Context Navigation

source: bootcd/isolinux/syslinux-6.03/com32/lua/doc/manual.html

Last change on this file was e16e8f2, checked in by Edwin Eefting <edwin@datux.nl>, 3 years ago
bootstuff
Property mode set to `100644`
File size: 299.1 KB

Line
1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2	<html>
3
4	<head>
5	<title>Lua 5.2 Reference Manual</title>
6	<link rel="stylesheet" type="text/css" href="lua.css">
7	<link rel="stylesheet" type="text/css" href="manual.css">
8	<META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1">
9	</head>
10
11	<body>
12
13	<hr>
14	<h1>
15	<a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a>
16	Lua 5.2 Reference Manual
17	</h1>
18
19	by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
20	<p>
21	<small>
22	Copyright © 2011–2013 Lua.org, PUC-Rio.
23	Freely available under the terms of the
24	<a href="http://www.lua.org/license.html">Lua license</a>.
25	</small>
26	<hr>
27	<p>
28
29	<a href="contents.html#contents">contents</A>
30	·
31	<a href="contents.html#index">index</A>
32
33	<!-- ====================================================================== -->
34	<p>
35
36	<!-- $Id: manual.of,v 1.103 2013/03/14 18:51:56 roberto Exp $ -->
37
38
39
40
41	<h1>1 – <a name="1">Introduction</a></h1>
42
43	<p>
44	Lua is an extension programming language designed to support
45	general procedural programming with data description
46	facilities.
47	It also offers good support for object-oriented programming,
48	functional programming, and data-driven programming.
49	Lua is intended to be used as a powerful, lightweight,
50	embeddable scripting language for any program that needs one.
51	Lua is implemented as a library, written in <em>clean C</em>,
52	the common subset of Standard C and C++.
53
54
55	<p>
56	Being an extension language, Lua has no notion of a "main" program:
57	it only works <em>embedded</em> in a host client,
58	called the <em>embedding program</em> or simply the <em>host</em>.
59	The host program can invoke functions to execute a piece of Lua code,
60	can write and read Lua variables,
61	and can register C functions to be called by Lua code.
62	Through the use of C functions, Lua can be augmented to cope with
63	a wide range of different domains,
64	thus creating customized programming languages sharing a syntactical framework.
65	The Lua distribution includes a sample host program called <code>lua</code>,
66	which uses the Lua library to offer a complete, standalone Lua interpreter,
67	for interactive or batch use.
68
69
70	<p>
71	Lua is free software,
72	and is provided as usual with no guarantees,
73	as stated in its license.
74	The implementation described in this manual is available
75	at Lua's official web site, <code>www.lua.org</code>.
76
77
78	<p>
79	Like any other reference manual,
80	this document is dry in places.
81	For a discussion of the decisions behind the design of Lua,
82	see the technical papers available at Lua's web site.
83	For a detailed introduction to programming in Lua,
84	see Roberto's book, <em>Programming in Lua</em>.
85
86
87
88	<h1>2 – <a name="2">Basic Concepts</a></h1>
89
90	<p>
91	This section describes the basic concepts of the language.
92
93
94
95	<h2>2.1 – <a name="2.1">Values and Types</a></h2>
96
97	<p>
98	Lua is a <em>dynamically typed language</em>.
99	This means that
100	variables do not have types; only values do.
101	There are no type definitions in the language.
102	All values carry their own type.
103
104
105	<p>
106	All values in Lua are <em>first-class values</em>.
107	This means that all values can be stored in variables,
108	passed as arguments to other functions, and returned as results.
109
110
111	<p>
112	There are eight basic types in Lua:
113	<em>nil</em>, <em>boolean</em>, <em>number</em>,
114	<em>string</em>, <em>function</em>, <em>userdata</em>,
115	<em>thread</em>, and <em>table</em>.
116	<em>Nil</em> is the type of the value <b>nil</b>,
117	whose main property is to be different from any other value;
118	it usually represents the absence of a useful value.
119	<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
120	Both <b>nil</b> and <b>false</b> make a condition false;
121	any other value makes it true.
122	<em>Number</em> represents real (double-precision floating-point) numbers.
123	Operations on numbers follow the same rules of
124	the underlying C implementation,
125	which, in turn, usually follows the IEEE 754 standard.
126	(It is easy to build Lua interpreters that use other
127	internal representations for numbers,
128	such as single-precision floats or long integers;
129	see file <code>luaconf.h</code>.)
130	<em>String</em> represents immutable sequences of bytes.
131
132	Lua is 8-bit clean:
133	strings can contain any 8-bit value,
134	including embedded zeros ('<code>\0</code>').
135
136
137	<p>
138	Lua can call (and manipulate) functions written in Lua and
139	functions written in C
140	(see <a href="#3.4.9">§3.4.9</a>).
141
142
143	<p>
144	The type <em>userdata</em> is provided to allow arbitrary C data to
145	be stored in Lua variables.
146	A userdata value is a pointer to a block of raw memory.
147	There are two kinds of userdata:
148	full userdata, where the block of memory is managed by Lua,
149	and light userdata, where the block of memory is managed by the host.
150	Userdata has no predefined operations in Lua,
151	except assignment and identity test.
152	By using <em>metatables</em>,
153	the programmer can define operations for full userdata values
154	(see <a href="#2.4">§2.4</a>).
155	Userdata values cannot be created or modified in Lua,
156	only through the C API.
