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| <a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a> | |
| Lua 5.1 Reference Manual | |
| </h1> | |
| by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes | |
| <p> | |
| <small> | |
| Copyright © 2006-2008 Lua.org, PUC-Rio. | |
| Freely available under the terms of the | |
| <a href="http://www.lua.org/license.html#5">Lua license</a>. | |
| </small> | |
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| <p> | |
| <a href="contents.html#contents">contents</A> | |
| · | |
| <a href="contents.html#index">index</A> | |
| <!-- ====================================================================== --> | |
| <p> | |
| <!-- $Id: manual.of,v 1.48 2008/08/18 15:24:20 roberto Exp $ --> | |
| <h1>1 - <a name="1">Introduction</a></h1> | |
| <p> | |
| Lua is an extension programming language designed to support | |
| general procedural programming with data description | |
| facilities. | |
| It also offers good support for object-oriented programming, | |
| functional programming, and data-driven programming. | |
| Lua is intended to be used as a powerful, light-weight | |
| scripting language for any program that needs one. | |
| Lua is implemented as a library, written in <em>clean</em> C | |
| (that is, in the common subset of ANSI C and C++). | |
| <p> | |
| Being an extension language, Lua has no notion of a "main" program: | |
| it only works <em>embedded</em> in a host client, | |
| called the <em>embedding program</em> or simply the <em>host</em>. | |
| This host program can invoke functions to execute a piece of Lua code, | |
| can write and read Lua variables, | |
| and can register C functions to be called by Lua code. | |
| Through the use of C functions, Lua can be augmented to cope with | |
| a wide range of different domains, | |
| thus creating customized programming languages sharing a syntactical framework. | |
| The Lua distribution includes a sample host program called <code>lua</code>, | |
| which uses the Lua library to offer a complete, stand-alone Lua interpreter. | |
| <p> | |
| Lua is free software, | |
| and is provided as usual with no guarantees, | |
| as stated in its license. | |
| The implementation described in this manual is available | |
| at Lua's official web site, <code>www.lua.org</code>. | |
| <p> | |
| Like any other reference manual, | |
| this document is dry in places. | |
| For a discussion of the decisions behind the design of Lua, | |
| see the technical papers available at Lua's web site. | |
| For a detailed introduction to programming in Lua, | |
| see Roberto's book, <em>Programming in Lua (Second Edition)</em>. | |
| <h1>2 - <a name="2">The Language</a></h1> | |
| <p> | |
| This section describes the lexis, the syntax, and the semantics of Lua. | |
| In other words, | |
| this section describes | |
| which tokens are valid, | |
| how they can be combined, | |
| and what their combinations mean. | |
| <p> | |
| The language constructs will be explained using the usual extended BNF notation, | |
| in which | |
| {<em>a</em>} means 0 or more <em>a</em>'s, and | |
| [<em>a</em>] means an optional <em>a</em>. | |
| Non-terminals are shown like non-terminal, | |
| keywords are shown like <b>kword</b>, | |
| and other terminal symbols are shown like `<b>=</b>´. | |
| The complete syntax of Lua can be found in <a href="#8">§8</a> | |
| at the end of this manual. | |
| <h2>2.1 - <a name="2.1">Lexical Conventions</a></h2> | |
| <p> | |
| <em>Names</em> | |
| (also called <em>identifiers</em>) | |
| in Lua can be any string of letters, | |
| digits, and underscores, | |
| not beginning with a digit. | |
| This coincides with the definition of names in most languages. | |
| (The definition of letter depends on the current locale: | |
| any character considered alphabetic by the current locale | |
| can be used in an identifier.) | |
| Identifiers are used to name variables and table fields. | |
| <p> | |
| The following <em>keywords</em> are reserved | |
| and cannot be used as names: | |
| <pre> | |
| and break do else elseif | |
| end false for function if | |
| in local nil not or | |
| repeat return then true until while | |
| </pre> | |
| <p> | |
| Lua is a case-sensitive language: | |
| <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> | |
| are two different, valid names. | |
| As a convention, names starting with an underscore followed by | |
| uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>) | |
| are reserved for internal global variables used by Lua. | |
| <p> | |
| The following strings denote other tokens: | |
| <pre> | |
| + - * / % ^ # | |
| == ~= <= >= < > = | |
| ( ) { } [ ] | |
| ; : , . .. ... | |
| </pre> | |
| <p> | |
| <em>Literal strings</em> | |
| can be delimited by matching single or double quotes, | |
| and can contain the following C-like escape sequences: | |
| '<code>\a</code>' (bell), | |
| '<code>\b</code>' (backspace), | |
| '<code>\f</code>' (form feed), | |
| '<code>\n</code>' (newline), | |
| '<code>\r</code>' (carriage return), | |
| '<code>\t</code>' (horizontal tab), | |
| '<code>\v</code>' (vertical tab), | |
| '<code>\\</code>' (backslash), | |
| '<code>\"</code>' (quotation mark [double quote]), | |
| and '<code>\'</code>' (apostrophe [single quote]). | |
| Moreover, a backslash followed by a real newline | |
| results in a newline in the string. | |
| A character in a string can also be specified by its numerical value | |
| using the escape sequence <code>\<em>ddd</em></code>, | |
| where <em>ddd</em> is a sequence of up to three decimal digits. | |
| (Note that if a numerical escape is to be followed by a digit, | |
| it must be expressed using exactly three digits.) | |
| Strings in Lua can contain any 8-bit value, including embedded zeros, | |
| which can be specified as '<code>\0</code>'. | |
| <p> | |
| Literal strings can also be defined using a long format | |
| enclosed by <em>long brackets</em>. | |
| We define an <em>opening long bracket of level <em>n</em></em> as an opening | |
| square bracket followed by <em>n</em> equal signs followed by another | |
| opening square bracket. | |
| So, an opening long bracket of level 0 is written as <code>[[</code>, | |
| an opening long bracket of level 1 is written as <code>[=[</code>, | |
| and so on. | |
| A <em>closing long bracket</em> is defined similarly; | |
| for instance, a closing long bracket of level 4 is written as <code>]====]</code>. | |
| A long string starts with an opening long bracket of any level and | |
| ends at the first closing long bracket of the same level. | |
| Literals in this bracketed form can run for several lines, | |
| do not interpret any escape sequences, | |
| and ignore long brackets of any other level. | |
| They can contain anything except a closing bracket of the proper level. | |
| <p> | |
| For convenience, | |
| when the opening long bracket is immediately followed by a newline, | |
| the newline is not included in the string. | |
| As an example, in a system using ASCII | |
| (in which '<code>a</code>' is coded as 97, | |
| newline is coded as 10, and '<code>1</code>' is coded as 49), | |
| the five literal strings below denote the same string: | |
| <pre> | |
| a = 'alo\n123"' | |
| a = "alo\n123\"" | |
| a = '\97lo\10\04923"' | |
| a = [[alo | |
| 123"]] | |
| a = [==[ | |
| alo | |
| 123"]==] | |
| </pre> | |
| <p> | |
| A <em>numerical constant</em> can be written with an optional decimal part | |
| and an optional decimal exponent. | |
| Lua also accepts integer hexadecimal constants, | |
| by prefixing them with <code>0x</code>. | |
| Examples of valid numerical constants are | |
| <pre> | |
| 3 3.0 3.1416 314.16e-2 0.31416E1 0xff 0x56 | |
| </pre> | |
| <p> | |
| A <em>comment</em> starts with a double hyphen (<code>--</code>) | |
| anywhere outside a string. | |
| If the text immediately after <code>--</code> is not an opening long bracket, | |
| the comment is a <em>short comment</em>, | |
| which runs until the end of the line. | |
| Otherwise, it is a <em>long comment</em>, | |
| which runs until the corresponding closing long bracket. | |
| Long comments are frequently used to disable code temporarily. | |
| <h2>2.2 - <a name="2.2">Values and Types</a></h2> | |
| <p> | |
| Lua is a <em>dynamically typed language</em>. | |
| This means that | |
| variables do not have types; only values do. | |
| There are no type definitions in the language. | |
| All values carry their own type. | |
| <p> | |
| All values in Lua are <em>first-class values</em>. | |
| This means that all values can be stored in variables, | |
| passed as arguments to other functions, and returned as results. | |
| <p> | |
| There are eight basic types in Lua: | |
| <em>nil</em>, <em>boolean</em>, <em>number</em>, | |
| <em>string</em>, <em>function</em>, <em>userdata</em>, | |
| <em>thread</em>, and <em>table</em>. | |
| <em>Nil</em> is the type of the value <b>nil</b>, | |
| whose main property is to be different from any other value; | |
| it usually represents the absence of a useful value. | |
| <em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>. | |
| Both <b>nil</b> and <b>false</b> make a condition false; | |
| any other value makes it true. | |
| <em>Number</em> represents real (double-precision floating-point) numbers. | |
| (It is easy to build Lua interpreters that use other | |
| internal representations for numbers, | |
| such as single-precision float or long integers; | |
| see file <code>luaconf.h</code>.) | |
| <em>String</em> represents arrays of characters. | |
| Lua is 8-bit clean: | |
| strings can contain any 8-bit character, | |
| including embedded zeros ('<code>\0</code>') (see <a href="#2.1">§2.1</a>). | |
| <p> | |
| Lua can call (and manipulate) functions written in Lua and | |
| functions written in C | |
| (see <a href="#2.5.8">§2.5.8</a>). | |
| <p> | |
| The type <em>userdata</em> is provided to allow arbitrary C data to | |
| be stored in Lua variables. | |
| This type corresponds to a block of raw memory | |
| and has no pre-defined operations in Lua, | |
| except assignment and identity test. | |
| However, by using <em>metatables</em>, | |
| the programmer can define operations for userdata values | |
| (see <a href="#2.8">§2.8</a>). | |
| Userdata values cannot be created or modified in Lua, | |
| only through the C API. | |
| This guarantees the integrity of data owned by the host program. | |
| <p> | |
| The type <em>thread</em> represents independent threads of execution | |
| and it is used to implement coroutines (see <a href="#2.11">§2.11</a>). | |
| Do not confuse Lua threads with operating-system threads. | |
| Lua supports coroutines on all systems, | |
| even those that do not support threads. | |
| <p> | |
| The type <em>table</em> implements associative arrays, | |
| that is, arrays that can be indexed not only with numbers, | |
| but with any value (except <b>nil</b>). | |
| Tables can be <em>heterogeneous</em>; | |
| that is, they can contain values of all types (except <b>nil</b>). | |
| Tables are the sole data structuring mechanism in Lua; | |
| they can be used to represent ordinary arrays, | |
| symbol tables, sets, records, graphs, trees, etc. | |
| To represent records, Lua uses the field name as an index. | |
| The language supports this representation by | |
| providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. | |
| There are several convenient ways to create tables in Lua | |
| (see <a href="#2.5.7">§2.5.7</a>). | |
| <p> | |
| Like indices, | |
| the value of a table field can be of any type (except <b>nil</b>). | |
| In particular, | |
| because functions are first-class values, | |
| table fields can contain functions. | |
| Thus tables can also carry <em>methods</em> (see <a href="#2.5.9">§2.5.9</a>). | |
| <p> | |
| Tables, functions, threads, and (full) userdata values are <em>objects</em>: | |
| variables do not actually <em>contain</em> these values, | |
| only <em>references</em> to them. | |
| Assignment, parameter passing, and function returns | |
| always manipulate references to such values; | |
| these operations do not imply any kind of copy. | |
| <p> | |
| The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type | |
| of a given value. | |
| <h3>2.2.1 - <a name="2.2.1">Coercion</a></h3> | |
| <p> | |
| Lua provides automatic conversion between | |
| string and number values at run time. | |
| Any arithmetic operation applied to a string tries to convert | |
| this string to a number, following the usual conversion rules. | |
| Conversely, whenever a number is used where a string is expected, | |
| the number is converted to a string, in a reasonable format. | |
| For complete control over how numbers are converted to strings, | |
| use the <code>format</code> function from the string library | |
| (see <a href="#pdf-string.format"><code>string.format</code></a>). | |
| <h2>2.3 - <a name="2.3">Variables</a></h2> | |
| <p> | |
| Variables are places that store values. | |
| There are three kinds of variables in Lua: | |
| global variables, local variables, and table fields. | |
| <p> | |
| A single name can denote a global variable or a local variable | |
| (or a function's formal parameter, | |
| which is a particular kind of local variable): | |
| <pre> | |
| var ::= Name | |
| </pre><p> | |
| Name denotes identifiers, as defined in <a href="#2.1">§2.1</a>. | |
| <p> | |
| Any variable is assumed to be global unless explicitly declared | |
| as a local (see <a href="#2.4.7">§2.4.7</a>). | |
| Local variables are <em>lexically scoped</em>: | |
| local variables can be freely accessed by functions | |
| defined inside their scope (see <a href="#2.6">§2.6</a>). | |
| <p> | |
| Before the first assignment to a variable, its value is <b>nil</b>. | |
| <p> | |
| Square brackets are used to index a table: | |
| <pre> | |
| var ::= prefixexp `<b>[</b>´ exp `<b>]</b>´ | |
| </pre><p> | |
| The meaning of accesses to global variables | |
| and table fields can be changed via metatables. | |
| An access to an indexed variable <code>t[i]</code> is equivalent to | |
| a call <code>gettable_event(t,i)</code>. | |
| (See <a href="#2.8">§2.8</a> for a complete description of the | |
| <code>gettable_event</code> function. | |
| This function is not defined or callable in Lua. | |
| We use it here only for explanatory purposes.) | |
| <p> | |
| The syntax <code>var.Name</code> is just syntactic sugar for | |
| <code>var["Name"]</code>: | |
| <pre> | |
| var ::= prefixexp `<b>.</b>´ Name | |
| </pre> | |
| <p> | |
| All global variables live as fields in ordinary Lua tables, | |
| called <em>environment tables</em> or simply | |
| <em>environments</em> (see <a href="#2.9">§2.9</a>). | |
| Each function has its own reference to an environment, | |
| so that all global variables in this function | |
| will refer to this environment table. | |
| When a function is created, | |
| it inherits the environment from the function that created it. | |
| To get the environment table of a Lua function, | |
| you call <a href="#pdf-getfenv"><code>getfenv</code></a>. | |
| To replace it, | |
| you call <a href="#pdf-setfenv"><code>setfenv</code></a>. | |
| (You can only manipulate the environment of C functions | |
| through the debug library; (see <a href="#5.9">§5.9</a>).) | |
| <p> | |
| An access to a global variable <code>x</code> | |
| is equivalent to <code>_env.x</code>, | |
| which in turn is equivalent to | |
| <pre> | |
| gettable_event(_env, "x") | |
| </pre><p> | |
| where <code>_env</code> is the environment of the running function. | |
| (See <a href="#2.8">§2.8</a> for a complete description of the | |
| <code>gettable_event</code> function. | |
| This function is not defined or callable in Lua. | |
| Similarly, the <code>_env</code> variable is not defined in Lua. | |
| We use them here only for explanatory purposes.) | |
| <h2>2.4 - <a name="2.4">Statements</a></h2> | |
| <p> | |
| Lua supports an almost conventional set of statements, | |
| similar to those in Pascal or C. | |
| This set includes | |
| assignments, control structures, function calls, | |
| and variable declarations. | |
| <h3>2.4.1 - <a name="2.4.1">Chunks</a></h3> | |
| <p> | |
| The unit of execution of Lua is called a <em>chunk</em>. | |
| A chunk is simply a sequence of statements, | |
| which are executed sequentially. | |
| Each statement can be optionally followed by a semicolon: | |
| <pre> | |
| chunk ::= {stat [`<b>;</b>´]} | |
| </pre><p> | |
| There are no empty statements and thus '<code>;;</code>' is not legal. | |
| <p> | |
| Lua handles a chunk as the body of an anonymous function | |
| with a variable number of arguments | |
| (see <a href="#2.5.9">§2.5.9</a>). | |
| As such, chunks can define local variables, | |
| receive arguments, and return values. | |
| <p> | |
| A chunk can be stored in a file or in a string inside the host program. | |
| To execute a chunk, | |
| Lua first pre-compiles the chunk into instructions for a virtual machine, | |
| and then it executes the compiled code | |
| with an interpreter for the virtual machine. | |
| <p> | |
| Chunks can also be pre-compiled into binary form; | |
| see program <code>luac</code> for details. | |
| Programs in source and compiled forms are interchangeable; | |
| Lua automatically detects the file type and acts accordingly. | |
| <h3>2.4.2 - <a name="2.4.2">Blocks</a></h3><p> | |
| A block is a list of statements; | |
| syntactically, a block is the same as a chunk: | |
| <pre> | |
| block ::= chunk | |
| </pre> | |
| <p> | |
| A block can be explicitly delimited to produce a single statement: | |
| <pre> | |
| stat ::= <b>do</b> block <b>end</b> | |
| </pre><p> | |
| Explicit blocks are useful | |
| to control the scope of variable declarations. | |
| Explicit blocks are also sometimes used to | |
| add a <b>return</b> or <b>break</b> statement in the middle | |
| of another block (see <a href="#2.4.4">§2.4.4</a>). | |
| <h3>2.4.3 - <a name="2.4.3">Assignment</a></h3> | |
| <p> | |
| Lua allows multiple assignments. | |
| Therefore, the syntax for assignment | |
| defines a list of variables on the left side | |
| and a list of expressions on the right side. | |
| The elements in both lists are separated by commas: | |
| <pre> | |
| stat ::= varlist `<b>=</b>´ explist | |
| varlist ::= var {`<b>,</b>´ var} | |
| explist ::= exp {`<b>,</b>´ exp} | |
| </pre><p> | |
| Expressions are discussed in <a href="#2.5">§2.5</a>. | |
| <p> | |
| Before the assignment, | |
| the list of values is <em>adjusted</em> to the length of | |
| the list of variables. | |
| If there are more values than needed, | |
| the excess values are thrown away. | |
| If there are fewer values than needed, | |
| the list is extended with as many <b>nil</b>'s as needed. | |
| If the list of expressions ends with a function call, | |
| then all values returned by that call enter the list of values, | |
| before the adjustment | |
| (except when the call is enclosed in parentheses; see <a href="#2.5">§2.5</a>). | |
| <p> | |
| The assignment statement first evaluates all its expressions | |
| and only then are the assignments performed. | |
| Thus the code | |
| <pre> | |
| i = 3 | |
| i, a[i] = i+1, 20 | |
| </pre><p> | |
| sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> | |
| because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) | |
| before it is assigned 4. | |
| Similarly, the line | |
| <pre> | |
| x, y = y, x | |
| </pre><p> | |
| exchanges the values of <code>x</code> and <code>y</code>, | |
| and | |
| <pre> | |
| x, y, z = y, z, x | |
| </pre><p> | |
| cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. | |
| <p> | |
| The meaning of assignments to global variables | |
| and table fields can be changed via metatables. | |
| An assignment to an indexed variable <code>t[i] = val</code> is equivalent to | |
| <code>settable_event(t,i,val)</code>. | |
| (See <a href="#2.8">§2.8</a> for a complete description of the | |
| <code>settable_event</code> function. | |
| This function is not defined or callable in Lua. | |
| We use it here only for explanatory purposes.) | |
| <p> | |
| An assignment to a global variable <code>x = val</code> | |
| is equivalent to the assignment | |
| <code>_env.x = val</code>, | |
| which in turn is equivalent to | |
| <pre> | |
| settable_event(_env, "x", val) | |
| </pre><p> | |
| where <code>_env</code> is the environment of the running function. | |
| (The <code>_env</code> variable is not defined in Lua. | |
| We use it here only for explanatory purposes.) | |
| <h3>2.4.4 - <a name="2.4.4">Control Structures</a></h3><p> | |
| The control structures | |
| <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and | |
| familiar syntax: | |
| <pre> | |
| stat ::= <b>while</b> exp <b>do</b> block <b>end</b> | |
| stat ::= <b>repeat</b> block <b>until</b> exp | |
| stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | |
| </pre><p> | |
| Lua also has a <b>for</b> statement, in two flavors (see <a href="#2.4.5">§2.4.5</a>). | |
| <p> | |
| The condition expression of a | |
| control structure can return any value. | |
| Both <b>false</b> and <b>nil</b> are considered false. | |
| All values different from <b>nil</b> and <b>false</b> are considered true | |
| (in particular, the number 0 and the empty string are also true). | |
| <p> | |
| In the <b>repeat</b>–<b>until</b> loop, | |
| the inner block does not end at the <b>until</b> keyword, | |
| but only after the condition. | |
| So, the condition can refer to local variables | |
| declared inside the loop block. | |
| <p> | |
| The <b>return</b> statement is used to return values | |
| from a function or a chunk (which is just a function). | |
| Functions and chunks can return more than one value, | |
| and so the syntax for the <b>return</b> statement is | |
| <pre> | |
| stat ::= <b>return</b> [explist] | |
| </pre> | |
| <p> | |
| The <b>break</b> statement is used to terminate the execution of a | |
| <b>while</b>, <b>repeat</b>, or <b>for</b> loop, | |
| skipping to the next statement after the loop: | |
| <pre> | |
| stat ::= <b>break</b> | |
| </pre><p> | |
| A <b>break</b> ends the innermost enclosing loop. | |
| <p> | |
| The <b>return</b> and <b>break</b> | |
| statements can only be written as the <em>last</em> statement of a block. | |
| If it is really necessary to <b>return</b> or <b>break</b> in the | |
| middle of a block, | |
| then an explicit inner block can be used, | |
| as in the idioms | |
| <code>do return end</code> and <code>do break end</code>, | |
| because now <b>return</b> and <b>break</b> are the last statements in | |
| their (inner) blocks. | |
| <h3>2.4.5 - <a name="2.4.5">For Statement</a></h3> | |
| <p> | |
| The <b>for</b> statement has two forms: | |
| one numeric and one generic. | |
| <p> | |
| The numeric <b>for</b> loop repeats a block of code while a | |
| control variable runs through an arithmetic progression. | |
| It has the following syntax: | |
| <pre> | |
| stat ::= <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> | |
| </pre><p> | |
| The <em>block</em> is repeated for <em>name</em> starting at the value of | |
| the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the | |
| third <em>exp</em>. | |
| More precisely, a <b>for</b> statement like | |
| <pre> | |
| for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end | |
| </pre><p> | |
| is equivalent to the code: | |
| <pre> | |
| do | |
| local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>) | |
| if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end | |
| while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do | |
| local v = <em>var</em> | |
| <em>block</em> | |
| <em>var</em> = <em>var</em> + <em>step</em> | |
| end | |
| end | |
| </pre><p> | |
| Note the following: | |
| <ul> | |
| <li> | |
| All three control expressions are evaluated only once, | |
| before the loop starts. | |
| They must all result in numbers. | |
| </li> | |
| <li> | |
| <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. | |
| The names shown here are for explanatory purposes only. | |
| </li> | |
| <li> | |
| If the third expression (the step) is absent, | |
| then a step of 1 is used. | |
| </li> | |
| <li> | |
| You can use <b>break</b> to exit a <b>for</b> loop. | |
| </li> | |
| <li> | |
| The loop variable <code>v</code> is local to the loop; | |
| you cannot use its value after the <b>for</b> ends or is broken. | |
| If you need this value, | |
| assign it to another variable before breaking or exiting the loop. | |
| </li> | |
| </ul> | |
| <p> | |
| The generic <b>for</b> statement works over functions, | |
| called <em>iterators</em>. | |
| On each iteration, the iterator function is called to produce a new value, | |
| stopping when this new value is <b>nil</b>. | |
| The generic <b>for</b> loop has the following syntax: | |
| <pre> | |
| stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | |
| namelist ::= Name {`<b>,</b>´ Name} | |
| </pre><p> | |
| A <b>for</b> statement like | |
| <pre> | |
| for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end | |
| </pre><p> | |
| is equivalent to the code: | |
| <pre> | |
| do | |
| local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> | |
| while true do | |
| local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) | |
| <em>var</em> = <em>var_1</em> | |
| if <em>var</em> == nil then break end | |
| <em>block</em> | |
| end | |
| end | |
| </pre><p> | |
| Note the following: | |
| <ul> | |
| <li> | |
| <code><em>explist</em></code> is evaluated only once. | |
| Its results are an <em>iterator</em> function, | |
| a <em>state</em>, | |
| and an initial value for the first <em>iterator variable</em>. | |
| </li> | |
| <li> | |
| <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables. | |
| The names are here for explanatory purposes only. | |
| </li> | |
| <li> | |
| You can use <b>break</b> to exit a <b>for</b> loop. | |
| </li> | |
| <li> | |
| The loop variables <code><em>var_i</em></code> are local to the loop; | |
| you cannot use their values after the <b>for</b> ends. | |
| If you need these values, | |
| then assign them to other variables before breaking or exiting the loop. | |
| </li> | |
| </ul> | |
| <h3>2.4.6 - <a name="2.4.6">Function Calls as Statements</a></h3><p> | |
| To allow possible side-effects, | |
| function calls can be executed as statements: | |
| <pre> | |
| stat ::= functioncall | |
| </pre><p> | |
| In this case, all returned values are thrown away. | |
| Function calls are explained in <a href="#2.5.8">§2.5.8</a>. | |
| <h3>2.4.7 - <a name="2.4.7">Local Declarations</a></h3><p> | |
| Local variables can be declared anywhere inside a block. | |
| The declaration can include an initial assignment: | |
| <pre> | |
| stat ::= <b>local</b> namelist [`<b>=</b>´ explist] | |
| </pre><p> | |
| If present, an initial assignment has the same semantics | |
| of a multiple assignment (see <a href="#2.4.3">§2.4.3</a>). | |
| Otherwise, all variables are initialized with <b>nil</b>. | |
| <p> | |
| A chunk is also a block (see <a href="#2.4.1">§2.4.1</a>), | |
| and so local variables can be declared in a chunk outside any explicit block. | |
| The scope of such local variables extends until the end of the chunk. | |
| <p> | |
| The visibility rules for local variables are explained in <a href="#2.6">§2.6</a>. | |
| <h2>2.5 - <a name="2.5">Expressions</a></h2> | |
| <p> | |
| The basic expressions in Lua are the following: | |
| <pre> | |
| exp ::= prefixexp | |
| exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | |
| exp ::= Number | |
| exp ::= String | |
| exp ::= function | |
| exp ::= tableconstructor | |
| exp ::= `<b>...</b>´ | |
| exp ::= exp binop exp | |
| exp ::= unop exp | |
| prefixexp ::= var | functioncall | `<b>(</b>´ exp `<b>)</b>´ | |
| </pre> | |
| <p> | |
| Numbers and literal strings are explained in <a href="#2.1">§2.1</a>; | |
| variables are explained in <a href="#2.3">§2.3</a>; | |
| function definitions are explained in <a href="#2.5.9">§2.5.9</a>; | |
| function calls are explained in <a href="#2.5.8">§2.5.8</a>; | |
| table constructors are explained in <a href="#2.5.7">§2.5.7</a>. | |
| Vararg expressions, | |
| denoted by three dots ('<code>...</code>'), can only be used when | |
| directly inside a vararg function; | |
| they are explained in <a href="#2.5.9">§2.5.9</a>. | |
| <p> | |
| Binary operators comprise arithmetic operators (see <a href="#2.5.1">§2.5.1</a>), | |
| relational operators (see <a href="#2.5.2">§2.5.2</a>), logical operators (see <a href="#2.5.3">§2.5.3</a>), | |
| and the concatenation operator (see <a href="#2.5.4">§2.5.4</a>). | |
| Unary operators comprise the unary minus (see <a href="#2.5.1">§2.5.1</a>), | |
| the unary <b>not</b> (see <a href="#2.5.3">§2.5.3</a>), | |
| and the unary <em>length operator</em> (see <a href="#2.5.5">§2.5.5</a>). | |
| <p> | |
| Both function calls and vararg expressions can result in multiple values. | |
| If an expression is used as a statement | |
| (only possible for function calls (see <a href="#2.4.6">§2.4.6</a>)), | |
| then its return list is adjusted to zero elements, | |
| thus discarding all returned values. | |
| If an expression is used as the last (or the only) element | |
| of a list of expressions, | |
| then no adjustment is made | |
| (unless the call is enclosed in parentheses). | |
| In all other contexts, | |
| Lua adjusts the result list to one element, | |
| discarding all values except the first one. | |
| <p> | |
| Here are some examples: | |
| <pre> | |
| f() -- adjusted to 0 results | |
| g(f(), x) -- f() is adjusted to 1 result | |
| g(x, f()) -- g gets x plus all results from f() | |
| a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil) | |
| a,b = ... -- a gets the first vararg parameter, b gets | |
| -- the second (both a and b can get nil if there | |
| -- is no corresponding vararg parameter) | |
| a,b,c = x, f() -- f() is adjusted to 2 results | |
| a,b,c = f() -- f() is adjusted to 3 results | |
| return f() -- returns all results from f() | |
| return ... -- returns all received vararg parameters | |
| return x,y,f() -- returns x, y, and all results from f() | |
| {f()} -- creates a list with all results from f() | |
| {...} -- creates a list with all vararg parameters | |
| {f(), nil} -- f() is adjusted to 1 result | |
| </pre> | |
| <p> | |
| Any expression enclosed in parentheses always results in only one value. | |
| Thus, | |
| <code>(f(x,y,z))</code> is always a single value, | |
| even if <code>f</code> returns several values. | |
| (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> | |
| or <b>nil</b> if <code>f</code> does not return any values.) | |
| <h3>2.5.1 - <a name="2.5.1">Arithmetic Operators</a></h3><p> | |
| Lua supports the usual arithmetic operators: | |
| the binary <code>+</code> (addition), | |
| <code>-</code> (subtraction), <code>*</code> (multiplication), | |
| <code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation); | |
| and unary <code>-</code> (negation). | |
| If the operands are numbers, or strings that can be converted to | |
| numbers (see <a href="#2.2.1">§2.2.1</a>), | |
| then all operations have the usual meaning. | |
| Exponentiation works for any exponent. | |
| For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>. | |
| Modulo is defined as | |
| <pre> | |
| a % b == a - math.floor(a/b)*b | |
| </pre><p> | |
| That is, it is the remainder of a division that rounds | |
| the quotient towards minus infinity. | |
