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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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+<title>Lua 5.3 Reference Manual</title>
+<link rel="stylesheet" type="text/css" href="../../lua.css">
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+<h1>
+<a href="../../home.html"><img src="../../images/logo.gif" alt="" border="0"></a>
+Lua 5.3 Reference Manual
+</h1>
+by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
+<p>
+<small>
+Copyright &copy; 2015 Lua.org, PUC-Rio.
+Freely available under the terms of the
+<a href="../../license.html">Lua license</a>.
+</small>
+<hr>
+<p>
+<a href="contents.html#contents">contents</A>
+&middot;
+<a href="contents.html#index">index</A>
+&middot;
+<a href="../">other versions</A>
+<!-- ====================================================================== -->
+<p>
+<!-- $Id: manual.of,v 1.146 2015/01/06 11:23:01 roberto Exp $ -->
+<h1>1 &ndash; <a name="1">Introduction</a></h1>
+<p>
+Lua is an extension programming language designed to support
+general procedural programming with data description
+facilities.
+Lua also offers good support for object-oriented programming,
+functional programming, and data-driven programming.
+Lua is intended to be used as a powerful, lightweight,
+embeddable scripting language for any program that needs one.
+Lua is implemented as a library, written in <em>clean C</em>,
+the common subset of Standard&nbsp;C and C++.
+<p>
+As an extension language, Lua has no notion of a "main" program:
+it only works <em>embedded</em> in a host client,
+called the <em>embedding program</em> or simply the <em>host</em>.
+The host program can invoke functions to execute a piece of Lua code,
+can write and read Lua variables,
+and can register C&nbsp;functions to be called by Lua code.
+Through the use of C&nbsp;functions, Lua can be augmented to cope with
+a wide range of different domains,
+thus creating customized programming languages sharing a syntactical framework.
+The Lua distribution includes a sample host program called <code>lua</code>,
+which uses the Lua library to offer a complete, standalone Lua interpreter,
+for interactive or batch use.
+<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 &ndash; <a name="2">Basic Concepts</a></h1>
+<p>
+This section describes the basic concepts of the language.
+<h2>2.1 &ndash; <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>.
+<em>Nil</em> is the type of the value <b>nil</b>,
+whose main property is to be different from any other value;
+it usually represents the absence of a useful value.
+<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
+Both <b>nil</b> and <b>false</b> make a condition false;
+any other value makes it true.
+<em>Number</em> represents both
+integer numbers and real (floating-point) numbers.
+<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,
+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">&sect;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">&sect;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&nbsp;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&nbsp;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">&sect;2.4</a>).
+Userdata values cannot be created or modified in Lua,
+only through the C&nbsp;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">&sect;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 numeric value used to represent
+undefined or unrepresentable 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">&sect;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">&sect;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">&sect;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">&sect;6.1</a>).
+<h2>2.2 &ndash; <a name="2.2">Environments and the Global Environment</a></h2>
+<p>
+As will be discussed in <a href="#3.2">&sect;3.2</a> and <a href="#3.3.3">&sect;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">&sect;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">&sect;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">&sect;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 &ndash; <a name="2.3">Error Handling</a></h2>
+<p>
+Because Lua is an embedded extension language,
+all Lua actions start from C&nbsp;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 message
+and returns a new error message.
+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 &ndash; <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 keys in a metatable are derived from the <em>event</em> names;
+the corresponding values are called <em>metamethods</em>.
+In the previous example, the event is <code>"add"</code>
+and the metamethod is the function that performs the addition.
+<p>
+You can query the metatable of any value
+using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
+<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
+(except by using the debug library (<a href="#6.10">&sect;6.10</a>));
+you must use the C&nbsp;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">&sect;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">&sect;2.5</a>).
+<p>
+A detailed list of events controlled by metatables is given next.
+Each operation is identified by its corresponding event name.
+The key for each event is a string with its name prefixed by
+two underscores, '<code>__</code>';
+for instance, the key for operation "add" is the
+string "<code>__add</code>".
+Note that queries for metamethods are always raw;
+the access to a metamethod does not invoke other metamethods.
+You can emulate how Lua queries a metamethod for an object <code>obj</code>
+with the following code:
+<pre>
+rawget(getmetatable(obj) or {}, "__" .. event_name)
+</pre>
+<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.)
+<ul>
+<li><b>"add": </b>
+the <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 the "<code>__add</code>" event,
+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>"sub": </b>
+the <code>-</code> operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"mul": </b>
+the <code>*</code> operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"div": </b>
+the <code>/</code> operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"mod": </b>
+the <code>%</code> operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"pow": </b>
+the <code>^</code> (exponentiation) operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"unm": </b>
+the <code>-</code> (unary minus) operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"idiv": </b>
+the <code>//</code> (floor division) operation.
+Behavior similar to the "add" operation.
+</li>
+<li><b>"band": </b>
+the <code>&amp;</code> (bitwise and) operation.
+Behavior similar to the "add" operation,
+except that Lua will try a metamethod
+if any operator is neither an integer
+nor a value coercible to an integer (see <a href="#3.4.3">&sect;3.4.3</a>).
+</li>
+<li><b>"bor": </b>
+the <code>|</code> (bitwise or) operation.
+Behavior similar to the "band" operation.
+</li>
+<li><b>"bxor": </b>
+the <code>~</code> (bitwise exclusive or) operation.
+Behavior similar to the "band" operation.
+</li>
+<li><b>"bnot": </b>
+the <code>~</code> (bitwise unary not) operation.
+Behavior similar to the "band" operation.
+</li>
+<li><b>"shl": </b>
+the <code>&lt;&lt;</code> (bitwise left shift) operation.
+Behavior similar to the "band" operation.
+</li>
+<li><b>"shr": </b>
+the <code>&gt;&gt;</code> (bitwise right shift) operation.
+Behavior similar to the "band" operation.
+</li>
+<li><b>"concat": </b>
+the <code>..</code> (concatenation) operation.
+Behavior similar to the "add" operation,
+except that Lua will try a metamethod
+if any operator is neither a string nor a number
+(which is always coercible to a string).
+</li>
+<li><b>"len": </b>
+the <code>#</code> (length) 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">&sect;3.4.7</a>).
+Otherwise, Lua raises an error.
+</li>
+<li><b>"eq": </b>
+the <code>==</code> (equal) operation.
+Behavior similar to the "add" 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>"lt": </b>
+the <code>&lt;</code> (less than) operation.