157	This guarantees the integrity of data owned by the host program.
158
159
160	<p>
161	The type <em>thread</em> represents independent threads of execution
162	and it is used to implement coroutines (see <a href="#2.6">§2.6</a>).
163	Do not confuse Lua threads with operating-system threads.
164	Lua supports coroutines on all systems,
165	even those that do not support threads.
166
167
168	<p>
169	The type <em>table</em> implements associative arrays,
170	that is, arrays that can be indexed not only with numbers,
171	but with any Lua value except <b>nil</b> and NaN
172	(<em>Not a Number</em>, a special numeric value used to represent
173	undefined or unrepresentable results, such as <code>0/0</code>).
174	Tables can be <em>heterogeneous</em>;
175	that is, they can contain values of all types (except <b>nil</b>).
176	Any key with value <b>nil</b> is not considered part of the table.
177	Conversely, any key that is not part of a table has
178	an associated value <b>nil</b>.
179
180
181	<p>
182	Tables are the sole data structuring mechanism in Lua;
183	they can be used to represent ordinary arrays, sequences,
184	symbol tables, sets, records, graphs, trees, etc.
185	To represent records, Lua uses the field name as an index.
186	The language supports this representation by
187	providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
188	There are several convenient ways to create tables in Lua
189	(see <a href="#3.4.8">§3.4.8</a>).
190
191
192	<p>
193	We use the term <em>sequence</em> to denote a table where
194	the set of all positive numeric keys is equal to <em>{1..n}</em>
195	for some integer <em>n</em>,
196	which is called the length of the sequence (see <a href="#3.4.6">§3.4.6</a>).
197
198
199	<p>
200	Like indices,
201	the values of table fields can be of any type.
202	In particular,
203	because functions are first-class values,
204	table fields can contain functions.
205	Thus tables can also carry <em>methods</em> (see <a href="#3.4.10">§3.4.10</a>).
206
207
208	<p>
209	The indexing of tables follows
210	the definition of raw equality in the language.
211	The expressions <code>a[i]</code> and <code>a[j]</code>
212	denote the same table element
213	if and only if <code>i</code> and <code>j</code> are raw equal
214	(that is, equal without metamethods).
215
216
217	<p>
218	Tables, functions, threads, and (full) userdata values are <em>objects</em>:
219	variables do not actually <em>contain</em> these values,
220	only <em>references</em> to them.
221	Assignment, parameter passing, and function returns
222	always manipulate references to such values;
223	these operations do not imply any kind of copy.
224
225
226	<p>
227	The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
228	of a given value (see <a href="#6.1">§6.1</a>).
229
230
231
232
233
234	<h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2>
235
236	<p>
237	As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>,
238	any reference to a global name <code>var</code> is syntactically translated
239	to <code>_ENV.var</code>.
240	Moreover, every chunk is compiled in the scope of
241	an external local variable called <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>),
242	so <code>_ENV</code> itself is never a global name in a chunk.
243
244
245	<p>
246	Despite the existence of this external <code>_ENV</code> variable and
247	the translation of global names,
248	<code>_ENV</code> is a completely regular name.
249	In particular,
250	you can define new variables and parameters with that name.
251	Each reference to a global name uses the <code>_ENV</code> that is
252	visible at that point in the program,
253	following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>).
254
255
256	<p>
257	Any table used as the value of <code>_ENV</code> is called an <em>environment</em>.
258
259
260	<p>
261	Lua keeps a distinguished environment called the <em>global environment</em>.
262	This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>).
263	In Lua, the variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value.
264
265
266	<p>
267	When Lua compiles a chunk,
268	it initializes the value of its <code>_ENV</code> upvalue
269	with the global environment (see <a href="#pdf-load"><code>load</code></a>).
270	Therefore, by default,
271	global variables in Lua code refer to entries in the global environment.
272	Moreover, all standard libraries are loaded in the global environment
273	and several functions there operate on that environment.
274	You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>)
275	to load a chunk with a different environment.
276	(In C, you have to load the chunk and then change the value
277	of its first upvalue.)
278
279
280	<p>
281	If you change the global environment in the registry
282	(through C code or the debug library),
283	all chunks loaded after the change will get the new environment.
284	Previously loaded chunks are not affected, however,
285	as each has its own reference to the environment in its <code>_ENV</code> variable.
286	Moreover, the variable <a href="#pdf-_G"><code>_G</code></a>
287	(which is stored in the original global environment)
288	is never updated by Lua.
289
290
291
292
293
294	<h2>2.3 – <a name="2.3">Error Handling</a></h2>
295
296	<p>
297	Because Lua is an embedded extension language,
298	all Lua actions start from C code in the host program
299	calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
300	Whenever an error occurs during
301	the compilation or execution of a Lua chunk,
302	control returns to the host,
303	which can take appropriate measures
304	(such as printing an error message).
305
306
307	<p>
308	Lua code can explicitly generate an error by calling the
309	<a href="#pdf-error"><code>error</code></a> function.
310	If you need to catch errors in Lua,
311	you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a>
312	to call a given function in <em>protected mode</em>.
313
314
315	<p>
316	Whenever there is an error,
317	an <em>error object</em> (also called an <em>error message</em>)
318	is propagated with information about the error.
319	Lua itself only generates errors where the error object is a string,
320	but programs may generate errors with
321	any value for the error object.
