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diff --git a/libs/liblua/doc/manual.html b/libs/liblua/doc/manual.html deleted file mode 100644 index 5fb26b23c8..0000000000 --- a/libs/liblua/doc/manual.html +++ /dev/null @@ -1,10910 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> -<HTML> -<HEAD> -<TITLE>Lua 5.3 Reference Manual</TITLE> -<LINK REL="stylesheet" TYPE="text/css" HREF="lua.css"> -<LINK REL="stylesheet" TYPE="text/css" HREF="manual.css"> -<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1"> -</HEAD> - -<BODY> - -<H1> -<A HREF="http://www.lua.org/"><IMG SRC="logo.gif" ALT="Lua"></A> -Lua 5.3 Reference Manual -</H1> - -<P> -by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes - -<P> -<SMALL> -Copyright © 2015–2016 Lua.org, PUC-Rio. -Freely available under the terms of the -<a href="http://www.lua.org/license.html">Lua license</a>. -</SMALL> - -<DIV CLASS="menubar"> -<A HREF="contents.html#contents">contents</A> -· -<A HREF="contents.html#index">index</A> -· -<A HREF="http://www.lua.org/manual/">other versions</A> -</DIV> - -<!-- ====================================================================== --> -<p> - -<!-- $Id: manual.of,v 1.162 2016/05/30 15:57:03 roberto Exp $ --> - - - - -<h1>1 – <a name="1">Introduction</a></h1> - -<p> -Lua is a powerful, efficient, lightweight, embeddable scripting language. -It supports procedural programming, -object-oriented programming, functional programming, -data-driven programming, and data description. - - -<p> -Lua combines simple procedural syntax with powerful data description -constructs based on associative arrays and extensible semantics. -Lua is dynamically typed, -runs by interpreting bytecode with a register-based -virtual machine, -and has automatic memory management with -incremental garbage collection, -making it ideal for configuration, scripting, -and rapid prototyping. - - -<p> -Lua is implemented as a library, written in <em>clean C</em>, -the common subset of Standard C and C++. -The Lua distribution includes a host program called <code>lua</code>, -which uses the Lua library to offer a complete, -standalone Lua interpreter, -for interactive or batch use. -Lua is intended to be used both as a powerful, lightweight, -embeddable scripting language for any program that needs one, -and as a powerful but lightweight and efficient stand-alone language. - - -<p> -As an extension language, Lua has no notion of a "main" program: -it works <em>embedded</em> in a host client, -called the <em>embedding program</em> or simply the <em>host</em>. -(Frequently, this host is the stand-alone <code>lua</code> program.) -The host program can invoke functions to execute a piece of Lua code, -can write and read Lua variables, -and can register C functions to be called by Lua code. -Through the use of C functions, Lua can be augmented to cope with -a wide range of different domains, -thus creating customized programming languages sharing a syntactical framework. - - -<p> -Lua is free software, -and is provided as usual with no guarantees, -as stated in its license. -The implementation described in this manual is available -at Lua's official web site, <code>www.lua.org</code>. - - -<p> -Like any other reference manual, -this document is dry in places. -For a discussion of the decisions behind the design of Lua, -see the technical papers available at Lua's web site. -For a detailed introduction to programming in Lua, -see Roberto's book, <em>Programming in Lua</em>. - - - -<h1>2 – <a name="2">Basic Concepts</a></h1> - -<p> -This section describes the basic concepts of the language. - - - -<h2>2.1 – <a name="2.1">Values and Types</a></h2> - -<p> -Lua is a <em>dynamically typed language</em>. -This means that -variables do not have types; only values do. -There are no type definitions in the language. -All values carry their own type. - - -<p> -All values in Lua are <em>first-class values</em>. -This means that all values can be stored in variables, -passed as arguments to other functions, and returned as results. - - -<p> -There are eight basic types in Lua: -<em>nil</em>, <em>boolean</em>, <em>number</em>, -<em>string</em>, <em>function</em>, <em>userdata</em>, -<em>thread</em>, and <em>table</em>. -The type <em>nil</em> has one single value, <b>nil</b>, -whose main property is to be different from any other value; -it usually represents the absence of a useful value. -The type <em>boolean</em> has two values, <b>false</b> and <b>true</b>. -Both <b>nil</b> and <b>false</b> make a condition false; -any other value makes it true. -The type <em>number</em> represents both -integer numbers and real (floating-point) numbers. -The type <em>string</em> represents immutable sequences of bytes. - -Lua is 8-bit clean: -strings can contain any 8-bit value, -including embedded zeros ('<code>\0</code>'). -Lua is also encoding-agnostic; -it makes no assumptions about the contents of a string. - - -<p> -The type <em>number</em> uses two internal representations, -or two subtypes, -one called <em>integer</em> and the other called <em>float</em>. -Lua has explicit rules about when each representation is used, -but it also converts between them automatically as needed (see <a href="#3.4.3">§3.4.3</a>). -Therefore, -the programmer may choose to mostly ignore the difference -between integers and floats -or to assume complete control over the representation of each number. -Standard Lua uses 64-bit integers and double-precision (64-bit) floats, -but you can also compile Lua so that it -uses 32-bit integers and/or single-precision (32-bit) floats. -The option with 32 bits for both integers and floats -is particularly attractive -for small machines and embedded systems. -(See macro <code>LUA_32BITS</code> in file <code>luaconf.h</code>.) - - -<p> -Lua can call (and manipulate) functions written in Lua and -functions written in C (see <a href="#3.4.10">§3.4.10</a>). -Both are represented by the type <em>function</em>. - - -<p> -The type <em>userdata</em> is provided to allow arbitrary C data to -be stored in Lua variables. -A userdata value represents a block of raw memory. -There are two kinds of userdata: -<em>full userdata</em>, -which is an object with a block of memory managed by Lua, -and <em>light userdata</em>, -which is simply a C pointer value. -Userdata has no predefined operations in Lua, -except assignment and identity test. -By using <em>metatables</em>, -the programmer can define operations for full userdata values -(see <a href="#2.4">§2.4</a>). -Userdata values cannot be created or modified in Lua, -only through the C API. -This guarantees the integrity of data owned by the host program. - - -<p> -The type <em>thread</em> represents independent threads of execution -and it is used to implement coroutines (see <a href="#2.6">§2.6</a>). -Lua threads are not related to operating-system threads. -Lua supports coroutines on all systems, -even those that do not support threads natively. - - -<p> -The type <em>table</em> implements associative arrays, -that is, arrays that can be indexed not only with numbers, -but with any Lua value except <b>nil</b> and NaN. -(<em>Not a Number</em> is a special value used to represent -undefined or unrepresentable numerical results, such as <code>0/0</code>.) -Tables can be <em>heterogeneous</em>; -that is, they can contain values of all types (except <b>nil</b>). -Any key with value <b>nil</b> is not considered part of the table. -Conversely, any key that is not part of a table has -an associated value <b>nil</b>. - - -<p> -Tables are the sole data-structuring mechanism in Lua; -they can be used to represent ordinary arrays, sequences, -symbol tables, sets, records, graphs, trees, etc. -To represent records, Lua uses the field name as an index. -The language supports this representation by -providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. -There are several convenient ways to create tables in Lua -(see <a href="#3.4.9">§3.4.9</a>). - - -<p> -We use the term <em>sequence</em> to denote a table where -the set of all positive numeric keys is equal to {1..<em>n</em>} -for some non-negative integer <em>n</em>, -which is called the length of the sequence (see <a href="#3.4.7">§3.4.7</a>). - - -<p> -Like indices, -the values of table fields can be of any type. -In particular, -because functions are first-class values, -table fields can contain functions. -Thus tables can also carry <em>methods</em> (see <a href="#3.4.11">§3.4.11</a>). - - -<p> -The indexing of tables follows -the definition of raw equality in the language. -The expressions <code>a[i]</code> and <code>a[j]</code> -denote the same table element -if and only if <code>i</code> and <code>j</code> are raw equal -(that is, equal without metamethods). -In particular, floats with integral values -are equal to their respective integers -(e.g., <code>1.0 == 1</code>). -To avoid ambiguities, -any float with integral value used as a key -is converted to its respective integer. -For instance, if you write <code>a[2.0] = true</code>, -the actual key inserted into the table will be the -integer <code>2</code>. -(On the other hand, -2 and "<code>2</code>" are different Lua values and therefore -denote different table entries.) - - -<p> -Tables, functions, threads, and (full) userdata values are <em>objects</em>: -variables do not actually <em>contain</em> these values, -only <em>references</em> to them. -Assignment, parameter passing, and function returns -always manipulate references to such values; -these operations do not imply any kind of copy. - - -<p> -The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type -of a given value (see <a href="#6.1">§6.1</a>). - - - - - -<h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2> - -<p> -As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>, -any reference to a free name -(that is, a name not bound to any declaration) <code>var</code> -is syntactically translated to <code>_ENV.var</code>. -Moreover, every chunk is compiled in the scope of -an external local variable named <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>), -so <code>_ENV</code> itself is never a free name in a chunk. - - -<p> -Despite the existence of this external <code>_ENV</code> variable and -the translation of free names, -<code>_ENV</code> is a completely regular name. -In particular, -you can define new variables and parameters with that name. -Each reference to a free name uses the <code>_ENV</code> that is -visible at that point in the program, -following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>). - - -<p> -Any table used as the value of <code>_ENV</code> is called an <em>environment</em>. - - -<p> -Lua keeps a distinguished environment called the <em>global environment</em>. -This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>). -In Lua, the global variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value. -(<a href="#pdf-_G"><code>_G</code></a> is never used internally.) - - -<p> -When Lua loads a chunk, -the default value for its <code>_ENV</code> upvalue -is the global environment (see <a href="#pdf-load"><code>load</code></a>). -Therefore, by default, -free names in Lua code refer to entries in the global environment -(and, therefore, they are also called <em>global variables</em>). -Moreover, all standard libraries are loaded in the global environment -and some functions there operate on that environment. -You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>) -to load a chunk with a different environment. -(In C, you have to load the chunk and then change the value -of its first upvalue.) - - - - - -<h2>2.3 – <a name="2.3">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. -(When you use Lua standalone, -the <code>lua</code> application is the host program.) -Whenever an error occurs during -the compilation or execution of a Lua chunk, -control returns to the host, -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 <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a> -to call a given function in <em>protected mode</em>. - - -<p> -Whenever there is an error, -an <em>error object</em> (also called an <em>error message</em>) -is propagated with information about the error. -Lua itself only generates errors whose error object is a string, -but programs may generate errors with -any value as the error object. -It is up to the Lua program or its host to handle such error objects. - - -<p> -When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>, -you may give a <em>message handler</em> -to be called in case of errors. -This function is called with the original error object -and returns a new error object. -It is called before the error unwinds the stack, -so that it can gather more information about the error, -for instance by inspecting the stack and creating a stack traceback. -This message handler is still protected by the protected call; -so, an error inside the message handler -will call the message handler again. -If this loop goes on for too long, -Lua breaks it and returns an appropriate message. - - - - - -<h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2> - -<p> -Every value in Lua can have a <em>metatable</em>. -This <em>metatable</em> is an ordinary Lua table -that defines the behavior of the original value -under certain special operations. -You can change several aspects of the behavior -of operations over a value by setting specific fields in its metatable. -For instance, when a non-numeric value is the operand of an addition, -Lua checks for a function in the field "<code>__add</code>" of the value's metatable. -If it finds one, -Lua calls this function to perform the addition. - - -<p> -The key for each event in a metatable is a string -with the event name prefixed by two underscores; -the corresponding values are called <em>metamethods</em>. -In the previous example, the key is "<code>__add</code>" -and the metamethod is the function that performs the addition. - - -<p> -You can query the metatable of any value -using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. -Lua queries metamethods in metatables using a raw access (see <a href="#pdf-rawget"><code>rawget</code></a>). -So, to retrieve the metamethod for event <code>ev</code> in object <code>o</code>, -Lua does the equivalent to the following code: - -<pre> - rawget(getmetatable(<em>o</em>) or {}, "__<em>ev</em>") -</pre> - -<p> -You can replace the metatable of tables -using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function. -You cannot change the metatable of other types from Lua code -(except by using the debug library (<a href="#6.10">§6.10</a>)); -you should use the C API for that. - - -<p> -Tables and full userdata have individual metatables -(although multiple tables and userdata can share their metatables). -Values of all other types share one single metatable per type; -that is, there is one single metatable for all numbers, -one for all strings, etc. -By default, a value has no metatable, -but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>). - - -<p> -A metatable controls how an object behaves in -arithmetic operations, bitwise operations, -order comparisons, concatenation, length operation, calls, and indexing. -A metatable also can define a function to be called -when a userdata or a table is garbage collected (<a href="#2.5">§2.5</a>). - - -<p> -For the unary operators (negation, length, and bitwise NOT), -the metamethod is computed and called with a dummy second operand, -equal to the first one. -This extra operand is only to simplify Lua's internals -(by making these operators behave like a binary operation) -and may be removed in future versions. -(For most uses this extra operand is irrelevant.) - - -<p> -A detailed list of events controlled by metatables is given next. -Each operation is identified by its corresponding key. - - - -<ul> - -<li><b><code>__add</code>: </b> -the addition (<code>+</code>) operation. -If any operand for an addition is not a number -(nor a string coercible to a number), -Lua will try to call a metamethod. -First, Lua will check the first operand (even if it is valid). -If that operand does not define a metamethod for <code>__add</code>, -then Lua will check the second operand. -If Lua can find a metamethod, -it calls the metamethod with the two operands as arguments, -and the result of the call -(adjusted to one value) -is the result of the operation. -Otherwise, -it raises an error. -</li> - -<li><b><code>__sub</code>: </b> -the subtraction (<code>-</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__mul</code>: </b> -the multiplication (<code>*</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__div</code>: </b> -the division (<code>/</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__mod</code>: </b> -the modulo (<code>%</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__pow</code>: </b> -the exponentiation (<code>^</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__unm</code>: </b> -the negation (unary <code>-</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__idiv</code>: </b> -the floor division (<code>//</code>) operation. -Behavior similar to the addition operation. -</li> - -<li><b><code>__band</code>: </b> -the bitwise AND (<code>&</code>) operation. -Behavior similar to the addition operation, -except that Lua will try a metamethod -if any operand is neither an integer -nor a value coercible to an integer (see <a href="#3.4.3">§3.4.3</a>). -</li> - -<li><b><code>__bor</code>: </b> -the bitwise OR (<code>|</code>) operation. -Behavior similar to the bitwise AND operation. -</li> - -<li><b><code>__bxor</code>: </b> -the bitwise exclusive OR (binary <code>~</code>) operation. -Behavior similar to the bitwise AND operation. -</li> - -<li><b><code>__bnot</code>: </b> -the bitwise NOT (unary <code>~</code>) operation. -Behavior similar to the bitwise AND operation. -</li> - -<li><b><code>__shl</code>: </b> -the bitwise left shift (<code><<</code>) operation. -Behavior similar to the bitwise AND operation. -</li> - -<li><b><code>__shr</code>: </b> -the bitwise right shift (<code>>></code>) operation. -Behavior similar to the bitwise AND operation. -</li> - -<li><b><code>__concat</code>: </b> -the concatenation (<code>..</code>) operation. -Behavior similar to the addition operation, -except that Lua will try a metamethod -if any operand is neither a string nor a number -(which is always coercible to a string). -</li> - -<li><b><code>__len</code>: </b> -the length (<code>#</code>) operation. -If the object is not a string, -Lua will try its metamethod. -If there is a metamethod, -Lua calls it with the object as argument, -and the result of the call -(always adjusted to one value) -is the result of the operation. -If there is no metamethod but the object is a table, -then Lua uses the table length operation (see <a href="#3.4.7">§3.4.7</a>). -Otherwise, Lua raises an error. -</li> - -<li><b><code>__eq</code>: </b> -the equal (<code>==</code>) operation. -Behavior similar to the addition operation, -except that Lua will try a metamethod only when the values -being compared are either both tables or both full userdata -and they are not primitively equal. -The result of the call is always converted to a boolean. -</li> - -<li><b><code>__lt</code>: </b> -the less than (<code><</code>) operation. -Behavior similar to the addition operation, -except that Lua will try a metamethod only when the values -being compared are neither both numbers nor both strings. -The result of the call is always converted to a boolean. -</li> - -<li><b><code>__le</code>: </b> -the less equal (<code><=</code>) operation. -Unlike other operations, -the less-equal operation can use two different events. -First, Lua looks for the <code>__le</code> metamethod in both operands, -like in the less than operation. -If it cannot find such a metamethod, -then it will try the <code>__lt</code> metamethod, -assuming that <code>a <= b</code> is equivalent to <code>not (b < a)</code>. -As with the other comparison operators, -the result is always a boolean. -(This use of the <code>__lt</code> event can be removed in future versions; -it is also slower than a real <code>__le</code> metamethod.) -</li> - -<li><b><code>__index</code>: </b> -The indexing access <code>table[key]</code>. -This event happens when <code>table</code> is not a table or -when <code>key</code> is not present in <code>table</code>. -The metamethod is looked up in <code>table</code>. - - -<p> -Despite the name, -the metamethod for this event can be either a function or a table. -If it is a function, -it is called with <code>table</code> and <code>key</code> as arguments, -and the result of the call -(adjusted to one value) -is the result of the operation. -If it is a table, -the final result is the result of indexing this table with <code>key</code>. -(This indexing is regular, not raw, -and therefore can trigger another metamethod.) -</li> - -<li><b><code>__newindex</code>: </b> -The indexing assignment <code>table[key] = value</code>. -Like the index event, -this event happens when <code>table</code> is not a table or -when <code>key</code> is not present in <code>table</code>. -The metamethod is looked up in <code>table</code>. - - -<p> -Like with indexing, -the metamethod for this event can be either a function or a table. -If it is a function, -it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments. -If it is a table, -Lua does an indexing assignment to this table with the same key and value. -(This assignment is regular, not raw, -and therefore can trigger another metamethod.) - - -<p> -Whenever there is a <code>__newindex</code> metamethod, -Lua does not perform the primitive assignment. -(If necessary, -the metamethod itself can call <a href="#pdf-rawset"><code>rawset</code></a> -to do the assignment.) -</li> - -<li><b><code>__call</code>: </b> -The call operation <code>func(args)</code>. -This event happens when Lua tries to call a non-function value -(that is, <code>func</code> is not a function). -The metamethod is looked up in <code>func</code>. -If present, -the metamethod is called with <code>func</code> as its first argument, -followed by the arguments of the original call (<code>args</code>). -All results of the call -are the result of the operation. -(This is the only metamethod that allows multiple results.) -</li> - -</ul> - -<p> -It is a good practice to add all needed metamethods to a table -before setting it as a metatable of some object. -In particular, the <code>__gc</code> metamethod works only when this order -is followed (see <a href="#2.5.1">§2.5.1</a>). - - -<p> -Because metatables are regular tables, -they can contain arbitrary fields, -not only the event names defined above. -Some functions in the standard library -(e.g., <a href="#pdf-tostring"><code>tostring</code></a>) -use other fields in metatables for their own purposes. - - - - - -<h2>2.5 – <a name="2.5">Garbage Collection</a></h2> - -<p> -Lua performs automatic memory management. -This means that -you do not have to worry about allocating memory for new objects -or freeing it when the objects are no longer needed. -Lua manages memory automatically by running -a <em>garbage collector</em> to collect all <em>dead objects</em> -(that is, objects that are no longer accessible from Lua). -All memory used by Lua is subject to automatic management: -strings, tables, userdata, functions, threads, internal structures, etc. - - -<p> -Lua implements an incremental mark-and-sweep collector. -It uses two numbers to control its garbage-collection cycles: -the <em>garbage-collector pause</em> and -the <em>garbage-collector step multiplier</em>. -Both use percentage points as units -(e.g., a value of 100 means an internal value of 1). - - -<p> -The garbage-collector pause -controls how long the collector waits before starting a new cycle. -Larger values make the collector less aggressive. -Values smaller than 100 mean the collector will not wait to -start a new cycle. -A value of 200 means that the collector waits for the total memory in use -to double before starting a new cycle. - - -<p> -The garbage-collector 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. -You should not use values smaller than 100, -because they make the collector too slow and -can result in the collector never finishing a cycle. -The default is 200, -which means that the collector runs at "twice" -the speed of memory allocation. - - -<p> -If you set the step multiplier to a very large number -(larger than 10% of the maximum number of -bytes that the program may use), -the collector behaves like a stop-the-world collector. -If you then set the pause to 200, -the collector behaves as in old Lua versions, -doing a complete collection every time Lua doubles its -memory usage. - - -<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. -You can also use these functions to control -the collector directly (e.g., stop and restart it). - - - -<h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3> - -<p> -You can set garbage-collector metamethods for tables -and, using the C API, -for full userdata (see <a href="#2.4">§2.4</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> -For an object (table or userdata) to be finalized when collected, -you must <em>mark</em> it for finalization. - -You mark an object for finalization when you set its metatable -and the metatable has a field indexed by the string "<code>__gc</code>". -Note that if you set a metatable without a <code>__gc</code> field -and later create that field in the metatable, -the object will not be marked for finalization. - - -<p> -When a marked object becomes garbage, -it is not collected immediately by the garbage collector. -Instead, Lua puts it in a list. -After the collection, -Lua goes through that list. -For each object in the list, -it checks the object's <code>__gc</code> metamethod: -If it is a function, -Lua calls it with the object as its single argument; -if the metamethod is not a function, -Lua simply ignores it. - - -<p> -At the end of each garbage-collection cycle, -the finalizers for objects are called in -the reverse order that the objects were marked for finalization, -among those collected in that cycle; -that is, the first finalizer to be called is the one associated -with the object marked last in the program. -The execution of each finalizer may occur at any point during -the execution of the regular code. - - -<p> -Because the object being collected must still be used by the finalizer, -that object (and other objects accessible only through it) -must be <em>resurrected</em> by Lua. -Usually, this resurrection is transient, -and the object memory is freed in the next garbage-collection cycle. -However, if the finalizer stores the object in some global place -(e.g., a global variable), -then the resurrection is permanent. -Moreover, if the finalizer marks a finalizing object for finalization again, -its finalizer will be called again in the next cycle where the -object is unreachable. -In any case, -the object memory is freed only in a GC cycle where -the object is unreachable and not marked for finalization. - - -<p> -When you close a state (see <a href="#lua_close"><code>lua_close</code></a>), -Lua calls the finalizers of all objects marked for finalization, -following the reverse order that they were marked. -If any finalizer marks objects for collection during that phase, -these marks have no effect. - - - - - -<h3>2.5.2 – <a name="2.5.2">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 that object. - - -<p> -A weak table can have weak keys, weak values, or both. -A table with weak values allows the collection of its values, -but prevents the collection of its keys. -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> -A table with weak keys and strong values -is also called an <em>ephemeron table</em>. -In an ephemeron table, -a value is considered reachable only if its key is reachable. -In particular, -if the only reference to a key comes through its value, -the pair is removed. - - -<p> -Any change in the weakness of a table may take effect only -at the next collect cycle. -In particular, if you change the weakness to a stronger mode, -Lua may still collect some items from that table -before the change takes effect. - - -<p> -Only objects that have an explicit construction -are removed from weak tables. -Values, such as numbers and light C functions, -are not subject to garbage collection, -and therefore are not removed from weak tables -(unless their associated values are collected). -Although strings are subject to garbage collection, -they do not have an explicit construction, -and therefore are not removed from weak tables. - - -<p> -Resurrected objects -(that is, objects being finalized -and objects accessible only through objects being finalized) -have a special behavior in weak tables. -They are removed from weak values before running their finalizers, -but are removed from weak keys only in the next collection -after running their finalizers, when such objects are actually freed. -This behavior allows the finalizer to access properties -associated with the object through weak tables. - - -<p> -If a weak table is among the resurrected objects in a collection cycle, -it may not be properly cleared until the next cycle. - - - - - - - -<h2>2.6 – <a name="2.6">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 by calling <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. - - -<p> -You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. -When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, -passing as its first argument -a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, -the coroutine starts its execution by -calling its main function. -Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed -as arguments to that 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 case of normal termination, -<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 object. - - -<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 of how coroutines work, -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> - -<p> -You can also create and manipulate coroutines through the C API: -see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>, -and <a href="#lua_yield"><code>lua_yield</code></a>. - - - - - -<h1>3 – <a name="3">The Language</a></h1> - -<p> -This section describes the lexis, the syntax, and