+Behavior similar to the "add" 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>"le": </b>
+the <code>&lt;=</code> (less equal) 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 "lt" operation.
+If it cannot find such a metamethod,
+then it will try the "<code>__lt</code>" event,
+assuming that <code>a &lt;= b</code> is equivalent to <code>not (b &lt; a)</code>.
+As with the other comparison operators,
+the result is always a boolean.
+</li>
+<li><b>"index": </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.
+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>"newindex": </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 "newindex" 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>"call": </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>).
+</li>
+</ul>
+<h2>2.5 &ndash; <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 &ndash; <a name="2.5.1">Garbage-Collection Metamethods</a></h3>
+<p>
+You can set garbage-collector metamethods for tables
+and, using the C&nbsp;API,
+for full userdata (see <a href="#2.4">&sect;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.
+However, after an object has been marked,
+you can freely change the <code>__gc</code> field of its metatable.
+<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 the 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 &ndash; <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 keys allows the collection of its keys,
+but prevents the collection of its values.
+A table with both weak keys and weak values allows the collection of
+both keys and values.
+In any case, if either the key or the value is collected,
+the whole pair is removed from the table.
+The weakness of a table is controlled by the
+<code>__mode</code> field of its metatable.
+If the <code>__mode</code> field is a string containing the character&nbsp;'<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 &ndash; <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,
+at the first line of its main function.
+Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed
+as arguments to the coroutine's main function.
+After the coroutine starts running,
+it runs until it terminates or <em>yields</em>.
+<p>
+A coroutine can terminate its execution in two ways:
+normally, when its main function returns
+(explicitly or implicitly, after the last instruction);
+and abnormally, if there is an unprotected error.
+In 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 message.
+<p>
+A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
+When a coroutine yields,
+the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
+even if the yield happens inside nested function calls
+(that is, not in the main function,
+but in a function directly or indirectly called by the main function).
+In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
+plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
+The next time you resume the same coroutine,
+it continues its execution from the point where it yielded,
+with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
+arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
+<p>
+Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
+the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
+but instead of returning the coroutine itself,
+it returns a function that, when called, resumes the coroutine.
+Any arguments passed to this function
+go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
+<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
+except the first one (the boolean error code).
+Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
+<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
+any error is propagated to the caller.
+<p>
+As an example 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 &ndash; <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>}&nbsp;means&nbsp;0 or more <em>a</em>'s, and
+[<em>a</em>]&nbsp;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 &lsquo;<b>=</b>&rsquo;.
+The complete syntax of Lua can be found in <a href="#9">&sect;9</a>
+at the end of this manual.
+<h2>3.1 &ndash; <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.
+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>
++     -     *     /     %     ^     #
+&amp;     ~     |     &lt;&lt;    &gt;&gt;    //
+==    ~=    &lt;=    &gt;=    &lt;     &gt;     =
+(     )     {     }     [     ]     ::
+;     :     ,     .     ..    ...
+</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 numerical 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&nbsp;0 is written as <code>[[</code>,
+an opening long bracket of level&nbsp;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&nbsp;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 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&nbsp;97,
+newline is coded as&nbsp;10, and '<code>1</code>' is coded as&nbsp;49),
+the five literal strings below denote the same string:
+<pre>
+a = 'alo\n123"'
+a = "alo\n123\""
+a = '\97lo\10\04923"'
+a = [[alo
+123"]]
+a = [==[
+alo
+123"]==]
+</pre>
+<p>
+A <em>numerical constant</em> (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 fractional dot or an exponent
+denotes a float;
+otherwise 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 &ndash; <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">&sect;3.1</a>.
+<p>
+Any variable name is assumed to be global unless explicitly declared
+as a local (see <a href="#3.3.7">&sect;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">&sect;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 &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo;
+</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">&sect;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 &lsquo;<b>.</b>&rsquo; 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">&sect;2.2</a>).
+<h2>3.3 &ndash; <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 &ndash; <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 ::= &lsquo;<b>;</b>&rsquo;
+</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">&sect;3.3.4</a>).
+<h3>3.3.2 &ndash; <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">&sect;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">&sect;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 &ndash; <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 &lsquo;<b>=</b>&rsquo; explist
+	varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
+	explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
+</pre><p>
+Expressions are discussed in <a href="#3.4">&sect;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">&sect;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&nbsp;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">&sect;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">&sect;2.2</a>).
+<h3>3.3.4 &ndash; <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">&sect;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>&ndash;<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 ::= &lsquo;<b>::</b>&rsquo; Name &lsquo;<b>::</b>&rsquo;
+</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] [&lsquo;<b>;</b>&rsquo;]
+</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 &ndash; <a name="3.3.5">For Statement</a></h3>
+<p>
+The <b>for</b> statement has two forms:
+one numeric and one generic.
+<p>
+The numeric <b>for</b> loop repeats a block of code while a
+control variable runs through an arithmetic progression.
+It has the following syntax:
+<pre>
+	stat ::= <b>for</b> Name &lsquo;<b>=</b>&rsquo; exp &lsquo;<b>,</b>&rsquo; exp [&lsquo;<b>,</b>&rsquo; 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> &gt;= 0 and <em>var</em> &gt; <em>limit</em>) or (<em>step</em> &lt; 0 and <em>var</em> &lt; <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&nbsp;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 {&lsquo;<b>,</b>&rsquo; Name}
+</pre><p>
+A <b>for</b> statement like
+<pre>
+for <em>var_1</em>, &middot;&middot;&middot;, <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>, &middot;&middot;&middot;, <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 &ndash; <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">&sect;3.4.10</a>.
+<h3>3.3.7 &ndash; <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 [&lsquo;<b>=</b>&rsquo; explist]
+</pre><p>
+If present, an initial assignment has the same semantics
+of a multiple assignment (see <a href="#3.3.3">&sect;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">&sect;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">&sect;3.5</a>.
+<h2>3.4 &ndash; <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 ::= &lsquo;<b>...</b>&rsquo;
+	exp ::= exp binop exp
+	exp ::= unop exp
+	prefixexp ::= var | functioncall | &lsquo;<b>(</b>&rsquo; exp &lsquo;<b>)</b>&rsquo;
+</pre>
+<p>
+Numerals and literal strings are explained in <a href="#3.1">&sect;3.1</a>;
+variables are explained in <a href="#3.2">&sect;3.2</a>;
+function definitions are explained in <a href="#3.4.11">&sect;3.4.11</a>;
+function calls are explained in <a href="#3.4.10">&sect;3.4.10</a>;
+table constructors are explained in <a href="#3.4.9">&sect;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">&sect;3.4.11</a>.