322
323
324	<p>
325	When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>,
326	you may give a <em>message handler</em>
327	to be called in case of errors.
328	This function is called with the original error message
329	and returns a new error message.
330	It is called before the error unwinds the stack,
331	so that it can gather more information about the error,
332	for instance by inspecting the stack and creating a stack traceback.
333	This message handler is still protected by the protected call;
334	so, an error inside the message handler
335	will call the message handler again.
336	If this loop goes on, Lua breaks it and returns an appropriate message.
337
338
339
340
341
342	<h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2>
343
344	<p>
345	Every value in Lua can have a <em>metatable</em>.
346	This <em>metatable</em> is an ordinary Lua table
347	that defines the behavior of the original value
348	under certain special operations.
349	You can change several aspects of the behavior
350	of operations over a value by setting specific fields in its metatable.
351	For instance, when a non-numeric value is the operand of an addition,
352	Lua checks for a function in the field "<code>__add</code>" of the value's metatable.
353	If it finds one,
354	Lua calls this function to perform the addition.
355
356
357	<p>
358	The keys in a metatable are derived from the <em>event</em> names;
359	the corresponding values are called <em>metamethods</em>.
360	In the previous example, the event is <code>"add"</code>
361	and the metamethod is the function that performs the addition.
362
363
364	<p>
365	You can query the metatable of any value
366	using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
367
368
369	<p>
370	You can replace the metatable of tables
371	using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function.
372	You cannot change the metatable of other types from Lua
373	(except by using the debug library);
374	you must use the C API for that.
375
376
377	<p>
378	Tables and full userdata have individual metatables
379	(although multiple tables and userdata can share their metatables).
380	Values of all other types share one single metatable per type;
381	that is, there is one single metatable for all numbers,
382	one for all strings, etc.
383	By default, a value has no metatable,
384	but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>).
385
386
387	<p>
388	A metatable controls how an object behaves in arithmetic operations,
389	order comparisons, concatenation, length operation, and indexing.
390	A metatable also can define a function to be called
391	when a userdata or a table is garbage collected.
392	When Lua performs one of these operations over a value,
393	it checks whether this value has a metatable with the corresponding event.
394	If so, the value associated with that key (the metamethod)
395	controls how Lua will perform the operation.
396
397
398	<p>
399	Metatables control the operations listed next.
400	Each operation is identified by its corresponding name.
401	The key for each operation is a string with its name prefixed by
402	two underscores, '<code>__</code>';
403	for instance, the key for operation "add" is the
404	string "<code>__add</code>".
405
406
407	<p>
408	The semantics of these operations is better explained by a Lua function
409	describing how the interpreter executes the operation.
410	The code shown here in Lua is only illustrative;
411	the real behavior is hard coded in the interpreter
412	and it is much more efficient than this simulation.
413	All functions used in these descriptions
414	(<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.)
415	are described in <a href="#6.1">§6.1</a>.
416	In particular, to retrieve the metamethod of a given object,
417	we use the expression
418
419	<pre>
420	metatable(obj)[event]
421	</pre><p>
422	This should be read as
423
424	<pre>
425	rawget(getmetatable(obj) or {}, event)
426	</pre><p>
427	This means that the access to a metamethod does not invoke other metamethods,
428	and access to objects with no metatables does not fail
429	(it simply results in <b>nil</b>).
430
431
432	<p>
433	For the unary <code>-</code> and <code>#</code> operators,
434	the metamethod is called with a dummy second argument.
435	This extra argument is only to simplify Lua's internals;
436	it may be removed in future versions and therefore it is not present
437	in the following code.
438	(For most uses this extra argument is irrelevant.)
439
440
441
442	<ul>
443
444	<li><b>"add": </b>
445	the <code>+</code> operation.
446
447
448
449	<p>
450	The function <code>getbinhandler</code> below defines how Lua chooses a handler
451	for a binary operation.
452	First, Lua tries the first operand.
453	If its type does not define a handler for the operation,
454	then Lua tries the second operand.
455
456	<pre>
457	function getbinhandler (op1, op2, event)
458	return metatable(op1)[event] or metatable(op2)[event]
459	end
460	</pre><p>
461	By using this function,
462	the behavior of the <code>op1 + op2</code> is
463
464	<pre>
465	function add_event (op1, op2)
466	local o1, o2 = tonumber(op1), tonumber(op2)
467	if o1 and o2 then -- both operands are numeric?
468	return o1 + o2 -- '+' here is the primitive 'add'
469	else -- at least one of the operands is not numeric
470	local h = getbinhandler(op1, op2, "__add")
471	if h then
472	-- call the handler with both operands
473	return (h(op1, op2))
474	else -- no handler available: default behavior
475	error(···)
476	end
477	end
478	end
479	</pre><p>
480	</li>
481
482	<li><b>"sub": </b>
483	the <code>-</code> operation.
484
485	Behavior similar to the "add" operation.
486	</li>
487
488	<li><b>"mul": </b>
489	the <code>*</code> operation.
490
491	Behavior similar to the "add" operation.
492	</li>
493
494	<li><b>"div": </b>
495	the <code>/</code> operation.
496
497	Behavior similar to the "add" operation.
498	</li>
499
500	<li><b>"mod": </b>
501	the <code>%</code> operation.
502
503	Behavior similar to the "add" operation,
504	with the operation
505	<code>o1 - floor(o1/o2)*o2</code> as the primitive operation.