the semantics of Lua. -In other words, -this section describes -which tokens are valid, -how they can be combined, -and what their combinations mean. - - -<p> -Language constructs will be explained using the usual extended BNF notation, -in which -{<em>a</em>} means 0 or more <em>a</em>'s, and -[<em>a</em>] means an optional <em>a</em>. -Non-terminals are shown like non-terminal, -keywords are shown like <b>kword</b>, -and other terminal symbols are shown like ‘<b>=</b>’. -The complete syntax of Lua can be found in <a href="#9">§9</a> -at the end of this manual. - - - -<h2>3.1 – <a name="3.1">Lexical Conventions</a></h2> - -<p> -Lua is a free-form language. -It ignores spaces (including new lines) and comments -between lexical elements (tokens), -except as delimiters between names and keywords. - - -<p> -<em>Names</em> -(also called <em>identifiers</em>) -in Lua can be any string of letters, -digits, and underscores, -not beginning with a digit and -not being a reserved word. -Identifiers are used to name variables, table fields, and labels. - - -<p> -The following <em>keywords</em> are reserved -and cannot be used as names: - - -<pre> - and break do else elseif end - false for function goto if in - local nil not or repeat return - then true until while -</pre> - -<p> -Lua is a case-sensitive language: -<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> -are two different, valid names. -As a convention, -programs should avoid creating -names that start with an underscore followed by -one or more uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>). - - -<p> -The following strings denote other tokens: - -<pre> - + - * / % ^ # - & ~ | << >> // - == ~= <= >= < > = - ( ) { } [ ] :: - ; : , . .. ... -</pre> - -<p> -<em>Literal strings</em> -can be delimited by matching single or double quotes, -and can contain the following C-like escape sequences: -'<code>\a</code>' (bell), -'<code>\b</code>' (backspace), -'<code>\f</code>' (form feed), -'<code>\n</code>' (newline), -'<code>\r</code>' (carriage return), -'<code>\t</code>' (horizontal tab), -'<code>\v</code>' (vertical tab), -'<code>\\</code>' (backslash), -'<code>\"</code>' (quotation mark [double quote]), -and '<code>\'</code>' (apostrophe [single quote]). -A backslash followed by a real newline -results in a newline in the string. -The escape sequence '<code>\z</code>' skips the following span -of white-space characters, -including line breaks; -it is particularly useful to break and indent a long literal string -into multiple lines without adding the newlines and spaces -into the string contents. - - -<p> -Strings in Lua can contain any 8-bit value, including embedded zeros, -which can be specified as '<code>\0</code>'. -More generally, -we can specify any byte in a literal string by its numeric value. -This can be done -with the escape sequence <code>\x<em>XX</em></code>, -where <em>XX</em> is a sequence of exactly two hexadecimal digits, -or with the escape sequence <code>\<em>ddd</em></code>, -where <em>ddd</em> is a sequence of up to three decimal digits. -(Note that if a decimal escape sequence is to be followed by a digit, -it must be expressed using exactly three digits.) - - -<p> -The UTF-8 encoding of a Unicode character -can be inserted in a literal string with -the escape sequence <code>\u{<em>XXX</em>}</code> -(note the mandatory enclosing brackets), -where <em>XXX</em> is a sequence of one or more hexadecimal digits -representing the character code point. - - -<p> -Literal strings can also be defined using a long format -enclosed by <em>long brackets</em>. -We define an <em>opening long bracket of level <em>n</em></em> as an opening -square bracket followed by <em>n</em> equal signs followed by another -opening square bracket. -So, an opening long bracket of level 0 is written as <code>[[</code>, -an opening long bracket of level 1 is written as <code>[=[</code>, -and so on. -A <em>closing long bracket</em> is defined similarly; -for instance, -a closing long bracket of level 4 is written as <code>]====]</code>. -A <em>long literal</em> starts with an opening long bracket of any level and -ends at the first closing long bracket of the same level. -It can contain any text except a closing bracket of the same level. -Literals in this bracketed form can run for several lines, -do not interpret any escape sequences, -and ignore long brackets of any other level. -Any kind of end-of-line sequence -(carriage return, newline, carriage return followed by newline, -or newline followed by carriage return) -is converted to a simple newline. - - -<p> -Any byte in a literal string not -explicitly affected by the previous rules represents itself. -However, Lua opens files for parsing in text mode, -and the system file functions may have problems with -some control characters. -So, it is safer to represent -non-text data as a quoted literal with -explicit escape sequences for the non-text characters. - - -<p> -For convenience, -when the opening long bracket is immediately followed by a newline, -the newline is not included in the string. -As an example, in a system using ASCII -(in which '<code>a</code>' is coded as 97, -newline is coded as 10, and '<code>1</code>' is coded as 49), -the five literal strings below denote the same string: - -<pre> - a = 'alo\n123"' - a = "alo\n123\"" - a = '\97lo\10\04923"' - a = [[alo - 123"]] - a = [==[ - alo - 123"]==] -</pre> - -<p> -A <em>numeric constant</em> (or <em>numeral</em>) -can be written with an optional fractional part -and an optional decimal exponent, -marked by a letter '<code>e</code>' or '<code>E</code>'. -Lua also accepts hexadecimal constants, -which start with <code>0x</code> or <code>0X</code>. -Hexadecimal constants also accept an optional fractional part -plus an optional binary exponent, -marked by a letter '<code>p</code>' or '<code>P</code>'. -A numeric constant with a radix point or an exponent -denotes a float; -otherwise, -if its value fits in an integer, -it denotes an integer. -Examples of valid integer constants are - -<pre> - 3 345 0xff 0xBEBADA -</pre><p> -Examples of valid float constants are - -<pre> - 3.0 3.1416 314.16e-2 0.31416E1 34e1 - 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1 -</pre> - -<p> -A <em>comment</em> starts with a double hyphen (<code>--</code>) -anywhere outside a string. -If the text immediately after <code>--</code> is not an opening long bracket, -the comment is a <em>short comment</em>, -which runs until the end of the line. -Otherwise, it is a <em>long comment</em>, -which runs until the corresponding closing long bracket. -Long comments are frequently used to disable code temporarily. - - - - - -<h2>3.2 – <a name="3.2">Variables</a></h2> - -<p> -Variables are places that store values. -There are three kinds of variables in Lua: -global variables, local variables, and table fields. - - -<p> -A single name can denote a global variable or a local variable -(or a function's formal parameter, -which is a particular kind of local variable): - -<pre> - var ::= Name -</pre><p> -Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>. - - -<p> -Any variable name is assumed to be global unless explicitly declared -as a local (see <a href="#3.3.7">§3.3.7</a>). -Local variables are <em>lexically scoped</em>: -local variables can be freely accessed by functions -defined inside their scope (see <a href="#3.5">§3.5</a>). - - -<p> -Before the first assignment to a variable, its value is <b>nil</b>. - - -<p> -Square brackets are used to index a table: - -<pre> - var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ -</pre><p> -The meaning of accesses to table fields can be changed via metatables. -An access to an indexed variable <code>t[i]</code> is equivalent to -a call <code>gettable_event(t,i)</code>. -(See <a href="#2.4">§2.4</a> for a complete description of the -<code>gettable_event</code> function. -This function is not defined or callable in Lua. -We use it here only for explanatory purposes.) - - -<p> -The syntax <code>var.Name</code> is just syntactic sugar for -<code>var["Name"]</code>: - -<pre> - var ::= prefixexp ‘<b>.</b>’ Name -</pre> - -<p> -An access to a global variable <code>x</code> -is equivalent to <code>_ENV.x</code>. -Due to the way that chunks are compiled, -<code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>). - - - - - -<h2>3.3 – <a name="3.3">Statements</a></h2> - -<p> -Lua supports an almost conventional set of statements, -similar to those in Pascal or C. -This set includes -assignments, control structures, function calls, -and variable declarations. - - - -<h3>3.3.1 – <a name="3.3.1">Blocks</a></h3> - -<p> -A block is a list of statements, -which are executed sequentially: - -<pre> - block ::= {stat} -</pre><p> -Lua has <em>empty statements</em> -that allow you to separate statements with semicolons, -start a block with a semicolon -or write two semicolons in sequence: - -<pre> - stat ::= ‘<b>;</b>’ -</pre> - -<p> -Function calls and assignments -can start with an open parenthesis. -This possibility leads to an ambiguity in Lua's grammar. -Consider the following fragment: - -<pre> - a = b + c - (print or io.write)('done') -</pre><p> -The grammar could see it in two ways: - -<pre> - a = b + c(print or io.write)('done') - - a = b + c; (print or io.write)('done') -</pre><p> -The current parser always sees such constructions -in the first way, -interpreting the open parenthesis -as the start of the arguments to a call. -To avoid this ambiguity, -it is a good practice to always precede with a semicolon -statements that start with a parenthesis: - -<pre> - ;(print or io.write)('done') -</pre> - -<p> -A block can be explicitly delimited to produce a single statement: - -<pre> - stat ::= <b>do</b> block <b>end</b> -</pre><p> -Explicit blocks are useful -to control the scope of variable declarations. -Explicit blocks are also sometimes used to -add a <b>return</b> statement in the middle -of another block (see <a href="#3.3.4">§3.3.4</a>). - - - - - -<h3>3.3.2 – <a name="3.3.2">Chunks</a></h3> - -<p> -The unit of compilation of Lua is called a <em>chunk</em>. -Syntactically, -a chunk is simply a block: - -<pre> - chunk ::= block -</pre> - -<p> -Lua handles a chunk as the body of an anonymous function -with a variable number of arguments -(see <a href="#3.4.11">§3.4.11</a>). -As such, chunks can define local variables, -receive arguments, and return values. -Moreover, such anonymous function is compiled as in the -scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>). -The resulting function always has <code>_ENV</code> as its only upvalue, -even if it does not use that variable. - - -<p> -A chunk can be stored in a file or in a string inside the host program. -To execute a chunk, -Lua first <em>loads</em> it, -precompiling the chunk's code into instructions for a virtual machine, -and then Lua executes the compiled code -with an interpreter for the virtual machine. - - -<p> -Chunks can also be precompiled into binary form; -see program <code>luac</code> and function <a href="#pdf-string.dump"><code>string.dump</code></a> for details. -Programs in source and compiled forms are interchangeable; -Lua automatically detects the file type and acts accordingly (see <a href="#pdf-load"><code>load</code></a>). - - - - - -<h3>3.3.3 – <a name="3.3.3">Assignment</a></h3> - -<p> -Lua allows multiple assignments. -Therefore, the syntax for assignment -defines a list of variables on the left side -and a list of expressions on the right side. -The elements in both lists are separated by commas: - -<pre> - stat ::= varlist ‘<b>=</b>’ explist - varlist ::= var {‘<b>,</b>’ var} - explist ::= exp {‘<b>,</b>’ exp} -</pre><p> -Expressions are discussed in <a href="#3.4">§3.4</a>. - - -<p> -Before the assignment, -the list of values is <em>adjusted</em> to the length of -the list of variables. -If there are more values than needed, -the excess values are thrown away. -If there are fewer values than needed, -the list is extended with as many <b>nil</b>'s as needed. -If the list of expressions ends with a function call, -then all values returned by that call enter the list of values, -before the adjustment -(except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>). - - -<p> -The assignment statement first evaluates all its expressions -and only then the assignments are performed. -Thus the code - -<pre> - i = 3 - i, a[i] = i+1, 20 -</pre><p> -sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> -because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) -before it is assigned 4. -Similarly, the line - -<pre> - x, y = y, x -</pre><p> -exchanges the values of <code>x</code> and <code>y</code>, -and - -<pre> - x, y, z = y, z, x -</pre><p> -cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. - - -<p> -The meaning of assignments to global variables -and table fields can be changed via metatables. -An assignment to an indexed variable <code>t[i] = val</code> is equivalent to -<code>settable_event(t,i,val)</code>. -(See <a href="#2.4">§2.4</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 name <code>x = val</code> -is equivalent to the assignment -<code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>). - - - - - -<h3>3.3.4 – <a name="3.3.4">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="#3.3.5">§3.3.5</a>). - - -<p> -The condition expression of a -control structure can return any value. -Both <b>false</b> and <b>nil</b> are considered false. -All values different from <b>nil</b> and <b>false</b> are considered true -(in particular, the number 0 and the empty string are also true). - - -<p> -In the <b>repeat</b>–<b>until</b> loop, -the inner block does not end at the <b>until</b> keyword, -but only after the condition. -So, the condition can refer to local variables -declared inside the loop block. - - -<p> -The <b>goto</b> statement transfers the program control to a label. -For syntactical reasons, -labels in Lua are considered statements too: - - - -<pre> - stat ::= <b>goto</b> Name - stat ::= label - label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ -</pre> - -<p> -A label is visible in the entire block where it is defined, -except -inside nested blocks where a label with the same name is defined and -inside nested functions. -A goto may jump to any visible label as long as it does not -enter into the scope of a local variable. - - -<p> -Labels and empty statements are called <em>void statements</em>, -as they perform no actions. - - -<p> -The <b>break</b> statement terminates 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> statement is used to return values -from a function or a chunk -(which is an anonymous function). - -Functions can return more than one value, -so the syntax for the <b>return</b> statement is - -<pre> - stat ::= <b>return</b> [explist] [‘<b>;</b>’] -</pre> - -<p> -The <b>return</b> statement can only be written -as the last statement of a block. -If it is really necessary to <b>return</b> in the middle of a block, -then an explicit inner block can be used, -as in the idiom <code>do return end</code>, -because now <b>return</b> is the last statement in its (inner) block. - - - - - -<h3>3.3.5 – <a name="3.3.5">For Statement</a></h3> - -<p> - -The <b>for</b> statement has two forms: -one numerical and one generic. - - -<p> -The numerical <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 - <em>var</em> = <em>var</em> - <em>step</em> - while true do - <em>var</em> = <em>var</em> + <em>step</em> - if (<em>step</em> >= 0 and <em>var</em> > <em>limit</em>) or (<em>step</em> < 0 and <em>var</em> < <em>limit</em>) then - break - end - local v = <em>var</em> - <em>block</em> - end - end -</pre> - -<p> -Note the following: - -<ul> - -<li> -All three control expressions are evaluated only once, -before the loop starts. -They must all result in numbers. -</li> - -<li> -<code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. -The names shown here are for explanatory purposes only. -</li> - -<li> -If the third expression (the step) is absent, -then a step of 1 is used. -</li> - -<li> -You can use <b>break</b> and <b>goto</b> to exit a <b>for</b> loop. -</li> - -<li> -The loop variable <code>v</code> is local to the loop body. -If you need its value after the loop, -assign it to another variable before exiting the loop. -</li> - -</ul> - -<p> -The generic <b>for</b> statement works over functions, -called <em>iterators</em>. -On each iteration, the iterator function is called to produce a new value, -stopping when this new value is <b>nil</b>. -The generic <b>for</b> loop has the following syntax: - -<pre> - stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> - namelist ::= Name {‘<b>,</b>’ Name} -</pre><p> -A <b>for</b> statement like - -<pre> - for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end -</pre><p> -is equivalent to the code: - -<pre> - do - local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> - while true do - local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) - if <em>var_1</em> == nil then break end - <em>var</em> = <em>var_1</em> - <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>3.3.6 – <a name="3.3.6">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="#3.4.10">§3.4.10</a>. - - - - - -<h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p> -Local variables can be declared anywhere inside a block. -The declaration can include an initial assignment: - -<pre> - stat ::= <b>local</b> namelist [‘<b>=</b>’ explist] -</pre><p> -If present, an initial assignment has the same semantics -of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>). -Otherwise, all variables are initialized with <b>nil</b>. - - -<p> -A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>), -and so local variables can be declared in a chunk outside any explicit block. - - -<p> -The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>. - - - - - - - -<h2>3.4 – <a name="3.4">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 ::= Numeral - exp ::= LiteralString - exp ::= functiondef - exp ::= tableconstructor - exp ::= ‘<b>...</b>’ - exp ::= exp binop exp - exp ::= unop exp - prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ -</pre> - -<p> -Numerals and literal strings are explained in <a href="#3.1">§3.1</a>; -variables are explained in <a href="#3.2">§3.2</a>; -function definitions are explained in <a href="#3.4.11">§3.4.11</a>; -function calls are explained in <a href="#3.4.10">§3.4.10</a>; -table constructors are explained in <a href="#3.4.9">§3.4.9</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="#3.4.11">§3.4.11</a>. - - -<p> -Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>), -bitwise operators (see <a href="#3.4.2">§3.4.2</a>), -relational operators (see <a href="#3.4.4">§3.4.4</a>), logical operators (see <a href="#3.4.5">§3.4.5</a>), -and the concatenation operator (see <a href="#3.4.6">§3.4.6</a>). -Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>), -the unary bitwise NOT (see <a href="#3.4.2">§3.4.2</a>), -the unary logical <b>not</b> (see <a href="#3.4.5">§3.4.5</a>), -and the unary <em>length operator</em> (see <a href="#3.4.7">§3.4.7</a>). - - -<p> -Both function calls and vararg expressions can result in multiple values. -If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>), -then its return list is adjusted to zero elements, -thus discarding all returned values. -If an expression is used as the last (or the only) element -of a list of expressions, -then no adjustment is made -(unless the expression is enclosed in parentheses). -In all other contexts, -Lua adjusts the result list to one element, -either discarding all values except the first one -or adding a single <b>nil</b> if there are no values. - - -<p> -Here are some examples: - -<pre> - f() -- adjusted to 0 results - g(f(), x) -- f() is adjusted to 1 result - g(x, f()) -- g gets x plus all results from f() - a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil) - a,b = ... -- a gets the first vararg parameter, b gets - -- the second (both a and b can get nil if there - -- is no corresponding vararg parameter) - - a,b,c = x, f() -- f() is adjusted to 2 results - a,b,c = f() -- f() is adjusted to 3 results - return f() -- returns all results from f() - return ... -- returns all received vararg parameters - return x,y,f() -- returns x, y, and all results from f() - {f()} -- creates a list with all results from f() - {...} -- creates a list with all vararg parameters - {f(), nil} -- f() is adjusted to 1 result -</pre> - -<p> -Any expression enclosed in parentheses always results in only one value. -Thus, -<code>(f(x,y,z))</code> is always a single value, -even if <code>f</code> returns several values. -(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> -or <b>nil</b> if <code>f</code> does not return any values.) - - - -<h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p> -Lua supports the following arithmetic operators: - -<ul> -<li><b><code>+</code>: </b>addition</li> -<li><b><code>-</code>: </b>subtraction</li> -<li><b><code>*</code>: </b>multiplication</li> -<li><b><code>/</code>: </b>float division</li> -<li><b><code>//</code>: </b>floor division</li> -<li><b><code>%</code>: </b>modulo</li> -<li><b><code>^</code>: </b>exponentiation</li> -<li><b><code>-</code>: </b>unary minus</li> -</ul> - -<p> -With the exception of exponentiation and float division, -the arithmetic operators work as follows: -If both operands are integers, -the operation is performed over integers and the result is an integer. -Otherwise, if both operands are numbers -or strings that can be converted to -numbers (see <a href="#3.4.3">§3.4.3</a>), -then they are converted to floats, -the operation is performed following the usual rules -for floating-point arithmetic -(usually the IEEE 754 standard), -and the result is a float. - - -<p> -Exponentiation and float division (<code>/</code>) -always convert their operands to floats -and the result is always a float. -Exponentiation uses the ISO C function <code>pow</code>, -so that it works for non-integer exponents too. - - -<p> -Floor division (<code>//</code>) is a division -that rounds the quotient towards minus infinity, -that is, the floor of the division of its operands. - - -<p> -Modulo is defined as the remainder of a division -that rounds the quotient towards minus infinity (floor division). - - -<p> -In case of overflows in integer arithmetic, -all operations <em>wrap around</em>, -according to the usual rules of two-complement arithmetic. -(In other words, -they return the unique representable integer -that is equal modulo <em>2<sup>64</sup></em> to the mathematical result.) - - - -<h3>3.4.2 – <a name="3.4.2">Bitwise Operators</a></h3><p> -Lua supports the following bitwise operators: - -<ul> -<li><b><code>&</code>: </b>bitwise AND</li> -<li><b><code>|</code>: </b>bitwise OR</li> -<li><b><code>~</code>: </b>bitwise exclusive OR</li> -<li><b><code>>></code>: </b>right shift</li> -<li><b><code><<</code>: </b>left shift</li> -<li><b><code>~</code>: </b>unary bitwise NOT</li> -</ul> - -<p> -All bitwise operations convert its operands to integers -(see <a href="#3.4.3">§3.4.3</a>), -operate on all bits of those integers, -and result in an integer. - - -<p> -Both right and left shifts fill the vacant bits with zeros. -Negative displacements shift to the other direction; -displacements with absolute values equal to or higher than -the number of bits in an integer -result in zero (as all bits are shifted out). - - - - - -<h3>3.4.3 – <a name="3.4.3">Coercions and Conversions</a></h3><p> -Lua provides some automatic conversions between some -types and representations at run time. -Bitwise operators always convert float operands to integers. -Exponentiation and float division -always convert integer operands to floats. -All other arithmetic operations applied to mixed numbers -(integers and floats) convert the integer operand to a float; -this is called the <em>usual rule</em>. -The C API also converts both integers to floats and -floats to integers, as needed. -Moreover, string concatenation accepts numbers as arguments, -besides strings. - - -<p> -Lua also converts strings to numbers, -whenever a number is expected. - - -<p> -In a conversion from integer to float, -if the integer value has an exact representation as a float, -that is the result. -Otherwise, -the conversion gets the nearest higher or -the nearest lower representable value. -This kind of conversion never fails. - - -<p> -The conversion from float to integer -checks whether the float has an exact representation as an integer -(that is, the float has an integral value and -it is in the range of integer representation). -If it does, that representation is the result. -Otherwise, the conversion fails. - - -<p> -The conversion from strings to numbers goes as follows: -First, the string is converted to an integer or a float, -following its syntax and the rules of the Lua lexer. -(The string may have also leading and trailing spaces and a sign.) -Then, the resulting number (float or integer) -is converted to the type (float or integer) required by the context -(e.g., the operation that forced the conversion). - - -<p> -All conversions from strings to numbers -accept both a dot and the current locale mark -as the radix character. -(The Lua lexer, however, accepts only a dot.) - - -<p> -The conversion from numbers to strings uses a -non-specified human-readable format. -For complete control over how numbers are converted to strings, -use the <code>format</code> function from the string library -(see <a href="#pdf-string.format"><code>string.format</code></a>). - - - - - -<h3>3.4.4 – <a name="3.4.4">Relational Operators</a></h3><p> -Lua supports the following relational operators: - -<ul> -<li><b><code>==</code>: </b>equality</li> -<li><b><code>~=</code>: </b>inequality</li> -<li><b><code><</code>: </b>less than</li> -<li><b><code>></code>: </b>greater than</li> -<li><b><code><=</code>: </b>less or equal</li> -<li><b><code>>=</code>: </b>greater or equal</li> -</ul><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. -Strings are compared in the obvious way. -Numbers are equal if they denote the same mathematical value. - - -<p> -Tables, userdata, and threads -are compared by reference: -two objects are considered equal only if they are the same object. -Every time you create a new object -(a table, userdata, or thread), -this new object is different from any previously existing object. -Closures with the same reference are always equal. -Closures with any detectable difference -(different behavior, different definition) are always different. - - -<p> -You can change the way that Lua compares tables and userdata -by using the "eq" metamethod (see <a href="#2.4">§2.4</a>). - - -<p> -Equality comparisons do not convert strings to numbers -or vice versa. -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 according to their mathematical values -(regardless of their subtypes). -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="#2.4">§2.4</a>). -A comparison <code>a > b</code> is translated to <code>b < a</code> -and <code>a >= b</code> is translated to <code>b <= a</code>. - - -<p> -Following the IEEE 754 standard, -NaN is considered neither smaller than, -nor equal to, nor greater than any value (including itself). - - - - - -<h3>3.4.5 – <a name="3.4.5">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="#3.3.4">§3.3.4</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-circuit evaluation; -that is, -the second operand is evaluated only if necessary. -Here are some examples: - -<pre> - 10 or 20 --> 10 - 10 or error() --> 10 - nil or "a" --> "a" - nil and 10 --> nil - false and error() --> false - false and nil --> false - false or nil --> nil - 10 and 20 --> 20 -</pre><p> -(In this manual, -<code>--></code> indicates the result of the preceding expression.) - - - - - -<h3>3.4.6 – <a name="3.4.6">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 described in <a href="#3.4.3">§3.4.3</a>. -Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>). - - - - - -<h3>3.4.7 – <a name="3.4.7">The Length Operator</a></h3> - -<p> -The length operator is denoted by the unary prefix 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> -A program can modify the behavior of the length operator for -any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>). - - -<p> -Unless a <code>__len</code> metamethod is given, -the length of a table <code>t</code> is only defined if the -table is a <em>sequence</em>, -that is, -the set of its positive numeric keys is equal to <em>{1..n}</em> -for some non-negative integer <em>n</em>. -In that case, <em>n</em> is its length. -Note that a table like - -<pre> - {10, 20, nil, 40} -</pre><p> -is not a sequence, because it has the key <code>4</code> -but does not have the key <code>3</code>. -(So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal -to the set of positive numeric keys of that table.) -Note, however, that non-numeric keys do not interfere -with whether a table is a sequence. - - - - - -<h3>3.4.8 – <a name="3.4.8">Precedence</a></h3><p> -Operator precedence in Lua follows the table below, -from lower to higher priority: - -<pre> - or - and - < > <= >= ~= == - | - ~ - & - << >> - .. - + - - * / // % - unary operators (not # - ~) - ^ -</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>3.4.9 – <a name="3.4.9">Table Constructors</a></h3><p> -Table constructors are expressions that create tables. -Every time a constructor is evaluated, a new table is created. -A constructor can be used to create an empty table -or to create a table and initialize some of its fields. -The general syntax for constructors is - -<pre> - tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ - fieldlist ::= field {fieldsep field} [fieldsep] - field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp - fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ -</pre> - -<p> -Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry -with key <code>exp1</code> and value <code>exp2</code>. -A field of the form <code>name = exp</code> is equivalent to -<code>["name"] = exp</code>. -Finally, fields of the form <code>exp</code> are equivalent to -<code>[i] = exp</code>, where <code>i</code> are consecutive 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> -The order of the assignments in a constructor is undefined. -(This order would be relevant only when there are repeated keys.) - - -<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="#3.4.10">§3.4.10</a>). - - -<p> -The field list can have an optional trailing separator, -as a convenience for machine-generated code. - - - - - -<h3>3.4.10 – <a name="3.4.10">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="#2.4">§2.4</a>). - - -<p> -The form - -<pre> - functioncall ::= prefixexp ‘<b>:</b>’ Name args -</pre><p> -can be used to call "methods". -A call <code>v:name(<em>args</em>)</code> -is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, -except that <code>v</code> is evaluated only once. - - -<p> -Arguments have the following syntax: - -<pre> - args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ - args ::= tableconstructor - args ::= LiteralString -</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> -A call of the form <code>return <em>functioncall</em></code> 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>3.4.11 – <a name="3.4.11">Function Definitions</a></h3> - -<p> -The syntax for function definition is - -<pre> - functiondef ::= <b>function</b> funcbody - funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> -</pre> - -<p> -The following syntactic sugar simplifies function definitions: - -<pre> - stat ::= <b>function</b> funcname funcbody - stat ::= <b>local</b> <b>function</b> Name funcbody - funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] -</pre><p> -The statement - -<pre> - function f () <em>body</em> end -</pre><p> -translates to - -<pre> - f = function () <em>body</em> end -</pre><p> -The statement - -<pre> - function t.a.b.c.f () <em>body</em> end -</pre><p> -translates to - -<pre> - t.a.b.c.f = function () <em>body</em> end -</pre><p> -The statement - -<pre> - local function f () <em>body</em> end -</pre><p> -translates to - -<pre> - local f; f = function () <em>body</em> end -</pre><p> -not 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 precompiles a chunk, -all its function bodies are precompiled 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. - - -<p> -Parameters act as local variables that are -initialized with the argument values: - -<pre> - parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ -</pre><p> -When a function is called, -the list of arguments is adjusted to -the length of the list of parameters, -unless the function is a <em>vararg function</em>, -which is indicated by three dots ('<code>...