+<p>
+Binary operators comprise arithmetic operators (see <a href="#3.4.1">&sect;3.4.1</a>),
+bitwise operators (see <a href="#3.4.2">&sect;3.4.2</a>),
+relational operators (see <a href="#3.4.4">&sect;3.4.4</a>), logical operators (see <a href="#3.4.5">&sect;3.4.5</a>),
+and the concatenation operator (see <a href="#3.4.6">&sect;3.4.6</a>).
+Unary operators comprise the unary minus (see <a href="#3.4.1">&sect;3.4.1</a>),
+the unary bitwise not (see <a href="#3.4.2">&sect;3.4.2</a>),
+the unary logical <b>not</b> (see <a href="#3.4.5">&sect;3.4.5</a>),
+and the unary <em>length operator</em> (see <a href="#3.4.7">&sect;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">&sect;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 &ndash; <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">&sect;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&nbsp;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 infinite,
+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 infinite (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 &ndash; <a name="3.4.2">Bitwise Operators</a></h3><p>
+Lua supports the following bitwise operators:
+<ul>
+<li><b><code>&amp;</code>: </b>bitwise and</li>
+<li><b><code>&#124;</code>: </b>bitwise or</li>
+<li><b><code>~</code>: </b>bitwise exclusive or</li>
+<li><b><code>&gt;&gt;</code>: </b>right shift</li>
+<li><b><code>&lt;&lt;</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">&sect;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 &ndash; <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 is converted to the required type
+(float or integer) according to the previous rules.
+<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 &ndash; <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>&lt;</code>: </b>less than</li>
+<li><b><code>&gt;</code>: </b>greater than</li>
+<li><b><code>&lt;=</code>: </b>less or equal</li>
+<li><b><code>&gt;=</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 follow the usual rule for binary operations:
+if both operands are integers,
+they are compared as integers;
+otherwise, they are converted to floats
+and compared as such.
+<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">&sect;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 following
+the usual rule for binary operations.
+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">&sect;2.4</a>).
+A comparison <code>a &gt; b</code> is translated to <code>b &lt; a</code>
+and <code>a &gt;= b</code> is translated to <code>b &lt;= a</code>.
+<h3>3.4.5 &ndash; <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">&sect;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            --&gt; 10
+10 or error()       --&gt; 10
+nil or "a"          --&gt; "a"
+nil and 10          --&gt; nil
+false and error()   --&gt; false
+false and nil       --&gt; false
+false or nil        --&gt; nil
+10 and 20           --&gt; 20
+</pre><p>
+(In this manual,
+<code>--&gt;</code> indicates the result of the preceding expression.)
+<h3>3.4.6 &ndash; <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">&sect;3.4.3</a>.
+Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">&sect;2.4</a>).
+<h3>3.4.7 &ndash; <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">&sect;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 &ndash; <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
+&lt;     &gt;     &lt;=    &gt;=    ~=    ==
+|
+~
+&amp;
+&lt;&lt;    &gt;&gt;
+..
++     -
+*     /     //    %
+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 &ndash; <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 ::= &lsquo;<b>{</b>&rsquo; [fieldlist] &lsquo;<b>}</b>&rsquo;
+	fieldlist ::= field {fieldsep field} [fieldsep]
+	field ::= &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; &lsquo;<b>=</b>&rsquo; exp | Name &lsquo;<b>=</b>&rsquo; exp | exp
+	fieldsep ::= &lsquo;<b>,</b>&rsquo; | &lsquo;<b>;</b>&rsquo;
+</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">&sect;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 &ndash; <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">&sect;2.4</a>).
+<p>
+The form
+<pre>
+	functioncall ::= prefixexp &lsquo;<b>:</b>&rsquo; 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 ::= &lsquo;<b>(</b>&rsquo; [explist] &lsquo;<b>)</b>&rsquo;
+	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 &ndash; <a name="3.4.11">Function Definitions</a></h3>
+<p>
+The syntax for function definition is
+<pre>
+	functiondef ::= <b>function</b> funcbody
+	funcbody ::= &lsquo;<b>(</b>&rsquo; [parlist] &lsquo;<b>)</b>&rsquo; 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 {&lsquo;<b>.</b>&rsquo; Name} [&lsquo;<b>:</b>&rsquo; 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 [&lsquo;<b>,</b>&rsquo; &lsquo;<b>...</b>&rsquo;] | &lsquo;<b>...</b>&rsquo;
+</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, ... --&gt;  (nothing)
+g(3, 4)          a=3, b=4,   ... --&gt;  (nothing)
+g(3, 4, 5, 8)    a=3, b=4,   ... --&gt;  5  8
+g(5, r())        a=5, b=1,   ... --&gt;  2  3
+</pre>
+<p>
+Results are returned using the <b>return</b> statement (see <a href="#3.3.4">&sect;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 &ndash; <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)            --&gt; 10
+x = x+1
+do                  -- another block
+local x = x+1     -- another 'x'
+print(x)          --&gt; 12
+end
+print(x)            --&gt; 11
+end
+print(x)              --&gt; 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 &ndash; <a name="4">The Application Program Interface</a></h1>
+<p>
+This section describes the C&nbsp;API for Lua, that is,
+the set of C&nbsp;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&nbsp;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 &ndash; <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&nbsp;functions that are still active.
+This stack initially contains any arguments to the C&nbsp;function
+and it is where the C&nbsp;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&nbsp;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&nbsp;1 represents the first element
+(that is, the element that was pushed onto the stack first)
+and
+index&nbsp;<em>n</em> represents the last element;
+index&nbsp;-1 also represents the last element
+(that is, the element at the&nbsp;top)
+and index <em>-n</em> represents the first element.
+<h2>4.2 &ndash; <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 &ndash; <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
+real position within the stack, that is,
+its position lies between&nbsp;1 and the stack top
+(<code>1 &le; abs(index) &le; top</code>).
+Usually, functions that can modify the value at an index
+require valid indices.
+<p>
+Unless otherwise noted,
+any function that accepts valid indices also accepts <em>pseudo-indices</em>,
+which represent some Lua values that are accessible to C&nbsp;code
+but which are not in the stack.
+Pseudo-indices are used to access the registry
+and the upvalues of a C&nbsp;function (see <a href="#4.4">&sect;4.4</a>).
+<p>
+Functions that do not need a specific stack position,
+but only a value in the stack (e.g., query functions),
+can be called with acceptable indices.
