8521 lines
237 KiB
HTML
8521 lines
237 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<html>
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<head>
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<title>Lua 5.1 Reference Manual</title>
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<link rel="stylesheet" href="lua.css">
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<link rel="stylesheet" href="manual.css">
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</head>
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<body>
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<hr>
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<h1>
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<a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a>
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Lua 5.1 Reference Manual
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</h1>
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by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
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<p>
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<small>
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Copyright © 2006-2007 Lua.org, PUC-Rio.
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Freely available under the terms of the
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<a href="http://www.lua.org/license.html#5">Lua license</a>.
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</small>
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<hr>
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<p>
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<a href="contents.html#contents">contents</A>
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·
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<a href="contents.html#index">index</A>
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<!-- ====================================================================== -->
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<p>
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<h1>1 - <a name="1">Introduction</a></h1>
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<p>
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Lua is an extension programming language designed to support
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general procedural programming with data description
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facilities.
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It also offers good support for object-oriented programming,
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functional programming, and data-driven programming.
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Lua is intended to be used as a powerful, light-weight
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scripting language for any program that needs one.
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Lua is implemented as a library, written in <em>clean</em> C
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(that is, in the common subset of ANSI C and C++).
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<p>
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Being an extension language, Lua has no notion of a "main" program:
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it only works <em>embedded</em> in a host client,
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called the <em>embedding program</em> or simply the <em>host</em>.
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This host program can invoke functions to execute a piece of Lua code,
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can write and read Lua variables,
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and can register C functions to be called by Lua code.
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Through the use of C functions, Lua can be augmented to cope with
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a wide range of different domains,
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thus creating customized programming languages sharing a syntactical framework.
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The Lua distribution includes a sample host program called <code>lua</code>,
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which uses the Lua library to offer a complete, stand-alone Lua interpreter.
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<p>
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Lua is free software,
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and is provided as usual with no guarantees,
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as stated in its license.
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The implementation described in this manual is available
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at Lua's official web site, <code>www.lua.org</code>.
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<p>
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Like any other reference manual,
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this document is dry in places.
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For a discussion of the decisions behind the design of Lua,
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see the technical papers available at Lua's web site.
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For a detailed introduction to programming in Lua,
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see Roberto's book, <em>Programming in Lua (Second Edition)</em>.
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<h1>2 - <a name="2">The Language</a></h1>
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<p>
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This section describes the lexis, the syntax, and the semantics of Lua.
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In other words,
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this section describes
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which tokens are valid,
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how they can be combined,
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and what their combinations mean.
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<p>
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The language constructs will be explained using the usual extended BNF notation,
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in which
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{<em>a</em>} means 0 or more <em>a</em>'s, and
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[<em>a</em>] means an optional <em>a</em>.
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Non-terminals are shown like non-terminal,
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keywords are shown like <b>kword</b>,
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and other terminal symbols are shown like `<b>=</b>´.
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The complete syntax of Lua can be found at the end of this manual.
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<h2>2.1 - <a name="2.1">Lexical Conventions</a></h2>
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<p>
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<em>Names</em>
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(also called <em>identifiers</em>)
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in Lua can be any string of letters,
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digits, and underscores,
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not beginning with a digit.
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This coincides with the definition of names in most languages.
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(The definition of letter depends on the current locale:
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any character considered alphabetic by the current locale
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can be used in an identifier.)
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Identifiers are used to name variables and table fields.
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<p>
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The following <em>keywords</em> are reserved
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and cannot be used as names:
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<pre>
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and break do else elseif
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end false for function if
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in local nil not or
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repeat return then true until while
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</pre>
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<p>
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Lua is a case-sensitive language:
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<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
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are two different, valid names.
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As a convention, names starting with an underscore followed by
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uppercase letters (such as <code>_VERSION</code>)
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are reserved for internal global variables used by Lua.
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<p>
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The following strings denote other tokens:
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<pre>
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+ - * / % ^ #
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== ~= <= >= < > =
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( ) { } [ ]
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; : , . .. ...
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</pre>
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<p>
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<em>Literal strings</em>
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can be delimited by matching single or double quotes,
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and can contain the following C-like escape sequences:
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'<code>\a</code>' (bell),
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'<code>\b</code>' (backspace),
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'<code>\f</code>' (form feed),
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'<code>\n</code>' (newline),
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'<code>\r</code>' (carriage return),
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'<code>\t</code>' (horizontal tab),
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'<code>\v</code>' (vertical tab),
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'<code>\\</code>' (backslash),
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'<code>\"</code>' (quotation mark [double quote]),
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and '<code>\'</code>' (apostrophe [single quote]).
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Moreover, a backslash followed by a real newline
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results in a newline in the string.
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A character in a string may also be specified by its numerical value
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using the escape sequence <code>\<em>ddd</em></code>,
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where <em>ddd</em> is a sequence of up to three decimal digits.
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(Note that if a numerical escape is to be followed by a digit,
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it must be expressed using exactly three digits.)