| <h3>2.5.2 - <a name="2.5.2">Relational Operators</a></h3><p> | |
| The relational operators in Lua are | |
| <pre> | |
| == ~= < > <= >= | |
| </pre><p> | |
| These operators always result in <b>false</b> or <b>true</b>. | |
| <p> | |
| Equality (<code>==</code>) first compares the type of its operands. | |
| If the types are different, then the result is <b>false</b>. | |
| Otherwise, the values of the operands are compared. | |
| Numbers and strings are compared in the usual way. | |
| Objects (tables, userdata, threads, and functions) | |
| are compared by <em>reference</em>: | |
| two objects are considered equal only if they are the <em>same</em> object. | |
| Every time you create a new object | |
| (a table, userdata, thread, or function), | |
| this new object is different from any previously existing object. | |
| <p> | |
| You can change the way that Lua compares tables and userdata | |
| by using the "eq" metamethod (see <a href="#2.8">§2.8</a>). | |
| <p> | |
| The conversion rules of <a href="#2.2.1">§2.2.1</a> | |
| <em>do not</em> apply to equality comparisons. | |
| Thus, <code>"0"==0</code> evaluates to <b>false</b>, | |
| and <code>t[0]</code> and <code>t["0"]</code> denote different | |
| entries in a table. | |
| <p> | |
| The operator <code>~=</code> is exactly the negation of equality (<code>==</code>). | |
| <p> | |
| The order operators work as follows. | |
| If both arguments are numbers, then they are compared as such. | |
| Otherwise, if both arguments are strings, | |
| then their values are compared according to the current locale. | |
| Otherwise, Lua tries to call the "lt" or the "le" | |
| metamethod (see <a href="#2.8">§2.8</a>). | |
| A comparison <code>a > b</code> is translated to <code>b < a</code> | |
| and <code>a >= b</code> is translated to <code>b <= a</code>. | |
| <h3>2.5.3 - <a name="2.5.3">Logical Operators</a></h3><p> | |
| The logical operators in Lua are | |
| <b>and</b>, <b>or</b>, and <b>not</b>. | |
| Like the control structures (see <a href="#2.4.4">§2.4.4</a>), | |
| all logical operators consider both <b>false</b> and <b>nil</b> as false | |
| and anything else as true. | |
| <p> | |
| The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>. | |
| The conjunction operator <b>and</b> returns its first argument | |
| if this value is <b>false</b> or <b>nil</b>; | |
| otherwise, <b>and</b> returns its second argument. | |
| The disjunction operator <b>or</b> returns its first argument | |
| if this value is different from <b>nil</b> and <b>false</b>; | |
| otherwise, <b>or</b> returns its second argument. | |
| Both <b>and</b> and <b>or</b> use short-cut evaluation; | |
| that is, | |
| the second operand is evaluated only if necessary. | |
| Here are some examples: | |
| <pre> | |
| 10 or 20 --> 10 | |
| 10 or error() --> 10 | |
| nil or "a" --> "a" | |
| nil and 10 --> nil | |
| false and error() --> false | |
| false and nil --> false | |
| false or nil --> nil | |
| 10 and 20 --> 20 | |
| </pre><p> | |
| (In this manual, | |
| <code>--></code> indicates the result of the preceding expression.) | |
| <h3>2.5.4 - <a name="2.5.4">Concatenation</a></h3><p> | |
| The string concatenation operator in Lua is | |
| denoted by two dots ('<code>..</code>'). | |
| If both operands are strings or numbers, then they are converted to | |
| strings according to the rules mentioned in <a href="#2.2.1">§2.2.1</a>. | |
| Otherwise, the "concat" metamethod is called (see <a href="#2.8">§2.8</a>). | |
| <h3>2.5.5 - <a name="2.5.5">The Length Operator</a></h3> | |
| <p> | |
| The length operator is denoted by the unary operator <code>#</code>. | |
| The length of a string is its number of bytes | |
| (that is, the usual meaning of string length when each | |
| character is one byte). | |
| <p> | |
| The length of a table <code>t</code> is defined to be any | |
| integer index <code>n</code> | |
| such that <code>t[n]</code> is not <b>nil</b> and <code>t[n+1]</code> is <b>nil</b>; | |
| moreover, if <code>t[1]</code> is <b>nil</b>, <code>n</code> can be zero. | |
| For a regular array, with non-nil values from 1 to a given <code>n</code>, | |
| its length is exactly that <code>n</code>, | |
| the index of its last value. | |
| If the array has "holes" | |
| (that is, <b>nil</b> values between other non-nil values), | |
| then <code>#t</code> can be any of the indices that | |
| directly precedes a <b>nil</b> value | |
| (that is, it may consider any such <b>nil</b> value as the end of | |
| the array). | |
| <h3>2.5.6 - <a name="2.5.6">Precedence</a></h3><p> | |
| Operator precedence in Lua follows the table below, | |
| from lower to higher priority: | |
| <pre> | |
| or | |
| and | |
| < > <= >= ~= == | |
| .. | |
| + - | |
| * / % | |
| not # - (unary) | |
| ^ | |
| </pre><p> | |
| As usual, | |
| you can use parentheses to change the precedences of an expression. | |
| The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>') | |
| operators are right associative. | |
| All other binary operators are left associative. | |
| <h3>2.5.7 - <a name="2.5.7">Table Constructors</a></h3><p> | |
| Table constructors are expressions that create tables. | |
| Every time a constructor is evaluated, a new table is created. | |
| A constructor can be used to create an empty table | |
| or to create a table and initialize some of its fields. | |
| The general syntax for constructors is | |
| <pre> | |
| tableconstructor ::= `<b>{</b>´ [fieldlist] `<b>}</b>´ | |
| fieldlist ::= field {fieldsep field} [fieldsep] | |
| field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp | |
| fieldsep ::= `<b>,</b>´ | `<b>;</b>´ | |
| </pre> | |
| <p> | |
| Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry | |
| with key <code>exp1</code> and value <code>exp2</code>. | |
| A field of the form <code>name = exp</code> is equivalent to | |
| <code>["name"] = exp</code>. | |
| Finally, fields of the form <code>exp</code> are equivalent to | |
| <code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers, | |
| starting with 1. | |
| Fields in the other formats do not affect this counting. | |
| For example, | |
| <pre> | |
| a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 } | |
| </pre><p> | |
| is equivalent to | |
| <pre> | |
| do | |
| local t = {} | |
| t[f(1)] = g | |
| t[1] = "x" -- 1st exp | |
| t[2] = "y" -- 2nd exp | |
| t.x = 1 -- t["x"] = 1 | |
| t[3] = f(x) -- 3rd exp | |
| t[30] = 23 | |
| t[4] = 45 -- 4th exp | |
| a = t | |
| end | |
| </pre> | |
| <p> | |
| If the last field in the list has the form <code>exp</code> | |
| and the expression is a function call or a vararg expression, | |
| then all values returned by this expression enter the list consecutively | |
| (see <a href="#2.5.8">§2.5.8</a>). | |
| To avoid this, | |
| enclose the function call or the vararg expression | |
| in parentheses (see <a href="#2.5">§2.5</a>). | |
| <p> | |
| The field list can have an optional trailing separator, | |
| as a convenience for machine-generated code. | |
| <h3>2.5.8 - <a name="2.5.8">Function Calls</a></h3><p> | |
| A function call in Lua has the following syntax: | |
| <pre> | |
| functioncall ::= prefixexp args | |
| </pre><p> | |
| In a function call, | |
| first prefixexp and args are evaluated. | |
| If the value of prefixexp has type <em>function</em>, | |
| then this function is called | |
| with the given arguments. | |
| Otherwise, the prefixexp "call" metamethod is called, | |
| having as first parameter the value of prefixexp, | |
| followed by the original call arguments | |
| (see <a href="#2.8">§2.8</a>). | |
| <p> | |
| The form | |
| <pre> | |
| functioncall ::= prefixexp `<b>:</b>´ Name args | |
| </pre><p> | |
| can be used to call "methods". | |
| A call <code>v:name(<em>args</em>)</code> | |
| is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, | |
| except that <code>v</code> is evaluated only once. | |
| <p> | |
| Arguments have the following syntax: | |
| <pre> | |
| args ::= `<b>(</b>´ [explist] `<b>)</b>´ | |
| args ::= tableconstructor | |
| args ::= String | |
| </pre><p> | |
| All argument expressions are evaluated before the call. | |
| A call of the form <code>f{<em>fields</em>}</code> is | |
| syntactic sugar for <code>f({<em>fields</em>})</code>; | |
| that is, the argument list is a single new table. | |
| A call of the form <code>f'<em>string</em>'</code> | |
| (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>) | |
| is syntactic sugar for <code>f('<em>string</em>')</code>; | |
| that is, the argument list is a single literal string. | |
| <p> | |
| As an exception to the free-format syntax of Lua, | |
| you cannot put a line break before the '<code>(</code>' in a function call. | |
| This restriction avoids some ambiguities in the language. | |
| If you write | |
| <pre> | |
| a = f | |
| (g).x(a) | |
| </pre><p> | |
| Lua would see that as a single statement, <code>a = f(g).x(a)</code>. | |
| So, if you want two statements, you must add a semi-colon between them. | |
| If you actually want to call <code>f</code>, | |
| you must remove the line break before <code>(g)</code>. | |
| <p> | |
| A call of the form <code>return</code> <em>functioncall</em> is called | |
| a <em>tail call</em>. | |
| Lua implements <em>proper tail calls</em> | |
| (or <em>proper tail recursion</em>): | |
| in a tail call, | |
| the called function reuses the stack entry of the calling function. | |
| Therefore, there is no limit on the number of nested tail calls that | |
| a program can execute. | |
| However, a tail call erases any debug information about the | |
| calling function. | |
| Note that a tail call only happens with a particular syntax, | |
| where the <b>return</b> has one single function call as argument; | |
| this syntax makes the calling function return exactly | |
| the returns of the called function. | |
| So, none of the following examples are tail calls: | |
| <pre> | |
| return (f(x)) -- results adjusted to 1 | |
| return 2 * f(x) | |
| return x, f(x) -- additional results | |
| f(x); return -- results discarded | |
| return x or f(x) -- results adjusted to 1 | |
| </pre> | |
| <h3>2.5.9 - <a name="2.5.9">Function Definitions</a></h3> | |
| <p> | |
| The syntax for function definition is | |
| <pre> | |
| function ::= <b>function</b> funcbody | |
| funcbody ::= `<b>(</b>´ [parlist] `<b>)</b>´ block <b>end</b> | |
| </pre> | |
| <p> | |
| The following syntactic sugar simplifies function definitions: | |
| <pre> | |
| stat ::= <b>function</b> funcname funcbody | |
| stat ::= <b>local</b> <b>function</b> Name funcbody | |
| funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name] | |
| </pre><p> | |
| The statement | |
| <pre> | |
| function f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| f = function () <em>body</em> end | |
| </pre><p> | |
| The statement | |
| <pre> | |
| function t.a.b.c.f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| t.a.b.c.f = function () <em>body</em> end | |
| </pre><p> | |
| The statement | |
| <pre> | |
| local function f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| local f; f = function () <em>body</em> end | |
| </pre><p> | |
| <em>not</em> to | |
| <pre> | |
| local f = function () <em>body</em> end | |
| </pre><p> | |
| (This only makes a difference when the body of the function | |
| contains references to <code>f</code>.) | |
| <p> | |
| A function definition is an executable expression, | |
| whose value has type <em>function</em>. | |
| When Lua pre-compiles a chunk, | |
| all its function bodies are pre-compiled too. | |
| Then, whenever Lua executes the function definition, | |
| the function is <em>instantiated</em> (or <em>closed</em>). | |
| This function instance (or <em>closure</em>) | |
| is the final value of the expression. | |
| Different instances of the same function | |
| can refer to different external local variables | |
| and can have different environment tables. | |
| <p> | |
| Parameters act as local variables that are | |
| initialized with the argument values: | |
| <pre> | |
| parlist ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ | |
| </pre><p> | |
| When a function is called, | |
| the list of arguments is adjusted to | |
| the length of the list of parameters, | |
| unless the function is a variadic or <em>vararg function</em>, | |
| which is | |
| indicated by three dots ('<code>...</code>') at the end of its parameter list. | |
| A vararg function does not adjust its argument list; | |
| instead, it collects all extra arguments and supplies them | |
| to the function through a <em>vararg expression</em>, | |
| which is also written as three dots. | |
| The value of this expression is a list of all actual extra arguments, | |
| similar to a function with multiple results. | |
| If a vararg expression is used inside another expression | |
| or in the middle of a list of expressions, | |
| then its return list is adjusted to one element. | |
| If the expression is used as the last element of a list of expressions, | |
| then no adjustment is made | |
| (unless that last expression is enclosed in parentheses). | |
| <p> | |
| As an example, consider the following definitions: | |
| <pre> | |
| function f(a, b) end | |
| function g(a, b, ...) end | |
| function r() return 1,2,3 end | |
| </pre><p> | |
| Then, we have the following mapping from arguments to parameters and | |
| to the vararg expression: | |
| <pre> | |
| CALL PARAMETERS | |
| f(3) a=3, b=nil | |
| f(3, 4) a=3, b=4 | |
| f(3, 4, 5) a=3, b=4 | |
| f(r(), 10) a=1, b=10 | |
| f(r()) a=1, b=2 | |
| g(3) a=3, b=nil, ... --> (nothing) | |
| g(3, 4) a=3, b=4, ... --> (nothing) | |
| g(3, 4, 5, 8) a=3, b=4, ... --> 5 8 | |
| g(5, r()) a=5, b=1, ... --> 2 3 | |
| </pre> | |
| <p> | |
| Results are returned using the <b>return</b> statement (see <a href="#2.4.4">§2.4.4</a>). | |
| If control reaches the end of a function | |
| without encountering a <b>return</b> statement, | |
| then the function returns with no results. | |
| <p> | |
| The <em>colon</em> syntax | |
| is used for defining <em>methods</em>, | |
| that is, functions that have an implicit extra parameter <code>self</code>. | |
| Thus, the statement | |
| <pre> | |
| function t.a.b.c:f (<em>params</em>) <em>body</em> end | |
| </pre><p> | |
| is syntactic sugar for | |
| <pre> | |
| t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end | |
| </pre> | |
| <h2>2.6 - <a name="2.6">Visibility Rules</a></h2> | |
| <p> | |
| Lua is a lexically scoped language. | |
| The scope of variables begins at the first statement <em>after</em> | |
| their declaration and lasts until the end of the innermost block that | |
| includes the declaration. | |
| Consider the following example: | |
| <pre> | |
| x = 10 -- global variable | |
| do -- new block | |
| local x = x -- new 'x', with value 10 | |
| print(x) --> 10 | |
| x = x+1 | |
| do -- another block | |
| local x = x+1 -- another 'x' | |
| print(x) --> 12 | |
| end | |
| print(x) --> 11 | |
| end | |
| print(x) --> 10 (the global one) | |
| </pre> | |
| <p> | |
| Notice that, in a declaration like <code>local x = x</code>, | |
| the new <code>x</code> being declared is not in scope yet, | |
| and so the second <code>x</code> refers to the outside variable. | |
| <p> | |
| Because of the lexical scoping rules, | |
| local variables can be freely accessed by functions | |
| defined inside their scope. | |
| A local variable used by an inner function is called | |
| an <em>upvalue</em>, or <em>external local variable</em>, | |
| inside the inner function. | |
| <p> | |
| Notice that each execution of a <b>local</b> statement | |
| defines new local variables. | |
| Consider the following example: | |
| <pre> | |
| a = {} | |
| local x = 20 | |
| for i=1,10 do | |
| local y = 0 | |
| a[i] = function () y=y+1; return x+y end | |
| end | |
| </pre><p> | |
| The loop creates ten closures | |
| (that is, ten instances of the anonymous function). | |
| Each of these closures uses a different <code>y</code> variable, | |
| while all of them share the same <code>x</code>. | |
| <h2>2.7 - <a name="2.7">Error Handling</a></h2> | |
| <p> | |
| Because Lua is an embedded extension language, | |
| all Lua actions start from C code in the host program | |
| calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>). | |
| Whenever an error occurs during Lua compilation or execution, | |
| control returns to C, | |
| which can take appropriate measures | |
| (such as printing an error message). | |
| <p> | |
| Lua code can explicitly generate an error by calling the | |
| <a href="#pdf-error"><code>error</code></a> function. | |
| If you need to catch errors in Lua, | |
| you can use the <a href="#pdf-pcall"><code>pcall</code></a> function. | |
| <h2>2.8 - <a name="2.8">Metatables</a></h2> | |
| <p> | |
| Every value in Lua can have a <em>metatable</em>. | |
| This <em>metatable</em> is an ordinary Lua table | |
| that defines the behavior of the original value | |
| under certain special operations. | |
| You can change several aspects of the behavior | |
| of operations over a value by setting specific fields in its metatable. | |
| For instance, when a non-numeric value is the operand of an addition, | |
| Lua checks for a function in the field <code>"__add"</code> in its metatable. | |
| If it finds one, | |
| Lua calls this function to perform the addition. | |
| <p> | |
| We call the keys in a metatable <em>events</em> | |
| and the values <em>metamethods</em>. | |
| In the previous example, the event is <code>"add"</code> | |
| and the metamethod is the function that performs the addition. | |
| <p> | |
| You can query the metatable of any value | |
| through the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. | |
| <p> | |
| You can replace the metatable of tables | |
| through the <a href="#pdf-setmetatable"><code>setmetatable</code></a> | |
| function. | |
| You cannot change the metatable of other types from Lua | |
| (except by using the debug library); | |
| you must use the C API for that. | |
| <p> | |
| Tables and full userdata have individual metatables | |
| (although multiple tables and userdata can share their metatables). | |
| Values of all other types share one single metatable per type; | |
| that is, there is one single metatable for all numbers, | |
| one for all strings, etc. | |
| <p> | |
| A metatable controls how an object behaves in arithmetic operations, | |
| order comparisons, concatenation, length operation, and indexing. | |
| A metatable also can define a function to be called when a userdata | |
| is garbage collected. | |
| For each of these operations Lua associates a specific key | |
| called an <em>event</em>. | |
| When Lua performs one of these operations over a value, | |
| it checks whether this value has a metatable with the corresponding event. | |
| If so, the value associated with that key (the metamethod) | |
| controls how Lua will perform the operation. | |
| <p> | |
| Metatables control the operations listed next. | |
| Each operation is identified by its corresponding name. | |
| The key for each operation is a string with its name prefixed by | |
| two underscores, '<code>__</code>'; | |
| for instance, the key for operation "add" is the | |
| string <code>"__add"</code>. | |
| The semantics of these operations is better explained by a Lua function | |
| describing how the interpreter executes the operation. | |
| <p> | |
| The code shown here in Lua is only illustrative; | |
| the real behavior is hard coded in the interpreter | |
| and it is much more efficient than this simulation. | |
| All functions used in these descriptions | |
| (<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.) | |
| are described in <a href="#5.1">§5.1</a>. | |
| In particular, to retrieve the metamethod of a given object, | |
| we use the expression | |
| <pre> | |
| metatable(obj)[event] | |
| </pre><p> | |
| This should be read as | |
| <pre> | |
| rawget(getmetatable(obj) or {}, event) | |
| </pre><p> | |
| That is, the access to a metamethod does not invoke other metamethods, | |
| and the access to objects with no metatables does not fail | |
| (it simply results in <b>nil</b>). | |
| <ul> | |
| <li><b>"add":</b> | |
| the <code>+</code> operation. | |
| <p> | |
| The function <code>getbinhandler</code> below defines how Lua chooses a handler | |
| for a binary operation. | |
| First, Lua tries the first operand. | |
| If its type does not define a handler for the operation, | |
| then Lua tries the second operand. | |
| <pre> | |
| function getbinhandler (op1, op2, event) | |
| return metatable(op1)[event] or metatable(op2)[event] | |
| end | |
| </pre><p> | |
| By using this function, | |
| the behavior of the <code>op1 + op2</code> is | |
| <pre> | |
| function add_event (op1, op2) | |
| local o1, o2 = tonumber(op1), tonumber(op2) | |
| if o1 and o2 then -- both operands are numeric? | |
| return o1 + o2 -- '+' here is the primitive 'add' | |
| else -- at least one of the operands is not numeric | |
| local h = getbinhandler(op1, op2, "__add") | |
| if h then | |
| -- call the handler with both operands | |
| return (h(op1, op2)) | |
| else -- no handler available: default behavior | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"sub":</b> | |
| the <code>-</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"mul":</b> | |
| the <code>*</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"div":</b> | |
| the <code>/</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"mod":</b> | |
| the <code>%</code> operation. | |
| Behavior similar to the "add" operation, | |
| with the operation | |
| <code>o1 - floor(o1/o2)*o2</code> as the primitive operation. | |
| </li> | |
| <li><b>"pow":</b> | |
| the <code>^</code> (exponentiation) operation. | |
| Behavior similar to the "add" operation, | |
| with the function <code>pow</code> (from the C math library) | |
| as the primitive operation. | |
| </li> | |
| <li><b>"unm":</b> | |
| the unary <code>-</code> operation. | |
| <pre> | |
| function unm_event (op) | |
| local o = tonumber(op) | |
| if o then -- operand is numeric? | |
| return -o -- '-' here is the primitive 'unm' | |
| else -- the operand is not numeric. | |
| -- Try to get a handler from the operand | |
| local h = metatable(op).__unm | |
| if h then | |
| -- call the handler with the operand | |
| return (h(op)) | |
| else -- no handler available: default behavior | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"concat":</b> | |
| the <code>..</code> (concatenation) operation. | |
| <pre> | |
| function concat_event (op1, op2) | |
| if (type(op1) == "string" or type(op1) == "number") and | |
| (type(op2) == "string" or type(op2) == "number") then | |
| return op1 .. op2 -- primitive string concatenation | |
| else | |
| local h = getbinhandler(op1, op2, "__concat") | |
| if h then | |
| return (h(op1, op2)) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"len":</b> | |
| the <code>#</code> operation. | |
| <pre> | |
| function len_event (op) | |
| if type(op) == "string" then | |
| return strlen(op) -- primitive string length | |
| elseif type(op) == "table" then | |
| return #op -- primitive table length | |
| else | |
| local h = metatable(op).__len | |
| if h then | |
| -- call the handler with the operand | |
| return (h(op)) | |
| else -- no handler available: default behavior | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| See <a href="#2.5.5">§2.5.5</a> for a description of the length of a table. | |
| </li> | |
| <li><b>"eq":</b> | |
| the <code>==</code> operation. | |
| The function <code>getcomphandler</code> defines how Lua chooses a metamethod | |
| for comparison operators. | |
| A metamethod only is selected when both objects | |
| being compared have the same type | |
| and the same metamethod for the selected operation. | |
| <pre> | |
| function getcomphandler (op1, op2, event) | |
| if type(op1) ~= type(op2) then return nil end | |
| local mm1 = metatable(op1)[event] | |
| local mm2 = metatable(op2)[event] | |
| if mm1 == mm2 then return mm1 else return nil end | |
| end | |
| </pre><p> | |
| The "eq" event is defined as follows: | |
| <pre> | |
| function eq_event (op1, op2) | |
| if type(op1) ~= type(op2) then -- different types? | |
| return false -- different objects | |
| end | |
| if op1 == op2 then -- primitive equal? | |
| return true -- objects are equal | |
| end | |
| -- try metamethod | |
| local h = getcomphandler(op1, op2, "__eq") | |
| if h then | |
| return (h(op1, op2)) | |
| else | |
| return false | |
| end | |
| end | |
| </pre><p> | |
| <code>a ~= b</code> is equivalent to <code>not (a == b)</code>. | |
| </li> | |
| <li><b>"lt":</b> | |
| the <code><</code> operation. | |
| <pre> | |
| function lt_event (op1, op2) | |
| if type(op1) == "number" and type(op2) == "number" then | |
| return op1 < op2 -- numeric comparison | |
| elseif type(op1) == "string" and type(op2) == "string" then | |
| return op1 < op2 -- lexicographic comparison | |
| else | |
| local h = getcomphandler(op1, op2, "__lt") | |
| if h then | |
| return (h(op1, op2)) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| <code>a > b</code> is equivalent to <code>b < a</code>. | |
| </li> | |
| <li><b>"le":</b> | |
| the <code><=</code> operation. | |
| <pre> | |
| function le_event (op1, op2) | |
| if type(op1) == "number" and type(op2) == "number" then | |
| return op1 <= op2 -- numeric comparison | |
| elseif type(op1) == "string" and type(op2) == "string" then | |
| return op1 <= op2 -- lexicographic comparison | |
| else | |
| local h = getcomphandler(op1, op2, "__le") | |
| if h then | |
| return (h(op1, op2)) | |
| else | |
| h = getcomphandler(op1, op2, "__lt") | |
| if h then | |
| return not h(op2, op1) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| end | |
| </pre><p> | |
| <code>a >= b</code> is equivalent to <code>b <= a</code>. | |
| Note that, in the absence of a "le" metamethod, | |
| Lua tries the "lt", assuming that <code>a <= b</code> is | |
| equivalent to <code>not (b < a)</code>. | |
| </li> | |
| <li><b>"index":</b> | |
| The indexing access <code>table[key]</code>. | |
| <pre> | |
| function gettable_event (table, key) | |
| local h | |
| if type(table) == "table" then | |
| local v = rawget(table, key) | |
| if v ~= nil then return v end | |
| h = metatable(table).__index | |
| if h == nil then return nil end | |
| else | |
| h = metatable(table).__index | |
| if h == nil then | |
| error(···) | |
| end | |
| end | |
| if type(h) == "function" then | |
| return (h(table, key)) -- call the handler | |
| else return h[key] -- or repeat operation on it | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"newindex":</b> | |
| The indexing assignment <code>table[key] = value</code>. | |
| <pre> | |
| function settable_event (table, key, value) | |
| local h | |
| if type(table) == "table" then | |
| local v = rawget(table, key) | |
| if v ~= nil then rawset(table, key, value); return end | |
| h = metatable(table).__newindex | |
| if h == nil then rawset(table, key, value); return end | |
| else | |
| h = metatable(table).__newindex | |
| if h == nil then | |
| error(···) | |
| end | |
| end | |
| if type(h) == "function" then | |
| h(table, key,value) -- call the handler | |
| else h[key] = value -- or repeat operation on it | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"call":</b> | |
| called when Lua calls a value. | |
| <pre> | |
| function function_event (func, ...) | |
| if type(func) == "function" then | |
| return func(...) -- primitive call | |
| else | |
| local h = metatable(func).__call | |
| if h then | |
| return h(func, ...) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| </ul> | |
| <h2>2.9 - <a name="2.9">Environments</a></h2> | |
| <p> | |
| Besides metatables, | |
| objects of types thread, function, and userdata | |
| have another table associated with them, | |
| called their <em>environment</em>. | |
| Like metatables, environments are regular tables and | |
| multiple objects can share the same environment. | |
| <p> | |
| Threads are created sharing the environment of the creating thread. | |
| Userdata and C functions are created sharing the environment | |
| of the creating C function. | |
| Non-nested Lua functions | |
| (created by <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>) | |
| are created sharing the environment of the creating thread. | |
| Nested Lua functions are created sharing the environment of | |
| the creating Lua function. | |
| <p> | |
| Environments associated with userdata have no meaning for Lua. | |
| It is only a convenience feature for programmers to associate a table to | |
| a userdata. | |
| <p> | |
| Environments associated with threads are called | |
| <em>global environments</em>. | |
| They are used as the default environment for threads and | |
| non-nested Lua functions created by the thread | |
| and can be directly accessed by C code (see <a href="#3.3">§3.3</a>). | |
| <p> | |
| The environment associated with a C function can be directly | |
| accessed by C code (see <a href="#3.3">§3.3</a>). | |
| It is used as the default environment for other C functions | |
| and userdata created by the function. | |
| <p> | |
| Environments associated with Lua functions are used to resolve | |
| all accesses to global variables within the function (see <a href="#2.3">§2.3</a>). | |
| They are used as the default environment for nested Lua functions | |
| created by the function. | |
| <p> | |
| You can change the environment of a Lua function or the | |
| running thread by calling <a href="#pdf-setfenv"><code>setfenv</code></a>. | |
| You can get the environment of a Lua function or the running thread | |
| by calling <a href="#pdf-getfenv"><code>getfenv</code></a>. | |
| To manipulate the environment of other objects | |
| (userdata, C functions, other threads) you must | |
| use the C API. | |
| <h2>2.10 - <a name="2.10">Garbage Collection</a></h2> | |
| <p> | |
| Lua performs automatic memory management. | |
| This means that | |
| you have to worry neither about allocating memory for new objects | |
| nor about freeing it when the objects are no longer needed. | |
| Lua manages memory automatically by running | |
| a <em>garbage collector</em> from time to time | |
| to collect all <em>dead objects</em> | |
| (that is, objects that are no longer accessible from Lua). | |
| All memory used by Lua is subject to automatic management: | |
| tables, userdata, functions, threads, strings, etc. | |
| <p> | |
| Lua implements an incremental mark-and-sweep collector. | |
| It uses two numbers to control its garbage-collection cycles: | |
| the <em>garbage-collector pause</em> and | |
| the <em>garbage-collector step multiplier</em>. | |
| Both use percentage points as units | |
| (so that a value of 100 means an internal value of 1). | |
| <p> | |
| The garbage-collector pause | |
| controls how long the collector waits before starting a new cycle. | |
| Larger values make the collector less aggressive. | |
| Values smaller than 100 mean the collector will not wait to | |
| start a new cycle. | |
| A value of 200 means that the collector waits for the total memory in use | |
| to double before starting a new cycle. | |
| <p> | |
| The step multiplier | |
| controls the relative speed of the collector relative to | |
| memory allocation. | |
| Larger values make the collector more aggressive but also increase | |
| the size of each incremental step. | |
| Values smaller than 100 make the collector too slow and | |
