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diff --git a/doc/manual.html b/doc/manual.html new file mode 100644 index 00000000..b55232bd --- /dev/null +++ b/doc/manual.html @@ -0,0 +1,5980 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<html> + +<head> +<title>Lua 5.1 Reference Manual</title> +<LINK REL="stylesheet" TYPE="text/css" HREF="lua.css"> +</head> + +<body BGCOLOR="#FFFFFF"> + +<hr> +<h1> +<a href="http://www.lua.org/home.html"><img src="logo.gif" ALT="[Lua logo]" border=0></a> +Lua 5.1 Reference Manual +</h1> + +by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes +<p> +<small> +<a href="http://www.lua.org/copyright.html">Copyright</a> +© 2005 Lua.org, PUC-Rio. All rights reserved. +</small> +<hr> + +<p> +<p> +<!-- ====================================================================== --> + + + +<p> +<a name="1"></a><h1>1 - Introduction</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 +configuration 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. + +<p>The Lua distribution includes a stand-alone embedding program, +<code>lua</code>, that uses the Lua library to offer a complete Lua interpreter. + +<p>Lua is free software, +and is provided as usual with no guarantees, +as stated in its copyright notice. +The implementation described in this manual is available +at Lua's official web site, <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 papers below, +which are available at Lua's web site. +<ul> +<li> +R. Ierusalimschy, L. H. de Figueiredo, and W. Celes. +Lua—an extensible extension language. +<em>Software: Practice & Experience</em> <b>26</b>:6 (1996) 635–652. +<li> +L. H. de Figueiredo, R. Ierusalimschy, and W. Celes. +The design and implementation of a language for extending applications. +<em>Proceedings of XXI Brazilian Seminar on Software and Hardware</em> +(1994) 273–283. +<li> +L. H. de Figueiredo, R. Ierusalimschy, and W. Celes. +Lua: an extensible embedded language. +<em>Dr. Dobb's Journal</em> <b>21</b>:12 (Dec 1996) 26–33. +<li> +R. Ierusalimschy, L. H. de Figueiredo, and W. Celes. +The evolution of an extension language: a history of Lua, +<em>Proceedings of V Brazilian Symposium on Programming Languages</em> (2001) B-14–B-28. +</ul> + +<p>Lua means "moon" in Portuguese and is pronounced LOO-ah. + +<p> +<a name="language"></a><a name="2"></a><h1>2 - The Language</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, +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 in <em>italics</em>, +keywords are shown in <b>bold</b>, +and other terminal symbols are shown in <code>typewriter</code> font, +enclosed in single quotes. + +<p><a name="lexical"></a><a name="2.1"></a><h2>2.1 - Lexical Conventions</h2> + +<p><em>Names</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.) + +<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 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: +<ul> +<li><b><code>\a</code></b> — bell +<li><b><code>\b</code></b> — backspace +<li><b><code>\f</code></b> — form feed +<li><b><code>\n</code></b> — newline +<li><b><code>\r</code></b> — carriage return +<li><b><code>\t</code></b> — horizontal tab +<li><b><code>\v</code></b> — vertical tab +<li><b><code>\\</code></b> — backslash +<li><b><code>\"</code></b> — quotation mark +<li><b><code>\'</code></b> — apostrophe +</ul> +Moreover, a `<code>\</code><em>newline</em>´ +(that is, a backslash followed by a real newline) +results in a newline in the string. +A character in a string may also be specified by its numerical value +using the escape sequence `<code>\</code><em>ddd</em>´, +where <em>ddd</em> is a sequence of up to three decimal digits. +Strings in Lua may contain any 8-bit value, including embedded zeros, +which can be specified as `<code>\0</code>´. + +<p>Literal strings can also be defined using a long format +enclosed by <em>l-brackets</em> (long brackets). +We define an <em>opening l-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 l-bracket of level 0 is written as <code>[[</code>, +an opening l-bracket of level 1 is written as <code>[=[</code>, +and so on. +A <em>closing l-bracket</em> is defined similarly; +for instance, a closing l-bracket of level 4 is written as <code>]====]</code>. +A long string starts with an opening l-bracket of any level and +ends at the first closing l-bracket of the same level. +Literals in this bracketed form may run for several lines, +do not interpret any escape sequences, +and ignore l-brackets of any other level. + +<p>For convenience, +when the opening l-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 four literals below denote the same string: +<PRE> + (1) "alo\n123\"" + (2) '\97lo\10\04923"' + (3) [[alo + 123"]] + (4) [==[ + alo + 123"]==] +</PRE> + +<p><em>Numerical constants</em> may be written with an optional decimal part +and an optional decimal exponent. +Examples of valid numerical constants are +<PRE> + 3 3.0 3.1416 314.16e-2 0.31416E1 +</PRE> + +<p><em>Comments</em> start anywhere outside a string with a +double hyphen (<code>--</code>). +If the text immediately after <code>--</code> is not an opening l-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 l-bracket. + +<p><a name="TypesSec"></a><a name="2.2"></a><h2>2.2 - Values and Types</h2> + +<p>Lua is a <em>dynamically typed language</em>. +That means that +variables do not have types; only values do. +There are no type definitions in the language. +All values carry their own type. + +<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; +usually it represents the absence of a useful value. +<em>Boolean</em> is the type of the values <B>false</B> and <B>true</B>. +In Lua, 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 may contain any 8-bit character, +including embedded zeros (<code>'\0'</code>) (see <a href="#lexical">2.1</a>). + +<p>Functions are <em>first-class values</em> in Lua. +That means that functions can be stored in variables, +passed as arguments to other functions, and returned as results. +Lua can call (and manipulate) functions written in Lua and +functions written in C +(see <a href="#functioncall">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="#metatable">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="#coroutine">2.11</a>). + +<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>). +Moreover, +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 may be used to represent ordinary arrays, +symbol tables, sets, records, graphs, trees, etc. +To represent records, Lua uses the field name as an index. +The language supports this representation by +providing <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="#tableconstructor">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 may contain functions. +Thus tables may also carry <em>methods</em> (see <a href="#func-def">2.5.9</a>). + +<p>Tables, functions, and 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. + +<p><a name="coercion"></a><a name="2.2.1"></a><h3>2.2.1 - Coercion</h3> + +<p>Lua provides automatic conversion between +string and number values at run time. +Any arithmetic operation applied to a string tries to convert +that string to a number, following the usual rules. +Conversely, whenever a number is used where a string is expected, +the number is converted to a string, in a reasonable format. +For complete control of how numbers are converted to strings, +use the <code>format</code> function from the string library +(see <a href="#pdf-string.format"><code>string.format</code></a>). + +<p><a name="variables"></a><a name="2.3"></a><h2>2.3 - Variables</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 formal parameter of a function, +which is a particular form of local variable): +<pre> + var ::= Name +</pre> +Variables are assumed to be global unless explicitly declared local +(see <a href="#localvar">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="#visibility">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> +The first expression (<em>prefixexp</em>) should result in a table value; +the second expression (<em>exp</em>) +identifies a specific entry inside that table. +The expression denoting the table to be indexed has a restricted syntax; +see <a href="#expressions">2.5</a> for details. + +<p>The syntax <code>var.NAME</code> is just syntactic sugar for +<code>var["NAME"]</code>: +<pre> + var ::= prefixexp `<b>.</b>´ Name +</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="#metatable">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>All global variables live as fields in ordinary Lua tables, +called <em>environment tables</em> or simply +<em>environments</em> (see <a href="#environ">2.9</a>). +Each function has its own reference to an environment, +so that all global variables in that function +will refer to that environment table. +When a function is created, +it inherits the environment from the function that created it. +To replace or get the environment table of a Lua function, +you call <a href="#pdf-setfenv"><code>setfenv</code></a> or <a href="#pdf-getfenv"><code>getfenv</code></a>. +(You can only manipulate the environment of C functions +through the debug library; (see <a href="#libdebug">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> +where <code>_env</code> is the environment of the running function. +(See <a href="#metatable">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.) + +<p><a name="stats"></a><a name="2.4"></a><h2>2.4 - Statements</h2> + +<p>Lua supports an almost conventional set of statements, +similar to those in Pascal or C. +This set includes +assignment, control structures, procedure calls, +table constructors, and variable declarations. + +<p><a name="chunks"></a><a name="2.4.1"></a><h3>2.4.1 - Chunks</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>Lua handles a chunk as the body of an anonymous function +with a variable number of arguments +(see <a href="#func-def">2.5.9</a>). +As such, chunks can define local variables, +receive arguments, and return values. + +<p>A chunk may be stored in a file or in a string inside the host program. +When a chunk is executed, first it is pre-compiled into opcodes for +a virtual machine, +and then the compiled code is executed +by an interpreter for the virtual machine. + +<p>Chunks may 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. + + +<p><a name="2.4.2"></a><h3>2.4.2 - Blocks</h3> +A block is a list of statements; +syntactically, a block is equal to a chunk: +<pre> + block ::= chunk +</pre> + +<p>A block may be explicitly delimited to produce a single statement: +<pre> + stat ::= <b>do</b> block <b>end</b> +</pre> +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="#control">2.4.4</a>). + + +<p><a name="assignment"></a><a name="2.4.3"></a><h3>2.4.3 - Assignment</h3> + +<p>Lua allows multiple assignment. +Therefore, the syntax for assignment +defines a list of variables on the left side +and a list of expressions on the right side. +The elements in both lists are separated by commas: +<pre> + stat ::= varlist1 `<b>=</b>´ explist1 + varlist1 ::= var {`<b>,</b>´ var} + explist1 ::= exp {`<b>,</b>´ exp} +</pre> +Expressions are discussed in <a href="#expressions">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 function call enter in the list of values, +before the adjustment +(except when the call is enclosed in parentheses; see <a href="#expressions">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> +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> +exchanges the values of <code>x</code> and <code>y</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="#metatable">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> +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.) + +<p><a name="control"></a><a name="2.4.4"></a><h3>2.4.4 - Control Structures</h3> +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> +Lua also has a <b>for</b> statement, in two flavors (see <a href="#for">2.4.5</a>). + +<p>The condition expression <em>exp</em> of a +control structure may 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. +That means the condition can refer to local variables +declared inside the loop. + +<p>The <b>return</b> statement is used to return values +from a function or from a chunk. + +Functions and chunks may return more than one value, +so the syntax for the <b>return</b> statement is +<pre> + stat ::= <b>return</b> [explist1] +</pre> + +<p>The <b>break</b> statement can be 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> +A <b>break</b> ends the innermost enclosing loop. + +<p>For syntactic reasons, <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. + +<p><a name="for"></a><a name="2.4.5"></a><h3>2.4.5 - For Statement</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> +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 var = e1, e2, e3 do block end +</PRE> +is equivalent to the code: +<PRE> + do + local _var, _limit, _step = tonumber(e1), tonumber(e2), tonumber(e3) + if not (_var and _limit and _step) then error() end + while (_step>0 and _var<=_limit) or (_step<=0 and _var>=_limit) do + local var = _var + block + _var = _var + _step + end + end +</PRE> +Note the following: +<ul> +<li> All three control expressions are evaluated only once, +before the loop starts. +They must all result in numbers. +<li> <code>_var</code>, <code>_limit</code>, and <code>_step</code> are invisible variables. +The names are here for explanatory purposes only. +<li> If the third expression (the step) is absent, +then a step of 1 is used. +<li> You can use <b>break</b> to exit a <b>for</b> loop. +<li> The loop variable <code>var</code> is local to the loop; +you cannot use its value after the <b>for</b> ends or is broken. +If you need the value of the loop variable <code>var</code>, +then assign it to another variable before breaking or exiting the loop. +</ul> + +<p>The generic <b>for</b> statement works over functions, +called <em>iterators</em>. +For each iteration, it calls its iterator function to produce a new value, +stopping when the new value is <B>nil</B>. +The generic <b>for</b> loop has the following syntax: +<pre> + stat ::= <b>for</b> Name {`<b>,</b>´ Name} <b>in</b> explist1 <b>do</b> block <b>end</b> +</pre> +A <b>for</b> statement like +<PRE> + for var_1, ..., var_n in explist do block end +</PRE> +is equivalent to the code: +<PRE> + do + local _f, _s, _var = explist + while true do + local var_1, ... , var_n = _f(_s, _var) + _var = var_1 + if _var == nil then break end + block + end + end +</PRE> +Note the following: +<ul> +<li> <code>explist</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> <code>_f</code>, <code>_s</code>, and <code>_var</code> are invisible variables. +The names are here for explanatory purposes only. +<li> You can use <b>break</b> to exit a <b>for</b> loop. +<li> The loop variables <code>var_i</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. +</ul> + +<p><a name="funcstat"></a><a name="2.4.6"></a><h3>2.4.6 - Function Calls as Statements</h3> +To allow possible side-effects, +function calls can be executed as statements: +<pre> + stat ::= functioncall +</pre> +In this case, all returned values are thrown away. +Function calls are explained in <a href="#functioncall">2.5.8</a>. + +<p><a name="localvar"></a><a name="2.4.7"></a><h3>2.4.7 - Local Declarations</h3> +Local variables may be declared anywhere inside a block. +The declaration may include an initial assignment: +<pre> + stat ::= <b>local</b> namelist [`<b>=</b>´ explist1] + namelist ::= Name {`<b>,</b>´ Name} +</pre> +If present, an initial assignment has the same semantics +of a multiple assignment (see <a href="#assignment">2.4.3</a>). +Otherwise, all variables are initialized with <B>nil</B>. + +<p>A chunk is also a block (see <a href="#chunks">2.4.1</a>), +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="#visibility">2.6</a>. + +<p><a name="expressions"></a><a name="2.5"></a><h2>2.5 - Expressions</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 ::= Literal + 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="#lexical">2.1</a>; +variables are explained in <a href="#variables">2.3</a>; +function definitions are explained in <a href="#func-def">2.5.9</a>; +function calls are explained in <a href="#functioncall">2.5.8</a>; +table constructors are explained in <a href="#tableconstructor">2.5.7</a>. +Vararg expressions, +denoted by three dots (...), can only be used inside +vararg functions; +they are explained in <a href="#func-def">2.5.9</a>. + + +<p>Binary operators comprise arithmetic operators (see <a href="#arith">2.5.1</a>), +relational operators (see <a href="#rel-ops">2.5.2</a>), and logical operators (see <a href="#logic">2.5.3</a>). +Unary operators comprise the unary minus (see <a href="#arith">2.5.1</a>), +the unary <b>not</b> (see <a href="#logic">2.5.3</a>), +and the unary <em>length operator</em> (see <a href="#len-op">2.5.5</a>). + +<p>Both function calls and vararg expressions may result in multiple values. +If the expression is used as a statement (see <a href="#funcstat">2.4.6</a>) +(only possible for function calls), +then its return list is adjusted to zero elements, +thus discarding all returned values. +If the expression is used inside another expression +or in the middle of a list of expressions, +then its result list is adjusted to one element, +thus discarding all values except the first one. +If the expression is used as the last element of a list of expressions, +then no adjustment is made, +unless the call is enclosed in parentheses. + +<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 values returned by 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 may 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 values returned by f() + return ... -- returns all received vararg parameters + return x,y,f() -- returns x, y, and all values returned by f() + {f()} -- creates a list with all values returned by f() + {...