506	</li>
507
508	<li><b>"pow": </b>
509	the <code>^</code> (exponentiation) operation.
510
511	Behavior similar to the "add" operation,
512	with the function <code>pow</code> (from the C math library)
513	as the primitive operation.
514	</li>
515
516	<li><b>"unm": </b>
517	the unary <code>-</code> operation.
518
519
520	<pre>
521	function unm_event (op)
522	local o = tonumber(op)
523	if o then -- operand is numeric?
524	return -o -- '-' here is the primitive 'unm'
525	else -- the operand is not numeric.
526	-- Try to get a handler from the operand
527	local h = metatable(op).__unm
528	if h then
529	-- call the handler with the operand
530	return (h(op))
531	else -- no handler available: default behavior
532	error(···)
533	end
534	end
535	end
536	</pre><p>
537	</li>
538
539	<li><b>"concat": </b>
540	the <code>..</code> (concatenation) operation.
541
542
543	<pre>
544	function concat_event (op1, op2)
545	if (type(op1) == "string" or type(op1) == "number") and
546	(type(op2) == "string" or type(op2) == "number") then
547	return op1 .. op2 -- primitive string concatenation
548	else
549	local h = getbinhandler(op1, op2, "__concat")
550	if h then
551	return (h(op1, op2))
552	else
553	error(···)
554	end
555	end
556	end
557	</pre><p>
558	</li>
559
560	<li><b>"len": </b>
561	the <code>#</code> operation.
562
563
564	<pre>
565	function len_event (op)
566	if type(op) == "string" then
567	return strlen(op) -- primitive string length
568	else
569	local h = metatable(op).__len
570	if h then
571	return (h(op)) -- call handler with the operand
572	elseif type(op) == "table" then
573	return #op -- primitive table length
574	else -- no handler available: error
575	error(···)
576	end
577	end
578	end
579	</pre><p>
580	See <a href="#3.4.6">§3.4.6</a> for a description of the length of a table.
581	</li>
582
583	<li><b>"eq": </b>
584	the <code>==</code> operation.
585
586	The function <code>getequalhandler</code> defines how Lua chooses a metamethod
587	for equality.
588	A metamethod is selected only when both values
589	being compared have the same type
590	and the same metamethod for the selected operation,
591	and the values are either tables or full userdata.
592
593	<pre>
594	function getequalhandler (op1, op2)
595	if type(op1) ~= type(op2) or
596	(type(op1) ~= "table" and type(op1) ~= "userdata") then
597	return nil -- different values
598	end
599	local mm1 = metatable(op1).__eq
600	local mm2 = metatable(op2).__eq
601	if mm1 == mm2 then return mm1 else return nil end
602	end
603	</pre><p>
604	The "eq" event is defined as follows:
605
606	<pre>
607	function eq_event (op1, op2)
608	if op1 == op2 then -- primitive equal?
609	return true -- values are equal
610	end
611	-- try metamethod
612	local h = getequalhandler(op1, op2)
613	if h then
614	return not not h(op1, op2)
615	else
616	return false
617	end
618	end
619	</pre><p>
620	Note that the result is always a boolean.
621	</li>
622
623	<li><b>"lt": </b>
624	the <code><</code> operation.
625
626
627	<pre>
628	function lt_event (op1, op2)
629	if type(op1) == "number" and type(op2) == "number" then
630	return op1 < op2 -- numeric comparison
631	elseif type(op1) == "string" and type(op2) == "string" then
632	return op1 < op2 -- lexicographic comparison
633	else
634	local h = getbinhandler(op1, op2, "__lt")
635	if h then
636	return not not h(op1, op2)
637	else
638	error(···)
639	end
640	end
641	end
642	</pre><p>
643	Note that the result is always a boolean.
644	</li>
645
646	<li><b>"le": </b>
647	the <code><=</code> operation.
648
649
650	<pre>
651	function le_event (op1, op2)
652	if type(op1) == "number" and type(op2) == "number" then
653	return op1 <= op2 -- numeric comparison
654	elseif type(op1) == "string" and type(op2) == "string" then
655	return op1 <= op2 -- lexicographic comparison
656	else
657	local h = getbinhandler(op1, op2, "__le")
658	if h then
659	return not not h(op1, op2)
660	else
661	h = getbinhandler(op1, op2, "__lt")
662	if h then
663	return not h(op2, op1)
664	else
665	error(···)
666	end
667	end
668	end
669	end
670	</pre><p>
671	Note that, in the absence of a "le" metamethod,
672	Lua tries the "lt", assuming that <code>a <= b</code> is
673	equivalent to <code>not (b < a)</code>.
674
675
676	<p>
677	As with the other comparison operators,
678	the result is always a boolean.
679	</li>
680
681	<li><b>"index": </b>
682	The indexing access <code>table[key]</code>.
683	Note that the metamethod is tried only
684	when <code>key</code> is not present in <code>table</code>.
685	(When <code>table</code> is not a table,
686	no key is ever present,
687	so the metamethod is always tried.)
688
689
690	<pre>
691	function gettable_event (table, key)
692	local h
693	if type(table) == "table" then
694	local v = rawget(table, key)
695	-- if key is present, return raw value
696	if v ~= nil then return v end
697	h = metatable(table).__index
698	if h == nil then return nil end
699	else
700	h = metatable(table).__index
701	if h == nil then
702	error(···)
703	end
704	end
705	if type(h) == "function" then
706	return (h(table, key)) -- call the handler
707	else return h[key] -- or repeat operation on it
708	end
709	end
710	</pre><p>
711	</li>
712
713	<li><b>"newindex": </b>
714	The indexing assignment <code>table[key] = value</code>.
715	Note that the metamethod is tried only
716	when <code>key</code> is not present in <code>table</code>.