+An <em>acceptable index</em> can be any valid index,
+including the pseudo-indices,
+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&nbsp;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 &ndash; <a name="4.4">C Closures</a></h2>
+<p>
+When a C&nbsp;function is created,
+it is possible to associate some values with it,
+thus creating a <em>C&nbsp;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&nbsp;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 value associated with a function is at position
+<code>lua_upvalueindex(1)</code>, and so on.
+Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
+where <em>n</em> is greater than the number of upvalues of the
+current function (but not greater than 256),
+produces an acceptable but invalid index.
+<h2>4.5 &ndash; <a name="4.5">Registry</a></h2>
+<p>
+Lua provides a <em>registry</em>,
+a predefined table that can be used by any C&nbsp;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>,
+which is a valid index.
+Any C&nbsp;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&nbsp;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 &ndash; <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">&sect;2.3</a>);
+in particular, the error message 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">&sect;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&nbsp;function you can raise an error by calling <a href="#lua_error"><code>lua_error</code></a>.
+<h2>4.7 &ndash; <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 &ndash; <a name="4.8">Functions and Types</a></h2>
+<p>
+Here we list all functions and types from the C&nbsp;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>e</code>' means the function may raise errors;
+'<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, &ndash;]</span>
+<pre>int lua_absindex (lua_State *L, int idx);</pre>
+<p>
+Converts the acceptable index <code>idx</code> into an 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 &gt;= 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&nbsp;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&nbsp;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 negation (<code>~</code>)</li>
+<li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise and (<code>&amp;</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>&lt;&lt;</code>)</li>
+<li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>&gt;&gt;</code>)</li>
+</ul>
+<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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">&sect;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.
+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&nbsp;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">&sect;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&nbsp;functions.
+<p>
+In order to communicate properly with Lua,
+a C&nbsp;function must use the following protocol,
+which defines the way parameters and results are passed:
+a C&nbsp;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&nbsp;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&nbsp;function called by Lua can also return
+many results.
+<p>
+As an example, the following function receives a variable number
+of numerical arguments and returns their average and 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 &lt;= 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, &ndash;]</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.
+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 is already larger than the new size,
+it is left unchanged.
+<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;0.
+Also returns&nbsp;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>&lt;</code>)</li>
+<li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code>&lt;=</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>&nbsp;is&nbsp;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">&sect;3.4.6</a>).
+<hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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>e</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 pre-allocation 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, <em>e</em>]</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 is created without debug information
+about the function.
+<p>
+The value returned is the error code returned by the last
+call to the writer;
+0&nbsp;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>e</em>]</span>
+<pre>int lua_gc (lua_State *L, int what, int data);</pre>
+<p>
+Controls the garbage collector.
+<p>
+This function performs several tasks,
+according to the value of the parameter <code>what</code>:
+<ul>
+<li><b><code>LUA_GCSTOP</code>: </b>
+stops the garbage collector.
+</li>
+<li><b><code>LUA_GCRESTART</code>: </b>
+restarts the garbage collector.
+</li>
+<li><b><code>LUA_GCCOLLECT</code>: </b>
+performs a full garbage-collection cycle.
+</li>
+<li><b><code>LUA_GCCOUNT</code>: </b>
+returns the current amount of memory (in Kbytes) in use by Lua.
+</li>
+<li><b><code>LUA_GCCOUNTB</code>: </b>
+returns the remainder of dividing the current amount of bytes of
+memory in use by Lua by 1024.
+</li>
+<li><b><code>LUA_GCSTEP</code>: </b>
+performs an incremental step of garbage collection.
+</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">&sect;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">&sect;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, &ndash;]</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">&sect;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, &ndash;]</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">&sect;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), &ndash;]</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&nbsp;1.
+Otherwise,
+the function returns&nbsp;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">&sect;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, &ndash;]</span>
+<pre>int lua_gettop (lua_State *L);</pre>
+<p>
+Returns the index of the top element in the stack.
+Because indices start at&nbsp;1,
+this result is equal to the number of elements in the stack;
+in particular, 0&nbsp;means an empty stack.
+<hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p>
+<span class="apii">[-0, +1, &ndash;]</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, &ndash;]</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</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, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</span>
+<pre>int lua_iscfunction (lua_State *L, int index);</pre>
+<p>
+Returns 1 if the value at the given index is a C&nbsp;function,
+and 0&nbsp;otherwise.
+<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</span>
+<pre>int lua_isnone (lua_State *L, int index);</pre>
+<p>
+Returns 1 if the given index is not valid,
+and 0&nbsp;otherwise.
+<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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&nbsp;otherwise.
+<hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</span>
+<pre>int lua_isyieldable (lua_State *L);</pre>
+<p>
+Returns 1 if the given coroutine can yield,
+and 0&nbsp;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 numerical 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">&sect;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">&sect;3.4.7</a>) and
+may trigger a metamethod for the "length" event (see <a href="#2.4">&sect;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, &ndash;]</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 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">&sect;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">&sect;4.5</a>).
+When loading main chunks,
+this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">&sect;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, &ndash;]</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>e</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>e</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>e</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&ndash;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 double 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.
+(See <code>LUA_REAL</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), &ndash;]</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 message),
+and returns an error code.
+Like <a href="#lua_call"><code>lua_call</code></a>,
+<a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
+and its arguments from the stack.
+<p>
+If <code>msgh</code> is 0,
+then the error message returned on the stack
+is exactly the original error message.
+Otherwise, <code>msgh</code> is the stack index of a
+<em>message handler</em>.
+(In the current implementation, this index cannot be a pseudo-index.)
+In case of runtime errors,
+this function will be called with the error message
+and its return value will be the message
+returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
+<p>
+Typically, the message handler is used to add more debug
+information to the error message, such as a stack traceback.
+Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
+since by then the stack has unwound.
+<p>
+The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns 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), &ndash;]</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">&sect;4.7</a>).
+<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
+<span class="apii">[-n, +0, &ndash;]</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, &ndash;]</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>e</em>]</span>
+<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
+<p>
+Pushes a new C&nbsp;closure onto the stack.
+<p>
+When a C&nbsp;function is created,
+it is possible to associate some values with it,
+thus creating a C&nbsp;closure (see <a href="#4.4">&sect;4.4</a>);
+these values are then accessible to the function whenever it is called.
+To associate values with a C&nbsp;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&nbsp;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&nbsp;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, &ndash;]</span>
+<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
+<p>
+Pushes a C&nbsp;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&nbsp;function.