} -- creates a list with all vararg parameters + {f(), nil} -- f() is adjusted to 1 result +</PRE> + +<p>An 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.) + +<p><a name="arith"></a><a name="2.5.1"></a><h3>2.5.1 - Arithmetic Operators</h3> +Lua supports the usual arithmetic operators: +the binary <code>+</code> (addition), +<code>-</code> (subtraction), <code>*</code> (multiplication), +<code>/</code> (division), <code>%</code> (modulus), 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="#coercion">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>. +Modulus is defined as +<PRE> + a % b == a - math.floor(a/b)*b +</PRE> +That is, it is the remaining of a division that rounds +the quotient towards minus infinity. + +<p><a name="rel-ops"></a><a name="2.5.2"></a><h3>2.5.2 - Relational Operators</h3> +The relational operators in Lua are +<PRE> + == ~= < > <= >= +</PRE> +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, or function), +this new object is different from any previously existing object. + +<p>You can change the way that Lua compares tables and userdata +using the "eq" metamethod (see <a href="#metatable">2.8</a>). + +<p>The conversion rules of <a href="#coercion">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="#metatable">2.8</a>). + +<p><a name="logic"></a><a name="2.5.3"></a><h3>2.5.3 - Logical Operators</h3> +The logical operators in Lua are + +<PRE> + and or not +</PRE> +Like the control structures (see <a href="#control">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 operator <b>not</b> always returns <B>false</B> or <B>true</B>. + +<p>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. +For example, +<PRE> + 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><a name="concat"></a><a name="2.5.4"></a><h3>2.5.4 - Concatenation</h3> +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="#coercion">2.2.1</a>. +Otherwise, the "concat" metamethod is called (see <a href="#metatable">2.8</a>). + +<p><a name="len-op"></a><a name="2.5.5"></a><h3>2.5.5 - The Length Operator</h3> + +<p>The length operator is denoted by the prefix <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). +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> may be zero. + +<p>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> may be any of the indices that precede a <B>nil</B> value +(that is, it may consider any such <B>nil</B> value as the end of +the array). + +<p><a name="2.5.6"></a><h3>2.5.6 - Precedence</h3> +Operator precedence in Lua follows the table below, +from lower to higher priority: +<PRE> + or + and + < > <= >= ~= == + .. + + - + * / % + not # - (unary) + ^ +</PRE> +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. + +<p><a name="tableconstructor"></a><a name="2.5.7"></a><h3>2.5.7 - Table Constructors</h3> +Table constructors are expressions that create tables. +Every time a constructor is evaluated, a new table is created. +Constructors can be used to create empty tables, +or to create a table and initialize some of its fields. +The general syntax for constructors is +<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> +is equivalent to +<PRE> + do + local temp = {} + temp[f(1)] = g + temp[1] = "x" -- 1st exp + temp[2] = "y" -- 2nd exp + temp.x = 1 -- temp["x"] = 1 + temp[3] = f(x) -- 3rd exp + temp[30] = 23 + temp[4] = 45 -- 4th exp + a = temp + end +</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 that expression enter the list consecutively +(see <a href="#functioncall">2.5.8</a>). +To avoid this, +enclose the function call (or the vararg expression) +in parentheses (see <a href="#expressions">2.5</a>). + +<p>The field list may have an optional trailing separator, +as a convenience for machine-generated code. + +<p><a name="functioncall"></a><a name="2.5.8"></a><h3>2.5.8 - Function Calls</h3> +A function call in Lua has the following syntax: +<pre> + functioncall ::= prefixexp args +</pre> +In a function call, +first <em>prefixexp</em> and <em>args</em> are evaluated. +If the value of <em>prefixexp</em> has type <em>function</em>, +then that function is called +with the given arguments. +Otherwise, its "call" metamethod is called, +having as first parameter the value of <em>prefixexp</em>, +followed by the original call arguments +(see <a href="#metatable">2.8</a>). + +<p>The form +<pre> + functioncall ::= prefixexp `<b>:</b>´ Name args +</pre> +can be used to call "methods". +A call <code>v:name(...)</code> +is syntactic sugar for <code>v.name(v,...)</code>, +except that <code>v</code> is evaluated only once. + +<p>Arguments have the following syntax: +<pre> + args ::= `<b>(</b>´ [explist1] `<b>)</b>´ + args ::= tableconstructor + args ::= Literal +</pre> +All argument expressions are evaluated before the call. +A call of the form <code>f{...}</code> is syntactic sugar for +<code>f({...})</code>, that is, +the argument list is a single new table. +A call of the form <code>f'...'</code> +(or <code>f"..."</code> or <code>f[[...]]</code>) is syntactic sugar for +<code>f('...')</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. +That restriction avoids some ambiguities in the language. +If you write +<PRE> + a = f + (g).x(a) +</PRE> +Lua would read that as <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 returns exactly +the returns of the called function. +So, all the following examples are not 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> + +<p><a name="func-def"></a><a name="2.5.9"></a><h3>2.5.9 - Function Definitions</h3> + +<p>The syntax for function definition is +<pre> + function ::= <b>function</b> funcbody + funcbody ::= `<b>(</b>´ [parlist1] `<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> +The statement +<PRE> + function f () ... end +</PRE> +translates to +<PRE> + f = function () ... end +</PRE> +The statement +<PRE> + function t.a.b.c.f () ... end +</PRE> +translates to +<PRE> + t.a.b.c.f = function () ... end +</PRE> +The statement +<PRE> + local function f () ... end +</PRE> +translates to +<PRE> + local f; f = function () ... end +</PRE> + +<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 +may refer to different external local variables +and may have different environment tables. + +<p>Parameters act as local variables that are +initialized with the argument values: +<pre> + parlist1 ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ +</pre> +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 the call 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> +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="#control">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 (...) ... end +</PRE> +is syntactic sugar for +<PRE> + t.a.b.c.f = function (self, ...) ... end +</PRE> + +<p><a name="visibility"></a><a name="2.6"></a><h2>2.6 - Visibility Rules</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. +For instance: +<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> +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. +For instance: +<PRE> + local counter = 0 + function inc (x) + counter = counter + x + return counter + end +</PRE> +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> +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>. + +<p><a name="error"></a><a name="2.7"></a><h2>2.7 - Error Handling</h2> + +<p>Because Lua is an extension language, +all Lua actions start from C code in the host program +calling a function from the Lua library (see <a href="#lua_pcall"></a>). +Whenever an error occurs during Lua compilation or execution, +control returns to C, +which can take appropriate measures +(such as print 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. + +<p><a name="metatable"></a><a name="2.8"></a><h2>2.8 - Metatables</h2> + +<p>Every value in Lua may 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 that 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 using the debug library); +you must use the C API for that. + +<p>Tables and userdata have individual metatables +(although multiple tables and userdata can share +a same table as their metatable); +values of all other types share one single metatable per type. +So, there is one single metatable for all numbers, +and for all strings, etc. + +<p>A metatable may control how an object behaves in arithmetic operations, +order comparisons, concatenation, and indexing. +A metatable can also define a function to be called when a userdata +is garbage collected. +For each of those operations Lua associates a specific key +called an <em>event</em>. +When Lua performs one of those operations over a value, +it checks whether that value has a metatable with the corresponding event. +If so, the value associated with that key (the <em>metamethod</em>) +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; +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 that 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="#predefined">5.1</a>. +In particular, to retrieve the metamethod of a given object, +we use the expression +<PRE> + metatable(obj)[event] +</PRE> +This should be read as +<PRE> + rawget(metatable(obj) or {}, event) +</PRE> +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>). + +<p><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> +Using that 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><b>"sub":</b> +the <code>-</code> operation. +Behavior similar to the "add" operation. + +<p><li><b>"mul":</b> +the <code>*</code> operation. +Behavior similar to the "add" operation. + +<p><li><b>"div":</b> +the <code>/</code> operation. +Behavior similar to the "add" operation. + +<p><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. + +<p><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. + +<p><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><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><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> +See <a href="#len-op">2.5.5</a> for a description of the length of a table. + +<p><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> +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> +<code>a ~= b</code> is equivalent to <code>not (a == b)</code>. + +<p><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> +<code>a > b</code> is equivalent to <code>b < a</code>. + +<p><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> +<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>. + +<p><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><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 + return h(table, key,value) -- call the handler + else h[key] = value -- or repeat operation on it + end + end +</PRE> + +<p><li><b>"call":</b> +called when Lua calls a value. +<PRE> + function function_event (func, ...) + if type(func) == "function" then + return func(unpack(arg)) -- primitive call + else + local h = metatable(func).__call + if h then + return h(func, unpack(arg)) + else + error("...") + end + end + end +</PRE> + +<p></ul> + +<p><a name="environ"></a><a name="2.9"></a><h2>2.9 - Environments</h2> + +<p>Besides metatables, +objects of types thread, function, and userdata +have another table associated with them, +called <em>environment</em>. +Like metatables, environments are regular tables and +multiple objects can share the same environment. + +<p>Environments associated with userdata has no meaning for Lua. +It is only a 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 functions created by that thread +(through <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>) +and can be directly accessed by C code (see <a href="#pseudo-index">3.3</a>). + +<p>Environments associated with C functions can be directly +accessed by C code (see <a href="#pseudo-index">3.3</a>). +They are used as the default environment for other C functions +created by that function. + +<p>Environments associated with Lua functions are used to resolve +all accesses to global variables within that function (see <a href="#variables">2.3</a>). +They are used as the default environment for other Lua functions +created by that function. + +<p>You can change the environment of a Lua function of the +running thread calling <a href="#pdf-setfenv"><code>setfenv</code></a>. +You can get the environment of a Lua function or the running thread +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. + +<p><a name="GC"></a><a name="2.10"></a><h2>2.10 - Garbage Collection</h2> + +<p>Lua does automatic memory management. +That means that +you do not have to worry about allocating memory for new objects +and 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, those objects that are no longer accessible from Lua). +All objects in Lua are subject to automatic management: +tables, userdata, functions, threads, and strings. + +<p>Lua 5.1 implements an incremental mark-and-sweep collector. +It uses two numbers to control its garbage-collection cycles. +One number, the <em>garbage-collector pause</em>, +controls how long the collector waits before starting a new cycle. +Larger values make the collector less aggressive. +Values smaller than 1 mean the collector will not wait to +start a new cycle. +A value of 2 means that the collector waits more or less to double +the total memory in use before starting a new cycle. + +<p>The other number, the <em>garbage-collector multiplier</em>, +controls the relative speed of the collector relative to +memory allocation. +Larger values make the collector more aggressive but also increases +the size of each incremental step. +Values smaller than 1 make the collector too slow and +may result in the collector never finishing a cycle. +The default, 2, means that the collector runs at "twice" +the speed of memory allocation. + +<p>You can change those numbers calling <a href="#lua_gc"><code>lua_gc</code></a> in C +or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. +Both get as arguments percentage points +(so an argument 100 means a real value of 1). +With those functions you can also get direct control +of the collector (e.g., stop and restart it). + +<p><a name="2.10.1"></a><h3>2.10.1 - Garbage-Collection Metamethods</h3> + +<p>Using the C API, +you can set garbage-collector