| can result in the collector never finishing a cycle. | |
| The default, 200, means that the collector runs at "twice" | |
| the speed of memory allocation. | |
| <p> | |
| You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C | |
| or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. | |
| With these functions you can also control | |
| the collector directly (e.g., stop and restart it). | |
| <h3>2.10.1 - <a name="2.10.1">Garbage-Collection Metamethods</a></h3> | |
| <p> | |
| Using the C API, | |
| you can set garbage-collector metamethods for userdata (see <a href="#2.8">§2.8</a>). | |
| These metamethods are also called <em>finalizers</em>. | |
| Finalizers allow you to coordinate Lua's garbage collection | |
| with external resource management | |
| (such as closing files, network or database connections, | |
| or freeing your own memory). | |
| <p> | |
| Garbage userdata with a field <code>__gc</code> in their metatables are not | |
| collected immediately by the garbage collector. | |
| Instead, Lua puts them in a list. | |
| After the collection, | |
| Lua does the equivalent of the following function | |
| for each userdata in that list: | |
| <pre> | |
| function gc_event (udata) | |
| local h = metatable(udata).__gc | |
| if h then | |
| h(udata) | |
| end | |
| end | |
| </pre> | |
| <p> | |
| At the end of each garbage-collection cycle, | |
| the finalizers for userdata are called in <em>reverse</em> | |
| order of their creation, | |
| among those collected in that cycle. | |
| That is, the first finalizer to be called is the one associated | |
| with the userdata created last in the program. | |
| The userdata itself is freed only in the next garbage-collection cycle. | |
| <h3>2.10.2 - <a name="2.10.2">Weak Tables</a></h3> | |
| <p> | |
| A <em>weak table</em> is a table whose elements are | |
| <em>weak references</em>. | |
| A weak reference is ignored by the garbage collector. | |
| In other words, | |
| if the only references to an object are weak references, | |
| then the garbage collector will collect this object. | |
| <p> | |
| A weak table can have weak keys, weak values, or both. | |
| A table with weak keys allows the collection of its keys, | |
| but prevents the collection of its values. | |
| A table with both weak keys and weak values allows the collection of | |
| both keys and values. | |
| In any case, if either the key or the value is collected, | |
| the whole pair is removed from the table. | |
| The weakness of a table is controlled by the | |
| <code>__mode</code> field of its metatable. | |
| If the <code>__mode</code> field is a string containing the character '<code>k</code>', | |
| the keys in the table are weak. | |
| If <code>__mode</code> contains '<code>v</code>', | |
| the values in the table are weak. | |
| <p> | |
| After you use a table as a metatable, | |
| you should not change the value of its <code>__mode</code> field. | |
| Otherwise, the weak behavior of the tables controlled by this | |
| metatable is undefined. | |
| <h2>2.11 - <a name="2.11">Coroutines</a></h2> | |
| <p> | |
| Lua supports coroutines, | |
| also called <em>collaborative multithreading</em>. | |
| A coroutine in Lua represents an independent thread of execution. | |
| Unlike threads in multithread systems, however, | |
| a coroutine only suspends its execution by explicitly calling | |
| a yield function. | |
| <p> | |
| You create a coroutine with a call to <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>. | |
| Its sole argument is a function | |
| that is the main function of the coroutine. | |
| The <code>create</code> function only creates a new coroutine and | |
| returns a handle to it (an object of type <em>thread</em>); | |
| it does not start the coroutine execution. | |
| <p> | |
| When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| passing as its first argument | |
| a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, | |
| the coroutine starts its execution, | |
| at the first line of its main function. | |
| Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on | |
| to the coroutine main function. | |
| After the coroutine starts running, | |
| it runs until it terminates or <em>yields</em>. | |
| <p> | |
| A coroutine can terminate its execution in two ways: | |
| normally, when its main function returns | |
| (explicitly or implicitly, after the last instruction); | |
| and abnormally, if there is an unprotected error. | |
| In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>, | |
| plus any values returned by the coroutine main function. | |
| In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b> | |
| plus an error message. | |
| <p> | |
| A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. | |
| When a coroutine yields, | |
| the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately, | |
| even if the yield happens inside nested function calls | |
| (that is, not in the main function, | |
| but in a function directly or indirectly called by the main function). | |
| In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>, | |
| plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. | |
| The next time you resume the same coroutine, | |
| it continues its execution from the point where it yielded, | |
| with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra | |
| arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. | |
| <p> | |
| Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, | |
| the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine, | |
| but instead of returning the coroutine itself, | |
| it returns a function that, when called, resumes the coroutine. | |
| Any arguments passed to this function | |
| go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. | |
| <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| except the first one (the boolean error code). | |
| Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors; | |
| any error is propagated to the caller. | |
| <p> | |
| As an example, | |
| consider the following code: | |
| <pre> | |
| function foo (a) | |
| print("foo", a) | |
| return coroutine.yield(2*a) | |
| end | |
| co = coroutine.create(function (a,b) | |
| print("co-body", a, b) | |
| local r = foo(a+1) | |
| print("co-body", r) | |
| local r, s = coroutine.yield(a+b, a-b) | |
| print("co-body", r, s) | |
| return b, "end" | |
| end) | |
| print("main", coroutine.resume(co, 1, 10)) | |
| print("main", coroutine.resume(co, "r")) | |
| print("main", coroutine.resume(co, "x", "y")) | |
| print("main", coroutine.resume(co, "x", "y")) | |
| </pre><p> | |
| When you run it, it produces the following output: | |
| <pre> | |
| co-body 1 10 | |
| foo 2 | |
| main true 4 | |
| co-body r | |
| main true 11 -9 | |
| co-body x y | |
| main true 10 end | |
| main false cannot resume dead coroutine | |
| </pre> | |
| <h1>3 - <a name="3">The Application Program Interface</a></h1> | |
| <p> | |
| This section describes the C API for Lua, that is, | |
| the set of C functions available to the host program to communicate | |
| with Lua. | |
| All API functions and related types and constants | |
| are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>. | |
| <p> | |
| Even when we use the term "function", | |
| any facility in the API may be provided as a macro instead. | |
| All such macros use each of their arguments exactly once | |
| (except for the first argument, which is always a Lua state), | |
| and so do not generate any hidden side-effects. | |
| <p> | |
| As in most C libraries, | |
| the Lua API functions do not check their arguments for validity or consistency. | |
| However, you can change this behavior by compiling Lua | |
| with a proper definition for the macro <a name="pdf-luai_apicheck"><code>luai_apicheck</code></a>, | |
| in file <code>luaconf.h</code>. | |
| <h2>3.1 - <a name="3.1">The Stack</a></h2> | |
| <p> | |
| Lua uses a <em>virtual stack</em> to pass values to and from C. | |
| Each element in this stack represents a Lua value | |
| (<b>nil</b>, number, string, etc.). | |
| <p> | |
| Whenever Lua calls C, the called function gets a new stack, | |
| which is independent of previous stacks and of stacks of | |
| C functions that are still active. | |
| This stack initially contains any arguments to the C function | |
| and it is where the C function pushes its results | |
| to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). | |
| <p> | |
| For convenience, | |
| most query operations in the API do not follow a strict stack discipline. | |
| Instead, they can refer to any element in the stack | |
| by using an <em>index</em>: | |
| A positive index represents an <em>absolute</em> stack position | |
| (starting at 1); | |
| a negative index represents an <em>offset</em> relative to the top of the stack. | |
| More specifically, if the stack has <em>n</em> elements, | |
| then index 1 represents the first element | |
| (that is, the element that was pushed onto the stack first) | |
| and | |
| index <em>n</em> represents the last element; | |
| index -1 also represents the last element | |
| (that is, the element at the top) | |
| and index <em>-n</em> represents the first element. | |
| We say that an index is <em>valid</em> | |
| if it lies between 1 and the stack top | |
| (that is, if <code>1 ≤ abs(index) ≤ top</code>). | |
| <h2>3.2 - <a name="3.2">Stack Size</a></h2> | |
| <p> | |
| When you interact with Lua API, | |
| you are responsible for ensuring consistency. | |
| In particular, | |
| <em>you are responsible for controlling stack overflow</em>. | |
| You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a> | |
| to grow the stack size. | |
| <p> | |
| Whenever Lua calls C, | |
| it ensures that at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> stack positions are available. | |
| <code>LUA_MINSTACK</code> is defined as 20, | |
| so that usually you do not have to worry about stack space | |
| unless your code has loops pushing elements onto the stack. | |
| <p> | |
| Most query functions accept as indices any value inside the | |
| available stack space, that is, indices up to the maximum stack size | |
| you have set through <a href="#lua_checkstack"><code>lua_checkstack</code></a>. | |
| Such indices are called <em>acceptable indices</em>. | |
| More formally, we define an <em>acceptable index</em> | |
| as follows: | |
| <pre> | |
| (index < 0 && abs(index) <= top) || | |
| (index > 0 && index <= stackspace) | |
| </pre><p> | |
| Note that 0 is never an acceptable index. | |
| <h2>3.3 - <a name="3.3">Pseudo-Indices</a></h2> | |
| <p> | |
| Unless otherwise noted, | |
| any function that accepts valid indices can also be called with | |
| <em>pseudo-indices</em>, | |
| which represent some Lua values that are accessible to C code | |
| but which are not in the stack. | |
| Pseudo-indices are used to access the thread environment, | |
| the function environment, | |
| the registry, | |
| and the upvalues of a C function (see <a href="#3.4">§3.4</a>). | |
| <p> | |
| The thread environment (where global variables live) is | |
| always at pseudo-index <a name="pdf-LUA_GLOBALSINDEX"><code>LUA_GLOBALSINDEX</code></a>. | |
| The environment of the running C function is always | |
| at pseudo-index <a name="pdf-LUA_ENVIRONINDEX"><code>LUA_ENVIRONINDEX</code></a>. | |
| <p> | |
| To access and change the value of global variables, | |
| you can use regular table operations over an environment table. | |
| For instance, to access the value of a global variable, do | |
| <pre> | |
| lua_getfield(L, LUA_GLOBALSINDEX, varname); | |
| </pre> | |
| <h2>3.4 - <a name="3.4">C Closures</a></h2> | |
| <p> | |
| When a C function is created, | |
| it is possible to associate some values with it, | |
| thus creating a <em>C closure</em>; | |
| these values are called <em>upvalues</em> and are | |
| accessible to the function whenever it is called | |
| (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>). | |
| <p> | |
| Whenever a C function is called, | |
| its upvalues are located at specific pseudo-indices. | |
| These pseudo-indices are produced by the macro | |
| <a name="lua_upvalueindex"><code>lua_upvalueindex</code></a>. | |
| The first value associated with a function is at position | |
| <code>lua_upvalueindex(1)</code>, and so on. | |
| Any access to <code>lua_upvalueindex(<em>n</em>)</code>, | |
| where <em>n</em> is greater than the number of upvalues of the | |
| current function (but not greater than 256), | |
| produces an acceptable (but invalid) index. | |
| <h2>3.5 - <a name="3.5">Registry</a></h2> | |
| <p> | |
| Lua provides a <em>registry</em>, | |
| a pre-defined table that can be used by any C code to | |
| store whatever Lua value it needs to store. | |
| This table is always located at pseudo-index | |
| <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>. | |
| Any C library can store data into this table, | |
| but it should take care to choose keys different from those used | |
| by other libraries, to avoid collisions. | |
| Typically, you should use as key a string containing your library name | |
| or a light userdata with the address of a C object in your code. | |
| <p> | |
| The integer keys in the registry are used by the reference mechanism, | |
| implemented by the auxiliary library, | |
| and therefore should not be used for other purposes. | |
| <h2>3.6 - <a name="3.6">Error Handling in C</a></h2> | |
| <p> | |
| Internally, Lua uses the C <code>longjmp</code> facility to handle errors. | |
| (You can also choose to use exceptions if you use C++; | |
| see file <code>luaconf.h</code>.) | |
| When Lua faces any error | |
| (such as memory allocation errors, type errors, syntax errors, | |
| and runtime errors) | |
| it <em>raises</em> an error; | |
| that is, it does a long jump. | |
| A <em>protected environment</em> uses <code>setjmp</code> | |
| to set a recover point; | |
| any error jumps to the most recent active recover point. | |
| <p> | |
| Most functions in the API can throw an error, | |
| for instance due to a memory allocation error. | |
| The documentation for each function indicates whether | |
| it can throw errors. | |
| <p> | |
| Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>. | |
| <h2>3.7 - <a name="3.7">Functions and Types</a></h2> | |
| <p> | |
| Here we list all functions and types from the C API in | |
| alphabetical order. | |
| Each function has an indicator like this: | |
| <span class="apii">[-o, +p, <em>x</em>]</span> | |
| <p> | |
| The first field, <code>o</code>, | |
| is how many elements the function pops from the stack. | |
| The second field, <code>p</code>, | |
| is how many elements the function pushes onto the stack. | |
| (Any function always pushes its results after popping its arguments.) | |
| A field in the form <code>x|y</code> means the function can push (or pop) | |
| <code>x</code> or <code>y</code> elements, | |
| depending on the situation; | |
| an interrogation mark '<code>?</code>' means that | |
| we cannot know how many elements the function pops/pushes | |
| by looking only at its arguments | |
| (e.g., they may depend on what is on the stack). | |
| The third field, <code>x</code>, | |
| tells whether the function may throw errors: | |
| '<code>-</code>' means the function never throws any error; | |
| '<code>m</code>' means the function may throw an error | |
| only due to not enough memory; | |
| '<code>e</code>' means the function may throw other kinds of errors; | |
| '<code>v</code>' means the function may throw an error on purpose. | |
| <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3> | |
| <pre>typedef void * (*lua_Alloc) (void *ud, | |
| void *ptr, | |
| size_t osize, | |
| size_t nsize);</pre> | |
| <p> | |
| The type of the memory-allocation function used by Lua states. | |
| The allocator function must provide a | |
| functionality similar to <code>realloc</code>, | |
| but not exactly the same. | |
| Its arguments are | |
| <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>; | |
| <code>ptr</code>, a pointer to the block being allocated/reallocated/freed; | |
| <code>osize</code>, the original size of the block; | |
| <code>nsize</code>, the new size of the block. | |
| <code>ptr</code> is <code>NULL</code> if and only if <code>osize</code> is zero. | |
| When <code>nsize</code> is zero, the allocator must return <code>NULL</code>; | |
| if <code>osize</code> is not zero, | |
| it should free the block pointed to by <code>ptr</code>. | |
| When <code>nsize</code> is not zero, the allocator returns <code>NULL</code> | |
| if and only if it cannot fill the request. | |
| When <code>nsize</code> is not zero and <code>osize</code> is zero, | |
| the allocator should behave like <code>malloc</code>. | |
| When <code>nsize</code> and <code>osize</code> are not zero, | |
| the allocator behaves like <code>realloc</code>. | |
| Lua assumes that the allocator never fails when | |
| <code>osize >= nsize</code>. | |
| <p> | |
| Here is a simple implementation for the allocator function. | |
| It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>. | |
| <pre> | |
| static void *l_alloc (void *ud, void *ptr, size_t osize, | |
| size_t nsize) { | |
| (void)ud; (void)osize; /* not used */ | |
| if (nsize == 0) { | |
| free(ptr); | |
| return NULL; | |
| } | |
| else | |
| return realloc(ptr, nsize); | |
| } | |
| </pre><p> | |
| This code assumes | |
| that <code>free(NULL)</code> has no effect and that | |
| <code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>. | |
| ANSI C ensures both behaviors. | |
| <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> | |
| <p> | |
| Sets a new panic function and returns the old one. | |
| <p> | |
| If an error happens outside any protected environment, | |
| Lua calls a <em>panic function</em> | |
| and then calls <code>exit(EXIT_FAILURE)</code>, | |
| thus exiting the host application. | |
| Your panic function can avoid this exit by | |
| never returning (e.g., doing a long jump). | |
| <p> | |
| The panic function can access the error message at the top of the stack. | |
| <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> | |
| <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> | |
| <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> | |
| <p> | |
| Calls a function. | |
| <p> | |
| To call a function you must use the following protocol: | |
| first, the function to be called is pushed onto the stack; | |
| then, the arguments to the function are pushed | |
| in direct order; | |
| that is, the first argument is pushed first. | |
| Finally you call <a href="#lua_call"><code>lua_call</code></a>; | |
| <code>nargs</code> is the number of arguments that you pushed onto the stack. | |
| All arguments and the function value are popped from the stack | |
| when the function is called. | |
| The function results are pushed onto the stack when the function returns. | |
| The number of results is adjusted to <code>nresults</code>, | |
| unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. | |
| In this case, <em>all</em> results from the function are pushed. | |
| Lua takes care that the returned values fit into the stack space. | |
| The function results are pushed onto the stack in direct order | |
| (the first result is pushed first), | |
| so that after the call the last result is on the top of the stack. | |
| <p> | |
| Any error inside the called function is propagated upwards | |
| (with a <code>longjmp</code>). | |
| <p> | |
| The following example shows how the host program can do the | |
| equivalent to this Lua code: | |
| <pre> | |
| a = f("how", t.x, 14) | |
| </pre><p> | |
| Here it is in C: | |
| <pre> | |
| lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */ | |
| lua_pushstring(L, "how"); /* 1st argument */ | |
| lua_getfield(L, LUA_GLOBALSINDEX, "t"); /* table to be indexed */ | |
| lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */ | |
| lua_remove(L, -2); /* remove 't' from the stack */ | |
| lua_pushinteger(L, 14); /* 3rd argument */ | |
| lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */ | |
| lua_setfield(L, LUA_GLOBALSINDEX, "a"); /* set global 'a' */ | |
| </pre><p> | |
| Note that the code above is "balanced": | |
| at its end, the stack is back to its original configuration. | |
| This is considered good programming practice. | |
| <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3> | |
| <pre>typedef int (*lua_CFunction) (lua_State *L);</pre> | |
| <p> | |
| Type for C functions. | |
| <p> | |
| In order to communicate properly with Lua, | |
| a C function must use the following protocol, | |
| which defines the way parameters and results are passed: | |
| a C function receives its arguments from Lua in its stack | |
| in direct order (the first argument is pushed first). | |
| So, when the function starts, | |
| <code>lua_gettop(L)</code> returns the number of arguments received by the function. | |
| The first argument (if any) is at index 1 | |
| and its last argument is at index <code>lua_gettop(L)</code>. | |
| To return values to Lua, a C function just pushes them onto the stack, | |
| in direct order (the first result is pushed first), | |
| and returns the number of results. | |
| Any other value in the stack below the results will be properly | |
| discarded by Lua. | |
| Like a Lua function, a C function called by Lua can also return | |
| many results. | |
| <p> | |
| As an example, the following function receives a variable number | |
| of numerical arguments and returns their average and sum: | |
| <pre> | |
| static int foo (lua_State *L) { | |
| int n = lua_gettop(L); /* number of arguments */ | |
| lua_Number sum = 0; | |
| int i; | |
| for (i = 1; i <= n; i++) { | |
| if (!lua_isnumber(L, i)) { | |
| lua_pushstring(L, "incorrect argument"); | |
| lua_error(L); | |
| } | |
| sum += lua_tonumber(L, i); | |
| } | |
| lua_pushnumber(L, sum/n); /* first result */ | |
| lua_pushnumber(L, sum); /* second result */ | |
| return 2; /* number of results */ | |
| } | |
| </pre> | |
| <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>int lua_checkstack (lua_State *L, int extra);</pre> | |
| <p> | |
| Ensures that there are at least <code>extra</code> free stack slots in the stack. | |
| It returns false if it cannot grow the stack to that size. | |
| This function never shrinks the stack; | |
| if the stack is already larger than the new size, | |
| it is left unchanged. | |
| <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>void lua_close (lua_State *L);</pre> | |
| <p> | |
| Destroys all objects in the given Lua state | |
| (calling the corresponding garbage-collection metamethods, if any) | |
| and frees all dynamic memory used by this state. | |
| On several platforms, you may not need to call this function, | |
| because all resources are naturally released when the host program ends. | |
| On the other hand, long-running programs, | |
| such as a daemon or a web server, | |
| might need to release states as soon as they are not needed, | |
| to avoid growing too large. | |
| <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> | |
| <span class="apii">[-n, +1, <em>e</em>]</span> | |
| <pre>void lua_concat (lua_State *L, int n);</pre> | |
| <p> | |
| Concatenates the <code>n</code> values at the top of the stack, | |
| pops them, and leaves the result at the top. | |
| If <code>n</code> is 1, the result is the single value on the stack | |
| (that is, the function does nothing); | |
| if <code>n</code> is 0, the result is the empty string. | |
| Concatenation is performed following the usual semantics of Lua | |
| (see <a href="#2.5.4">§2.5.4</a>). | |
| <hr><h3><a name="lua_cpcall"><code>lua_cpcall</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>-</em>]</span> | |
| <pre>int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);</pre> | |
| <p> | |
| Calls the C function <code>func</code> in protected mode. | |
| <code>func</code> starts with only one element in its stack, | |
| a light userdata containing <code>ud</code>. | |
| In case of errors, | |
| <a href="#lua_cpcall"><code>lua_cpcall</code></a> returns the same error codes as <a href="#lua_pcall"><code>lua_pcall</code></a>, | |
| plus the error object on the top of the stack; | |
| otherwise, it returns zero, and does not change the stack. | |
| All values returned by <code>func</code> are discarded. | |
| <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> | |
| <p> | |
| Creates a new empty table and pushes it onto the stack. | |
| The new table has space pre-allocated | |
| for <code>narr</code> array elements and <code>nrec</code> non-array elements. | |
| This pre-allocation is useful when you know exactly how many elements | |
| the table will have. | |
| Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>. | |
| <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre> | |
| <p> | |
| Dumps a function as a binary chunk. | |
| Receives a Lua function on the top of the stack | |
| and produces a binary chunk that, | |
| if loaded again, | |
| results in a function equivalent to the one dumped. | |
| As it produces parts of the chunk, | |
| <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>) | |
| with the given <code>data</code> | |
| to write them. | |
| <p> | |
| The value returned is the error code returned by the last | |
| call to the writer; | |
| 0 means no errors. | |
| <p> | |
| This function does not pop the Lua function from the stack. | |
| <hr><h3><a name="lua_equal"><code>lua_equal</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_equal (lua_State *L, int index1, int index2);</pre> | |
| <p> | |
| Returns 1 if the two values in acceptable indices <code>index1</code> and | |
| <code>index2</code> are equal, | |
| following the semantics of the Lua <code>==</code> operator | |
| (that is, may call metamethods). | |
| Otherwise returns 0. | |
| Also returns 0 if any of the indices is non valid. | |
| <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>v</em>]</span> | |
| <pre>int lua_error (lua_State *L);</pre> | |
| <p> | |
| Generates a Lua error. | |
| The error message (which can actually be a Lua value of any type) | |
| must be on the stack top. | |
| This function does a long jump, | |
| and therefore never returns. | |
| (see <a href="#luaL_error"><code>luaL_error</code></a>). | |
| <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_gc (lua_State *L, int what, int data);</pre> | |
| <p> | |
| Controls the garbage collector. | |
| <p> | |
| This function performs several tasks, | |
| according to the value of the parameter <code>what</code>: | |
| <ul> | |
| <li><b><code>LUA_GCSTOP</code>:</b> | |
| stops the garbage collector. | |
| </li> | |
| <li><b><code>LUA_GCRESTART</code>:</b> | |
| restarts the garbage collector. | |
| </li> | |
| <li><b><code>LUA_GCCOLLECT</code>:</b> | |
| performs a full garbage-collection cycle. | |
| </li> | |
| <li><b><code>LUA_GCCOUNT</code>:</b> | |
| returns the current amount of memory (in Kbytes) in use by Lua. | |
| </li> | |
| <li><b><code>LUA_GCCOUNTB</code>:</b> | |
| returns the remainder of dividing the current amount of bytes of | |
| memory in use by Lua by 1024. | |
| </li> | |
| <li><b><code>LUA_GCSTEP</code>:</b> | |
| performs an incremental step of garbage collection. | |
| The step "size" is controlled by <code>data</code> | |
| (larger values mean more steps) in a non-specified way. | |
| If you want to control the step size | |
| you must experimentally tune the value of <code>data</code>. | |
| The function returns 1 if the step finished a | |
| garbage-collection cycle. | |
| </li> | |
| <li><b><code>LUA_GCSETPAUSE</code>:</b> | |
| sets <code>data</code> as the new value | |
| for the <em>pause</em> of the collector (see <a href="#2.10">§2.10</a>). | |
| The function returns the previous value of the pause. | |
| </li> | |
| <li><b><code>LUA_GCSETSTEPMUL</code>:</b> | |
| sets <code>data</code> as the new value for the <em>step multiplier</em> of | |
| the collector (see <a href="#2.10">§2.10</a>). | |
| The function returns the previous value of the step multiplier. | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> | |
| <p> | |
| Returns the memory-allocation function of a given state. | |
| If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the | |
| opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>. | |
| <hr><h3><a name="lua_getfenv"><code>lua_getfenv</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_getfenv (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the environment table of | |
| the value at the given index. | |
| <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_getfield (lua_State *L, int index, const char *k);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[k]</code>, | |
| where <code>t</code> is the value at the given valid index. | |
| As in Lua, this function may trigger a metamethod | |
| for the "index" event (see <a href="#2.8">§2.8</a>). | |
| <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_getglobal (lua_State *L, const char *name);</pre> | |
| <p> | |
| Pushes onto the stack the value of the global <code>name</code>. | |
| It is defined as a macro: | |
| <pre> | |
| #define lua_getglobal(L,s) lua_getfield(L, LUA_GLOBALSINDEX, s) | |
| </pre> | |
| <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>-</em>]</span> | |
| <pre>int lua_getmetatable (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the metatable of the value at the given | |
| acceptable index. | |
| If the index is not valid, | |
| or if the value does not have a metatable, | |
| the function returns 0 and pushes nothing on the stack. | |
| <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> | |
| <span class="apii">[-1, +1, <em>e</em>]</span> | |
| <pre>void lua_gettable (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[k]</code>, | |
| where <code>t</code> is the value at the given valid index | |
| and <code>k</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the key from the stack | |
| (putting the resulting value in its place). | |
| As in Lua, this function may trigger a metamethod | |
| for the "index" event (see <a href="#2.8">§2.8</a>). | |
| <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_gettop (lua_State *L);</pre> | |
| <p> | |
| Returns the index of the top element in the stack. | |
| Because indices start at 1, | |
| this result is equal to the number of elements in the stack | |
| (and so 0 means an empty stack). | |
| <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> | |
| <span class="apii">[-1, +1, <em>-</em>]</span> | |
| <pre>void lua_insert (lua_State *L, int index);</pre> | |
| <p> | |
| Moves the top element into the given valid index, | |
| shifting up the elements above this index to open space. | |
| Cannot be called with a pseudo-index, | |
| because a pseudo-index is not an actual stack position. | |
| <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3> | |
| <pre>typedef ptrdiff_t lua_Integer;</pre> | |
| <p> | |
| The type used by the Lua API to represent integral values. | |
| <p> | |
| By default it is a <code>ptrdiff_t</code>, | |
| which is usually the largest signed integral type the machine handles | |
| "comfortably". | |
| <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isboolean (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index has type boolean, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_iscfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a C function, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a function | |