717
718
719	<pre>
720	function settable_event (table, key, value)
721	local h
722	if type(table) == "table" then
723	local v = rawget(table, key)
724	-- if key is present, do raw assignment
725	if v ~= nil then rawset(table, key, value); return end
726	h = metatable(table).__newindex
727	if h == nil then rawset(table, key, value); return end
728	else
729	h = metatable(table).__newindex
730	if h == nil then
731	error(···)
732	end
733	end
734	if type(h) == "function" then
735	h(table, key,value) -- call the handler
736	else h[key] = value -- or repeat operation on it
737	end
738	end
739	</pre><p>
740	</li>
741
742	<li><b>"call": </b>
743	called when Lua calls a value.
744
745
746	<pre>
747	function function_event (func, ...)
748	if type(func) == "function" then
749	return func(...) -- primitive call
750	else
751	local h = metatable(func).__call
752	if h then
753	return h(func, ...)
754	else
755	error(···)
756	end
757	end
758	end
759	</pre><p>
760	</li>
761
762	</ul>
763
764
765
766
767	<h2>2.5 – <a name="2.5">Garbage Collection</a></h2>
768
769	<p>
770	Lua performs automatic memory management.
771	This means that
772	you have to worry neither about allocating memory for new objects
773	nor about freeing it when the objects are no longer needed.
774	Lua manages memory automatically by running
775	a <em>garbage collector</em> to collect all <em>dead objects</em>
776	(that is, objects that are no longer accessible from Lua).
777	All memory used by Lua is subject to automatic management:
778	strings, tables, userdata, functions, threads, internal structures, etc.
779
780
781	<p>
782	Lua implements an incremental mark-and-sweep collector.
783	It uses two numbers to control its garbage-collection cycles:
784	the <em>garbage-collector pause</em> and
785	the <em>garbage-collector step multiplier</em>.
786	Both use percentage points as units
787	(e.g., a value of 100 means an internal value of 1).
788
789
790	<p>
791	The garbage-collector pause
792	controls how long the collector waits before starting a new cycle.
793	Larger values make the collector less aggressive.
794	Values smaller than 100 mean the collector will not wait to
795	start a new cycle.
796	A value of 200 means that the collector waits for the total memory in use
797	to double before starting a new cycle.
798
799
800	<p>
801	The garbage-collector step multiplier
802	controls the relative speed of the collector relative to
803	memory allocation.
804	Larger values make the collector more aggressive but also increase
805	the size of each incremental step.
806	Values smaller than 100 make the collector too slow and
807	can result in the collector never finishing a cycle.
808	The default is 200,
809	which means that the collector runs at "twice"
810	the speed of memory allocation.
811
812
813	<p>
814	If you set the step multiplier to a very large number
815	(larger than 10% of the maximum number of
816	bytes that the program may use),
817	the collector behaves like a stop-the-world collector.
818	If you then set the pause to 200,
819	the collector behaves as in old Lua versions,
820	doing a complete collection every time Lua doubles its
821	memory usage.
822
823
824	<p>
825	You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
826	or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
827	You can also use these functions to control
828	the collector directly (e.g., stop and restart it).
829
830
831	<p>
832	As an experimental feature in Lua 5.2,
833	you can change the collector's operation mode
834	from incremental to <em>generational</em>.
835	A <em>generational collector</em> assumes that most objects die young,
836	and therefore it traverses only young (recently created) objects.
837	This behavior can reduce the time used by the collector,
838	but also increases memory usage (as old dead objects may accumulate).
839	To mitigate this second problem,
840	from time to time the generational collector performs a full collection.
841	Remember that this is an experimental feature;
842	you are welcome to try it,
843	but check your gains.
844
845
846
847	<h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3>
848
849	<p>
850	You can set garbage-collector metamethods for tables
851	and, using the C API,
852	for full userdata (see <a href="#2.4">§2.4</a>).
853	These metamethods are also called <em>finalizers</em>.
854	Finalizers allow you to coordinate Lua's garbage collection
855	with external resource management
856	(such as closing files, network or database connections,
857	or freeing your own memory).
858
859
860	<p>
861	For an object (table or userdata) to be finalized when collected,
862	you must <em>mark</em> it for finalization.
863
864	You mark an object for finalization when you set its metatable
865	and the metatable has a field indexed by the string "<code>__gc</code>".
866	Note that if you set a metatable without a <code>__gc</code> field
867	and later create that field in the metatable,
868	the object will not be marked for finalization.
869	However, after an object is marked,
870	you can freely change the <code>__gc</code> field of its metatable.
871
872
873	<p>
874	When a marked object becomes garbage,
875	it is not collected immediately by the garbage collector.
876	Instead, Lua puts it in a list.
877	After the collection,
878	Lua does the equivalent of the following function
879	for each object in that list:
880
881	<pre>
882	function gc_event (obj)
883	local h = metatable(obj).__gc
884	if type(h) == "function" then
885	h(obj)
886	end
887	end
888	</pre>
889
890	<p>
891	At the end of each garbage-collection cycle,
892	the finalizers for objects are called in
893	the reverse order that they were marked for collection,
894	among those collected in that cycle;
895	that is, the first finalizer to be called is the one associated
896	with the object marked last in the program.
