -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. - - - - - -<hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> -<span class="apii">[-1, +0, <em>-</em>]</span> -<pre>void lua_replace (lua_State *L, int index);</pre> - -<p> -Moves the top element into the given position (and pops it), -without shifting any element -(therefore replacing the value at the given position). - - - - - -<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> -<span class="apii">[-?, +?, <em>-</em>]</span> -<pre>int lua_resume (lua_State *L, int narg);</pre> - -<p> -Starts and resumes a coroutine in a given thread. - - -<p> -To start a coroutine, you first create a new thread -(see <a href="#lua_newthread"><code>lua_newthread</code></a>); -then you push onto its stack the main function plus any arguments; -then you call <a href="#lua_resume"><code>lua_resume</code></a>, -with <code>narg</code> 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 <a href="#lua_yield"><code>lua_yield</code></a>, -or all values returned by the body function. -<a href="#lua_resume"><code>lua_resume</code></a> returns -<a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields, -0 if the coroutine finishes its execution -without errors, -or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>). -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 <code>yield</code>, -and then call <a href="#lua_resume"><code>lua_resume</code></a>. - - - - - -<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> - -<p> -Changes the allocator function of a given state to <code>f</code> -with user data <code>ud</code>. - - - - - -<hr><h3><a name="lua_setfenv"><code>lua_setfenv</code></a></h3><p> -<span class="apii">[-1, +0, <em>-</em>]</span> -<pre>int lua_setfenv (lua_State *L, int index);</pre> - -<p> -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, -<a href="#lua_setfenv"><code>lua_setfenv</code></a> returns 0. -Otherwise it returns 1. - - - - - -<hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> -<span class="apii">[-1, +0, <em>e</em>]</span> -<pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> - -<p> -Does the equivalent to <code>t[k] = v</code>, -where <code>t</code> is the value at the given valid index -and <code>v</code> is the value at the top of the stack. - - -<p> -This function pops the value from the stack. -As in Lua, this function may trigger a metamethod -for the "newindex" event (see <a href="#2.8">§2.8</a>). - - - - - -<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> -<span class="apii">[-1, +0, <em>e</em>]</span> -<pre>void lua_setglobal (lua_State *L, const char *name);</pre> - -<p> -Pops a value from the stack and -sets it as the new value of global <code>name</code>. -It is defined as a macro: - -<pre> - #define lua_setglobal(L,s) lua_setfield(L, LUA_GLOBALSINDEX, s) -</pre> - - - - -<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> -<span class="apii">[-1, +0, <em>-</em>]</span> -<pre>int lua_setmetatable (lua_State *L, int index);</pre> - -<p> -Pops a table from the stack and -sets it as the new metatable for the value at the given -acceptable index. - - - - - -<hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> -<span class="apii">[-2, +0, <em>e</em>]</span> -<pre>void lua_settable (lua_State *L, int index);</pre> - -<p> -Does the equivalent to <code>t[k] = v</code>, -where <code>t</code> is the value at the given valid index, -<code>v</code> is the value at the top of the stack, -and <code>k</code> is the value just below the top. - - -<p> -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 <a href="#2.8">§2.8</a>). - - - - - -<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> -<span class="apii">[-?, +?, <em>-</em>]</span> -<pre>void lua_settop (lua_State *L, int index);</pre> - -<p> -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 <b>nil</b>. -If <code>index</code> is 0, then all stack elements are removed. - - - - - -<hr><h3><a name="lua_State"><code>lua_State</code></a></h3> -<pre>typedef struct lua_State lua_State;</pre> - -<p> -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. - - -<p> -A pointer to this state must be passed as the first argument to -every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, -which creates a Lua state from scratch. - - - - - -<hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_status (lua_State *L);</pre> - -<p> -Returns the status of the thread <code>L</code>. - - -<p> -The status can be 0 for a normal thread, -an error code if the thread finished its execution with an error, -or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. - - - - - -<hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_toboolean (lua_State *L, int index);</pre> - -<p> -Converts the Lua value at the given acceptable index to a C boolean -value (0 or 1). -Like all tests in Lua, -<a href="#lua_toboolean"><code>lua_toboolean</code></a> returns 1 for any Lua value -different from <b>false</b> and <b>nil</b>; -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 <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) - - - - - -<hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> - -<p> -Converts a value at the given acceptable index to a C function. -That value must be a C function; -otherwise, returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> - -<p> -Converts the Lua value at the given acceptable index -to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. -The Lua value must be a number or a string convertible to a number -(see <a href="#2.2.1">§2.2.1</a>); -otherwise, <a href="#lua_tointeger"><code>lua_tointeger</code></a> returns 0. - - -<p> -If the number is not an integer, -it is truncated in some non-specified way. - - - - - -<hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> - -<p> -Converts the Lua value at the given acceptable index to a C string. -If <code>len</code> is not <code>NULL</code>, -it also sets <code>*len</code> with the string length. -The Lua value must be a string or a number; -otherwise, the function returns <code>NULL</code>. -If the value is a number, -then <a href="#lua_tolstring"><code>lua_tolstring</code></a> also -<em>changes the actual value in the stack to a string</em>. -(This change confuses <a href="#lua_next"><code>lua_next</code></a> -when <a href="#lua_tolstring"><code>lua_tolstring</code></a> is applied to keys during a table traversal.) - - -<p> -<a href="#lua_tolstring"><code>lua_tolstring</code></a> returns a fully aligned pointer -to a string inside the Lua state. -This string always has a zero ('<code>\0</code>') -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 <a href="#lua_tolstring"><code>lua_tolstring</code></a> -will be valid after the corresponding value is removed from the stack. - - - - - -<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> - -<p> -Converts the Lua value at the given acceptable index -to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>). -The Lua value must be a number or a string convertible to a number -(see <a href="#2.2.1">§2.2.1</a>); -otherwise, <a href="#lua_tonumber"><code>lua_tonumber</code></a> returns 0. - - - - - -<hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>const void *lua_topointer (lua_State *L, int index);</pre> - -<p> -Converts the value at the given acceptable index to a generic -C pointer (<code>void*</code>). -The value can be a userdata, a table, a thread, or a function; -otherwise, <a href="#lua_topointer"><code>lua_topointer</code></a> returns <code>NULL</code>. -Different objects will give different pointers. -There is no way to convert the pointer back to its original value. - - -<p> -Typically this function is used only for debug information. - - - - - -<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>const char *lua_tostring (lua_State *L, int index);</pre> - -<p> -Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_State *lua_tothread (lua_State *L, int index);</pre> - -<p> -Converts the value at the given acceptable index to a Lua thread -(represented as <code>lua_State*</code>). -This value must be a thread; -otherwise, the function returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>void *lua_touserdata (lua_State *L, int index);</pre> - -<p> -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 <code>NULL</code>. - - - - - -<hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_type (lua_State *L, int index);</pre> - -<p> -Returns the type of the value in the given acceptable index, -or <code>LUA_TNONE</code> for a non-valid index -(that is, an index to an "empty" stack position). -The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants -defined in <code>lua.h</code>: -<code>LUA_TNIL</code>, -<code>LUA_TNUMBER</code>, -<code>LUA_TBOOLEAN</code>, -<code>LUA_TSTRING</code>, -<code>LUA_TTABLE</code>, -<code>LUA_TFUNCTION</code>, -<code>LUA_TUSERDATA</code>, -<code>LUA_TTHREAD</code>, -and -<code>LUA_TLIGHTUSERDATA</code>. - - - - - -<hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>const char *lua_typename (lua_State *L, int tp);</pre> - -<p> -Returns the name of the type encoded by the value <code>tp</code>, -which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. - - - - - -<hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> -<pre>typedef int (*lua_Writer) (lua_State *L, - const void* p, - size_t sz, - void* ud);</pre> - -<p> -The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. -Every time it produces another piece of chunk, -<a href="#lua_dump"><code>lua_dump</code></a> calls the writer, -passing along the buffer to be written (<code>p</code>), -its size (<code>sz</code>), -and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. - - -<p> -The writer returns an error code: -0 means no errors; -any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from -calling the writer again. - - - - - -<hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> -<span class="apii">[-?, +?, <em>-</em>]</span> -<pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> - -<p> -Exchange values between different threads of the <em>same</em> global state. - - -<p> -This function pops <code>n</code> values from the stack <code>from</code>, -and pushes them onto the stack <code>to</code>. - - - - - -<hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> -<span class="apii">[-?, +?, <em>-</em>]</span> -<pre>int lua_yield (lua_State *L, int nresults);</pre> - -<p> -Yields a coroutine. - - -<p> -This function should only be called as the -return expression of a C function, as follows: - -<pre> - return lua_yield (L, nresults); -</pre><p> -When a C function calls <a href="#lua_yield"><code>lua_yield</code></a> in that way, -the running coroutine suspends its execution, -and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns. -The parameter <code>nresults</code> is the number of values from the stack -that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. - - - - - - - -<h2>3.8 - <a name="3.8">The Debug Interface</a></h2> - -<p> -Lua has no built-in debugging facilities. -Instead, it offers a special interface -by means of functions and <em>hooks</em>. -This interface allows the construction of different -kinds of debuggers, profilers, and other tools -that need "inside information" from the interpreter. - - - -<hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3> -<pre>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 */ - <em>other fields</em> -} lua_Debug;</pre> - -<p> -A structure used to carry different pieces of -information about an active function. -<a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part -of this structure, for later use. -To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information, -call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. - - -<p> -The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning: - -<ul> - -<li><b><code>source</code>:</b> -If the function was defined in a string, -then <code>source</code> is that string. -If the function was defined in a file, -then <code>source</code> starts with a '<code>@</code>' followed by the file name. -</li> - -<li><b><code>short_src</code>:</b> -a "printable" version of <code>source</code>, to be used in error messages. -</li> - -<li><b><code>linedefined</code>:</b> -the line number where the definition of the function starts. -</li> - -<li><b><code>lastlinedefined</code>:</b> -the line number where the definition of the function ends. -</li> - -<li><b><code>what</code>:</b> -the string <code>"Lua"</code> if the function is a Lua function, -<code>"C"</code> if it is a C function, -<code>"main"</code> if it is the main part of a chunk, -and <code>"tail"</code> if it was a function that did a tail call. -In the latter case, -Lua has no other information about the function. -</li> - -<li><b><code>currentline</code>:</b> -the current line where the given function is executing. -When no line information is available, -<code>currentline</code> is set to -1. -</li> - -<li><b><code>name</code>:</b> -a reasonable name for the given function. -Because functions in Lua are first-class values, -they do not have a fixed name: -some functions can be the value of multiple global variables, -while others can be stored only in a table field. -The <code>lua_getinfo</code> function checks how the function was -called to find a suitable name. -If it cannot find a name, -then <code>name</code> is set to <code>NULL</code>. -</li> - -<li><b><code>namewhat</code>:</b> -explains the <code>name</code> field. -The value of <code>namewhat</code> can be -<code>"global"</code>, <code>"local"</code>, <code>"method"</code>, -<code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), -according to how the function was called. -(Lua uses the empty string when no other option seems to apply.) -</li> - -<li><b><code>nups</code>:</b> -the number of upvalues of the function. -</li> - -</ul> - - - - -<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_Hook lua_gethook (lua_State *L);</pre> - -<p> -Returns the current hook function. - - - - - -<hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_gethookcount (lua_State *L);</pre> - -<p> -Returns the current hook count. - - - - - -<hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_gethookmask (lua_State *L);</pre> - -<p> -Returns the current hook mask. - - - - - -<hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> -<span class="apii">[-(0|1), +(0|1|2), <em>m</em>]</span> -<pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> - -<p> -Returns information about a specific function or function invocation. - - -<p> -To get information about a function invocation, -the parameter <code>ar</code> must be a valid activation record that was -filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or -given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). - - -<p> -To get information about a function you push it onto the stack -and start the <code>what</code> string with the character '<code>></code>'. -(In that case, -<code>lua_getinfo</code> pops the function in the top of the stack.) -For instance, to know in which line a function <code>f</code> was defined, -you can write the following code: - -<pre> - lua_Debug ar; - lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* get global 'f' */ - lua_getinfo(L, ">S", &ar); - printf("%d\n", ar.linedefined); -</pre> - -<p> -Each character in the string <code>what</code> -selects some fields of the structure <code>ar</code> to be filled or -a value to be pushed on the stack: - -<ul> - -<li><b>'<code>n</code>':</b> fills in the field <code>name</code> and <code>namewhat</code>; -</li> - -<li><b>'<code>S</code>':</b> -fills in the fields <code>source</code>, <code>short_src</code>, -<code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>; -</li> - -<li><b>'<code>l</code>':</b> fills in the field <code>currentline</code>; -</li> - -<li><b>'<code>u</code>':</b> fills in the field <code>nups</code>; -</li> - -<li><b>'<code>f</code>':</b> -pushes onto the stack the function that is -running at the given level; -</li> - -<li><b>'<code>L</code>':</b> -pushes onto the stack a table whose indices are the -numbers of the lines that are valid on the function. -(A <em>valid line</em> is a line with some associated code, -that is, a line where you can put a break point. -Non-valid lines include empty lines and comments.) -</li> - -</ul> - -<p> -This function returns 0 on error -(for instance, an invalid option in <code>what</code>). - - - - - -<hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>-</em>]</span> -<pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre> - -<p> -Gets information about a local variable of a given activation record. -The parameter <code>ar</code> must be a valid activation record that was -filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or -given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). -The index <code>n</code> selects which local variable to inspect -(1 is the first parameter or active local variable, and so on, -until the last active local variable). -<a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack -and returns its name. - - -<p> -Variable names starting with '<code>(</code>' (open parentheses) -represent internal variables -(loop control variables, temporaries, and C function locals). - - -<p> -Returns <code>NULL</code> (and pushes nothing) -when the index is greater than -the number of active local variables. - - - - - -<hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> - -<p> -Get information about the interpreter runtime stack. - - -<p> -This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with -an identification of the <em>activation record</em> -of the function executing at a given level. -Level 0 is the current running function, -whereas level <em>n+1</em> is the function that has called level <em>n</em>. -When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; -when called with a level greater than the stack depth, -it returns 0. - - - - - -<hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>-</em>]</span> -<pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> - -<p> -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.) -<a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue, -pushes the upvalue's value onto the stack, -and returns its name. -<code>funcindex</code> 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.) - - -<p> -Returns <code>NULL</code> (and pushes nothing) -when the index is greater than the number of upvalues. -For C functions, this function uses the empty string <code>""</code> -as a name for all upvalues. - - - - - -<hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3> -<pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre> - -<p> -Type for debugging hook functions. - - -<p> -Whenever a hook is called, its <code>ar</code> argument has its field -<code>event</code> set to the specific event that triggered the hook. -Lua identifies these events with the following constants: -<a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>, -<a name="pdf-LUA_HOOKTAILRET"><code>LUA_HOOKTAILRET</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>, -and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>. -Moreover, for line events, the field <code>currentline</code> is also set. -To get the value of any other field in <code>ar</code>, -the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. -For return events, <code>event</code> can be <code>LUA_HOOKRET</code>, -the normal value, or <code>LUA_HOOKTAILRET</code>. -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 <a href="#lua_getinfo"><code>lua_getinfo</code></a>. - - -<p> -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. - - - - - -<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre> - -<p> -Sets the debugging hook function. - - -<p> -Argument <code>f</code> is the hook function. -<code>mask</code> specifies on which events the hook will be called: -it is formed by a bitwise or of the constants -<a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>, -<a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>, -<a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>, -and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>. -The <code>count</code> argument is only meaningful when the mask -includes <code>LUA_MASKCOUNT</code>. -For each event, the hook is called as explained below: - -<ul> - -<li><b>The call hook:</b> is called when the interpreter calls a function. -The hook is called just after Lua enters the new function, -before the function gets its arguments. -</li> - -<li><b>The return hook:</b> is called when the interpreter returns from a function. -The hook is called just before Lua leaves the function. -You have no access to the values to be returned by the function. -</li> - -<li><b>The line hook:</b> is called when the interpreter is about to -start the execution of a new line of code, -or when it jumps back in the code (even to the same line). -(This event only happens while Lua is executing a Lua function.) -</li> - -<li><b>The count hook:</b> is called after the interpreter executes every -<code>count</code> instructions. -(This event only happens while Lua is executing a Lua function.) -</li> - -</ul> - -<p> -A hook is disabled by setting <code>mask</code> to zero. - - - - - -<hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> -<span class="apii">[-(0|1), +0, <em>-</em>]</span> -<pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre> - -<p> -Sets the value of a local variable of a given activation record. -Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a> -(see <a href="#lua_getlocal"><code>lua_getlocal</code></a>). -<a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack -to the variable and returns its name. -It also pops the value from the stack. - - -<p> -Returns <code>NULL</code> (and pops nothing) -when the index is greater than -the number of active local variables. - - - - - -<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> -<span class="apii">[-(0|1), +0, <em>-</em>]</span> -<pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> - -<p> -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 <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> -(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>). - - -<p> -Returns <code>NULL</code> (and pops nothing) -when the index is greater than the number of upvalues. - - - - - - - -<h1>4 - <a name="4">The Auxiliary Library</a></h1> - -<p> - -The <em>auxiliary library</em> 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. - - -<p> -All functions from the auxiliary library -are defined in header file <code>lauxlib.h</code> and -have a prefix <code>luaL_</code>. - - -<p> -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. - - -<p> -Several functions in the auxiliary library are used to -check C function arguments. -Their names are always <code>luaL_check*</code> or <code>luaL_opt*</code>. -All of these functions throw an error if the check is not satisfied. -Because the error message is formatted for arguments -(e.g., "<code>bad argument #1</code>"), -you should not use these functions for other stack values. - - - -<h2>4.1 - <a name="4.1">Functions and Types</a></h2> - -<p> -Here we list all functions and types from the auxiliary library -in alphabetical order. - - - -<hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> - -<p> -Adds the character <code>c</code> to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). - - - - - -<hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> - -<p> -Adds the string pointed to by <code>s</code> with length <code>l</code> to -the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -The string may contain embedded zeros. - - - - - -<hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> - -<p> -Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) -a string of length <code>n</code> previously copied to the -buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). - - - - - -<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> - -<p> -Adds the zero-terminated string pointed to by <code>s</code> -to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -The string may not contain embedded zeros. - - - - - -<hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>void luaL_addvalue (luaL_Buffer *B);</pre> - -<p> -Adds the value at the top of the stack -to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -Pops the value. - - -<p> -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. - - - - - -<hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_argcheck (lua_State *L, - int cond, - int narg, - const char *extramsg);</pre> - -<p> -Checks whether <code>cond</code> is true. -If not, raises an error with the following message, -where <code>func</code> is retrieved from the call stack: - -<pre> - bad argument #<narg> to <func> (<extramsg>) -</pre> - - - - -<hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_argerror (lua_State *L, int narg, const char *extramsg);</pre> - -<p> -Raises an error with the following message, -where <code>func</code> is retrieved from the call stack: - -<pre> - bad argument #<narg> to <func> (<extramsg>) -</pre> - -<p> -This function never returns, -but it is an idiom to use it in C functions -as <code>return luaL_argerror(<em>args</em>)</code>. - - - - - -<hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3> -<pre>typedef struct luaL_Buffer luaL_Buffer;</pre> - -<p> -Type for a <em>string buffer</em>. - - -<p> -A string buffer allows C code to build Lua strings piecemeal. -Its pattern of use is as follows: - -<ul> - -<li>First you declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> - -<li>Then you initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> - -<li> -Then you add string pieces to the buffer calling any of -the <code>luaL_add*</code> functions. -</li> - -<li> -You finish by calling <code>luaL_pushresult(&b)</code>. -This call leaves the final string on the top of the stack. -</li> - -</ul> - -<p> -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 <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) -After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its -level when the buffer was initialized, -plus the final string on its top. - - - - - -<hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> - -<p> -Initializes a buffer <code>B</code>. -This function does not allocate any space; -the buffer must be declared as a variable -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). - - - - - -<hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>e</em>]</span> -<pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> - -<p> -Calls a metamethod. - - -<p> -If the object at index <code>obj</code> has a metatable and this -metatable has a field <code>e</code>, -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). - - - - - -<hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checkany (lua_State *L, int narg);</pre> - -<p> -Checks whether the function has an argument -of any type (including <b>nil</b>) at position <code>narg</code>. - - - - - -<hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_checkint (lua_State *L, int narg);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a number -and returns this number cast to an <code>int</code>. - - - - - -<hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Integer luaL_checkinteger (lua_State *L, int narg);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a number -and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. - - - - - -<hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>long luaL_checklong (lua_State *L, int narg);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a number -and returns this number cast to a <code>long</code>. - - - - - -<hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_checklstring (lua_State *L, int narg, size_t *l);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a string -and returns this string; -if <code>l</code> is not <code>NULL</code> fills <code>*l</code> -with the string's length. - - -<p> -This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, -so all conversions and caveats of that function apply here. - - - - - -<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Number luaL_checknumber (lua_State *L, int narg);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a number -and returns this number. - - - - - -<hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_checkoption (lua_State *L, - int narg, - const char *def, - const char *const lst[]);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a string and -searches for this string in the array <code>lst</code> -(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. - - -<p> -If <code>def</code> is not <code>NULL</code>, -the function uses <code>def</code> as a default value when -there is no argument <code>narg</code> or if this argument is <b>nil</b>. - - -<p> -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.) - - - - - -<hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> - -<p> -Grows the stack size to <code>top + sz</code> elements, -raising an error if the stack cannot grow to that size. -<code>msg</code> is an additional text to go into the error message. - - - - - -<hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_checkstring (lua_State *L, int narg);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a string -and returns this string. - - -<p> -This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, -so all conversions and caveats of that function apply here. - - - - - -<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checktype (lua_State *L, int narg, int t);</pre> - -<p> -Checks whether the function argument <code>narg</code> has type <code>t</code>. -See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. - - - - - -<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void *luaL_checkudata (lua_State *L, int narg, const char *tname);</pre> - -<p> -Checks whether the function argument <code>narg</code> is a userdata -of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). - - - - - -<hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> -<span class="apii">[-0, +?, <em>m</em>]</span> -<pre>int luaL_dofile (lua_State *L, const char *filename);</pre> - -<p> -Loads and runs the given file. -It is defined as the following macro: - -<pre> - (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) -</pre><p> -It returns 0 if there are no errors -or 1 in case of errors. - - - - - -<hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> -<span class="apii">[-0, +?, <em>m</em>]</span> -<pre>int luaL_dostring (lua_State *L, const char *str);</pre> - -<p> -Loads and runs the given string. -It is defined as the following macro: - -<pre> - (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) -</pre><p> -It returns 0 if there are no errors -or 1 in case of errors. - - - - - -<hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> - -<p> -Raises an error. -The error message format is given by <code>fmt</code> -plus any extra arguments, -following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. -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. - - -<p> -This function never returns, -but it is an idiom to use it in C functions -as <code>return luaL_error(<em>args</em>)</code>. - - - - - -<hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>m</em>]</span> -<pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> - -<p> -Pushes onto the stack the field <code>e</code> from the metatable -of the object at index <code>obj</code>. -If the object does not have a metatable, -or if the metatable does not have this field, -returns 0 and pushes nothing. - - - - - -<hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> -<span class="apii">[-0, +1, <em>-</em>]</span> -<pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre> - -<p> -Pushes onto the stack the metatable associated with name <code>tname</code> -in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). - - - - - -<hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *luaL_gsub (lua_State *L, - const char *s, - const char *p, - const char *r);</pre> - -<p> -Creates a copy of string <code>s</code> by replacing -any occurrence of the string <code>p</code> -with the string <code>r</code>. -Pushes the resulting string on the stack and returns it. - - - - - -<hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_loadbuffer (lua_State *L, - const char *buff, - size_t sz, - const char *name);</pre> - -<p> -Loads a buffer as a Lua chunk. -This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the -buffer pointed to by <code>buff</code> with size <code>sz</code>. - - -<p> -This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. -<code>name</code> is the chunk name, -used for debug information and error messages. - - - - - -<hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> - -<p> -Loads a file as a Lua chunk. -This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file -named <code>filename</code>. -If <code>filename</code> is <code>NULL</code>, -then it loads from the standard input. -The first line in the file is ignored if it starts with a <code>#</code>. - - -<p> -This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, -but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> -if it cannot open/read the file. - - -<p> -As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; -it does not run it. - - - - - -<hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_loadstring (lua_State *L, const char *s);</pre> - -<p> -Loads a string as a Lua chunk. -This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in -the zero-terminated string <code>s</code>. - - -<p> -This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. - - -<p> -Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; -it does not run it. - - - - - -<hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> - -<p> -If the registry already has the key <code>tname</code>, -returns 0. -Otherwise, -creates a new table to be used as a metatable for userdata, -adds it to the registry with key <code>tname</code>, -and returns 1. - - -<p> -In both cases pushes onto the stack the final value associated -with <code>tname</code> in the registry. - - - - - -<hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>lua_State *luaL_newstate (void);</pre> - -<p> -Creates a new Lua state. -It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an -allocator based on the standard C <code>realloc</code> function -and then sets a panic function (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) that prints -an error message to the standard error output in case of fatal -errors. - - -<p> -Returns the new state, -or <code>NULL</code> if there is a memory allocation error. - - - - - -<hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void luaL_openlibs (lua_State *L);</pre> - -<p> -Opens all standard Lua libraries into the given state. - - - - - -<hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_optint (lua_State *L, int narg, int d);</pre> - -<p> -If the function argument <code>narg</code> is a number, -returns this number cast to an <code>int</code>. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Integer luaL_optinteger (lua_State *L, - int narg, - lua_Integer d);</pre> - -<p> -If the function argument <code>narg</code> is a number, -returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>long luaL_optlong (lua_State *L, int narg, long d);</pre> - -<p> -If the function argument <code>narg</code> is a number, -returns this number cast to a <code>long</code>. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_optlstring (lua_State *L, - int narg, - const char *d, - size_t *l);</pre> - -<p> -If the function argument <code>narg</code> is a string, -returns this string. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - -<p> -If <code>l</code> is not <code>NULL</code>, -fills the position <code>*l</code> with the results's length. - - - - - -<hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);</pre> - -<p> -If the function argument <code>narg</code> is a number, -returns this number. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_optstring (lua_State *L, - int narg, - const char *d);</pre> - -<p> -If the function argument <code>narg</code> is a string, -returns this string. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> - -<p> -Returns an address to a space of size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a> -where you can copy a string to be added to buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -After copying the string into this space you must call -<a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add -it to the buffer. - - - - - -<hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> -<span class="apii">[-?, +1, <em>m</em>]</span> -<pre>void luaL_pushresult (luaL_Buffer *B);</pre> - -<p> -Finishes the use of buffer <code>B</code> leaving the final string on -the top of the stack. - - - - - -<hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>int luaL_ref (lua_State *L, int t);</pre> - -<p> -Creates and returns a <em>reference</em>, -in the table at index <code>t</code>, -for the object at the top of the stack (and pops the object). - - -<p> -A reference is a unique integer key. -As long as you do not manually add integer keys into table <code>t</code>, -<a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. -You can retrieve an object referred by reference <code>r</code> -by calling <code>lua_rawgeti(L, t, r)</code>. -Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. - - -<p> -If the object at the top of the stack is <b>nil</b>, -<a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. -The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different -from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. - - - - - -<hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> -<pre>typedef struct luaL_Reg { - const char *name; - lua_CFunction func; -} luaL_Reg;</pre> - -<p> -Type for arrays of functions to be registered by -<a href="#luaL_register"><code>luaL_register</code></a>. -<code>name</code> is the function name and <code>func</code> is a pointer to -the function. -Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry -in which both <code>name</code> and <code>func</code> are <code>NULL</code>. - - - - - -<hr><h3><a name="luaL_register"><code>luaL_register</code></a></h3><p> -<span class="apii">[-(0|1), +1, <em>m</em>]</span> -<pre>void luaL_register (lua_State *L, - const char *libname, - const luaL_Reg *l);</pre> - -<p> -Opens a library. - - -<p> -When called with <code>libname</code> equal to <code>NULL</code>, -it simply registers all functions in the list <code>l</code> -(see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack. - - -<p> -When called with a non-null <code>libname</code>, -<code>luaL_register</code> creates a new table <code>t</code>, -sets it as the value of the global variable <code>libname</code>, -sets it as the value of <code>package.loaded[libname]</code>, -and registers on it all functions in the list <code>l</code>. -If there is a table in <code>package.loaded[libname]</code> or in -variable <code>libname</code>, -reuses this table instead of creating a new one. - - -<p> -In any case the function leaves the table -on the top of the stack. - - - - - -<hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>const char *luaL_typename (lua_State *L, int index);</pre> - -<p> -Returns the name of the type of the value at the given index. - - - - - -<hr><h3><a name="luaL_typerror"><code>luaL_typerror</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_typerror (lua_State *L, int narg, const char *tname);</pre> - -<p> -Generates an error with a message like the following: - -<pre> - <em>location</em>: bad argument <em>narg</em> to '<em>func</em>' (<em>tname</em> expected, got <em>rt</em>) -</pre><p> -where <code><em>location</em></code> is produced by <a href="#luaL_where"><code>luaL_where</code></a>, -<code><em>func</em></code> is the name of the current function, -and <code><em>rt</em></code> is the type name of the actual argument. - - - - - -<hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> -<span class="apii">[-0, +0, <em>-</em>]</span> -<pre>void luaL_unref (lua_State *L, int t, int ref);</pre> - -<p> -Releases reference <code>ref</code> from the table at index <code>t</code> -(see <a href="#luaL_ref"><code>luaL_ref</code></a>). -The entry is removed from the table, -so that the referred object can be collected. -The reference <code>ref</code> is also freed to be used again. - - -<p> -If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, -<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. - - - - - -<hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void luaL_where (lua_State *L, int lvl);</pre> - -<p> -Pushes onto the stack a string identifying the current position -of the control at level <code>lvl</code> in the call stack. -Typically this string has the following format: - -<pre> - <em>chunkname</em>:<em>currentline</em>: -</pre><p> -Level 0 is the running function, -level 1 is the function that called the running function, -etc. - - -<p> -This function is used to build a prefix for error messages. - - - - - - - -<h1>5 - <a name="5">Standard Libraries</a></h1> - -<p> -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., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); -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., <a href="#pdf-table.sort"><code>table.sort</code></a>). - - -<p> -All libraries are implemented through the official C API -and are provided as separate C modules. -Currently, Lua has the following standard libraries: - -<ul> - -<li>basic library,</li> which includes the coroutine sub-library; - -<li>package library;</li> - -<li>string manipulation;</li> - -<li>table manipulation;</li> - -<li>mathematical functions (sin, log, etc.);</li> - -<li>input and output;</li> - -<li>operating system facilities;</li> - -<li>debug facilities.</li> - -</ul><p> -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. - - -<p> -To have access to these libraries, -the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function, -which opens all standard libraries. -Alternatively, -it can open them individually by calling -<a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library), -<a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library), -<a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), -<a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), -<a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), -<a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), -<a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library), -and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). -These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a> -and should not be called directly: -you must call them like any other Lua C function, -e.g., by using <a href="#lua_call"><code>lua_call</code></a>. - - - -<h2>5.1 - <a name="5.1">Basic Functions</a></h2> - -<p> -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. - - -<p> -<hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3> -Issues an error when -the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); -otherwise, returns all its arguments. -<code>message</code> is an error message; -when absent, it defaults to "assertion failed!" - - - - -<p> -<hr><h3><a name="pdf-collectgarbage"><code>collectgarbage (opt [, arg])</code></a></h3> - - -<p> -This function is a generic interface to the garbage collector. -It performs different functions according to its first argument, <code>opt</code>: - -<ul> - -<li><b>"stop":</b> -stops the garbage collector. -</li> - -<li><b>"restart":</b> -restarts the garbage collector. -</li> - -<li><b>"collect":</b> -performs a full garbage-collection cycle. -</li> - -<li><b>"count":</b> -returns the total memory in use by Lua (in Kbytes). -</li> - -<li><b>"step":</b> -performs a garbage-collection step. -The step "size" is controlled by <code>arg</code> -(larger values mean more steps) in a non-specified way. -If you want to control the step size -you must experimentally tune the value of <code>arg</code>. -Returns <b>true</b> if the step finished a collection cycle. -</li> - -<li><b>"setpause":</b> -sets <code>arg</code> as the new value for the <em>pause</em> of -the collector (see <a href="#2.10">§2.10</a>). -Returns the previous value for <em>pause</em>. -</li> - -<li><b>"setstepmul":</b> -sets <code>arg</code> as the new value for the <em>step multiplier</em> of -the collector (see <a href="#2.10">§2.10</a>). -Returns the previous value for <em>step</em>. -</li> - -</ul> - - - -<p> -<hr><h3><a name="pdf-dofile"><code>dofile (filename)</code></a></h3> -Opens the named file and executes its contents as a Lua chunk. -When called without arguments, -<code>dofile</code> executes the contents of the standard input (<code>stdin</code>). -Returns all values returned by the chunk. -In case of errors, <code>dofile</code> propagates the error -to its caller (that is, <code>dofile</code> does not run in protected mode). - - - - -<p> -<hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3> -Terminates the last protected function called -and returns <code>message</code> as the error message. -Function <code>error</code> never returns. - - -<p> -Usually, <code>error</code> adds some information about the error position -at the beginning of the message. -The <code>level</code> argument specifies how to get the error position. -With level 1 (the default), the error position is where the -<code>error</code> function was called. -Level 2 points the error to where the function -that called <code>error</code> was called; and so on. -Passing a level 0 avoids the addition of error position information -to the message. - - - - -<p> -<hr><h3><a name="pdf-_G"><code>_G</code></a></h3> -A global variable (not a function) that -holds the global environment (that is, <code>_G._G = _G</code>). -Lua itself does not use this variable; -changing its value does not affect any environment, -nor vice-versa. -(Use <a href="#pdf-setfenv"><code>setfenv</code></a> to change environments.) - - - - -<p> -<hr><h3><a name="pdf-getfenv"><code>getfenv ([f])</code></a></h3> -Returns the current environment in use by the function. -<code>f</code> can be a Lua function or a number -that specifies the function at that stack level: -Level 1 is the function calling <code>getfenv</code>. -If the given function is not a Lua function, -or if <code>f</code> is 0, -<code>getfenv</code> returns the global environment. -The default for <code>f</code> is 1. - - - - -<p> -<hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3> - - -<p> -If <code>object</code> does not have a metatable, returns <b>nil</b>. -Otherwise, -if the object's metatable has a <code>"__metatable"</code> field, -returns the associated value. -Otherwise, returns the metatable of the given object. - - - - -<p> -<hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3> - - -<p> -Returns three values: an iterator function, the table <code>t</code>, and 0, -so that the construction - -<pre> - for i,v in ipairs(t) do <em>body</em> end -</pre><p> -will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ···, -up to the first integer key absent from the table. - - - - -<p> -<hr><h3><a name="pdf-load"><code>load (func [, chunkname])</code></a></h3> - - -<p> -Loads a chunk using function <code>func</code> to get its pieces. -Each call to <code>func</code> must return a string that concatenates -with previous results. -A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. - - -<p> -If there are no errors, -returns the compiled chunk as a function; -otherwise, returns <b>nil</b> plus the error message. -The environment of the returned function is the global environment. - - -<p> -<code>chunkname</code> is used as the chunk name for error messages -and debug information. -When absent, -it defaults to "<code>=(load)</code>". - - - - -<p> -<hr><h3><a name="pdf-loadfile"><code>loadfile ([filename])</code></a></h3> - - -<p> -Similar to <a href="#pdf-load"><code>load</code></a>, -but gets the chunk from file <code>filename</code> -or from the standard input, -if no file name is given. - - - - -<p> -<hr><h3><a name="pdf-loadstring"><code>loadstring (string [, chunkname])</code></a></h3> - - -<p> -Similar to <a href="#pdf-load"><code>load</code></a>, -but gets the chunk from the given string. - - -<p> -To load and run a given string, use the idiom - -<pre> - assert(loadstring(s))() -</pre> - -<p> -When absent, -<code>chunkname</code> defaults to the given string. - - - - -<p> -<hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3> - - -<p> -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. -<code>next</code> returns the next index of the table -and its associated value. -When called with <b>nil</b> as its second argument, -<code>next</code> returns an initial index -and its associated value. -When called with the last index, -or with <b>nil</b> in an empty table, -<code>next</code> returns <b>nil</b>. -If the second argument is absent, then it is interpreted as <b>nil</b>. -In particular, -you can use <code>next(t)</code> to check whether a table is empty. - - -<p> -The order in which the indices are enumerated is not specified, -<em>even for numeric indices</em>. -(To traverse a table in numeric order, -use a numerical <b>for</b> or the <a href="#pdf-ipairs"><code>ipairs</code></a> function.) - - -<p> -The behavior of <code>next</code> is <em>undefined</em> 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. - - - - -<p> -<hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> - - -<p> -Returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>, -so that the construction - -<pre> - for k,v in pairs(t) do <em>body</em> end -</pre><p> -will iterate over all key–value pairs of table <code>t</code>. - - -<p> -See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying -the table during its traversal. - - - - -<p> -<hr><h3><a name="pdf-pcall"><code>pcall (f, arg1, ···)</code></a></h3> - - -<p> -Calls function <code>f</code> with -the given arguments in <em>protected mode</em>. -This means that any error inside <code>f</code> is not propagated; -instead, <code>pcall</code> 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, <code>pcall</code> also returns all results from the call, -after this first result. -In case of any error, <code>pcall</code> returns <b>false</b> plus the error message. - - - - -<p> -<hr><h3><a name="pdf-print"><code>print (···)</code></a></h3> -Receives any number of arguments, -and prints their values to <code>stdout</code>, -using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert them to strings. -<code>print</code> is not intended for formatted output, -but only as a quick way to show a value, -typically for debugging. -For formatted output, use <a href="#pdf-string.format"><code>string.format</code></a>. - - - - -<p> -<hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3> -Checks whether <code>v1</code> is equal to <code>v2</code>, -without invoking any metamethod. -Returns a boolean. - - - - -<p> -<hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3> -Gets the real value of <code>table[index]</code>, -without invoking any metamethod. -<code>table</code> must be a table; -<code>index</code> may be any value. - - - - -<p> -<hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3> -Sets the real value of <code>table[index]</code> to <code>value</code>, -without invoking any metamethod. -<code>table</code> must be a table, -<code>index</code> any value different from <b>nil</b>, -and <code>value</code> any Lua value. - - -<p> -This function returns <code>table</code>. - - - - -<p> -<hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3> - - -<p> -If <code>index</code> is a number, -returns all arguments after argument number <code>index</code>. -Otherwise, <code>index</code> must be the string <code>"#"</code>, -and <code>select</code> returns the total number of extra arguments it received. - - - - -<p> -<hr><h3><a name="pdf-setfenv"><code>setfenv (f, table)</code></a></h3> - - -<p> -Sets the environment to be used by the given function. -<code>f</code> can be a Lua function or a number -that specifies the function at that stack level: -Level 1 is the function calling <code>setfenv</code>. -<code>setfenv</code> returns the given function. - - -<p> -As a special case, when <code>f</code> is 0 <code>setfenv</code> changes -the environment of the running thread. -In this case, <code>setfenv</code> returns no values. - - - - -<p> -<hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> - - -<p> -Sets the metatable for the given table. -(You cannot change the metatable of other types from Lua, only from C.) -If <code>metatable</code> is <b>nil</b>, -removes the metatable of the given table. -If the original metatable has a <code>"__metatable"</code> field, -raises an error. - - -<p> -This function returns <code>table</code>. - - - - -<p> -<hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3> -Tries to convert its argument to a number. -If the argument is already a number or a string convertible -to a number, then <code>tonumber</code> returns this number; -otherwise, it returns <b>nil</b>. - - -<p> -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 '<code>A</code>' (in either upper or lower case) -represents 10, '<code>B</code>' represents 11, and so forth, -with '<code>Z</code>' representing 35. -In base 10 (the default), the number can have a decimal part, -as well as an optional exponent part (see <a href="#2.1">§2.1</a>). -In other bases, only unsigned integers are accepted. - - - - -<p> -<hr><h3><a name="pdf-tostring"><code>tostring (e)</code></a></h3> -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 <a href="#pdf-string.format"><code>string.format</code></a>. - - -<p> -If the metatable of <code>e</code> has a <code>"__tostring"</code> field, -then <code>tostring</code> calls the corresponding value -with <code>e</code> as argument, -and uses the result of the call as its result. - - - - -<p> -<hr><h3><a name="pdf-type"><code>type (v)</code></a></h3> -Returns the type of its only argument, coded as a string. -The possible results of this function are -"<code>nil</code>" (a string, not the value <b>nil</b>), -"<code>number</code>", -"<code>string</code>", -"<code>boolean</code>", -"<code>table</code>", -"<code>function</code>", -"<code>thread</code>", -and "<code>userdata</code>". - - - - -<p> -<hr><h3><a name="pdf-unpack"><code>unpack (list [, i [, j]])</code></a></h3> -Returns the elements from the given table. -This function is equivalent to - -<pre> - return list[i], list[i+1], ···, list[j] -</pre><p> -except that the above code can be written only for a fixed number -of elements. -By default, <code>i</code> is 1 and <code>j</code> is the length of the list, -as defined by the length operator (see <a href="#2.5.5">§2.5.5</a>). - - - - -<p> -<hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3> -A global variable (not a function) that -holds a string containing the current interpreter version. -The current contents of this variable is "<code>Lua 5.1</code>". - - - - -<p> -<hr><h3><a name="pdf-xpcall"><code>xpcall (f, err)</code></a></h3> - - -<p> -This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, -except that you can set a new error handler. - - -<p> -<code>xpcall</code> calls function <code>f</code> in protected mode, -using <code>err</code> as the error handler. -Any error inside <code>f</code> is not propagated; -instead, <code>xpcall</code> catches the error, -calls the <code>err</code> 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, <code>xpcall</code> also returns all results from the call, -after this first result. -In case of any error, -<code>xpcall</code> returns <b>false</b> plus the result from <code>err</code>. - - - - - - - -<h2>5.2 - <a name="5.2">Coroutine Manipulation</a></h2> - -<p> -The operations related to coroutines comprise a sub-library of -the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. -See <a href="#2.11">§2.11</a> for a general description of coroutines. - - -<p> -<hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3> - - -<p> -Creates a new coroutine, with body <code>f</code>. -<code>f</code> must be a Lua function. -Returns this new coroutine, -an object with type <code>"thread"</code>. - - - - -<p> -<hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3> - - -<p> -Starts or continues the execution of coroutine <code>co</code>. -The first time you resume a coroutine, -it starts running its body. -The values <code>val1</code>, ··· are passed -as the arguments to the body function. -If the coroutine has yielded, -<code>resume</code> restarts it; -the values <code>val1</code>, ··· are passed -as the results from the yield. - - -<p> -If the coroutine runs without any errors, -<code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code> -(if the coroutine yields) or any values returned by the body function -(if the coroutine terminates). -If there is any error, -<code>resume</code> returns <b>false</b> plus the error message. - - - - -<p> -<hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3> - - -<p> -Returns the running coroutine, -or <b>nil</b> when called by the main thread. - - - - -<p> -<hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3> - - -<p> -Returns the status of coroutine <code>co</code>, as a string: -<code>"running"</code>, -if the coroutine is running (that is, it called <code>status</code>); -<code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>, -or if it has not started running yet; -<code>"normal"</code> if the coroutine is active but not running -(that is, it has resumed another coroutine); -and <code>"dead"</code> if the coroutine has finished its body function, -or if it has stopped with an error. - - - - -<p> -<hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3> - - -<p> -Creates a new coroutine, with body <code>f</code>. -<code>f</code> 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 <code>resume</code>. -Returns the same values returned by <code>resume</code>, -except the first boolean. -In case of error, propagates the error. - - - - -<p> -<hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3> - - -<p> -Suspends the execution of the calling coroutine. -The coroutine cannot be running a C function, -a metamethod, or an iterator. -Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. - - - - - - - -<h2>5.3 - <a name="5.3">Modules</a></h2> - -<p> -The package library provides basic -facilities for loading and building modules in Lua. -It exports two of its functions directly in the global environment: -<a href="#pdf-require"><code>require</code></a> and <a href="#pdf-module"><code>module</code></a>. -Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. - - -<p> -<hr><h3><a name="pdf-module"><code>module (name [, ···])</code></a></h3> - - -<p> -Creates a module. -If there is a table in <code>package.loaded[name]</code>, -this table is the module. -Otherwise, if there is a global table <code>t</code> with the given name, -this table is the module. -Otherwise creates a new table <code>t</code> and -sets it as the value of the global <code>name</code> and -the value of <code>package.loaded[name]</code>. -This function also initializes <code>t._NAME</code> with the given name, -<code>t._M</code> with the module (<code>t</code> itself), -and <code>t._PACKAGE</code> with the package name -(the full module name minus last component; see below). -Finally, <code>module</code> sets <code>t</code> as