| (either C or Lua), and 0 otherwise. | |
| <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_islightuserdata (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a light userdata, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isnil (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is <b>nil</b>, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isnone (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the given acceptable index is not valid | |
| (that is, it refers to an element outside the current stack), | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isnoneornil (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the given acceptable index is not valid | |
| (that is, it refers to an element outside the current stack) | |
| or if the value at this index is <b>nil</b>, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isnumber (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a number | |
| or a string convertible to a number, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isstring (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a string | |
| or a number (which is always convertible to a string), | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_istable (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a table, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isthread (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a thread, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_isuserdata (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given acceptable index is a userdata | |
| (either full or light), and 0 otherwise. | |
| <hr><h3><a name="lua_lessthan"><code>lua_lessthan</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_lessthan (lua_State *L, int index1, int index2);</pre> | |
| <p> | |
| Returns 1 if the value at acceptable index <code>index1</code> is smaller | |
| than the value at acceptable index <code>index2</code>, | |
| following the semantics of the Lua <code><</code> operator | |
| (that is, may call metamethods). | |
| Otherwise returns 0. | |
| Also returns 0 if any of the indices is non valid. | |
| <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>int lua_load (lua_State *L, | |
| lua_Reader reader, | |
| void *data, | |
| const char *chunkname);</pre> | |
| <p> | |
| Loads a Lua chunk. | |
| If there are no errors, | |
| <a href="#lua_load"><code>lua_load</code></a> pushes the compiled chunk as a Lua | |
| function on top of the stack. | |
| Otherwise, it pushes an error message. | |
| The return values of <a href="#lua_load"><code>lua_load</code></a> are: | |
| <ul> | |
| <li><b>0:</b> no errors;</li> | |
| <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>:</b> | |
| syntax error during pre-compilation;</li> | |
| <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b> | |
| memory allocation error.</li> | |
| </ul> | |
| <p> | |
| This function only loads a chunk; | |
| it does not run it. | |
| <p> | |
| <a href="#lua_load"><code>lua_load</code></a> automatically detects whether the chunk is text or binary, | |
| and loads it accordingly (see program <code>luac</code>). | |
| <p> | |
| The <a href="#lua_load"><code>lua_load</code></a> function uses a user-supplied <code>reader</code> function | |
| to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>). | |
| The <code>data</code> argument is an opaque value passed to the reader function. | |
| <p> | |
| The <code>chunkname</code> argument gives a name to the chunk, | |
| which is used for error messages and in debug information (see <a href="#3.8">§3.8</a>). | |
| <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> | |
| <p> | |
| Creates a new, independent state. | |
| Returns <code>NULL</code> if cannot create the state | |
| (due to lack of memory). | |
| The argument <code>f</code> is the allocator function; | |
| Lua does all memory allocation for this state through this function. | |
| The second argument, <code>ud</code>, is an opaque pointer that Lua | |
| simply passes to the allocator in every call. | |
| <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_newtable (lua_State *L);</pre> | |
| <p> | |
| Creates a new empty table and pushes it onto the stack. | |
| It is equivalent to <code>lua_createtable(L, 0, 0)</code>. | |
| <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>lua_State *lua_newthread (lua_State *L);</pre> | |
| <p> | |
| Creates a new thread, pushes it on the stack, | |
| and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread. | |
| The new state returned by this function shares with the original state | |
| all global objects (such as tables), | |
| but has an independent execution stack. | |
| <p> | |
| There is no explicit function to close or to destroy a thread. | |
| Threads are subject to garbage collection, | |
| like any Lua object. | |
| <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> | |
| <p> | |
| This function allocates a new block of memory with the given size, | |
| pushes onto the stack a new full userdata with the block address, | |
| and returns this address. | |
| <p> | |
| Userdata represent C values in Lua. | |
| A <em>full userdata</em> represents a block of memory. | |
| It is an object (like a table): | |
| you must create it, it can have its own metatable, | |
| and you can detect when it is being collected. | |
| A full userdata is only equal to itself (under raw equality). | |
| <p> | |
| When Lua collects a full userdata with a <code>gc</code> metamethod, | |
| Lua calls the metamethod and marks the userdata as finalized. | |
| When this userdata is collected again then | |
| Lua frees its corresponding memory. | |
| <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> | |
| <span class="apii">[-1, +(2|0), <em>e</em>]</span> | |
| <pre>int lua_next (lua_State *L, int index);</pre> | |
| <p> | |
| Pops a key from the stack, | |
| and pushes a key-value pair from the table at the given index | |
| (the "next" pair after the given key). | |
| If there are no more elements in the table, | |
| then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). | |
| <p> | |
| A typical traversal looks like this: | |
| <pre> | |
| /* table is in the stack at index 't' */ | |
| lua_pushnil(L); /* first key */ | |
| while (lua_next(L, t) != 0) { | |
| /* uses 'key' (at index -2) and 'value' (at index -1) */ | |
| printf("%s - %s\n", | |
| lua_typename(L, lua_type(L, -2)), | |
| lua_typename(L, lua_type(L, -1))); | |
| /* removes 'value'; keeps 'key' for next iteration */ | |
| lua_pop(L, 1); | |
| } | |
| </pre> | |
| <p> | |
| While traversing a table, | |
| do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, | |
| unless you know that the key is actually a string. | |
| Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> <em>changes</em> | |
| the value at the given index; | |
| this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. | |
| <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> | |
| <pre>typedef double lua_Number;</pre> | |
| <p> | |
| The type of numbers in Lua. | |
| By default, it is double, but that can be changed in <code>luaconf.h</code>. | |
| <p> | |
| Through the configuration file you can change | |
| Lua to operate with another type for numbers (e.g., float or long). | |
| <hr><h3><a name="lua_objlen"><code>lua_objlen</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>size_t lua_objlen (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the "length" of the value at the given acceptable index: | |
| for strings, this is the string length; | |
| for tables, this is the result of the length operator ('<code>#</code>'); | |
| for userdata, this is the size of the block of memory allocated | |
| for the userdata; | |
| for other values, it is 0. | |
| <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> | |
| <span class="apii">[-(nargs + 1), +(nresults|1), <em>-</em>]</span> | |
| <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);</pre> | |
| <p> | |
| Calls a function in protected mode. | |
| <p> | |
| Both <code>nargs</code> and <code>nresults</code> have the same meaning as | |
| in <a href="#lua_call"><code>lua_call</code></a>. | |
| If there are no errors during the call, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>. | |
| However, if there is any error, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> catches it, | |
| pushes a single value on the stack (the error message), | |
| and returns an error code. | |
| Like <a href="#lua_call"><code>lua_call</code></a>, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function | |
| and its arguments from the stack. | |
| <p> | |
| If <code>errfunc</code> is 0, | |
| then the error message returned on the stack | |
| is exactly the original error message. | |
| Otherwise, <code>errfunc</code> is the stack index of an | |
| <em>error handler function</em>. | |
| (In the current implementation, this index cannot be a pseudo-index.) | |
| In case of runtime errors, | |
| this function will be called with the error message | |
| and its return value will be the message returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>. | |
| <p> | |
| Typically, the error handler function is used to add more debug | |
| information to the error message, such as a stack traceback. | |
| Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>, | |
| since by then the stack has unwound. | |
| <p> | |
| The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns 0 in case of success | |
| or one of the following error codes | |
| (defined in <code>lua.h</code>): | |
| <ul> | |
| <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>:</b> | |
| a runtime error. | |
| </li> | |
| <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>:</b> | |
| memory allocation error. | |
| For such errors, Lua does not call the error handler function. | |
| </li> | |
| <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>:</b> | |
| error while running the error handler function. | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> | |
| <span class="apii">[-n, +0, <em>-</em>]</span> | |
| <pre>void lua_pop (lua_State *L, int n);</pre> | |
| <p> | |
| Pops <code>n</code> elements from the stack. | |
| <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushboolean (lua_State *L, int b);</pre> | |
| <p> | |
| Pushes a boolean value with value <code>b</code> onto the stack. | |
| <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> | |
| <span class="apii">[-n, +1, <em>m</em>]</span> | |
| <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> | |
| <p> | |
| Pushes a new C closure onto the stack. | |
| <p> | |
| When a C function is created, | |
| it is possible to associate some values with it, | |
| thus creating a C closure (see <a href="#3.4">§3.4</a>); | |
| these values are then accessible to the function whenever it is called. | |
| To associate values with a C function, | |
| first these values should be pushed onto the stack | |
| (when there are multiple values, the first value is pushed first). | |
| Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> | |
| is called to create and push the C function onto the stack, | |
| with the argument <code>n</code> telling how many values should be | |
| associated with the function. | |
| <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. | |
| <p> | |
| The maximum value for <code>n</code> is 255. | |
| <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> | |
| <p> | |
| Pushes a C function onto the stack. | |
| This function receives a pointer to a C function | |
| and pushes onto the stack a Lua value of type <code>function</code> that, | |
| when called, invokes the corresponding C function. | |
| <p> | |
| Any function to be registered in Lua must | |
| follow the correct protocol to receive its parameters | |
| and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). | |
| <p> | |
| <code>lua_pushcfunction</code> is defined as a macro: | |
| <pre> | |
| #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0) | |
| </pre> | |
| <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> | |
| <p> | |
| Pushes onto the stack a formatted string | |
| and returns a pointer to this string. | |
| It is similar to the C function <code>sprintf</code>, | |
| but has some important differences: | |
| <ul> | |
| <li> | |
| You do not have to allocate space for the result: | |
| the result is a Lua string and Lua takes care of memory allocation | |
| (and deallocation, through garbage collection). | |
| </li> | |
| <li> | |
| The conversion specifiers are quite restricted. | |
| There are no flags, widths, or precisions. | |
| The conversion specifiers can only be | |
| '<code>%%</code>' (inserts a '<code>%</code>' in the string), | |
| '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions), | |
| '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>), | |
| '<code>%p</code>' (inserts a pointer as a hexadecimal numeral), | |
| '<code>%d</code>' (inserts an <code>int</code>), and | |
| '<code>%c</code>' (inserts an <code>int</code> as a character). | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> | |
| <p> | |
| Pushes a number with value <code>n</code> onto the stack. | |
| <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> | |
| <p> | |
| Pushes a light userdata onto the stack. | |
| <p> | |
| Userdata represent C values in Lua. | |
| A <em>light userdata</em> represents a pointer. | |
| It is a value (like a number): | |
| you do not create it, it has no individual metatable, | |
| and it is not collected (as it was never created). | |
| A light userdata is equal to "any" | |
| light userdata with the same C address. | |
| <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_pushliteral (lua_State *L, const char *s);</pre> | |
| <p> | |
| This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>, | |
| but can be used only when <code>s</code> is a literal string. | |
| In these cases, it automatically provides the string length. | |
| <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_pushlstring (lua_State *L, const char *s, size_t len);</pre> | |
| <p> | |
| Pushes the string pointed to by <code>s</code> with size <code>len</code> | |
| onto the stack. | |
| Lua makes (or reuses) an internal copy of the given string, | |
| so the memory at <code>s</code> can be freed or reused immediately after | |
| the function returns. | |
| The string can contain embedded zeros. | |
| <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushnil (lua_State *L);</pre> | |
| <p> | |
| Pushes a nil value onto the stack. | |
| <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> | |
| <p> | |
| Pushes a number with value <code>n</code> onto the stack. | |
| <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void lua_pushstring (lua_State *L, const char *s);</pre> | |
| <p> | |
| Pushes the zero-terminated string pointed to by <code>s</code> | |
| onto the stack. | |
| Lua makes (or reuses) an internal copy of the given string, | |
| so the memory at <code>s</code> can be freed or reused immediately after | |
| the function returns. | |
| The string cannot contain embedded zeros; | |
| it is assumed to end at the first zero. | |
| <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>int lua_pushthread (lua_State *L);</pre> | |
| <p> | |
| Pushes the thread represented by <code>L</code> onto the stack. | |
| Returns 1 if this thread is the main thread of its state. | |
| <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_pushvalue (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes a copy of the element at the given valid index | |
| onto the stack. | |
| <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>const char *lua_pushvfstring (lua_State *L, | |
| const char *fmt, | |
| va_list argp);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> | |
| instead of a variable number of arguments. | |
| <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> | |
| <p> | |
| Returns 1 if the two values in acceptable indices <code>index1</code> and | |
| <code>index2</code> are primitively equal | |
| (that is, without calling metamethods). | |
| Otherwise returns 0. | |
| Also returns 0 if any of the indices are non valid. | |
| <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> | |
| <span class="apii">[-1, +1, <em>-</em>]</span> | |
| <pre>void lua_rawget (lua_State *L, int index);</pre> | |
| <p> | |
| Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access | |
| (i.e., without metamethods). | |
| <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void lua_rawgeti (lua_State *L, int index, int n);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[n]</code>, | |
| where <code>t</code> is the value at the given valid index. | |
| The access is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p> | |
| <span class="apii">[-2, +0, <em>m</em>]</span> | |
| <pre>void lua_rawset (lua_State *L, int index);</pre> | |
| <p> | |
| Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment | |
| (i.e., without metamethods). | |
| <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>m</em>]</span> | |
| <pre>void lua_rawseti (lua_State *L, int index, int n);</pre> | |
| <p> | |
| Does the equivalent of <code>t[n] = v</code>, | |
| where <code>t</code> is the value at the given valid index | |
| and <code>v</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the value from the stack. | |
| The assignment is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> | |
| <pre>typedef const char * (*lua_Reader) (lua_State *L, | |
| void *data, | |
| size_t *size);</pre> | |
| <p> | |
| The reader function used by <a href="#lua_load"><code>lua_load</code></a>. | |
| Every time it needs another piece of the chunk, | |
| <a href="#lua_load"><code>lua_load</code></a> calls the reader, | |
| passing along its <code>data</code> parameter. | |
| The reader must return a pointer to a block of memory | |
| with a new piece of the chunk | |
| and set <code>size</code> to the block size. | |
| The block must exist until the reader function is called again. | |
| To signal the end of the chunk, | |
| the reader must return <code>NULL</code> or set <code>size</code> to zero. | |
| The reader function may return pieces of any size greater than zero. | |
| <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>void lua_register (lua_State *L, | |
| const char *name, | |
| lua_CFunction f);</pre> | |
| <p> | |
| Sets the C function <code>f</code> as the new value of global <code>name</code>. | |
| It is defined as a macro: | |
| <pre> | |
| #define lua_register(L,n,f) \ | |
| (lua_pushcfunction(L, f), lua_setglobal(L, n)) | |
| </pre> | |
| <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>-</em>]</span> | |
| <pre>void lua_remove (lua_State *L, int index);</pre> | |
| <p> | |
| Removes the element at the given valid index, | |
| shifting down the elements above this index to fill the gap. | |
| Cannot be called with a pseudo-index, | |
| because a pseudo-index is not an actual stack position. | |
| <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>-</em>]</span> | |
| <pre>void lua_replace (lua_State *L, int index);</pre> | |
| <p> | |
| Moves the top element into the given position (and pops it), | |
| without shifting any element | |
| (therefore replacing the value at the given position). | |
| <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>-</em>]</span> | |
| <pre>int lua_resume (lua_State *L, int narg);</pre> | |
| <p> | |
| Starts and resumes a coroutine in a given thread. | |
| <p> | |
| To start a coroutine, you first create a new thread | |
| (see <a href="#lua_newthread"><code>lua_newthread</code></a>); | |
| then you push onto its stack the main function plus any arguments; | |
| then you call <a href="#lua_resume"><code>lua_resume</code></a>, | |
| with <code>narg</code> being the number of arguments. | |
| This call returns when the coroutine suspends or finishes its execution. | |
| When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>, | |
| or all values returned by the body function. | |
| <a href="#lua_resume"><code>lua_resume</code></a> returns | |
| <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields, | |
| 0 if the coroutine finishes its execution | |
| without errors, | |
| or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>). | |
| In case of errors, | |
| the stack is not unwound, | |
| so you can use the debug API over it. | |
| The error message is on the top of the stack. | |
| To restart a coroutine, you put on its stack only the values to | |
| be passed as results from <code>yield</code>, | |
| and then call <a href="#lua_resume"><code>lua_resume</code></a>. | |
| <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> | |
| <p> | |
| Changes the allocator function of a given state to <code>f</code> | |
| with user data <code>ud</code>. | |
| <hr><h3><a name="lua_setfenv"><code>lua_setfenv</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>-</em>]</span> | |
| <pre>int lua_setfenv (lua_State *L, int index);</pre> | |
| <p> | |
| Pops a table from the stack and sets it as | |
| the new environment for the value at the given index. | |
| If the value at the given index is | |
| neither a function nor a thread nor a userdata, | |
| <a href="#lua_setfenv"><code>lua_setfenv</code></a> returns 0. | |
| Otherwise it returns 1. | |
| <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> | |
| <p> | |
| Does the equivalent to <code>t[k] = v</code>, | |
| where <code>t</code> is the value at the given valid index | |
| and <code>v</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the value from the stack. | |
| As in Lua, this function may trigger a metamethod | |
| for the "newindex" event (see <a href="#2.8">§2.8</a>). | |
| <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_setglobal (lua_State *L, const char *name);</pre> | |
| <p> | |
| Pops a value from the stack and | |
| sets it as the new value of global <code>name</code>. | |
| It is defined as a macro: | |
| <pre> | |
| #define lua_setglobal(L,s) lua_setfield(L, LUA_GLOBALSINDEX, s) | |
| </pre> | |
| <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>-</em>]</span> | |
| <pre>int lua_setmetatable (lua_State *L, int index);</pre> | |
| <p> | |
| Pops a table from the stack and | |
| sets it as the new metatable for the value at the given | |
| acceptable index. | |
| <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> | |
| <span class="apii">[-2, +0, <em>e</em>]</span> | |
| <pre>void lua_settable (lua_State *L, int index);</pre> | |
| <p> | |
| Does the equivalent to <code>t[k] = v</code>, | |
| where <code>t</code> is the value at the given valid index, | |
| <code>v</code> is the value at the top of the stack, | |
| and <code>k</code> is the value just below the top. | |
| <p> | |
| This function pops both the key and the value from the stack. | |
| As in Lua, this function may trigger a metamethod | |
| for the "newindex" event (see <a href="#2.8">§2.8</a>). | |
| <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>-</em>]</span> | |
| <pre>void lua_settop (lua_State *L, int index);</pre> | |
| <p> | |
| Accepts any acceptable index, or 0, | |
| and sets the stack top to this index. | |
| If the new top is larger than the old one, | |
| then the new elements are filled with <b>nil</b>. | |
| If <code>index</code> is 0, then all stack elements are removed. | |
| <hr><h3><a name="lua_State"><code>lua_State</code></a></h3> | |
| <pre>typedef struct lua_State lua_State;</pre> | |
| <p> | |
| Opaque structure that keeps the whole state of a Lua interpreter. | |
| The Lua library is fully reentrant: | |
| it has no global variables. | |
| All information about a state is kept in this structure. | |
| <p> | |
| A pointer to this state must be passed as the first argument to | |
| every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, | |
| which creates a Lua state from scratch. | |
| <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_status (lua_State *L);</pre> | |
| <p> | |
| Returns the status of the thread <code>L</code>. | |
| <p> | |
| The status can be 0 for a normal thread, | |
| an error code if the thread finished its execution with an error, | |
| or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. | |
| <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_toboolean (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the Lua value at the given acceptable index to a C boolean | |
| value (0 or 1). | |
| Like all tests in Lua, | |
| <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns 1 for any Lua value | |
| different from <b>false</b> and <b>nil</b>; | |
| otherwise it returns 0. | |
| It also returns 0 when called with a non-valid index. | |
| (If you want to accept only actual boolean values, | |
| use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) | |
| <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Converts a value at the given acceptable index to a C function. | |
| That value must be a C function; | |
| otherwise, returns <code>NULL</code>. | |
| <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the Lua value at the given acceptable index | |
| to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| The Lua value must be a number or a string convertible to a number | |
| (see <a href="#2.2.1">§2.2.1</a>); | |
| otherwise, <a href="#lua_tointeger"><code>lua_tointeger</code></a> returns 0. | |
| <p> | |
| If the number is not an integer, | |
| it is truncated in some non-specified way. | |
| <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> | |
| <p> | |
| Converts the Lua value at the given acceptable index to a C string. | |
| If <code>len</code> is not <code>NULL</code>, | |
| it also sets <code>*len</code> with the string length. | |
| The Lua value must be a string or a number; | |
| otherwise, the function returns <code>NULL</code>. | |
| If the value is a number, | |
| then <a href="#lua_tolstring"><code>lua_tolstring</code></a> also | |
| <em>changes the actual value in the stack to a string</em>. | |
| (This change confuses <a href="#lua_next"><code>lua_next</code></a> | |
| when <a href="#lua_tolstring"><code>lua_tolstring</code></a> is applied to keys during a table traversal.) | |
| <p> | |
| <a href="#lua_tolstring"><code>lua_tolstring</code></a> returns a fully aligned pointer | |
| to a string inside the Lua state. | |
| This string always has a zero ('<code>\0</code>') | |
| after its last character (as in C), | |
| but can contain other zeros in its body. | |
| Because Lua has garbage collection, | |
| there is no guarantee that the pointer returned by <a href="#lua_tolstring"><code>lua_tolstring</code></a> | |
| will be valid after the corresponding value is removed from the stack. | |
| <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the Lua value at the given acceptable index | |
| to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>). | |
| The Lua value must be a number or a string convertible to a number | |
| (see <a href="#2.2.1">§2.2.1</a>); | |
| otherwise, <a href="#lua_tonumber"><code>lua_tonumber</code></a> returns 0. | |
| <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>const void *lua_topointer (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the value at the given acceptable index to a generic | |
| C pointer (<code>void*</code>). | |
| The value can be a userdata, a table, a thread, or a function; | |
| otherwise, <a href="#lua_topointer"><code>lua_topointer</code></a> returns <code>NULL</code>. | |
| Different objects will give different pointers. | |
| There is no way to convert the pointer back to its original value. | |
| <p> | |
| Typically this function is used only for debug information. | |
| <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>const char *lua_tostring (lua_State *L, int index);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_State *lua_tothread (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the value at the given acceptable index to a Lua thread | |
| (represented as <code>lua_State*</code>). | |
| This value must be a thread; | |
| otherwise, the function returns <code>NULL</code>. | |
| <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>void *lua_touserdata (lua_State *L, int index);</pre> | |
| <p> | |
| If the value at the given acceptable index is a full userdata, | |
| returns its block address. | |
| If the value is a light userdata, | |
| returns its pointer. | |
| Otherwise, returns <code>NULL</code>. | |
| <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_type (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the type of the value in the given acceptable index, | |
| or <code>LUA_TNONE</code> for a non-valid index | |
| (that is, an index to an "empty" stack position). | |
| The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants | |
| defined in <code>lua.h</code>: | |
| <code>LUA_TNIL</code>, | |
| <code>LUA_TNUMBER</code>, | |
| <code>LUA_TBOOLEAN</code>, | |
| <code>LUA_TSTRING</code>, | |
| <code>LUA_TTABLE</code>, | |
| <code>LUA_TFUNCTION</code>, | |
| <code>LUA_TUSERDATA</code>, | |
| <code>LUA_TTHREAD</code>, | |
| and | |
| <code>LUA_TLIGHTUSERDATA</code>. | |
| <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>const char *lua_typename (lua_State *L, int tp);</pre> | |
| <p> | |
| Returns the name of the type encoded by the value <code>tp</code>, | |
| which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. | |
| <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> | |
| <pre>typedef int (*lua_Writer) (lua_State *L, | |
| const void* p, | |
| size_t sz, | |
| void* ud);</pre> | |
| <p> | |
| The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. | |
| Every time it produces another piece of chunk, | |
| <a href="#lua_dump"><code>lua_dump</code></a> calls the writer, | |
| passing along the buffer to be written (<code>p</code>), | |
| its size (<code>sz</code>), | |
| and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. | |
| <p> | |
| The writer returns an error code: | |
| 0 means no errors; | |
| any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from | |
| calling the writer again. | |
| <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>-</em>]</span> | |
| <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> | |
| <p> | |
| Exchange values between different threads of the <em>same</em> global state. | |
| <p> | |
| This function pops <code>n</code> values from the stack <code>from</code>, | |
| and pushes them onto the stack <code>to</code>. | |
| <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>-</em>]</span> | |
| <pre>int lua_yield (lua_State *L, int nresults);</pre> | |
| <p> | |
| Yields a coroutine. | |
| <p> | |
| This function should only be called as the | |
| return expression of a C function, as follows: | |
| <pre> | |
| return lua_yield (L, nresults); | |
| </pre><p> | |
| When a C function calls <a href="#lua_yield"><code>lua_yield</code></a> in that way, | |
| the running coroutine suspends its execution, | |
| and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns. | |
| The parameter <code>nresults</code> is the number of values from the stack | |
| that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. | |
| <h2>3.8 - <a name="3.8">The Debug Interface</a></h2> | |
| <p> | |
| Lua has no built-in debugging facilities. | |
| Instead, it offers a special interface | |
| by means of functions and <em>hooks</em>. | |
| This interface allows the construction of different | |
| kinds of debuggers, profilers, and other tools | |