897	The execution of each finalizer may occur at any point during
898	the execution of the regular code.
899
900
901	<p>
902	Because the object being collected must still be used by the finalizer,
903	it (and other objects accessible only through it)
904	must be <em>resurrected</em> by Lua.
905	Usually, this resurrection is transient,
906	and the object memory is freed in the next garbage-collection cycle.
907	However, if the finalizer stores the object in some global place
908	(e.g., a global variable),
909	then there is a permanent resurrection.
910	In any case,
911	the object memory is freed only when it becomes completely inaccessible;
912	its finalizer will never be called twice.
913
914
915	<p>
916	When you close a state (see <a href="#lua_close"><code>lua_close</code></a>),
917	Lua calls the finalizers of all objects marked for finalization,
918	following the reverse order that they were marked.
919	If any finalizer marks new objects for collection during that phase,
920	these new objects will not be finalized.
921
922
923
924
925
926	<h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3>
927
928	<p>
929	A <em>weak table</em> is a table whose elements are
930	<em>weak references</em>.
931	A weak reference is ignored by the garbage collector.
932	In other words,
933	if the only references to an object are weak references,
934	then the garbage collector will collect that object.
935
936
937	<p>
938	A weak table can have weak keys, weak values, or both.
939	A table with weak keys allows the collection of its keys,
940	but prevents the collection of its values.
941	A table with both weak keys and weak values allows the collection of
942	both keys and values.
943	In any case, if either the key or the value is collected,
944	the whole pair is removed from the table.
945	The weakness of a table is controlled by the
946	<code>__mode</code> field of its metatable.
947	If the <code>__mode</code> field is a string containing the character '<code>k</code>',
948	the keys in the table are weak.
949	If <code>__mode</code> contains '<code>v</code>',
950	the values in the table are weak.
951
952
953	<p>
954	A table with weak keys and strong values
955	is also called an <em>ephemeron table</em>.
956	In an ephemeron table,
957	a value is considered reachable only if its key is reachable.
958	In particular,
959	if the only reference to a key comes through its value,
960	the pair is removed.
961
962
963	<p>
964	Any change in the weakness of a table may take effect only
965	at the next collect cycle.
966	In particular, if you change the weakness to a stronger mode,
967	Lua may still collect some items from that table
968	before the change takes effect.
969
970
971	<p>
972	Only objects that have an explicit construction
973	are removed from weak tables.
974	Values, such as numbers and light C functions,
975	are not subject to garbage collection,
976	and therefore are not removed from weak tables
977	(unless its associated value is collected).
978	Although strings are subject to garbage collection,
979	they do not have an explicit construction,
980	and therefore are not removed from weak tables.
981
982
983	<p>
984	Resurrected objects
985	(that is, objects being finalized
986	and objects accessible only through objects being finalized)
987	have a special behavior in weak tables.
988	They are removed from weak values before running their finalizers,
989	but are removed from weak keys only in the next collection
990	after running their finalizers, when such objects are actually freed.
991	This behavior allows the finalizer to access properties
992	associated with the object through weak tables.
993
994
995	<p>
996	If a weak table is among the resurrected objects in a collection cycle,
997	it may not be properly cleared until the next cycle.
998
999
1000
1001
1002
1003
1004
1005	<h2>2.6 – <a name="2.6">Coroutines</a></h2>
1006
1007	<p>
1008	Lua supports coroutines,
1009	also called <em>collaborative multithreading</em>.
1010	A coroutine in Lua represents an independent thread of execution.
1011	Unlike threads in multithread systems, however,
1012	a coroutine only suspends its execution by explicitly calling
1013	a yield function.
1014
1015
1016	<p>
1017	You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
1018	Its sole argument is a function
1019	that is the main function of the coroutine.
1020	The <code>create</code> function only creates a new coroutine and
1021	returns a handle to it (an object of type <em>thread</em>);
1022	it does not start the coroutine.
1023
1024
1025	<p>
1026	You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1027	When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
1028	passing as its first argument
1029	a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
1030	the coroutine starts its execution,
1031	at the first line of its main function.
1032	Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
1033	to the coroutine main function.
1034	After the coroutine starts running,
1035	it runs until it terminates or <em>yields</em>.
1036
1037
1038	<p>
1039	A coroutine can terminate its execution in two ways:
1040	normally, when its main function returns
1041	(explicitly or implicitly, after the last instruction);
1042	and abnormally, if there is an unprotected error.
1043	In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
1044	plus any values returned by the coroutine main function.
1045	In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
1046	plus an error message.
1047
1048
1049	<p>
1050	A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
1051	When a coroutine yields,
1052	the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
1053	even if the yield happens inside nested function calls
1054	(that is, not in the main function,
1055	but in a function directly or indirectly called by the main function).
1056	In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
1057	plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
1058	The next time you resume the same coroutine,
1059	it continues its execution from the point where it yielded,
1060	with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
1061	arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1062
1063
1064	<p>
1065	Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
1066	the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
1067	but instead of returning the coroutine itself,
1068	it returns a function that, when called, resumes the coroutine.
1069	Any arguments passed to this function
1070	go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1071	<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>,
1072	except the first one (the boolean error code).
1073	Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
1074	<a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
1075	any error is propagated to the caller.