</code>') -at the end of its parameter list. -A vararg function does not adjust its argument list; -instead, it collects all extra arguments and supplies them -to the function through a <em>vararg expression</em>, -which is also written as three dots. -The value of this expression is a list of all actual extra arguments, -similar to a function with multiple results. -If a vararg expression is used inside another expression -or in the middle of a list of expressions, -then its return list is adjusted to one element. -If the expression is used as the last element of a list of expressions, -then no adjustment is made -(unless that last expression is enclosed in parentheses). - - -<p> -As an example, consider the following definitions: - -<pre> - function f(a, b) end - function g(a, b, ...) end - function r() return 1,2,3 end -</pre><p> -Then, we have the following mapping from arguments to parameters and -to the vararg expression: - -<pre> - CALL PARAMETERS - - f(3) a=3, b=nil - f(3, 4) a=3, b=4 - f(3, 4, 5) a=3, b=4 - f(r(), 10) a=1, b=10 - f(r()) a=1, b=2 - - g(3) a=3, b=nil, ... --> (nothing) - g(3, 4) a=3, b=4, ... --> (nothing) - g(3, 4, 5, 8) a=3, b=4, ... --> 5 8 - g(5, r()) a=5, b=1, ... --> 2 3 -</pre> - -<p> -Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>). -If control reaches the end of a function -without encountering a <b>return</b> statement, -then the function returns with no results. - - -<p> - -There is a system-dependent limit on the number of values -that a function may return. -This limit is guaranteed to be larger than 1000. - - -<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>3.5 – <a name="3.5">Visibility Rules</a></h2> - -<p> - -Lua is a lexically scoped language. -The scope of a local variable begins at the first statement after -its declaration and lasts until the last non-void statement -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>. - - - - - -<h1>4 – <a name="4">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. -Except where stated otherwise, -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 the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined. - - - -<h2>4.1 – <a name="4.1">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 absolute stack position -(starting at 1); -a negative index represents an offset relative to the top of the stack. -More specifically, if the stack has <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. - - - - - -<h2>4.2 – <a name="4.2">Stack Size</a></h2> - -<p> -When you interact with the 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 ensure that the stack has enough space for pushing new elements. - - -<p> -Whenever Lua calls C, -it ensures that the stack has space for -at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots. -<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> -When you call a Lua function -without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>), -Lua ensures that the stack has enough space for all results, -but it does not ensure any extra space. -So, before pushing anything in the stack after such a call -you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>. - - - - - -<h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2> - -<p> -Any function in the API that receives stack indices -works only with <em>valid indices</em> or <em>acceptable indices</em>. - - -<p> -A <em>valid index</em> is an index that refers to a -position that stores a modifiable Lua value. -It comprises stack indices between 1 and the stack top -(<code>1 ≤ abs(index) ≤ top</code>) - -plus <em>pseudo-indices</em>, -which represent some positions that are accessible to C code -but that are not in the stack. -Pseudo-indices are used to access the registry (see <a href="#4.5">§4.5</a>) -and the upvalues of a C function (see <a href="#4.4">§4.4</a>). - - -<p> -Functions that do not need a specific mutable position, -but only a value (e.g., query functions), -can be called with acceptable indices. -An <em>acceptable index</em> can be any valid index, -but it also can be any positive index after the stack top -within the space allocated for the stack, -that is, indices up to the stack size. -(Note that 0 is never an acceptable index.) -Except when noted otherwise, -functions in the API work with acceptable indices. - - -<p> -Acceptable indices serve to avoid extra tests -against the stack top when querying the stack. -For instance, a C function can query its third argument -without the need to first check whether there is a third argument, -that is, without the need to check whether 3 is a valid index. - - -<p> -For functions that can be called with acceptable indices, -any non-valid index is treated as if it -contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>, -which behaves like a nil value. - - - - - -<h2>4.4 – <a name="4.4">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> -(see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>); -these values are called <em>upvalues</em> and are -accessible to the function whenever it is called. - - -<p> -Whenever a C function is called, -its upvalues are located at specific pseudo-indices. -These pseudo-indices are produced by the macro -<a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>. -The first upvalue associated with a function is at index -<code>lua_upvalueindex(1)</code>, and so on. -Any access to <code>lua_upvalueindex(<em>n</em>)</code>, -where <em>n</em> is greater than the number of upvalues of the -current function -(but not greater than 256, -which is one plus the maximum number of upvalues in a closure), -produces an acceptable but invalid index. - - - - - -<h2>4.5 – <a name="4.5">Registry</a></h2> - -<p> -Lua provides a <em>registry</em>, -a predefined table that can be used by any C code to -store whatever Lua values it needs to store. -The registry 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 must take care to choose keys -that are 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, -or any Lua object created by your code. -As with variable names, -string keys starting with an underscore followed by -uppercase letters are reserved for Lua. - - -<p> -The integer keys in the registry are used -by the reference mechanism (see <a href="#luaL_ref"><code>luaL_ref</code></a>) -and by some predefined values. -Therefore, integer keys must not be used for other purposes. - - -<p> -When you create a new Lua state, -its registry comes with some predefined values. -These predefined values are indexed with integer keys -defined as constants in <code>lua.h</code>. -The following constants are defined: - -<ul> -<li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has -the main thread of the state. -(The main thread is the one created together with the state.) -</li> - -<li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has -the global environment. -</li> -</ul> - - - - -<h2>4.6 – <a name="4.6">Error Handling in C</a></h2> - -<p> -Internally, Lua uses the C <code>longjmp</code> facility to handle errors. -(Lua will use exceptions if you compile it as C++; -search for <code>LUAI_THROW</code> in the source code for details.) -When Lua faces any error -(such as a memory allocation error, 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 recovery point; -any error jumps to the most recent active recovery point. - - -<p> -If an error happens outside any protected environment, -Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) -and then calls <code>abort</code>, -thus exiting the host application. -Your panic function can avoid this exit by -never returning -(e.g., doing a long jump to your own recovery point outside Lua). - - -<p> -The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>); -in particular, the error object is at the top of the stack. -However, there is no guarantee about stack space. -To push anything on the stack, -the panic function must first check the available space (see <a href="#4.2">§4.2</a>). - - -<p> -Most functions in the API can raise an error, -for instance due to a memory allocation error. -The documentation for each function indicates whether -it can raise errors. - - -<p> -Inside a C function you can raise an error by calling <a href="#lua_error"><code>lua_error</code></a>. - - - - - -<h2>4.7 – <a name="4.7">Handling Yields in C</a></h2> - -<p> -Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine. -Therefore, if a C function <code>foo</code> calls an API function -and this API function yields -(directly or indirectly by calling another function that yields), -Lua cannot return to <code>foo</code> any more, -because the <code>longjmp</code> removes its frame from the C stack. - - -<p> -To avoid this kind of problem, -Lua raises an error whenever it tries to yield across an API call, -except for three functions: -<a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>. -All those functions receive a <em>continuation function</em> -(as a parameter named <code>k</code>) to continue execution after a yield. - - -<p> -We need to set some terminology to explain continuations. -We have a C function called from Lua which we will call -the <em>original function</em>. -This original function then calls one of those three functions in the C API, -which we will call the <em>callee function</em>, -that then yields the current thread. -(This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>, -or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a> -and the function called by them yields.) - - -<p> -Suppose the running thread yields while executing the callee function. -After the thread resumes, -it eventually will finish running the callee function. -However, -the callee function cannot return to the original function, -because its frame in the C stack was destroyed by the yield. -Instead, Lua calls a <em>continuation function</em>, -which was given as an argument to the callee function. -As the name implies, -the continuation function should continue the task -of the original function. - - -<p> -As an illustration, consider the following function: - -<pre> - int original_function (lua_State *L) { - ... /* code 1 */ - status = lua_pcall(L, n, m, h); /* calls Lua */ - ... /* code 2 */ - } -</pre><p> -Now we want to allow -the Lua code being run by <a href="#lua_pcall"><code>lua_pcall</code></a> to yield. -First, we can rewrite our function like here: - -<pre> - int k (lua_State *L, int status, lua_KContext ctx) { - ... /* code 2 */ - } - - int original_function (lua_State *L) { - ... /* code 1 */ - return k(L, lua_pcall(L, n, m, h), ctx); - } -</pre><p> -In the above code, -the new function <code>k</code> is a -<em>continuation function</em> (with type <a href="#lua_KFunction"><code>lua_KFunction</code></a>), -which should do all the work that the original function -was doing after calling <a href="#lua_pcall"><code>lua_pcall</code></a>. -Now, we must inform Lua that it must call <code>k</code> if the Lua code -being executed by <a href="#lua_pcall"><code>lua_pcall</code></a> gets interrupted in some way -(errors or yielding), -so we rewrite the code as here, -replacing <a href="#lua_pcall"><code>lua_pcall</code></a> by <a href="#lua_pcallk"><code>lua_pcallk</code></a>: - -<pre> - int original_function (lua_State *L) { - ... /* code 1 */ - return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1); - } -</pre><p> -Note the external, explicit call to the continuation: -Lua will call the continuation only if needed, that is, -in case of errors or resuming after a yield. -If the called function returns normally without ever yielding, -<a href="#lua_pcallk"><code>lua_pcallk</code></a> (and <a href="#lua_callk"><code>lua_callk</code></a>) will also return normally. -(Of course, instead of calling the continuation in that case, -you can do the equivalent work directly inside the original function.) - - -<p> -Besides the Lua state, -the continuation function has two other parameters: -the final status of the call plus the context value (<code>ctx</code>) that -was passed originally to <a href="#lua_pcallk"><code>lua_pcallk</code></a>. -(Lua does not use this context value; -it only passes this value from the original function to the -continuation function.) -For <a href="#lua_pcallk"><code>lua_pcallk</code></a>, -the status is the same value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>, -except that it is <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when being executed after a yield -(instead of <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>). -For <a href="#lua_yieldk"><code>lua_yieldk</code></a> and <a href="#lua_callk"><code>lua_callk</code></a>, -the status is always <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when Lua calls the continuation. -(For these two functions, -Lua will not call the continuation in case of errors, -because they do not handle errors.) -Similarly, when using <a href="#lua_callk"><code>lua_callk</code></a>, -you should call the continuation function -with <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> as the status. -(For <a href="#lua_yieldk"><code>lua_yieldk</code></a>, there is not much point in calling -directly the continuation function, -because <a href="#lua_yieldk"><code>lua_yieldk</code></a> usually does not return.) - - -<p> -Lua treats the continuation function as if it were the original function. -The continuation function receives the same Lua stack -from the original function, -in the same state it would be if the callee function had returned. -(For instance, -after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are -removed from the stack and replaced by the results from the call.) -It also has the same upvalues. -Whatever it returns is handled by Lua as if it were the return -of the original function. - - - - - -<h2>4.8 – <a name="4.8">Functions and Types</a></h2> - -<p> -Here we list all functions and types from the C API in -alphabetical order. -Each function has an indicator like this: -<span class="apii">[-o, +p, <em>x</em>]</span> - - -<p> -The first field, <code>o</code>, -is how many elements the function pops from the stack. -The second field, <code>p</code>, -is how many elements the function pushes onto the stack. -(Any function always pushes its results after popping its arguments.) -A field in the form <code>x|y</code> means the function can push (or pop) -<code>x</code> or <code>y</code> elements, -depending on the situation; -an interrogation mark '<code>?</code>' means that -we cannot know how many elements the function pops/pushes -by looking only at its arguments -(e.g., they may depend on what is on the stack). -The third field, <code>x</code>, -tells whether the function may raise errors: -'<code>-</code>' means the function never raises any error; -'<code>m</code>' means the function may raise out-of-memory errors -and errors running a <code>__gc</code> metamethod; -'<code>e</code>' means the function may raise any errors -(it can run arbitrary Lua code, -either directly or through metamethods); -'<code>v</code>' means the function may raise an error on purpose. - - - -<hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_absindex (lua_State *L, int idx);</pre> - -<p> -Converts the acceptable index <code>idx</code> -into an equivalent absolute index -(that is, one that does not depend on the stack top). - - - - - -<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 or some code about what -is being allocated; -and <code>nsize</code>, the new size of the block. - - -<p> -When <code>ptr</code> is not <code>NULL</code>, -<code>osize</code> is the size of the block pointed by <code>ptr</code>, -that is, the size given when it was allocated or reallocated. - - -<p> -When <code>ptr</code> is <code>NULL</code>, -<code>osize</code> encodes the kind of object that Lua is allocating. -<code>osize</code> is any of -<a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, -<a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when) -Lua is creating a new object of that type. -When <code>osize</code> is some other value, -Lua is allocating memory for something else. - - -<p> -Lua assumes the following behavior from the allocator function: - - -<p> -When <code>nsize</code> is zero, -the allocator must behave like <code>free</code> -and return <code>NULL</code>. - - -<p> -When <code>nsize</code> is not zero, -the allocator must behave like <code>realloc</code>. -The allocator returns <code>NULL</code> -if and only if it cannot fulfill the request. -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> -Note that Standard C ensures -that <code>free(NULL)</code> has no effect and that -<code>realloc(NULL,size)</code> is equivalent to <code>malloc(size)</code>. -This code assumes that <code>realloc</code> does not fail when shrinking a block. -(Although Standard C does not ensure this behavior, -it seems to be a safe assumption.) - - - - - -<hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p> -<span class="apii">[-(2|1), +1, <em>e</em>]</span> -<pre>void lua_arith (lua_State *L, int op);</pre> - -<p> -Performs an arithmetic or bitwise operation over the two values -(or one, in the case of negations) -at the top of the stack, -with the value at the top being the second operand, -pops these values, and pushes the result of the operation. -The function follows the semantics of the corresponding Lua operator -(that is, it may call metamethods). - - -<p> -The value of <code>op</code> must be one of the following constants: - -<ul> - -<li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li> -<li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li> -<li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li> -<li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs float division (<code>/</code>)</li> -<li><b><a name="pdf-LUA_OPIDIV"><code>LUA_OPIDIV</code></a>: </b> performs floor division (<code>//</code>)</li> -<li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li> -<li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li> -<li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li> -<li><b><a name="pdf-LUA_OPBNOT"><code>LUA_OPBNOT</code></a>: </b> performs bitwise NOT (<code>~</code>)</li> -<li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise AND (<code>&</code>)</li> -<li><b><a name="pdf-LUA_OPBOR"><code>LUA_OPBOR</code></a>: </b> performs bitwise OR (<code>|</code>)</li> -<li><b><a name="pdf-LUA_OPBXOR"><code>LUA_OPBXOR</code></a>: </b> performs bitwise exclusive OR (<code>~</code>)</li> -<li><b><a name="pdf-LUA_OPSHL"><code>LUA_OPSHL</code></a>: </b> performs left shift (<code><<</code>)</li> -<li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>>></code>)</li> - -</ul> - - - - -<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> - -<p> -Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>). - - - - - -<hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> -<span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span> -<pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> - -<p> -Calls a function. - - -<p> -To call a function you must use the following protocol: -first, the function to be called is pushed onto the stack; -then, the arguments to the function are pushed -in direct order; -that is, the first argument is pushed first. -Finally you call <a href="#lua_call"><code>lua_call</code></a>; -<code>nargs</code> is the number of arguments that you pushed onto the stack. -All arguments and the function value are popped from the stack -when the function is called. -The function results are pushed onto the stack when the function returns. -The number of results is adjusted to <code>nresults</code>, -unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. -In this case, all results from the function are pushed. -Lua takes care that the returned values fit into the stack space, -but it does not ensure any extra space in the stack. -The function results are pushed onto the stack in direct order -(the first result is pushed first), -so that after the call the last result is on the top of the stack. - - -<p> -Any error inside the called function is propagated upwards -(with a <code>longjmp</code>). - - -<p> -The following example shows how the host program can do the -equivalent to this Lua code: - -<pre> - a = f("how", t.x, 14) -</pre><p> -Here it is in C: - -<pre> - lua_getglobal(L, "f"); /* function to be called */ - lua_pushliteral(L, "how"); /* 1st argument */ - lua_getglobal(L, "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_setglobal(L, "a"); /* set global 'a' */ -</pre><p> -Note that the code above is <em>balanced</em>: -at its end, the stack is back to its original configuration. -This is considered good programming practice. - - - - - -<hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p> -<span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> -<pre>void lua_callk (lua_State *L, - int nargs, - int nresults, - lua_KContext ctx, - lua_KFunction k);</pre> - -<p> -This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>, -but allows the called function to yield (see <a href="#4.7">§4.7</a>). - - - - - -<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 numeric arguments and returns their average and their sum: - -<pre> - static int foo (lua_State *L) { - int n = lua_gettop(L); /* number of arguments */ - lua_Number sum = 0.0; - int i; - for (i = 1; i <= n; i++) { - if (!lua_isnumber(L, i)) { - lua_pushliteral(L, "incorrect argument"); - lua_error(L); - } - sum += lua_tonumber(L, i); - } - lua_pushnumber(L, sum/n); /* first result */ - lua_pushnumber(L, sum); /* second result */ - return 2; /* number of results */ - } -</pre> - - - - -<hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_checkstack (lua_State *L, int n);</pre> - -<p> -Ensures that the stack has space for at least <code>n</code> extra slots -(that is, that you can safely push up to <code>n</code> values into it). -It returns false if it cannot fulfill the request, -either because it would cause the stack -to be larger than a fixed maximum size -(typically at least several thousand elements) or -because it cannot allocate memory for the extra space. -This function never shrinks the stack; -if the stack already has space for the extra slots, -it is left unchanged. - - - - - -<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void lua_close (lua_State *L);</pre> - -<p> -Destroys all objects in the given Lua state -(calling the corresponding garbage-collection metamethods, if any) -and frees all dynamic memory used by this state. -On several platforms, you may not need to call this function, -because all resources are naturally released when the host program ends. -On the other hand, long-running programs that create multiple states, -such as daemons or web servers, -will probably need to close states as soon as they are not needed. - - - - - -<hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre> - -<p> -Compares two Lua values. -Returns 1 if the value at index <code>index1</code> satisfies <code>op</code> -when compared with the value at index <code>index2</code>, -following the semantics of the corresponding Lua operator -(that is, it may call metamethods). -Otherwise returns 0. -Also returns 0 if any of the indices is not valid. - - -<p> -The value of <code>op</code> must be one of the following constants: - -<ul> - -<li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li> -<li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li> -<li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li> - -</ul> - - - - -<hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> -<span class="apii">[-n, +1, <em>e</em>]</span> -<pre>void lua_concat (lua_State *L, int n);</pre> - -<p> -Concatenates the <code>n</code> values at the top of the stack, -pops them, and leaves the result at the top. -If <code>n</code> is 1, the result is the single value on the stack -(that is, the function does nothing); -if <code>n</code> is 0, the result is the empty string. -Concatenation is performed following the usual semantics of Lua -(see <a href="#3.4.6">§3.4.6</a>). - - - - - -<hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre> - -<p> -Copies the element at index <code>fromidx</code> -into the valid index <code>toidx</code>, -replacing the value at that position. -Values at other positions are not affected. - - - - - -<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> - -<p> -Creates a new empty table and pushes it onto the stack. -Parameter <code>narr</code> is a hint for how many elements the table -will have as a sequence; -parameter <code>nrec</code> is a hint for how many other elements -the table will have. -Lua may use these hints to preallocate memory for the new table. -This preallocation is useful for performance when you know in advance -how many elements the table will have. -Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>. - - - - - -<hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_dump (lua_State *L, - lua_Writer writer, - void *data, - int strip);</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> -If <code>strip</code> is true, -the binary representation may not include all debug information -about the function, -to save space. - - -<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_error"><code>lua_error</code></a></h3><p> -<span class="apii">[-1, +0, <em>v</em>]</span> -<pre>int lua_error (lua_State *L);</pre> - -<p> -Generates a Lua error, -using the value at the top of the stack as the error object. -This function does a long jump, -and therefore never returns -(see <a href="#luaL_error"><code>luaL_error</code></a>). - - - - - -<hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>int lua_gc (lua_State *L, int what, int data);</pre> - -<p> -Controls the garbage collector. - - -<p> -This function performs several tasks, -according to the value of the parameter <code>what</code>: - -<ul> - -<li><b><code>LUA_GCSTOP</code>: </b> -stops the garbage collector. -</li> - -<li><b><code>LUA_GCRESTART</code>: </b> -restarts the garbage collector. -</li> - -<li><b><code>LUA_GCCOLLECT</code>: </b> -performs a full garbage-collection cycle. -</li> - -<li><b><code>LUA_GCCOUNT</code>: </b> -returns the current amount of memory (in Kbytes) in use by Lua. -</li> - -<li><b><code>LUA_GCCOUNTB</code>: </b> -returns the remainder of dividing the current amount of bytes of -memory in use by Lua by 1024. -</li> - -<li><b><code>LUA_GCSTEP</code>: </b> -performs an incremental step of garbage collection. -</li> - -<li><b><code>LUA_GCSETPAUSE</code>: </b> -sets <code>data</code> as the new value -for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>) -and returns the previous value of the pause. -</li> - -<li><b><code>LUA_GCSETSTEPMUL</code>: </b> -sets <code>data</code> as the new value for the <em>step multiplier</em> of -the collector (see <a href="#2.5">§2.5</a>) -and returns the previous value of the step multiplier. -</li> - -<li><b><code>LUA_GCISRUNNING</code>: </b> -returns a boolean that tells whether the collector is running -(i.e., not stopped). -</li> - -</ul> - -<p> -For more details about these options, -see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>. - - - - - -<hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> - -<p> -Returns the memory-allocation function of a given state. -If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the -opaque pointer given when the memory-allocator function was set. - - - - - -<hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>int 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 index. -As in Lua, this function may trigger a metamethod -for the "index" event (see <a href="#2.4">§2.4</a>). - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_getextraspace"><code>lua_getextraspace</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void *lua_getextraspace (lua_State *L);</pre> - -<p> -Returns a pointer to a raw memory area associated with the -given Lua state. -The application can use this area for any purpose; -Lua does not use it for