metamethods for userdata (see <a href="#metatable">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>Free 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. + +<p><a name="weak-table"></a><a name="2.10.2"></a><h3>2.10.2 - Weak Tables</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 that 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 value of 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 field <code>__mode</code>. +Otherwise, the weak behavior of the tables controlled by this +metatable is undefined. + +<p><a name="coroutine"></a><a name="2.11"></a><h2>2.11 - Coroutines</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 <code>coroutine.create</code>. +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 <code>coroutine.resume</code>, +passing as its first argument +the 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 given as +parameters for 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 <code>coroutine.yield</code>. +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>The <code>coroutine.wrap</code> function creates a coroutine +like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, +but instead of returning the coroutine itself, +it returns a function that, when called, resumes the coroutine. +Any arguments passed to that function +go as extra arguments to resume. +The function returns all the values returned by resume, +except the first one (the boolean error code). +Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, +this function does not catch errors; +any error is propagated to the caller. + +<p>As an example, +consider the next code: +<PRE> +function foo1 (a) + print("foo", a) + return coroutine.yield(2*a) +end + +co = coroutine.create(function (a,b) + print("co-body", a, b) + local r = foo1(a+1) + print("co-body", r) + local r, s = coroutine.yield(a+b, a-b) + print("co-body", r, s) + return b, "end" +end) + +a, b = coroutine.resume(co, 1, 10) +print("main", a, b) +a, b, c = coroutine.resume(co, "r") +print("main", a, b, c) +a, b, c = coroutine.resume(co, "x", "y") +print("main", a, b, c) +a, b = coroutine.resume(co, "x", "y") +print("main", a, b) +</PRE> +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> + +<p> +<a name="API"></a><a name="3"></a><h1>3 - The Application Program Interface</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 <code>lua.h</code>. + +<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 its arguments exactly once +(except for the first argument, which is always a Lua state), +and so do not generate hidden side-effects. + +<p>Like in most C libraries, +the Lua API functions do not check their arguments. +However, you can change this behavior by compiling Lua +with a proper definition for the macro <code>luai_apicheck</code>, +in file <code>luaconf.h</code>. + +<p><a name="3.1"></a><h2>3.1 - The Stack</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. +That 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> from 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 <em>-1</em> 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>). + + +<p><a name="3.2"></a><h2>3.2 - Stack Size</h2> + +<p>When you interact with Lua API, +<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 <code>LUA_MINSTACK</code> 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> +Note that 0 is never an acceptable index. + +<p><a name="pseudo-index"></a><a name="3.3"></a><h2>3.3 - Pseudo-Indices</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 the C code +but 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="#c-closure">3.4</a>). + +<p>The thread environment (where global variables live) is +always at pseudo-index <code>LUA_GLOBALSINDEX</code>. +The environment of the running C function is always +at pseudo-index <code>LUA_ENVIRONINDEX</code>. + +<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> + +<p><a name="c-closure"></a><a name="3.4"></a><h2>3.4 - C Closures</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 then 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 associated values are located at specific pseudo-indices. +Those pseudo-indices are produced by the macro +<code>lua_upvalueindex</code>. +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, +produces an acceptable (but invalid) index. + +<p><a name="registry"></a><a name="3.5"></a><h2>3.5 - Registry</h2> + +<p>Lua provides a registry, +a pre-defined table that can be used by any C code to +store whatever Lua value it needs to store. +This table is always located at pseudo-index +<code>LUA_REGISTRYINDEX</code>. +Any C library can store data into this table, +as long as it chooses keys different from other libraries. +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 by other purposes. + +<p><a name="3.6"></a><h2>3.6 - Error Handling in C</h2> + +<p>Internally, Lua uses the C <code>longjmp</code> facility to handle errors. +When Lua faces any error +(such as memory allocation errors, type errors, syntax 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>Almost any function in the API may raise an error, +for instance due to a memory allocation error. +The following functions run in protected mode +(that is, they create a protected environment to run), +so they never raise an error: +<a href="#lua_newstate"><code>lua_newstate</code></a>, <a href="#lua_close"><code>lua_close</code></a>, <a href="#lua_load"><code>lua_load</code></a>, +<a href="#lua_pcall"><code>lua_pcall</code></a>, and <a href="#lua_cpcall"><code>lua_cpcall</code></a>. + +<p>Inside a C function you can raise an error calling <a href="#lua_error"><code>lua_error</code></a>. + +<p><a name="3.7"></a><h2>3.7 - Functions and Types</h2> + +<p>Here we list all functions and types from the C API in +alphabetical order. + +<p><a name="lua_Alloc"></a> +<hr><h3><code>lua_Alloc</code></h3> +<pre> + typedef void * (*lua_Alloc) (void *ud, + void *ptr, + size_t osize, + size_t nsize); + +</pre> + + +<p>The allocator 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>, +the 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 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 behaves 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>A simple implementation for the allocator function could be like this: +<PRE> +static void *l_alloc (void *ud, void *ptr, size_t osize, size_t nsize) { + (void)ud; /* not used */ + (void)osize; /* not used */ + if (nsize == 0) { + free(ptr); /* ANSI ensures that free(NULL) has no effect */ + return NULL; + } + else + /* ANSI ensures that realloc(NULL, size) == malloc(size) */ + return realloc(ptr, nsize); +} +</PRE> + +<p><a name="lua_atpanic"></a> +<hr><h3><code>lua_atpanic</code></h3> +<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>. +Your new panic function may avoid the application 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. + +<p><a name="lua_call"></a> +<hr><h3><code>lua_call</code></h3> +<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, +and the function results are pushed. +The number of results are adjusted to <code>nresults</code>, +unless <code>nresults</code> is <code>LUA_MULTRET</code>. +In that 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. + +<p>Any error inside the called function is propagated upwards +(with a <code>longjmp</code>). + +<p>The following example shows how the host program may do the +equivalent to this Lua code: +<PRE> + a = f("how", t.x, 14) +</PRE> +Here it is in C: +<PRE> + lua_getfield(L, LUA_GLOBALSINDEX, "t"); /* global `t' (for later use) */ + lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */ + lua_pushstring(L, "how"); /* 1st argument */ + lua_getfield(L, -3, "x"); /* push result of t.x (2nd arg) */ + lua_pushinteger(L, 14); /* 3rd argument */ + lua_call(L, 3, 1); /* call function with 3 arguments and 1 result */ + lua_setfield(L, LUA_GLOBALSINDEX, "a"); /* set global variable `a' */ + lua_pop(L, 1); /* remove `t' from the stack */ +</PRE> +Note that the code above is "balanced": +at its end, the stack is back to its original configuration. +This is considered good programming practice. + +<p><a name="lua_CFunction"></a> +<hr><h3><code>lua_CFunction</code></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 follow the following protocol, +which defines the way parameters and results are passed: +A C function receives its arguments from Lua in its stack +in direct order (the first argument is pushed first). +So, when the function starts, +its first argument (if any) is at index 1. +To return values to Lua, a C function just pushes them onto the stack, +in direct order (the first result is pushed first), +and returns the number of results. +Any other value in the stack below the results will be properly +discharged by Lua. +Like a Lua function, a C function called by Lua can also return +many results. + +<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 to function `average'"); + 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> + +<p><a name="lua_checkstack"></a> +<hr><h3><code>lua_checkstack</code></h3> +<pre> + int lua_checkstack (lua_State *L, int extra); +</pre> + + +<p>Grows the stack size to <code>top + extra</code> elements; +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. + +<p><a name="lua_close"></a> +<hr><h3><code>lua_close</code></h3> +<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 that 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. + +<p><a name="lua_concat"></a> +<hr><h3><code>lua_concat</code></h3> +<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 that single string +(that is, the function does nothing); +if <code>n</code> is 0, the result is the empty string. +Concatenation is done following the usual semantics of Lua +(see <a href="#concat">2.5.4</a>). + +<p><a name="lua_cpcall"></a> +<hr><h3><code>lua_cpcall</code></h3> +<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. +Any value returned by <code>func</code> is discarded. + +<p><a name="lua_createtable"></a> +<hr><h3><code>lua_createtable</code></h3> +<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 plus <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>. + +<p><a name="lua_dump"></a> +<hr><h3><code>lua_dump</code></h3> +<pre> + int lua_dump (lua_State *L, lua_Writer writer, void *data); +</pre> + + +<p>Dumps a function as a binary chunk. +This function 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>) +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 function from the stack. + +<p><a name="lua_equal"></a> +<hr><h3><code>lua_equal</code></h3> +<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 are non valid. + +<p><a name="lua_error"></a> +<hr><h3><code>lua_error</code></h3> +<pre> + int lua_error (lua_State *L); +</pre> + + +<p>Generates a Lua error. +The error message (which actually can be any type of object) +must be on the stack top. +This function does a long jump, +and therefore never returns. + +<p><a name="lua_gc"></a> +<hr><h3><code>lua_gc</code></h3> +<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> <code>LUA_GCSTOP</code>— stops the garbage collector. +<li> <code>LUA_GCRESTART</code>— restarts the garbage collector. +<li> <code>LUA_GCCOLLECT</code>— performs a full garbage-collection cycle. +<li> <code>LUA_GCCOUNT</code>— returns the current +amount of memory (in Kbytes) in use by Lua. +<li> <code>LUA_GCSTEP</code>— 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 tune experimentally the value of <code>data</code>. +The function returns 1 if that step finished a +garbage-collection cycle. +<li> <code>LUA_GCSETPAUSE</code>— +sets <em><code>data</code>/100</em> as the new value +for the <em>pause</em> of the collector (see <a href="#GC">2.10</a>). +<li> <code>LUA_GCSETSTEPMUL</code>— +sets <em><code>arg</code>/100</em> as the new value for the <em>step multiplier</em> of +the collector (see <a href="#GC">2.10</a>). +</ul> + +<p><a name="lua_getallocf"></a> +<hr><h3><code>lua_getallocf</code></h3> +<pre> + lua_Alloc lua_getallocf (lua_State *L, void **ud); +</pre> + + +<p>Returns the allocator 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>. + +<p><a name="lua_getfenv"></a> +<hr><h3><code>lua_getfenv</code></h3> +<pre> + void lua_getfenv (lua_State *L, int index); +</pre> + + +<p>Pushes on the stack the environment table of +the value at the given index. + +<p><a name="lua_getfield"></a> +<hr><h3><code>lua_getfield</code></h3> +<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 <code>index</code>. +As in Lua, this function may trigger a metamethod +for the "index" event (see <a href="#metatable">2.8</a>). + +<p><a name="lua_getmetatable"></a> +<hr><h3><code>lua_getmetatable</code></h3> +<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, +returns 0 and pushes nothing on the stack. + +<p><a name="lua_gettable"></a> +<hr><h3><code>lua_gettable</code></h3> +<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 <code>index</code> +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="#metatable">2.8</a>). + +<p><a name="lua_gettop"></a> +<hr><h3><code>lua_gettop</code></h3> +<pre> + int lua_gettop (lua_State *L); +</pre> + + +<p>Returns the index of the top element in the stack. +Because indices start at 1, +that result is equal to the number of elements in the stack +(and so 0 means an empty stack). + +<p><a name="lua_insert"></a> +<hr><h3><code>lua_insert</code></h3> +<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 that position to open space. +Cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + +<p><a name="lua_Integer"></a> +<hr><h3><code>lua_Integer</code></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 type the machine handles +"comfortably". + +<p><a name="lua_isboolean"></a> +<hr><h3><code>lua_isboolean</code></h3> +<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. + +<p><a name="lua_iscfunction"></a> +<hr><h3><code>lua_iscfunction</code></h3> +<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. + +<p><a name="lua_isfunction"></a> +<hr><h3><code>lua_isfunction</code></h3> +<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. + +<p><a name="lua_islightuserdata"></a> +<hr><h3><code>lua_islightuserdata</code></h3> +<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. + +<p><a name="lua_isnil"></a> +<hr><h3><code>lua_isnil</code></h3> +<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. + +<p><a name="lua_isnumber"></a> +<hr><h3><code>lua_isnumber</code></h3> +<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. + +<p><a name="lua_isstring"></a> +<hr><h3><code>lua_isstring</code></h3> +<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. + +<p><a name="lua_istable"></a> +<hr><h3><code>lua_istable</code></h3> +<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. + +<p><a name="lua_isthread"></a> +<hr><h3><code>lua_isthread</code></h3> +<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. + +<p><a name="lua_isuserdata"></a> +<hr><h3><code>lua_isuserdata</code></h3> +<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. + +<p><a name="lua_lessthan"></a> +<hr><h3><code>lua_lessthan</code></h3> +<pre> + int lua_lessthan (lua_State *L, int index1, int index2); +</pre> + + +<p>Returns 1 if the value in acceptable index <code>index1</code> is smaller +than the value in 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 are non valid. + +<p><a name="lua_load"></a> +<hr><h3><code>lua_load</code></h3> +<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> 0 — no errors; +<li> <code>LUA_ERRSYNTAX</code> — +syntax error during pre-compilation. +<li> <code>LUA_ERRMEM</code> — +memory allocation error. +</ul> + +<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><a href="#lua_load"><code>lua_load</code></a> 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 the chunk name. +It is used for error messages and debug information (see <a href="#debugI">3.8</a>). + +<p><a name="lua_newstate"></a> +<hr><h3><code>lua_newstate</code></h3> +<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 +(not enough memory). +The argument <code>f</code> is the allocator function; +Lua