1076
1077
1078	<p>
1079	As an example of how coroutines work,
1080	consider the following code:
1081
1082	<pre>
1083	function foo (a)
1084	print("foo", a)
1085	return coroutine.yield(2*a)
1086	end
1087
1088	co = coroutine.create(function (a,b)
1089	print("co-body", a, b)
1090	local r = foo(a+1)
1091	print("co-body", r)
1092	local r, s = coroutine.yield(a+b, a-b)
1093	print("co-body", r, s)
1094	return b, "end"
1095	end)
1096
1097	print("main", coroutine.resume(co, 1, 10))
1098	print("main", coroutine.resume(co, "r"))
1099	print("main", coroutine.resume(co, "x", "y"))
1100	print("main", coroutine.resume(co, "x", "y"))
1101	</pre><p>
1102	When you run it, it produces the following output:
1103
1104	<pre>
1105	co-body 1 10
1106	foo 2
1107	main true 4
1108	co-body r
1109	main true 11 -9
1110	co-body x y
1111	main true 10 end
1112	main false cannot resume dead coroutine
1113	</pre>
1114
1115	<p>
1116	You can also create and manipulate coroutines through the C API:
1117	see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>,
1118	and <a href="#lua_yield"><code>lua_yield</code></a>.
1119
1120
1121
1122
1123
1124	<h1>3 – <a name="3">The Language</a></h1>
1125
1126	<p>
1127	This section describes the lexis, the syntax, and the semantics of Lua.
1128	In other words,
1129	this section describes
1130	which tokens are valid,
1131	how they can be combined,
1132	and what their combinations mean.
1133
1134
1135	<p>
1136	Language constructs will be explained using the usual extended BNF notation,
1137	in which
1138	{<em>a</em>} means 0 or more <em>a</em>'s, and
1139	[<em>a</em>] means an optional <em>a</em>.
1140	Non-terminals are shown like non-terminal,
1141	keywords are shown like <b>kword</b>,
1142	and other terminal symbols are shown like ‘<b>=</b>’.
1143	The complete syntax of Lua can be found in <a href="#9">§9</a>
1144	at the end of this manual.
1145
1146
1147
1148	<h2>3.1 – <a name="3.1">Lexical Conventions</a></h2>
1149
1150	<p>
1151	Lua is a free-form language.
1152	It ignores spaces (including new lines) and comments
1153	between lexical elements (tokens),
1154	except as delimiters between names and keywords.
1155
1156
1157	<p>
1158	<em>Names</em>
1159	(also called <em>identifiers</em>)
1160	in Lua can be any string of letters,
1161	digits, and underscores,
1162	not beginning with a digit.
1163	Identifiers are used to name variables, table fields, and labels.
1164
1165
1166	<p>
1167	The following <em>keywords</em> are reserved
1168	and cannot be used as names:
1169
1170
1171	<pre>
1172	and break do else elseif end
1173	false for function goto if in
1174	local nil not or repeat return
1175	then true until while
1176	</pre>
1177
1178	<p>
1179	Lua is a case-sensitive language:
1180	<code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
1181	are two different, valid names.
1182	As a convention, names starting with an underscore followed by
1183	uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>)
1184	are reserved for variables used by Lua.
1185
1186
1187	<p>
1188	The following strings denote other tokens:
1189
1190	<pre>
1191	+ - * / % ^ #
1192	== ~= <= >= < > =
1193	( ) { } [ ] ::
1194	; : , . .. ...
1195	</pre>
1196
1197	<p>
1198	<em>Literal strings</em>
1199	can be delimited by matching single or double quotes,
1200	and can contain the following C-like escape sequences:
1201	'<code>\a</code>' (bell),
1202	'<code>\b</code>' (backspace),
1203	'<code>\f</code>' (form feed),
1204	'<code>\n</code>' (newline),
1205	'<code>\r</code>' (carriage return),
1206	'<code>\t</code>' (horizontal tab),
1207	'<code>\v</code>' (vertical tab),
1208	'<code>\\</code>' (backslash),
1209	'<code>\"</code>' (quotation mark [double quote]),
1210	and '<code>\'</code>' (apostrophe [single quote]).
1211	A backslash followed by a real newline
1212	results in a newline in the string.
1213	The escape sequence '<code>\z</code>' skips the following span
1214	of white-space characters,
1215	including line breaks;
1216	it is particularly useful to break and indent a long literal string
1217	into multiple lines without adding the newlines and spaces
1218	into the string contents.
1219
1220
1221	<p>
1222	A byte in a literal string can also be specified by its numerical value.
1223	This can be done with the escape sequence <code>\x<em>XX</em></code>,
1224	where <em>XX</em> is a sequence of exactly two hexadecimal digits,
1225	or with the escape sequence <code>\<em>ddd</em></code>,
1226	where <em>ddd</em> is a sequence of up to three decimal digits.
1227	(Note that if a decimal escape is to be followed by a digit,
1228	it must be expressed using exactly three digits.)
1229	Strings in Lua can contain any 8-bit value, including embedded zeros,
1230	which can be specified as '<code>\0</code>'.
1231
1232
1233	<p>
1234	Literal strings can also be defined using a long format
1235	enclosed by <em>long brackets</em>.
1236	We define an <em>opening long bracket of level <em>n</em></em> as an opening
1237	square bracket followed by <em>n</em> equal signs followed by another
1238	opening square bracket.