the new environment -of the current function and the new value of <code>package.loaded[name]</code>, -so that <a href="#pdf-require"><code>require</code></a> returns <code>t</code>. - - -<p> -If <code>name</code> is a compound name -(that is, one with components separated by dots), -<code>module</code> creates (or reuses, if they already exist) -tables for each component. -For instance, if <code>name</code> is <code>a.b.c</code>, -then <code>module</code> stores the module table in field <code>c</code> of -field <code>b</code> of global <code>a</code>. - - -<p> -This function can receive optional <em>options</em> after -the module name, -where each option is a function to be applied over the module. - - - - -<p> -<hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> - - -<p> -Loads the given module. -The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table -to determine whether <code>modname</code> is already loaded. -If it is, then <code>require</code> returns the value stored -at <code>package.loaded[modname]</code>. -Otherwise, it tries to find a <em>loader</em> for the module. - - -<p> -To find a loader, -<code>require</code> is guided by the <a href="#pdf-package.loaders"><code>package.loaders</code></a> array. -By changing this array, -we can change how <code>require</code> looks for a module. -The following explanation is based on the default configuration -for <a href="#pdf-package.loaders"><code>package.loaders</code></a>. - - -<p> -First <code>require</code> queries <code>package.preload[modname]</code>. -If it has a value, -this value (which should be a function) is the loader. -Otherwise <code>require</code> searches for a Lua loader using the -path stored in <a href="#pdf-package.path"><code>package.path</code></a>. -If that also fails, it searches for a C loader using the -path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. -If that also fails, -it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.loaders"><code>package.loaders</code></a>). - - -<p> -Once a loader is found, -<code>require</code> calls the loader with a single argument, <code>modname</code>. -If the loader returns any value, -<code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. -If the loader returns no value and -has not assigned any value to <code>package.loaded[modname]</code>, -then <code>require</code> assigns <b>true</b> to this entry. -In any case, <code>require</code> returns the -final value of <code>package.loaded[modname]</code>. - - -<p> -If there is any error loading or running the module, -or if it cannot find any loader for the module, -then <code>require</code> signals an error. - - - - -<p> -<hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3> - - -<p> -The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader. - - -<p> -Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way -it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, -using the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a> -or a default path defined in <code>luaconf.h</code>. - - - - -<p> - -<hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> - - -<p> -A table used by <a href="#pdf-require"><code>require</code></a> to control which -modules are already loaded. -When you require a module <code>modname</code> and -<code>package.loaded[modname]</code> is not false, -<a href="#pdf-require"><code>require</code></a> simply returns the value stored there. - - - - -<p> -<hr><h3><a name="pdf-package.loaders"><code>package.loaders</code></a></h3> - - -<p> -A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. - - -<p> -Each entry in this table is a <em>searcher function</em>. -When looking for a module, -<a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, -with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its -sole parameter. -The function can return another function (the module <em>loader</em>) -or a string explaining why it did not find that module -(or <b>nil</b> if it has nothing to say). -Lua initializes this table with four functions. - - -<p> -The first searcher simply looks for a loader in the -<a href="#pdf-package.preload"><code>package.preload</code></a> table. - - -<p> -The second searcher looks for a loader as a Lua library, -using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. -A path is a sequence of <em>templates</em> separated by semicolons. -For each template, -the searcher will change each interrogation -mark in the template by <code>filename</code>, -which is the module name with each dot replaced by a -"directory separator" (such as "<code>/</code>" in Unix); -then it will try to open the resulting file name. -So, for instance, if the Lua path is the string - -<pre> - "./?.lua;./?.lc;/usr/local/?/init.lua" -</pre><p> -the search for a Lua file for module <code>foo</code> -will try to open the files -<code>./foo.lua</code>, <code>./foo.lc</code>, and -<code>/usr/local/foo/init.lua</code>, in that order. - - -<p> -The third searcher looks for a loader as a C library, -using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. -For instance, -if the C path is the string - -<pre> - "./?.so;./?.dll;/usr/local/?/init.so" -</pre><p> -the searcher for module <code>foo</code> -will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, -and <code>/usr/local/foo/init.so</code>, 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 "<code>luaopen_</code>" -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 <code>a.v1-b.c</code>, -the function name will be <code>luaopen_b_c</code>. - - -<p> -The fourth searcher tries an <em>all-in-one loader</em>. -It searches the C path for a library for -the root name of the given module. -For instance, when requiring <code>a.b.c</code>, -it will search for a C library for <code>a</code>. -If found, it looks into it for an open function for -the submodule; -in our example, that would be <code>luaopen_a_b_c</code>. -With this facility, a package can pack several C submodules -into one single library, -with each submodule keeping its original open function. - - - - -<p> -<hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3> - - -<p> -Dynamically links the host program with the C library <code>libname</code>. -Inside this library, looks for a function <code>funcname</code> -and returns this function as a C function. -(So, <code>funcname</code> must follow the protocol (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>)). - - -<p> -This is a low-level function. -It completely bypasses the package and module system. -Unlike <a href="#pdf-require"><code>require</code></a>, -it does not perform any path searching and -does not automatically adds extensions. -<code>libname</code> must be the complete file name of the C library, -including if necessary a path and extension. -<code>funcname</code> must be the exact name exported by the C library -(which may depend on the C compiler and linker used). - - -<p> -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 <code>dlfcn</code> standard). - - - - -<p> -<hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3> - - -<p> -The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader. - - -<p> -At start-up, Lua initializes this variable with -the value of the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or -with a default path defined in <code>luaconf.h</code>, -if the environment variable is not defined. -Any "<code>;;</code>" in the value of the environment variable -is replaced by the default path. - - - - -<p> -<hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> - - -<p> -A table to store loaders for specific modules -(see <a href="#pdf-require"><code>require</code></a>). - - - - -<p> -<hr><h3><a name="pdf-package.seeall"><code>package.seeall (module)</code></a></h3> - - -<p> -Sets a metatable for <code>module</code> with -its <code>__index</code> field referring to the global environment, -so that this module inherits values -from the global environment. -To be used as an option to function <a href="#pdf-module"><code>module</code></a>. - - - - - - - -<h2>5.4 - <a name="5.4">String Manipulation</a></h2> - -<p> -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. - - -<p> -The string library provides all its functions inside the table -<a name="pdf-string"><code>string</code></a>. -It also sets a metatable for strings -where the <code>__index</code> field points to the <code>string</code> table. -Therefore, you can use the string functions in object-oriented style. -For instance, <code>string.byte(s, i)</code> -can be written as <code>s:byte(i)</code>. - - -<p> -The string library assumes one-byte character encodings. - - -<p> -<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> -Returns the internal numerical codes of the characters <code>s[i]</code>, -<code>s[i+1]</code>, ···, <code>s[j]</code>. -The default value for <code>i</code> is 1; -the default value for <code>j</code> is <code>i</code>. - - -<p> -Note that numerical codes are not necessarily portable across platforms. - - - - -<p> -<hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3> -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. - - -<p> -Note that numerical codes are not necessarily portable across platforms. - - - - -<p> -<hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3> - - -<p> -Returns a string containing a binary representation of the given function, -so that a later <a href="#pdf-loadstring"><code>loadstring</code></a> on this string returns -a copy of the function. -<code>function</code> must be a Lua function without upvalues. - - - - -<p> -<hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> -Looks for the first match of -<code>pattern</code> in the string <code>s</code>. -If it finds a match, then <code>find</code> returns the indices of <code>s</code> -where this occurrence starts and ends; -otherwise, it returns <b>nil</b>. -A third, optional numerical argument <code>init</code> specifies -where to start the search; -its default value is 1 and can be negative. -A value of <b>true</b> as a fourth, optional argument <code>plain</code> -turns off the pattern matching facilities, -so the function does a plain "find substring" operation, -with no characters in <code>pattern</code> being considered "magic". -Note that if <code>plain</code> is given, then <code>init</code> must be given as well. - - -<p> -If the pattern has captures, -then in a successful match -the captured values are also returned, -after the two indices. - - - - -<p> -<hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> -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 <code>printf</code> family of -standard C functions. -The only differences are that the options/modifiers -<code>*</code>, <code>l</code>, <code>L</code>, <code>n</code>, <code>p</code>, -and <code>h</code> are not supported -and that there is an extra option, <code>q</code>. -The <code>q</code> 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 - -<pre> - string.format('%q', 'a string with "quotes" and \n new line') -</pre><p> -will produce the string: - -<pre> - "a string with \"quotes\" and \ - new line" -</pre> - -<p> -The options <code>c</code>, <code>d</code>, <code>E</code>, <code>e</code>, <code>f</code>, -<code>g</code>, <code>G</code>, <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> all -expect a number as argument, -whereas <code>q</code> and <code>s</code> expect a string. - - -<p> -This function does not accept string values -containing embedded zeros, -except as arguments to the <code>q</code> option. - - - - -<p> -<hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3> -Returns an iterator function that, -each time it is called, -returns the next captures from <code>pattern</code> over string <code>s</code>. -If <code>pattern</code> specifies no captures, -then the whole match is produced in each call. - - -<p> -As an example, the following loop - -<pre> - s = "hello world from Lua" - for w in string.gmatch(s, "%a+") do - print(w) - end -</pre><p> -will iterate over all the words from string <code>s</code>, -printing one per line. -The next example collects all pairs <code>key=value</code> from the -given string into a table: - -<pre> - t = {} - s = "from=world, to=Lua" - for k, v in string.gmatch(s, "(%w+)=(%w+)") do - t[k] = v - end -</pre> - -<p> -For this function, a '<code>^</code>' at the start of a pattern does not -work as an anchor, as this would prevent the iteration. - - - - -<p> -<hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> -Returns a copy of <code>s</code> -in which all (or the first <code>n</code>, if given) -occurrences of the <code>pattern</code> have been -replaced by a replacement string specified by <code>repl</code>, -which can be a string, a table, or a function. -<code>gsub</code> also returns, as its second value, -the total number of matches that occurred. - - -<p> -If <code>repl</code> is a string, then its value is used for replacement. -The character <code>%</code> works as an escape character: -any sequence in <code>repl</code> of the form <code>%<em>n</em></code>, -with <em>n</em> between 1 and 9, -stands for the value of the <em>n</em>-th captured substring (see below). -The sequence <code>%0</code> stands for the whole match. -The sequence <code>%%</code> stands for a single <code>%</code>. - - -<p> -If <code>repl</code> 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. - - -<p> -If <code>repl</code> 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. - - -<p> -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 <b>false</b> or <b>nil</b>, -then there is no replacement -(that is, the original match is kept in the string). - - -<p> -Here are some examples: - -<pre> - 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" -</pre> - - - -<p> -<hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3> -Receives a string and returns its length. -The empty string <code>""</code> has length 0. -Embedded zeros are counted, -so <code>"a\000bc\000"</code> has length 5. - - - - -<p> -<hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3> -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. - - - - -<p> -<hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3> -Looks for the first <em>match</em> of -<code>pattern</code> in the string <code>s</code>. -If it finds one, then <code>match</code> returns -the captures from the pattern; -otherwise it returns <b>nil</b>. -If <code>pattern</code> specifies no captures, -then the whole match is returned. -A third, optional numerical argument <code>init</code> specifies -where to start the search; -its default value is 1 and can be negative. - - - - -<p> -<hr><h3><a name="pdf-string.rep"><code>string.rep (s, n)</code></a></h3> -Returns a string that is the concatenation of <code>n</code> copies of -the string <code>s</code>. - - - - -<p> -<hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> -Returns a string that is the string <code>s</code> reversed. - - - - -<p> -<hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> -Returns the substring of <code>s</code> that -starts at <code>i</code> and continues until <code>j</code>; -<code>i</code> and <code>j</code> can be negative. -If <code>j</code> is absent, then it is assumed to be equal to -1 -(which is the same as the string length). -In particular, -the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> -with length <code>j</code>, -and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code> -with length <code>i</code>. - - - - -<p> -<hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3> -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. - - - -<h3>5.4.1 - <a name="5.4.1">Patterns</a></h3> - - -<h4>Character Class:</h4><p> -A <em>character class</em> is used to represent a set of characters. -The following combinations are allowed in describing a character class: - -<ul> - -<li><b><em>x</em>:</b> -(where <em>x</em> is not one of the <em>magic characters</em> -<code>^$()%.