does all memory allocation for that state through that function. +The second argument, <code>ud</code>, is an opaque pointer that Lua +simply passes to the allocator in every call. + +<p><a name="lua_newtable"></a> +<hr><h3><code>lua_newtable</code></h3> +<pre> + void lua_newtable (lua_State *L); +</pre> + + +<p>Creates a new empty table and pushes it onto the stack. +Equivalent to <code>lua_createtable(L, 0, 0)</code>. + +<p><a name="lua_newthread"></a> +<hr><h3><code>lua_newthread</code></h3> +<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 run-time stack. + +<p>There is no explicit function to close or to destroy a thread. +Threads are subject to garbage collection, +like any Lua object. + +<p><a name="lua_newuserdata"></a> +<hr><h3><code>lua_newuserdata</code></h3> +<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 on the stack a new full userdata with the block address, +and returns this address. + +<p>Userdata represents 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, +it calls the userdata's <code>gc</code> metamethod, if any, +and then it frees the userdata's corresponding memory. + +<p><a name="lua_next"></a> +<hr><h3><code>lua_next</code></h3> +<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 +(the "next" pair after the given key). +If there are no more elements, +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) { + /* `key' is at index -2 and `value' at index -1 */ + printf("%s - %s\n", + lua_typename(L, lua_type(L, -2)), lua_typename(L, lua_type(L, -1))); + lua_pop(L, 1); /* removes `value'; keeps `key' for next iteration */ + } +</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>. + +<p><a name="lua_Number"></a> +<hr><h3><code>lua_Number</code></h3> +<pre> + typedef double lua_Number; +</pre> + + +<p>The type of numbers in Lua. + +<p>Through the configuration file you can change +Lua to operate with other type for numbers (e.g., float or long). + +<p><a name="lua_objlen"></a> +<hr><h3><code>lua_objlen</code></h3> +<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 userdatum. +For other values, returns 0. + +<p><a name="lua_pcall"></a> +<hr><h3><code>lua_pcall</code></h3> +<pre> + 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 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, that index cannot be a pseudo-index.) +In case of runtime errors, +that function will be called with the error message +and its return value will be the message returned by <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> <code>LUA_ERRRUN</code> — a runtime error. +<li> <code>LUA_ERRMEM</code> — memory allocation error. +For such errors, Lua does not call the error handler function. +<li> <code>LUA_ERRERR</code> — +error while running the error handler function. +</ul> + +<p><a name="lua_pop"></a> +<hr><h3><code>lua_pop</code></h3> +<pre> + void lua_pop (lua_State *L, int n); +</pre> + + +<p>Pops <code>n</code> elements from the stack. + +<p><a name="lua_pushboolean"></a> +<hr><h3><code>lua_pushboolean</code></h3> +<pre> + void lua_pushboolean (lua_State *L, int b); +</pre> + + +<p>Pushes a boolean value with value <code>b</code> onto the stack. + +<p><a name="lua_pushcclosure"></a> +<hr><h3><code>lua_pushcclosure</code></h3> +<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 <em>C closure</em> (see <a href="#c-closure">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 the function <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> +is used 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><a name="lua_pushcfunction"></a> +<hr><h3><code>lua_pushcfunction</code></h3> +<pre> + void lua_pushcfunction (lua_State *L, lua_CFunction f); +</pre> + + +<p>Pushes a C function onto the stack. +This function is equivalent to <code>lua_pushcclosure(L, f, 0);</code>. + +<p><a name="lua_pushfstring"></a> +<hr><h3><code>lua_pushfstring</code></h3> +<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 that string. +It is similar to the C function <code>sprintf</code> +but with some important differences: +<ul> +<li> You do not have to allocate the space for the result: +The result is a Lua string and Lua takes care of memory allocation +(and deallocation, through garbage collection). +<li> The conversion specifiers are quite restricted. +There are no flags, widths, or precisions. +The conversion specifiers can be simply +`<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 an hexadecimal numeral), +`<code>%d</code>´ (inserts an <code>int</code>), and +`<code>%c</code>´ (inserts an <code>int</code> as a character). +</ul> + +<p><a name="lua_pushinteger"></a> +<hr><h3><code>lua_pushinteger</code></h3> +<pre> + void lua_pushinteger (lua_State *L, lua_Integer n); +</pre> + + +<p>Pushes a number with value <code>n</code> onto the stack. + +<p><a name="lua_pushlightuserdata"></a> +<hr><h3><code>lua_pushlightuserdata</code></h3> +<pre> + void lua_pushlightuserdata (lua_State *L, void *p); +</pre> + + +<p>Pushes a light userdata onto the stack. + +<p>Userdata represents 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 metatables, +it is not collected (as it was never created). +A light userdata is equal to "any" +light userdata with the same C address. + +<p><a name="lua_pushlstring"></a> +<hr><h3><code>lua_pushlstring</code></h3> +<pre> + void lua_pushlstring (lua_State *L, const char *s, size_t len); +</pre> + + +<p>Pushes the string pointed 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. + +<p><a name="lua_pushnil"></a> +<hr><h3><code>lua_pushnil</code></h3> +<pre> + void lua_pushnil (lua_State *L); +</pre> + + +<p>Pushes a nil value onto the stack. + +<p><a name="lua_pushnumber"></a> +<hr><h3><code>lua_pushnumber</code></h3> +<pre> + void lua_pushnumber (lua_State *L, lua_Number n); +</pre> + + +<p>Pushes a number with value <code>n</code> onto the stack. + +<p><a name="lua_pushstring"></a> +<hr><h3><code>lua_pushstring</code></h3> +<pre> + void lua_pushstring (lua_State *L, const char *s); +</pre> + + +<p>Pushes the zero-terminated string pointed 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. + +<p><a name="lua_pushvalue"></a> +<hr><h3><code>lua_pushvalue</code></h3> +<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. + +<p><a name="lua_pushvfstring"></a> +<hr><h3><code>lua_pushvfstring</code></h3> +<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. + +<p><a name="lua_rawequal"></a> +<hr><h3><code>lua_rawequal</code></h3> +<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. + +<p><a name="lua_rawget"></a> +<hr><h3><code>lua_rawget</code></h3> +<pre> + void lua_rawget (lua_State *L, int index); +</pre> + + +<p>Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but doing a raw indexing +(i.e., without metamethods). + +<p><a name="lua_rawgeti"></a> +<hr><h3><code>lua_rawgeti</code></h3> +<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 <code>index</code>. +The access is raw, +that is, it does not invoke metamethods. + +<p><a name="lua_rawset"></a> +<hr><h3><code>lua_rawset</code></h3> +<pre> + void lua_rawset (lua_State *L, int index); +</pre> + + +<p>Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but doing a raw assignment +(i.e., without metamethods). + +<p><a name="lua_rawseti"></a> +<hr><h3><code>lua_rawseti</code></h3> +<pre> + void lua_rawseti (lua_State *L, int index, int n); +</pre> + + +<p>Does the equivalent to <code>t[n] = v</code>, +where <code>t</code> is the value at the given valid index <code>index</code> +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. + +<p><a name="lua_Reader"></a> +<hr><h3><code>lua_Reader</code></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. +To signal the end of the chunk, the reader returns <code>NULL</code>. +The reader function may return pieces of any size greater than zero. + +<p><a name="lua_remove"></a> +<hr><h3><code>lua_remove</code></h3> +<pre> + void lua_remove (lua_State *L, int index); +</pre> + + +<p>Removes the element at the given valid index, +shifting down the elements above that position to fill the gap. +Cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + +<p><a name="lua_replace"></a> +<hr><h3><code>lua_replace</code></h3> +<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). + +<p><a name="lua_resume"></a> +<hr><h3><code>lua_resume</code></h3> +<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 on its stack the body function plus any eventual 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 0 if there are no errors running the coroutine, +or an error code (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>. + +<p><a name="lua_setfenv"></a> +<hr><h3><code>lua_setfenv</code></h3> +<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 (false). + +<p><a name="lua_setfield"></a> +<hr><h3><code>lua_setfield</code></h3> +<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 <code>index</code> +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="#metatable">2.8</a>). + +<p><a name="lua_setmetatable"></a> +<hr><h3><code>lua_setmetatable</code></h3> +<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. + +<p><a name="lua_settable"></a> +<hr><h3><code>lua_settable</code></h3> +<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>index</code>, +<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="#metatable">2.8</a>). + +<p><a name="lua_settop"></a> +<hr><h3><code>lua_settop</code></h3> +<pre> + void lua_settop (lua_State *L, int index); +</pre> + + +<p>Accepts any acceptable index, or 0, +and sets the stack top to that 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. + +<p><a name="lua_State"></a> +<hr><h3><code>lua_State</code></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. + +<p><a name="lua_toboolean"></a> +<hr><h3><code>lua_toboolean</code></h3> +<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 real boolean values, +use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) + +<p><a name="lua_tocfunction"></a> +<hr><h3><code>lua_tocfunction</code></h3> +<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>. + +<p><a name="lua_tointeger"></a> +<hr><h3><code>lua_tointeger</code></h3> +<pre> + lua_Integer lua_tointeger (lua_State *L, int idx); +</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 number +(see <a href="#coercion">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. + +<p><a name="lua_tolstring"></a> +<hr><h3><code>lua_tolstring</code></h3> +<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 string +(<code>const char*</code>). +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.) + +<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 may 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. + +<p><a name="lua_tonumber"></a> +<hr><h3><code>lua_tonumber</code></h3> +<pre> + lua_Number lua_tonumber (lua_State *L, int index); +</pre> + + +<p>Converts the Lua value at the given acceptable index +to a number (see <a href="#lua_Number"><code>lua_Number</code></a>). +The Lua value must be a number or a string convertible to number +(see <a href="#coercion">2.2.1</a>); +otherwise, <a href="#lua_tonumber"><code>lua_tonumber</code></a> returns 0. + +<p><a name="lua_topointer"></a> +<hr><h3><code>lua_topointer</code></h3> +<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 may be a userdata, a table, a thread, or a function; +otherwise, <a href="#lua_topointer"><code>lua_topointer</code></a> returns <code>NULL</code>. +Lua ensures that different objects return different pointers. +There is no direct way to convert the pointer back to its original value. + +<p>Typically this function is used for debug information. + +<p><a name="lua_tostring"></a> +<hr><h3><code>lua_tostring</code></h3> +<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>. + +<p><a name="lua_tothread"></a> +<hr><h3><code>lua_tothread</code></h3> +<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>. + +<p><a name="lua_touserdata"></a> +<hr><h3><code>lua_touserdata</code></h3> +<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>. + +<p><a name="lua_type"></a> +<hr><h3><code>lua_type</code></h3> +<pre> + int lua_type (lua_State *L, int index); +</pre> + + +<p>Returns the type of a 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>, +<code>LUA_TLIGHTUSERDATA</code>. + +<p><a name="lua_Writer"></a> +<hr><h3><code>lua_Writer</code></h3> +<pre> + typedef int (*lua_Writer) + (lua_State *L, const void* p, size_t sz, void* ud); + +</pre> + + +<p>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. + +<p><a name="lua_xmove"></a> +<hr><h3><code>lua_xmove</code></h3> +<pre> + void lua_xmove (lua_State *from, lua_State *to, int n); +</pre> + + +<p>Exchange values between different threads of the same global state. + +<p>This function pops <code>n</code> values from the stack <code>from</code>, +and pushes them into the stack <code>to</code>. + +<p><a name="lua_yield"></a> +<hr><h3><code>lua_yield</code></h3> +<pre> + int lua_yield (lua_State *L, int nresults); +</pre> + + +<p>Yields a coroutine. + +<p>This function can only be called as the +return expression of a C function, as follows: +<PRE> + return lua_yield (L, nresults); +</PRE> +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>. + +<p> +<a name="debugI"></a><a name="3.8"></a><h2>3.8 - The Debug Interface</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. + +<p><a name="lua_Debug"></a> +<hr><h3><code>lua_Debug</code></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) */ + +<p> /* private part */ + ... + } 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. + +<p><li><b><code>short_src</code></b> +A "printable" version of <code>source</code>, to be used in error messages. + +<p><li><b><code>linedefined</code></b> +the line number where the definition of the function starts. + +<p><li><b><code>lastlinedefined</code></b> +the line number where the definition of the function ends. + +<p><li><b><code>what</code></b> the string <code>"Lua"</code> if this is a Lua function, +<code>"C"</code> if this is a C function, +<code>"main"</code> if this is the main part of a chunk, +and <code>"tail"</code> if this was a function that did a tail call. +In the latter case, +Lua has no other information about this function. + +<p><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 <em>-1</em>. + +<p><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 may be the value of multiple global variables, +while others may 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>. + +<p><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.) + +<p><li><b><code>nups</code></b> +The number of upvalues of the function. + +<p></ul> + +<p><a name="lua_gethook"></a> +<hr><h3><code>lua_gethook</code></h3> +<pre> + lua_Hook lua_gethook (lua_State *L); +</pre> + + +<p>Returns the current hook function. + +<p><a name="lua_gethookcount"></a> +<hr><h3><code>lua_gethookcount</code></h3> +<pre> + int lua_gethookcount (lua_State *L); +</pre> + + +<p>Returns the current hook count. + +<p><a name="lua_gethookmask"></a> +<hr><h3><code>lua_gethookmask</code></h3> +<pre> + int lua_gethookmask (lua_State *L); +</pre> + + +<p>Returns the current hook mask. + +<p><a name="lua_getinfo"></a> +<hr><h3><code>lua_getinfo</code></h3> +<pre> + int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar); +</pre> + + +<p>Fills the fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information. + +<p>This function returns 0 on error +(for instance, an invalid option in <code>what</code>). +Each character in the string <code>what</code> +selects some fields of the structure <code>ar</code> to be filled, +as indicated by the letter in parentheses in the definition of <a href="#lua_Debug"><code>lua_Debug</code></a>: +`<code>S</code>´ fills in the fields <code>source</code>, <code>linedefined</code>, +<code>lastlinedefined</code>, +and <code>what</code>; +`<code>l</code>´ fills in the field <code>currentline</code>, etc. +Moreover, `<code>f</code>´ pushes onto the stack the function that is +running at the given level. + +<p>To get information about a function that is not active +(that is, not in the stack), +you