| that need "inside information" from the interpreter. | |
| <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3> | |
| <pre>typedef struct lua_Debug { | |
| int event; | |
| const char *name; /* (n) */ | |
| const char *namewhat; /* (n) */ | |
| const char *what; /* (S) */ | |
| const char *source; /* (S) */ | |
| int currentline; /* (l) */ | |
| int nups; /* (u) number of upvalues */ | |
| int linedefined; /* (S) */ | |
| int lastlinedefined; /* (S) */ | |
| char short_src[LUA_IDSIZE]; /* (S) */ | |
| /* private part */ | |
| <em>other fields</em> | |
| } lua_Debug;</pre> | |
| <p> | |
| A structure used to carry different pieces of | |
| information about an active function. | |
| <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part | |
| of this structure, for later use. | |
| To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information, | |
| call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. | |
| <p> | |
| The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning: | |
| <ul> | |
| <li><b><code>source</code>:</b> | |
| If the function was defined in a string, | |
| then <code>source</code> is that string. | |
| If the function was defined in a file, | |
| then <code>source</code> starts with a '<code>@</code>' followed by the file name. | |
| </li> | |
| <li><b><code>short_src</code>:</b> | |
| a "printable" version of <code>source</code>, to be used in error messages. | |
| </li> | |
| <li><b><code>linedefined</code>:</b> | |
| the line number where the definition of the function starts. | |
| </li> | |
| <li><b><code>lastlinedefined</code>:</b> | |
| the line number where the definition of the function ends. | |
| </li> | |
| <li><b><code>what</code>:</b> | |
| the string <code>"Lua"</code> if the function is a Lua function, | |
| <code>"C"</code> if it is a C function, | |
| <code>"main"</code> if it is the main part of a chunk, | |
| and <code>"tail"</code> if it was a function that did a tail call. | |
| In the latter case, | |
| Lua has no other information about the function. | |
| </li> | |
| <li><b><code>currentline</code>:</b> | |
| the current line where the given function is executing. | |
| When no line information is available, | |
| <code>currentline</code> is set to -1. | |
| </li> | |
| <li><b><code>name</code>:</b> | |
| a reasonable name for the given function. | |
| Because functions in Lua are first-class values, | |
| they do not have a fixed name: | |
| some functions can be the value of multiple global variables, | |
| while others can be stored only in a table field. | |
| The <code>lua_getinfo</code> function checks how the function was | |
| called to find a suitable name. | |
| If it cannot find a name, | |
| then <code>name</code> is set to <code>NULL</code>. | |
| </li> | |
| <li><b><code>namewhat</code>:</b> | |
| explains the <code>name</code> field. | |
| The value of <code>namewhat</code> can be | |
| <code>"global"</code>, <code>"local"</code>, <code>"method"</code>, | |
| <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), | |
| according to how the function was called. | |
| (Lua uses the empty string when no other option seems to apply.) | |
| </li> | |
| <li><b><code>nups</code>:</b> | |
| the number of upvalues of the function. | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_Hook lua_gethook (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook function. | |
| <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_gethookcount (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook count. | |
| <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_gethookmask (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook mask. | |
| <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> | |
| <span class="apii">[-(0|1), +(0|1|2), <em>m</em>]</span> | |
| <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> | |
| <p> | |
| Returns information about a specific function or function invocation. | |
| <p> | |
| To get information about a function invocation, | |
| the parameter <code>ar</code> must be a valid activation record that was | |
| filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or | |
| given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). | |
| <p> | |
| To get information about a function you push it onto the stack | |
| and start the <code>what</code> string with the character '<code>></code>'. | |
| (In that case, | |
| <code>lua_getinfo</code> pops the function in the top of the stack.) | |
| For instance, to know in which line a function <code>f</code> was defined, | |
| you can write the following code: | |
| <pre> | |
| lua_Debug ar; | |
| lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* get global 'f' */ | |
| lua_getinfo(L, ">S", &ar); | |
| printf("%d\n", ar.linedefined); | |
| </pre> | |
| <p> | |
| Each character in the string <code>what</code> | |
| selects some fields of the structure <code>ar</code> to be filled or | |
| a value to be pushed on the stack: | |
| <ul> | |
| <li><b>'<code>n</code>':</b> fills in the field <code>name</code> and <code>namewhat</code>; | |
| </li> | |
| <li><b>'<code>S</code>':</b> | |
| fills in the fields <code>source</code>, <code>short_src</code>, | |
| <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>; | |
| </li> | |
| <li><b>'<code>l</code>':</b> fills in the field <code>currentline</code>; | |
| </li> | |
| <li><b>'<code>u</code>':</b> fills in the field <code>nups</code>; | |
| </li> | |
| <li><b>'<code>f</code>':</b> | |
| pushes onto the stack the function that is | |
| running at the given level; | |
| </li> | |
| <li><b>'<code>L</code>':</b> | |
| pushes onto the stack a table whose indices are the | |
| numbers of the lines that are valid on the function. | |
| (A <em>valid line</em> is a line with some associated code, | |
| that is, a line where you can put a break point. | |
| Non-valid lines include empty lines and comments.) | |
| </li> | |
| </ul> | |
| <p> | |
| This function returns 0 on error | |
| (for instance, an invalid option in <code>what</code>). | |
| <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>-</em>]</span> | |
| <pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre> | |
| <p> | |
| Gets information about a local variable of a given activation record. | |
| The parameter <code>ar</code> must be a valid activation record that was | |
| filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or | |
| given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). | |
| The index <code>n</code> selects which local variable to inspect | |
| (1 is the first parameter or active local variable, and so on, | |
| until the last active local variable). | |
| <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack | |
| and returns its name. | |
| <p> | |
| Variable names starting with '<code>(</code>' (open parentheses) | |
| represent internal variables | |
| (loop control variables, temporaries, and C function locals). | |
| <p> | |
| Returns <code>NULL</code> (and pushes nothing) | |
| when the index is greater than | |
| the number of active local variables. | |
| <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> | |
| <p> | |
| Get information about the interpreter runtime stack. | |
| <p> | |
| This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with | |
| an identification of the <em>activation record</em> | |
| of the function executing at a given level. | |
| Level 0 is the current running function, | |
| whereas level <em>n+1</em> is the function that has called level <em>n</em>. | |
| When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; | |
| when called with a level greater than the stack depth, | |
| it returns 0. | |
| <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>-</em>]</span> | |
| <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> | |
| <p> | |
| Gets information about a closure's upvalue. | |
| (For Lua functions, | |
| upvalues are the external local variables that the function uses, | |
| and that are consequently included in its closure.) | |
| <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue, | |
| pushes the upvalue's value onto the stack, | |
| and returns its name. | |
| <code>funcindex</code> points to the closure in the stack. | |
| (Upvalues have no particular order, | |
| as they are active through the whole function. | |
| So, they are numbered in an arbitrary order.) | |
| <p> | |
| Returns <code>NULL</code> (and pushes nothing) | |
| when the index is greater than the number of upvalues. | |
| For C functions, this function uses the empty string <code>""</code> | |
| as a name for all upvalues. | |
| <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3> | |
| <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre> | |
| <p> | |
| Type for debugging hook functions. | |
| <p> | |
| Whenever a hook is called, its <code>ar</code> argument has its field | |
| <code>event</code> set to the specific event that triggered the hook. | |
| Lua identifies these events with the following constants: | |
| <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>, | |
| <a name="pdf-LUA_HOOKTAILRET"><code>LUA_HOOKTAILRET</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>, | |
| and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>. | |
| Moreover, for line events, the field <code>currentline</code> is also set. | |
| To get the value of any other field in <code>ar</code>, | |
| the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. | |
| For return events, <code>event</code> can be <code>LUA_HOOKRET</code>, | |
| the normal value, or <code>LUA_HOOKTAILRET</code>. | |
| In the latter case, Lua is simulating a return from | |
| a function that did a tail call; | |
| in this case, it is useless to call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. | |
| <p> | |
| While Lua is running a hook, it disables other calls to hooks. | |
| Therefore, if a hook calls back Lua to execute a function or a chunk, | |
| this execution occurs without any calls to hooks. | |
| <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre> | |
| <p> | |
| Sets the debugging hook function. | |
| <p> | |
| Argument <code>f</code> is the hook function. | |
| <code>mask</code> specifies on which events the hook will be called: | |
| it is formed by a bitwise or of the constants | |
| <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>, | |
| <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>, | |
| <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>, | |
| and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>. | |
| The <code>count</code> argument is only meaningful when the mask | |
| includes <code>LUA_MASKCOUNT</code>. | |
| For each event, the hook is called as explained below: | |
| <ul> | |
| <li><b>The call hook:</b> is called when the interpreter calls a function. | |
| The hook is called just after Lua enters the new function, | |
| before the function gets its arguments. | |
| </li> | |
| <li><b>The return hook:</b> is called when the interpreter returns from a function. | |
| The hook is called just before Lua leaves the function. | |
| You have no access to the values to be returned by the function. | |
| </li> | |
| <li><b>The line hook:</b> is called when the interpreter is about to | |
| start the execution of a new line of code, | |
| or when it jumps back in the code (even to the same line). | |
| (This event only happens while Lua is executing a Lua function.) | |
| </li> | |
| <li><b>The count hook:</b> is called after the interpreter executes every | |
| <code>count</code> instructions. | |
| (This event only happens while Lua is executing a Lua function.) | |
| </li> | |
| </ul> | |
| <p> | |
| A hook is disabled by setting <code>mask</code> to zero. | |
| <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> | |
| <span class="apii">[-(0|1), +0, <em>-</em>]</span> | |
| <pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre> | |
| <p> | |
| Sets the value of a local variable of a given activation record. | |
| Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a> | |
| (see <a href="#lua_getlocal"><code>lua_getlocal</code></a>). | |
| <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack | |
| to the variable and returns its name. | |
| It also pops the value from the stack. | |
| <p> | |
| Returns <code>NULL</code> (and pops nothing) | |
| when the index is greater than | |
| the number of active local variables. | |
| <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> | |
| <span class="apii">[-(0|1), +0, <em>-</em>]</span> | |
| <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> | |
| <p> | |
| Sets the value of a closure's upvalue. | |
| It assigns the value at the top of the stack | |
| to the upvalue and returns its name. | |
| It also pops the value from the stack. | |
| Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> | |
| (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>). | |
| <p> | |
| Returns <code>NULL</code> (and pops nothing) | |
| when the index is greater than the number of upvalues. | |
| <h1>4 - <a name="4">The Auxiliary Library</a></h1> | |
| <p> | |
| The <em>auxiliary library</em> provides several convenient functions | |
| to interface C with Lua. | |
| While the basic API provides the primitive functions for all | |
| interactions between C and Lua, | |
| the auxiliary library provides higher-level functions for some | |
| common tasks. | |
| <p> | |
| All functions from the auxiliary library | |
| are defined in header file <code>lauxlib.h</code> and | |
| have a prefix <code>luaL_</code>. | |
| <p> | |
| All functions in the auxiliary library are built on | |
| top of the basic API, | |
| and so they provide nothing that cannot be done with this API. | |
| <p> | |
| Several functions in the auxiliary library are used to | |
| check C function arguments. | |
| Their names are always <code>luaL_check*</code> or <code>luaL_opt*</code>. | |
| All of these functions throw an error if the check is not satisfied. | |
| Because the error message is formatted for arguments | |
| (e.g., "<code>bad argument #1</code>"), | |
| you should not use these functions for other stack values. | |
| <h2>4.1 - <a name="4.1">Functions and Types</a></h2> | |
| <p> | |
| Here we list all functions and types from the auxiliary library | |
| in alphabetical order. | |
| <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> | |
| <p> | |
| Adds the character <code>c</code> to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> | |
| <p> | |
| Adds the string pointed to by <code>s</code> with length <code>l</code> to | |
| the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| The string may contain embedded zeros. | |
| <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> | |
| <p> | |
| Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) | |
| a string of length <code>n</code> previously copied to the | |
| buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). | |
| <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> | |
| <p> | |
| Adds the zero-terminated string pointed to by <code>s</code> | |
| to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| The string may not contain embedded zeros. | |
| <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>m</em>]</span> | |
| <pre>void luaL_addvalue (luaL_Buffer *B);</pre> | |
| <p> | |
| Adds the value at the top of the stack | |
| to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| Pops the value. | |
| <p> | |
| This is the only function on string buffers that can (and must) | |
| be called with an extra element on the stack, | |
| which is the value to be added to the buffer. | |
| <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_argcheck (lua_State *L, | |
| int cond, | |
| int narg, | |
| const char *extramsg);</pre> | |
| <p> | |
| Checks whether <code>cond</code> is true. | |
| If not, raises an error with the following message, | |
| where <code>func</code> is retrieved from the call stack: | |
| <pre> | |
| bad argument #<narg> to <func> (<extramsg>) | |
| </pre> | |
| <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_argerror (lua_State *L, int narg, const char *extramsg);</pre> | |
| <p> | |
| Raises an error with the following message, | |
| where <code>func</code> is retrieved from the call stack: | |
| <pre> | |
| bad argument #<narg> to <func> (<extramsg>) | |
| </pre> | |
| <p> | |
| This function never returns, | |
| but it is an idiom to use it in C functions | |
| as <code>return luaL_argerror(<em>args</em>)</code>. | |
| <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3> | |
| <pre>typedef struct luaL_Buffer luaL_Buffer;</pre> | |
| <p> | |
| Type for a <em>string buffer</em>. | |
| <p> | |
| A string buffer allows C code to build Lua strings piecemeal. | |
| Its pattern of use is as follows: | |
| <ul> | |
| <li>First you declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> | |
| <li>Then you initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> | |
| <li> | |
| Then you add string pieces to the buffer calling any of | |
| the <code>luaL_add*</code> functions. | |
| </li> | |
| <li> | |
| You finish by calling <code>luaL_pushresult(&b)</code>. | |
| This call leaves the final string on the top of the stack. | |
| </li> | |
| </ul> | |
| <p> | |
| During its normal operation, | |
| a string buffer uses a variable number of stack slots. | |
| So, while using a buffer, you cannot assume that you know where | |
| the top of the stack is. | |
| You can use the stack between successive calls to buffer operations | |
| as long as that use is balanced; | |
| that is, | |
| when you call a buffer operation, | |
| the stack is at the same level | |
| it was immediately after the previous buffer operation. | |
| (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) | |
| After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its | |
| level when the buffer was initialized, | |
| plus the final string on its top. | |
| <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> | |
| <p> | |
| Initializes a buffer <code>B</code>. | |
| This function does not allocate any space; | |
| the buffer must be declared as a variable | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>e</em>]</span> | |
| <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> | |
| <p> | |
| Calls a metamethod. | |
| <p> | |
| If the object at index <code>obj</code> has a metatable and this | |
| metatable has a field <code>e</code>, | |
| this function calls this field and passes the object as its only argument. | |
| In this case this function returns 1 and pushes onto the | |
| stack the value returned by the call. | |
| If there is no metatable or no metamethod, | |
| this function returns 0 (without pushing any value on the stack). | |
| <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checkany (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function has an argument | |
| of any type (including <b>nil</b>) at position <code>narg</code>. | |
| <hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_checkint (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a number | |
| and returns this number cast to an <code>int</code>. | |
| <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Integer luaL_checkinteger (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a number | |
| and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| <hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>long luaL_checklong (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a number | |
| and returns this number cast to a <code>long</code>. | |
| <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_checklstring (lua_State *L, int narg, size_t *l);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a string | |
| and returns this string; | |
| if <code>l</code> is not <code>NULL</code> fills <code>*l</code> | |
| with the string's length. | |
| <p> | |
| This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, | |
| so all conversions and caveats of that function apply here. | |
| <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Number luaL_checknumber (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a number | |
| and returns this number. | |
| <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_checkoption (lua_State *L, | |
| int narg, | |
| const char *def, | |
| const char *const lst[]);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a string and | |
| searches for this string in the array <code>lst</code> | |
| (which must be NULL-terminated). | |
| Returns the index in the array where the string was found. | |
| Raises an error if the argument is not a string or | |
| if the string cannot be found. | |
| <p> | |
| If <code>def</code> is not <code>NULL</code>, | |
| the function uses <code>def</code> as a default value when | |
| there is no argument <code>narg</code> or if this argument is <b>nil</b>. | |
| <p> | |
| This is a useful function for mapping strings to C enums. | |
| (The usual convention in Lua libraries is | |
| to use strings instead of numbers to select options.) | |
| <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> | |
| <p> | |
| Grows the stack size to <code>top + sz</code> elements, | |
| raising an error if the stack cannot grow to that size. | |
| <code>msg</code> is an additional text to go into the error message. | |
| <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_checkstring (lua_State *L, int narg);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a string | |
| and returns this string. | |
| <p> | |
| This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, | |
| so all conversions and caveats of that function apply here. | |
| <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checktype (lua_State *L, int narg, int t);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> has type <code>t</code>. | |
| See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. | |
| <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void *luaL_checkudata (lua_State *L, int narg, const char *tname);</pre> | |
| <p> | |
| Checks whether the function argument <code>narg</code> is a userdata | |
| of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). | |
| <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> | |
| <span class="apii">[-0, +?, <em>m</em>]</span> | |
| <pre>int luaL_dofile (lua_State *L, const char *filename);</pre> | |
| <p> | |
| Loads and runs the given file. | |
| It is defined as the following macro: | |
| <pre> | |
| (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) | |
| </pre><p> | |
| It returns 0 if there are no errors | |
| or 1 in case of errors. | |
| <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> | |
| <span class="apii">[-0, +?, <em>m</em>]</span> | |
| <pre>int luaL_dostring (lua_State *L, const char *str);</pre> | |
| <p> | |
| Loads and runs the given string. | |
| It is defined as the following macro: | |
| <pre> | |
| (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) | |
| </pre><p> | |
| It returns 0 if there are no errors | |
| or 1 in case of errors. | |
| <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> | |
| <p> | |
| Raises an error. | |
| The error message format is given by <code>fmt</code> | |
| plus any extra arguments, | |
| following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. | |
| It also adds at the beginning of the message the file name and | |
| the line number where the error occurred, | |
| if this information is available. | |
| <p> | |
| This function never returns, | |
| but it is an idiom to use it in C functions | |
| as <code>return luaL_error(<em>args</em>)</code>. | |
| <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>m</em>]</span> | |
| <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> | |
| <p> | |
| Pushes onto the stack the field <code>e</code> from the metatable | |
| of the object at index <code>obj</code>. | |
| If the object does not have a metatable, | |
| or if the metatable does not have this field, | |
| returns 0 and pushes nothing. | |
| <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>-</em>]</span> | |
| <pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre> | |
| <p> | |
| Pushes onto the stack the metatable associated with name <code>tname</code> | |
| in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). | |
| <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>const char *luaL_gsub (lua_State *L, | |
| const char *s, | |
| const char *p, | |
| const char *r);</pre> | |
| <p> | |
| Creates a copy of string <code>s</code> by replacing | |
| any occurrence of the string <code>p</code> | |
| with the string <code>r</code>. | |
| Pushes the resulting string on the stack and returns it. | |
| <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>int luaL_loadbuffer (lua_State *L, | |
| const char *buff, | |
| size_t sz, | |
| const char *name);</pre> | |
| <p> | |
| Loads a buffer as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the | |
| buffer pointed to by <code>buff</code> with size <code>sz</code>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. | |
| <code>name</code> is the chunk name, | |
| used for debug information and error messages. | |
| <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> | |
| <p> | |
| Loads a file as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file | |
| named <code>filename</code>. | |
| If <code>filename</code> is <code>NULL</code>, | |
| then it loads from the standard input. | |
| The first line in the file is ignored if it starts with a <code>#</code>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, | |
| but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> | |
| if it cannot open/read the file. | |
| <p> | |
| As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; | |
| it does not run it. | |
| <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>int luaL_loadstring (lua_State *L, const char *s);</pre> | |
| <p> | |
| Loads a string as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in | |
| the zero-terminated string <code>s</code>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. | |
| <p> | |
| Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; | |
| it does not run it. | |
| <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> | |
| <p> | |
| If the registry already has the key <code>tname</code>, | |
| returns 0. | |
| Otherwise, | |
| creates a new table to be used as a metatable for userdata, | |
| adds it to the registry with key <code>tname</code>, | |
| and returns 1. | |
| <p> | |
| In both cases pushes onto the stack the final value associated | |
| with <code>tname</code> in the registry. | |
| <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>lua_State *luaL_newstate (void);</pre> | |
| <p> | |
| Creates a new Lua state. | |
| It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an | |
| allocator based on the standard C <code>realloc</code> function | |
| and then sets a panic function (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) that prints | |
| an error message to the standard error output in case of fatal | |
| errors. | |
| <p> | |
| Returns the new state, | |
| or <code>NULL</code> if there is a memory allocation error. | |
| <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>m</em>]</span> | |
| <pre>void luaL_openlibs (lua_State *L);</pre> | |
| <p> | |
| Opens all standard Lua libraries into the given state. | |
| <hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_optint (lua_State *L, int narg, int d);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a number, | |
| returns this number cast to an <code>int</code>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Integer luaL_optinteger (lua_State *L, | |
| int narg, | |
| lua_Integer d);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a number, | |
| returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>long luaL_optlong (lua_State *L, int narg, long d);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a number, | |
| returns this number cast to a <code>long</code>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_optlstring (lua_State *L, | |
| int narg, | |
| const char *d, | |
| size_t *l);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a string, | |
| returns this string. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <p> | |
| If <code>l</code> is not <code>NULL</code>, | |
| fills the position <code>*l</code> with the results's length. | |
| <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a number, | |
| returns this number. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_optstring (lua_State *L, | |
| int narg, | |
| const char *d);</pre> | |
| <p> | |
| If the function argument <code>narg</code> is a string, | |
| returns this string. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> | |
| <p> | |
| Returns an address to a space of size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a> | |
| where you can copy a string to be added to buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| After copying the string into this space you must call | |
| <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add | |
| it to the buffer. | |
| <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> | |
| <span class="apii">[-?, +1, <em>m</em>]</span> | |
| <pre>void luaL_pushresult (luaL_Buffer *B);</pre> | |
| <p> | |
| Finishes the use of buffer <code>B</code> leaving the final string on | |
| the top of the stack. | |
| <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>m</em>]</span> | |
| <pre>int luaL_ref (lua_State *L, int t);</pre> | |
| <p> | |
| Creates and returns a <em>reference</em>, | |
| in the table at index <code>t</code>, | |
| for the object at the top of the stack (and pops the object). | |
| <p> | |
| A reference is a unique integer key. | |
| As long as you do not manually add integer keys into table <code>t</code>, | |
| <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. | |
| You can retrieve an object referred by reference <code>r</code> | |
| by calling <code>lua_rawgeti(L, t, r)</code>. | |
| Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. | |
| <p> | |
| If the object at the top of the stack is <b>nil</b>, | |
| <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. | |
| The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different | |
| from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. | |
| <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> | |
| <pre>typedef struct luaL_Reg { | |
| const char *name; | |
| lua_CFunction func; | |
| } luaL_Reg;</pre> | |
| <p> | |
| Type for arrays of functions to be registered by | |
| <a href="#luaL_register"><code>luaL_register</code></a>. | |
| <code>name</code> is the function name and <code>func</code> is a pointer to | |
| the function. | |
| Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry | |
| in which both <code>name</code> and <code>func</code> are <code>NULL</code>. | |
| <hr><h3><a name="luaL_register"><code>luaL_register</code></a></h3><p> | |
| <span class="apii">[-(0|1), +1, <em>m</em>]</span> | |
| <pre>void luaL_register (lua_State *L, | |
| const char *libname, | |
| const luaL_Reg *l);</pre> | |
| <p> | |
| Opens a library. | |
| <p> | |
| When called with <code>libname</code> equal to <code>NULL</code>, | |
| it simply registers all functions in the list <code>l</code> | |
| (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack. | |
| <p> | |
| When called with a non-null <code>libname</code>, | |
| <code>luaL_register</code> creates a new table <code>t</code>, | |