anything. - - -<p> -Each new thread has this area initialized with a copy -of the area of the main thread. - - -<p> -By default, this area has the size of a pointer to void, -but you can recompile Lua with a different size for this area. -(See <code>LUA_EXTRASPACE</code> in <code>luaconf.h</code>.) - - - - - -<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>int lua_getglobal (lua_State *L, const char *name);</pre> - -<p> -Pushes onto the stack the value of the global <code>name</code>. -Returns the type of that value. - - - - - -<hr><h3><a name="lua_geti"><code>lua_geti</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>int lua_geti (lua_State *L, int index, lua_Integer i);</pre> - -<p> -Pushes onto the stack the value <code>t[i]</code>, -where <code>t</code> is the value at the given index. -As in Lua, this function may trigger a metamethod -for the "index" event (see <a href="#2.4">§2.4</a>). - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> -<span class="apii">[-0, +(0|1), –]</span> -<pre>int lua_getmetatable (lua_State *L, int index);</pre> - -<p> -If the value at the given index has a metatable, -the function pushes that metatable onto the stack and returns 1. -Otherwise, -the function returns 0 and pushes nothing on the stack. - - - - - -<hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> -<span class="apii">[-1, +1, <em>e</em>]</span> -<pre>int 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 index -and <code>k</code> is the value at the top of the stack. - - -<p> -This function pops the key from the stack, -pushing the resulting value in its place. -As in Lua, this function may trigger a metamethod -for the "index" event (see <a href="#2.4">§2.4</a>). - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_gettop (lua_State *L);</pre> - -<p> -Returns the index of the top element in the stack. -Because indices start at 1, -this result is equal to the number of elements in the stack; -in particular, 0 means an empty stack. - - - - - -<hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int lua_getuservalue (lua_State *L, int index);</pre> - -<p> -Pushes onto the stack the Lua value associated with the userdata -at the given index. - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> -<span class="apii">[-1, +1, –]</span> -<pre>void lua_insert (lua_State *L, int index);</pre> - -<p> -Moves the top element into the given valid index, -shifting up the elements above this index to open space. -This function 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 ... lua_Integer;</pre> - -<p> -The type of integers in Lua. - - -<p> -By default this type is <code>long long</code>, -(usually a 64-bit two-complement integer), -but that can be changed to <code>long</code> or <code>int</code> -(usually a 32-bit two-complement integer). -(See <code>LUA_INT_TYPE</code> in <code>luaconf.h</code>.) - - -<p> -Lua also defines the constants -<a name="pdf-LUA_MININTEGER"><code>LUA_MININTEGER</code></a> and <a name="pdf-LUA_MAXINTEGER"><code>LUA_MAXINTEGER</code></a>, -with the minimum and the maximum values that fit in this type. - - - - - -<hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isboolean (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a boolean, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_iscfunction (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a C function, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isfunction (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a function -(either C or Lua), and 0 otherwise. - - - - - -<hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isinteger (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is an integer -(that is, the value is a number and is represented as an integer), -and 0 otherwise. - - - - - -<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_islightuserdata (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a light userdata, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isnil (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is <b>nil</b>, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isnone (lua_State *L, int index);</pre> - -<p> -Returns 1 if the given index is not valid, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isnoneornil (lua_State *L, int index);</pre> - -<p> -Returns 1 if the given index is not valid -or if the value at this index is <b>nil</b>, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isnumber (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a number -or a string convertible to a number, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isstring (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a string -or a number (which is always convertible to a string), -and 0 otherwise. - - - - - -<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_istable (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a table, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isthread (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a thread, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isuserdata (lua_State *L, int index);</pre> - -<p> -Returns 1 if the value at the given index is a userdata -(either full or light), and 0 otherwise. - - - - - -<hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_isyieldable (lua_State *L);</pre> - -<p> -Returns 1 if the given coroutine can yield, -and 0 otherwise. - - - - - -<hr><h3><a name="lua_KContext"><code>lua_KContext</code></a></h3> -<pre>typedef ... lua_KContext;</pre> - -<p> -The type for continuation-function contexts. -It must be a numeric type. -This type is defined as <code>intptr_t</code> -when <code>intptr_t</code> is available, -so that it can store pointers too. -Otherwise, it is defined as <code>ptrdiff_t</code>. - - - - - -<hr><h3><a name="lua_KFunction"><code>lua_KFunction</code></a></h3> -<pre>typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);</pre> - -<p> -Type for continuation functions (see <a href="#4.7">§4.7</a>). - - - - - -<hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>void lua_len (lua_State *L, int index);</pre> - -<p> -Returns the length of the value at the given index. -It is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>) and -may trigger a metamethod for the "length" event (see <a href="#2.4">§2.4</a>). -The result is pushed on the stack. - - - - - -<hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int lua_load (lua_State *L, - lua_Reader reader, - void *data, - const char *chunkname, - const char *mode);</pre> - -<p> -Loads a Lua chunk without running it. -If there are no errors, -<code>lua_load</code> pushes the compiled chunk as a Lua -function on top of the stack. -Otherwise, it pushes an error message. - - -<p> -The return values of <code>lua_load</code> are: - -<ul> - -<li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li> - -<li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b> -syntax error during precompilation;</li> - -<li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> -memory allocation (out-of-memory) error;</li> - -<li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> -error while running a <code>__gc</code> metamethod. -(This error has no relation with the chunk being loaded. -It is generated by the garbage collector.) -</li> - -</ul> - -<p> -The <code>lua_load</code> 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="#4.9">§4.9</a>). - - -<p> -<code>lua_load</code> automatically detects whether the chunk is text or binary -and loads it accordingly (see program <code>luac</code>). -The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>, -with the addition that -a <code>NULL</code> value is equivalent to the string "<code>bt</code>". - - -<p> -<code>lua_load</code> uses the stack internally, -so the reader function must always leave the stack -unmodified when returning. - - -<p> -If the resulting function has upvalues, -its first upvalue is set to the value of the global environment -stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>). -When loading main chunks, -this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). -Other upvalues are initialized with <b>nil</b>. - - - - - -<hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> - -<p> -Creates a new thread running in a new, independent state. -Returns <code>NULL</code> if it cannot create the thread or 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 -passes to the allocator in every call. - - - - - -<hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void lua_newtable (lua_State *L);</pre> - -<p> -Creates a new empty table and pushes it onto the stack. -It is equivalent to <code>lua_createtable(L, 0, 0)</code>. - - - - - -<hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>lua_State *lua_newthread (lua_State *L);</pre> - -<p> -Creates a new thread, pushes it on the stack, -and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread. -The new thread returned by this function shares with the original thread -its global environment, -but has an independent execution stack. - - -<p> -There is no explicit function to close or to destroy a thread. -Threads are subject to garbage collection, -like any Lua object. - - - - - -<hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> - -<p> -This function allocates a new block of memory with the given size, -pushes onto the stack a new full userdata with the block address, -and returns this address. -The host program can freely use this memory. - - - - - -<hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> -<span class="apii">[-1, +(2|0), <em>e</em>]</span> -<pre>int lua_next (lua_State *L, int index);</pre> - -<p> -Pops a key from the stack, -and pushes a key–value pair from the table at the given index -(the "next" pair after the given key). -If there are no more elements in the table, -then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). - - -<p> -A typical traversal looks like this: - -<pre> - /* table is in the stack at index 't' */ - lua_pushnil(L); /* first key */ - while (lua_next(L, t) != 0) { - /* uses 'key' (at index -2) and 'value' (at index -1) */ - printf("%s - %s\n", - lua_typename(L, lua_type(L, -2)), - lua_typename(L, lua_type(L, -1))); - /* removes 'value'; keeps 'key' for next iteration */ - lua_pop(L, 1); - } -</pre> - -<p> -While traversing a table, -do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, -unless you know that the key is actually a string. -Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change -the value at the given index; -this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. - - -<p> -See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying -the table during its traversal. - - - - - -<hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> -<pre>typedef ... lua_Number;</pre> - -<p> -The type of floats in Lua. - - -<p> -By default this type is double, -but that can be changed to a single float or a long double. -(See <code>LUA_FLOAT_TYPE</code> in <code>luaconf.h</code>.) - - - - - -<hr><h3><a name="lua_numbertointeger"><code>lua_numbertointeger</code></a></h3> -<pre>int lua_numbertointeger (lua_Number n, lua_Integer *p);</pre> - -<p> -Converts a Lua float to a Lua integer. -This macro assumes that <code>n</code> has an integral value. -If that value is within the range of Lua integers, -it is converted to an integer and assigned to <code>*p</code>. -The macro results in a boolean indicating whether the -conversion was successful. -(Note that this range test can be tricky to do -correctly without this macro, -due to roundings.) - - -<p> -This macro may evaluate its arguments more than once. - - - - - -<hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> -<span class="apii">[-(nargs + 1), +(nresults|1), –]</span> -<pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</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 object), -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>msgh</code> is 0, -then the error object returned on the stack -is exactly the original error object. -Otherwise, <code>msgh</code> is the stack index of a -<em>message handler</em>. -(This index cannot be a pseudo-index.) -In case of runtime errors, -this function will be called with the error object -and its return value will be the object -returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>. - - -<p> -Typically, the message handler is used to add more debug -information to the error object, 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 one of the following constants -(defined in <code>lua.h</code>): - -<ul> - -<li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b> -success.</li> - -<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 message handler. -</li> - -<li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b> -error while running the message handler. -</li> - -<li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> -error while running a <code>__gc</code> metamethod. -(This error typically has no relation with the function being called.) -</li> - -</ul> - - - - -<hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p> -<span class="apii">[-(nargs + 1), +(nresults|1), –]</span> -<pre>int lua_pcallk (lua_State *L, - int nargs, - int nresults, - int msgh, - lua_KContext ctx, - lua_KFunction k);</pre> - -<p> -This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>, -but allows the called function to yield (see <a href="#4.7">§4.7</a>). - - - - - -<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> -<span class="apii">[-n, +0, –]</span> -<pre>void lua_pop (lua_State *L, int n);</pre> - -<p> -Pops <code>n</code> elements from the stack. - - - - - -<hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushboolean (lua_State *L, int b);</pre> - -<p> -Pushes a boolean value with value <code>b</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> -<span class="apii">[-n, +1, <em>m</em>]</span> -<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> - -<p> -Pushes a new C closure onto the stack. - - -<p> -When a C function is created, -it is possible to associate some values with it, -thus creating a C closure (see <a href="#4.4">§4.4</a>); -these values are then accessible to the function whenever it is called. -To associate values with a C function, -first these values must 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 will be -associated with the function. -<a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. - - -<p> -The maximum value for <code>n</code> is 255. - - -<p> -When <code>n</code> is zero, -this function creates a <em>light C function</em>, -which is just a pointer to the C function. -In that case, it never raises a memory error. - - - - - -<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> - -<p> -Pushes a C function onto the stack. -This function receives a pointer to a C function -and pushes onto the stack a Lua value of type <code>function</code> that, -when called, invokes the corresponding C function. - - -<p> -Any function to be callable by Lua must -follow the correct protocol to receive its parameters -and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). - - - - - -<hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> - -<p> -Pushes onto the stack a formatted string -and returns a pointer to this string. -It is similar to the ISO 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 the character '<code>%</code>'), -'<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>%I</code>' (inserts a <a href="#lua_Integer"><code>lua_Integer</code></a>), -'<code>%p</code>' (inserts a pointer as a hexadecimal numeral), -'<code>%d</code>' (inserts an <code>int</code>), -'<code>%c</code>' (inserts an <code>int</code> as a one-byte character), and -'<code>%U</code>' (inserts a <code>long int</code> as a UTF-8 byte sequence). -</li> - -</ul> - -<p> -Unlike other push functions, -this function checks for the stack space it needs, -including the slot for its result. - - - - - -<hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushglobaltable (lua_State *L);</pre> - -<p> -Pushes the global environment onto the stack. - - - - - -<hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> - -<p> -Pushes an integer with value <code>n</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> - -<p> -Pushes a light userdata onto the stack. - - -<p> -Userdata represent C values in Lua. -A <em>light userdata</em> represents a pointer, a <code>void*</code>. -It is a value (like a number): -you do not create it, it has no individual metatable, -and it is not collected (as it was never created). -A light userdata is equal to "any" -light userdata with the same C address. - - - - - -<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre> - -<p> -This macro is equivalent to <a href="#lua_pushstring"><code>lua_pushstring</code></a>, -but should be used only when <code>s</code> is a literal string. - - - - - -<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *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 any binary data, -including embedded zeros. - - -<p> -Returns a pointer to the internal copy of the string. - - - - - -<hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushnil (lua_State *L);</pre> - -<p> -Pushes a nil value onto the stack. - - - - - -<hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> - -<p> -Pushes a float with value <code>n</code> onto the stack. - - - - - -<hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *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. - - -<p> -Returns a pointer to the internal copy of the string. - - -<p> -If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int lua_pushthread (lua_State *L);</pre> - -<p> -Pushes the thread represented by <code>L</code> onto the stack. -Returns 1 if this thread is the main thread of its state. - - - - - -<hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>void lua_pushvalue (lua_State *L, int index);</pre> - -<p> -Pushes a copy of the element at the given index -onto the stack. - - - - - -<hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *lua_pushvfstring (lua_State *L, - const char *fmt, - va_list argp);</pre> - -<p> -Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> -instead of a variable number of arguments. - - - - - -<hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> - -<p> -Returns 1 if the two values in indices <code>index1</code> and -<code>index2</code> are primitively equal -(that is, without calling the <code>__eq</code> metamethod). -Otherwise returns 0. -Also returns 0 if any of the indices are not valid. - - - - - -<hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> -<span class="apii">[-1, +1, –]</span> -<pre>int lua_rawget (lua_State *L, int index);</pre> - -<p> -Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access -(i.e., without metamethods). - - - - - -<hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int lua_rawgeti (lua_State *L, int index, lua_Integer n);</pre> - -<p> -Pushes onto the stack the value <code>t[n]</code>, -where <code>t</code> is the table at the given index. -The access is raw, -that is, it does not invoke the <code>__index</code> metamethod. - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int lua_rawgetp (lua_State *L, int index, const void *p);</pre> - -<p> -Pushes onto the stack the value <code>t[k]</code>, -where <code>t</code> is the table at the given index and -<code>k</code> is the pointer <code>p</code> represented as a light userdata. -The access is raw; -that is, it does not invoke the <code>__index</code> metamethod. - - -<p> -Returns the type of the pushed value. - - - - - -<hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>size_t lua_rawlen (lua_State *L, int index);</pre> - -<p> -Returns the raw "length" of the value at the given index: -for strings, this is the string length; -for tables, this is the result of the length operator ('<code>#</code>') -with no metamethods; -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_rawset"><code>lua_rawset</code></a></h3><p> -<span class="apii">[-2, +0, <em>m</em>]</span> -<pre>void lua_rawset (lua_State *L, int index);</pre> - -<p> -Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment -(i.e., without metamethods). - - - - - -<hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>void lua_rawseti (lua_State *L, int index, lua_Integer i);</pre> - -<p> -Does the equivalent of <code>t[i] = v</code>, -where <code>t</code> is the table at the given index -and <code>v</code> is the value at the top of the stack. - - -<p> -This function pops the value from the stack. -The assignment is raw, -that is, it does not invoke the <code>__newindex</code> metamethod. - - - - - -<hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre> - -<p> -Does the equivalent of <code>t[p] = v</code>, -where <code>t</code> is the table at the given index, -<code>p</code> is encoded as a light userdata, -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 <code>__newindex</code> metamethod. - - - - - -<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> -<pre>typedef const char * (*lua_Reader) (lua_State *L, - void *data, - size_t *size);</pre> - -<p> -The reader function used by <a href="#lua_load"><code>lua_load</code></a>. -Every time it needs another piece of the chunk, -<a href="#lua_load"><code>lua_load</code></a> calls the reader, -passing along its <code>data</code> parameter. -The reader must return a pointer to a block of memory -with a new piece of the chunk -and set <code>size</code> to the block size. -The block must exist until the reader function is called again. -To signal the end of the chunk, -the reader must return <code>NULL</code> or set <code>size</code> to zero. -The reader function may return pieces of any size greater than zero. - - - - - -<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre> - -<p> -Sets the C function <code>f</code> as the new value of global <code>name</code>. -It is defined as a macro: - -<pre> - #define lua_register(L,n,f) \ - (lua_pushcfunction(L, f), lua_setglobal(L, n)) -</pre> - - - - -<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> -<span class="apii">[-1, +0, –]</span> -<pre>void lua_remove (lua_State *L, int index);</pre> - -<p> -Removes the element at the given valid index, -shifting down the elements above this index to fill the gap. -This function cannot be called with a pseudo-index, -because a pseudo-index is not an actual stack position. - - - - - -<hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> -<span class="apii">[-1, +0, –]</span> -<pre>void lua_replace (lua_State *L, int index);</pre> - -<p> -Moves the top element into the given valid index -without shifting any element -(therefore replacing the value at that given index), -and then pops the top element. - - - - - -<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> -<span class="apii">[-?, +?, –]</span> -<pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre> - -<p> -Starts and resumes a coroutine in the given thread <code>L</code>. - - -<p> -To start a coroutine, -you push onto the thread stack the main function plus any arguments; -then you call <a href="#lua_resume"><code>lua_resume</code></a>, -with <code>nargs</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, -<a href="#pdf-LUA_OK"><code>LUA_OK</code></a> 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>). - - -<p> -In case of errors, -the stack is not unwound, -so you can use the debug API over it. -The error object is on the top of the stack. - - -<p> -To resume a coroutine, -you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>, -put on its stack only the values to -be passed as results from <code>yield</code>, -and then call <a href="#lua_resume"><code>lua_resume</code></a>. - - -<p> -The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>. -If there is no such coroutine, -this parameter can be <code>NULL</code>. - - - - - -<hr><h3><a name="lua_rotate"><code>lua_rotate</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void lua_rotate (lua_State *L, int idx, int n);</pre> - -<p> -Rotates the stack elements between the valid index <code>idx</code> -and the top of the stack. -The elements are rotated <code>n</code> positions in the direction of the top, -for a positive <code>n</code>, -or <code>-n</code> positions in the direction of the bottom, -for a negative <code>n</code>. -The absolute value of <code>n</code> must not be greater than the size -of the slice being rotated. -This function cannot be called with a pseudo-index, -because a pseudo-index is not an actual stack position. - - - - - -<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> - -<p> -Changes the allocator function of a given state to <code>f</code> -with user data <code>ud</code>. - - - - - -<hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> -<span class="apii">[-1, +0, <em>e</em>]</span> -<pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> - -<p> -Does the equivalent to <code>t[k] = v</code>, -where <code>t</code> is the value at the given index -and <code>v</code> is the value at the top of the stack. - - -<p> -This function pops the value from the stack. -As in Lua, this function may trigger a metamethod -for the "newindex" event (see <a href="#2.4">§2.4</a>). - - - - - -<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> -<span class="apii">[-1, +0, <em>e</em>]</span> -<pre>void lua_setglobal (lua_State *L, const char *name);</pre> - -<p> -Pops a value from the stack and -sets it as the new value of global <code>name</code>. - - - - - -<hr><h3><a name="lua_seti"><code>lua_seti</code></a></h3><p> -<span class="apii">[-1, +0, <em>e</em>]</span> -<pre>void lua_seti (lua_State *L, int index, lua_Integer n);</pre> - -<p> -Does the equivalent to <code>t[n] = v</code>, -where <code>t</code> is the value at the given index -and <code>v</code> is the value at the top of the stack. - - -<p> -This function pops the value from the stack. -As in Lua, this function may trigger a metamethod -for the "newindex" event (see <a href="#2.4">§2.4</a>). - - - - - -<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> -<span class="apii">[-1, +0, –]</span> -<pre>void 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 index. - - - - - -<hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> -<span class="apii">[-2, +0, <em>e</em>]</span> -<pre>void lua_settable (lua_State *L, int index);</pre> - -<p> -Does the equivalent to <code>t[k] = v</code>, -where <code>t</code> is the value at the given index, -<code>v</code> is the value at the top of the stack, -and <code>k</code> is the value just below the top. - - -<p> -This function pops both the key and the value from the stack. -As in Lua, this function may trigger a metamethod -for the "newindex" event (see <a href="#2.4">§2.4</a>). - - - - - -<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> -<span class="apii">[-?, +?, –]</span> -<pre>void lua_settop (lua_State *L, int index);</pre> - -<p> -Accepts any 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_setuservalue"><code>lua_setuservalue</code></a></h3><p> -<span class="apii">[-1, +0, –]</span> -<pre>void lua_setuservalue (lua_State *L, int index);</pre> - -<p> -Pops a value from the stack and sets it as -the new value associated to the userdata at the given index. - - - - - -<hr><h3><a name="lua_State"><code>lua_State</code></a></h3> -<pre>typedef struct lua_State lua_State;</pre> - -<p> -An opaque structure that points to a thread and indirectly -(through the thread) to the whole state of a Lua interpreter. -The Lua library is fully reentrant: -it has no global variables. -All information about a state is accessible through this structure. - - -<p> -A pointer to this structure must be passed as the first argument to -every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, -which creates a Lua state from scratch. - - - - - -<hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_status (lua_State *L);</pre> - -<p> -Returns the status of the thread <code>L</code>. - - -<p> -The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread, -an error code if the thread finished the execution -of a <a href="#lua_resume"><code>lua_resume</code></a> with an error, -or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. - - -<p> -You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>. -You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> -(to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> -(to resume a coroutine). - - - - - -<hr><h3><a name="lua_stringtonumber"><code>lua_stringtonumber</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>size_t lua_stringtonumber (lua_State *L, const char *s);</pre> - -<p> -Converts the zero-terminated string <code>s</code> to a number, -pushes that number into the stack, -and returns the total size of the string, -that is, its length plus one. -The conversion can result in an integer or a float, -according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). -The string may have leading and trailing spaces and a sign. -If the string is not a valid numeral, -returns 0 and pushes nothing. -(Note that the result can be used as a boolean, -true if the conversion succeeds.) - - - - - -<hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_toboolean (lua_State *L, int index);</pre> - -<p> -Converts the Lua value at the given index to a C boolean -value (0 or 1). -Like all tests in Lua, -<a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value -different from <b>false</b> and <b>nil</b>; -otherwise it returns false. -(If you want to accept only actual boolean values, -use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) - - - - - -<hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> - -<p> -Converts a value at the given index to a C function. -That value must be a C function; -otherwise, returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> - -<p> -Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre> - -<p> -Converts the Lua value at the given index -to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. -The Lua value must be an integer, -or a number or string convertible to an integer (see <a href="#3.4.3">§3.4.3</a>); -otherwise, <code>lua_tointegerx</code> returns 0. - - -<p> -If <code>isnum</code> is not <code>NULL</code>, -its referent is assigned a boolean value that -indicates whether the operation succeeded. - - - - - -<hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> - -<p> -Converts the Lua value at the given index to a C