push it onto the stack +and start the <code>what</code> string with the character `<code>></code>´. +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><a name="lua_getlocal"></a> +<hr><h3><code>lua_getlocal</code></h3> +<pre> + const char *lua_getlocal (lua_State *L, const 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>Returns <code>NULL</code> (and pushes nothing) +when the index is greater than +the number of active local variables. + +<p><a name="lua_getstack"></a> +<hr><h3><code>lua_getstack</code></h3> +<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. + +<p><a name="lua_getupvalue"></a> +<hr><h3><code>lua_getupvalue</code></h3> +<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 consequently are 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.) + +<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. + +<p><a name="lua_Hook"></a> +<hr><h3><code>lua_Hook</code></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: +<code>LUA_HOOKCALL</code>, <code>LUA_HOOKRET</code>, +<code>LUA_HOOKTAILRET</code>, <code>LUA_HOOKLINE</code>, +and <code>LUA_HOOKCOUNT</code>. +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> may 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, +that execution occurs without any calls to hooks. + +<p><a name="lua_sethook"></a> +<hr><h3><code>lua_sethook</code></h3> +<pre> + int lua_sethook (lua_State *L, lua_Hook func, int mask, int count); +</pre> + + +<p>Sets the debugging hook function. + +<p><code>func</code> is the hook function. +<code>mask</code> specifies on which events the hook will be called: +It is formed by a disjunction of the constants +<code>LUA_MASKCALL</code>, +<code>LUA_MASKRET</code>, +<code>LUA_MASKLINE</code>, +and <code>LUA_MASKCOUNT</code>. +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. +<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. +<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><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.) +</ul> + +<p>A hook is disabled by setting <code>mask</code> to zero. + +<p><a name="lua_setlocal"></a> +<hr><h3><code>lua_setlocal</code></h3> +<pre> + const char *lua_setlocal (lua_State *L, const 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 like in <a href="#lua_getlocal"><code>lua_getlocal</code></a> +(see <a href="#lua_getlocal"></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. + +<p><a name="lua_setupvalue"></a> +<hr><h3><code>lua_setupvalue</code></h3> +<pre> + const char *lua_setupvalue (lua_State *L, int funcindex, int n); +</pre> + + +<p>Sets the value of a closure's upvalue. +Parameters <code>funcindex</code> and <code>n</code> are like in <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> +(see <a href="#lua_getupvalue"></a>). +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. + +<p>Returns <code>NULL</code> (and pops nothing) +when the index is greater than the number of upvalues. + +<p> +<a name="4"></a><h1>4 - The Auxiliary Library</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 build on +top of the basic API, so they provide nothing that cannot +be done with that 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 those functions raise 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 those functions for other stack values. + +<p><a name="4.1"></a><h2>4.1 - Functions and Types</h2> + +<p>Here we list all functions and types from the auxiliary library +in alphabetical order. + +<p><a name="luaL_addchar"></a> +<hr><h3><code>luaL_addchar</code></h3> +<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>). + +<p><a name="luaL_addlstring"></a> +<hr><h3><code>luaL_addlstring</code></h3> +<pre> + void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l); +</pre> + + +<p>Adds the string pointed 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>). + +<p><a name="luaL_addsize"></a> +<hr><h3><code>luaL_addsize</code></h3> +<pre> + void luaL_addsize (luaL_Buffer B, size_t n); +</pre> + + +<p>Adds a string of length <code>n</code> previously copied to the +buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>) to the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). + +<p><a name="luaL_addstring"></a> +<hr><h3><code>luaL_addstring</code></h3> +<pre> + void luaL_addstring (luaL_Buffer *B, const char *s); +</pre> + + +<p>Adds the zero-terminated string pointed by <code>s</code> +to the buffer <code>B</code> +(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). + +<p><a name="luaL_addvalue"></a> +<hr><h3><code>luaL_addvalue</code></h3> +<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. + +<p><a name="luaL_argcheck"></a> +<hr><h3><code>luaL_argcheck</code></h3> +<pre> + void luaL_argcheck (lua_State *L, int cond, int numarg, + const char *extramsg); +</pre> + + +<p>Checks whether <code>cond</code> is true. +If not, raise an error with message +<code>"bad argument #<numarg> to <func> (<extramsg>)"</code>, +where <code>func</code> is retrieved from the call stack. + +<p><a name="luaL_argerror"></a> +<hr><h3><code>luaL_argerror</code></h3> +<pre> + int luaL_argerror (lua_State *L, int numarg, const char *extramsg); +</pre> + + +<p>Raises an error with message +<code>"bad argument #<numarg> to <func> (<extramsg>)"</code>, +where <code>func</code> is retrieved from the call stack. + +<p>This function never returns. + +<p><a name="luaL_Buffer"></a> +<hr><h3><code>luaL_Buffer</code></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> Fist you declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>. +<li> Then you initialize it with a call <code>luaL_buffinit(L, &b);</code>. +<li> Then you add string pieces to the buffer calling any of +the <code>luaL_add*</code> functions. +<li> You finish calling <code>luaL_pushresult(&b)</code>. +That call leaves the final string on the top of the stack. +</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 +is the top of the stack. +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. + +<p><a name="luaL_buffinit"></a> +<hr><h3><code>luaL_buffinit</code></h3> +<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>). + +<p><a name="luaL_callmeta"></a> +<hr><h3><code>luaL_callmeta</code></h3> +<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 that +metatable has a field <code>e</code>, +calls that field passing the object as argument. +In that case the function returns 1 and pushes on the +stack the value returned by the call. +If there is no metatable or no metamethod returns 0 +(without pushing any value on the stack). + +<p><a name="luaL_checkany"></a> +<hr><h3><code>luaL_checkany</code></h3> +<pre> + void luaL_checkany (lua_State *L, int narg); +</pre> + + +<p>Checks whether the function has an argument <code>narg</code>. + +<p><a name="luaL_checkint"></a> +<hr><h3><code>luaL_checkint</code></h3> +<pre> + int luaL_checkint (lua_State *L, int narg); +</pre> + + +<p>Checks whether the function argument <code>narg</code> is a number +and returns that number casted to an <code>int</code>. + +<p><a name="luaL_checkinteger"></a> +<hr><h3><code>luaL_checkinteger</code></h3> +<pre> + lua_Integer luaL_checkinteger (lua_State *L, int numArg); +</pre> + + +<p>Checks whether the function argument <code>narg</code> is a number +and returns that number casted to a <a href="#lua_Integer"><code>lua_Integer</code></a>. + +<p><a name="luaL_checklong"></a> +<hr><h3><code>luaL_checklong</code></h3> +<pre> + long luaL_checklong (lua_State *L, int narg); +</pre> + + +<p>Checks whether the function argument <code>narg</code> is a number +and returns that number casted to a <code>long</code>. + +<p><a name="luaL_checklstring"></a> +<hr><h3><code>luaL_checklstring</code></h3> +<pre> + const char *luaL_checklstring (lua_State *L, int numArg, size_t *l); +</pre> + + +<p>Checks whether the function argument <code>narg</code> is a string +and returns that string; +if <code>l</code> is not <code>NULL</code> fills the position <code>*l</code> +with the string's length. + +<p><a name="luaL_checknumber"></a> +<hr><h3><code>luaL_checknumber</code></h3> +<pre> + lua_Number luaL_checknumber (lua_State *L, int numArg); +</pre> + + +<p>Checks whether the function argument <code>narg</code> is a number +and returns that number. + +<p><a name="luaL_checkoption"></a> +<hr><h3><code>luaL_checkoption</code></h3> +<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 that string into the array <code>lst</code> +(which must be NULL-terminated). +If <code>def</code> is not <code>NULL</code>, +uses <code>def</code> as a default value when +the function has no argument <code>narg</code> or if that argument is <B>nil</B>. + +<p>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><a name="luaL_checkstack"></a> +<hr><h3><code>luaL_checkstack</code></h3> +<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. + +<p><a name="luaL_checkstring"></a> +<hr><h3><code>luaL_checkstring</code></h3> +<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 that string. + +<p><a name="luaL_checktype"></a> +<hr><h3><code>luaL_checktype</code></h3> +<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>. + +<p><a name="luaL_checkudata"></a> +<hr><h3><code>luaL_checkudata</code></h3> +<pre> + void *luaL_checkudata (lua_State *L, int ud, 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>). + +<p><a name="luaL_error"></a> +<hr><h3><code>luaL_error</code></h3> +<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 argument, +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 that information is available. + +<p>This function never returns. + +<p><a name="luaL_getmetafield"></a> +<hr><h3><code>luaL_getmetafield</code></h3> +<pre> + int luaL_getmetafield (lua_State *L, int obj, const char *e); +</pre> + + +<p>Pushes on 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 that field, +returns 0 (false) and pushes nothing. + +<p><a name="luaL_getmetatable"></a> +<hr><h3><code>luaL_getmetatable</code></h3> +<pre> + void luaL_getmetatable (lua_State *L, const char *tname); +</pre> + + +<p>Pushes on the stack the metatable associated to name <code>tname</code> +in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). + +<p><a name="luaL_gsub"></a> +<hr><h3><code>luaL_gsub</code></h3> +<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> changing any occurrence of <code>p</code> +by the string <code>r</code>. +Pushes the resulting string on the stack and returns it. + +<p><a name="luaL_loadbuffer"></a> +<hr><h3><code>luaL_loadbuffer</code></h3> +<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 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. + +<p><a name="luaL_loadfile"></a> +<hr><h3><code>luaL_loadfile</code></h3> +<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 the file's first line starts with a <code>#</code> it is ignored. + +<p>This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, +but it has an extra error code <code>LUA_ERRFILE</code> +if it cannot open the file. + +<p><a name="luaL_loadstring"></a> +<hr><h3><code>luaL_loadstring</code></h3> +<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><a name="luaL_newmetatable"></a> +<hr><h3><code>luaL_newmetatable</code></h3> +<pre> + int luaL_newmetatable (lua_State *L, const char *tname); +</pre> + + +<p>If the register already has the key <code>"tname"</code>, +returns 0. +Otherwise, +creates a new table to be used as metatables for userdata, +adds it to the register with key <code>"tname"</code>, +and returns 1. + +<p>In both cases pushes on the stack the final value associated +with <code>"tname"</code> in the registry. + +<p><a name="luaL_newstate"></a> +<hr><h3><code>luaL_newstate</code></h3> +<pre> + lua_State *luaL_newstate (void); +</pre> + + +<p>Creates a new Lua state, calling <a href="#lua_newstate"><code>lua_newstate</code></a> with an +allocation function based on the standard C <code>realloc</code> function +and setting 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. + +<p><a name="luaL_optint"></a> +<hr><h3><code>luaL_optint</code></h3> +<pre> + int luaL_optint (lua_State *L, int narg, int d); +</pre> + + +<p>If the function argument <code>narg</code> is a number, +returns that number casted to an <code>int</code>. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p><a name="luaL_optinteger"></a> +<hr><h3><code>luaL_optinteger</code></h3> +<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 that number casted to a <a href="#lua_Integer"><code>lua_Integer</code></a>. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p><a name="luaL_optlong"></a> +<hr><h3><code>luaL_optlong</code></h3> +<pre> + long luaL_optlong (lua_State *L, int narg, long d); +</pre> + + +<p>If the function argument <code>narg</code> is a number, +returns that number casted to a <code>long</code>. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p><a name="luaL_optlstring"></a> +<hr><h3><code>luaL_optlstring</code></h3> +<pre> + const char *luaL_optlstring (lua_State *L, int numArg, + const char *d, size_t *l); +</pre> + + +<p>If the function argument <code>narg</code> is a string, +returns that string. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p>If <code>l</code> is not <code>NULL</code> fills the position <code>*l</code> +with the results's length. + +<p><a name="luaL_optnumber"></a> +<hr><h3><code>luaL_optnumber</code></h3> +<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 that number. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p><a name="luaL_optstring"></a> +<hr><h3><code>luaL_optstring</code></h3> +<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 that string. +If that argument is absent or is <B>nil</B>, +returns <code>d</code>. +Otherwise, raise an error. + +<p><a name="luaL_prepbuffer"></a> +<hr><h3><code>luaL_prepbuffer</code></h3> +<pre> + char *luaL_prepbuffer (luaL_Buffer *B); +</pre> + + +<p>Returns an address to a space of size <code>LUAL_BUFFERSIZE</code> +wherein 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 that 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. + +<p><a name="luaL_pushresult"></a> +<hr><h3><code>luaL_pushresult</code></h3> +<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. + +<p><a name="luaL_ref"></a> +<hr><h3><code>luaL_ref</code></h3> +<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 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> +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>Whenever the object at the top of the stack is <B>nil</B>, +<a href="#luaL_ref"><code>luaL_ref</code></a> returns the same reference <code>LUA_REFNIL</code>. +The constant <code>LUA_NOREF</code> is garanteed to be different +from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. + +<p><a name="luaL_Reg"></a> +<hr><h3><code>luaL_Reg</code></h3> +<pre> + typedef struct luaL_Reg { + const char *name; + lua_CFunction func; + } luaL_Reg; + +</pre> + + +<p>Format 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 +wherein both <code>name</code> and <code>func</code> are <code>NULL</code>. + +<p><a name="luaL_register"></a> +<hr><h3><code>luaL_register</code></h3> +<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>, +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>, +creates a new table <code>t</code>, +sets it as the value of the 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 that table instead of creating a new one. + +<p>In any case the function leaves the table +on the top of the stack. + +<p><a name="luaL_typename"></a> +<hr><h3><code>luaL_typename</code></h3> +<pre> + const char *luaL_typename (lua_State *L, int idx); +</pre> + + +<p>Returns the name of the type of the value at index <code>idx</code>. + +<p><a name="luaL_typerror"></a> +<hr><h3><code>luaL_typerror</code></h3> +<pre> + int luaL_typerror (lua_State *L, int narg, const char *tname); +</pre> + + +<p>Generates an error with a message like +<PRE> +<location>: bad argument <narg> to <function> (<tname> expected, got <realt>) +</PRE> +where <code><location></code> is produced by <a href="#luaL_where"><code>luaL_where</code></a>, +<code><function></code> is the name of the current function, +and <code><realt></code> is the type name of the actual argument. + +<p><a name="luaL_unref"></a> +<hr><h3><code>luaL_unref</code></h3> +<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 <code>LUA_NOREF</code> or <code>LUA_REFNIL</code>, +<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. + +<p><a name="luaL_where"></a> +<hr><h3><code>luaL_where</code></h3> +<pre> + void luaL_where (lua_State *L, int lvl); +</pre> + + +<p>Pushes on 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 format <code><chunkname>:<currentline>:</code>. +Level 0 is the running function, +level 1 is the function that called the running function. + +<p>This function is used to build a prefix for error messages. + +<p> +<a name="libraries"></a><a name="5"></a><h1>5 - Standard Libraries</h1> + +<p>The standard libraries provide useful functions +that are implemented directly through the C API. +Some of these functions provide essential services to the language +(e.g., <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 to +deserve an implementation in C (e.g., <code>sort</code>). + +<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> package library; +<li> string manipulation; +<li> table manipulation; +<li> mathematical functions (sin, log, etc.); +<li> input and output; +<li> operating system facilities; +<li> debug facilities. +</ul> +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 must first call the function +<code>luaL_openlibs</code>; +or else it can open them individually calling +<code>luaopen_base</code> (for the basic library), +<code>luaopen_package</code> (for the package library), +<code>luaopen_string</code> (for the string library), +<code>luaopen_table</code> (for the table library), +<code>luaopen_math</code> (for the mathematical library), +<code>luaopen_io</code> (for the I/O and the Operating System libraries), +and <code>luaopen_debug</code> (for the debug library). +These functions are declared in <code>lualib.h</code>. + +<p><a name="predefined"></a><a name="5.1"></a><h2>5.1 - Basic Functions</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 some alternative +implementation for some of its facilities. + +<p><a name="pdf-assert"></a><hr><h3><code>assert (v [, message])</code></h3> +Issues an error when +the value of its argument <code>v</code> is <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><a name="pdf-collectgarbage"></a><hr><h3><code>collectgarbage (opt [, arg])</code></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><b>"restart"</b> restarts the garbage collector. +<li><b>"collect"</b> performs a full garbage-collection cycle. +<li><b>"count"</b> returns the total memory in use by Lua (in Kbytes). +<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 tune experimentally the value of <code>arg</code>. +<li><b>"steppause"</b> +sets <em><code>arg</code>/100</em> as the new value for the <em>pause</em> of +the collector (see <a href="#GC">2.10</a>). +<li><b>"setstepmul"</b> +sets <em><code>arg</code>/100</em> as the new value for the <em>step multiplier</em> of +the collector (see <a href="#GC">2.10</a>). +</ul> + +<p><a name="pdf-dofile"></a><hr><h3><code>dofile (filename)</code></h3> +Opens the named file and executes its contents as a Lua chunk. +When called without arguments, +<a href="#pdf-dofile"><code>dofile</code></a> executes the contents of the standard input (<code>stdin</code>). +Returns any value returned by the chunk. +In case of errors, <a href="#pdf-dofile"><code>dofile</code></a> propagates the error +to its caller (that is, it does not run in protected mode). + +<p><a name="pdf-error"></a><hr><h3><code>error (message [, level])</code></h3> +Terminates the last protected function called +and returns <code>message</code> as the error message. +Function <a href="#pdf-error"><code>error</code></a> never returns. + +<p>Usually, <a href="#pdf-error"><code>error</code></a> 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 +<a href="#pdf-error"><code>error</code></a> function was called. +Level 2 points the error to where the function +that called <a href="#pdf-error"><code>error</code></a> was called; and so on. +Passing a level 0 avoids the addition of error position information +to the message. + +<p><a name="pdf-_G"></a><hr><h3><code>_G</code></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. +(Use <a href="#pdf-setfenv"><code>setfenv</code></a> to change environments.) + +<p><a name="pdf-getfenv"></a><hr><h3><code>getfenv (f)</code></h3> +Returns the current environment in use by the function. +<code>f</code> can be a Lua function or a number, +which specifies the function at that stack level: +Level 1 is the function calling <a href="#pdf-getfenv"><code>getfenv</code></a>. +If the given function is not a Lua function, +or if <code>f</code> is 0, +<a href="#pdf-getfenv"><code>getfenv</code></a> returns the global environment. +The default for <code>f</code> is 1. + +<p><a name="pdf-getmetatable"></a><hr><h3><code>getmetatable (object)</code></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><a name="pdf-ipairs"></a><hr><h3><code>ipairs (t)</code></h3> + +<p>Returns an iterator function, the table <code>t</code>, and 0, +so that the construction +<PRE> + for i,v in ipairs(t) do ... end +</PRE> +will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ..., +up to the first integer key with a nil value in the table. + +<p><a name="pdf-load"></a><hr><h3><code>load (func [, chunkname])</code></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 <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. + +<p><a name="pdf-loadfile"></a><hr><h3><code>loadfile (filename)</code></h3> + +<p>Similar to <a href="#pdf-load"><code>load</code></a>, +but gets the chunk from file <code>filename</code>. + +<p><a name="pdf-loadstring"></a><hr><h3><code>loadstring (string [, chunkname])</code></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><a name="pdf-next"></a><hr><h3><code>next (table [, index])</code></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. +<a href="#pdf-next"><code>next</code></a> returns the next index of the table and the +value associated with the index. +When called with <B>nil</B> as its second argument, +<a href="#pdf-next"><code>next</code></a> returns the first index +of the table and its associated value. +When called with the last index, +or with <B>nil</B> in an empty table, +<a href="#pdf-next"><code>next</code></a> returns <B>nil</B>. +If the second argument is absent, then it is interpreted as <B>nil</B>. + +<p>Lua has no declaration of fields; +There is no difference between a +field not present in a table or a field with value <B>nil</B>. +Therefore, <a href="#pdf-next"><code>next</code></a> only considers fields with non-<B>nil</B> values. +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 <a href="#pdf-next"><code>next</code></a> is <em>undefined</em> if, +during the traversal, +you assign any value to a non-existent field in the table. + +<p><a name="pdf-pairs"></a><hr><h3><code>pairs (t)</code></h3> + +<p>Returns the <a href="#pdf-next"><code>next</code></a> function and the table <code>t</code> (plus a <B>nil</B>), +so that the construction +<PRE> + for k,v in pairs(t) do ... end +</PRE> +will iterate over all key–value pairs of table <code>t</code>. + +<p><a name="pdf-pcall"></a><hr><h3><code>pcall (f, arg1, arg2, ...)</code></h3> + +<p>Calls function <code>f</code> with +the given arguments in protected mode. +That means that any error inside <code>f</code> is not propagated; +instead, <a href="#pdf-pcall"><code>pcall</code></a> 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, <a href="#pdf-pcall"><code>pcall</code></a> also returns all results from the call, +after this first result. +In case of any error, <a href="#pdf-pcall"><code>pcall</code></a> returns <B>false</B> plus the error message. + +<p><a name="pdf-print"></a><hr><h3><code>print (e1, e2, ...)</code></h3> +Receives any number of arguments, +and prints their values in <code>stdout</code>, +using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert them to strings. +This function is not intended for formatted output, +but only as a quick way to show a value, +typically for debugging. +For formatted output, use <code>format</code> (see <a href="#format">5.4</a>). + +<p><a name="pdf-rawequal"></a><hr><h3><code>rawequal (v1, v2)</code></h3> +Checks whether <code>v1</code> is equal to <code>v2</code>, +without invoking any metamethod. +Returns a boolean. + +<p><a name="pdf-rawget"></a><hr><h3><code>rawget (table, index)</code></h3> +Gets the real value of <code>table[index]</code>, +without invoking any metamethod. +<code>table</code> must be a table; +<code>index</code> is any value different from <B>nil</B>. + +<p><a name="pdf-rawset"></a><hr><h3><code>rawset (table, index, value)</code></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> is any value different from <B>nil</B>, +and <code>value</code> is any Lua value. + +<p><a name="pdf-select"></a><hr><h3><code>select (index, ...)</code></h3> + +<p>If <code>index</code> is a number, +returns all argument 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><a name="setfenv"></a><a name="pdf-setfenv"></a><hr><h3><code>setfenv (f, table)</code></h3> + +<p>Sets the environment to be used by the given function. +<code>f</code> can be a Lua function or a number, +which specifies the function at that stack level: +Level 1 is the function calling <a href="#pdf-setfenv"><code>setfenv</code></a>. +<a href="#pdf-setfenv"><code>setfenv</code></a> returns the given function. + +<p>As a special case, when <code>f</code> is 0 <a href="#pdf-setfenv"><code>setfenv</code></a> changes +the environment of the running thread. +In this case, <a href="#pdf-setfenv"><code>setfenv</code></a> returns no values. + +<p><a name="pdf-setmetatable"></a><hr><h3><code>setmetatable (table, metatable)</code></h3> + +<p>Sets the metatable for the given table. +(You cannot change the metatable of other types from Lua.) +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><a name="pdf-tonumber"></a><hr><h3><code>tonumber (e [, base])</code></h3> +Tries to convert its argument to a number. +If the argument is already a number or a string convertible +to a number, then <a href="#pdf-tonumber"><code>tonumber</code></a> returns that 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 may have a decimal part, +as well as an optional exponent part (see <a href="#coercion">2.2.1</a>). +In other bases, only unsigned integers are accepted. + +<p><a name="pdf-tostring"></a><hr><h3><code>tostring (e)</code></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> (see <a href="#format">5.4</a>). + +<p>If the metatable of <code>e</code> has a <code>"__tostring"</code> field, +<a href="#pdf-tostring"><code>tostring</code></a> calls the corresponding value +with <code>e</code> as argument, +and uses the result of the call as its result. + +<p><a name="pdf-type"></a><hr><h3><code>type (v)</code></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><a name="pdf-unpack"></a><hr><h3><code>unpack (list [, i [, j]])</code></h3> +Returns the elements from the given list. +This function is equivalent to +<PRE> + return list[i], list[i+1], ..., list[j] +</PRE> +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. + +<p><a name="pdf-_VERSION"></a><hr><h3><code>_VERSION</code></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><a name="pdf-xpcall"></a><hr><h3><code>xpcall (f, err)</code></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><a href="#pdf-xpcall"><code>xpcall</code></a> 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, <a href="#pdf-xpcall"><code>xpcall</code></a> 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 such case, <a href="#pdf-xpcall"><code>xpcall</code></a> also returns all results from the call, +after this first result. +In case of any error, +<a href="#pdf-xpcall"><code>xpcall</code></a> returns false plus the result from <code>err</code>. + +<p><a name="5.2"></a><h2>5.2 - Coroutine Manipulation</h2> + +<p>The operations related to coroutines comprise a sub-library of +the basic library and come inside the table <code>coroutine</code>. +See <a href="#coroutine">2.11</a> for a general description of coroutines. + +<p><a name="pdf-coroutine.create"></a><hr><h3><code>coroutine.create (f)</code></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><a name="pdf-coroutine.resume"></a><hr><h3><code>coroutine.resume (co, val1, ...)</code></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 arguments <code>val1</code>, ... go as the arguments to the body function. +If the coroutine has yielded, +<code>resume</code> restarts it; +the arguments <code>val1</code>, ... go 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><a name="pdf-coroutine.running"></a><hr><h3><code>coroutine.running ()</code></h3> + +<p>Returns the running coroutine, +or <B>nil</B> when called by the main thread. + +<p><a name="pdf-coroutine.status"></a><hr><h3><code>coroutine.status (co)</code></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><a name="pdf-coroutine.wrap"></a><hr><h3><code>coroutine.wrap (f)</code></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><a name="pdf-coroutine.yield"></a><hr><h3><code>coroutine.yield (val1, ...)</code></h3> + +<p>Suspends the execution of the calling coroutine. +The coroutine cannot be running neither a C function, +nor a metamethod, nor an iterator. +Any arguments to <code>yield</code> go as extra results to <code>resume</code>. + +<p><a name="5.3"></a><h2>5.3 - Packages and Modules</h2> + +<p>The package library provides basic +facilities for packages and 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 <code>package</code>. + +<p><a name="pdf-module"></a><hr><h3><code>module (name [, ...])