[]*+-?</code>) -represents the character <em>x</em> itself. -</li> - -<li><b><code>.</code>:</b> (a dot) represents all characters.</li> - -<li><b><code>%a</code>:</b> represents all letters.</li> - -<li><b><code>%c</code>:</b> represents all control characters.</li> - -<li><b><code>%d</code>:</b> represents all digits.</li> - -<li><b><code>%l</code>:</b> represents all lowercase letters.</li> - -<li><b><code>%p</code>:</b> represents all punctuation characters.</li> - -<li><b><code>%s</code>:</b> represents all space characters.</li> - -<li><b><code>%u</code>:</b> represents all uppercase letters.</li> - -<li><b><code>%w</code>:</b> represents all alphanumeric characters.</li> - -<li><b><code>%x</code>:</b> represents all hexadecimal digits.</li> - -<li><b><code>%z</code>:</b> represents the character with representation 0.</li> - -<li><b><code>%<em>x</em></code>:</b> (where <em>x</em> is any non-alphanumeric character) -represents the character <em>x</em>. -This is the standard way to escape the magic characters. -Any punctuation character (even the non magic) -can be preceded by a '<code>%</code>' -when used to represent itself in a pattern. -</li> - -<li><b><code>[<em>set</em>]</code>:</b> -represents the class which is the union of all -characters in <em>set</em>. -A range of characters can be specified by -separating the end characters of the range with a '<code>-</code>'. -All classes <code>%</code><em>x</em> described above can also be used as -components in <em>set</em>. -All other characters in <em>set</em> represent themselves. -For example, <code>[%w_]</code> (or <code>[_%w]</code>) -represents all alphanumeric characters plus the underscore, -<code>[0-7]</code> represents the octal digits, -and <code>[0-7%l%-]</code> represents the octal digits plus -the lowercase letters plus the '<code>-</code>' character. - - -<p> -The interaction between ranges and classes is not defined. -Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> -have no meaning. -</li> - -<li><b><code>[^<em>set</em>]</code>:</b> -represents the complement of <em>set</em>, -where <em>set</em> is interpreted as above. -</li> - -</ul><p> -For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), -the corresponding uppercase letter represents the complement of the class. -For instance, <code>%S</code> represents all non-space characters. - - -<p> -The definitions of letter, space, and other character groups -depend on the current locale. -In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. - - - - - -<h4>Pattern Item:</h4><p> -A <em>pattern item</em> can be - -<ul> - -<li> -a single character class, -which matches any single character in the class; -</li> - -<li> -a single character class followed by '<code>*</code>', -which matches 0 or more repetitions of characters in the class. -These repetition items will always match the longest possible sequence; -</li> - -<li> -a single character class followed by '<code>+</code>', -which matches 1 or more repetitions of characters in the class. -These repetition items will always match the longest possible sequence; -</li> - -<li> -a single character class followed by '<code>-</code>', -which also matches 0 or more repetitions of characters in the class. -Unlike '<code>*</code>', -these repetition items will always match the <em>shortest</em> possible sequence; -</li> - -<li> -a single character class followed by '<code>?</code>', -which matches 0 or 1 occurrence of a character in the class; -</li> - -<li> -<code>%<em>n</em></code>, for <em>n</em> between 1 and 9; -such item matches a substring equal to the <em>n</em>-th captured string -(see below); -</li> - -<li> -<code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters; -such item matches strings that start with <em>x</em>, end with <em>y</em>, -and where the <em>x</em> and <em>y</em> are <em>balanced</em>. -This means that, if one reads the string from left to right, -counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>, -the ending <em>y</em> is the first <em>y</em> where the count reaches 0. -For instance, the item <code>%b()</code> matches expressions with -balanced parentheses. -</li> - -</ul> - - - - -<h4>Pattern:</h4><p> -A <em>pattern</em> is a sequence of pattern items. -A '<code>^</code>' at the beginning of a pattern anchors the match at the -beginning of the subject string. -A '<code>$</code>' at the end of a pattern anchors the match at the -end of the subject string. -At other positions, -'<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. - - - - - -<h4>Captures:</h4><p> -A pattern can contain sub-patterns enclosed in parentheses; -they describe <em>captures</em>. -When a match succeeds, the substrings of the subject string -that match captures are stored (<em>captured</em>) for future use. -Captures are numbered according to their left parentheses. -For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, -the part of the string matching <code>"a*(.)%w(%s*)"</code> is -stored as the first capture (and therefore has number 1); -the character matching "<code>.</code>" is captured with number 2, -and the part matching "<code>%s*</code>" has number 3. - - -<p> -As a special case, the empty capture <code>()</code> captures -the current string position (a number). -For instance, if we apply the pattern <code>"()aa()"</code> on the -string <code>"flaaap"</code>, there will be two captures: 3 and 5. - - -<p> -A pattern cannot contain embedded zeros. Use <code>%z</code> instead. - - - - - - - - - - - -<h2>5.5 - <a name="5.5">Table Manipulation</a></h2><p> -This library provides generic functions for table manipulation. -It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>. - - -<p> -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. - - -<p> -<hr><h3><a name="pdf-table.concat"><code>table.concat (table [, sep [, i [, j]]])</code></a></h3> -Given an array where all elements are strings or numbers, -returns <code>table[i]..sep..table[i+1] ··· sep..table[j]</code>. -The default value for <code>sep</code> is the empty string, -the default for <code>i</code> is 1, -and the default for <code>j</code> is the length of the table. -If <code>i</code> is greater than <code>j</code>, returns the empty string. - - - - -<p> -<hr><h3><a name="pdf-table.insert"><code>table.insert (table, [pos,] value)</code></a></h3> - - -<p> -Inserts element <code>value</code> at position <code>pos</code> in <code>table</code>, -shifting up other elements to open space, if necessary. -The default value for <code>pos</code> is <code>n+1</code>, -where <code>n</code> is the length of the table (see <a href="#2.5.5">§2.5.5</a>), -so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end -of table <code>t</code>. - - - - -<p> -<hr><h3><a name="pdf-table.maxn"><code>table.maxn (table)</code></a></h3> - - -<p> -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.) - - - - -<p> -<hr><h3><a name="pdf-table.remove"><code>table.remove (table [, pos])</code></a></h3> - - -<p> -Removes from <code>table</code> the element at position <code>pos</code>, -shifting down other elements to close the space, if necessary. -Returns the value of the removed element. -The default value for <code>pos</code> is <code>n</code>, -where <code>n</code> is the length of the table, -so that a call <code>table.remove(t)</code> removes the last element -of table <code>t</code>. - - - - -<p> -<hr><h3><a name="pdf-table.sort"><code>table.sort (table [, comp])</code></a></h3> -Sorts table elements in a given order, <em>in-place</em>, -from <code>table[1]</code> to <code>table[n]</code>, -where <code>n</code> is the length of the table. -If <code>comp</code> 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 <code>not comp(a[i+1],a[i])</code> will be true after the sort). -If <code>comp</code> is not given, -then the standard Lua operator <code><</code> is used instead. - - -<p> -The sort algorithm is not stable; -that is, elements considered equal by the given order -may have their relative positions changed by the sort. - - - - - - - -<h2>5.6 - <a name="5.6">Mathematical Functions</a></h2> - -<p> -This library is an interface to the standard C math library. -It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>. - - -<p> -<hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> - - -<p> -Returns the absolute value of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3> - - -<p> -Returns the arc cosine of <code>x</code> (in radians). - - - - -<p> -<hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3> - - -<p> -Returns the arc sine of <code>x</code> (in radians). - - - - -<p> -<hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3> - - -<p> -Returns the arc tangent of <code>x</code> (in radians). - - - - -<p> -<hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3> - - -<p> -Returns the arc tangent of <code>y/x</code> (in radians), -but uses the signs of both parameters to find the -quadrant of the result. -(It also handles correctly the case of <code>x</code> being zero.) - - - - -<p> -<hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> - - -<p> -Returns the smallest integer larger than or equal to <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3> - - -<p> -Returns the cosine of <code>x</code> (assumed to be in radians). - - - - -<p> -<hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3> - - -<p> -Returns the hyperbolic cosine of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3> - - -<p> -Returns the angle <code>x</code> (given in radians) in degrees. - - - - -<p> -<hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> - - -<p> -Returns the value <em>e<sup>x</sup></em>. - - - - -<p> -<hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> - - -<p> -Returns the largest integer smaller than or equal to <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> - - -<p> -Returns the remainder of the division of <code>x</code> by <code>y</code> -that rounds the quotient towards zero. - - - - -<p> -<hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3> - - -<p> -Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>, -<code>e</code> is an integer and the absolute value of <code>m</code> is -in the range <em>[0.5, 1)</em> -(or zero when <code>x</code> is zero). - - - - -<p> -<hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> - - -<p> -The value <code>HUGE_VAL</code>, -a value larger than or equal to any other numerical value. - - - - -<p> -<hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3> - - -<p> -Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer). - - - - -<p> -<hr><h3><a name="pdf-math.log"><code>math.log (x)</code></a></h3> - - -<p> -Returns the natural logarithm of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.log10"><code>math.log10 (x)</code></a></h3> - - -<p> -Returns the base-10 logarithm of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> - - -<p> -Returns the maximum value among its arguments. - - - - -<p> -<hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> - - -<p> -Returns the minimum value among its arguments. - - - - -<p> -<hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> - - -<p> -Returns two numbers, -the integral part of <code>x</code> and the fractional part of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> - - -<p> -The value of <em>pi</em>. - - - - -<p> -<hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3> - - -<p> -Returns <em>x<sup>y</sup></em>. -(You can also use the expression <code>x^y</code> to compute this value.) - - - - -<p> -<hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> - - -<p> -Returns the angle <code>x</code> (given in degrees) in radians. - - - - -<p> -<hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> - - -<p> -This function is an interface to the simple -pseudo-random generator function <code>rand</code> provided by ANSI C. -(No guarantees can be given for its statistical properties.) - - -<p> -When called without arguments, -returns a uniform pseudo-random real number -in the range <em>[0,1)</em>. -When called with an integer number <code>m</code>, -<code>math.random</code> returns -a uniform pseudo-random integer in the range <em>[1, m]</em>. -When called with two integer numbers <code>m</code> and <code>n</code>, -<code>math.random</code> returns a uniform pseudo-random -integer in the range <em>[m, n]</em>. - - - - -<p> -<hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3> - - -<p> -Sets <code>x</code> as the "seed" -for the pseudo-random generator: -equal seeds produce equal sequences of numbers. - - - - -<p> -<hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3> - - -<p> -Returns the sine of <code>x</code> (assumed to be in radians). - - - - -<p> -<hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3> - - -<p> -Returns the hyperbolic sine of <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3> - - -<p> -Returns the square root of <code>x</code>. -(You can also use the expression <code>x^0.5</code> to compute this value.) - - - - -<p> -<hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3> - - -<p> -Returns the tangent of <code>x</code> (assumed to be in radians). - - - - -<p> -<hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3> - - -<p> -Returns the hyperbolic tangent of <code>x</code>. - - - - - - - -<h2>5.7 - <a name="5.7">Input and Output Facilities</a></h2> - -<p> -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. - - -<p> -When using implicit file descriptors, -all operations are supplied by table <a name="pdf-io"><code>io</code></a>. -When using explicit file descriptors, -the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor -and then all operations are supplied as methods of the file descriptor. - - -<p> -The table <code>io</code> also provides -three predefined file descriptors with their usual meanings from C: -<a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. -The I/O library never closes these files. - - -<p> -Unless otherwise stated, -all I/O functions return <b>nil</b> 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 <b>nil</b> on success. - - -<p> -<hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3> - - -<p> -Equivalent to <code>file:close()</code>. -Without a <code>file</code>, closes the default output file. - - - - -<p> -<hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3> - - -<p> -Equivalent to <code>file:flush</code> over the default output file. - - - - -<p> -<hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3> - - -<p> -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. - - -<p> -In case of errors this function raises the error, -instead of returning an error code. - - - - -<p> -<hr><h3><a name="pdf-io.lines"><code>io.lines ([filename])</code></a></h3> - - -<p> -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 - -<pre> - for line in io.lines(filename) do <em>body</em> end -</pre><p> -will iterate over all lines of the file. -When the iterator function detects the end of file, -it returns <b>nil</b> (to finish the loop) and automatically closes the file. - - -<p> -The call <code>io.lines()</code> (with no file name) is equivalent -to <code>io.input():lines()</code>; -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. - - - - -<p> -<hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3> - - -<p> -This function opens a file, -in the mode specified in the string <code>mode</code>. -It returns a new file handle, -or, in case of errors, <b>nil</b> plus an error message. - - -<p> -The <code>mode</code> string can be any of the following: - -<ul> -<li><b>"r":</b> read mode (the default);</li> -<li><b>"w":</b> write mode;</li> -<li><b>"a":</b> append mode;</li> -<li><b>"r+":</b> update mode, all previous data is preserved;</li> -<li><b>"w+":</b> update mode, all previous data is erased;</li> -<li><b>"a+":</b> append update mode, previous data is preserved, - writing is only allowed at the end of file.