+<p>
+Any function to be registered in Lua must
+follow the correct protocol to receive its parameters
+and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
+<p>
+<code>lua_pushcfunction</code> is defined as a macro:
+<pre>
+#define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)
+</pre><p>
+Note that <code>f</code> is used twice.
+<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&nbsp;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>%L</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>
+<hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
+<span class="apii">[-0, +1, &ndash;]</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, &ndash;]</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, &ndash;]</span>
+<pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
+<p>
+Pushes a light userdata onto the stack.
+<p>
+Userdata represent C&nbsp;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&nbsp;address.
+<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
+<span class="apii">[-0, +1, <em>e</em>]</span>
+<pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre>
+<p>
+This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
+but can be used only when <code>s</code> is a literal string.
+It automatically provides the string length.
+<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
+<span class="apii">[-0, +1, <em>e</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, &ndash;]</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, &ndash;]</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>e</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, &ndash;]</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, &ndash;]</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>e</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, &ndash;]</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 metamethods).
+Otherwise returns&nbsp;0.
+Also returns&nbsp;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, &ndash;]</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, &ndash;]</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 metamethods.
+<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, &ndash;]</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 metamethods.
+<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, &ndash;]</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&nbsp;0.
+<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
+<span class="apii">[-2, +0, <em>e</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>e</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 metamethods.
+<hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
+<span class="apii">[-1, +0, <em>e</em>]</span>
+<pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre>
+<p>
+Does the equivalent of <code>t[k] = v</code>,
+where <code>t</code> is the table at the given index,
+<code>k</code> is the pointer <code>p</code> represented 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 metamethods.
+<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
+<pre>typedef const char * (*lua_Reader) (lua_State *L,
+void *data,
+size_t *size);</pre>
+<p>
+The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
+Every time it needs another piece of the chunk,
+<a href="#lua_load"><code>lua_load</code></a> calls the reader,
+passing along its <code>data</code> parameter.
+The reader must return a pointer to a block of memory
+with a new piece of the chunk
+and set <code>size</code> to the block size.
+The block must exist until the reader function is called again.
+To signal the end of the chunk,
+the reader must return <code>NULL</code> or set <code>size</code> to zero.
+The reader function may return pieces of any size greater than zero.
+<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
+<span class="apii">[-0, +0, <em>e</em>]</span>
+<pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre>
+<p>
+Sets the C function <code>f</code> as the new value of global <code>name</code>.
+It is defined as a macro:
+<pre>
+#define lua_register(L,n,f) \
+(lua_pushcfunction(L, f), lua_setglobal(L, n))
+</pre>
+<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
+<span class="apii">[-1, +0, &ndash;]</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, &ndash;]</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 the given index),
+and then pops the top element.
+<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
+<span class="apii">[-?, +?, &ndash;]</span>
+<pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre>
+<p>
+Starts and resumes a coroutine in a given thread.
+<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 message 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, &ndash;]</span>
+<pre>void lua_rotate (lua_State *L, int idx, int n);</pre>
+<p>
+Rotates the stack elements from <code>idx</code> to the top <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.
+<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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">&sect;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">&sect;2.4</a>).
+<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
+<span class="apii">[-1, +0, &ndash;]</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">&sect;2.4</a>).
+<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
+<span class="apii">[-?, +?, &ndash;]</span>
+<pre>void lua_settop (lua_State *L, int index);</pre>
+<p>
+Accepts any index, or&nbsp;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&nbsp;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, &ndash;]</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, &ndash;]</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, &ndash;]</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">&sect;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, &ndash;]</span>
+<pre>int lua_toboolean (lua_State *L, int index);</pre>
+<p>
+Converts the Lua value at the given index to a C&nbsp;boolean
+value (0&nbsp;or&nbsp;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, &ndash;]</span>
+<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
+<p>
+Converts a value at the given index to a C&nbsp;function.
+That value must be a C&nbsp;function;
+otherwise, returns <code>NULL</code>.
+<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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, &ndash;]</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">&sect;3.4.3</a>);
+otherwise, <code>lua_tointegerx</code> returns&nbsp;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>e</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&nbsp;string.
+If <code>len</code> is not <code>NULL</code>,
+it also sets <code>*len</code> with the string length.
+The Lua value must be a string or a number;
+otherwise, the function returns <code>NULL</code>.
+If the value is a number,
+then <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 fully aligned pointer
+to a string inside the Lua state.
+This string always has a zero ('<code>\0</code>')
+after its last character (as in&nbsp;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, &ndash;]</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, &ndash;]</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&nbsp;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">&sect;3.4.3</a>);
+otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns&nbsp;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, &ndash;]</span>
+<pre>const void *lua_topointer (lua_State *L, int index);</pre>
+<p>
+Converts the value at the given index to a generic
+C&nbsp;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 debug information.
+<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
+<span class="apii">[-0, +0, <em>e</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, &ndash;]</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, &ndash;]</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, &ndash;]</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>,
+<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, &ndash;]</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, &ndash;]</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">&sect;4.4</a>).
+<hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
+<span class="apii">[-0, +0, <em>v</em>]</span>
+<pre>const lua_Number *lua_version (lua_State *L);</pre>
+<p>
+Returns the address of the version number 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&nbsp;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">[-?, +?, &ndash;]</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">&sect;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&nbsp;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">&sect;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 hook (see <a href="#4.9">&sect;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 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 &ndash; <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&nbsp;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&nbsp;for C&nbsp;functions).
+</li>
+<li><b><code>isvararg</code>: </b>
+true if the function is a vararg function
+(always true for C&nbsp;functions).
+</li>
+</ul>
+<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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, &ndash;]</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, &ndash;]</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>&gt;</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, "&gt;S", &amp;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), &ndash;]</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, &ndash;]</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&nbsp;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), &ndash;]</span>
+<pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
+<p>
+Gets information about a closure's upvalue.
+(For Lua functions,
+upvalues are the external local variables that the function uses,
+and that are consequently included in its closure.)
+<a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
+pushes the upvalue's value onto the stack,
+and returns its name.
+<code>funcindex</code> points to the closure in the stack.
+(Upvalues have no particular order,
+as they are active through the whole function.
+So, they are numbered in an arbitrary order.)
+<p>
+Returns <code>NULL</code> (and pushes nothing)
+when the index is greater than the number of upvalues.
+For C&nbsp;functions, this function uses the empty string <code>""</code>
+as a name for all upvalues.
+<hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
+<pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
+<p>
+Type for debugging hook functions.