</code></h3> + +<p>Creates a module. +If there is a table in <code>package.loaded[name]</code>, +that table is the module. +Otherwise, if there is a global table <code>t</code> with the given name, +that 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 exists) +tables for each component. +For instance, if <code>name</code> is <code>a.b.c</code>, +<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 may receive optional <em>options</em> after +the module name, +where each option is a function to be applied over the module. + +<p><a name="pdf-require"></a><hr><h3><code>require (modname)</code></h3> + +<p>Loads the given module. +The function starts by looking into the table <code>package.loaded</code> +to determine whether <code>modname</code> is already loaded. +If it is, then <a href="#pdf-require"><code>require</code></a> returns the value stored +at <code>package.loaded[modname]</code>. +Otherwise, it tries to find a loader for that module. + +<p>To find a loader, +first <a href="#pdf-require"><code>require</code></a> queries <code>package.preload[modname]</code>. +If it is a true value, +that value (which should be a function) is the loader. +Otherwise <a href="#pdf-require"><code>require</code></a> searches for a Lua loader using the +path stored in <code>package.path</code>. +if that also fails, it searches for a C loader using the +path stored in <code>package.cpath</code>. +If that also fails, +it tries an <em>all-in-one</em> loader. + +<p>When loading a C library, +<a href="#pdf-require"><code>require</code></a> first uses a dynamic link facility to link the +application with the library. +Then it tries to find a C function inside that library to +be used as the loader. +The name of that C function is the string <code>"luaopen_"</code> +concatenated with a copy of the module name wherein each dot +is replaced by an underscore. +Moreover, if the module name has a colon, +its prefix up to (and including) the first colon 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>If <a href="#pdf-require"><code>require</code></a> finds neither a Lua library nor a +C library for a module, +it calls the <em>all-in-one loader</em>. +That loader 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 that facility, a package can pack several C submodules +into one single library, +with each submodule keeping its original open function. + +<p>Once a loader is found, +<a href="#pdf-require"><code>require</code></a> calls the loader with a sinle argument, <code>modname</code>. +If the loader returns any value, +<a href="#pdf-require"><code>require</code></a> assigns it to <code>package.loaded[modname]</code>. +If the loader returns no value and +has not assigned any value to <code>package.loaded[modname]</code>, +<a href="#pdf-require"><code>require</code></a> assigns <b>true</b> to that entry. +In any case, require 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 that module, +then <a href="#pdf-require"><code>require</code></a> signals an error. + +<p><a name="pdf-package.cpath"></a><hr><h3><code>package.cpath</code></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 <code>package.cpath</code> in the same way +it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, +using the environment variable <code>LUA_CPATH</code> +(plus another compiled-defined default path). + +<p><a name="pdf-package.loaded"></a><hr><h3><code>package.loaded</code></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><a name="pdf-package.loadlib"></a><hr><h3><code>package.loadlib (libname, funcname)</code></h3> + +<p>Links the program with the dynamic C library <code>libname</code>. +Inside this library, looks for a function <code>funcname</code> +and returns this function as a C function. + +<p><code>libname</code> must be the complete file name of the C library, +including any eventual path and extension. + +<p>This function is not supported by ANSI C. +As such, it is only available on some platforms +(Windows, Linux, Solaris, BSD, plus other Unix systems that +support the <code>dlfcn</code> standard). + +<p><a name="pdf-package.path"></a><hr><h3><code>package.path</code></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 <code>LUA_PATH</code> or +with a compiled-defined default path, +if the environment variable is not defined. +Any <code>";;"</code> in the value of the environment variable +is replaced by the default path. + +<p>A path is a sequence of <em>templates</em> separated by semicolons. +For each template, <a href="#pdf-require"><code>require</code></a> will change each interrogation +mark in the template by <code>filename</code>, +which is <code>modname</code> with each dot replaced by a +"directory separator" (such as <code>"/"</code> in Unix); +then it will try to load the resulting file name. +So, for instance, if the Lua path is +<PRE> + "./?.lua;./?.lc;/usr/local/?/init.lua" +</PRE> +the search for a Lua loader for module <code>mod</code> +will try to load the files +<code>./mod.lua</code>, <code>./mod.lc</code>, and +<code>/usr/local/mod/init.lua</code>, in that order. + +<p><a name="pdf-package.preload"></a><hr><h3><code>package.preload</code></h3> + +<p>A table to store loaders for specific modules +(see <a href="#pdf-require"><code>require</code></a>). + +<p><a name="pdf-package.seeall"></a><hr><h3><code>package.seeall (module)</code></h3> + +<p>Sets a metatable for <code>module</code> with +its <code>__index</code> field refering to the global environment, +so that this module inherits undefined values +from the global environment. +To be used as an option to function <a href="#pdf-module"><code>module</code></a>. + +<p><a name="5.4"></a><h2>5.4 - String Manipulation</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 <em>-1</em>, and so on. + +<p>The string library provides all its functions inside the table +<code>string</code>. +It also sets a metatable for strings +wherein <code>__index</code> points to itself. +Therefore, you can use the string function is object-oriented style. +For instance, <code>string.byte(s, i)</code> +can be written as <code>s:byte(i)</code>. + +<p><a name="pdf-string.byte"></a><hr><h3><code>string.byte (s [, i [, j]])</code></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><a name="pdf-string.char"></a><hr><h3><code>string.char (i1, i2, ...)</code></h3> +Receives 0 or more integers. +Returns a string with length equal to the number of arguments, +in which each character has the internal numerical code equal +to its correspondent argument. + +<p>Note that numerical codes are not necessarily portable across platforms. + +<p><a name="pdf-string.dump"></a><hr><h3><code>string.dump (function)</code></h3> + +<p>Returns a binary representation of the given function, +so that a later <a href="#pdf-loadstring"><code>loadstring</code></a> on that string returns +a copy of the function. +<code>function</code> must be a Lua function. + +<p><a name="pdf-string.find"></a><hr><h3><code>string.find (s, pattern [, init [, plain]])</code></h3> +Looks for the first <em>match</em> of +<code>pattern</code> in the string <code>s</code>. +If it finds one, 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 may 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 too. + +<p><a name="format"></a><a name="pdf-string.format"></a><hr><h3><code>string.format (formatstring, e1, e2, ...)</code></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 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, 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> +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. + +<p><a name="pdf-string.gmatch"></a><hr><h3><code>string.gmatch (s, pat)</code></h3> +Returns an iterator function that, +each time it is called, +returns the next captures from pattern <code>pat</code> over string <code>s</code>. + +<p>If <code>pat</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> +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><a name="pdf-string.gsub"></a><hr><h3><code>string.gsub (s, pat, repl [, n])</code></h3> +Returns a copy of <code>s</code> +in which all occurrences of the pattern <code>pat</code> have been +replaced by a replacement string specified by <code>repl</code>. +<code>gsub</code> also returns, as a second value, +the total number of substitutions made. + +<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>%</code><em>n</em>, +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 function, then this function is called every time a +match occurs, with all captured substrings passed as arguments, +in order; +if the pattern specifies no captures, +then the whole match is passed as a sole argument. +If the value returned by this function is a string, +then it is used as the replacement string; +otherwise, the replacement string is the empty string. + +<p>The optional last parameter <code>n</code> limits +the maximum number of substitutions to occur. +For instance, when <code>n</code> is 1 only the first occurrence of +<code>pat</code> is replaced. + +<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="5.0"} + x = string.gsub("$name_$version.tar.gz", "%$(%w+)", function (v) + return t[v] + end) + --> x="lua_5.0.tar.gz" +</PRE> + +<p><a name="pdf-string.len"></a><hr><h3><code>string.len (s)</code></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><a name="pdf-string.lower"></a><hr><h3><code>string.lower (s)</code></h3> +Receives a string and returns a copy of that string with all +uppercase letters changed to lowercase. +All other characters are left unchanged. +The definition of what is an uppercase letter depends on the current locale. + +<p><a name="pdf-string.match"></a><hr><h3><code>string.match (s, pattern [, init])</code></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 may be negative. + +<p><a name="pdf-string.rep"></a><hr><h3><code>string.rep (s, n)</code></h3> +Returns a string that is the concatenation of <code>n</code> copies of +the string <code>s</code>. + +<p><a name="pdf-string.reverse"></a><hr><h3><code>string.reverse (s)</code></h3> +Returns a string that is the string <code>s</code> reversed. + +<p><a name="pdf-string.sub"></a><hr><h3><code>string.sub (s, i [, j])</code></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> may be negative. +If <code>j</code> is absent, then it is assumed to be equal to <em>-1</em> +(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><a name="pdf-string.upper"></a><hr><h3><code>string.upper (s)</code></h3> +Receives a string and returns a copy of that string with all +lowercase letters changed to uppercase. +All other characters are left unchanged. +The definition of what is a lowercase letter depends on the current locale. + +<p><a name="pm"></a><h3>Patterns</h3> + +<p><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 magic characters +<code>^$()%.[]*+-?</code>) +— represents the character <em>x</em> itself. +<li><b><code>.</code></b> — (a dot) represents all characters. +<li><b><code>%a</code></b> — represents all letters. +<li><b><code>%c</code></b> — represents all control characters. +<li><b><code>%d</code></b> — represents all digits. +<li><b><code>%l</code></b> — represents all lowercase letters. +<li><b><code>%p</code></b> — represents all punctuation characters. +<li><b><code>%s</code></b> — represents all space characters. +<li><b><code>%u</code></b> — represents all uppercase letters. +<li><b><code>%w</code></b> — represents all alphanumeric characters. +<li><b><code>%x</code></b> — represents all hexadecimal digits. +<li><b><code>%z</code></b> — represents the character with representation 0. +<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. + +<p><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 may be specified by +separating the end characters of the range with a `<code>-</code>´. +All classes <code>%</code><em>x</em> described above may 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. + +<p><li><b><code>[^<em>set</em>]</code></b> — +represents the complement of <em>set</em>, +where <em>set</em> is interpreted as above. +</ul> +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>. + +<p><p> +A <em>pattern item</em> may be +<ul> +<li> +a single character class, +which matches any single character in the class; +<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> +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> +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> +a single character class followed by `<code>?</code>´, +which matches 0 or 1 occurrence of a character in the class; +<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> +<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. +</ul> + +<p><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. + +<p><p> +A pattern may 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. + +<p><a name="5.5"></a><h2>5.5 - Table Manipulation</h2> +This library provides generic functions for table manipulation. +It provides all its functions inside the table <code>table</code>. + +<p>Most functions in the table library assume that the table +represents an array or a list. +For those functions, when we talk about "the length" of a table +we mean the result of the length operator. + +<p><a name="pdf-table.concat"></a><hr><h3><code>table.concat (table [, sep [, i [, j]]])</code></h3> +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><a name="pdf-table.sort"></a><hr><h3><code>table.sort (table [, comp])</code></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. + +<p><a name="pdf-table.insert"></a><hr><h3><code>table.insert (table, [pos,] value)</code></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="#len-op">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><a name="pdf-table.remove"></a><hr><h3><code>table.remove (table [, pos])</code></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><a name="mathlib"></a><a name="5.6"></a><h2>5.6 - Mathematical Functions</h2> + +<p>This library is an interface to the standard C math library. +It provides all its functions inside the table <code>math</code>. +The library provides the following functions: + + + + + + + +<PRE> + math.abs math.acos math.asin math.atan math.atan2 + math.ceil math.cosh math.cos math.deg math.exp + math.floor math.fmod math.frexp math.ldexp math.log + math.log10 math.max math.min math.modf math.pow + math.rad math.random math.randomseed math.sin + math.sinh math.sqrt math.tan math.tanh +</PRE> +plus a variable <code>math.pi</code> and +a variable <code>math.huge</code>, +with the value <code>HUGE_VAL</code>. +Most of those functions +are only interfaces to the corresponding functions in the C library. +All trigonometric functions work in radians. +The functions <code>math.deg</code> and <code>math.rad</code> convert +between radians and degrees. + +<p>The function <code>math.max</code> returns the maximum +value of its numeric arguments. +Similarly, <code>math.min</code> computes the minimum. +Both can be used with 1, 2, or more arguments. + +<p>The function <code>math.modf</code> corresponds to the <code>modf</code> C function. +It returns two values: +The integral part and the fractional part of its argument. +The function <code>math.frexp</code> also returns 2 values: +The normalized fraction and the exponent of its argument. + +<p>The functions <code>math.random</code> and <code>math.randomseed</code> +are interfaces to the simple random generator functions +<code>rand</code> and <code>srand</code> that are provided by ANSI C. +(No guarantees can be given for their statistical properties.) +When called without arguments, +<code>math.random</code> returns a pseudo-random real number +in the range <em>[0,1)</em>. +When called with a number <em>n</em>, +<code>math.random</code> returns +a pseudo-random integer in the range <em>[1,n]</em>. +When called with two arguments, +<em>l</em> and <em>u</em>, +<code>math.random</code> returns a pseudo-random +integer in the range <em>[l,u]</em>. +The <code>math.randomseed</code> function sets a "seed" +for the pseudo-random generator: +Equal seeds produce equal sequences of numbers. + +<p><a name="libio"></a><a name="5.7"></a><h2>5.7 - Input and Output Facilities</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 those default files. +The second style uses explicit file descriptors. + +<p>When using implicit file descriptors, +all operations are supplied by table <code>io</code>. +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: +<code>io.stdin</code>, <code>io.stdout</code>, and <code>io.stderr</code>. + +<p>Unless otherwise stated, +all I/O functions return <B>nil</B> on failure +(plus an error message as a second result) +and some value different from <B>nil</B> on success. + +<p><a name="pdf-io.close"></a><hr><h3><code>io.close ([file])</code></h3> + +<p>Equivalent to <code>file:close()</code>. +Without a <code>file</code>, closes the default output file. + +<p><a name="pdf-io.flush"></a><hr><h3><code>io.flush ()</code></h3> + +<p>Equivalent to <code>file:flush</code> over the default output file. + +<p><a name="pdf-io.input"></a><hr><h3><code>io.input ([file])</code></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 that 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><a name="pdf-io.lines"></a><hr><h3><code>io.lines ([filename])</code></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 ... end +</PRE> +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> (without a file name) is equivalent +to <code>io.input():lines()</code>, that is, it iterates over the +lines of the default input file. +In that case it does not close the file when the loop ends. + +<p><a name="pdf-io.open"></a><hr><h3><code>io.open (filename [, mode])</code></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><b>"w"</b> write mode; +<li><b>"a"</b> append mode; +<li><b>"r+"</b> update mode, all previous data is preserved; +<li><b>"w+"</b> update mode, all previous data is erased; +<li><b>"a+"</b> append update mode, previous data is preserved, + writing is only allowed at the end of file. +</ul> +The <code>mode</code> string may 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><a name="pdf-io.output"></a><hr><h3><code>io.output ([file])</code></h3> + +<p>Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. + +<p><a name="pdf-io.popen"></a><hr><h3><code>io.popen ([prog [, mode]])</code></h3> + +<p>Starts program <code>prog</code> in a separated process and returns +a file handle that you can use to read data from that program +(if <code>mode</code> is <code>"r"</code>, the default) +or to write data to that program +(if <code>mode</code> is <code>"w"</code>). + +<p>This function is system dependent and is not available +in all platforms. + +<p><a name="pdf-io.read"></a><hr><h3><code>io.read (format1, ...)