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Strings in Lua may contain any 8-bit value, including embedded zeros,
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which can be specified as '<code>\0</code>'.
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<p>
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To put a double (single) quote, a newline, a backslash,
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or an embedded zero
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inside a literal string enclosed by double (single) quotes
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you must use an escape sequence.
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Any other character may be directly inserted into the literal.
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(Some control characters may cause problems for the file system,
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but Lua has no problem with them.)
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<p>
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Literal strings can also be defined using a long format
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enclosed by <em>long brackets</em>.
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We define an <em>opening long bracket of level <em>n</em></em> as an opening
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square bracket followed by <em>n</em> equal signs followed by another
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opening square bracket.
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So, an opening long bracket of level 0 is written as <code>[[</code>,
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an opening long bracket of level 1 is written as <code>[=[</code>,
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and so on.
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A <em>closing long bracket</em> is defined similarly;
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for instance, a closing long bracket of level 4 is written as <code>]====]</code>.
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A long string starts with an opening long bracket of any level and
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ends at the first closing long bracket of the same level.
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Literals in this bracketed form may run for several lines,
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do not interpret any escape sequences,
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and ignore long brackets of any other level.
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They may contain anything except a closing bracket of the proper level.
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<p>
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For convenience,
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when the opening long bracket is immediately followed by a newline,
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the newline is not included in the string.
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As an example, in a system using ASCII
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(in which '<code>a</code>' is coded as 97,
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newline is coded as 10, and '<code>1</code>' is coded as 49),
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the five literals below denote the same string:
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<pre>
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a = 'alo\n123"'
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a = "alo\n123\""
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a = '\97lo\10\04923"'
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a = [[alo
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123"]]
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a = [==[
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alo
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123"]==]
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</pre>
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<p>
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A <em>numerical constant</em> may be written with an optional decimal part
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and an optional decimal exponent.
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Lua also accepts integer hexadecimal constants,
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by prefixing them with <code>0x</code>.
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Examples of valid numerical constants are
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<pre>
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3 3.0 3.1416 314.16e-2 0.31416E1 0xff 0x56
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</pre>
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<p>
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A <em>comment</em> starts with a double hyphen (<code>--</code>)
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anywhere outside a string.
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If the text immediately after <code>--</code> is not an opening long bracket,
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the comment is a <em>short comment</em>,
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which runs until the end of the line.
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Otherwise, it is a <em>long comment</em>,
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which runs until the corresponding closing long bracket.
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Long comments are frequently used to disable code temporarily.
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<h2>2.2 - <a name="2.2">Values and Types</a></h2>
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<p>
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Lua is a <em>dynamically typed language</em>.
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This means that
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variables do not have types; only values do.
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There are no type definitions in the language.
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All values carry their own type.
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<p>
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All values in Lua are <em>first-class values</em>.
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This means that all values can be stored in variables,
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passed as arguments to other functions, and returned as results.
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<p>
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There are eight basic types in Lua:
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<em>nil</em>, <em>boolean</em>, <em>number</em>,
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<em>string</em>, <em>function</em>, <em>userdata</em>,
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<em>thread</em>, and <em>table</em>.
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<em>Nil</em> is the type of the value <b>nil</b>,
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whose main property is to be different from any other value;
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it usually represents the absence of a useful value.
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<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
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Both <b>nil</b> and <b>false</b> make a condition false;
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any other value makes it true.
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<em>Number</em> represents real (double-precision floating-point) numbers.
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(It is easy to build Lua interpreters that use other
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internal representations for numbers,
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such as single-precision float or long integers;
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see file <code>luaconf.h</code>.)
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<em>String</em> represents arrays of characters.
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Lua is 8-bit clean:
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strings may contain any 8-bit character,
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including embedded zeros ('<code>\0</code>') (see <a href="#2.1">§2.1</a>).
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<p>
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Lua can call (and manipulate) functions written in Lua and
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functions written in C
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(see <a href="#2.5.8">§2.5.8</a>).
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<p>
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The type <em>userdata</em> is provided to allow arbitrary C data to
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be stored in Lua variables.
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This type corresponds to a block of raw memory
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and has no pre-defined operations in Lua,
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except assignment and identity test.
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However, by using <em>metatables</em>,
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the programmer can define operations for userdata values
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(see <a href="#2.8">§2.8</a>).
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Userdata values cannot be created or modified in Lua,
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only through the C API.
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This guarantees the integrity of data owned by the host program.
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<p>
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The type <em>thread</em> represents independent threads of execution
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and it is used to implement coroutines (see <a href="#2.11">§2.11</a>).
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Do not confuse Lua threads with operating-system threads.
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Lua supports coroutines on all systems,
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even those that do not support threads.
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<p>
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The type <em>table</em> implements associative arrays,
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that is, arrays that can be indexed not only with numbers,
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but with any value (except <b>nil</b>).
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Tables can be <em>heterogeneous</em>;
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that is, they can contain values of all types (except <b>nil</b>).
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Tables are the sole data structuring mechanism in Lua;
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they may be used to represent ordinary arrays,
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symbol tables, sets, records, graphs, trees, etc.