+<p>
+Whenever a hook is called, its <code>ar</code> argument has its field
+<code>event</code> set to the specific event that triggered the hook.
+Lua identifies these events with the following constants:
+<a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
+<a name="pdf-LUA_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
+and they cannot yield any value;
+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.
+<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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, &ndash;]</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.
+Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
+(see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
+<a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
+to the variable and returns its name.
+It also pops the value from the stack.
+<p>
+Returns <code>NULL</code> (and pops nothing)
+when the index is greater than
+the number of active local variables.
+<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
+<span class="apii">[-(0|1), +0, &ndash;]</span>
+<pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
+<p>
+Sets the value of a closure's upvalue.
+It assigns the value at the top of the stack
+to the upvalue and returns its name.
+It also pops the value from the stack.
+Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
+(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
+<p>
+Returns <code>NULL</code> (and pops nothing)
+when the index is greater than the number of upvalues.
+<hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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>.
+Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
+(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>)
+(but <code>n</code> cannot be greater than the number of upvalues).
+<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.
+<hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
+<span class="apii">[-0, +0, &ndash;]</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 &ndash; <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&nbsp;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 &ndash; <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>e</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>e</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">[-?, +?, <em>e</em>]</span>
+<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
+<p>
+Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
+a string of length <code>n</code> previously copied to the
+buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
+<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
+<span class="apii">[-?, +?, <em>e</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>e</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&nbsp;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, &amp;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(&amp;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, &amp;b, sz)</code>.</li>
+<li>Then copy the string into that space.</li>
+<li>
+Finish by calling <code>luaL_pushresultsize(&amp;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, &ndash;]</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>e</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&nbsp;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, &ndash;]</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, +?, &ndash;]</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&nbsp;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>e</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>e</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>e</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, &ndash;]</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>).
+If there is no metatable associated with <code>tname</code>,
+returns false and pushes <b>nil</b>.
+<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>e</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">&sect;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, &ndash;]</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, &ndash;]</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>e</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>e</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, &ndash;]</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>e</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>e</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>e</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, &ndash;]</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&nbsp;C <code>realloc</code> function
+and then sets a panic function (see <a href="#4.6">&sect;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_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.
+<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>e</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>e</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>e</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>e</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>e</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>e</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, &ndash;]</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,
+the field value is changed 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>e</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&nbsp;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>e</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, &ndash;]</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, &ndash;]</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>e</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&nbsp;0 is the running function,
+level&nbsp;1 is the function that called the running function,
+etc.
+<p>
+This function is used to build a prefix for error messages.
+<h1>6 &ndash; <a name="6">Standard Libraries</a></h1>
+<p>
+The standard Lua libraries provide useful functions
+that are implemented directly through the C&nbsp;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&nbsp;API
+and are provided as separate C&nbsp;modules.
+Currently, Lua has the following standard libraries:
+<ul>
+<li>basic library (<a href="#6.1">&sect;6.1</a>);</li>
+<li>coroutine library (<a href="#6.2">&sect;6.2</a>);</li>
+<li>package library (<a href="#6.3">&sect;6.3</a>);</li>
+<li>string manipulation (<a href="#6.4">&sect;6.4</a>);</li>
+<li>basic UTF-8 support (<a href="#6.5">&sect;6.5</a>);</li>
+<li>table manipulation (<a href="#6.6">&sect;6.6</a>);</li>
+<li>mathematical functions (<a href="#6.7">&sect;6.7</a>) (sin, log, etc.);</li>
+<li>input and output (<a href="#6.8">&sect;6.8</a>);</li>
+<li>operating system facilities (<a href="#6.9">&sect;6.9</a>);</li>
+<li>debug facilities (<a href="#6.10">&sect;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&nbsp;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 &ndash; <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">&sect;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">&sect;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&nbsp;1 (the default), the error position is where the
+<code>error</code> function was called.
+Level&nbsp;2 points the error to where the function
+that called <code>error</code> was called; and so on.
+Passing a level&nbsp;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">&sect;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&ndash;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">&sect;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">&sect;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 numeric 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&ndash;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, &middot;&middot;&middot;])</code></a></h3>
+<p>
+Calls function <code>f</code> with
+the given arguments in <em>protected mode</em>.
+This means that any error inside&nbsp;<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 (&middot;&middot;&middot;)</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 any metamethod.
+Returns a boolean.
+<p>
+<hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
+Gets the real value of <code>table[index]</code>,
+without invoking any metamethod.
+<code>table</code> must be a table;
+<code>index</code> may be any value.
+<p>
+<hr><h3><a name="pdf-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 any 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 any 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, &middot;&middot;&middot;)</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.
+(You cannot change the metatable of other types from Lua, only from&nbsp;C.)
+If <code>metatable</code> is <b>nil</b>,
+removes the metatable of the given table.
+If the original metatable has a <code>"__metatable"</code> field,
+raises an error.
+<p>
+This function returns <code>table</code>.
+<p>
+<hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
+<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">&sect;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&nbsp;10, the letter '<code>A</code>' (in either upper or lower case)
+represents&nbsp;10, '<code>B</code>' represents&nbsp;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.
+Floats always produce strings with some
+floating-point indication (either a decimal dot or an exponent).
+(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>
+A global variable (not a function) that
+holds a string containing the current interpreter 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, &middot;&middot;&middot;])</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 &ndash; <a name="6.2">Coroutine Manipulation</a></h2>
+<p>
+The operations related to coroutines comprise a sub-library of
+the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
+See <a href="#2.6">&sect;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 Lua 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, &middot;&middot;&middot;])</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 Lua function.
+Returns a function that resumes the coroutine each time it is called.
+Any arguments passed to the function behave as the
+extra arguments to <code>resume</code>.
+Returns the same values returned by <code>resume</code>,
+except the first boolean.
+In case of error, propagates the error.
+<p>
+<hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (&middot;&middot;&middot;)</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 &ndash; <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&nbsp;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&nbsp;loader.
+<p>
+Lua initializes the C&nbsp;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&nbsp;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&nbsp;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&nbsp;library,
+including if necessary a path and an extension.
+<code>funcname</code> must be the exact name exported by the C&nbsp;library
+(which may depend on the C&nbsp;compiler and linker used).
+<p>
+This function is not supported by Standard&nbsp;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&nbsp;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&nbsp;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&nbsp;library,
+this searcher first uses a dynamic link facility to link the
+application with the library.
+Then it tries to find a C&nbsp;function inside the library to
+be used as the loader.
+The name of this C&nbsp;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&nbsp;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&nbsp;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&nbsp;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 &ndash; <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&nbsp;1
+(not at&nbsp;0, as in C).