string. -If <code>len</code> is not <code>NULL</code>, -it 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 <code>lua_tolstring</code> 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 <code>lua_tolstring</code> is applied to keys during a table traversal.) - - -<p> -<code>lua_tolstring</code> returns a pointer -to a string inside the Lua state. -This string always has a zero ('<code>\0</code>') -after its last character (as in C), -but can contain other zeros in its body. - - -<p> -Because Lua has garbage collection, -there is no guarantee that the pointer returned by <code>lua_tolstring</code> -will be valid after the corresponding Lua value is removed from the stack. - - - - - -<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> - -<p> -Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre> - -<p> -Converts the Lua value at the given 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="#3.4.3">§3.4.3</a>); -otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0. - - -<p> -If <code>isnum</code> is not <code>NULL</code>, -its referent is assigned a boolean value that -indicates whether the operation succeeded. - - - - - -<hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>const void *lua_topointer (lua_State *L, int index);</pre> - -<p> -Converts the value at the given index to a generic -C pointer (<code>void*</code>). -The value can be a userdata, a table, a thread, or a function; -otherwise, <code>lua_topointer</code> 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 hashing and debug information. - - - - - -<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>const char *lua_tostring (lua_State *L, int index);</pre> - -<p> -Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_State *lua_tothread (lua_State *L, int index);</pre> - -<p> -Converts the value at the given index to a Lua thread -(represented as <code>lua_State*</code>). -This value must be a thread; -otherwise, the function returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void *lua_touserdata (lua_State *L, int index);</pre> - -<p> -If the value at the given index is a full userdata, -returns its block address. -If the value is a light userdata, -returns its pointer. -Otherwise, returns <code>NULL</code>. - - - - - -<hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_type (lua_State *L, int index);</pre> - -<p> -Returns the type of the value in the given valid index, -or <code>LUA_TNONE</code> for a non-valid (but acceptable) index. -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>: -<a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a> (0), -<a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>, -<a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>, -<a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, -<a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, -<a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, -<a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, -<a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>, -and -<a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>. - - - - - -<hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>const char *lua_typename (lua_State *L, int tp);</pre> - -<p> -Returns the name of the type encoded by the value <code>tp</code>, -which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. - - - - - -<hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3> -<pre>typedef ... lua_Unsigned;</pre> - -<p> -The unsigned version of <a href="#lua_Integer"><code>lua_Integer</code></a>. - - - - - -<hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_upvalueindex (int i);</pre> - -<p> -Returns the pseudo-index that represents the <code>i</code>-th upvalue of -the running function (see <a href="#4.4">§4.4</a>). - - - - - -<hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>const lua_Number *lua_version (lua_State *L);</pre> - -<p> -Returns the address of the version number -(a C static variable) -stored in the Lua core. -When called with a valid <a href="#lua_State"><code>lua_State</code></a>, -returns the address of the version used to create that state. -When called with <code>NULL</code>, -returns the address of the version running the call. - - - - - -<hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> -<pre>typedef int (*lua_Writer) (lua_State *L, - const void* p, - size_t sz, - void* ud);</pre> - -<p> -The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. -Every time it produces another piece of chunk, -<a href="#lua_dump"><code>lua_dump</code></a> calls the writer, -passing along the buffer to be written (<code>p</code>), -its size (<code>sz</code>), -and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. - - -<p> -The writer returns an error code: -0 means no errors; -any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from -calling the writer again. - - - - - -<hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> -<span class="apii">[-?, +?, –]</span> -<pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> - -<p> -Exchange values between different threads of the same state. - - -<p> -This function pops <code>n</code> values from the stack <code>from</code>, -and pushes them onto the stack <code>to</code>. - - - - - -<hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> -<span class="apii">[-?, +?, <em>e</em>]</span> -<pre>int lua_yield (lua_State *L, int nresults);</pre> - -<p> -This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>, -but it has no continuation (see <a href="#4.7">§4.7</a>). -Therefore, when the thread resumes, -it continues the function that called -the function calling <code>lua_yield</code>. - - - - - -<hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p> -<span class="apii">[-?, +?, <em>e</em>]</span> -<pre>int lua_yieldk (lua_State *L, - int nresults, - lua_KContext ctx, - lua_KFunction k);</pre> - -<p> -Yields a coroutine (thread). - - -<p> -When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a>, -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 will be passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. - - -<p> -When the coroutine is resumed again, -Lua calls the given continuation function <code>k</code> to continue -the execution of the C function that yielded (see <a href="#4.7">§4.7</a>). -This continuation function receives the same stack -from the previous function, -with the <code>n</code> results removed and -replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>. -Moreover, -the continuation function receives the value <code>ctx</code> -that was passed to <a href="#lua_yieldk"><code>lua_yieldk</code></a>. - - -<p> -Usually, this function does not return; -when the coroutine eventually resumes, -it continues executing the continuation function. -However, there is one special case, -which is when this function is called -from inside a line or a count hook (see <a href="#4.9">§4.9</a>). -In that case, <code>lua_yieldk</code> should be called with no continuation -(probably in the form of <a href="#lua_yield"><code>lua_yield</code></a>) and no results, -and the hook should return immediately after the call. -Lua will yield and, -when the coroutine resumes again, -it will continue the normal execution -of the (Lua) function that triggered the hook. - - -<p> -This function can raise an error if it is called from a thread -with a pending C call with no continuation function, -or it is called from a thread that is not running inside a resume -(e.g., the main thread). - - - - - - - -<h2>4.9 – <a name="4.9">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 linedefined; /* (S) */ - int lastlinedefined; /* (S) */ - unsigned char nups; /* (u) number of upvalues */ - unsigned char nparams; /* (u) number of parameters */ - char isvararg; /* (u) */ - char istailcall; /* (t) */ - 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 a function or an activation record. -<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> -the name of the chunk that created the function. -If <code>source</code> starts with a '<code>@</code>', -it means that the function was defined in a file where -the file name follows the '<code>@</code>'. -If <code>source</code> starts with a '<code>=</code>', -the remainder of its contents describe the source in a user-dependent manner. -Otherwise, -the function was defined in a string where -<code>source</code> is that string. -</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. -</li> - -<li><b><code>currentline</code>: </b> -the current line where the given function is executing. -When no line information is available, -<code>currentline</code> is set to -1. -</li> - -<li><b><code>name</code>: </b> -a reasonable name for the given function. -Because functions in Lua are first-class values, -they do not have a fixed name: -some functions can be the value of multiple global variables, -while others can be stored only in a table field. -The <code>lua_getinfo</code> function checks how the function was -called to find a suitable name. -If it cannot find a name, -then <code>name</code> is set to <code>NULL</code>. -</li> - -<li><b><code>namewhat</code>: </b> -explains the <code>name</code> field. -The value of <code>namewhat</code> can be -<code>"global"</code>, <code>"local"</code>, <code>"method"</code>, -<code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), -according to how the function was called. -(Lua uses the empty string when no other option seems to apply.) -</li> - -<li><b><code>istailcall</code>: </b> -true if this function invocation was called by a tail call. -In this case, the caller of this level is not in the stack. -</li> - -<li><b><code>nups</code>: </b> -the number of upvalues of the function. -</li> - -<li><b><code>nparams</code>: </b> -the number of fixed parameters of the function -(always 0 for C functions). -</li> - -<li><b><code>isvararg</code>: </b> -true if the function is a vararg function -(always true for C functions). -</li> - -</ul> - - - - -<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_Hook lua_gethook (lua_State *L);</pre> - -<p> -Returns the current hook function. - - - - - -<hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_gethookcount (lua_State *L);</pre> - -<p> -Returns the current hook count. - - - - - -<hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_gethookmask (lua_State *L);</pre> - -<p> -Returns the current hook mask. - - - - - -<hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> -<span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span> -<pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> - -<p> -Gets 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 from 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_getglobal(L, "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>t</code>': </b> fills in the field <code>istailcall</code>; -</li> - -<li><b>'<code>u</code>': </b> fills in the fields -<code>nups</code>, <code>nparams</code>, and <code>isvararg</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.) - - -<p> -If this option is given together with option '<code>f</code>', -its table is pushed after the function. -</li> - -</ul> - -<p> -This function returns 0 on error -(for instance, an invalid option in <code>what</code>). - - - - - -<hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> -<span class="apii">[-0, +(0|1), –]</span> -<pre>const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);</pre> - -<p> -Gets information about a local variable of -a given activation record or a given function. - - -<p> -In the first case, -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; -see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices -and names. - - -<p> -<a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack -and returns its name. - - -<p> -In the second case, <code>ar</code> must be <code>NULL</code> and the function -to be inspected must be at the top of the stack. -In this case, only parameters of Lua functions are visible -(as there is no information about what variables are active) -and no values are pushed onto the stack. - - -<p> -Returns <code>NULL</code> (and pushes nothing) -when the index is greater than -the number of active local variables. - - - - - -<hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> - -<p> -Gets 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> -(except for tail calls, which do not count on the stack). -When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; -when called with a level greater than the stack depth, -it returns 0. - - - - - -<hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> -<span class="apii">[-0, +(0|1), –]</span> -<pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> - -<p> -Gets information about the <code>n</code>-th upvalue -of the closure at index <code>funcindex</code>. -It pushes the upvalue's value onto the stack -and returns its name. -Returns <code>NULL</code> (and pushes nothing) -when the index <code>n</code> is greater than the number of upvalues. - - -<p> -For C functions, this function uses the empty string <code>""</code> -as a name for all upvalues. -(For Lua functions, -upvalues are the external local variables that the function uses, -and that are consequently included in its closure.) - - -<p> -Upvalues have no particular order, -as they are active through the whole function. -They are numbered in an arbitrary order. - - - - - -<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_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</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>. - - -<p> -For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>, -the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call; -in this case, there will be no corresponding return event. - - -<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. - - -<p> -Hook functions cannot have continuations, -that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>, -<a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>. - - -<p> -Hook functions can yield under the following conditions: -Only count and line events can yield; -to yield, a hook function must finish its execution -calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero -(that is, with no values). - - - - - -<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void 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. -There is no standard way to access the values -to be returned by the function. -</li> - -<li><b>The line hook: </b> is called when the interpreter is about to -start the execution of a new line of code, -or when it jumps back in the code (even to the same line). -(This event only happens while Lua is executing a Lua function.) -</li> - -<li><b>The count hook: </b> is called after the interpreter executes every -<code>count</code> instructions. -(This event only happens while Lua is executing a Lua function.) -</li> - -</ul> - -<p> -A hook is disabled by setting <code>mask</code> to zero. - - - - - -<hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> -<span class="apii">[-(0|1), +0, –]</span> -<pre>const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);</pre> - -<p> -Sets the value of a local variable of a given activation record. -It assigns the value at the top of the stack -to the variable and returns its name. -It also pops the value from the stack. - - -<p> -Returns <code>NULL</code> (and pops nothing) -when the index is greater than -the number of active local variables. - - -<p> -Parameters <code>ar</code> and <code>n</code> are as in function <a href="#lua_getlocal"><code>lua_getlocal</code></a>. - - - - - -<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> -<span class="apii">[-(0|1), +0, –]</span> -<pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> - -<p> -Sets the value of a closure's upvalue. -It assigns the value at the top of the stack -to the upvalue and returns its name. -It also pops the value from the stack. - - -<p> -Returns <code>NULL</code> (and pops nothing) -when the index <code>n</code> is greater than the number of upvalues. - - -<p> -Parameters <code>funcindex</code> and <code>n</code> are as in function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>. - - - - - -<hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre> - -<p> -Returns a unique identifier for the upvalue numbered <code>n</code> -from the closure at index <code>funcindex</code>. - - -<p> -These unique identifiers allow a program to check whether different -closures share upvalues. -Lua closures that share an upvalue -(that is, that access a same external local variable) -will return identical ids for those upvalue indices. - - -<p> -Parameters <code>funcindex</code> and <code>n</code> are as in function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>, -but <code>n</code> cannot be greater than the number of upvalues. - - - - - -<hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1, - int funcindex2, int n2);</pre> - -<p> -Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code> -refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>. - - - - - - - -<h1>5 – <a name="5">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 and types 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 that API. -Nevertheless, the use of the auxiliary library ensures -more consistency to your code. - - -<p> -Several functions in the auxiliary library use internally some -extra stack slots. -When a function in the auxiliary library uses less than five slots, -it does not check the stack size; -it simply assumes that there are enough slots. - - -<p> -Several functions in the auxiliary library are used to -check C function arguments. -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. - - -<p> -Functions called <code>luaL_check*</code> -always raise an error if the check is not satisfied. - - - -<h2>5.1 – <a name="5.1">Functions and Types</a></h2> - -<p> -Here we list all functions and types from the auxiliary library -in alphabetical order. - - - -<hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> - -<p> -Adds the byte <code>c</code> to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). - - - - - -<hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> - -<p> -Adds the string pointed to by <code>s</code> with length <code>l</code> to -the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -The string can contain embedded zeros. - - - - - -<hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> -<span class="apii">[-?, +?, –]</span> -<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> - -<p> -Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) -a string of length <code>n</code> previously copied to the -buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). - - - - - -<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> - -<p> -Adds the zero-terminated string pointed to by <code>s</code> -to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). - - - - - -<hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> -<span class="apii">[-1, +?, <em>m</em>]</span> -<pre>void luaL_addvalue (luaL_Buffer *B);</pre> - -<p> -Adds the value at the top of the stack -to the buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -Pops the value. - - -<p> -This is the only function on string buffers that can (and must) -be called with an extra element on the stack, -which is the value to be added to the buffer. - - - - - -<hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_argcheck (lua_State *L, - int cond, - int arg, - const char *extramsg);</pre> - -<p> -Checks whether <code>cond</code> is true. -If it is not, raises an error with a standard message (see <a href="#luaL_argerror"><code>luaL_argerror</code></a>). - - - - - -<hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre> - -<p> -Raises an error reporting a problem with argument <code>arg</code> -of the C function that called it, -using a standard message -that includes <code>extramsg</code> as a comment: - -<pre> - bad argument #<em>arg</em> to '<em>funcname</em>' (<em>extramsg</em>) -</pre><p> -This function never returns. - - - - - -<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 declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> - -<li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> - -<li> -Then add string pieces to the buffer calling any of -the <code>luaL_add*</code> functions. -</li> - -<li> -Finish by calling <code>luaL_pushresult(&b)</code>. -This call leaves the final string on the top of the stack. -</li> - -</ul> - -<p> -If you know beforehand the total size of the resulting string, -you can use the buffer like this: - -<ul> - -<li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> - -<li>Then initialize it and preallocate a space of -size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li> - -<li>Then copy the string into that space.</li> - -<li> -Finish by calling <code>luaL_pushresultsize(&b, sz)</code>, -where <code>sz</code> is the total size of the resulting string -copied into that space. -</li> - -</ul> - -<p> -During its normal operation, -a string buffer uses a variable number of stack slots. -So, while using a buffer, you cannot assume that you know where -the top of the stack is. -You can use the stack between successive calls to buffer operations -as long as that use is balanced; -that is, -when you call a buffer operation, -the stack is at the same level -it was immediately after the previous buffer operation. -(The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) -After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its -level when the buffer was initialized, -plus the final string on its top. - - - - - -<hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> - -<p> -Initializes a buffer <code>B</code>. -This function does not allocate any space; -the buffer must be declared as a variable -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). - - - - - -<hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre> - -<p> -Equivalent to the sequence -<a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>. - - - - - -<hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>e</em>]</span> -<pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> - -<p> -Calls a metamethod. - - -<p> -If the object at index <code>obj</code> has a metatable and this -metatable has a field <code>e</code>, -this function calls this field passing the object as its only argument. -In this case this function returns true and pushes onto the -stack the value returned by the call. -If there is no metatable or no metamethod, -this function returns false (without pushing any value on the stack). - - - - - -<hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checkany (lua_State *L, int arg);</pre> - -<p> -Checks whether the function has an argument -of any type (including <b>nil</b>) at position <code>arg</code>. - - - - - -<hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre> - -<p> -Checks whether the function argument <code>arg</code> is an integer -(or can be converted to an integer) -and returns this integer cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. - - - - - -<hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre> - -<p> -Checks whether the function argument <code>arg</code> is a string -and returns this string; -if <code>l</code> is not <code>NULL</code> fills <code>*l</code> -with the string's length. - - -<p> -This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, -so all conversions and caveats of that function apply here. - - - - - -<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre> - -<p> -Checks whether the function argument <code>arg</code> is a number -and returns this number. - - - - - -<hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_checkoption (lua_State *L, - int arg, - const char *def, - const char *const lst[]);</pre> - -<p> -Checks whether the function argument <code>arg</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>arg</code> or when this argument is <b>nil</b>. - - -<p> -This is a useful function for mapping strings to C enums. -(The usual convention in Lua libraries is -to use strings instead of numbers to select options.) - - - - - -<hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> - -<p> -Grows the stack size to <code>top + sz</code> elements, -raising an error if the stack cannot grow to that size. -<code>msg</code> is an additional text to go into the error message -(or <code>NULL</code> for no additional text). - - - - - -<hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_checkstring (lua_State *L, int arg);</pre> - -<p> -Checks whether the function argument <code>arg</code> is a string -and returns this string. - - -<p> -This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, -so all conversions and caveats of that function apply here. - - - - - -<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checktype (lua_State *L, int arg, int t);</pre> - -<p> -Checks whether the function argument <code>arg</code> has type <code>t</code>. -See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. - - - - - -<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre> - -<p> -Checks whether the function argument <code>arg</code> is a userdata -of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and -returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>). - - - - - -<hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>void luaL_checkversion (lua_State *L);</pre> - -<p> -Checks whether the core running the call, -the core that created the Lua state, -and the code making the call are all using the same version of Lua. -Also checks whether the core running the call -and the core that created the Lua state -are using the same address space. - - - - - -<hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> -<span class="apii">[-0, +?, <em>e</em>]</span> -<pre>int luaL_dofile (lua_State *L, const char *filename);</pre> - -<p> -Loads and runs the given file. -It is defined as the following macro: - -<pre> - (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) -</pre><p> -It returns false if there are no errors -or true in case of errors. - - - - - -<hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> -<span class="apii">[-0, +?, –]</span> -<pre>int luaL_dostring (lua_State *L, const char *str);</pre> - -<p> -Loads and runs the given string. -It is defined as the following macro: - -<pre> - (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) -</pre><p> -It returns false if there are no errors -or true in case of errors. - - - - - -<hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> - -<p> -Raises an error. -The error message format is given by <code>fmt</code> -plus any extra arguments, -following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. -It also adds at the beginning of the message the file name and -the line number where the error occurred, -if this information is available. - - -<p> -This function never returns, -but it is an idiom to use it in C functions -as <code>return luaL_error(<em>args</em>)</code>. - - - - - -<hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p> -<span class="apii">[-0, +3, <em>m</em>]</span> -<pre>int luaL_execresult (lua_State *L, int stat);</pre> - -<p> -This function produces the return values for -process-related functions in the standard library -(<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>). - - - - - -<hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p> -<span class="apii">[-0, +(1|3), <em>m</em>]</span> -<pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre> - -<p> -This function produces the return values for -file-related functions in the standard library -(<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.). - - - - - -<hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> -<span class="apii">[-0, +(0|1), <em>m</em>]</span> -<pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> - -<p> -Pushes onto the stack the field <code>e</code> from the metatable -of the object at index <code>obj</code> and returns the type of pushed value. -If the object does not have a metatable, -or if the metatable does not have this field, -pushes nothing and returns <code>LUA_TNIL</code>. - - - - - -<hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int 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>) -(<b>nil</b> if there is no metatable associated with that name). -Returns the type of the pushed value. - - - - - -<hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre> - -<p> -Ensures that the value <code>t[fname]</code>, -where <code>t</code> is the value at index <code>idx</code>, -is a table, -and pushes that table onto the stack. -Returns true if it finds a previous table there -and false if it creates a new table. - - - - - -<hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>const char *luaL_gsub (lua_State *L, - const char *s, - const char *p, - const char *r);</pre> - -<p> -Creates a copy of string <code>s</code> by replacing -any occurrence of the string <code>p</code> -with the string <code>r</code>. -Pushes the resulting string on the stack and returns it. - - - - - -<hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>lua_Integer luaL_len (lua_State *L, int index);</pre> - -<p> -Returns the "length" of the value at the given index -as a number; -it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>). -Raises an error if the result of the operation is not an integer. -(This case only can happen through metamethods.) - - - - - -<hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int luaL_loadbuffer (lua_State *L, - const char *buff, - size_t sz, - const char *name);</pre> - -<p> -Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int luaL_loadbufferx (lua_State *L, - const char *buff, - size_t sz, - const char *name, - const char *mode);</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. -The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. - - - - - -<hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> - -<p> -Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>. - - - - - -<hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_loadfilex (lua_State *L, const char *filename, - const char *mode);</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> -The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. - - -<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 or the file has a wrong mode. - - -<p> -As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; -it does not run it. - - - - - -<hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> -<span class="apii">[-0, +1, –]</span> -<pre>int luaL_loadstring (lua_State *L, const char *s);</pre> - -<p> -Loads a string as a Lua chunk. -This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in -the zero-terminated string <code>s</code>. - - -<p> -This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. - - -<p> -Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; -it does not run it. - - - - - -<hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void luaL_newlib (lua_State *L, const luaL_Reg l[]);</pre> - -<p> -Creates a new table and registers there -the functions in list <code>l</code>. - - -<p> -It is implemented as the following macro: - -<pre> - (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0)) -</pre><p> -The array <code>l</code> must be the actual array, -not a pointer to it. - - - - - -<hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre> - -<p> -Creates a new table with a size optimized -to store all entries in the array <code>l</code> -(but does not actually store them). -It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> -(see <a href="#luaL_newlib"><code>luaL_newlib</code></a>). - - -<p> -It is implemented as a macro. -The array <code>l</code> must be the actual array, -not a pointer to it. - - - - - -<hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> - -<p> -If the registry already has the key <code>tname</code>, -returns 0. -Otherwise, -creates a new table to be used as a metatable for userdata, -adds to this new table the pair <code>__name = tname</code>, -adds to the registry the pair <code>[tname] = new table</code>, -and returns 1. -(The entry <code>__name</code> is used by some error-reporting functions.) - - -<p> -In both cases pushes onto the stack the final value associated -with <code>tname</code> in the registry. - - - - - -<hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>lua_State *luaL_newstate (void);</pre> - -<p> -Creates a new Lua state. -It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an -allocator based on the standard C <code>realloc</code> function -and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints -an error message to the standard error output in case of fatal -errors. - - -<p> -Returns the new state, -or <code>NULL</code> if there is a memory allocation error. - - - - - -<hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>void luaL_openlibs (lua_State *L);</pre> - -<p> -Opens all standard Lua libraries into the given state. - - - - - -<hr><h3><a name="luaL_opt"><code>luaL_opt</code></a></h3><p> -<span class="apii">[-0, +0, <em>e</em>]</span> -<pre>T luaL_opt (L, func, arg, dflt);</pre> - -<p> -This macro is defined as follows: - -<pre> - (lua_isnoneornil(L,(arg)) ? (dflt) : func(L,(arg))) -</pre><p> -In words, if the argument <code>arg</code> is nil or absent, -the macro results in the default <code>dflt</code>. -Otherwise, it results in the result of calling <code>func</code> -with the state <code>L</code> and the argument index <code>arg</code> as -parameters. -Note that it evaluates the expression <code>dflt</code> only if needed. - - - - - -<hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Integer luaL_optinteger (lua_State *L, - int arg, - lua_Integer d);</pre> - -<p> -If the function argument <code>arg</code> is an integer -(or convertible to an integer), -returns this integer. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_optlstring (lua_State *L, - int arg, - const char *d, - size_t *l);</pre> - -<p> -If the function argument <code>arg</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 result's length. -If the result is <code>NULL</code> -(only possible when returning <code>d</code> and <code>d == NULL</code>), -its length is considered zero. - - - - - -<hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre> - -<p> -If the function argument <code>arg</code> is a number, -returns this number. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> -<span class="apii">[-0, +0, <em>v</em>]</span> -<pre>const char *luaL_optstring (lua_State *L, - int arg, - const char *d);</pre> - -<p> -If the function argument <code>arg</code> is a string, -returns this string. -If this argument is absent or is <b>nil</b>, -returns <code>d</code>. -Otherwise, raises an error. - - - - - -<hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> - -<p> -Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a> -with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>. - - - - - -<hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p> -<span class="apii">[-?, +?, <em>m</em>]</span> -<pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre> - -<p> -Returns an address to a space of size <code>sz</code> -where you can copy a string to be added to buffer <code>B</code> -(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). -After copying the string into this space you must call -<a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add -it to the buffer. - - - - - -<hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> -<span class="apii">[-?, +1, <em>m</em>]</span> -<pre>void luaL_pushresult (luaL_Buffer *B);</pre> - -<p> -Finishes the use of buffer <code>B</code> leaving the final string on -the top of the stack. - - - - - -<hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p> -<span class="apii">[-?, +1, <em>m</em>]</span> -<pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre> - -<p> -Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>. - - - - - -<hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> -<span class="apii">[-1, +0, <em>m</em>]</span> -<pre>int luaL_ref (lua_State *L, int t);</pre> - -<p> -Creates and returns a <em>reference</em>, -in the table at index <code>t</code>, -for the object at the top of the stack (and pops the object). - - -<p> -A reference is a unique integer key. -As long as you do not manually add integer keys into table <code>t</code>, -<a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. -You can retrieve an object referred by reference <code>r</code> -by calling <code>lua_rawgeti(L, t, r)</code>. -Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. - - -<p> -If the object at the top of the stack is <b>nil</b>, -<a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. -The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different -from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. - - - - - -<hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> -<pre>typedef struct luaL_Reg { - const char *name; - lua_CFunction func; -} luaL_Reg;</pre> - -<p> -Type for arrays of functions to be registered by -<a href="#luaL_setfuncs"><code>luaL_setfuncs</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 a sentinel entry -in which both <code>name</code> and <code>func</code> are <code>NULL</code>. - - - - - -<hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>void luaL_requiref (lua_State *L, const char *modname, - lua_CFunction openf, int glb);</pre> - -<p> -If <code>modname</code> is not already present in <a href="#pdf-package.loaded"><code>package.loaded</code></a>, -calls function <code>openf</code> with string <code>modname</code> as an argument -and sets the call result in <code>package.loaded[modname]</code>, -as if that function has been called through <a href="#pdf-require"><code>require</code></a>. - - -<p> -If <code>glb</code> is true, -also stores the module into global <code>modname</code>. - - -<p> -Leaves a copy of the module on the stack. - - - - - -<hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p> -<span class="apii">[-nup, +0, <em>m</em>]</span> -<pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre> - -<p> -Registers all functions in the array <code>l</code> -(see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack -(below optional upvalues, see next). - - -<p> -When <code>nup</code> is not zero, -all functions are created sharing <code>nup</code> upvalues, -which must be previously pushed on the stack -on top of the library table. -These values are popped from the stack after the registration. - - - - - -<hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre> - -<p> -Sets the metatable of the object at the top of the stack -as 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_Stream"><code>luaL_Stream</code></a></h3> -<pre>typedef struct luaL_Stream { - FILE *f; - lua_CFunction closef; -} luaL_Stream;</pre> - -<p> -The standard representation for file handles, -which is used by the standard I/O library. - - -<p> -A file handle is implemented as a full userdata, -with a metatable called <code>LUA_FILEHANDLE</code> -(where <code>LUA_FILEHANDLE</code> is a macro with the actual metatable's name). -The metatable is created by the I/O library -(see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). - - -<p> -This userdata must start with the structure <code>luaL_Stream</code>; -it can contain other data after this initial structure. -Field <code>f</code> points to the corresponding C stream -(or it can be <code>NULL</code> to indicate an incompletely created handle). -Field <code>closef</code> points to a Lua function -that will be called to close the stream -when the handle is closed or collected; -this function receives the file handle as its sole argument and -must return either <b>true</b> (in case of success) -or <b>nil</b> plus an error message (in case of error). -Once Lua calls this field, -it changes the field value to <code>NULL</code> -to signal that the handle is closed. - - - - - -<hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p> -<span class="apii">[-0, +0, <em>m</em>]</span> -<pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre> - -<p> -This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>, -except that, when the test fails, -it returns <code>NULL</code> instead of raising an error. - - - - - -<hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p> -<span class="apii">[-0, +1, <em>e</em>]</span> -<pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre> - -<p> -Converts any Lua value at the given index to a C string -in a reasonable format. -The resulting string is pushed onto the stack and also -returned by the function. -If <code>len</code> is not <code>NULL</code>, -the function also sets <code>*len</code> with the string length. - - -<p> -If the value has a metatable with a <code>__tostring</code> field, -then <code>luaL_tolstring</code> calls the corresponding metamethod -with the value as argument, -and uses the result of the call as its result. - - - - - -<hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg, - int level);</pre> - -<p> -Creates and pushes a traceback of the stack <code>L1</code>. -If <code>msg</code> is not <code>NULL</code> it is appended -at the beginning of the traceback. -The <code>level</code> parameter tells at which level -to start the traceback. - - - - - -<hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>const char *luaL_typename (lua_State *L, int index);</pre> - -<p> -Returns the name of the type of the value at the given index. - - - - - -<hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> -<span class="apii">[-0, +0, –]</span> -<pre>void luaL_unref (lua_State *L, int t, int ref);</pre> - -<p> -Releases reference <code>ref</code> from the table at index <code>t</code> -(see <a href="#luaL_ref"><code>luaL_ref</code></a>). -The entry is removed from the table, -so that the referred object can be collected. -The reference <code>ref</code> is also freed to be used again. - - -<p> -If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, -<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. - - - - - -<hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> -<span class="apii">[-0, +1, <em>m</em>]</span> -<pre>void luaL_where (lua_State *L, int lvl);</pre> - -<p> -Pushes onto the stack a string identifying the current position -of the control at level <code>lvl</code> in the call stack. -Typically this string has the following format: - -<pre> - <em>chunkname</em>:<em>currentline</em>: -</pre><p> -Level 0 is the running function, -level 1 is the function that called the running function, -etc. - - -<p> -This function is used to build a prefix for error messages. - - - - - - - -<h1>6 – <a name="6">Standard Libraries</a></h1> - -<p> -The standard Lua libraries provide useful functions -that are implemented directly through the C API. -Some of these functions provide essential services to the language -(e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); -others provide access to "outside" services (e.g., I/O); -and others could be implemented in Lua itself, -but are quite useful or have critical performance requirements that -deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>). - - -<p> -All libraries are implemented through the official C API -and are provided as separate C modules. -Currently, Lua has the following standard libraries: - -<ul> - -<li>basic library (<a href="#6.1">§6.1</a>);</li> - -<li>coroutine library (<a href="#6.2">§6.2</a>);</li> - -<li>package library (<a href="#6.3">§6.3</a>);</li> - -<li>string manipulation (<a href="#6.4">§6.4</a>);</li> - -<li>basic UTF-8 support (<a href="#6.5">§6.5</a>);</li> - -<li>table manipulation (<a href="#6.6">§6.6</a>);</li> - -<li>mathematical functions (<a href="#6.7">§6.7</a>) (sin, log, etc.);</li> - -<li>input and output (<a href="#6.8">§6.8</a>);</li> - -<li>operating system facilities (<a href="#6.9">§6.9</a>);</li> - -<li>debug facilities (<a href="#6.10">§6.10</a>).</li> - -</ul><p> -Except for the basic and the 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, -the host program can open them individually by using -<a href="#luaL_requiref"><code>luaL_requiref</code></a> to call -<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_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library), -<a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), -<a name="pdf-luaopen_utf8"><code>luaopen_utf8</code></a> (for the UTF8 library), -<a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), -<a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), -<a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), -<a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the operating system library), -and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). -These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>. - - - -<h2>6.1 – <a name="6.1">Basic Functions</a></h2> - -<p> -The basic library provides 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> - - -<p> -Calls <a href="#pdf-error"><code>error</code></a> if -the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); -otherwise, returns all its arguments. -In case of error, -<code>message</code> is the error object; -when absent, it defaults to "<code>assertion failed!</code>" - - - - -<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>"<code>collect</code>": </b> -performs a full garbage-collection cycle. -This is the default option. -</li> - -<li><b>"<code>stop</code>": </b> -stops automatic execution of the garbage collector. -The collector will run only when explicitly invoked, -until a call to restart it. -</li> - -<li><b>"<code>restart</code>": </b> -restarts automatic execution of the garbage collector. -</li> - -<li><b>"<code>count</code>": </b> -returns the total memory in use by Lua in Kbytes. -The value has a fractional part, -so that it multiplied by 1024 -gives the exact number of bytes in use by Lua -(except for overflows). -</li> - -<li><b>"<code>step</code>": </b> -performs a garbage-collection step. -The step "size" is controlled by <code>arg</code>. -With a zero value, -the collector will perform one basic (indivisible) step. -For non-zero values, -the collector will perform as if that amount of memory -(in KBytes) had been allocated by Lua. -Returns <b>true</b> if the step finished a collection cycle. -</li> - -<li><b>"<code>setpause</code>": </b> -sets <code>arg</code> as the new value for the <em>pause</em> of -the collector (see <a href="#2.5">§2.5</a>). -Returns the previous value for <em>pause</em>. -</li> - -<li><b>"<code>setstepmul</code>": </b> -sets <code>arg</code> as the new value for the <em>step multiplier</em> of -the collector (see <a href="#2.5">§2.5</a>). -Returns the previous value for <em>step</em>. -</li> - -<li><b>"<code>isrunning</code>": </b> -returns a boolean that tells whether the collector is running -(i.e., not stopped). -</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 object. -Function <code>error</code> never returns. - - -<p> -Usually, <code>error</code> adds some information about the error position -at the beginning of the message, if the message is a string. -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 (see <a href="#2.2">§2.2</a>). -Lua itself does not use this variable; -changing its value does not affect any environment, -nor vice versa. - - - - -<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 key–value pairs -(<code>1,t[1]</code>), (<code>2,t[2]</code>), ..., -up to the first nil value. - - - - -<p> -<hr><h3><a name="pdf-load"><code>load (chunk [, chunkname [, mode [, env]]])</code></a></h3> - - -<p> -Loads a chunk. - - -<p> -If <code>chunk</code> is a string, the chunk is this string. -If <code>chunk</code> is a function, -<code>load</code> calls it repeatedly to get the chunk pieces. -Each call to <code>chunk</code> must return a string that concatenates -with previous results. -A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. - - -<p> -If there are no syntactic errors, -returns the compiled chunk as a function; -otherwise, returns <b>nil</b> plus the error message. - - -<p> -If the resulting function has upvalues, -the first upvalue is set to the value of <code>env</code>, -if that parameter is given, -or to the value of the global environment. -Other upvalues are initialized with <b>nil</b>. -(When you load a main chunk, -the resulting function will always have exactly one upvalue, -the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). -However, -when you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>), -the resulting function can have an arbitrary number of upvalues.) -All upvalues are fresh, that is, -they are not shared with any other function. - - -<p> -<code>chunkname</code> is used as the name of the chunk for error messages -and debug information (see <a href="#4.9">§4.9</a>). -When absent, -it defaults to <code>chunk</code>, if <code>chunk</code> is a string, -or to "<code>=(load)</code>" otherwise. - - -<p> -The string <code>mode</code> controls whether the chunk can be text or binary -(that is, a precompiled chunk). -It may be the string "<code>b</code>" (only binary chunks), -"<code>t</code>" (only text chunks), -or "<code>bt</code>" (both binary and text). -The default is "<code>bt</code>". - - -<p> -Lua does not check the consistency of binary chunks. -Maliciously crafted binary chunks can crash -the interpreter. - - - - -<p> -<hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</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-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 numerical order, -use a numerical <b>for</b>.) - - -<p> -The behavior of <code>next</code> is undefined if, -during the traversal, -you assign any value to a non-existent field in the table. -You may however modify existing fields. -In particular, you may clear existing fields. - - - - -<p> -<hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> - - -<p> -If <code>t</code> has a metamethod <code>__pairs</code>, -calls it with <code>t</code> as argument and returns the first three -results from the call. - - -<p> -Otherwise, -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 each argument to a string. -<code>print</code> is not intended for formatted output, -but only as a quick way to show a value, -for instance for debugging. -For complete control over the output, -use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</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 the <code>__eq</code> 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 the <code>__index</code> metamethod. -<code>table</code> must be a table; -<code>index</code> may be any value. - - - - -<p> -<hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3> -Returns the length of the object <code>v</code>, -which must be a table or a string, -without invoking the <code>__len</code> metamethod. -Returns an integer. - - - - -<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 the <code>__newindex</code> metamethod. -<code>table</code> must be a table, -<code>index</code> any value different from <b>nil</b> and NaN, -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>; -a negative number indexes from the end (-1 is the last argument). -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-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> - - -<p> -Sets the metatable for the given table. -(To change the metatable of other types from Lua code, -you must use the debug library (<a href="#6.10">§6.10</a>).) -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> - - -<p> -When called with no <code>base</code>, -<code>tonumber</code> 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> -The conversion of strings can result in integers or floats, -according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). -(The string may have leading and trailing spaces and a sign.) - - -<p> -When called with <code>base</code>, -then <code>e</code> must be a string to be interpreted as -an integer numeral in that base. -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. -If the string <code>e</code> is not a valid numeral in the given base, -the function returns <b>nil</b>. - - - - -<p> -<hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3> -Receives a value of any type and -converts it to a string in a human-readable 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>v</code> has a <code>__tostring</code> field, -then <code>tostring</code> calls the corresponding value -with <code>v</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-_VERSION"><code>_VERSION</code></a></h3> - - -<p> -A global variable (not a function) that -holds a string containing the running Lua version. -The current value of this variable is "<code>Lua 5.3</code>". - - - - -<p> -<hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3> - - -<p> -This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, -except that it sets a new message handler <code>msgh</code>. - - - - - - - -<h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2> - -<p> -This library comprises the operations to manipulate coroutines, -which come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. -See <a href="#2.6">§2.6</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 function. -Returns this new coroutine, -an object with type <code>"thread"</code>. - - - - -<p> -<hr><h3><a name="pdf-coroutine.isyieldable"><code>coroutine.isyieldable ()</code></a></h3> - - -<p> -Returns true when the running coroutine can yield. - - -<p> -A running coroutine is yieldable if it is not the main thread and -it is not inside a non-yieldable C function. - - - - -<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> -(when the coroutine yields) or any values returned by the body function -(when 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 plus a boolean, -true when the running coroutine is the main one. - - - - -<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 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. -Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. - - - - - - - -<h2>6.3 – <a name="6.3">Modules</a></h2> - -<p> -The package library provides basic -facilities for loading modules in Lua. -It exports one function directly in the global environment: -<a href="#pdf-require"><code>require</code></a>. -Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. - - -<p> -<hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> - - -<p> -Loads the given module. -The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table -to determine whether <code>modname</code> is already loaded. -If it is, then <code>require</code> returns the value stored -at <code>package.loaded[modname]</code>. -Otherwise, it tries to find a <em>loader</em> for the module. - - -<p> -To find a loader, -<code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence. -By changing this sequence, -we can change how <code>require</code> looks for a module. -The following explanation is based on the default configuration -for <a href="#pdf-package.searchers"><code>package.searchers</code></a>. - - -<p> -First <code>require</code> queries <code>package.preload[modname]</code>. -If it has a value, -this value (which must be a function) is the loader. -Otherwise <code>require</code> searches for a Lua loader using the -path stored in <a href="#pdf-package.path"><code>package.path</code></a>. -If that also fails, it searches for a C loader using the -path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. -If that also fails, -it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>). - - -<p> -Once a loader is found, -<code>require</code> calls the loader with two arguments: -<code>modname</code> and an extra value dependent on how it got the loader. -(If the loader came from a file, -this extra value is the file name.) -If the loader returns any non-nil value, -<code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. -If the loader does not return a non-nil 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> raises an error. - - - - -<p> -<hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3> - - -<p> -A string describing some compile-time configurations for packages. -This string is a sequence of lines: - -<ul> - -<li>The first line is the directory separator string. -Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li> - -<li>The second line is the character that separates templates in a path. -Default is '<code>;</code>'.</li> - -<li>The third line is the string that marks the -substitution points in a template. -Default is '<code>?</code>'.</li> - -<li>The fourth line is a string that, in a path in Windows, -is replaced by the executable's directory. -Default is '<code>!</code>'.</li> - -<li>The fifth line is a mark to ignore all text after it -when building the <code>luaopen_</code> function name. -Default is '<code>-</code>'.</li> - -</ul> - - - -<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_5_3"><code>LUA_CPATH_5_3</code></a> -or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a> -or a default path defined in <code>luaconf.h</code>. - - - - -<p> -<hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> - - -<p> -A table used by <a href="#pdf-require"><code>require</code></a> to control which -modules are already loaded. -When you require a module <code>modname</code> and -<code>package.loaded[modname]</code> is not false, -<a href="#pdf-require"><code>require</code></a> simply returns the value stored there. - - -<p> -This variable is only a reference to the real table; -assignments to this variable do not change the -table used by <a href="#pdf-require"><code>require</code></a>. - - - - -<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>. - - -<p> -If <code>funcname</code> is "<code>*</code>", -then it only links with the library, -making the symbols exported by the library -available to other dynamically linked libraries. -Otherwise, -it looks for a function <code>funcname</code> inside the library -and returns this function as a C function. -So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype -(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 an 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 Standard 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_5_3"><code>LUA_PATH_5_3</code></a> or -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 those environment variables are not defined. -Any "<code>;;</code>" in the value of the environment variable -is replaced by the default path. - - - - -<p> -<hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> - - -<p> -A table to store loaders for specific modules -(see <a href="#pdf-require"><code>require</code></a>). - - -<p> -This variable is only a reference to the real table; -assignments to this variable do not change the -table used by <a href="#pdf-require"><code>require</code></a>. - - - - -<p> -<hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3> - - -<p> -A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. - - -<p> -Each entry in this table is a <em>searcher function</em>. -When looking for a module, -<a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, -with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its -sole parameter. -The function can return another function (the module <em>loader</em>) -plus an extra value that will be passed to that loader, -or a string explaining why it did not find that module -(or <b>nil</b> if it has nothing to say). - - -<p> -Lua initializes this table with four searcher functions. - - -<p> -The first searcher simply looks for a loader in the -<a href="#pdf-package.preload"><code>package.preload</code></a> table. - - -<p> -The second searcher looks for a loader as a Lua library, -using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. -The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. - - -<p> -The third searcher looks for a loader as a C library, -using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. -Again, -the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. -For instance, -if the C path is the string - -<pre> - "./?.so;./?.dll;/usr/local/?