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To represent records, Lua uses the field name as an index.
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The language supports this representation by
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providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
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There are several convenient ways to create tables in Lua
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(see <a href="#2.5.7">§2.5.7</a>).
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<p>
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Like indices,
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the value of a table field can be of any type (except <b>nil</b>).
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In particular,
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because functions are first-class values,
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table fields may contain functions.
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Thus tables may also carry <em>methods</em> (see <a href="#2.5.9">§2.5.9</a>).
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<p>
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Tables, functions, threads, and (full) userdata values are <em>objects</em>:
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variables do not actually <em>contain</em> these values,
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only <em>references</em> to them.
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Assignment, parameter passing, and function returns
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always manipulate references to such values;
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these operations do not imply any kind of copy.
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<p>
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The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
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of a given value.
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<h3>2.2.1 - <a name="2.2.1">Coercion</a></h3>
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<p>
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Lua provides automatic conversion between
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string and number values at run time.
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Any arithmetic operation applied to a string tries to convert
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this string to a number, following the usual conversion rules.
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Conversely, whenever a number is used where a string is expected,
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the number is converted to a string, in a reasonable format.
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For complete control over how numbers are converted to strings,
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use the <code>format</code> function from the string library
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(see <a href="#pdf-string.format"><code>string.format</code></a>).
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<h2>2.3 - <a name="2.3">Variables</a></h2>
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<p>
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Variables are places that store values.
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There are three kinds of variables in Lua:
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global variables, local variables, and table fields.
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<p>
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A single name can denote a global variable or a local variable
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(or a function's formal parameter,
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which is a particular kind of local variable):
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<pre>
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var ::= Name
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</pre><p>
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Name denotes identifiers, as defined in <a href="#2.1">§2.1</a>.
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<p>
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Any variable is assumed to be global unless explicitly declared
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as a local (see <a href="#2.4.7">§2.4.7</a>).
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Local variables are <em>lexically scoped</em>:
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local variables can be freely accessed by functions
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defined inside their scope (see <a href="#2.6">§2.6</a>).
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<p>
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Before the first assignment to a variable, its value is <b>nil</b>.
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<p>
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Square brackets are used to index a table:
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<pre>
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var ::= prefixexp `<b>[</b>´ exp `<b>]</b>´
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</pre><p>
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The meaning of accesses to global variables
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and table fields can be changed via metatables.
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An access to an indexed variable <code>t[i]</code> is equivalent to
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a call <code>gettable_event(t,i)</code>.
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(See <a href="#2.8">§2.8</a> for a complete description of the
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<code>gettable_event</code> function.
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This function is not defined or callable in Lua.
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We use it here only for explanatory purposes.)
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<p>
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The syntax <code>var.Name</code> is just syntactic sugar for
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<code>var["Name"]</code>:
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<pre>
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var ::= prefixexp `<b>.</b>´ Name
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</pre>
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<p>
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All global variables live as fields in ordinary Lua tables,
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called <em>environment tables</em> or simply
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<em>environments</em> (see <a href="#2.9">§2.9</a>).
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Each function has its own reference to an environment,
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so that all global variables in this function
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will refer to this environment table.
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When a function is created,
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it inherits the environment from the function that created it.
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To get the environment table of a Lua function,
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you call <a href="#pdf-getfenv"><code>getfenv</code></a>.
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To replace it,
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you call <a href="#pdf-setfenv"><code>setfenv</code></a>.
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(You can only manipulate the environment of C functions
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through the debug library; (see <a href="#5.9">§5.9</a>).)
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<p>
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An access to a global variable <code>x</code>
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is equivalent to <code>_env.x</code>,
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which in turn is equivalent to
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<pre>
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gettable_event(_env, "x")
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</pre><p>
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where <code>_env</code> is the environment of the running function.
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(See <a href="#2.8">§2.8</a> for a complete description of the
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<code>gettable_event</code> function.
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This function is not defined or callable in Lua.
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Similarly, the <code>_env</code> variable is not defined in Lua.
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We use them here only for explanatory purposes.)
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<h2>2.4 - <a name="2.4">Statements</a></h2>
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<p>
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Lua supports an almost conventional set of statements,
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similar to those in Pascal or C.
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This set includes
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assignment, control structures, function calls,
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and variable declarations.
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<h3>2.4.1 - <a name="2.4.1">Chunks</a></h3>
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<p>
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The unit of execution of Lua is called a <em>chunk</em>.
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A chunk is simply a sequence of statements,
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which are executed sequentially.
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Each statement can be optionally followed by a semicolon:
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<pre>
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chunk ::= {stat [`<b>;</b>´]}
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</pre><p>
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There are no empty statements and thus '<code>;;</code>' is not legal.
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<p>
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Lua handles a chunk as the body of an anonymous function
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with a variable number of arguments
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(see <a href="#2.5.9">§2.5.9</a>).
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As such, chunks can define local variables,
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receive arguments, and return values.
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<p>
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A chunk may be stored in a file or in a string inside the host program.