+Indices are allowed to be negative and are interpreted as indexing backwards,
+from the end of the string.
+Thus, the last character is at position -1, and so on.
+<p>
+The string library provides all its functions inside the table
+<a name="pdf-string"><code>string</code></a>.
+It also sets a metatable for strings
+where the <code>__index</code> field points to the <code>string</code> table.
+Therefore, you can use the string functions in object-oriented style.
+For instance, <code>string.byte(s,i)</code>
+can be written as <code>s:byte(i)</code>.
+<p>
+The string library assumes one-byte character encodings.
+<p>
+<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
+Returns the internal numerical codes of the characters <code>s[i]</code>,
+<code>s[i+1]</code>, ..., <code>s[j]</code>.
+The default value for <code>i</code> is&nbsp;1;
+the default value for <code>j</code> is&nbsp;<code>i</code>.
+These indices are corrected
+following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
+<p>
+Numerical codes are not necessarily portable across platforms.
+<p>
+<hr><h3><a name="pdf-string.char"><code>string.char (&middot;&middot;&middot;)</code></a></h3>
+Receives zero or more integers.
+Returns a string with length equal to the number of arguments,
+in which each character has the internal numerical code equal
+to its corresponding argument.
+<p>
+Numerical 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 is created without debug information
+about the function
+(local variable names, lines, etc.).
+<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">&sect;6.4.1</a>) in the string <code>s</code>.
+If it finds a match, then <code>find</code> returns the indices of&nbsp;<code>s</code>
+where this occurrence starts and ends;
+otherwise, it returns <b>nil</b>.
+A third, optional numerical argument <code>init</code> specifies
+where to start the search;
+its default value is&nbsp;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, &middot;&middot;&middot;)</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&nbsp;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>.
+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> and <code>a</code> (when available),
+<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.
+Option <code>q</code> expects a string;
+option <code>s</code> expects a string without embedded zeros.
+If the argument to option <code>s</code> is not a string,
+it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
+<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">&sect;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">&sect;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&nbsp;<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&nbsp;<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")
+--&gt; x="hello hello world world"
+x = string.gsub("hello world", "%w+", "%0 %0", 1)
+--&gt; x="hello hello world"
+x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
+--&gt; x="world hello Lua from"
+x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
+--&gt; x="home = /home/roberto, user = roberto"
+x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
+return load(s)()
+end)
+--&gt; x="4+5 = 9"
+local t = {name="lua", version="5.3"}
+x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
+--&gt; 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">&sect;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 numerical argument <code>init</code> specifies
+where to start the search;
+its default value is&nbsp;1 and can be negative.
+<p>
+<hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, &middot;&middot;&middot;)</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">&sect;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">&sect;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>
+<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">&sect;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 &ndash; <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 punctuations, 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>
+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&nbsp;<em>x</em>, end with&nbsp;<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&nbsp;1);
+the character matching "<code>.</code>" is captured with number&nbsp;2,
+and the part matching "<code>%s*</code>" has number&nbsp;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&nbsp;and&nbsp;5.
+<h3>6.4.2 &ndash; <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>&lt;</code>: </b>sets little endian</li>
+<li><b><code>&gt;</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 &lt;=&gt;!</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 &ndash; <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 (&middot;&middot;&middot;)</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">&sect;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 &ndash; <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">&sect;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] &middot;&middot;&middot; 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], &middot;&middot;&middot;, 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>.
+This function performs the equivalent to the following
+multiple assignment:
+<code>a2[t],&middot;&middot;&middot; = a1[f],&middot;&middot;&middot;,a1[e]</code>.
+The default for <code>a2</code> is <code>a1</code>.
+The destination range can overlap with the source range.
+Index <code>f</code> must be positive.
+<p>
+<hr><h3><a name="pdf-table.pack"><code>table.pack (&middot;&middot;&middot;)</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], &middot;&middot;&middot;, 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 <code>not comp(list[i+1],list[i])</code> will be true after the sort).
+If <code>comp</code> is not given,
+then the standard Lua operator <code>&lt;</code> is used instead.
+<p>
+The sort algorithm is not stable;
+that is, elements considered equal by the given order
+may have their relative positions changed by the sort.
+<p>
+<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], &middot;&middot;&middot;, list[j]
+</pre><p>
+By default, <code>i</code> is&nbsp;1 and <code>j</code> is <code>#list</code>.
+<h2>6.7 &ndash; <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 numerical 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, &middot;&middot;&middot;)</code></a></h3>
+<p>
+Returns the argument with the maximum value,
+according to the Lua operator <code>&lt;</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, &middot;&middot;&middot;)</code></a></h3>
+<p>
+Returns the argument with the minimum value,
+according to the Lua operator <code>&lt;</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>&pi;</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>m-n</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.
+No guarantees can be given for its statistical properties.
+<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 &ndash; <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 &middot;&middot;&middot;])</code></a></h3>
+<p>
+Opens the given file name in read mode
+and returns an iterator function that
+works like <code>file:lines(&middot;&middot;&middot;)</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>.
+It returns a new file handle,
+or, in case of errors, <b>nil</b> plus an error message.
+<p>
+The <code>mode</code> string can be any of the following:
+<ul>
+<li><b>"<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 (&middot;&middot;&middot;)</code></a></h3>
+<p>
+Equivalent to <code>io.input():read(&middot;&middot;&middot;)</code>.
+<p>
+<hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
+<p>
+Returns a handle for a temporary file.
+This file is opened in update mode
+and it is automatically removed when the program ends.
+<p>
+<hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
+<p>
+Checks whether <code>obj</code> is a valid file handle.
+Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
+<code>"closed file"</code> if <code>obj</code> is a closed file handle,
+or <b>nil</b> if <code>obj</code> is not a file handle.
+<p>
+<hr><h3><a name="pdf-io.write"><code>io.write (&middot;&middot;&middot;)</code></a></h3>
+<p>
+Equivalent to <code>io.output():write(&middot;&middot;&middot;)</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 (&middot;&middot;&middot;)</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 (&middot;&middot;&middot;)</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 number;
+if that prefix does not form a valid number
+(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>i</code>": </b>
+reads an integral number and returns it as an integer.
+</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 (&middot;&middot;&middot;)</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 &ndash; <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> (four digits), <code>month</code> (1&ndash;12), <code>day</code> (1&ndash;31),
+<code>hour</code> (0&ndash;23), <code>min</code> (0&ndash;59), <code>sec</code> (0&ndash;61),
+<code>wday</code> (weekday, Sunday is&nbsp;1),
+<code>yday</code> (day of the year),
+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&nbsp;C function <code>strftime</code>.