/init.so" -</pre><p> -the searcher for module <code>foo</code> -will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, -and <code>/usr/local/foo/init.so</code>, in that order. -Once it finds a C library, -this searcher first uses a dynamic link facility to link the -application with the library. -Then it tries to find a C function inside the library to -be used as the loader. -The name of this C function is the string "<code>luaopen_</code>" -concatenated with a copy of the module name where each dot -is replaced by an underscore. -Moreover, if the module name has a hyphen, -its suffix after (and including) the first hyphen is removed. -For instance, if the module name is <code>a.b.c-v2.1</code>, -the function name will be <code>luaopen_a_b_c</code>. - - -<p> -The fourth searcher tries an <em>all-in-one loader</em>. -It searches the C path for a library for -the root name of the given module. -For instance, when requiring <code>a.b.c</code>, -it will search for a C library for <code>a</code>. -If found, it looks into it for an open function for -the submodule; -in our example, that would be <code>luaopen_a_b_c</code>. -With this facility, a package can pack several C submodules -into one single library, -with each submodule keeping its original open function. - - -<p> -All searchers except the first one (preload) return as the extra value -the file name where the module was found, -as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. -The first searcher returns no extra value. - - - - -<p> -<hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3> - - -<p> -Searches for the given <code>name</code> in the given <code>path</code>. - - -<p> -A path is a string containing a sequence of -<em>templates</em> separated by semicolons. -For each template, -the function replaces each interrogation mark (if any) -in the template with a copy of <code>name</code> -wherein all occurrences of <code>sep</code> -(a dot, by default) -were replaced by <code>rep</code> -(the system's directory separator, by default), -and then tries to open the resulting file name. - - -<p> -For instance, if the path is the string - -<pre> - "./?.lua;./?.lc;/usr/local/?/init.lua" -</pre><p> -the search for the name <code>foo.a</code> -will try to open the files -<code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and -<code>/usr/local/foo/a/init.lua</code>, in that order. - - -<p> -Returns the resulting name of the first file that it can -open in read mode (after closing the file), -or <b>nil</b> plus an error message if none succeeds. -(This error message lists all file names it tried to open.) - - - - - - - -<h2>6.4 – <a name="6.4">String Manipulation</a></h2> - -<p> -This library provides generic functions for string manipulation, -such as finding and extracting substrings, and pattern matching. -When indexing a string in Lua, the first character is at position 1 -(not at 0, as in C). -Indices are allowed to be negative and are interpreted as indexing backwards, -from the end of the string. -Thus, the last character is at position -1, and so on. - - -<p> -The string library provides all its functions inside the table -<a name="pdf-string"><code>string</code></a>. -It also sets a metatable for strings -where the <code>__index</code> field points to the <code>string</code> table. -Therefore, you can use the string functions in object-oriented style. -For instance, <code>string.byte(s,i)</code> -can be written as <code>s:byte(i)</code>. - - -<p> -The string library assumes one-byte character encodings. - - -<p> -<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> -Returns the internal numeric 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>. -These indices are corrected -following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>. - - -<p> -Numeric 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 numeric code equal -to its corresponding argument. - - -<p> -Numeric codes are not necessarily portable across platforms. - - - - -<p> -<hr><h3><a name="pdf-string.dump"><code>string.dump (function [, strip])</code></a></h3> - - -<p> -Returns a string containing a binary representation -(a <em>binary chunk</em>) -of the given function, -so that a later <a href="#pdf-load"><code>load</code></a> on this string returns -a copy of the function (but with new upvalues). -If <code>strip</code> is a true value, -the binary representation may not include all debug information -about the function, -to save space. - - -<p> -Functions with upvalues have only their number of upvalues saved. -When (re)loaded, -those upvalues receive fresh instances containing <b>nil</b>. -(You can use the debug library to serialize -and reload the upvalues of a function -in a way adequate to your needs.) - - - - -<p> -<hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> - - -<p> -Looks for the first match of -<code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) 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 numeric argument <code>init</code> specifies -where to start the search; -its default value is 1 and can be negative. -A value of <b>true</b> as a fourth, optional argument <code>plain</code> -turns off the pattern matching facilities, -so the function does a plain "find substring" operation, -with no characters in <code>pattern</code> being considered magic. -Note that if <code>plain</code> is given, then <code>init</code> must be given as well. - - -<p> -If the pattern has captures, -then in a successful match -the captured values are also returned, -after the two indices. - - - - -<p> -<hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> - - -<p> -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 ISO C function <code>sprintf</code>. -The only differences are that the options/modifiers -<code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>, -and <code>p</code> are not supported -and that there is an extra option, <code>q</code>. - - -<p> -The <code>q</code> option formats a string between double quotes, -using escape sequences when necessary to ensure that -it can safely be read back by the Lua interpreter. -For instance, the call - -<pre> - string.format('%q', 'a string with "quotes" and \n new line') -</pre><p> -may produce the string: - -<pre> - "a string with \"quotes\" and \ - new line" -</pre> - -<p> -Options -<code>A</code>, <code>a</code>, <code>E</code>, <code>e</code>, <code>f</code>, -<code>G</code>, and <code>g</code> all expect a number as argument. -Options <code>c</code>, <code>d</code>, -<code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> -expect an integer. -When Lua is compiled with a C89 compiler, -options <code>A</code> and <code>a</code> (hexadecimal floats) -do not support any modifier (flags, width, length). - - -<p> -Option <code>s</code> expects a string; -if its argument is not a string, -it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>. -If the option has any modifier (flags, width, length), -the string argument should not contain embedded zeros. - - - - -<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> (see <a href="#6.4.1">§6.4.1</a>) -over the 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 -will iterate over all the words from string <code>s</code>, -printing one per line: - -<pre> - s = "hello world from Lua" - for w in string.gmatch(s, "%a+") do - print(w) - end -</pre><p> -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 caret '<code>^</code>' at the start of a pattern does not -work as an anchor, as this would prevent the iteration. - - - - -<p> -<hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> -Returns a copy of <code>s</code> -in which all (or the first <code>n</code>, if given) -occurrences of the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) have been -replaced by a replacement string specified by <code>repl</code>, -which can be a string, a table, or a function. -<code>gsub</code> also returns, as its second value, -the total number of matches that occurred. -The name <code>gsub</code> comes from <em>Global SUBstitution</em>. - - -<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>d</em></code>, -with <em>d</em> between 1 and 9, -stands for the value of the <em>d</em>-th captured substring. -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. - - -<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. - - -<p> -In any case, -if the pattern specifies no captures, -then it behaves as if the whole pattern was inside a capture. - - -<p> -If the value returned by the table query or by the function call -is a string or a number, -then it is used as the replacement string; -otherwise, if it is <b>false</b> or <b>nil</b>, -then there is no replacement -(that is, the original match is kept in the string). - - -<p> -Here are some examples: - -<pre> - x = string.gsub("hello world", "(%w+)", "%1 %1") - --> x="hello hello world world" - - x = string.gsub("hello world", "%w+", "%0 %0", 1) - --> x="hello hello world" - - x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1") - --> x="world hello Lua from" - - x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv) - --> x="home = /home/roberto, user = roberto" - - x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s) - return load(s)() - end) - --> x="4+5 = 9" - - local t = {name="lua", version="5.3"} - x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) - --> x="lua-5.3.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> (see <a href="#6.4.1">§6.4.1</a>) 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 numeric argument <code>init</code> specifies -where to start the search; -its default value is 1 and can be negative. - - - - -<p> -<hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, ···)</code></a></h3> - - -<p> -Returns a binary string containing the values <code>v1</code>, <code>v2</code>, etc. -packed (that is, serialized in binary form) -according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). - - - - -<p> -<hr><h3><a name="pdf-string.packsize"><code>string.packsize (fmt)</code></a></h3> - - -<p> -Returns the size of a string resulting from <a href="#pdf-string.pack"><code>string.pack</code></a> -with the given format. -The format string cannot have the variable-length options -'<code>s</code>' or '<code>z</code>' (see <a href="#6.4.2">§6.4.2</a>). - - - - -<p> -<hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3> -Returns a string that is the concatenation of <code>n</code> copies of -the string <code>s</code> separated by the string <code>sep</code>. -The default value for <code>sep</code> is the empty string -(that is, no separator). -Returns the empty string if <code>n</code> is not positive. - - -<p> -(Note that it is very easy to exhaust the memory of your machine -with a single call to this function.) - - - - -<p> -<hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> -Returns a string that is the string <code>s</code> reversed. - - - - -<p> -<hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> -Returns the substring of <code>s</code> that -starts at <code>i</code> and continues until <code>j</code>; -<code>i</code> and <code>j</code> can be negative. -If <code>j</code> is absent, then it is assumed to be equal to -1 -(which is the same as the string length). -In particular, -the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> -with length <code>j</code>, -and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code> -with length <code>i</code>. - - -<p> -If, after the translation of negative indices, -<code>i</code> is less than 1, -it is corrected to 1. -If <code>j</code> is greater than the string length, -it is corrected to that length. -If, after these corrections, -<code>i</code> is greater than <code>j</code>, -the function returns the empty string. - - - - -<p> -<hr><h3><a name="pdf-string.unpack"><code>string.unpack (fmt, s [, pos])</code></a></h3> - - -<p> -Returns the values packed in string <code>s</code> (see <a href="#pdf-string.pack"><code>string.pack</code></a>) -according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). -An optional <code>pos</code> marks where -to start reading in <code>s</code> (default is 1). -After the read values, -this function also returns the index of the first unread byte in <code>s</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>6.4.1 – <a name="6.4.1">Patterns</a></h3> - -<p> -Patterns in Lua are described by regular strings, -which are interpreted as patterns by the pattern-matching functions -<a href="#pdf-string.find"><code>string.find</code></a>, -<a href="#pdf-string.gmatch"><code>string.gmatch</code></a>, -<a href="#pdf-string.gsub"><code>string.gsub</code></a>, -and <a href="#pdf-string.match"><code>string.match</code></a>. -This section describes the syntax and the meaning -(that is, what they match) of these strings. - - - -<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>%g</code>: </b> represents all printable characters except space.</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>%<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 non-alphanumeric character -(including all punctuation characters, even the non-magical) -can be preceded by a '<code>%</code>' -when used to represent itself in a pattern. -</li> - -<li><b><code>[<em>set</em>]</code>: </b> -represents the class which is the union of all -characters in <em>set</em>. -A range of characters can be specified by -separating the end characters of the range, -in ascending order, with a '<code>-</code>'. -All classes <code>%</code><em>x</em> described above can also be used as -components in <em>set</em>. -All other characters in <em>set</em> represent themselves. -For example, <code>[%w_]</code> (or <code>[_%w]</code>) -represents all alphanumeric characters plus the underscore, -<code>[0-7]</code> represents the octal digits, -and <code>[0-7%l%-]</code> represents the octal digits plus -the lowercase letters plus the '<code>-</code>' character. - - -<p> -You can put a closing square bracket in a set -by positioning it as the first character in the set. -You can put an hyphen in a set -by positioning it as the first or the last character in the set. -(You can also use an escape for both cases.) - - -<p> -The interaction between ranges and classes is not defined. -Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> -have no meaning. -</li> - -<li><b><code>[^<em>set</em>]</code>: </b> -represents the complement of <em>set</em>, -where <em>set</em> is interpreted as above. -</li> - -</ul><p> -For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), -the corresponding uppercase letter represents the complement of the class. -For instance, <code>%S</code> represents all non-space characters. - - -<p> -The definitions of letter, space, and other character groups -depend on the current locale. -In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. - - - - - -<h4>Pattern Item:</h4><p> -A <em>pattern item</em> can be - -<ul> - -<li> -a single character class, -which matches any single character in the class; -</li> - -<li> -a single character class followed by '<code>*</code>', -which matches zero 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 one 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 zero or more repetitions of characters in the class. -Unlike '<code>*</code>', -these repetition items will always match the shortest possible sequence; -</li> - -<li> -a single character class followed by '<code>?</code>', -which matches zero or one occurrence of a character in the class. -It always matches one occurrence if possible; -</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> - -<li> -<code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>; -such item matches an empty string at any position such that -the next character belongs to <em>set</em> -and the previous character does not belong to <em>set</em>. -The set <em>set</em> is interpreted as previously described. -The beginning and the end of the subject are handled as if -they were the character '<code>\0</code>'. -</li> - -</ul> - - - - -<h4>Pattern:</h4><p> -A <em>pattern</em> is a sequence of pattern items. -A caret '<code>^</code>' at the beginning of a pattern anchors the match at the -beginning of the subject string. -A '<code>$</code>' at the end of a pattern anchors the match at the -end of the subject string. -At other positions, -'<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. - - - - - -<h4>Captures:</h4><p> -A pattern can contain sub-patterns enclosed in parentheses; -they describe <em>captures</em>. -When a match succeeds, the substrings of the subject string -that match captures are stored (<em>captured</em>) for future use. -Captures are numbered according to their left parentheses. -For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, -the part of the string matching <code>"a*(.)%w(%s*)"</code> is -stored as the first capture (and therefore has number 1); -the character matching "<code>.</code>" is captured with number 2, -and the part matching "<code>%s*</code>" has number 3. - - -<p> -As a special case, the empty capture <code>()</code> captures -the current string position (a number). -For instance, if we apply the pattern <code>"()aa()"</code> on the -string <code>"flaaap"</code>, there will be two captures: 3 and 5. - - - - - - - -<h3>6.4.2 – <a name="6.4.2">Format Strings for Pack and Unpack</a></h3> - -<p> -The first argument to <a href="#pdf-string.pack"><code>string.pack</code></a>, -<a href="#pdf-string.packsize"><code>string.packsize</code></a>, and <a href="#pdf-string.unpack"><code>string.unpack</code></a> -is a format string, -which describes the layout of the structure being created or read. - - -<p> -A format string is a sequence of conversion options. -The conversion options are as follows: - -<ul> -<li><b><code><</code>: </b>sets little endian</li> -<li><b><code>></code>: </b>sets big endian</li> -<li><b><code>=</code>: </b>sets native endian</li> -<li><b><code>![<em>n</em>]</code>: </b>sets maximum alignment to <code>n</code> -(default is native alignment)</li> -<li><b><code>b</code>: </b>a signed byte (<code>char</code>)</li> -<li><b><code>B</code>: </b>an unsigned byte (<code>char</code>)</li> -<li><b><code>h</code>: </b>a signed <code>short</code> (native size)</li> -<li><b><code>H</code>: </b>an unsigned <code>short</code> (native size)</li> -<li><b><code>l</code>: </b>a signed <code>long</code> (native size)</li> -<li><b><code>L</code>: </b>an unsigned <code>long</code> (native size)</li> -<li><b><code>j</code>: </b>a <code>lua_Integer</code></li> -<li><b><code>J</code>: </b>a <code>lua_Unsigned</code></li> -<li><b><code>T</code>: </b>a <code>size_t</code> (native size)</li> -<li><b><code>i[<em>n</em>]</code>: </b>a signed <code>int</code> with <code>n</code> bytes -(default is native size)</li> -<li><b><code>I[<em>n</em>]</code>: </b>an unsigned <code>int</code> with <code>n</code> bytes -(default is native size)</li> -<li><b><code>f</code>: </b>a <code>float</code> (native size)</li> -<li><b><code>d</code>: </b>a <code>double</code> (native size)</li> -<li><b><code>n</code>: </b>a <code>lua_Number</code></li> -<li><b><code>c<em>n</em></code>: </b>a fixed-sized string with <code>n</code> bytes</li> -<li><b><code>z</code>: </b>a zero-terminated string</li> -<li><b><code>s[<em>n</em>]</code>: </b>a string preceded by its length -coded as an unsigned integer with <code>n</code> bytes -(default is a <code>size_t</code>)</li> -<li><b><code>x</code>: </b>one byte of padding</li> -<li><b><code>X<em>op</em></code>: </b>an empty item that aligns -according to option <code>op</code> -(which is otherwise ignored)</li> -<li><b>'<code> </code>': </b>(empty space) ignored</li> -</ul><p> -(A "<code>[<em>n</em>]</code>" means an optional integral numeral.) -Except for padding, spaces, and configurations -(options "<code>xX <=>!</code>"), -each option corresponds to an argument (in <a href="#pdf-string.pack"><code>string.pack</code></a>) -or a result (in <a href="#pdf-string.unpack"><code>string.unpack</code></a>). - - -<p> -For options "<code>!<em>n</em></code>", "<code>s<em>n</em></code>", "<code>i<em>n</em></code>", and "<code>I<em>n</em></code>", -<code>n</code> can be any integer between 1 and 16. -All integral options check overflows; -<a href="#pdf-string.pack"><code>string.pack</code></a> checks whether the given value fits in the given size; -<a href="#pdf-string.unpack"><code>string.unpack</code></a> checks whether the read value fits in a Lua integer. - - -<p> -Any format string starts as if prefixed by "<code>!1=</code>", -that is, -with maximum alignment of 1 (no alignment) -and native endianness. - - -<p> -Alignment works as follows: -For each option, -the format gets extra padding until the data starts -at an offset that is a multiple of the minimum between the -option size and the maximum alignment; -this minimum must be a power of 2. -Options "<code>c</code>" and "<code>z</code>" are not aligned; -option "<code>s</code>" follows the alignment of its starting integer. - - -<p> -All padding is filled with zeros by <a href="#pdf-string.pack"><code>string.pack</code></a> -(and ignored by <a href="#pdf-string.unpack"><code>string.unpack</code></a>). - - - - - - - -<h2>6.5 – <a name="6.5">UTF-8 Support</a></h2> - -<p> -This library provides basic support for UTF-8 encoding. -It provides all its functions inside the table <a name="pdf-utf8"><code>utf8</code></a>. -This library does not provide any support for Unicode other -than the handling of the encoding. -Any operation that needs the meaning of a character, -such as character classification, is outside its scope. - - -<p> -Unless stated otherwise, -all functions that expect a byte position as a parameter -assume that the given position is either the start of a byte sequence -or one plus the length of the subject string. -As in the string library, -negative indices count from the end of the string. - - -<p> -<hr><h3><a name="pdf-utf8.char"><code>utf8.char (···)</code></a></h3> -Receives zero or more integers, -converts each one to its corresponding UTF-8 byte sequence -and returns a string with the concatenation of all these sequences. - - - - -<p> -<hr><h3><a name="pdf-utf8.charpattern"><code>utf8.charpattern</code></a></h3> -The pattern (a string, not a function) "<code>[\0-\x7F\xC2-\xF4][\x80-\xBF]*</code>" -(see <a href="#6.4.1">§6.4.1</a>), -which matches exactly one UTF-8 byte sequence, -assuming that the subject is a valid UTF-8 string. - - - - -<p> -<hr><h3><a name="pdf-utf8.codes"><code>utf8.codes (s)</code></a></h3> - - -<p> -Returns values so that the construction - -<pre> - for p, c in utf8.codes(s) do <em>body</em> end -</pre><p> -will iterate over all characters in string <code>s</code>, -with <code>p</code> being the position (in bytes) and <code>c</code> the code point -of each character. -It raises an error if it meets any invalid byte sequence. - - - - -<p> -<hr><h3><a name="pdf-utf8.codepoint"><code>utf8.codepoint (s [, i [, j]])</code></a></h3> -Returns the codepoints (as integers) from all characters in <code>s</code> -that start between byte position <code>i</code> and <code>j</code> (both included). -The default for <code>i</code> is 1 and for <code>j</code> is <code>i</code>. -It raises an error if it meets any invalid byte sequence. - - - - -<p> -<hr><h3><a name="pdf-utf8.len"><code>utf8.len (s [, i [, j]])</code></a></h3> -Returns the number of UTF-8 characters in string <code>s</code> -that start between positions <code>i</code> and <code>j</code> (both inclusive). -The default for <code>i</code> is 1 and for <code>j</code> is -1. -If it finds any invalid byte sequence, -returns a false value plus the position of the first invalid byte. - - - - -<p> -<hr><h3><a name="pdf-utf8.offset"><code>utf8.offset (s, n [, i])</code></a></h3> -Returns the position (in bytes) where the encoding of the -<code>n</code>-th character of <code>s</code> -(counting from position <code>i</code>) starts. -A negative <code>n</code> gets characters before position <code>i</code>. -The default for <code>i</code> is 1 when <code>n</code> is non-negative -and <code>#s + 1</code> otherwise, -so that <code>utf8.offset(s, -n)</code> gets the offset of the -<code>n</code>-th character from the end of the string. -If the specified character is neither in the subject -nor right after its end, -the function returns <b>nil</b>. - - -<p> -As a special case, -when <code>n</code> is 0 the function returns the start of the encoding -of the character that contains the <code>i</code>-th byte of <code>s</code>. - - -<p> -This function assumes that <code>s</code> is a valid UTF-8 string. - - - - - - - -<h2>6.6 – <a name="6.6">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> -Remember that, whenever an operation needs the length of a table, -the table must be a proper sequence -or have a <code>__len</code> metamethod (see <a href="#3.4.7">§3.4.7</a>). -All functions ignore non-numeric keys -in the tables given as arguments. - - -<p> -<hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3> - - -<p> -Given a list where all elements are strings or numbers, -returns the string <code>list[i]..sep..list[i+1] ··· sep..list[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 <code>#list</code>. -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 (list, [pos,] value)</code></a></h3> - - -<p> -Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>, -shifting up the elements -<code>list[pos], list[pos+1], ···, list[#list]</code>. -The default value for <code>pos</code> is <code>#list+1</code>, -so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end -of list <code>t</code>. - - - - -<p> -<hr><h3><a name="pdf-table.move"><code>table.move (a1, f, e, t [,a2])</code></a></h3> - - -<p> -Moves elements from table <code>a1</code> to table <code>a2</code>, -performing the equivalent to the following -multiple assignment: -<code>a2[t],··· = a1[f],···,a1[e]</code>. -The default for <code>a2</code> is <code>a1</code>. -The destination range can overlap with the source range. -The number of elements to be moved must fit in a Lua integer. - - -<p> -Returns the destination table <code>a2</code>. - - - - -<p> -<hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3> - - -<p> -Returns a new table with all parameters stored into keys 1, 2, etc. -and with a field "<code>n</code>" with the total number of parameters. -Note that the resulting table may not be a sequence. - - - - -<p> -<hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3> - - -<p> -Removes from <code>list</code> the element at position <code>pos</code>, -returning the value of the removed element. -When <code>pos</code> is an integer between 1 and <code>#list</code>, -it shifts down the elements -<code>list[pos+1], list[pos+2], ···, list[#list]</code> -and erases element <code>list[#list]</code>; -The index <code>pos</code> can also be 0 when <code>#list</code> is 0, -or <code>#list + 1</code>; -in those cases, the function erases the element <code>list[pos]</code>. - - -<p> -The default value for <code>pos</code> is <code>#list</code>, -so that a call <code>table.remove(l)</code> removes the last element -of list <code>l</code>. - - - - -<p> -<hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3> - - -<p> -Sorts list elements in a given order, <em>in-place</em>, -from <code>list[1]</code> to <code>list[#list]</code>. -If <code>comp</code> is given, -then it must be a function that receives two list elements -and returns true when the first element must come -before the second in the final order -(so that, after the sort, -<code>i < j</code> implies <code>not comp(list[j],list[i])</code>). -If <code>comp</code> is not given, -then the standard Lua operator <code><</code> is used instead. - - -<p> -Note that the <code>comp</code> function must define -a strict partial order over the elements in the list; -that is, it must be asymmetric and transitive. -Otherwise, no valid sort may be possible. - - -<p> -The sort algorithm is not stable; -that is, elements not comparable by the given order -(e.g., equal elements) -may have their relative positions changed by the sort. - - - - -<p> -<hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3> - - -<p> -Returns the elements from the given list. -This function is equivalent to - -<pre> - return list[i], list[i+1], ···, list[j] -</pre><p> -By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>. - - - - - - - -<h2>6.7 – <a name="6.7">Mathematical Functions</a></h2> - -<p> -This library provides basic mathematical functions. -It provides all its functions and constants inside the table <a name="pdf-math"><code>math</code></a>. -Functions with the annotation "<code>integer/float</code>" give -integer results for integer arguments -and float results for float (or mixed) arguments. -Rounding functions -(<a href="#pdf-math.ceil"><code>math.ceil</code></a>, <a href="#pdf-math.floor"><code>math.floor</code></a>, and <a href="#pdf-math.modf"><code>math.modf</code></a>) -return an integer when the result fits in the range of an integer, -or a float otherwise. - - -<p> -<hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> - - -<p> -Returns the absolute value of <code>x</code>. (integer/float) - - - - -<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 (y [, x])</code></a></h3> - - -<p> - -Returns the arc tangent of <code>y/x</code> (in radians), -but uses the signs of both parameters to find the -quadrant of the result. -(It also handles correctly the case of <code>x</code> being zero.) - - -<p> -The default value for <code>x</code> is 1, -so that the call <code>math.atan(y)</code> -returns the arc tangent of <code>y</code>. - - - - -<p> -<hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> - - -<p> -Returns the smallest integral value 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.deg"><code>math.deg (x)</code></a></h3> - - -<p> -Converts the angle <code>x</code> from radians to degrees. - - - - -<p> -<hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> - - -<p> -Returns the value <em>e<sup>x</sup></em> -(where <code>e</code> is the base of natural logarithms). - - - - -<p> -<hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> - - -<p> -Returns the largest integral value smaller than or equal to <code>x</code>. - - - - -<p> -<hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> - - -<p> -Returns the remainder of the division of <code>x</code> by <code>y</code> -that rounds the quotient towards zero. (integer/float) - - - - -<p> -<hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> - - -<p> -The float value <code>HUGE_VAL</code>, -a value larger than any other numeric value. - - - - -<p> -<hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3> - - -<p> -Returns the logarithm of <code>x</code> in the given base. -The default for <code>base</code> is <em>e</em> -(so that the function returns the natural logarithm of <code>x</code>). - - - - -<p> -<hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> - - -<p> -Returns the argument with the maximum value, -according to the Lua operator <code><</code>. (integer/float) - - - - -<p> -<hr><h3><a name="pdf-math.maxinteger"><code>math.maxinteger</code></a></h3> -An integer with the maximum value for an integer. - - - - -<p> -<hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> - - -<p> -Returns the argument with the minimum value, -according to the Lua operator <code><</code>. (integer/float) - - - - -<p> -<hr><h3><a name="pdf-math.mininteger"><code>math.mininteger</code></a></h3> -An integer with the minimum value for an integer. - - - - -<p> -<hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> - - -<p> -Returns the integral part of <code>x</code> and the fractional part of <code>x</code>. -Its second result is always a float. - - - - -<p> -<hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> - - -<p> -The value of <em>π</em>. - - - - -<p> -<hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> - - -<p> -Converts the angle <code>x</code> from degrees to radians. - - - - -<p> -<hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> - - -<p> -When called without arguments, -returns a pseudo-random float with uniform distribution -in the range <em>[0,1)</em>. -When called with two integers <code>m</code> and <code>n</code>, -<code>math.random</code> returns a pseudo-random integer -with uniform distribution in the range <em>[m, n]</em>. -(The value <em>n-m</em> cannot be negative and must fit in a Lua integer.) -The call <code>math.random(n)</code> is equivalent to <code>math.random(1,n)</code>. - - -<p> -This function is an interface to the underling -pseudo-random generator function provided by C. - - - - -<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.