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When a chunk is executed, first it is pre-compiled into instructions for
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a virtual machine,
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and then the compiled code is executed
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by an interpreter for the virtual machine.
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<p>
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Chunks may also be pre-compiled into binary form;
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see program <code>luac</code> for details.
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Programs in source and compiled forms are interchangeable;
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Lua automatically detects the file type and acts accordingly.
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|
|
|
|
<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 may 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 assignment.
|
|
Therefore, the syntax for assignment
|
|
defines a list of variables on the left side
|
|
and a list of expressions on the right side.
|
|
The elements in both lists are separated by commas:
|
|
|
|
<pre>
|
|
stat ::= varlist1 `<b>=</b>´ explist1
|
|
varlist1 ::= var {`<b>,</b>´ var}
|
|
explist1 ::= exp {`<b>,</b>´ exp}
|
|
</pre><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 this call enter in 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>.
|
|
|
|
|
|
<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 may return any value.
|
|
Both <b>false</b> and <b>nil</b> are considered false.
|
|
All values different from <b>nil</b> and <b>false</b> are considered true
|
|
(in particular, the number 0 and the empty string are also true).
|
|
|
|
|
|
<p>
|
|
In the <b>repeat</b>–<b>until</b> loop,
|
|
the inner block does not end at the <b>until</b> keyword,
|
|
but only after the condition.
|
|
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 may return more than one value,
|
|
so the syntax for the <b>return</b> statement is
|
|
|
|
<pre>
|
|
stat ::= <b>return</b> [explist1]
|
|
</pre>
|
|
|
|
<p>
|
|
The <b>break</b> statement 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 are here 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> explist1 <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 may be declared anywhere inside a block.
|
|
The declaration may include an initial assignment:
|
|
|
|
<pre>
|
|
stat ::= <b>local</b> namelist [`<b>=</b>´ explist1]
|
|
</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 may result in multiple values.
|
|
If the expression is used as a statement (see <a href="#2.4.6">§2.4.6</a>)
|
|
(only possible for function calls),
|
|
then its return list is adjusted to zero elements,
|
|
thus discarding all returned values.
|
|
If the expression is used 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 may get nil if there
|
|
-- is no corresponding vararg parameter)
|
|
|
|
a,b,c = x, f() -- f() is adjusted to 2 results
|
|
a,b,c = f() -- f() is adjusted to 3 results
|
|
return f() -- returns all 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>
|
|
An expression enclosed in parentheses always results in only one value.
|
|
Thus,
|
|
<code>(f(x,y,z))</code> is always a single value,
|
|
even if <code>f</code> returns several values.
|
|
(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
|
|
or <b>nil</b> if <code>f</code> does not return any values.)
|
|
|
|
|
|
|
|
<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>).
|
|
|
|
|
|
|
|
|
|
|
|
<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,
|
|
--> 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> may 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> may 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.
|
|
Constructors can be used to create empty tables,
|
|
or to create a table and initialize some of its fields.
|
|
The general syntax for constructors is
|
|
|
|
<pre>
|
|
tableconstructor ::= `<b>{</b>´ [fieldlist] `<b>}</b>´
|
|
fieldlist ::= field {fieldsep field} [fieldsep]
|
|
field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp
|
|
fieldsep ::= `<b>,</b>´ | `<b>;</b>´
|
|
</pre>
|
|
|
|
<p>
|
|
Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
|
|
with key <code>exp1</code> and value <code>exp2</code>.
|
|
A field of the form <code>name = exp</code> is equivalent to
|
|
<code>["name"] = exp</code>.
|
|
Finally, fields of the form <code>exp</code> are equivalent to
|
|
<code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers,
|
|
starting with 1.
|
|
Fields in the other formats do not affect this counting.
|
|
For example,
|
|
|
|
<pre>
|
|
a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
|
|
</pre><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 may 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>´ [explist1] `<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>´ [parlist1] `<b>)</b>´ block <b>end</b>
|
|
</pre>
|
|
|
|
<p>
|
|
The following syntactic sugar simplifies function definitions:
|
|
|
|
<pre>
|
|
stat ::= <b>function</b> funcname funcbody
|
|
stat ::= <b>local</b> <b>function</b> Name funcbody
|
|
funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name]
|
|
</pre><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
|
|
may refer to different external local variables
|
|
and may have different environment tables.
|
|
|
|
|
|
<p>
|
|
Parameters act as local variables that are
|
|
initialized with the argument values:
|
|
|
|
<pre>
|
|
parlist1 ::= namelist [`<b>,</b>´ `<b>...</b>´] | `<b>...</b>´
|
|
</pre><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 the call is enclosed in parentheses).
|
|
|
|
|
|
<p>
|
|
As an example, consider the following definitions:
|
|
|
|
<pre>
|
|
function f(a, b) end
|
|
function g(a, b, ...) end
|
|
function r() return 1,2,3 end
|
|
</pre><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 may have a <em>metatable</em>.