</li> -</ul><p> -The <code>mode</code> string can also have a '<code>b</code>' 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 <code>fopen</code>. - - - - -<p> -<hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3> - - -<p> -Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. - - - - -<p> -<hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3> - - -<p> -Starts program <code>prog</code> in a separated process and returns -a file handle that you can use to read data from this program -(if <code>mode</code> is <code>"r"</code>, the default) -or to write data to this program -(if <code>mode</code> is <code>"w"</code>). - - -<p> -This function is system dependent and is not available -on all platforms. - - - - -<p> -<hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3> - - -<p> -Equivalent to <code>io.input():read</code>. - - - - -<p> -<hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3> - - -<p> -Returns a handle for a temporary file. -This file is opened in update mode -and it is automatically removed when the program ends. - - - - -<p> -<hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3> - - -<p> -Checks whether <code>obj</code> is a valid file handle. -Returns the string <code>"file"</code> if <code>obj</code> is an open file handle, -<code>"closed file"</code> if <code>obj</code> is a closed file handle, -or <b>nil</b> if <code>obj</code> is not a file handle. - - - - -<p> -<hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3> - - -<p> -Equivalent to <code>io.output():write</code>. - - - - -<p> -<hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3> - - -<p> -Closes <code>file</code>. -Note that files are automatically closed when -their handles are garbage collected, -but that takes an unpredictable amount of time to happen. - - - - -<p> -<hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3> - - -<p> -Saves any written data to <code>file</code>. - - - - -<p> -<hr><h3><a name="pdf-file:lines"><code>file:lines ()</code></a></h3> - - -<p> -Returns an iterator function that, -each time it is called, -returns a new line from the file. -Therefore, the construction - -<pre> - for line in file:lines() do <em>body</em> end -</pre><p> -will iterate over all lines of the file. -(Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file -when the loop ends.) - - - - -<p> -<hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3> - - -<p> -Reads the file <code>file</code>, -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 <b>nil</b> 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). - - -<p> -The available formats are - -<ul> - -<li><b>"*n":</b> -reads a number; -this is the only format that returns a number instead of a string. -</li> - -<li><b>"*a":</b> -reads the whole file, starting at the current position. -On end of file, it returns the empty string. -</li> - -<li><b>"*l":</b> -reads the next line (skipping the end of line), -returning <b>nil</b> on end of file. -This is the default format. -</li> - -<li><b><em>number</em>:</b> -reads a string with up to this number of characters, -returning <b>nil</b> on end of file. -If number is zero, -it reads nothing and returns an empty string, -or <b>nil</b> on end of file. -</li> - -</ul> - - - -<p> -<hr><h3><a name="pdf-file:seek"><code>file:seek ([whence] [, offset])</code></a></h3> - - -<p> -Sets and gets the file position, -measured from the beginning of the file, -to the position given by <code>offset</code> plus a base -specified by the string <code>whence</code>, as follows: - -<ul> -<li><b>"set":</b> base is position 0 (beginning of the file);</li> -<li><b>"cur":</b> base is current position;</li> -<li><b>"end":</b> base is end of file;</li> -</ul><p> -In case of success, function <code>seek</code> returns the final file position, -measured in bytes from the beginning of the file. -If this function fails, it returns <b>nil</b>, -plus a string describing the error. - - -<p> -The default value for <code>whence</code> is <code>"cur"</code>, -and for <code>offset</code> is 0. -Therefore, the call <code>file:seek()</code> returns the current -file position, without changing it; -the call <code>file:seek("set")</code> sets the position to the -beginning of the file (and returns 0); -and the call <code>file:seek("end")</code> sets the position to the -end of the file, and returns its size. - - - - -<p> -<hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3> - - -<p> -Sets the buffering mode for an output file. -There are three available modes: - -<ul> - -<li><b>"no":</b> -no buffering; the result of any output operation appears immediately. -</li> - -<li><b>"full":</b> -full buffering; output operation is performed only -when the buffer is full (or when you explicitly <code>flush</code> the file -(see <a href="#pdf-io.flush"><code>io.flush</code></a>)). -</li> - -<li><b>"line":</b> -line buffering; output is buffered until a newline is output -or there is any input from some special files -(such as a terminal device). -</li> - -</ul><p> -For the last two cases, <code>size</code> -specifies the size of the buffer, in bytes. -The default is an appropriate size. - - - - -<p> -<hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3> - - -<p> -Writes the value of each of its arguments to -the <code>file</code>. -The arguments must be strings or numbers. -To write other values, -use <a href="#pdf-tostring"><code>tostring</code></a> or <a href="#pdf-string.format"><code>string.format</code></a> before <code>write</code>. - - - - - - - -<h2>5.8 - <a name="5.8">Operating System Facilities</a></h2> - -<p> -This library is implemented through table <a name="pdf-os"><code>os</code></a>. - - -<p> -<hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3> - - -<p> -Returns an approximation of the amount in seconds of CPU time -used by the program. - - - - -<p> -<hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3> - - -<p> -Returns a string or a table containing date and time, -formatted according to the given string <code>format</code>. - - -<p> -If the <code>time</code> argument is present, -this is the time to be formatted -(see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value). -Otherwise, <code>date</code> formats the current time. - - -<p> -If <code>format</code> starts with '<code>!</code>', -then the date is formatted in Coordinated Universal Time. -After this optional character, -if <code>format</code> is the string "<code>*t</code>", -then <code>date</code> returns a table with the following fields: -<code>year</code> (four digits), <code>month</code> (1--12), <code>day</code> (1--31), -<code>hour</code> (0--23), <code>min</code> (0--59), <code>sec</code> (0--61), -<code>wday</code> (weekday, Sunday is 1), -<code>yday</code> (day of the year), -and <code>isdst</code> (daylight saving flag, a boolean). - - -<p> -If <code>format</code> is not "<code>*t</code>", -then <code>date</code> returns the date as a string, -formatted according to the same rules as the C function <code>strftime</code>. - - -<p> -When called without arguments, -<code>date</code> returns a reasonable date and time representation that depends on -the host system and on the current locale -(that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>). - - - - -<p> -<hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> - - -<p> -Returns the number of seconds from time <code>t1</code> to time <code>t2</code>. -In POSIX, Windows, and some other systems, -this value is exactly <code>t2</code><em>-</em><code>t1</code>. - - - - -<p> -<hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3> - - -<p> -This function is equivalent to the C function <code>system</code>. -It passes <code>command</code> to be executed by an operating system shell. -It returns a status code, which is system-dependent. -If <code>command</code> is absent, then it returns nonzero if a shell is available -and zero otherwise. - - - - -<p> -<hr><h3><a name="pdf-os.exit"><code>os.exit ([code])</code></a></h3> - - -<p> -Calls the C function <code>exit</code>, -with an optional <code>code</code>, -to terminate the host program. -The default value for <code>code</code> is the success code. - - - - -<p> -<hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3> - - -<p> -Returns the value of the process environment variable <code>varname</code>, -or <b>nil</b> if the variable is not defined. - - - - -<p> -<hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3> - - -<p> -Deletes the file or directory with the given name. -Directories must be empty to be removed. -If this function fails, it returns <b>nil</b>, -plus a string describing the error. - - - - -<p> -<hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3> - - -<p> -Renames file or directory named <code>oldname</code> to <code>newname</code>. -If this function fails, it returns <b>nil</b>, -plus a string describing the error. - - - - -<p> -<hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3> - - -<p> -Sets the current locale of the program. -<code>locale</code> is a string specifying a locale; -<code>category</code> is an optional string describing which category to change: -<code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, -<code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; -the default category is <code>"all"</code>. -The function returns the name of the new locale, -or <b>nil</b> if the request cannot be honored. - - -<p> -If <code>locale</code> is the empty string, -the current locale is set to an implementation-defined native locale. -If <code>locale</code> is the string "<code>C</code>", -the current locale is set to the standard C locale. - - -<p> -When called with <b>nil</b> as the first argument, -this function only returns the name of the current locale -for the given category. - - - - -<p> -<hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3> - - -<p> -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 <code>year</code>, <code>month</code>, and <code>day</code>, -and may have fields <code>hour</code>, <code>min</code>, <code>sec</code>, and <code>isdst</code> -(for a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function). - - -<p> -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 <code>time</code> can be used only as an argument to -<code>date</code> and <code>difftime</code>. - - - - -<p> -<hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> - - -<p> -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. - - -<p> -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). - - -<p> -When possible, -you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, -which automatically removes the file when the program ends. - - - - - - - -<h2>5.9 - <a name="5.9">The Debug Library</a></h2> - -<p> -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. - - -<p> -All functions in this library are provided -inside the <a name="pdf-debug"><code>debug</code></a> 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. - - -<p> -<hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3> - - -<p> -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 <code>cont</code> finishes this function, -so that the caller continues its execution. - - -<p> -Note that commands for <code>debug.debug</code> are not lexically nested -within any function, and so have no direct access to local variables. - - - - -<p> -<hr><h3><a name="pdf-debug.getfenv"><code>debug.getfenv (o)</code></a></h3> -Returns the environment of object <code>o</code>. - - - - -<p> -<hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3> - - -<p> -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 <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). - - - - -<p> -<hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] function [, what])</code></a></h3> - - -<p> -Returns a table with information about a function. -You can give the function directly, -or you can give a number as the value of <code>function</code>, -which means the function running at level <code>function</code> of the call stack -of the given thread: -level 0 is the current function (<code>getinfo</code> itself); -level 1 is the function that called <code>getinfo</code>; -and so on. -If <code>function</code> is a number larger than the number of active functions, -then <code>getinfo</code> returns <b>nil</b>. - - -<p> -The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, -with the string <code>what</code> describing which fields to fill in. -The default for <code>what</code> is to get all information available, -except the table of valid lines. -If present, -the option '<code>f</code>' -adds a field named <code>func</code> with the function itself. -If present, -the option '<code>L</code>' -adds a field named <code>activelines</code> with the table of -valid lines. - - -<p> -For instance, the expression <code>debug.getinfo(1,"n").name</code> returns -a table with a name for the current function, -if a reasonable name can be found, -and the expression <code>debug.getinfo(print)</code> -returns a table with all available information -about the <a href="#pdf-print"><code>print</code></a> function. - - - - -<p> -<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] level, local)</code></a></h3> - - -<p> -This function returns the name and the value of the local variable -with index <code>local</code> of the function at level <code>level</code> of the stack. -(The first parameter or local variable has index 1, and so on, -until the last active local variable.) -The function returns <b>nil</b> if there is no local -variable with the given index, -and raises an error when called with a <code>level</code> out of range. -(You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.) - - -<p> -Variable names starting with '<code>(</code>' (open parentheses) -represent internal variables -(loop control variables, temporaries, and C function locals). - - - - -<p> -<hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (object)</code></a></h3> - - -<p> -Returns the metatable of the given <code>object</code> -or <b>nil</b> if it does not have a metatable. - - - - -<p> -<hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3> - - -<p> -Returns the registry table (see <a href="#3.5">§3.5</a>). - - - - -<p> -<hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (func, up)</code></a></h3> - - -<p> -This function returns the name and the value of the upvalue -with index <code>up</code> of the function <code>func</code>. -The function returns <b>nil</b> if there is no upvalue with the given index. - - - - -<p> -<hr><h3><a name="pdf-debug.setfenv"><code>debug.setfenv (object, table)</code></a></h3> - - -<p> -Sets the environment of the given <code>object</code> to the given <code>table</code>. -Returns <code>object</code>. - - - - -<p> -<hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3> - - -<p> -Sets the given function as a hook. -The string <code>mask</code> and the number <code>count</code> describe -when the hook will be called. -The string mask may have the following characters, -with the given meaning: - -<ul> -<li><b><code>"c"</code>:</b> the hook is called every time Lua calls a function;</li> -<li><b><code>"r"</code>:</b> the hook is called every time Lua returns from a function;</li> -<li><b><code>"l"</code>:</b> the hook is called every time Lua enters a new line of code.</li> -</ul><p> -With a <code>count</code> different from zero, -the hook is called after every <code>count</code> instructions. - - -<p> -When called without arguments, -<a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook. - - -<p> -When the hook is called, its first parameter is a string -describing the event that has triggered its call: -<code>"call"</code>, <code>"return"</code> (or <code>"tail return"</code>, -when simulating a return from a tail call), -<code>"line"</code>, and <code>"count"</code>. -For line events, -the hook also gets the new line number as its second parameter. -Inside a hook, -you can call <code>getinfo</code> with level 2 to get more information about -the running function -(level 0 is the <code>getinfo</code> function, -and level 1 is the hook function), -unless the event is <code>"tail return"</code>. -In this case, Lua is only simulating the return, -and a call to <code>getinfo</code> will return invalid data. - - - - -<p> -<hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3> - - -<p> -This function assigns the value <code>value</code> to the local variable -with index <code>local</code> of the function at level <code>level</code> of the stack. -The function returns <b>nil</b> if there is no local -variable with the given index, -and raises an error when called with a <code>level</code> out of range. -(You can call <code>getinfo</code> to check whether the level is valid.) -Otherwise, it returns the name of the local variable. - - - - -<p> -<hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (object, table)</code></a></h3> - - -<p> -Sets the metatable for the given <code>object</code> to the given <code>table</code> -(which can be <b>nil</b>). - - - - -<p> -<hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (func, up, value)</code></a></h3> - - -<p> -This function assigns the value <code>value</code> to the upvalue -with index <code>up</code> of the function <code>func</code>. -The function returns <b>nil</b> if there is no upvalue -with the given index. -Otherwise, it returns the name of the upvalue. - - - - -<p> -<hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message] [, level])</code></a></h3> - - -<p> -Returns a string with a traceback of the call stack. -An optional <code>message</code> string is appended -at the beginning of the traceback. -An optional <code>level</code> number tells at which level -to start the traceback -(default is 1, the function calling <code>traceback</code>). - - - - - - - -<h1>6 - <a name="6">Lua Stand-alone</a></h1> - -<p> -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 <code>lua</code>, -is provided with the standard distribution. -The stand-alone interpreter includes -all standard libraries, including the debug library. -Its usage is: - -<pre> - lua [options] [script [args]] -</pre><p> -The options are: - -<ul> -<li><b><code>-e <em>stat</em></code>:</b> executes string <em>stat</em>;</li> -<li><b><code>-l <em>mod</em></code>:</b> "requires" <em>mod</em>;</li> -<li><b><code>-i</code>:</b> enters interactive mode after running <em>script</em>;</li> -<li><b><code>-v</code>:</b> prints version information;</li> -<li><b><code>--</code>:</b> stops handling options;</li> -<li><b><code>-</code>:</b> executes <code>stdin</code> as a file and stops handling options.</li> -</ul><p> -After handling its options, <code>lua</code> runs the given <em>script</em>, -passing to it the given <em>args</em> as string arguments. -When called without arguments, -<code>lua</code> behaves as <code>lua -v -i</code> -when the standard input (<code>stdin</code>) is a terminal, -and as <code>lua -</code> otherwise. - - -<p> -Before running any argument, -the interpreter checks for an environment variable <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a>. -If its format is <code>@<em>filename</em></code>, -then <code>lua</code> executes the file. -Otherwise, <code>lua</code> executes the string itself. - - -<p> -All options are handled in order, except <code>-i</code>. -For instance, an invocation like - -<pre> - $ lua -e'a=1' -e 'print(a)' script.lua -</pre><p> -will first set <code>a</code> to 1, then print the value of <code>a</code> (which is '<code>1</code>'), -and finally run the file <code>script.lua</code> with no arguments. -(Here <code>$</code> is the shell prompt. Your prompt may be different.) - - -<p> -Before starting to run the script, -<code>lua</code> collects all arguments in the command line -in a global table called <code>arg</code>. -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 - -<pre> - $ lua -la b.lua t1 t2 -</pre><p> -the interpreter first runs the file <code>a.lua</code>, -then creates a table - -<pre> - arg = { [-2] = "lua", [-1] = "-la", - [0] = "b.lua", - [1] = "t1", [2] = "t2" } -</pre><p> -and finally runs the file <code>b.lua</code>. -The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ··· -as arguments; -it can also access these arguments with the vararg expression '<code>...</code>'. - - -<p> -In interactive mode, -if you write an incomplete statement, -the interpreter waits for its completion -by issuing a different prompt. - - -<p> -If the global variable <a name="pdf-_PROMPT"><code>_PROMPT</code></a> contains a string, -then its value is used as the prompt. -Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> 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 <code>_PROMPT</code>. -See the next example: - -<pre> - $ lua -e"_PROMPT='myprompt> '" -i -</pre><p> -(The outer pair of quotes is for the shell, -the inner pair is for Lua.) -Note the use of <code>-i</code> to enter interactive mode; -otherwise, -the program would just end silently -right after the assignment to <code>_PROMPT</code>. - - -<p> -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 <code>#</code>. -Therefore, Lua scripts can be made into executable programs -by using <code>chmod +x</code> and the <code>#!</code> form, -as in - -<pre> - #!/usr/local/bin/lua -</pre><p> -(Of course, -the location of the Lua interpreter may be different in your machine. -If <code>lua</code> is in your <code>PATH</code>, -then - -<pre> - #!/usr/bin/env lua -</pre><p> -is a more portable solution.) - - - -<h1>7 - <a name="7">Incompatibilities with the Previous Version</a></h1> - -<p> -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 <code>luaconf.h</code>). -However, -all these compatibility options will be removed in the next version of Lua. - - - -<h2>7.1 - <a name="7.1">Changes in the Language</a></h2> -<ul> - -<li> -The vararg system changed from the pseudo-argument <code>arg</code> with a -table with the extra arguments to the vararg expression. -(See compile-time option <code>LUA_COMPAT_VARARG</code> in <code>luaconf.h</code>.) -</li> - -<li> -There was a subtle change in the scope of the implicit -variables of the <b>for</b> statement and for the <b>repeat</b> statement. -</li> - -<li> -The long string/long comment syntax (<code>[[<em>string</em>]]</code>) -does not allow nesting. -You can use the new syntax (<code>[=[<em>string</em>]=]</code>) in these cases. -(See compile-time option <code>LUA_COMPAT_LSTR</code> in <code>luaconf.h</code>.) -</li> - -</ul> - - - - -<h2>7.2 - <a name="7.2">Changes in the Libraries</a></h2> -<ul> - -<li> -Function <code>string.gfind</code> was renamed <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>. -(See compile-time option <code>LUA_COMPAT_GFIND</code> in <code>luaconf.h</code>.) -</li> - -<li> -When <a href="#pdf-string.gsub"><code>string.gsub</code></a> is called with a function as its -third argument, -whenever this function returns <b>nil</b> or <b>false</b> the -replacement string is the whole match, -instead of the empty string. -</li> - -<li> -Function <code>table.setn</code> was deprecated. -Function <code>table.getn</code> corresponds -to the new length operator (<code>#</code>); -use the operator instead of the function. -(See compile-time option <code>LUA_COMPAT_GETN</code> in <code>luaconf.h</code>.) -</li> - -<li> -Function <code>loadlib</code> was renamed <a href="#pdf-package.loadlib"><code>package.loadlib</code></a>. -(See compile-time option <code>LUA_COMPAT_LOADLIB</code> in <code>luaconf.h</code>.) -</li> - -<li> -Function <code>math.mod</code> was renamed <a href="#pdf-math.fmod"><code>math.fmod</code></a>. -(See compile-time option <code>LUA_COMPAT_MOD</code> in <code>luaconf.h</code>.) -</li> - -<li> -Functions <code>table.foreach</code> and <code>table.foreachi</code> are deprecated. -You can use a for loop with <code>pairs</code> or <code>ipairs</code> instead. -</li> - -<li> -There were substantial changes in function <a href="#pdf-require"><code>require</code></a> due to -the new module system. -However, the new behavior is mostly compatible with the old, -but <code>require</code> gets the path from <a href="#pdf-package.path"><code>package.path</code></a> instead -of from <code>LUA_PATH</code>. -</li> - -<li> -Function <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> has different arguments. -Function <code>gcinfo</code> is deprecated; -use <code>collectgarbage("count")</code> instead. -</li> - -</ul> - - - - -<h2>7.3 - <a name="7.3">Changes in the API</a></h2> -<ul> - -<li> -The <code>luaopen_*</code> functions (to open libraries) -cannot be called directly, -like a regular C function. -They must be called through Lua, -like a Lua function. -</li> - -<li> -Function <code>lua_open</code> was replaced by <a href="#lua_newstate"><code>lua_newstate</code></a> to -allow the user to set a memory-allocation function. -You can use <a href="#luaL_newstate"><code>luaL_newstate</code></a> from the standard library to -create a state with a standard allocation function -(based on <code>realloc</code>). -</li> - -<li> -Functions <code>luaL_getn</code> and <code>luaL_setn</code> -(from the auxiliary library) are deprecated. -Use <a href="#lua_objlen"><code>lua_objlen</code></a> instead of <code>luaL_getn</code> -and nothing instead of <code>luaL_setn</code>. -</li> - -<li> -Function <code>luaL_openlib</code> was replaced by <a href="#luaL_register"><code>luaL_register</code></a>. -</li> - -<li> -Function <code>luaL_checkudata</code> now throws an error when the given value -is not a userdata of the expected type. -(In Lua 5.0 it returned <code>NULL</code>.) -</li> - -</ul> - - - - -<h1>8 - <a name="8">The Complete Syntax of Lua</a></h1> - -<p> -Here is the complete syntax of Lua in extended BNF. -(It does not describe operator precedences.) - - - - -<pre> - - chunk ::= {stat [`<b>;</b>´]} [laststat [`<b>;</b>´]] - - block ::= chunk - - stat ::= varlist `<b>=</b>´ explist | - functioncall | - <b>do</b> block <b>end</b> | - <b>while</b> exp <b>do</b> block <b>end</b> | - <b>repeat</b> block <b>until</b> exp | - <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | - <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> | - <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | - <b>function</b> funcname funcbody | - <b>local</b> <b>function</b> Name funcbody | - <b>local</b> namelist [`<b>=</b>´ explist] - - laststat ::= <b>return</b> [explist] | <b>break</b> - - funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name] - - varlist ::= var {`<b>,</b>´ var} - - var ::= Name | prefixexp `<b>[</b>´ exp `<b>]</b>´ | prefixexp `<b>.</b>´ Name - - namelist ::= Name {`<b>,</b>´ Name} - - explist ::= {exp `<b>,</b>´} exp - - exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | `<b>...</b>´ | function | - prefixexp | tableconstructor | exp binop exp | unop exp - - prefixexp ::= var | functioncall | `<b>(</b>´ exp `<b>)</b>´ - - functioncall ::= prefixexp args | prefixexp `<b>:</b>´ Name args - - args ::= `<b>(</b>´ [explist] `<b>)</b>´ | tableconstructor | String - - function ::= <b>function</b> funcbody - - funcbody ::= `<b>(</b>´ [parlist] `<b>)</b>´ block <b>end</b> - - parlist ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ - - tableconstructor ::= `<b>{</b>´ [fieldlist] `<b>}</b>´ - - fieldlist ::= field {fieldsep field} [fieldsep] - - field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp - - fieldsep ::= `<b>,</b>´ | `<b>;</b>´ - - binop ::= `<b>+</b>´ | `<b>-</b>´ | `<b>*</b>´ | `<b>/</b>´ | `<b>^</b>´ | `<b>%</b>´ | `<b>..</b>´ | - `<b><</b>´ | `<b><=</b>´ | `<b>></b>´ | `<b>>=</b>´ | `<b>==</b>´ | `<b>~=</b>´ | - <b>and</b> | <b>or</b> - - unop ::= `<b>-</b>´ | <b>not</b> | `<b>#</b>´ - -</pre> - -<p> - - - - - - - -<HR> -<SMALL> -Last update: -Mon Aug 18 13:25:46 BRT 2008 -</SMALL> -<!-- -Last change: revised for Lua 5.1.4 ---> - -</body></html> |