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.tointeger"><code>math.tointeger (x)</code></a></h3> - - -<p> -If the value <code>x</code> is convertible to an integer, -returns that integer. -Otherwise, returns <b>nil</b>. - - - - -<p> -<hr><h3><a name="pdf-math.type"><code>math.type (x)</code></a></h3> - - -<p> -Returns "<code>integer</code>" if <code>x</code> is an integer, -"<code>float</code>" if it is a float, -or <b>nil</b> if <code>x</code> is not a number. - - - - -<p> -<hr><h3><a name="pdf-math.ult"><code>math.ult (m, n)</code></a></h3> - - -<p> -Returns a boolean, -true if integer <code>m</code> is below integer <code>n</code> when -they are compared as unsigned integers. - - - - - - - -<h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2> - -<p> -The I/O library provides two different styles for file manipulation. -The first one uses implicit file handles; -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 handles. - - -<p> -When using implicit file handles, -all operations are supplied by table <a name="pdf-io"><code>io</code></a>. -When using explicit file handles, -the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file handle -and then all operations are supplied as methods of the file handle. - - -<p> -The table <code>io</code> also provides -three predefined file handles with their usual meanings from C: -<a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. -The I/O library never closes these files. - - -<p> -Unless otherwise stated, -all I/O functions return <b>nil</b> on failure -(plus an error message as a second result and -a system-dependent error code as a third result) -and some value different from <b>nil</b> on success. -On non-POSIX systems, -the computation of the error message and error code -in case of errors -may be not thread safe, -because they rely on the global C variable <code>errno</code>. - - -<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>io.output():flush()</code>. - - - - -<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 -works like <code>file:lines(···)</code> over the opened file. -When the iterator function detects the end of file, -it returns no values (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("*l")</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> -In case of errors this function raises the error, -instead of returning an error code. - - - - -<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>. -In case of success, -it returns a new file handle. - - -<p> -The <code>mode</code> string can be any of the following: - -<ul> -<li><b>"<code>r</code>": </b> read mode (the default);</li> -<li><b>"<code>w</code>": </b> write mode;</li> -<li><b>"<code>a</code>": </b> append mode;</li> -<li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li> -<li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li> -<li><b>"<code>a+</code>": </b> append update mode, previous data is preserved, - writing is only allowed at the end of file.</li> -</ul><p> -The <code>mode</code> string can also have a '<code>b</code>' at the end, -which is needed in some systems to open the file in binary mode. - - - - -<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> -This function is system dependent and is not available -on all platforms. - - -<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> -<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> -In case of success, -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> -When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>, -<a href="#pdf-file:close"><code>file:close</code></a> returns the same values -returned by <a href="#pdf-os.execute"><code>os.execute</code></a>. - - - - -<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, -reads the file according to the given formats. -When no format is given, -uses "<code>l</code>" as a default. -As an example, the construction - -<pre> - for c in file:lines(1) do <em>body</em> end -</pre><p> -will iterate over all characters of the file, -starting at the current position. -Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file -when the loop ends. - - -<p> -In case of errors this function raises the error, -instead of returning an error code. - - - - -<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. -(In this latter case, -the function does not read subsequent formats.) -When called without formats, -it uses a default format that reads the next line -(see below). - - -<p> -The available formats are - -<ul> - -<li><b>"<code>n</code>": </b> -reads a numeral and returns it as a float or an integer, -following the lexical conventions of Lua. -(The numeral may have leading spaces and a sign.) -This format always reads the longest input sequence that -is a valid prefix for a numeral; -if that prefix does not form a valid numeral -(e.g., an empty string, "<code>0x</code>", or "<code>3.4e-</code>"), -it is discarded and the function returns <b>nil</b>. -</li> - -<li><b>"<code>a</code>": </b> -reads the whole file, starting at the current position. -On end of file, it returns the empty string. -</li> - -<li><b>"<code>l</code>": </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>"<code>L</code>": </b> -reads the next line keeping the end-of-line character (if present), -returning <b>nil</b> on end of file. -</li> - -<li><b><em>number</em>: </b> -reads a string with up to this number of bytes, -returning <b>nil</b> on end of file. -If <code>number</code> is zero, -it reads nothing and returns an empty string, -or <b>nil</b> on end of file. -</li> - -</ul><p> -The formats "<code>l</code>" and "<code>L</code>" should be used only for text files. - - - - -<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>"<code>set</code>": </b> base is position 0 (beginning of the file);</li> -<li><b>"<code>cur</code>": </b> base is current position;</li> -<li><b>"<code>end</code>": </b> base is end of file;</li> -</ul><p> -In case of success, <code>seek</code> returns the final file position, -measured in bytes from the beginning of the file. -If <code>seek</code> 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>"<code>no</code>": </b> -no buffering; the result of any output operation appears immediately. -</li> - -<li><b>"<code>full</code>": </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>"<code>line</code>": </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 <code>file</code>. -The arguments must be strings or numbers. - - -<p> -In case of success, this function returns <code>file</code>. -Otherwise it returns <b>nil</b> plus a string describing the error. - - - - - - - -<h2>6.9 – <a name="6.9">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>, <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, 1–7, Sunday is 1), -<code>yday</code> (day of the year, 1–366), -and <code>isdst</code> (daylight saving flag, a boolean). -This last field may be absent -if the information is not available. - - -<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 ISO 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. -(More specifically, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>.) - - -<p> -On non-POSIX systems, -this function may be not thread safe -because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>. - - - - -<p> -<hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> - - -<p> -Returns the difference, in seconds, -from time <code>t1</code> to time <code>t2</code> -(where the times are values returned by <a href="#pdf-os.time"><code>os.time</code></a>). -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 ISO C function <code>system</code>. -It passes <code>command</code> to be executed by an operating system shell. -Its first result is <b>true</b> -if the command terminated successfully, -or <b>nil</b> otherwise. -After this first result -the function returns a string plus a number, -as follows: - -<ul> - -<li><b>"<code>exit</code>": </b> -the command terminated normally; -the following number is the exit status of the command. -</li> - -<li><b>"<code>signal</code>": </b> -the command was terminated by a signal; -the following number is the signal that terminated the command. -</li> - -</ul> - -<p> -When called without a <code>command</code>, -<code>os.execute</code> returns a boolean that is true if a shell is available. - - - - -<p> -<hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close]])</code></a></h3> - - -<p> -Calls the ISO C function <code>exit</code> to terminate the host program. -If <code>code</code> is <b>true</b>, -the returned status is <code>EXIT_SUCCESS</code>; -if <code>code</code> is <b>false</b>, -the returned status is <code>EXIT_FAILURE</code>; -if <code>code</code> is a number, -the returned status is this number. -The default value for <code>code</code> is <b>true</b>. - - -<p> -If the optional second argument <code>close</code> is true, -closes the Lua state before exiting. - - - - -<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 empty directory, on POSIX systems) -with the given name. -If this function fails, it returns <b>nil</b>, -plus a string describing the error and the error code. - - - - -<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 and the error code. - - - - -<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 system-dependent string specifying a locale; -<code>category</code> is an optional string describing which category to change: -<code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, -<code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; -the default category is <code>"all"</code>. -The function returns the name of the new locale, -or <b>nil</b> if the request cannot be honored. - - -<p> -If <code>locale</code> is the empty string, -the current locale is set to an implementation-defined native locale. -If <code>locale</code> is the string "<code>C</code>", -the current locale is set to the standard C locale. - - -<p> -When called with <b>nil</b> as the first argument, -this function only returns the name of the current locale -for the given category. - - -<p> -This function may be not thread safe -because of its reliance on C function <code>setlocale</code>. - - - - -<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 local 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> (default is 12), -<code>min</code> (default is 0), -<code>sec</code> (default is 0), -and <code>isdst</code> (default is <b>nil</b>). -Other fields are ignored. -For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function. - - -<p> -The values in these fields do not need to be inside their valid ranges. -For instance, if <code>sec</code> is -10, -it means -10 seconds from the time specified by the other fields; -if <code>hour</code> is 1000, -it means +1000 hours from the time specified by the other fields. - - -<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 -<a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>. - - - - -<p> -<hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> - - -<p> -Returns a string with a file name that can -be used for a temporary file. -The file must be explicitly opened before its use -and explicitly removed when no longer needed. - - -<p> -On POSIX systems, -this function also creates a file with that name, -to avoid security risks. -(Someone else might create the file with wrong permissions -in the time between getting the name and creating the file.) -You still have to open the file to use it -and to remove it (even if you do not use it). - - -<p> -When possible, -you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, -which automatically removes the file when the program ends. - - - - - - - -<h2>6.10 – <a name="6.10">The Debug Library</a></h2> - -<p> -This library provides -the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs. -You should exert care when using this library. -Several of its functions -violate basic assumptions about Lua code -(e.g., that variables local to a function -cannot be accessed from outside; -that userdata metatables cannot be changed by Lua code; -that Lua programs do not crash) -and therefore can compromise otherwise secure code. -Moreover, some functions in this library may be slow. - - -<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.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,] f [, 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>f</code>, -which means the function running at level <code>f</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> -(except for tail calls, which do not count on the stack); -and so on. -If <code>f</code> is a number larger than the number of active functions, -then <code>getinfo</code> returns <b>nil</b>. - - -<p> -The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, -with the string <code>what</code> describing which fields to fill in. -The default for <code>what</code> is to get all information available, -except the table of valid lines. -If present, -the option '<code>f</code>' -adds a field named <code>func</code> with the function itself. -If present, -the option '<code>L</code>' -adds a field named <code>activelines</code> with the table of -valid lines. - - -<p> -For instance, the expression <code>debug.getinfo(1,"n").name</code> returns -a name for the current function, -if a reasonable name can be found, -and the expression <code>debug.getinfo(print)</code> -returns a table with all available information -about the <a href="#pdf-print"><code>print</code></a> function. - - - - -<p> -<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, 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>f</code> of the stack. -This function accesses not only explicit local variables, -but also parameters, temporaries, etc. - - -<p> -The first parameter or local variable has index 1, and so on, -following the order that they are declared in the code, -counting only the variables that are active -in the current scope of the function. -Negative indices refer to vararg parameters; --1 is the first vararg parameter. -The function returns <b>nil</b> if there is no variable with the given index, -and raises an error when called with a level 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 parenthesis) -represent variables with no known names -(internal variables such as loop control variables, -and variables from chunks saved without debug information). - - -<p> -The parameter <code>f</code> may also be a function. -In that case, <code>getlocal</code> returns only the name of function parameters. - - - - -<p> -<hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3> - - -<p> -Returns the metatable of the given <code>value</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="#4.5">§4.5</a>). - - - - -<p> -<hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, 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>f</code>. -The function returns <b>nil</b> if there is no upvalue with the given index. - - -<p> -Variable names starting with '<code>(</code>' (open parenthesis) -represent variables with no known names -(variables from chunks saved without debug information). - - - - -<p> -<hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3> - - -<p> -Returns the Lua value associated to <code>u</code>. -If <code>u</code> is not a userdata, -returns <b>nil</b>. - - - - -<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 any combination of 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> -Moreover, -with a <code>count</code> different from zero, -the hook is called also 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> (or <code>"tail call"</code>), -<code>"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). - - - - -<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> -See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about -variable indices and names. - - - - -<p> -<hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3> - - -<p> -Sets the metatable for the given <code>value</code> to the given <code>table</code> -(which can be <b>nil</b>). -Returns <code>value</code>. - - - - -<p> -<hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, 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>f</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.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3> - - -<p> -Sets the given <code>value</code> as -the Lua value associated to the given <code>udata</code>. -<code>udata</code> must be a full userdata. - - -<p> -Returns <code>udata</code>. - - - - -<p> -<hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3> - - -<p> -If <code>message</code> is present but is neither a string nor <b>nil</b>, -this function returns <code>message</code> without further processing. -Otherwise, -it returns a string with a traceback of the call stack. -The 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>). - - - - -<p> -<hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3> - - -<p> -Returns a unique identifier (as a light userdata) -for the upvalue numbered <code>n</code> -from the given function. - - -<p> -These unique identifiers allow a program to check whether different -closures share upvalues. -Lua closures that share an upvalue -(that is, that access a same external local variable) -will return identical ids for those upvalue indices. - - - - -<p> -<hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3> - - -<p> -Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code> -refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>. - - - - - - - -<h1>7 – <a name="7">Lua Standalone</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 standalone language. -An interpreter for Lua as a standalone language, -called simply <code>lua</code>, -is provided with the standard distribution. -The standalone 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>-E</code>: </b> ignores environment variables;</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>. -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> -When called without option <code>-E</code>, -the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_3"><code>LUA_INIT_5_3</code></a> -(or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if the versioned name is not defined) -before running any argument. -If the variable content has the format <code>@<em>filename</em></code>, -then <code>lua</code> executes the file. -Otherwise, <code>lua</code> executes the string itself. - - -<p> -When called with option <code>-E</code>, -besides ignoring <code>LUA_INIT</code>, -Lua also ignores -the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>, -setting the values of -<a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a> -with the default paths defined in <code>luaconf.h</code>. - - -<p> -All options are handled in order, except <code>-i</code> and <code>-E</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>, -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 running any code, -<code>lua</code> collects all command-line arguments -in a global table called <code>arg</code>. -The script name goes to 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 its options) -go to negative indices. -For instance, in the call - -<pre> - $ lua -la b.lua t1 t2 -</pre><p> -the table is like this: - -<pre> - arg = { [-2] = "lua", [-1] = "-la", - [0] = "b.lua", - [1] = "t1", [2] = "t2" } -</pre><p> -If there is no script in the call, -the interpreter name goes to index 0, -followed by the other arguments. -For instance, the call - -<pre> - $ lua -e "print(arg[1])" -</pre><p> -will print "<code>-e</code>". -If there is a script, -the script is called with parameters -<code>arg[1]</code>, ···, <code>arg[#arg]</code>. -(Like all chunks in Lua, -the script is compiled as a vararg function.) - - -<p> -In interactive mode, -Lua repeatedly prompts and waits for a line. -After reading a line, -Lua first try to interpret the line as an expression. -If it succeeds, it prints its value. -Otherwise, it interprets the line as a statement. -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). - - -<p> -In case of unprotected errors in the script, -the interpreter reports the error to the standard error stream. -If the error object is not a string but -has a metamethod <code>__tostring</code>, -the interpreter calls this metamethod to produce the final message. -Otherwise, the interpreter converts the error object to a string -and adds a stack traceback to it. - - -<p> -When finishing normally, -the interpreter closes its main Lua state -(see <a href="#lua_close"><code>lua_close</code></a>). -The script can avoid this step by -calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate. - - -<p> -To allow the use of Lua as a -script interpreter in Unix systems, -the standalone 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>8 – <a name="8">Incompatibilities with the Previous Version</a></h1> - -<p> -Here we list the incompatibilities that you may find when moving a program -from Lua 5.2 to Lua 5.3. -You can avoid some incompatibilities by compiling Lua with -appropriate options (see file <code>luaconf.h</code>). -However, -all these compatibility options will be removed in the future. - - -<p> -Lua versions can always change the C API in ways that -do not imply source-code changes in a program, -such as the numeric values for constants -or the implementation of functions as macros. -Therefore, -you should not assume that binaries are compatible between -different Lua versions. -Always recompile clients of the Lua API when -using a new version. - - -<p> -Similarly, Lua versions can always change the internal representation -of precompiled chunks; -precompiled chunks are not compatible between different Lua versions. - - -<p> -The standard paths in the official distribution may -change between versions. - - - -<h2>8.1 – <a name="8.1">Changes in the Language</a></h2> -<ul> - -<li> -The main difference between Lua 5.2 and Lua 5.3 is the -introduction of an integer subtype for numbers. -Although this change should not affect "normal" computations, -some computations -(mainly those that involve some kind of overflow) -can give different results. - - -<p> -You can fix these differences by forcing a number to be a float -(in Lua 5.2 all numbers were float), -in particular writing constants with an ending <code>.0</code> -or using <code>x = x + 0.0</code> to convert a variable. -(This recommendation is only for a quick fix -for an occasional incompatibility; -it is not a general guideline for good programming. -For good programming, -use floats where you need floats -and integers where you need integers.) -</li> - -<li> -The conversion of a float to a string now adds a <code>.0</code> suffix -to the result if it looks like an integer. -(For instance, the float 2.0 will be printed as <code>2.0</code>, -not as <code>2</code>.) -You should always use an explicit format -when you need a specific format for numbers. - - -<p> -(Formally this is not an incompatibility, -because Lua does not specify how numbers are formatted as strings, -but some programs assumed a specific format.) -</li> - -<li> -The generational mode for the garbage collector was removed. -(It was an experimental feature in Lua 5.2.) -</li> - -</ul> - - - - -<h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2> -<ul> - -<li> -The <code>bit32</code> library has been deprecated. -It is easy to require a compatible external library or, -better yet, to replace its functions with appropriate bitwise operations. -(Keep in mind that <code>bit32</code> operates on 32-bit integers, -while the bitwise operators in Lua 5.3 operate on Lua integers, -which by default have 64 bits.) -</li> - -<li> -The Table library now respects metamethods -for setting and getting elements. -</li> - -<li> -The <a href="#pdf-ipairs"><code>ipairs</code></a> iterator now respects metamethods and -its <code>__ipairs</code> metamethod has been deprecated. -</li> - -<li> -Option names in <a href="#pdf-io.read"><code>io.read</code></a> do not have a starting '<code>*</code>' anymore. -For compatibility, Lua will continue to accept (and ignore) this character. -</li> - -<li> -The following functions were deprecated in the mathematical library: -<code>atan2</code>, <code>cosh</code>, <code>sinh</code>, <code>tanh</code>, <code>pow</code>, -<code>frexp</code>, and <code>ldexp</code>. -You can replace <code>math.pow(x,y)</code> with <code>x^y</code>; -you can replace <code>math.atan2</code> with <code>math.atan</code>, -which now accepts one or two parameters; -you can replace <code>math.ldexp(x,exp)</code> with <code>x * 2.0^exp</code>. -For the other operations, -you can either use an external library or -implement them in Lua. -</li> - -<li> -The searcher for C loaders used by <a href="#pdf-require"><code>require</code></a> -changed the way it handles versioned names. -Now, the version should come after the module name -(as is usual in most other tools). -For compatibility, that searcher still tries the old format -if it cannot find an open function according to the new style. -(Lua 5.2 already worked that way, -but it did not document the change.) -</li> - -<li> -The call <code>collectgarbage("count")</code> now returns only one result. -(You can compute that second result from the fractional part -of the first result.) -</li> - -</ul> - - - - -<h2>8.3 – <a name="8.3">Changes in the API</a></h2> - - -<ul> - -<li> -Continuation functions now receive as parameters what they needed -to get through <code>lua_getctx</code>, -so <code>lua_getctx</code> has been removed. -Adapt your code accordingly. -</li> - -<li> -Function <a href="#lua_dump"><code>lua_dump</code></a> has an extra parameter, <code>strip</code>. -Use 0 as the value of this parameter to get the old behavior. -</li> - -<li> -Functions to inject/project unsigned integers -(<code>lua_pushunsigned</code>, <code>lua_tounsigned</code>, <code>lua_tounsignedx</code>, -<code>luaL_checkunsigned</code>, <code>luaL_optunsigned</code>) -were deprecated. -Use their signed equivalents with a type cast. -</li> - -<li> -Macros to project non-default integer types -(<code>luaL_checkint</code>, <code>luaL_optint</code>, <code>luaL_checklong</code>, <code>luaL_optlong</code>) -were deprecated. -Use their equivalent over <a href="#lua_Integer"><code>lua_Integer</code></a> with a type cast -(or, when possible, use <a href="#lua_Integer"><code>lua_Integer</code></a> in your code). -</li> - -</ul> - - - - -<h1>9 – <a name="9">The Complete Syntax of Lua</a></h1> - -<p> -Here is the complete syntax of Lua in extended BNF. -As usual in extended BNF, -{A} means 0 or more As, -and [A] means an optional A. -(For operator precedences, see <a href="#3.4.8">§3.4.8</a>; -for a description of the terminals -Name, Numeral, -and LiteralString, see <a href="#3.1">§3.1</a>.) - - - - -<pre> - - chunk ::= block - - block ::= {stat} [retstat] - - stat ::= ‘<b>;</b>’ | - varlist ‘<b>=</b>’ explist | - functioncall | - label | - <b>break</b> | - <b>goto</b> Name | - <b>do</b> block <b>end</b> | - <b>while</b> exp <b>do</b> block <b>end</b> | - <b>repeat</b> block <b>until</b> exp | - <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | - <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> | - <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | - <b>function</b> funcname funcbody | - <b>local</b> <b>function</b> Name funcbody | - <b>local</b> namelist [‘<b>=</b>’ explist] - - retstat ::= <b>return</b> [explist] [‘<b>;</b>’] - - label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ - - funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] - - varlist ::= var {‘<b>,</b>’ var} - - var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name - - namelist ::= Name {‘<b>,</b>’ Name} - - explist ::= exp {‘<b>,</b>’ exp} - - exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | ‘<b>...</b>’ | functiondef | - prefixexp | tableconstructor | exp binop exp | unop exp - - prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ - - functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args - - args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | LiteralString - - functiondef ::= <b>function</b> funcbody - - funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> - - parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ - - tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ - - fieldlist ::= field {fieldsep field} [fieldsep] - - field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp - - fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ - - binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>//</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ | - ‘<b>&</b>’ | ‘<b>~</b>’ | ‘<b>|</b>’ | ‘<b>>></b>’ | ‘<b><<</b>’ | ‘<b>..</b>’ | - ‘<b><</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>’ | ‘<b>~</b>’ - -</pre> - -<p> - - - - - - - - -<P CLASS="footer"> -Last update: -Mon May 30 13:11:08 BRT 2016 -</P> -<!-- -Last change: revised for Lua 5.3.3 ---> - -</body></html> - |