|
|
This <em>metatable</em> is an ordinary Lua table
|
|
that defines the behavior of the original value
|
|
under certain special operations.
|
|
You can change several aspects of the behavior
|
|
of operations over a value by setting specific fields in its metatable.
|
|
For instance, when a non-numeric value is the operand of an addition,
|
|
Lua checks for a function in the field <code>"__add"</code> in its metatable.
|
|
If it finds one,
|
|
Lua calls 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 using the debug library);
|
|
you must use the C API for that.
|
|
|
|
|
|
<p>
|
|
Tables and userdata have individual metatables
|
|
(although multiple tables and userdata can share their metatables);
|
|
values of all other types share one single metatable per type.
|
|
So, there is one single metatable for all numbers,
|
|
and for all strings, etc.
|
|
|
|
|
|
<p>
|
|
A metatable may control how an object behaves in arithmetic operations,
|
|
order comparisons, concatenation, length operation, and indexing.
|
|
A metatable can also 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
|
|
return 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>
|
|
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 their threads and
|
|
non-nested functions created by the thread
|
|
(through <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>)
|
|
and can be directly accessed by C code (see <a href="#3.3">§3.3</a>).
|
|
|
|
|
|
<p>
|
|
Environments associated with C functions can be directly
|
|
accessed by C code (see <a href="#3.3">§3.3</a>).
|
|
They are used as the default environment for other C functions
|
|
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 other 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, these objects that are no longer accessible from Lua).
|
|
All objects in Lua are subject to automatic management:
|
|
tables, userdata, functions, threads, and strings.
|
|
|
|
|
|
<p>
|
|
Lua 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>.
|
|
|
|
|
|
<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 1 mean the collector will not wait to
|
|
start a new cycle.
|
|
A value of 2 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 1 make the collector too slow and
|
|
may result in the collector never finishing a cycle.
|
|
The default, 2, means that the collector runs at "twice"
|
|
the speed of memory allocation.
|
|
|
|
|
|
<p>
|
|
You can change 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.
|
|
Both get percentage points as arguments
|
|
(so an argument of 100 means a real value of 1).
|
|
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.
|
|
|
|
|
|
|
|
|
|
|
|
<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 field <code>__mode</code>.
|
|
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
|
|
the thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
|
|
the coroutine starts its execution,
|
|
at the first line of its main function.
|
|
Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are 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,
|
|
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>
|
|
Almost any function in the API may raise an error,
|
|
for instance due to a memory allocation error.
|
|
The following functions run in protected mode
|
|
(that is, they create a protected environment to run),
|
|
so they never raise an error:
|
|
<a href="#lua_newstate"><code>lua_newstate</code></a>, <a href="#lua_close"><code>lua_close</code></a>, <a href="#lua_load"><code>lua_load</code></a>,
|
|
<a href="#lua_pcall"><code>lua_pcall</code></a>, and <a href="#lua_cpcall"><code>lua_cpcall</code></a>.
|
|
|
|
|
|
<p>
|
|
Inside a C function you can raise an error 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.
|
|
|
|
|
|
|
|
<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>
|
|
<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 may 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>
|
|
<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 may 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>
|
|
<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>
|
|
<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>
|
|
<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 string on the stack
|
|
(that is, the function does nothing);
|
|
if <code>n</code> is 0, the result is the empty string.
|
|
Concatenation is done following the usual semantics of Lua
|
|
(see <a href="#2.5.4">§2.5.4</a>).
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_cpcall"><code>lua_cpcall</code></a></h3>
|
|
<pre>int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);</pre>
|
|
|
|
<p>
|
|
Calls the C function <code>func</code> in protected mode.
|
|
<code>func</code> starts with only one element in its stack,
|
|
a light userdata containing <code>ud</code>.
|
|
In case of errors,
|
|
<a href="#lua_cpcall"><code>lua_cpcall</code></a> returns the same error codes as <a href="#lua_pcall"><code>lua_pcall</code></a>,
|
|
plus the error object on the top of the stack;
|
|
otherwise, it returns zero, and does not change the stack.
|
|
All values returned by <code>func</code> are discarded.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3>
|
|
<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
|
|
|
|
<p>
|
|
Creates a new empty table and pushes it onto the stack.
|
|
The new table has space pre-allocated
|
|
for <code>narr</code> array elements 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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>/100 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>/100 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>
|
|
<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>
|
|
<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>
|
|
<pre>void lua_getfield (lua_State *L, int index, const char *k);</pre>
|
|
|
|
<p>
|
|
Pushes onto the stack the value <code>t[k]</code>,
|
|
where <code>t</code> is the value at the given valid index <code>index</code>.
|
|
As in Lua, this function may trigger a metamethod
|
|
for the "index" event (see <a href="#2.8">§2.8</a>).
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<pre>void lua_gettable (lua_State *L, int index);</pre>
|
|
|
|
<p>
|
|
Pushes onto the stack the value <code>t[k]</code>,
|
|
where <code>t</code> is the value at the given valid index <code>index</code>
|
|
and <code>k</code> is the value at the top of the stack.
|
|
|
|
|
|
<p>
|
|
This function pops the key from the stack
|
|
(putting the resulting value in its place).
|
|
As in Lua, this function may trigger a metamethod
|
|
for the "index" event (see <a href="#2.8">§2.8</a>).