| sets it as the value of the global variable <code>libname</code>, | |
| sets it as the value of <code>package.loaded[libname]</code>, | |
| and registers on it all functions in the list <code>l</code>. | |
| If there is a table in <code>package.loaded[libname]</code> or in | |
| variable <code>libname</code>, | |
| reuses this table instead of creating a new one. | |
| <p> | |
| In any case the function leaves the table | |
| on the top of the stack. | |
| <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>const char *luaL_typename (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the name of the type of the value at the given index. | |
| <hr><h3><a name="luaL_typerror"><code>luaL_typerror</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_typerror (lua_State *L, int narg, const char *tname);</pre> | |
| <p> | |
| Generates an error with a message like the following: | |
| <pre> | |
| <em>location</em>: bad argument <em>narg</em> to '<em>func</em>' (<em>tname</em> expected, got <em>rt</em>) | |
| </pre><p> | |
| where <code><em>location</em></code> is produced by <a href="#luaL_where"><code>luaL_where</code></a>, | |
| <code><em>func</em></code> is the name of the current function, | |
| and <code><em>rt</em></code> is the type name of the actual argument. | |
| <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>-</em>]</span> | |
| <pre>void luaL_unref (lua_State *L, int t, int ref);</pre> | |
| <p> | |
| Releases reference <code>ref</code> from the table at index <code>t</code> | |
| (see <a href="#luaL_ref"><code>luaL_ref</code></a>). | |
| The entry is removed from the table, | |
| so that the referred object can be collected. | |
| The reference <code>ref</code> is also freed to be used again. | |
| <p> | |
| If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, | |
| <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. | |
| <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>m</em>]</span> | |
| <pre>void luaL_where (lua_State *L, int lvl);</pre> | |
| <p> | |
| Pushes onto the stack a string identifying the current position | |
| of the control at level <code>lvl</code> in the call stack. | |
| Typically this string has the following format: | |
| <pre> | |
| <em>chunkname</em>:<em>currentline</em>: | |
| </pre><p> | |
| Level 0 is the running function, | |
| level 1 is the function that called the running function, | |
| etc. | |
| <p> | |
| This function is used to build a prefix for error messages. | |
| <h1>5 - <a name="5">Standard Libraries</a></h1> | |
| <p> | |
| The standard Lua libraries provide useful functions | |
| that are implemented directly through the C API. | |
| Some of these functions provide essential services to the language | |
| (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); | |
| others provide access to "outside" services (e.g., I/O); | |
| and others could be implemented in Lua itself, | |
| but are quite useful or have critical performance requirements that | |
| deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>). | |
| <p> | |
| All libraries are implemented through the official C API | |
| and are provided as separate C modules. | |
| Currently, Lua has the following standard libraries: | |
| <ul> | |
| <li>basic library,</li> which includes the coroutine sub-library; | |
| <li>package library;</li> | |
| <li>string manipulation;</li> | |
| <li>table manipulation;</li> | |
| <li>mathematical functions (sin, log, etc.);</li> | |
| <li>input and output;</li> | |
| <li>operating system facilities;</li> | |
| <li>debug facilities.</li> | |
| </ul><p> | |
| Except for the basic and package libraries, | |
| each library provides all its functions as fields of a global table | |
| or as methods of its objects. | |
| <p> | |
| To have access to these libraries, | |
| the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function, | |
| which opens all standard libraries. | |
| Alternatively, | |
| it can open them individually by calling | |
| <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library), | |
| <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library), | |
| <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), | |
| <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), | |
| <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), | |
| <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), | |
| <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library), | |
| and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). | |
| These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a> | |
| and should not be called directly: | |
| you must call them like any other Lua C function, | |
| e.g., by using <a href="#lua_call"><code>lua_call</code></a>. | |
| <h2>5.1 - <a name="5.1">Basic Functions</a></h2> | |
| <p> | |
| The basic library provides some core functions to Lua. | |
| If you do not include this library in your application, | |
| you should check carefully whether you need to provide | |
| implementations for some of its facilities. | |
| <p> | |
| <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3> | |
| Issues an error when | |
| the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); | |
| otherwise, returns all its arguments. | |
| <code>message</code> is an error message; | |
| when absent, it defaults to "assertion failed!" | |
| <p> | |
| <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage (opt [, arg])</code></a></h3> | |
| <p> | |
| This function is a generic interface to the garbage collector. | |
| It performs different functions according to its first argument, <code>opt</code>: | |
| <ul> | |
| <li><b>"stop":</b> | |
| stops the garbage collector. | |
| </li> | |
| <li><b>"restart":</b> | |
| restarts the garbage collector. | |
| </li> | |
| <li><b>"collect":</b> | |
| performs a full garbage-collection cycle. | |
| </li> | |
| <li><b>"count":</b> | |
| returns the total memory in use by Lua (in Kbytes). | |
| </li> | |
| <li><b>"step":</b> | |
| performs a garbage-collection step. | |
| The step "size" is controlled by <code>arg</code> | |
| (larger values mean more steps) in a non-specified way. | |
| If you want to control the step size | |
| you must experimentally tune the value of <code>arg</code>. | |
| Returns <b>true</b> if the step finished a collection cycle. | |
| </li> | |
| <li><b>"setpause":</b> | |
| sets <code>arg</code> as the new value for the <em>pause</em> of | |
| the collector (see <a href="#2.10">§2.10</a>). | |
| Returns the previous value for <em>pause</em>. | |
| </li> | |
| <li><b>"setstepmul":</b> | |
| sets <code>arg</code> as the new value for the <em>step multiplier</em> of | |
| the collector (see <a href="#2.10">§2.10</a>). | |
| Returns the previous value for <em>step</em>. | |
| </li> | |
| </ul> | |
| <p> | |
| <hr><h3><a name="pdf-dofile"><code>dofile (filename)</code></a></h3> | |
| Opens the named file and executes its contents as a Lua chunk. | |
| When called without arguments, | |
| <code>dofile</code> executes the contents of the standard input (<code>stdin</code>). | |
| Returns all values returned by the chunk. | |
| In case of errors, <code>dofile</code> propagates the error | |
| to its caller (that is, <code>dofile</code> does not run in protected mode). | |
| <p> | |
| <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3> | |
| Terminates the last protected function called | |
| and returns <code>message</code> as the error message. | |
| Function <code>error</code> never returns. | |
| <p> | |
| Usually, <code>error</code> adds some information about the error position | |
| at the beginning of the message. | |
| The <code>level</code> argument specifies how to get the error position. | |
| With level 1 (the default), the error position is where the | |
| <code>error</code> function was called. | |
| Level 2 points the error to where the function | |
| that called <code>error</code> was called; and so on. | |
| Passing a level 0 avoids the addition of error position information | |
| to the message. | |
| <p> | |
| <hr><h3><a name="pdf-_G"><code>_G</code></a></h3> | |
| A global variable (not a function) that | |
| holds the global environment (that is, <code>_G._G = _G</code>). | |
| Lua itself does not use this variable; | |
| changing its value does not affect any environment, | |
| nor vice-versa. | |
| (Use <a href="#pdf-setfenv"><code>setfenv</code></a> to change environments.) | |
| <p> | |
| <hr><h3><a name="pdf-getfenv"><code>getfenv ([f])</code></a></h3> | |
| Returns the current environment in use by the function. | |
| <code>f</code> can be a Lua function or a number | |
| that specifies the function at that stack level: | |
| Level 1 is the function calling <code>getfenv</code>. | |
| If the given function is not a Lua function, | |
| or if <code>f</code> is 0, | |
| <code>getfenv</code> returns the global environment. | |
| The default for <code>f</code> is 1. | |
| <p> | |
| <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3> | |
| <p> | |
| If <code>object</code> does not have a metatable, returns <b>nil</b>. | |
| Otherwise, | |
| if the object's metatable has a <code>"__metatable"</code> field, | |
| returns the associated value. | |
| Otherwise, returns the metatable of the given object. | |
| <p> | |
| <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3> | |
| <p> | |
| Returns three values: an iterator function, the table <code>t</code>, and 0, | |
| so that the construction | |
| <pre> | |
| for i,v in ipairs(t) do <em>body</em> end | |
| </pre><p> | |
| will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ···, | |
| up to the first integer key absent from the table. | |
| <p> | |
| <hr><h3><a name="pdf-load"><code>load (func [, chunkname])</code></a></h3> | |
| <p> | |
| Loads a chunk using function <code>func</code> to get its pieces. | |
| Each call to <code>func</code> must return a string that concatenates | |
| with previous results. | |
| A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. | |
| <p> | |
| If there are no errors, | |
| returns the compiled chunk as a function; | |
| otherwise, returns <b>nil</b> plus the error message. | |
| The environment of the returned function is the global environment. | |
| <p> | |
| <code>chunkname</code> is used as the chunk name for error messages | |
| and debug information. | |
| When absent, | |
| it defaults to "<code>=(load)</code>". | |
| <p> | |
| <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename])</code></a></h3> | |
| <p> | |
| Similar to <a href="#pdf-load"><code>load</code></a>, | |
| but gets the chunk from file <code>filename</code> | |
| or from the standard input, | |
| if no file name is given. | |
| <p> | |
| <hr><h3><a name="pdf-loadstring"><code>loadstring (string [, chunkname])</code></a></h3> | |
| <p> | |
| Similar to <a href="#pdf-load"><code>load</code></a>, | |
| but gets the chunk from the given string. | |
| <p> | |
| To load and run a given string, use the idiom | |
| <pre> | |
| assert(loadstring(s))() | |
| </pre> | |
| <p> | |
| When absent, | |
| <code>chunkname</code> defaults to the given string. | |
| <p> | |
| <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3> | |
| <p> | |
| Allows a program to traverse all fields of a table. | |
| Its first argument is a table and its second argument | |
| is an index in this table. | |
| <code>next</code> returns the next index of the table | |
| and its associated value. | |
| When called with <b>nil</b> as its second argument, | |
| <code>next</code> returns an initial index | |
| and its associated value. | |
| When called with the last index, | |
| or with <b>nil</b> in an empty table, | |
| <code>next</code> returns <b>nil</b>. | |
| If the second argument is absent, then it is interpreted as <b>nil</b>. | |
| In particular, | |
| you can use <code>next(t)</code> to check whether a table is empty. | |
| <p> | |
| The order in which the indices are enumerated is not specified, | |
| <em>even for numeric indices</em>. | |
| (To traverse a table in numeric order, | |
| use a numerical <b>for</b> or the <a href="#pdf-ipairs"><code>ipairs</code></a> function.) | |
| <p> | |
| The behavior of <code>next</code> is <em>undefined</em> if, | |
| during the traversal, | |
| you assign any value to a non-existent field in the table. | |
| You may however modify existing fields. | |
| In particular, you may clear existing fields. | |
| <p> | |
| <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> | |
| <p> | |
| Returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>, | |
| so that the construction | |
| <pre> | |
| for k,v in pairs(t) do <em>body</em> end | |
| </pre><p> | |
| will iterate over all key–value pairs of table <code>t</code>. | |
| <p> | |
| See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying | |
| the table during its traversal. | |
| <p> | |
| <hr><h3><a name="pdf-pcall"><code>pcall (f, arg1, ···)</code></a></h3> | |
| <p> | |
| Calls function <code>f</code> with | |
| the given arguments in <em>protected mode</em>. | |
| This means that any error inside <code>f</code> is not propagated; | |
| instead, <code>pcall</code> catches the error | |
| and returns a status code. | |
| Its first result is the status code (a boolean), | |
| which is true if the call succeeds without errors. | |
| In such case, <code>pcall</code> also returns all results from the call, | |
| after this first result. | |
| In case of any error, <code>pcall</code> returns <b>false</b> plus the error message. | |
| <p> | |
| <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3> | |
| Receives any number of arguments, | |
| and prints their values to <code>stdout</code>, | |
| using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert them to strings. | |
| <code>print</code> is not intended for formatted output, | |
| but only as a quick way to show a value, | |
| typically for debugging. | |
| For formatted output, use <a href="#pdf-string.format"><code>string.format</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3> | |
| Checks whether <code>v1</code> is equal to <code>v2</code>, | |
| without invoking any metamethod. | |
| Returns a boolean. | |
| <p> | |
| <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3> | |
| Gets the real value of <code>table[index]</code>, | |
| without invoking any metamethod. | |
| <code>table</code> must be a table; | |
| <code>index</code> may be any value. | |
| <p> | |
| <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3> | |
| Sets the real value of <code>table[index]</code> to <code>value</code>, | |
| without invoking any metamethod. | |
| <code>table</code> must be a table, | |
| <code>index</code> any value different from <b>nil</b>, | |
| and <code>value</code> any Lua value. | |
| <p> | |
| This function returns <code>table</code>. | |
| <p> | |
| <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3> | |
| <p> | |
| If <code>index</code> is a number, | |
| returns all arguments after argument number <code>index</code>. | |
| Otherwise, <code>index</code> must be the string <code>"#"</code>, | |
| and <code>select</code> returns the total number of extra arguments it received. | |
| <p> | |
| <hr><h3><a name="pdf-setfenv"><code>setfenv (f, table)</code></a></h3> | |
| <p> | |
| Sets the environment to be used by the given function. | |
| <code>f</code> can be a Lua function or a number | |
| that specifies the function at that stack level: | |
| Level 1 is the function calling <code>setfenv</code>. | |
| <code>setfenv</code> returns the given function. | |
| <p> | |
| As a special case, when <code>f</code> is 0 <code>setfenv</code> changes | |
| the environment of the running thread. | |
| In this case, <code>setfenv</code> returns no values. | |
| <p> | |
| <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> | |
| <p> | |
| Sets the metatable for the given table. | |
| (You cannot change the metatable of other types from Lua, only from C.) | |
| If <code>metatable</code> is <b>nil</b>, | |
| removes the metatable of the given table. | |
| If the original metatable has a <code>"__metatable"</code> field, | |
| raises an error. | |
| <p> | |
| This function returns <code>table</code>. | |
| <p> | |
| <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3> | |
| Tries to convert its argument to a number. | |
| If the argument is already a number or a string convertible | |
| to a number, then <code>tonumber</code> returns this number; | |
| otherwise, it returns <b>nil</b>. | |
| <p> | |
| An optional argument specifies the base to interpret the numeral. | |
| The base may be any integer between 2 and 36, inclusive. | |
| In bases above 10, the letter '<code>A</code>' (in either upper or lower case) | |
| represents 10, '<code>B</code>' represents 11, and so forth, | |
| with '<code>Z</code>' representing 35. | |
| In base 10 (the default), the number can have a decimal part, | |
| as well as an optional exponent part (see <a href="#2.1">§2.1</a>). | |
| In other bases, only unsigned integers are accepted. | |
| <p> | |
| <hr><h3><a name="pdf-tostring"><code>tostring (e)</code></a></h3> | |
| Receives an argument of any type and | |
| converts it to a string in a reasonable format. | |
| For complete control of how numbers are converted, | |
| use <a href="#pdf-string.format"><code>string.format</code></a>. | |
| <p> | |
| If the metatable of <code>e</code> has a <code>"__tostring"</code> field, | |
| then <code>tostring</code> calls the corresponding value | |
| with <code>e</code> as argument, | |
| and uses the result of the call as its result. | |
| <p> | |
| <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3> | |
| Returns the type of its only argument, coded as a string. | |
| The possible results of this function are | |
| "<code>nil</code>" (a string, not the value <b>nil</b>), | |
| "<code>number</code>", | |
| "<code>string</code>", | |
| "<code>boolean</code>", | |
| "<code>table</code>", | |
| "<code>function</code>", | |
| "<code>thread</code>", | |
| and "<code>userdata</code>". | |
| <p> | |
| <hr><h3><a name="pdf-unpack"><code>unpack (list [, i [, j]])</code></a></h3> | |
| Returns the elements from the given table. | |
| This function is equivalent to | |
| <pre> | |
| return list[i], list[i+1], ···, list[j] | |
| </pre><p> | |
| except that the above code can be written only for a fixed number | |
| of elements. | |
| By default, <code>i</code> is 1 and <code>j</code> is the length of the list, | |
| as defined by the length operator (see <a href="#2.5.5">§2.5.5</a>). | |
| <p> | |
| <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3> | |
| A global variable (not a function) that | |
| holds a string containing the current interpreter version. | |
| The current contents of this variable is "<code>Lua 5.1</code>". | |
| <p> | |
| <hr><h3><a name="pdf-xpcall"><code>xpcall (f, err)</code></a></h3> | |
| <p> | |
| This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, | |
| except that you can set a new error handler. | |
| <p> | |
| <code>xpcall</code> calls function <code>f</code> in protected mode, | |
| using <code>err</code> as the error handler. | |
| Any error inside <code>f</code> is not propagated; | |
| instead, <code>xpcall</code> catches the error, | |
| calls the <code>err</code> function with the original error object, | |
| and returns a status code. | |
| Its first result is the status code (a boolean), | |
| which is true if the call succeeds without errors. | |
| In this case, <code>xpcall</code> also returns all results from the call, | |
| after this first result. | |
| In case of any error, | |
| <code>xpcall</code> returns <b>false</b> plus the result from <code>err</code>. | |
| <h2>5.2 - <a name="5.2">Coroutine Manipulation</a></h2> | |
| <p> | |
| The operations related to coroutines comprise a sub-library of | |
| the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. | |
| See <a href="#2.11">§2.11</a> for a general description of coroutines. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3> | |
| <p> | |
| Creates a new coroutine, with body <code>f</code>. | |
| <code>f</code> must be a Lua function. | |
| Returns this new coroutine, | |
| an object with type <code>"thread"</code>. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3> | |
| <p> | |
| Starts or continues the execution of coroutine <code>co</code>. | |
| The first time you resume a coroutine, | |
| it starts running its body. | |
| The values <code>val1</code>, ··· are passed | |
| as the arguments to the body function. | |
| If the coroutine has yielded, | |
| <code>resume</code> restarts it; | |
| the values <code>val1</code>, ··· are passed | |
| as the results from the yield. | |
| <p> | |
| If the coroutine runs without any errors, | |
| <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code> | |
| (if the coroutine yields) or any values returned by the body function | |
| (if the coroutine terminates). | |
| If there is any error, | |
| <code>resume</code> returns <b>false</b> plus the error message. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3> | |
| <p> | |
| Returns the running coroutine, | |
| or <b>nil</b> when called by the main thread. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3> | |
| <p> | |
| Returns the status of coroutine <code>co</code>, as a string: | |
| <code>"running"</code>, | |
| if the coroutine is running (that is, it called <code>status</code>); | |
| <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>, | |
| or if it has not started running yet; | |
| <code>"normal"</code> if the coroutine is active but not running | |
| (that is, it has resumed another coroutine); | |
| and <code>"dead"</code> if the coroutine has finished its body function, | |
| or if it has stopped with an error. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3> | |
| <p> | |
| Creates a new coroutine, with body <code>f</code>. | |
| <code>f</code> must be a Lua function. | |
| Returns a function that resumes the coroutine each time it is called. | |
| Any arguments passed to the function behave as the | |
| extra arguments to <code>resume</code>. | |
| Returns the same values returned by <code>resume</code>, | |
| except the first boolean. | |
| In case of error, propagates the error. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3> | |
| <p> | |
| Suspends the execution of the calling coroutine. | |
| The coroutine cannot be running a C function, | |
| a metamethod, or an iterator. | |
| Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. | |
| <h2>5.3 - <a name="5.3">Modules</a></h2> | |
| <p> | |
| The package library provides basic | |
| facilities for loading and building modules in Lua. | |
| It exports two of its functions directly in the global environment: | |
| <a href="#pdf-require"><code>require</code></a> and <a href="#pdf-module"><code>module</code></a>. | |
| Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-module"><code>module (name [, ···])</code></a></h3> | |
| <p> | |
| Creates a module. | |
| If there is a table in <code>package.loaded[name]</code>, | |
| this table is the module. | |
| Otherwise, if there is a global table <code>t</code> with the given name, | |
| this table is the module. | |
| Otherwise creates a new table <code>t</code> and | |
| sets it as the value of the global <code>name</code> and | |
| the value of <code>package.loaded[name]</code>. | |
| This function also initializes <code>t._NAME</code> with the given name, | |
| <code>t._M</code> with the module (<code>t</code> itself), | |
| and <code>t._PACKAGE</code> with the package name | |
| (the full module name minus last component; see below). | |
| Finally, <code>module</code> sets <code>t</code> as the new environment | |
| of the current function and the new value of <code>package.loaded[name]</code>, | |
| so that <a href="#pdf-require"><code>require</code></a> returns <code>t</code>. | |
| <p> | |
| If <code>name</code> is a compound name | |
| (that is, one with components separated by dots), | |
| <code>module</code> creates (or reuses, if they already exist) | |
| tables for each component. | |
| For instance, if <code>name</code> is <code>a.b.c</code>, | |
| then <code>module</code> stores the module table in field <code>c</code> of | |
| field <code>b</code> of global <code>a</code>. | |
| <p> | |
| This function can receive optional <em>options</em> after | |
| the module name, | |
| where each option is a function to be applied over the module. | |
| <p> | |
| <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> | |
| <p> | |
| Loads the given module. | |
| The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table | |
| to determine whether <code>modname</code> is already loaded. | |
| If it is, then <code>require</code> returns the value stored | |
| at <code>package.loaded[modname]</code>. | |
| Otherwise, it tries to find a <em>loader</em> for the module. | |
| <p> | |
| To find a loader, | |
| <code>require</code> is guided by the <a href="#pdf-package.loaders"><code>package.loaders</code></a> array. | |
| By changing this array, | |
| we can change how <code>require</code> looks for a module. | |
| The following explanation is based on the default configuration | |
| for <a href="#pdf-package.loaders"><code>package.loaders</code></a>. | |
| <p> | |
| First <code>require</code> queries <code>package.preload[modname]</code>. | |
| If it has a value, | |
| this value (which should be a function) is the loader. | |
| Otherwise <code>require</code> searches for a Lua loader using the | |
| path stored in <a href="#pdf-package.path"><code>package.path</code></a>. | |
| If that also fails, it searches for a C loader using the | |
| path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. | |
| If that also fails, | |
| it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.loaders"><code>package.loaders</code></a>). | |
| <p> | |
| Once a loader is found, | |
| <code>require</code> calls the loader with a single argument, <code>modname</code>. | |
| If the loader returns any value, | |
| <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. | |
| If the loader returns no value and | |
| has not assigned any value to <code>package.loaded[modname]</code>, | |
| then <code>require</code> assigns <b>true</b> to this entry. | |
| In any case, <code>require</code> returns the | |
| final value of <code>package.loaded[modname]</code>. | |
| <p> | |
| If there is any error loading or running the module, | |
| or if it cannot find any loader for the module, | |
| then <code>require</code> signals an error. | |
| <p> | |
| <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3> | |
| <p> | |
| The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader. | |
| <p> | |
| Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way | |
| it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, | |
| using the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a> | |
| or a default path defined in <code>luaconf.h</code>. | |
| <p> | |
| <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> | |
| <p> | |
| A table used by <a href="#pdf-require"><code>require</code></a> to control which | |
| modules are already loaded. | |
| When you require a module <code>modname</code> and | |
| <code>package.loaded[modname]</code> is not false, | |
| <a href="#pdf-require"><code>require</code></a> simply returns the value stored there. | |
| <p> | |
| <hr><h3><a name="pdf-package.loaders"><code>package.loaders</code></a></h3> | |
| <p> | |
| A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. | |
| <p> | |
| Each entry in this table is a <em>searcher function</em>. | |
| When looking for a module, | |
| <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, | |
| with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its | |
| sole parameter. | |
| The function can return another function (the module <em>loader</em>) | |
| or a string explaining why it did not find that module | |
| (or <b>nil</b> if it has nothing to say). | |
| Lua initializes this table with four functions. | |
| <p> | |
| The first searcher simply looks for a loader in the | |
| <a href="#pdf-package.preload"><code>package.preload</code></a> table. | |
| <p> | |
| The second searcher looks for a loader as a Lua library, | |
| using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. | |
| A path is a sequence of <em>templates</em> separated by semicolons. | |
| For each template, | |
| the searcher will change each interrogation | |
| mark in the template by <code>filename</code>, | |
| which is the module name with each dot replaced by a | |
| "directory separator" (such as "<code>/</code>" in Unix); | |
| then it will try to open the resulting file name. | |
| So, for instance, if the Lua path is the string | |
| <pre> | |
| "./?.lua;./?.lc;/usr/local/?/init.lua" | |
| </pre><p> | |
| the search for a Lua file for module <code>foo</code> | |
| will try to open the files | |
| <code>./foo.lua</code>, <code>./foo.lc</code>, and | |
| <code>/usr/local/foo/init.lua</code>, in that order. | |
| <p> | |
| The third searcher looks for a loader as a C library, | |
| using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. | |
| For instance, | |
| if the C path is the string | |
| <pre> | |
| "./?.so;./?.dll;/usr/local/?/init.so" | |
| </pre><p> | |
| the searcher for module <code>foo</code> | |
| will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, | |
| and <code>/usr/local/foo/init.so</code>, in that order. | |
| Once it finds a C library, | |
| this searcher first uses a dynamic link facility to link the | |
| application with the library. | |
| Then it tries to find a C function inside the library to | |
| be used as the loader. | |
| The name of this C function is the string "<code>luaopen_</code>" | |
| concatenated with a copy of the module name where each dot | |
| is replaced by an underscore. | |
| Moreover, if the module name has a hyphen, | |
| its prefix up to (and including) the first hyphen is removed. | |
| For instance, if the module name is <code>a.v1-b.c</code>, | |
| the function name will be <code>luaopen_b_c</code>. | |
| <p> | |
| The fourth searcher tries an <em>all-in-one loader</em>. | |
| It searches the C path for a library for | |
| the root name of the given module. | |
| For instance, when requiring <code>a.b.c</code>, | |
| it will search for a C library for <code>a</code>. | |
| If found, it looks into it for an open function for | |
| the submodule; | |
| in our example, that would be <code>luaopen_a_b_c</code>. | |
| With this facility, a package can pack several C submodules | |
| into one single library, | |
| with each submodule keeping its original open function. | |
| <p> | |
| <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3> | |
| <p> | |
| Dynamically links the host program with the C library <code>libname</code>. | |
| Inside this library, looks for a function <code>funcname</code> | |
| and returns this function as a C function. | |
| (So, <code>funcname</code> must follow the protocol (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>)). | |
| <p> | |
| This is a low-level function. | |
| It completely bypasses the package and module system. | |
| Unlike <a href="#pdf-require"><code>require</code></a>, | |
| it does not perform any path searching and | |
| does not automatically adds extensions. | |
| <code>libname</code> must be the complete file name of the C library, | |
| including if necessary a path and extension. | |
| <code>funcname</code> must be the exact name exported by the C library | |