+<p>
+When called without arguments,
+<code>date</code> returns a reasonable date and time representation that depends on
+the host system and on the current locale
+(that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
+<p>
+On non-POSIX systems,
+this function may be not thread safe
+because of its reliance on C&nbsp;function <code>gmtime</code> and C&nbsp;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&nbsp;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&nbsp;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&nbsp;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 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>).
+For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
+<p>
+The returned value is a number, whose meaning depends on your system.
+In POSIX, Windows, and some other systems,
+this number counts the number
+of seconds since some given start time (the "epoch").
+In other systems, the meaning is not specified,
+and the number returned by <code>time</code> can be used only as an argument to
+<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 &ndash; <a name="6.10">The Debug Library</a></h2>
+<p>
+This library provides
+the functionality of the debug interface (<a href="#4.9">&sect;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&nbsp;0 is the current function (<code>getinfo</code> itself);
+level&nbsp;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 table with a name for the current function,
+if a reasonable name can be found,
+and the expression <code>debug.getinfo(print)</code>
+returns a table with all available information
+about the <a href="#pdf-print"><code>print</code></a> function.
+<p>
+<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] 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&nbsp;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">&sect;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&nbsp;2 to get more information about
+the running function
+(level&nbsp;0 is the <code>getinfo</code> function,
+and level&nbsp;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 &ndash; <a name="7">Lua Standalone</a></h1>
+<p>
+Although Lua has been designed as an extension language,
+to be embedded in a host C&nbsp;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>, &middot;&middot;&middot;, <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>
+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&nbsp;<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 &ndash; <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&nbsp;5.2 to Lua&nbsp;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 &ndash; <a name="8.1">Changes in the Language</a></h2>
+<ul>
+<li>
+The main difference between Lua&nbsp;5.2 and Lua&nbsp;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&nbsp;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&nbsp;5.2.)
+</li>
+</ul>
+<h2>8.2 &ndash; <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 standard Lua operate on 64-bit integers.)
+</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 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&nbsp;5.2 already worked that way,
+but it did not document the change.)
+</li>
+</ul>
+<h2>8.3 &ndash; <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 &ndash; <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">&sect;3.4.8</a>;
+for a description of the terminals
+Name, Numeral,
+and LiteralString, see <a href="#3.1">&sect;3.1</a>.)
+<pre>
+	chunk ::= block
+	block ::= {stat} [retstat]
+	stat ::=  &lsquo;<b>;</b>&rsquo; |
+		 varlist &lsquo;<b>=</b>&rsquo; 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 &lsquo;<b>=</b>&rsquo; exp &lsquo;<b>,</b>&rsquo; exp [&lsquo;<b>,</b>&rsquo; 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 [&lsquo;<b>=</b>&rsquo; explist]
+	retstat ::= <b>return</b> [explist] [&lsquo;<b>;</b>&rsquo;]
+	label ::= &lsquo;<b>::</b>&rsquo; Name &lsquo;<b>::</b>&rsquo;
+	funcname ::= Name {&lsquo;<b>.</b>&rsquo; Name} [&lsquo;<b>:</b>&rsquo; Name]
+	varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
+	var ::=  Name | prefixexp &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; | prefixexp &lsquo;<b>.</b>&rsquo; Name
+	namelist ::= Name {&lsquo;<b>,</b>&rsquo; Name}
+	explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
+	exp ::=  <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | &lsquo;<b>...</b>&rsquo; | functiondef |
+		 prefixexp | tableconstructor | exp binop exp | unop exp
+	prefixexp ::= var | functioncall | &lsquo;<b>(</b>&rsquo; exp &lsquo;<b>)</b>&rsquo;
+	functioncall ::=  prefixexp args | prefixexp &lsquo;<b>:</b>&rsquo; Name args
+	args ::=  &lsquo;<b>(</b>&rsquo; [explist] &lsquo;<b>)</b>&rsquo; | tableconstructor | LiteralString
+	functiondef ::= <b>function</b> funcbody
+	funcbody ::= &lsquo;<b>(</b>&rsquo; [parlist] &lsquo;<b>)</b>&rsquo; block <b>end</b>
+	parlist ::= namelist [&lsquo;<b>,</b>&rsquo; &lsquo;<b>...</b>&rsquo;] | &lsquo;<b>...</b>&rsquo;
+	tableconstructor ::= &lsquo;<b>{</b>&rsquo; [fieldlist] &lsquo;<b>}</b>&rsquo;
+	fieldlist ::= field {fieldsep field} [fieldsep]
+	field ::= &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; &lsquo;<b>=</b>&rsquo; exp | Name &lsquo;<b>=</b>&rsquo; exp | exp
+	fieldsep ::= &lsquo;<b>,</b>&rsquo; | &lsquo;<b>;</b>&rsquo;
+	binop ::=  &lsquo;<b>+</b>&rsquo; | &lsquo;<b>-</b>&rsquo; | &lsquo;<b>*</b>&rsquo; | &lsquo;<b>/</b>&rsquo; | &lsquo;<b>//</b>&rsquo; | &lsquo;<b>^</b>&rsquo; | &lsquo;<b>%</b>&rsquo; |
+		 &lsquo;<b>&amp;</b>&rsquo; | &lsquo;<b>~</b>&rsquo; | &lsquo;<b>|</b>&rsquo; | &lsquo;<b>&gt;&gt;</b>&rsquo; | &lsquo;<b>&lt;&lt;</b>&rsquo; | &lsquo;<b>..</b>&rsquo; |
+		 &lsquo;<b>&lt;</b>&rsquo; | &lsquo;<b>&lt;=</b>&rsquo; | &lsquo;<b>&gt;</b>&rsquo; | &lsquo;<b>&gt;=</b>&rsquo; | &lsquo;<b>==</b>&rsquo; | &lsquo;<b>~=</b>&rsquo; |
+		 <b>and</b> | <b>or</b>
+	unop ::= &lsquo;<b>-</b>&rsquo; | <b>not</b> | &lsquo;<b>#</b>&rsquo; | &lsquo;<b>~</b>&rsquo;
+</pre>
+<p>
+<HR>
+<SMALL CLASS="footer">
+Last update:
+Fri Jan 16 00:58:20 BRST 2015
+</SMALL>
+<!--
+Last change: minor edit
+-->
+</body></html>

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