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3>
|
|
<pre>int lua_gettop (lua_State *L);</pre>
|
|
|
|
<p>
|
|
Returns the index of the top element in the stack.
|
|
Because indices start at 1,
|
|
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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<pre>int lua_isnone (lua_State *L, int index);</pre>
|
|
|
|
<p>
|
|
Returns 1 if the 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>
|
|
<pre>int lua_isnoneornil (lua_State *L, int index);</pre>
|
|
|
|
<p>
|
|
Returns 1 if the 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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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_pushlstring"><code>lua_pushlstring</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<pre>void lua_rawgeti (lua_State *L, int index, int n);</pre>
|
|
|
|
<p>
|
|
Pushes onto the stack the value <code>t[n]</code>,
|
|
where <code>t</code> is the value at the given valid index <code>index</code>.
|
|
The access is raw;
|
|
that is, it does not invoke metamethods.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3>
|
|
<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>
|
|
<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 <code>index</code>
|
|
and <code>v</code> is the value at the top of the stack,
|
|
|
|
|
|
<p>
|
|
This function pops the value from the stack.
|
|
The assignment is raw;
|
|
that is, it does not invoke metamethods.
|
|
|
|
|
|
|
|
|
|
|
|
<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>.
|
|
The reader function may return pieces of any size greater than zero.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_register"><code>lua_register</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
|
|
|
|
<p>
|
|
Does the equivalent to <code>t[k] = v</code>,
|
|
where <code>t</code> is the value at the given valid index <code>index</code>
|
|
and <code>v</code> is the value at the top of the stack,
|
|
|
|
|
|
<p>
|
|
This function pops the value from the stack.
|
|
As in Lua, this function may trigger a metamethod
|
|
for the "newindex" event (see <a href="#2.8">§2.8</a>).
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<pre>void lua_settable (lua_State *L, int index);</pre>
|
|
|
|
<p>
|
|
Does the equivalent to <code>t[k] = v</code>,
|
|
where <code>t</code> is the value at the given valid index <code>index</code>,
|
|
<code>v</code> is the value at the top of the stack,
|
|
and <code>k</code> is the value just below the top.
|
|
|
|
|
|
<p>
|
|
This function pops both the key and the value from the stack.
|
|
As in Lua, this function may trigger a metamethod
|
|
for the "newindex" event (see <a href="#2.8">§2.8</a>).
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<pre>lua_Integer lua_tointeger (lua_State *L, int idx);</pre>
|
|
|
|
<p>
|
|
Converts the Lua value at the given acceptable index
|
|
to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
|
|
The Lua value must be a number or a string convertible to 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>
|
|
<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 may contain other zeros in its body.
|
|
Because Lua has garbage collection,
|
|
there is no guarantee that the pointer returned by <a href="#lua_tolstring"><code>lua_tolstring</code></a>
|
|
will be valid after the corresponding value is removed from the stack.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3>
|
|
<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>
|
|
<pre>const void *lua_topointer (lua_State *L, int index);</pre>
|
|
|
|
<p>
|
|
Converts the value at the given acceptable index to a generic
|
|
C pointer (<code>void*</code>).
|
|
The value may be a userdata, a table, a thread, or a function;
|
|
otherwise, <a href="#lua_topointer"><code>lua_topointer</code></a> returns <code>NULL</code>.
|
|
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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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 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>
|
|
<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>
|
|
<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 may be the value of multiple global variables,
|
|
while others may be stored only in a table field.
|
|
The <code>lua_getinfo</code> function checks how the function was
|
|
called to find a suitable name.
|
|
If it cannot find a name,
|
|
then <code>name</code> is set to <code>NULL</code>.
|
|
</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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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> may be <code>LUA_HOOKRET</code>,
|
|
the normal value, or <code>LUA_HOOKTAILRET</code>.
|
|
In the latter case, Lua is simulating a return from
|
|
a function that did a tail call;
|
|
in this case, it is useless to call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
|
|
|
|
|
|
<p>
|
|
While Lua is running a hook, it disables other calls to hooks.
|
|
Therefore, if a hook calls back Lua to execute a function or a chunk,
|
|
this execution occurs without any calls to hooks.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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 raise an error if the check is not satisfied.
|
|
Because the error message is formatted for arguments
|
|
(e.g., "<code>bad argument #1</code>"),
|
|
you should not use 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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3>
|
|
<pre>void luaL_checktype (lua_State *L, int narg, int t);</pre>
|
|
|
|
<p>
|
|
Checks whether the function argument <code>narg</code> has type <code>t</code>.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<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>
|
|
<pre>const char *luaL_typename (lua_State *L, int idx);</pre>
|
|
|
|
<p>
|
|
Returns the name of the type of the value at index <code>idx</code>.