| (which may depend on the C compiler and linker used). | |
| <p> | |
| This function is not supported by ANSI C. | |
| As such, it is only available on some platforms | |
| (Windows, Linux, Mac OS X, Solaris, BSD, | |
| plus other Unix systems that support the <code>dlfcn</code> standard). | |
| <p> | |
| <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3> | |
| <p> | |
| The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader. | |
| <p> | |
| At start-up, Lua initializes this variable with | |
| the value of the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or | |
| with a default path defined in <code>luaconf.h</code>, | |
| if the environment variable is not defined. | |
| Any "<code>;;</code>" in the value of the environment variable | |
| is replaced by the default path. | |
| <p> | |
| <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> | |
| <p> | |
| A table to store loaders for specific modules | |
| (see <a href="#pdf-require"><code>require</code></a>). | |
| <p> | |
| <hr><h3><a name="pdf-package.seeall"><code>package.seeall (module)</code></a></h3> | |
| <p> | |
| Sets a metatable for <code>module</code> with | |
| its <code>__index</code> field referring to the global environment, | |
| so that this module inherits values | |
| from the global environment. | |
| To be used as an option to function <a href="#pdf-module"><code>module</code></a>. | |
| <h2>5.4 - <a name="5.4">String Manipulation</a></h2> | |
| <p> | |
| This library provides generic functions for string manipulation, | |
| such as finding and extracting substrings, and pattern matching. | |
| When indexing a string in Lua, the first character is at position 1 | |
| (not at 0, as in C). | |
| Indices are allowed to be negative and are interpreted as indexing backwards, | |
| from the end of the string. | |
| Thus, the last character is at position -1, and so on. | |
| <p> | |
| The string library provides all its functions inside the table | |
| <a name="pdf-string"><code>string</code></a>. | |
| It also sets a metatable for strings | |
| where the <code>__index</code> field points to the <code>string</code> table. | |
| Therefore, you can use the string functions in object-oriented style. | |
| For instance, <code>string.byte(s, i)</code> | |
| can be written as <code>s:byte(i)</code>. | |
| <p> | |
| The string library assumes one-byte character encodings. | |
| <p> | |
| <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> | |
| Returns the internal numerical codes of the characters <code>s[i]</code>, | |
| <code>s[i+1]</code>, ···, <code>s[j]</code>. | |
| The default value for <code>i</code> is 1; | |
| the default value for <code>j</code> is <code>i</code>. | |
| <p> | |
| Note that numerical codes are not necessarily portable across platforms. | |
| <p> | |
| <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3> | |
| Receives zero or more integers. | |
| Returns a string with length equal to the number of arguments, | |
| in which each character has the internal numerical code equal | |
| to its corresponding argument. | |
| <p> | |
| Note that numerical codes are not necessarily portable across platforms. | |
| <p> | |
| <hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3> | |
| <p> | |
| Returns a string containing a binary representation of the given function, | |
| so that a later <a href="#pdf-loadstring"><code>loadstring</code></a> on this string returns | |
| a copy of the function. | |
| <code>function</code> must be a Lua function without upvalues. | |
| <p> | |
| <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> | |
| Looks for the first match of | |
| <code>pattern</code> in the string <code>s</code>. | |
| If it finds a match, then <code>find</code> returns the indices of <code>s</code> | |
| where this occurrence starts and ends; | |
| otherwise, it returns <b>nil</b>. | |
| A third, optional numerical argument <code>init</code> specifies | |
| where to start the search; | |
| its default value is 1 and can be negative. | |
| A value of <b>true</b> as a fourth, optional argument <code>plain</code> | |
| turns off the pattern matching facilities, | |
| so the function does a plain "find substring" operation, | |
| with no characters in <code>pattern</code> being considered "magic". | |
| Note that if <code>plain</code> is given, then <code>init</code> must be given as well. | |
| <p> | |
| If the pattern has captures, | |
| then in a successful match | |
| the captured values are also returned, | |
| after the two indices. | |
| <p> | |
| <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> | |
| Returns a formatted version of its variable number of arguments | |
| following the description given in its first argument (which must be a string). | |
| The format string follows the same rules as the <code>printf</code> family of | |
| standard C functions. | |
| The only differences are that the options/modifiers | |
| <code>*</code>, <code>l</code>, <code>L</code>, <code>n</code>, <code>p</code>, | |
| and <code>h</code> are not supported | |
| and that there is an extra option, <code>q</code>. | |
| The <code>q</code> option formats a string in a form suitable to be safely read | |
| back by the Lua interpreter: | |
| the string is written between double quotes, | |
| and all double quotes, newlines, embedded zeros, | |
| and backslashes in the string | |
| are correctly escaped when written. | |
| For instance, the call | |
| <pre> | |
| string.format('%q', 'a string with "quotes" and \n new line') | |
| </pre><p> | |
| will produce the string: | |
| <pre> | |
| "a string with \"quotes\" and \ | |
| new line" | |
| </pre> | |
| <p> | |
| The options <code>c</code>, <code>d</code>, <code>E</code>, <code>e</code>, <code>f</code>, | |
| <code>g</code>, <code>G</code>, <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> all | |
| expect a number as argument, | |
| whereas <code>q</code> and <code>s</code> expect a string. | |
| <p> | |
| This function does not accept string values | |
| containing embedded zeros, | |
| except as arguments to the <code>q</code> option. | |
| <p> | |
| <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3> | |
| Returns an iterator function that, | |
| each time it is called, | |
| returns the next captures from <code>pattern</code> over string <code>s</code>. | |
| If <code>pattern</code> specifies no captures, | |
| then the whole match is produced in each call. | |
| <p> | |
| As an example, the following loop | |
| <pre> | |
| s = "hello world from Lua" | |
| for w in string.gmatch(s, "%a+") do | |
| print(w) | |
| end | |
| </pre><p> | |
| will iterate over all the words from string <code>s</code>, | |
| printing one per line. | |
| The next example collects all pairs <code>key=value</code> from the | |
| given string into a table: | |
| <pre> | |
| t = {} | |
| s = "from=world, to=Lua" | |
| for k, v in string.gmatch(s, "(%w+)=(%w+)") do | |
| t[k] = v | |
| end | |
| </pre> | |
| <p> | |
| For this function, a '<code>^</code>' at the start of a pattern does not | |
| work as an anchor, as this would prevent the iteration. | |
| <p> | |
| <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> | |
| Returns a copy of <code>s</code> | |
| in which all (or the first <code>n</code>, if given) | |
| occurrences of the <code>pattern</code> have been | |
| replaced by a replacement string specified by <code>repl</code>, | |
| which can be a string, a table, or a function. | |
| <code>gsub</code> also returns, as its second value, | |
| the total number of matches that occurred. | |
| <p> | |
| If <code>repl</code> is a string, then its value is used for replacement. | |
| The character <code>%</code> works as an escape character: | |
| any sequence in <code>repl</code> of the form <code>%<em>n</em></code>, | |
| with <em>n</em> between 1 and 9, | |
| stands for the value of the <em>n</em>-th captured substring (see below). | |
| The sequence <code>%0</code> stands for the whole match. | |
| The sequence <code>%%</code> stands for a single <code>%</code>. | |
| <p> | |
| If <code>repl</code> is a table, then the table is queried for every match, | |
| using the first capture as the key; | |
| if the pattern specifies no captures, | |
| then the whole match is used as the key. | |
| <p> | |
| If <code>repl</code> is a function, then this function is called every time a | |
| match occurs, with all captured substrings passed as arguments, | |
| in order; | |
| if the pattern specifies no captures, | |
| then the whole match is passed as a sole argument. | |
| <p> | |
| If the value returned by the table query or by the function call | |
| is a string or a number, | |
| then it is used as the replacement string; | |
| otherwise, if it is <b>false</b> or <b>nil</b>, | |
| then there is no replacement | |
| (that is, the original match is kept in the string). | |
| <p> | |
| Here are some examples: | |
| <pre> | |
| x = string.gsub("hello world", "(%w+)", "%1 %1") | |
| --> x="hello hello world world" | |
| x = string.gsub("hello world", "%w+", "%0 %0", 1) | |
| --> x="hello hello world" | |
| x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1") | |
| --> x="world hello Lua from" | |
| x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv) | |
| --> x="home = /home/roberto, user = roberto" | |
| x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s) | |
| return loadstring(s)() | |
| end) | |
| --> x="4+5 = 9" | |
| local t = {name="lua", version="5.1"} | |
| x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) | |
| --> x="lua-5.1.tar.gz" | |
| </pre> | |
| <p> | |
| <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3> | |
| Receives a string and returns its length. | |
| The empty string <code>""</code> has length 0. | |
| Embedded zeros are counted, | |
| so <code>"a\000bc\000"</code> has length 5. | |
| <p> | |
| <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3> | |
| Receives a string and returns a copy of this string with all | |
| uppercase letters changed to lowercase. | |
| All other characters are left unchanged. | |
| The definition of what an uppercase letter is depends on the current locale. | |
| <p> | |
| <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3> | |
| Looks for the first <em>match</em> of | |
| <code>pattern</code> in the string <code>s</code>. | |
| If it finds one, then <code>match</code> returns | |
| the captures from the pattern; | |
| otherwise it returns <b>nil</b>. | |
| If <code>pattern</code> specifies no captures, | |
| then the whole match is returned. | |
| A third, optional numerical argument <code>init</code> specifies | |
| where to start the search; | |
| its default value is 1 and can be negative. | |
| <p> | |
| <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n)</code></a></h3> | |
| Returns a string that is the concatenation of <code>n</code> copies of | |
| the string <code>s</code>. | |
| <p> | |
| <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> | |
| Returns a string that is the string <code>s</code> reversed. | |
| <p> | |
| <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> | |
| Returns the substring of <code>s</code> that | |
| starts at <code>i</code> and continues until <code>j</code>; | |
| <code>i</code> and <code>j</code> can be negative. | |
| If <code>j</code> is absent, then it is assumed to be equal to -1 | |
| (which is the same as the string length). | |
| In particular, | |
| the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> | |
| with length <code>j</code>, | |
| and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code> | |
| with length <code>i</code>. | |
| <p> | |
| <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3> | |
| Receives a string and returns a copy of this string with all | |
| lowercase letters changed to uppercase. | |
| All other characters are left unchanged. | |
| The definition of what a lowercase letter is depends on the current locale. | |
| <h3>5.4.1 - <a name="5.4.1">Patterns</a></h3> | |
| <h4>Character Class:</h4><p> | |
| A <em>character class</em> is used to represent a set of characters. | |
| The following combinations are allowed in describing a character class: | |
| <ul> | |
| <li><b><em>x</em>:</b> | |
| (where <em>x</em> is not one of the <em>magic characters</em> | |
| <code>^$()%.[]*+-?</code>) | |
| represents the character <em>x</em> itself. | |
| </li> | |
| <li><b><code>.</code>:</b> (a dot) represents all characters.</li> | |
| <li><b><code>%a</code>:</b> represents all letters.</li> | |
| <li><b><code>%c</code>:</b> represents all control characters.</li> | |
| <li><b><code>%d</code>:</b> represents all digits.</li> | |
| <li><b><code>%l</code>:</b> represents all lowercase letters.</li> | |
| <li><b><code>%p</code>:</b> represents all punctuation characters.</li> | |
| <li><b><code>%s</code>:</b> represents all space characters.</li> | |
| <li><b><code>%u</code>:</b> represents all uppercase letters.</li> | |
| <li><b><code>%w</code>:</b> represents all alphanumeric characters.</li> | |
| <li><b><code>%x</code>:</b> represents all hexadecimal digits.</li> | |
| <li><b><code>%z</code>:</b> represents the character with representation 0.</li> | |
| <li><b><code>%<em>x</em></code>:</b> (where <em>x</em> is any non-alphanumeric character) | |
| represents the character <em>x</em>. | |
| This is the standard way to escape the magic characters. | |
| Any punctuation character (even the non magic) | |
| can be preceded by a '<code>%</code>' | |
| when used to represent itself in a pattern. | |
| </li> | |
| <li><b><code>[<em>set</em>]</code>:</b> | |
| represents the class which is the union of all | |
| characters in <em>set</em>. | |
| A range of characters can be specified by | |
| separating the end characters of the range with a '<code>-</code>'. | |
| All classes <code>%</code><em>x</em> described above can also be used as | |
| components in <em>set</em>. | |
| All other characters in <em>set</em> represent themselves. | |
| For example, <code>[%w_]</code> (or <code>[_%w]</code>) | |
| represents all alphanumeric characters plus the underscore, | |
| <code>[0-7]</code> represents the octal digits, | |
| and <code>[0-7%l%-]</code> represents the octal digits plus | |
| the lowercase letters plus the '<code>-</code>' character. | |
| <p> | |
| The interaction between ranges and classes is not defined. | |
| Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> | |
| have no meaning. | |
| </li> | |
| <li><b><code>[^<em>set</em>]</code>:</b> | |
| represents the complement of <em>set</em>, | |
| where <em>set</em> is interpreted as above. | |
| </li> | |
| </ul><p> | |
| For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), | |
| the corresponding uppercase letter represents the complement of the class. | |
| For instance, <code>%S</code> represents all non-space characters. | |
| <p> | |
| The definitions of letter, space, and other character groups | |
| depend on the current locale. | |
| In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. | |
| <h4>Pattern Item:</h4><p> | |
| A <em>pattern item</em> can be | |
| <ul> | |
| <li> | |
| a single character class, | |
| which matches any single character in the class; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>*</code>', | |
| which matches 0 or more repetitions of characters in the class. | |
| These repetition items will always match the longest possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>+</code>', | |
| which matches 1 or more repetitions of characters in the class. | |
| These repetition items will always match the longest possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>-</code>', | |
| which also matches 0 or more repetitions of characters in the class. | |
| Unlike '<code>*</code>', | |
| these repetition items will always match the <em>shortest</em> possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>?</code>', | |
| which matches 0 or 1 occurrence of a character in the class; | |
| </li> | |
| <li> | |
| <code>%<em>n</em></code>, for <em>n</em> between 1 and 9; | |
| such item matches a substring equal to the <em>n</em>-th captured string | |
| (see below); | |
| </li> | |
| <li> | |
| <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters; | |
| such item matches strings that start with <em>x</em>, end with <em>y</em>, | |
| and where the <em>x</em> and <em>y</em> are <em>balanced</em>. | |
| This means that, if one reads the string from left to right, | |
| counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>, | |
| the ending <em>y</em> is the first <em>y</em> where the count reaches 0. | |
| For instance, the item <code>%b()</code> matches expressions with | |
| balanced parentheses. | |
| </li> | |
| </ul> | |
| <h4>Pattern:</h4><p> | |
| A <em>pattern</em> is a sequence of pattern items. | |
| A '<code>^</code>' at the beginning of a pattern anchors the match at the | |
| beginning of the subject string. | |
| A '<code>$</code>' at the end of a pattern anchors the match at the | |
| end of the subject string. | |
| At other positions, | |
| '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. | |
| <h4>Captures:</h4><p> | |
| A pattern can contain sub-patterns enclosed in parentheses; | |
| they describe <em>captures</em>. | |
| When a match succeeds, the substrings of the subject string | |
| that match captures are stored (<em>captured</em>) for future use. | |
| Captures are numbered according to their left parentheses. | |
| For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, | |
| the part of the string matching <code>"a*(.)%w(%s*)"</code> is | |
| stored as the first capture (and therefore has number 1); | |
| the character matching "<code>.</code>" is captured with number 2, | |
| and the part matching "<code>%s*</code>" has number 3. | |
| <p> | |
| As a special case, the empty capture <code>()</code> captures | |
| the current string position (a number). | |
| For instance, if we apply the pattern <code>"()aa()"</code> on the | |
| string <code>"flaaap"</code>, there will be two captures: 3 and 5. | |
| <p> | |
| A pattern cannot contain embedded zeros. Use <code>%z</code> instead. | |
| <h2>5.5 - <a name="5.5">Table Manipulation</a></h2><p> | |
| This library provides generic functions for table manipulation. | |
| It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>. | |
| <p> | |
| Most functions in the table library assume that the table | |
| represents an array or a list. | |
| For these functions, when we talk about the "length" of a table | |
| we mean the result of the length operator. | |
| <p> | |
| <hr><h3><a name="pdf-table.concat"><code>table.concat (table [, sep [, i [, j]]])</code></a></h3> | |
| Given an array where all elements are strings or numbers, | |
| returns <code>table[i]..sep..table[i+1] ··· sep..table[j]</code>. | |
| The default value for <code>sep</code> is the empty string, | |
| the default for <code>i</code> is 1, | |
| and the default for <code>j</code> is the length of the table. | |
| If <code>i</code> is greater than <code>j</code>, returns the empty string. | |
| <p> | |
| <hr><h3><a name="pdf-table.insert"><code>table.insert (table, [pos,] value)</code></a></h3> | |
| <p> | |
| Inserts element <code>value</code> at position <code>pos</code> in <code>table</code>, | |
| shifting up other elements to open space, if necessary. | |
| The default value for <code>pos</code> is <code>n+1</code>, | |
| where <code>n</code> is the length of the table (see <a href="#2.5.5">§2.5.5</a>), | |
| so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end | |
| of table <code>t</code>. | |
| <p> | |
| <hr><h3><a name="pdf-table.maxn"><code>table.maxn (table)</code></a></h3> | |
| <p> | |
| Returns the largest positive numerical index of the given table, | |
| or zero if the table has no positive numerical indices. | |
| (To do its job this function does a linear traversal of | |
| the whole table.) | |
| <p> | |
| <hr><h3><a name="pdf-table.remove"><code>table.remove (table [, pos])</code></a></h3> | |
| <p> | |
| Removes from <code>table</code> the element at position <code>pos</code>, | |
| shifting down other elements to close the space, if necessary. | |
| Returns the value of the removed element. | |
| The default value for <code>pos</code> is <code>n</code>, | |
| where <code>n</code> is the length of the table, | |
| so that a call <code>table.remove(t)</code> removes the last element | |
| of table <code>t</code>. | |
| <p> | |
| <hr><h3><a name="pdf-table.sort"><code>table.sort (table [, comp])</code></a></h3> | |
| Sorts table elements in a given order, <em>in-place</em>, | |
| from <code>table[1]</code> to <code>table[n]</code>, | |
| where <code>n</code> is the length of the table. | |
| If <code>comp</code> is given, | |
| then it must be a function that receives two table elements, | |
| and returns true | |
| when the first is less than the second | |
| (so that <code>not comp(a[i+1],a[i])</code> will be true after the sort). | |
| If <code>comp</code> is not given, | |
| then the standard Lua operator <code><</code> is used instead. | |
| <p> | |
| The sort algorithm is not stable; | |
| that is, elements considered equal by the given order | |
| may have their relative positions changed by the sort. | |
| <h2>5.6 - <a name="5.6">Mathematical Functions</a></h2> | |
| <p> | |
| This library is an interface to the standard C math library. | |
| It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> | |
| <p> | |
| Returns the absolute value of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3> | |
| <p> | |
| Returns the arc cosine of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3> | |
| <p> | |
| Returns the arc sine of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3> | |
| <p> | |
| Returns the arc tangent of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3> | |
| <p> | |
| Returns the arc tangent of <code>y/x</code> (in radians), | |
| but uses the signs of both parameters to find the | |
| quadrant of the result. | |
| (It also handles correctly the case of <code>x</code> being zero.) | |
| <p> | |
| <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> | |
| <p> | |
| Returns the smallest integer larger than or equal to <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3> | |
| <p> | |
| Returns the cosine of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic cosine of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3> | |
| <p> | |
| Returns the angle <code>x</code> (given in radians) in degrees. | |
| <p> | |
| <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> | |
| <p> | |
| Returns the value <em>e<sup>x</sup></em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> | |
| <p> | |
| Returns the largest integer smaller than or equal to <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> | |
| <p> | |
| Returns the remainder of the division of <code>x</code> by <code>y</code> | |
| that rounds the quotient towards zero. | |
| <p> | |
| <hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3> | |
| <p> | |
| Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>, | |
| <code>e</code> is an integer and the absolute value of <code>m</code> is | |
| in the range <em>[0.5, 1)</em> | |
| (or zero when <code>x</code> is zero). | |
| <p> | |
| <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> | |
| <p> | |
| The value <code>HUGE_VAL</code>, | |
| a value larger than or equal to any other numerical value. | |
| <p> | |
| <hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3> | |
| <p> | |
| Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer). | |
| <p> | |
| <hr><h3><a name="pdf-math.log"><code>math.log (x)</code></a></h3> | |
| <p> | |
| Returns the natural logarithm of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.log10"><code>math.log10 (x)</code></a></h3> | |
| <p> | |
| Returns the base-10 logarithm of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> | |
| <p> | |
| Returns the maximum value among its arguments. | |
| <p> | |
| <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> | |
| <p> | |
| Returns the minimum value among its arguments. | |
| <p> | |
| <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> | |
| <p> | |
| Returns two numbers, | |
| the integral part of <code>x</code> and the fractional part of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> | |
| <p> | |
| The value of <em>pi</em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3> | |
| <p> | |
| Returns <em>x<sup>y</sup></em>. | |
| (You can also use the expression <code>x^y</code> to compute this value.) | |
| <p> | |
| <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> | |
| <p> | |
| Returns the angle <code>x</code> (given in degrees) in radians. | |
| <p> | |
| <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> | |
| <p> | |
| This function is an interface to the simple | |
| pseudo-random generator function <code>rand</code> provided by ANSI C. | |
| (No guarantees can be given for its statistical properties.) | |
| <p> | |
| When called without arguments, | |
| returns a uniform pseudo-random real number | |
| in the range <em>[0,1)</em>. | |
| When called with an integer number <code>m</code>, | |
| <code>math.random</code> returns | |
| a uniform pseudo-random integer in the range <em>[1, m]</em>. | |
| When called with two integer numbers <code>m</code> and <code>n</code>, | |
| <code>math.random</code> returns a uniform pseudo-random | |
| integer in the range <em>[m, n]</em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3> | |
| <p> | |
| Sets <code>x</code> as the "seed" | |
| for the pseudo-random generator: | |
| equal seeds produce equal sequences of numbers. | |
| <p> | |
| <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3> | |
| <p> | |
| Returns the sine of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic sine of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3> | |
| <p> | |
| Returns the square root of <code>x</code>. | |
| (You can also use the expression <code>x^0.5</code> to compute this value.) | |
| <p> | |
| <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3> | |
| <p> | |
| Returns the tangent of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic tangent of <code>x</code>. | |
| <h2>5.7 - <a name="5.7">Input and Output Facilities</a></h2> | |
| <p> | |
| The I/O library provides two different styles for file manipulation. | |
| The first one uses implicit file descriptors; | |
| that is, there are operations to set a default input file and a | |
| default output file, | |
| and all input/output operations are over these default files. | |
| The second style uses explicit file descriptors. | |
| <p> | |
| When using implicit file descriptors, | |
| all operations are supplied by table <a name="pdf-io"><code>io</code></a>. | |
| When using explicit file descriptors, | |
| the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor | |
| and then all operations are supplied as methods of the file descriptor. | |
| <p> | |
| The table <code>io</code> also provides | |
| three predefined file descriptors with their usual meanings from C: | |
| <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. | |
| The I/O library never closes these files. | |
| <p> | |
| Unless otherwise stated, | |
| all I/O functions return <b>nil</b> on failure | |
| (plus an error message as a second result and | |
| a system-dependent error code as a third result) | |
| and some value different from <b>nil</b> on success. | |
| <p> | |
| <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3> | |
| <p> | |
| Equivalent to <code>file:close()</code>. | |
| Without a <code>file</code>, closes the default output file. | |
| <p> | |
| <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3> | |
| <p> | |
| Equivalent to <code>file:flush</code> over the default output file. | |
| <p> | |
| <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3> | |
| <p> | |
| When called with a file name, it opens the named file (in text mode), | |
| and sets its handle as the default input file. | |
| When called with a file handle, | |
| it simply sets this file handle as the default input file. | |
| When called without parameters, | |
| it returns the current default input file. | |
| <p> | |
| In case of errors this function raises the error, | |
| instead of returning an error code. | |
| <p> | |
| <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename])</code></a></h3> | |
| <p> | |
| Opens the given file name in read mode | |
| and returns an iterator function that, | |
| each time it is called, | |
| returns a new line from the file. | |
| Therefore, the construction | |
| <pre> | |
| for line in io.lines(filename) do <em>body</em> end | |
| </pre><p> | |
| will iterate over all lines of the file. | |
| When the iterator function detects the end of file, | |
| it returns <b>nil</b> (to finish the loop) and automatically closes the file. | |
| <p> | |
| The call <code>io.lines()</code> (with no file name) is equivalent | |
| to <code>io.input():lines()</code>; | |
| that is, it iterates over the lines of the default input file. | |
| In this case it does not close the file when the loop ends. | |
| <p> | |
| <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3> | |
| <p> | |
| This function opens a file, | |
| in the mode specified in the string <code>mode</code>. | |
| It returns a new file handle, | |
| or, in case of errors, <b>nil</b> plus an error message. | |
| <p> | |
| The <code>mode</code> string can be any of the following: | |
| <ul> | |
| <li><b>"r":</b> read mode (the default);</li> | |
| <li><b>"w":</b> write mode;</li> | |
| <li><b>"a":</b> append mode;</li> | |
| <li><b>"r+":</b> update mode, all previous data is preserved;</li> | |
| <li><b>"w+":</b> update mode, all previous data is erased;</li> | |
| <li><b>"a+":</b> append update mode, previous data is preserved, | |
| writing is only allowed at the end of file.</li> | |
| </ul><p> | |
| The <code>mode</code> string can also have a '<code>b</code>' at the end, | |
| which is needed in some systems to open the file in binary mode. | |
| This string is exactly what is used in the | |
| standard C function <code>fopen</code>. | |
| <p> | |
| <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3> | |
| <p> | |
| Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. | |
| <p> | |
| <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3> | |
| <p> | |
| Starts program <code>prog</code> in a separated process and returns | |
| a file handle that you can use to read data from this program | |
| (if <code>mode</code> is <code>"r"</code>, the default) | |
| or to write data to this program | |
| (if <code>mode</code> is <code>"w"</code>). | |
| <p> | |
| This function is system dependent and is not available | |
| on all platforms. | |
| <p> | |
| <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3> | |
| <p> | |
| Equivalent to <code>io.input():read</code>. | |
| <p> | |
| <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3> | |
| <p> | |
| Returns a handle for a temporary file. | |
| This file is opened in update mode | |
| and it is automatically removed when the program ends. | |
| <p> | |
| <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3> | |
| <p> | |
| Checks whether <code>obj</code> is a valid file handle. | |
| Returns the string <code>"file"</code> if <code>obj</code> is an open file handle, | |
| <code>"closed file"</code> if <code>obj</code> is a closed file handle, | |
| or <b>nil</b> if <code>obj</code> is not a file handle. | |