</code></h3> + +<p>Equivalent to <code>io.input():read</code>. + +<p><a name="pdf-io.tmpfile"></a><hr><h3><code>io.tmpfile ()</code></h3> + +<p>Returns a handle for a temporary file. +This file is open in update mode +and it is automatically removed when the program ends. + +<p><a name="pdf-io.type"></a><hr><h3><code>io.type (obj)</code></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, +and <B>nil</B> if <code>obj</code> is not a file handle. + +<p><a name="pdf-io.write"></a><hr><h3><code>io.write (value1, ...)</code></h3> + +<p>Equivalent to <code>io.output():write</code>. + +<p><a name="pdf-file:close"></a><hr><h3><code>file:close ()</code></h3> + +<p>Closes <code>file</code>. +Note that files are automatically closed when garbage collected, +but that takes an unpredictable time to happen. + +<p><a name="flush"></a><a name="pdf-file:flush"></a><hr><h3><code>file:flush ()</code></h3> + +<p>Saves any written data to <code>file</code>. + +<p><a name="pdf-file:lines"></a><hr><h3><code>file:lines ()</code></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 ... end +</PRE> +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><a name="pdf-file:read"></a><hr><h3><code>file:read (format1, ...)</code></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><b>"*a"</b> reads the whole file, starting at the current position. +On end of file, it returns the empty string. +<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><b><em>number</em></b> reads a string with up to that 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. +</ul> + +<p><a name="pdf-file:seek"></a><hr><h3><code>file:seek ([whence] [, offset])</code></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><b>"cur"</b> base is current position; +<li><b>"end"</b> base is end of file; +</ul> +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><a name="pdf-file:setvbuf"></a><hr><h3><code>file:setvbuf (mode [, size])</code></h3> + +<p>Sets the buffering mode for an output file. +There are three available modes: +<ul> +<li><b>"no"</b> no buffering; any output operation appear immediately. +<li><b>"full"</b> full buffering; output operation is performed only +when the buffer is full (or when you <code>flush</code> the file (see <a href="#flush">5.7</a>)). +<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). +</ul> +For the last two cases, <code>sizes</code> +specifies the size of the buffer, in bytes. +The default is an appropriate size. + +<p><a name="pdf-file:write"></a><hr><h3><code>file:write (value1, ...)</code></h3> + +<p>Writes the value of each of its arguments to +the filehandle <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>. + +<p><a name="libiosys"></a><a name="5.8"></a><h2>5.8 - Operating System Facilities</h2> + +<p>This library is implemented through table <code>os</code>. + +<p><a name="pdf-os.clock"></a><hr><h3><code>os.clock ()</code></h3> + +<p>Returns an approximation of the amount of CPU time +used by the program, in seconds. + +<p><a name="pdf-os.date"></a><hr><h3><code>os.date ([format [, time]])</code></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 that optional character, +if <code>format</code> is <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><a name="pdf-os.difftime"></a><hr><h3><code>os.difftime (t2, t1)</code></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><a name="pdf-os.execute"></a><hr><h3><code>os.execute (command)</code></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. + +<p><a name="pdf-os.exit"></a><hr><h3><code>os.exit ([code])</code></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><a name="pdf-os.getenv"></a><hr><h3><code>os.getenv (varname)</code></h3> + +<p>Returns the value of the process environment variable <code>varname</code>, +or <B>nil</B> if the variable is not defined. + +<p><a name="pdf-os.remove"></a><hr><h3><code>os.remove (filename)</code></h3> + +<p>Deletes the file with the given name. +If this function fails, it returns <B>nil</B>, +plus a string describing the error. + +<p><a name="pdf-os.rename"></a><hr><h3><code>os.rename (oldname, newname)</code></h3> + +<p>Renames file named <code>oldname</code> to <code>newname</code>. +If this function fails, it returns <B>nil</B>, +plus a string describing the error. + +<p><a name="pdf-os.setlocale"></a><hr><h3><code>os.setlocale (locale [, category])</code></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><a name="pdf-os.time"></a><hr><h3><code>os.time ([table])</code></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><a name="pdf-os.tmpname"></a><hr><h3><code>os.tmpname ()</code></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 removed when no longer needed. + +<p><a name="libdebug"></a><a name="5.9"></a><h2>5.9 - The Reflexive Debug Interface</h2> + +<p>The <em>debug library</em> 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 its functions +violate some assumptions about Lua code +(e.g., that local variables cannot be accessed from outside or +that userdata metatables cannot be changed by Lua code) +and therefore can compromise some otherwise secure code. + +<p>All functions in this library are provided +inside a <code>debug</code> table. + +<p><a name="pdf-debug.debug"></a><hr><h3><code>debug.debug ()</code></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 <a href="#pdf-debug.debug"><code>debug.debug</code></a> are not lexically nested +with any function, so they have no direct access to local variables. + +<p><a name="pdf-debug.getfenv"></a><hr><h3><code>debug.getfenv (o)</code></h3> +Returns the environment of object <code>o</code>. + +<p><a name="pdf-debug.gethook"></a><hr><h3><code>debug.gethook ()</code></h3> + +<p>Returns the current hook settings, as three values: +the current hook function, the current hook mask, +and the current hook count +(as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). + +<p><a name="pdf-debug.getinfo"></a><hr><h3><code>debug.getinfo (function [, what])</code></h3> + +<p>This function returns a table with information about a function. +You can give the function directly, +or you can give a number as the value of <code>function</code>, +which means the function running at level <code>function</code> of the call stack: +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 contains 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. +If present, +the option `<code>f</code>´ +adds a field named <code>func</code> with the function itself. + +<p>For instance, the expression <code>debug.getinfo(1,"n").name</code> returns +the name of the current function, if a reasonable name can be found, +and <code>debug.getinfo(print)</code> returns a table with all available information +about the <a href="#pdf-print"><code>print</code></a> function. + +<p><a name="pdf-debug.getlocal"></a><hr><h3><code>debug.getlocal (level, local)</code></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><a name="pdf-debug.getmetatable"></a><hr><h3><code>debug.getmetatable (object)</code></h3> + +<p>If <code>object</code> does not have a metatable, returns <B>nil</B>. +Otherwise, returns the metatable of the given object. + +<p><a name="pdf-debug.getupvalue"></a><hr><h3><code>debug.getupvalue (func, up)</code></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><a name="pdf-debug.setfenv"></a><hr><h3><code>debug.setfenv (o, table)</code></h3> + +<p>Sets the environment of the given object. + +<p><a name="pdf-debug.sethook"></a><hr><h3><code>debug.sethook (hook, mask [, count])</code></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><b><code>"r"</code></b> The hook is called every time Lua returns from a function; +<li><b><code>"l"</code></b> The hook is called every time Lua enters a new line of code. +</ul> +With a <code>count</code> different from zero, +the hook is called after every <code>count</code> instructions. + +<p>When called without arguments, +the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function turns off the hook. + +<p>When the hook is called, its first parameter is always a string +describing the event that triggered its call: +<code>"call"</code>, <code>"return"</code> (or <code>"tail return"</code>), +<code>"line"</code>, and <code>"count"</code>. +Moreover, for line events, +it also gets as its second parameter the new line number. +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><a name="pdf-debug.setlocal"></a><hr><h3><code>debug.setlocal (level, local, value)</code></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><a name="pdf-debug.setmetatable"></a><hr><h3><code>debug.setmetatable (o, metatable)</code></h3> + +<p>Sets the metatable for the given object. + +<p><a name="pdf-debug.setupvalue"></a><hr><h3><code>debug.setupvalue (func, up, value)</code></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><a name="pdf-debug.traceback"></a><hr><h3><code>debug.traceback ([message])</code></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. +This function is typically used with <a href="#pdf-xpcall"><code>xpcall</code></a> to produce +better error messages. + +<p> +<a name="lua-sa"></a><a name="6"></a><h1>6 - Lua Stand-alone</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 plus the reflexive debug interface. +Its usage is: +<PRE> + lua [options] [script [args]] +</PRE> +The options are: +<ul> +<li><b><code>-</code> </b> executes <code>stdin</code> as a file; +<li><b><code>-e</code> <em>stat</em></b> executes string <em>stat</em>; +<li><b><code>-l</code> <em>mod</em></b> "requires" <em>mod</em>; +<li><b><code>-i</code></b> enters interactive mode after running <em>script</em>; +<li><b><code>-v</code></b> prints version information; +<li><b><code>--</code></b> stop handling options. +</ul> +After handling its options, <code>lua</code> runs the given <em>script</em>, +passing to it the given <em>args</em>. +When called without arguments, +<code>lua</code> behaves as <code>lua -v -i</code> when <code>stdin</code> is a terminal, +and as <code>lua -</code> otherwise. + +<p>Before running any argument, +the interpreter checks for an environment variable <code>LUA_INIT</code>. +If its format is @<em>filename</em>, +then lua executes the file. +Otherwise, lua 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> +will first set <code>a</code> to 1, then print <code>a</code>, +and finally run the file <code>script.lua</code>. +(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 in 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.lua b.lua t1 t2 +</PRE> +the interpreter first runs the file <code>a.lua</code>, +then creates a table +<PRE> + arg = { [-2] = "lua", [-1] = "-la.lua", [0] = "b.lua", + [1] = "t1", [2] = "t2" } +</PRE> +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 access those arguments with the vararg expression <code>...</code>. + +<p>In interactive mode, +if you write an incomplete statement, +the interpreter waits for its completion. + +<p>If the global variable <code>_PROMPT</code> is defined as a string, +then its value is used as the prompt. +Therefore, the prompt can be changed directly on the command line: +<PRE> + $ lua -e"_PROMPT='myprompt> '" -i +</PRE> +(the outer pair of quotes is for the shell, +the inner is for Lua), +or in any Lua programs by assigning to <code>_PROMPT</code>. +Note the use of <code>-i</code> to enter interactive mode; otherwise, +the program would end just 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> +(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> +is a more portable solution.) + +<p><hr> + +<p><h1>Incompatibilities with Previous Version</h1> + + +<p>Here we list the incompatibilities when moving a program +from Lua 5.0 to Lua 5.1. +You can avoid most of the incompatibilities compiling Lua with +appropriate options. +However, +all those compatibility options will be removed in the next version. + +<p><h2>Incompatibilities with version 5.0</h2> + +<p><h3>Changes in the Language</h3> +<ul> +<li> +The vararg system changed from the pseudo-argument <code>arg</code> with a +table with the extra arguments to the vararg expression. +(Option <code>LUA_COMPAT_VARARG</code>) + +<p><li> +There was a subtle change in the scope of the implicit +variables of the <b>for</b> constructor. + +<p><li> +The long string/long comment syntax (<code>[[...]]</code>) does not allow nesting. +You can use the new syntax (<code>[=[...]=]</code>) in those cases. +(Option <code>LUA_COMPAT_LSTR</code>) + +<p></ul> + +<p><h3>Changes in the Libraries</h3> +<ul> +<li> +Function <a href="#pdf-string.find"><code>string.find</code></a> does not return its captures. +Use <a href="#pdf-string.match"><code>string.match</code></a> for that. +(Option <code>LUA_COMPAT_FIND</code>) + +<p><li> +Function <code>string.gfind</code> was renamed <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>. +(Option <code>LUA_COMPAT_GFIND</code>) + +<p><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. +(Option <code>LUA_COMPAT_GETN</code>) + +<p><li> +Function <code>loadlib</code> was renamed <a href="#pdf-package.loadlib"><code>package.loadlib</code></a>. +(Option <code>LUA_COMPAT_LOADLIB</code>) + +<p><li> +Function <code>math.mod</code> was renamed <a href="#pdf-math.fmod"><code>math.fmod</code></a>. +(Option <code>LUA_COMPAT_MOD</code>) + +<p><li> +There was 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 it gets the path from <a href="#pdf-package.path"><code>package.path</code></a> instead +of from <code>LUA_PATH</code>. + +<p><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. + +<p></ul> + +<p><h3>Changes in the API</h3> +<ul> +<li> +Function <code>lua_open</code> was replaced by <a href="#lua_newstate"><code>lua_newstate</code></a> to +allow the user to set an 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>). + +<p><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>. + +<p><li> +Function <code>luaL_openlib</code> was replaced by <a href="#luaL_register"><code>luaL_register</code></a>. + +<p></ul> + +<p> + +<a name="BNF"></a><h1>The Complete Syntax of Lua</h1> + + +<p> + +<p><pre> + +<p> chunk ::= {stat [`<b>;</b>´]} + +<p> block ::= chunk + +<p> stat ::= varlist1 `<b>=</b>´ explist1 | 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>return</b> [explist1] | <b>break</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> explist1 <b>do</b> block <b>end</b> | <b>function</b> funcname funcbody | <b>local</b> <b>function</b> Name funcbody | <b>local</b> namelist [init] + +<p> funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name] + +<p> varlist1 ::= var {`<b>,</b>´ var} + +<p> var ::= Name | prefixexp `<b>[</b>´ exp `<b>]</b>´ | prefixexp `<b>.</b>´ Name + +<p> namelist ::= Name {`<b>,</b>´ Name} + +<p> init ::= `<b>=</b>´ explist1 + +<p> explist1 ::= {exp `<b>,</b>´} exp + +<p> exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | Literal | `<b>...</b>´ | function | prefixexp | tableconstructor | exp binop exp | unop exp + +<p> prefixexp ::= var | functioncall | `<b>(</b>´ exp `<b>)</b>´ + +<p> functioncall ::= prefixexp args | prefixexp `<b>:</b>´ Name args + +<p> args ::= `<b>(</b>´ [explist1] `<b>)</b>´ | tableconstructor | Literal + +<p> function ::= <b>function</b> funcbody + +<p> funcbody ::= `<b>(</b>´ [parlist1] `<b>)</b>´ block <b>end</b> + +<p> parlist1 ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ + +<p> 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>´ + +<p> 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> + +<p> unop ::= `<b>-</b>´ | <b>not</b> | `<b>#</b>´ + +<p></pre> + +<p> + +<p> + +<HR> +<SMALL> +Last update: +Wed Sep 7 13:53:49 BRT 2005 +</SMALL> + +</body></html> |