|
|
|
|
|
|
|
|
|
|
|
|
<hr><h3><a name="luaL_typerror"><code>luaL_typerror</code></a></h3>
|
|
<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>
|
|
<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>
|
|
<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., <code>sort</code>).
|
|
|
|
|
|
<p>
|
|
All libraries are implemented through the official C API
|
|
and are provided as separate C modules.
|
|
Currently, Lua has the following standard libraries:
|
|
|
|
<ul>
|
|
|
|
<li>basic library;</li>
|
|
|
|
<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 and the Operating System libraries),
|
|
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>/100 as the new value for the <em>pause</em> of
|
|
the collector (see <a href="#2.10">§2.10</a>).
|
|
</li>
|
|
|
|
<li><b>"setstepmul":</b>
|
|
sets <code>arg</code>/100 as the new value for the <em>step multiplier</em> of
|
|
the collector (see <a href="#2.10">§2.10</a>).
|
|
</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 <b>nil</b> (or no value) signals the end of the chunk.
|
|
|
|
|
|
<p>
|
|
If there are no errors,
|
|
returns the compiled chunk as a function;
|
|
otherwise, returns <b>nil</b> plus the error message.
|
|
The environment of the returned function is the global environment.
|
|
|
|
|
|
<p>
|
|
<code>chunkname</code> is used as the chunk name for error messages
|
|
and debug information.
|
|
|
|
|
|
|
|
|
|
<p>
|
|
<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>
|
|
<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 may 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 may 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,
|
|
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 below).
|
|
|
|
|
|
<p>
|
|
When loading a C library,
|
|
<code>require</code> first uses a dynamic link facility to link the
|
|
application with the library.
|
|
Then it tries to find a C function inside this 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>
|
|
If <code>require</code> finds neither a Lua library nor a
|
|
C library for a module,
|
|
it calls the <em>all-in-one loader</em>.
|
|
This loader searches the C path for a library for
|
|
the root name of the given module.
|
|
For instance, when requiring <code>a.b.c</code>,
|
|
it will search for a C library for <code>a</code>.
|
|
If found, it looks into it for an open function for
|
|
the submodule;
|
|
in our example, that would be <code>luaopen_a_b_c</code>.
|
|
With this facility, a package can pack several C submodules
|
|
into one single library,
|
|
with each submodule keeping its original open function.
|
|
|
|
|
|
<p>
|
|
Once a loader is found,
|
|
<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>
|
|
(plus another 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.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>
|
|
A path is a sequence of <em>templates</em> separated by semicolons.
|
|
For each template, <a href="#pdf-require"><code>require</code></a> will change each interrogation
|
|
mark in the template by <code>filename</code>,
|
|
which is <code>modname</code> with each dot replaced by a
|
|
"directory separator" (such as "<code>/</code>" in Unix);
|
|
then it will try to load the resulting file name.
|
|
So, for instance, if the Lua path is
|
|
|
|
<pre>
|
|
"./?.lua;./?.lc;/usr/local/?/init.lua"
|
|
</pre><p>
|
|
the search for a Lua loader for module <code>foo</code>
|
|
will try to load the files
|
|
<code>./foo.lua</code>, <code>./foo.lc</code>, and
|
|
<code>/usr/local/foo/init.lua</code>, in that order.
|
|
|
|
|
|
|
|
|
|
<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>
|
|
<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 may be negative.
|
|
A value of <b>true</b> as a fourth, optional argument <code>plain</code>
|
|
turns off the pattern matching facilities,
|
|
so the function does a plain "find substring" operation,
|
|
with no characters in <code>pattern</code> being considered "magic".
|
|
Note that if <code>plain</code> is given, then <code>init</code> must be given 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 occurrences of the <code>pattern</code> have been
|
|
replaced by a replacement string specified by <code>repl</code>,
|
|
which may be a string, a table, or a function.
|
|
<code>gsub</code> also returns, as its second value,
|
|
the total number of substitutions made.
|
|
|
|
|
|
<p>
|
|
If <code>repl</code> is a string, then its value is used for replacement.
|
|
The character <code>%</code> works as an escape character:
|
|
any sequence in <code>repl</code> of the form <code>%<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>
|
|
The optional last parameter <code>n</code> limits
|
|
the maximum number of substitutions to occur.
|
|
For instance, when <code>n</code> is 1 only the first occurrence of
|
|
<code>pattern</code> is replaced.
|
|
|
|
|
|
<p>
|
|
Here are some examples:
|
|
|
|
<pre>
|
|
x = string.gsub("hello world", "(%w+)", "%1 %1")
|
|
--> x="hello hello world world"
|
|
|
|
x = string.gsub("hello world", "%w+", "%0 %0", 1)
|
|
--> x="hello hello world"
|
|
|
|
x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
|
|
--> x="world hello Lua from"
|
|
|
|
x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
|
|
--> x="home = /home/roberto, user = roberto"
|
|
|
|
x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
|
|
return loadstring(s)()
|
|
end)
|
|
--> x="4+5 = 9"
|
|
|
|
local t = {name="lua", version="5.1"}
|
|
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 may 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> may 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 may be specified by
|
|
separating the end characters of the range with a '<code>-</code>'.