| <p> | |
| <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3> | |
| <p> | |
| Equivalent to <code>io.output():write</code>. | |
| <p> | |
| <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3> | |
| <p> | |
| Closes <code>file</code>. | |
| Note that files are automatically closed when | |
| their handles are garbage collected, | |
| but that takes an unpredictable amount of time to happen. | |
| <p> | |
| <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3> | |
| <p> | |
| Saves any written data to <code>file</code>. | |
| <p> | |
| <hr><h3><a name="pdf-file:lines"><code>file:lines ()</code></a></h3> | |
| <p> | |
| Returns an iterator function that, | |
| each time it is called, | |
| returns a new line from the file. | |
| Therefore, the construction | |
| <pre> | |
| for line in file:lines() do <em>body</em> end | |
| </pre><p> | |
| will iterate over all lines of the file. | |
| (Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file | |
| when the loop ends.) | |
| <p> | |
| <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3> | |
| <p> | |
| Reads the file <code>file</code>, | |
| according to the given formats, which specify what to read. | |
| For each format, | |
| the function returns a string (or a number) with the characters read, | |
| or <b>nil</b> if it cannot read data with the specified format. | |
| When called without formats, | |
| it uses a default format that reads the entire next line | |
| (see below). | |
| <p> | |
| The available formats are | |
| <ul> | |
| <li><b>"*n":</b> | |
| reads a number; | |
| this is the only format that returns a number instead of a string. | |
| </li> | |
| <li><b>"*a":</b> | |
| reads the whole file, starting at the current position. | |
| On end of file, it returns the empty string. | |
| </li> | |
| <li><b>"*l":</b> | |
| reads the next line (skipping the end of line), | |
| returning <b>nil</b> on end of file. | |
| This is the default format. | |
| </li> | |
| <li><b><em>number</em>:</b> | |
| reads a string with up to this number of characters, | |
| returning <b>nil</b> on end of file. | |
| If number is zero, | |
| it reads nothing and returns an empty string, | |
| or <b>nil</b> on end of file. | |
| </li> | |
| </ul> | |
| <p> | |
| <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence] [, offset])</code></a></h3> | |
| <p> | |
| Sets and gets the file position, | |
| measured from the beginning of the file, | |
| to the position given by <code>offset</code> plus a base | |
| specified by the string <code>whence</code>, as follows: | |
| <ul> | |
| <li><b>"set":</b> base is position 0 (beginning of the file);</li> | |
| <li><b>"cur":</b> base is current position;</li> | |
| <li><b>"end":</b> base is end of file;</li> | |
| </ul><p> | |
| In case of success, function <code>seek</code> returns the final file position, | |
| measured in bytes from the beginning of the file. | |
| If this function fails, it returns <b>nil</b>, | |
| plus a string describing the error. | |
| <p> | |
| The default value for <code>whence</code> is <code>"cur"</code>, | |
| and for <code>offset</code> is 0. | |
| Therefore, the call <code>file:seek()</code> returns the current | |
| file position, without changing it; | |
| the call <code>file:seek("set")</code> sets the position to the | |
| beginning of the file (and returns 0); | |
| and the call <code>file:seek("end")</code> sets the position to the | |
| end of the file, and returns its size. | |
| <p> | |
| <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3> | |
| <p> | |
| Sets the buffering mode for an output file. | |
| There are three available modes: | |
| <ul> | |
| <li><b>"no":</b> | |
| no buffering; the result of any output operation appears immediately. | |
| </li> | |
| <li><b>"full":</b> | |
| full buffering; output operation is performed only | |
| when the buffer is full (or when you explicitly <code>flush</code> the file | |
| (see <a href="#pdf-io.flush"><code>io.flush</code></a>)). | |
| </li> | |
| <li><b>"line":</b> | |
| line buffering; output is buffered until a newline is output | |
| or there is any input from some special files | |
| (such as a terminal device). | |
| </li> | |
| </ul><p> | |
| For the last two cases, <code>size</code> | |
| specifies the size of the buffer, in bytes. | |
| The default is an appropriate size. | |
| <p> | |
| <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3> | |
| <p> | |
| Writes the value of each of its arguments to | |
| the <code>file</code>. | |
| The arguments must be strings or numbers. | |
| To write other values, | |
| use <a href="#pdf-tostring"><code>tostring</code></a> or <a href="#pdf-string.format"><code>string.format</code></a> before <code>write</code>. | |
| <h2>5.8 - <a name="5.8">Operating System Facilities</a></h2> | |
| <p> | |
| This library is implemented through table <a name="pdf-os"><code>os</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3> | |
| <p> | |
| Returns an approximation of the amount in seconds of CPU time | |
| used by the program. | |
| <p> | |
| <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3> | |
| <p> | |
| Returns a string or a table containing date and time, | |
| formatted according to the given string <code>format</code>. | |
| <p> | |
| If the <code>time</code> argument is present, | |
| this is the time to be formatted | |
| (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value). | |
| Otherwise, <code>date</code> formats the current time. | |
| <p> | |
| If <code>format</code> starts with '<code>!</code>', | |
| then the date is formatted in Coordinated Universal Time. | |
| After this optional character, | |
| if <code>format</code> is the string "<code>*t</code>", | |
| then <code>date</code> returns a table with the following fields: | |
| <code>year</code> (four digits), <code>month</code> (1--12), <code>day</code> (1--31), | |
| <code>hour</code> (0--23), <code>min</code> (0--59), <code>sec</code> (0--61), | |
| <code>wday</code> (weekday, Sunday is 1), | |
| <code>yday</code> (day of the year), | |
| and <code>isdst</code> (daylight saving flag, a boolean). | |
| <p> | |
| If <code>format</code> is not "<code>*t</code>", | |
| then <code>date</code> returns the date as a string, | |
| formatted according to the same rules as the C function <code>strftime</code>. | |
| <p> | |
| When called without arguments, | |
| <code>date</code> returns a reasonable date and time representation that depends on | |
| the host system and on the current locale | |
| (that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>). | |
| <p> | |
| <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> | |
| <p> | |
| Returns the number of seconds from time <code>t1</code> to time <code>t2</code>. | |
| In POSIX, Windows, and some other systems, | |
| this value is exactly <code>t2</code><em>-</em><code>t1</code>. | |
| <p> | |
| <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3> | |
| <p> | |
| This function is equivalent to the C function <code>system</code>. | |
| It passes <code>command</code> to be executed by an operating system shell. | |
| It returns a status code, which is system-dependent. | |
| If <code>command</code> is absent, then it returns nonzero if a shell is available | |
| and zero otherwise. | |
| <p> | |
| <hr><h3><a name="pdf-os.exit"><code>os.exit ([code])</code></a></h3> | |
| <p> | |
| Calls the C function <code>exit</code>, | |
| with an optional <code>code</code>, | |
| to terminate the host program. | |
| The default value for <code>code</code> is the success code. | |
| <p> | |
| <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3> | |
| <p> | |
| Returns the value of the process environment variable <code>varname</code>, | |
| or <b>nil</b> if the variable is not defined. | |
| <p> | |
| <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3> | |
| <p> | |
| Deletes the file or directory with the given name. | |
| Directories must be empty to be removed. | |
| If this function fails, it returns <b>nil</b>, | |
| plus a string describing the error. | |
| <p> | |
| <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3> | |
| <p> | |
| Renames file or directory named <code>oldname</code> to <code>newname</code>. | |
| If this function fails, it returns <b>nil</b>, | |
| plus a string describing the error. | |
| <p> | |
| <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3> | |
| <p> | |
| Sets the current locale of the program. | |
| <code>locale</code> is a string specifying a locale; | |
| <code>category</code> is an optional string describing which category to change: | |
| <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, | |
| <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; | |
| the default category is <code>"all"</code>. | |
| The function returns the name of the new locale, | |
| or <b>nil</b> if the request cannot be honored. | |
| <p> | |
| If <code>locale</code> is the empty string, | |
| the current locale is set to an implementation-defined native locale. | |
| If <code>locale</code> is the string "<code>C</code>", | |
| the current locale is set to the standard C locale. | |
| <p> | |
| When called with <b>nil</b> as the first argument, | |
| this function only returns the name of the current locale | |
| for the given category. | |
| <p> | |
| <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3> | |
| <p> | |
| Returns the current time when called without arguments, | |
| or a time representing the date and time specified by the given table. | |
| This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>, | |
| and may have fields <code>hour</code>, <code>min</code>, <code>sec</code>, and <code>isdst</code> | |
| (for a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function). | |
| <p> | |
| The returned value is a number, whose meaning depends on your system. | |
| In POSIX, Windows, and some other systems, this number counts the number | |
| of seconds since some given start time (the "epoch"). | |
| In other systems, the meaning is not specified, | |
| and the number returned by <code>time</code> can be used only as an argument to | |
| <code>date</code> and <code>difftime</code>. | |
| <p> | |
| <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> | |
| <p> | |
| Returns a string with a file name that can | |
| be used for a temporary file. | |
| The file must be explicitly opened before its use | |
| and explicitly removed when no longer needed. | |
| <p> | |
| On some systems (POSIX), | |
| this function also creates a file with that name, | |
| to avoid security risks. | |
| (Someone else might create the file with wrong permissions | |
| in the time between getting the name and creating the file.) | |
| You still have to open the file to use it | |
| and to remove it (even if you do not use it). | |
| <p> | |
| When possible, | |
| you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, | |
| which automatically removes the file when the program ends. | |
| <h2>5.9 - <a name="5.9">The Debug Library</a></h2> | |
| <p> | |
| This library provides | |
| the functionality of the debug interface to Lua programs. | |
| You should exert care when using this library. | |
| The functions provided here should be used exclusively for debugging | |
| and similar tasks, such as profiling. | |
| Please resist the temptation to use them as a | |
| usual programming tool: | |
| they can be very slow. | |
| Moreover, several of these functions | |
| violate some assumptions about Lua code | |
| (e.g., that variables local to a function | |
| cannot be accessed from outside or | |
| that userdata metatables cannot be changed by Lua code) | |
| and therefore can compromise otherwise secure code. | |
| <p> | |
| All functions in this library are provided | |
| inside the <a name="pdf-debug"><code>debug</code></a> table. | |
| All functions that operate over a thread | |
| have an optional first argument which is the | |
| thread to operate over. | |
| The default is always the current thread. | |
| <p> | |
| <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3> | |
| <p> | |
| Enters an interactive mode with the user, | |
| running each string that the user enters. | |
| Using simple commands and other debug facilities, | |
| the user can inspect global and local variables, | |
| change their values, evaluate expressions, and so on. | |
| A line containing only the word <code>cont</code> finishes this function, | |
| so that the caller continues its execution. | |
| <p> | |
| Note that commands for <code>debug.debug</code> are not lexically nested | |
| within any function, and so have no direct access to local variables. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getfenv"><code>debug.getfenv (o)</code></a></h3> | |
| Returns the environment of object <code>o</code>. | |
| <p> | |
| <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3> | |
| <p> | |
| Returns the current hook settings of the thread, as three values: | |
| the current hook function, the current hook mask, | |
| and the current hook count | |
| (as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). | |
| <p> | |
| <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] function [, what])</code></a></h3> | |
| <p> | |
| Returns a table with information about a function. | |
| You can give the function directly, | |
| or you can give a number as the value of <code>function</code>, | |
| which means the function running at level <code>function</code> of the call stack | |
| of the given thread: | |
| level 0 is the current function (<code>getinfo</code> itself); | |
| level 1 is the function that called <code>getinfo</code>; | |
| and so on. | |
| If <code>function</code> is a number larger than the number of active functions, | |
| then <code>getinfo</code> returns <b>nil</b>. | |
| <p> | |
| The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, | |
| with the string <code>what</code> describing which fields to fill in. | |
| The default for <code>what</code> is to get all information available, | |
| except the table of valid lines. | |
| If present, | |
| the option '<code>f</code>' | |
| adds a field named <code>func</code> with the function itself. | |
| If present, | |
| the option '<code>L</code>' | |
| adds a field named <code>activelines</code> with the table of | |
| valid lines. | |
| <p> | |
| For instance, the expression <code>debug.getinfo(1,"n").name</code> returns | |
| a table with a name for the current function, | |
| if a reasonable name can be found, | |
| and the expression <code>debug.getinfo(print)</code> | |
| returns a table with all available information | |
| about the <a href="#pdf-print"><code>print</code></a> function. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] level, local)</code></a></h3> | |
| <p> | |
| This function returns the name and the value of the local variable | |
| with index <code>local</code> of the function at level <code>level</code> of the stack. | |
| (The first parameter or local variable has index 1, and so on, | |
| until the last active local variable.) | |
| The function returns <b>nil</b> if there is no local | |
| variable with the given index, | |
| and raises an error when called with a <code>level</code> out of range. | |
| (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.) | |
| <p> | |
| Variable names starting with '<code>(</code>' (open parentheses) | |
| represent internal variables | |
| (loop control variables, temporaries, and C function locals). | |
| <p> | |
| <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (object)</code></a></h3> | |
| <p> | |
| Returns the metatable of the given <code>object</code> | |
| or <b>nil</b> if it does not have a metatable. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3> | |
| <p> | |
| Returns the registry table (see <a href="#3.5">§3.5</a>). | |
| <p> | |
| <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (func, up)</code></a></h3> | |
| <p> | |
| This function returns the name and the value of the upvalue | |
| with index <code>up</code> of the function <code>func</code>. | |
| The function returns <b>nil</b> if there is no upvalue with the given index. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setfenv"><code>debug.setfenv (object, table)</code></a></h3> | |
| <p> | |
| Sets the environment of the given <code>object</code> to the given <code>table</code>. | |
| Returns <code>object</code>. | |
| <p> | |
| <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3> | |
| <p> | |
| Sets the given function as a hook. | |
| The string <code>mask</code> and the number <code>count</code> describe | |
| when the hook will be called. | |
| The string mask may have the following characters, | |
| with the given meaning: | |
| <ul> | |
| <li><b><code>"c"</code>:</b> the hook is called every time Lua calls a function;</li> | |
| <li><b><code>"r"</code>:</b> the hook is called every time Lua returns from a function;</li> | |
| <li><b><code>"l"</code>:</b> the hook is called every time Lua enters a new line of code.</li> | |
| </ul><p> | |
| With a <code>count</code> different from zero, | |
| the hook is called after every <code>count</code> instructions. | |
| <p> | |
| When called without arguments, | |
| <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook. | |
| <p> | |
| When the hook is called, its first parameter is a string | |
| describing the event that has triggered its call: | |
| <code>"call"</code>, <code>"return"</code> (or <code>"tail return"</code>, | |
| when simulating a return from a tail call), | |
| <code>"line"</code>, and <code>"count"</code>. | |
| For line events, | |
| the hook also gets the new line number as its second parameter. | |
| Inside a hook, | |
| you can call <code>getinfo</code> with level 2 to get more information about | |
| the running function | |
| (level 0 is the <code>getinfo</code> function, | |
| and level 1 is the hook function), | |
| unless the event is <code>"tail return"</code>. | |
| In this case, Lua is only simulating the return, | |
| and a call to <code>getinfo</code> will return invalid data. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3> | |
| <p> | |
| This function assigns the value <code>value</code> to the local variable | |
| with index <code>local</code> of the function at level <code>level</code> of the stack. | |
| The function returns <b>nil</b> if there is no local | |
| variable with the given index, | |
| and raises an error when called with a <code>level</code> out of range. | |
| (You can call <code>getinfo</code> to check whether the level is valid.) | |
| Otherwise, it returns the name of the local variable. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (object, table)</code></a></h3> | |
| <p> | |
| Sets the metatable for the given <code>object</code> to the given <code>table</code> | |
| (which can be <b>nil</b>). | |
| <p> | |
| <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (func, up, value)</code></a></h3> | |
| <p> | |
| This function assigns the value <code>value</code> to the upvalue | |
| with index <code>up</code> of the function <code>func</code>. | |
| The function returns <b>nil</b> if there is no upvalue | |
| with the given index. | |
| Otherwise, it returns the name of the upvalue. | |
| <p> | |
| <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message] [, level])</code></a></h3> | |
| <p> | |
| Returns a string with a traceback of the call stack. | |
| An optional <code>message</code> string is appended | |
| at the beginning of the traceback. | |
| An optional <code>level</code> number tells at which level | |
| to start the traceback | |
| (default is 1, the function calling <code>traceback</code>). | |
| <h1>6 - <a name="6">Lua Stand-alone</a></h1> | |
| <p> | |
| Although Lua has been designed as an extension language, | |
| to be embedded in a host C program, | |
| it is also frequently used as a stand-alone language. | |
| An interpreter for Lua as a stand-alone language, | |
| called simply <code>lua</code>, | |
| is provided with the standard distribution. | |
| The stand-alone interpreter includes | |
| all standard libraries, including the debug library. | |
| Its usage is: | |
| <pre> | |
| lua [options] [script [args]] | |
| </pre><p> | |
| The options are: | |
| <ul> | |
| <li><b><code>-e <em>stat</em></code>:</b> executes string <em>stat</em>;</li> | |
| <li><b><code>-l <em>mod</em></code>:</b> "requires" <em>mod</em>;</li> | |
| <li><b><code>-i</code>:</b> enters interactive mode after running <em>script</em>;</li> | |
| <li><b><code>-v</code>:</b> prints version information;</li> | |
| <li><b><code>--</code>:</b> stops handling options;</li> | |
| <li><b><code>-</code>:</b> executes <code>stdin</code> as a file and stops handling options.</li> | |
| </ul><p> | |
| After handling its options, <code>lua</code> runs the given <em>script</em>, | |
| passing to it the given <em>args</em> as string arguments. | |
| When called without arguments, | |
| <code>lua</code> behaves as <code>lua -v -i</code> | |
| when the standard input (<code>stdin</code>) is a terminal, | |
| and as <code>lua -</code> otherwise. | |
| <p> | |
| Before running any argument, | |
| the interpreter checks for an environment variable <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a>. | |
| If its format is <code>@<em>filename</em></code>, | |
| then <code>lua</code> executes the file. | |
| Otherwise, <code>lua</code> executes the string itself. | |
| <p> | |
| All options are handled in order, except <code>-i</code>. | |
| For instance, an invocation like | |
| <pre> | |
| $ lua -e'a=1' -e 'print(a)' script.lua | |
| </pre><p> | |
| will first set <code>a</code> to 1, then print the value of <code>a</code> (which is '<code>1</code>'), | |
| and finally run the file <code>script.lua</code> with no arguments. | |
| (Here <code>$</code> is the shell prompt. Your prompt may be different.) | |
| <p> | |
| Before starting to run the script, | |
| <code>lua</code> collects all arguments in the command line | |
| in a global table called <code>arg</code>. | |
| The script name is stored at index 0, | |
| the first argument after the script name goes to index 1, | |
| and so on. | |
| Any arguments before the script name | |
| (that is, the interpreter name plus the options) | |
| go to negative indices. | |
| For instance, in the call | |
| <pre> | |
| $ lua -la b.lua t1 t2 | |
| </pre><p> | |
| the interpreter first runs the file <code>a.lua</code>, | |
| then creates a table | |
| <pre> | |
| arg = { [-2] = "lua", [-1] = "-la", | |
| [0] = "b.lua", | |
| [1] = "t1", [2] = "t2" } | |
| </pre><p> | |
| and finally runs the file <code>b.lua</code>. | |
| The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ··· | |
| as arguments; | |
| it can also access these arguments with the vararg expression '<code>...</code>'. | |
| <p> | |
| In interactive mode, | |
| if you write an incomplete statement, | |
| the interpreter waits for its completion | |
| by issuing a different prompt. | |
| <p> | |
| If the global variable <a name="pdf-_PROMPT"><code>_PROMPT</code></a> contains a string, | |
| then its value is used as the prompt. | |
| Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> contains a string, | |
| its value is used as the secondary prompt | |
| (issued during incomplete statements). | |
| Therefore, both prompts can be changed directly on the command line | |
| or in any Lua programs by assigning to <code>_PROMPT</code>. | |
| See the next example: | |
| <pre> | |
| $ lua -e"_PROMPT='myprompt> '" -i | |
| </pre><p> | |
| (The outer pair of quotes is for the shell, | |
| the inner pair is for Lua.) | |
| Note the use of <code>-i</code> to enter interactive mode; | |
| otherwise, | |
| the program would just end silently | |
| right after the assignment to <code>_PROMPT</code>. | |
| <p> | |
| To allow the use of Lua as a | |
| script interpreter in Unix systems, | |
| the stand-alone interpreter skips | |
| the first line of a chunk if it starts with <code>#</code>. | |
| Therefore, Lua scripts can be made into executable programs | |
| by using <code>chmod +x</code> and the <code>#!</code> form, | |
| as in | |
| <pre> | |
| #!/usr/local/bin/lua | |
| </pre><p> | |
| (Of course, | |
| the location of the Lua interpreter may be different in your machine. | |
| If <code>lua</code> is in your <code>PATH</code>, | |
| then | |
| <pre> | |
| #!/usr/bin/env lua | |
| </pre><p> | |
| is a more portable solution.) | |
| <h1>7 - <a name="7">Incompatibilities with the Previous Version</a></h1> | |
| <p> | |
| Here we list the incompatibilities that you may find when moving a program | |
| from Lua 5.0 to Lua 5.1. | |
| You can avoid most of the incompatibilities compiling Lua with | |
| appropriate options (see file <code>luaconf.h</code>). | |
| However, | |
| all these compatibility options will be removed in the next version of Lua. | |
| <h2>7.1 - <a name="7.1">Changes in the Language</a></h2> | |
| <ul> | |
| <li> | |
| The vararg system changed from the pseudo-argument <code>arg</code> with a | |
| table with the extra arguments to the vararg expression. | |
| (See compile-time option <code>LUA_COMPAT_VARARG</code> in <code>luaconf.h</code>.) | |
| </li> | |
| <li> | |
| There was a subtle change in the scope of the implicit | |
| variables of the <b>for</b> statement and for the <b>repeat</b> statement. | |
| </li> | |
| <li> | |
| The long string/long comment syntax (<code>[[<em>string</em>]]</code>) | |
| does not allow nesting. | |
| You can use the new syntax (<code>[=[<em>string</em>]=]</code>) in these cases. | |
| (See compile-time option <code>LUA_COMPAT_LSTR</code> in <code>luaconf.h</code>.) | |
| </li> | |
| </ul> | |
| <h2>7.2 - <a name="7.2">Changes in the Libraries</a></h2> | |
| <ul> | |
| <li> | |
| Function <code>string.gfind</code> was renamed <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>. | |
| (See compile-time option <code>LUA_COMPAT_GFIND</code> in <code>luaconf.h</code>.) | |
| </li> | |
| <li> | |
| When <a href="#pdf-string.gsub"><code>string.gsub</code></a> is called with a function as its | |
| third argument, | |
| whenever this function returns <b>nil</b> or <b>false</b> the | |
| replacement string is the whole match, | |
| instead of the empty string. | |
| </li> | |
| <li> | |
| Function <code>table.setn</code> was deprecated. | |
| Function <code>table.getn</code> corresponds | |
| to the new length operator (<code>#</code>); | |
| use the operator instead of the function. | |
| (See compile-time option <code>LUA_COMPAT_GETN</code> in <code>luaconf.h</code>.) | |
| </li> | |
| <li> | |
| Function <code>loadlib</code> was renamed <a href="#pdf-package.loadlib"><code>package.loadlib</code></a>. | |
| (See compile-time option <code>LUA_COMPAT_LOADLIB</code> in <code>luaconf.h</code>.) | |
| </li> | |
| <li> | |
| Function <code>math.mod</code> was renamed <a href="#pdf-math.fmod"><code>math.fmod</code></a>. | |
| (See compile-time option <code>LUA_COMPAT_MOD</code> in <code>luaconf.h</code>.) | |
| </li> | |
| <li> | |
| Functions <code>table.foreach</code> and <code>table.foreachi</code> are deprecated. | |
| You can use a for loop with <code>pairs</code> or <code>ipairs</code> instead. | |
| </li> | |
| <li> | |
| There were substantial changes in function <a href="#pdf-require"><code>require</code></a> due to | |
| the new module system. | |
| However, the new behavior is mostly compatible with the old, | |
| but <code>require</code> gets the path from <a href="#pdf-package.path"><code>package.path</code></a> instead | |
| of from <code>LUA_PATH</code>. | |
| </li> | |
| <li> | |
| Function <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> has different arguments. | |
| Function <code>gcinfo</code> is deprecated; | |
| use <code>collectgarbage("count")</code> instead. | |
| </li> | |
| </ul> | |
| <h2>7.3 - <a name="7.3">Changes in the API</a></h2> | |
| <ul> | |
| <li> | |
| The <code>luaopen_*</code> functions (to open libraries) | |
| cannot be called directly, | |
| like a regular C function. | |
| They must be called through Lua, | |
| like a Lua function. | |
| </li> | |
| <li> | |
| Function <code>lua_open</code> was replaced by <a href="#lua_newstate"><code>lua_newstate</code></a> to | |
| allow the user to set a memory-allocation function. | |
| You can use <a href="#luaL_newstate"><code>luaL_newstate</code></a> from the standard library to | |
| create a state with a standard allocation function | |
| (based on <code>realloc</code>). | |
| </li> | |
| <li> | |
| Functions <code>luaL_getn</code> and <code>luaL_setn</code> | |
| (from the auxiliary library) are deprecated. | |
| Use <a href="#lua_objlen"><code>lua_objlen</code></a> instead of <code>luaL_getn</code> | |
| and nothing instead of <code>luaL_setn</code>. | |
| </li> | |
| <li> | |
| Function <code>luaL_openlib</code> was replaced by <a href="#luaL_register"><code>luaL_register</code></a>. | |
| </li> | |
| <li> | |
| Function <code>luaL_checkudata</code> now throws an error when the given value | |
| is not a userdata of the expected type. | |
| (In Lua 5.0 it returned <code>NULL</code>.) | |
| </li> | |
| </ul> | |
| <h1>8 - <a name="8">The Complete Syntax of Lua</a></h1> | |
| <p> | |
| Here is the complete syntax of Lua in extended BNF. | |
| (It does not describe operator precedences.) | |
| <pre> | |
| chunk ::= {stat [`<b>;</b>´]} [laststat [`<b>;</b>´]] | |
| block ::= chunk | |
| stat ::= varlist `<b>=</b>´ explist | | |
| functioncall | | |
| <b>do</b> block <b>end</b> | | |
| <b>while</b> exp <b>do</b> block <b>end</b> | | |
| <b>repeat</b> block <b>until</b> exp | | |
| <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | | |
| <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> | | |
| <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | | |
| <b>function</b> funcname funcbody | | |
| <b>local</b> <b>function</b> Name funcbody | | |
| <b>local</b> namelist [`<b>=</b>´ explist] | |
| laststat ::= <b>return</b> [explist] | <b>break</b> | |
| funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name] | |
| varlist ::= var {`<b>,</b>´ var} | |
| var ::= Name | prefixexp `<b>[</b>´ exp `<b>]</b>´ | prefixexp `<b>.</b>´ Name | |
| namelist ::= Name {`<b>,</b>´ Name} | |
| explist ::= {exp `<b>,</b>´} exp | |
| exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | `<b>...</b>´ | function | | |
| prefixexp | tableconstructor | exp binop exp | unop exp | |
| prefixexp ::= var | functioncall | `<b>(</b>´ exp `<b>)</b>´ | |
| functioncall ::= prefixexp args | prefixexp `<b>:</b>´ Name args | |
| args ::= `<b>(</b>´ [explist] `<b>)</b>´ | tableconstructor | String | |
| function ::= <b>function</b> funcbody | |
| funcbody ::= `<b>(</b>´ [parlist] `<b>)</b>´ block <b>end</b> | |
| parlist ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´ | |
| tableconstructor ::= `<b>{</b>´ [fieldlist] `<b>}</b>´ | |
| fieldlist ::= field {fieldsep field} [fieldsep] | |
| field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp | |
| fieldsep ::= `<b>,</b>´ | `<b>;</b>´ | |
| binop ::= `<b>+</b>´ | `<b>-</b>´ | `<b>*</b>´ | `<b>/</b>´ | `<b>^</b>´ | `<b>%</b>´ | `<b>..</b>´ | | |
| `<b><</b>´ | `<b><=</b>´ | `<b>></b>´ | `<b>>=</b>´ | `<b>==</b>´ | `<b>~=</b>´ | | |
| <b>and</b> | <b>or</b> | |
| unop ::= `<b>-</b>´ | <b>not</b> | `<b>#</b>´ | |
| </pre> | |
| <p> | |
| <HR> | |
| <SMALL> | |
| Last update: | |
| Mon Aug 18 13:25:46 BRT 2008 | |
| </SMALL> | |
| <!-- | |
| Last change: revised for Lua 5.1.4 | |
| --> | |
| </body></html> | |