|
|
All classes <code>%</code><em>x</em> described above may also be used as
|
|
components in <em>set</em>.
|
|
All other characters in <em>set</em> represent themselves.
|
|
For example, <code>[%w_]</code> (or <code>[_%w]</code>)
|
|
represents all alphanumeric characters plus the underscore,
|
|
<code>[0-7]</code> represents the octal digits,
|
|
and <code>[0-7%l%-]</code> represents the octal digits plus
|
|
the lowercase letters plus the '<code>-</code>' character.
|
|
|
|
|
|
<p>
|
|
The interaction between ranges and classes is not defined.
|
|
Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
|
|
have no meaning.
|
|
</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> may 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 may contain sub-patterns enclosed in parentheses;
|
|
they describe <em>captures</em>.
|
|
When a match succeeds, the substrings of the subject string
|
|
that match captures are stored (<em>captured</em>) for future use.
|
|
Captures are numbered according to their left parentheses.
|
|
For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
|
|
the part of the string matching <code>"a*(.)%w(%s*)"</code> is
|
|
stored as the first capture (and therefore has number 1);
|
|
the character matching "<code>.</code>" is captured with number 2,
|
|
and the part matching "<code>%s*</code>" has number 3.
|
|
|
|
|
|
<p>
|
|
As a special case, the empty capture <code>()</code> captures
|
|
the current string position (a number).
|
|
For instance, if we apply the pattern <code>"()aa()"</code> on the
|
|
string <code>"flaaap"</code>, there will be two captures: 3 and 5.
|
|
|
|
|
|
<p>
|
|
A pattern cannot contain embedded zeros. Use <code>%z</code> instead.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<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 (x, y)</code></a></h3>
|
|
|
|
|
|
<p>
|
|
Returns the arc tangent of <code>x/y</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>y</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 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>.
|
|
|
|
|
|
|
|
|
|
<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 pseudo-random real number
|
|
in the range <em>[0,1)</em>.
|
|
When called with a number <code>m</code>,
|
|
<code>math.random</code> returns
|
|
a pseudo-random integer in the range <em>[1, m]</em>.
|
|
When called with two numbers <code>m</code> and <code>n</code>,
|
|
<code>math.random</code> returns a 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>.
|
|
|
|
|
|
<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 may also have a '<code>b</code>' at the end,
|
|
which is needed in some systems to open the file in binary mode.
|
|
This string is exactly what is used in the
|
|
standard C function <code>fopen</code>.
|
|
|
|
|
|
|
|
|
|
<p>
|
|
<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 locate is set to an implementation-defined native locale.
|
|
If <code>locate</code> is the string "<code>C</code>",
|
|
the current locate 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.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<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 its 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 may 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 name of 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>),
|
|
<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.
|
|
For instance,
|
|
|
|
<pre>
|
|
$ lua -e"_PROMPT='myprompt> '" -i
|
|
</pre><p>
|
|
(the outer pair of quotes is for the shell,
|
|
the inner pair is for Lua),
|
|
or in any Lua programs by assigning to <code>_PROMPT</code>.
|
|
Note the use of <code>-i</code> to enter interactive mode; otherwise,
|
|
the program would 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 found 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 ::= varlist1 `<b>=</b>´ explist1 |
|
|
functioncall |
|
|
<b>do</b> block <b>end</b> |
|
|
<b>while</b> exp <b>do</b> block <b>end</b> |
|
|
<b>repeat</b> block <b>until</b> exp |
|
|
<b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
|
|
<b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> |
|
|
<b>for</b> namelist <b>in</b> explist1 <b>do</b> block <b>end</b> |
|
|
<b>function</b> funcname funcbody |
|
|
<b>local</b> <b>function</b> Name funcbody |
|
|
<b>local</b> namelist [`<b>=</b>´ explist1]
|
|
|
|
laststat ::= <b>return</b> [explist1] | <b>break</b>
|
|
|
|
funcname ::= Name {`<b>.</b>´ Name} [`<b>:</b>´ Name]
|
|
|
|
varlist1 ::= var {`<b>,</b>´ var}
|
|
|
|
var ::= Name | prefixexp `<b>[</b>´ exp `<b>]</b>´ | prefixexp `<b>.</b>´ Name
|
|
|
|
namelist ::= Name {`<b>,</b>´ Name}
|
|
|
|
explist1 ::= {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>´ [explist1] `<b>)</b>´ | tableconstructor | String
|
|
|
|
function ::= <b>function</b> funcbody
|
|
|
|
funcbody ::= `<b>(</b>´ [parlist1] `<b>)</b>´ block <b>end</b>
|
|
|
|
parlist1 ::= 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 Mar 26 12:59:26 BRT 2007
|
|
</SMALL>
|
|
<!--
|
|
Last change: ready for Lua 5.1.2
|
|
-->
|
|
|
|
</body></html>
|
|
|