1239	So, an opening long bracket of level 0 is written as <code>[[</code>,
1240	an opening long bracket of level 1 is written as <code>[=[</code>,
1241	and so on.
1242	A <em>closing long bracket</em> is defined similarly;
1243	for instance, a closing long bracket of level 4 is written as <code>]====]</code>.
1244	A <em>long literal</em> starts with an opening long bracket of any level and
1245	ends at the first closing long bracket of the same level.
1246	It can contain any text except a closing bracket of the proper level.
1247	Literals in this bracketed form can run for several lines,
1248	do not interpret any escape sequences,
1249	and ignore long brackets of any other level.
1250	Any kind of end-of-line sequence
1251	(carriage return, newline, carriage return followed by newline,
1252	or newline followed by carriage return)
1253	is converted to a simple newline.
1254
1255
1256	<p>
1257	Any byte in a literal string not
1258	explicitly affected by the previous rules represents itself.
1259	However, Lua opens files for parsing in text mode,
1260	and the system file functions may have problems with
1261	some control characters.
1262	So, it is safer to represent
1263	non-text data as a quoted literal with
1264	explicit escape sequences for non-text characters.
1265
1266
1267	<p>
1268	For convenience,
1269	when the opening long bracket is immediately followed by a newline,
1270	the newline is not included in the string.
1271	As an example, in a system using ASCII
1272	(in which '<code>a</code>' is coded as 97,
1273	newline is coded as 10, and '<code>1</code>' is coded as 49),
1274	the five literal strings below denote the same string:
1275
1276	<pre>
1277	a = 'alo\n123"'
1278	a = "alo\n123\""
1279	a = '\97lo\10\04923"'
1280	a = [[alo
1281	123"]]
1282	a = [==[
1283	alo
1284	123"]==]
1285	</pre>
1286
1287	<p>
1288	A <em>numerical constant</em> can be written with an optional fractional part
1289	and an optional decimal exponent,
1290	marked by a letter '<code>e</code>' or '<code>E</code>'.
1291	Lua also accepts hexadecimal constants,
1292	which start with <code>0x</code> or <code>0X</code>.
1293	Hexadecimal constants also accept an optional fractional part
1294	plus an optional binary exponent,
1295	marked by a letter '<code>p</code>' or '<code>P</code>'.
1296	Examples of valid numerical constants are
1297
1298	<pre>
1299	3 3.0 3.1416 314.16e-2 0.31416E1
1300	0xff 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
1301	</pre>
1302
1303	<p>
1304	A <em>comment</em> starts with a double hyphen (<code>--</code>)
1305	anywhere outside a string.
1306	If the text immediately after <code>--</code> is not an opening long bracket,
1307	the comment is a <em>short comment</em>,
1308	which runs until the end of the line.
1309	Otherwise, it is a <em>long comment</em>,
1310	which runs until the corresponding closing long bracket.
1311	Long comments are frequently used to disable code temporarily.
1312
1313
1314
1315
1316
1317	<h2>3.2 – <a name="3.2">Variables</a></h2>
1318
1319	<p>
1320	Variables are places that store values.
1321	There are three kinds of variables in Lua:
1322	global variables, local variables, and table fields.
1323
1324
1325	<p>
1326	A single name can denote a global variable or a local variable
1327	(or a function's formal parameter,
1328	which is a particular kind of local variable):
1329
1330	<pre>
1331	var ::= Name
1332	</pre><p>
1333	Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>.
1334
1335
1336	<p>
1337	Any variable name is assumed to be global unless explicitly declared
1338	as a local (see <a href="#3.3.7">§3.3.7</a>).
1339	Local variables are <em>lexically scoped</em>:
1340	local variables can be freely accessed by functions
1341	defined inside their scope (see <a href="#3.5">§3.5</a>).
1342
1343
1344	<p>
1345	Before the first assignment to a variable, its value is <b>nil</b>.
1346
1347
1348	<p>
1349	Square brackets are used to index a table:
1350
1351	<pre>
1352	var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’
1353	</pre><p>
1354	The meaning of accesses to table fields can be changed via metatables.
1355	An access to an indexed variable <code>t[i]</code> is equivalent to
1356	a call <code>gettable_event(t,i)</code>.
1357	(See <a href="#2.4">§2.4</a> for a complete description of the
1358	<code>gettable_event</code> function.
1359	This function is not defined or callable in Lua.
1360	We use it here only for explanatory purposes.)
1361
1362
1363	<p>
1364	The syntax <code>var.Name</code> is just syntactic sugar for
1365	<code>var["Name"]</code>:
1366
1367	<pre>
1368	var ::= prefixexp ‘<b>.</b>’ Name
1369	</pre>
1370
1371	<p>
1372	An access to a global variable <code>x</code>
1373	is equivalent to <code>_ENV.x</code>.
1374	Due to the way that chunks are compiled,
1375	<code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>).
1376
1377
1378
1379
1380
1381	<h2>3.3 – <a name="3.3">Statements</a></h2>
1382
1383	<p>
1384	Lua supports an almost conventional set of statements,
1385	similar to those in Pascal or C.
1386	This set includes
1387	assignments, control structures, function calls,
1388	and variable declarations.
1389
1390
1391
1392	<h3>3.3.1 – <a name="3.3.1">Blocks</a></h3>
1393
1394	<p>
1395	A block is a list of statements,
1396	which are executed sequentially:
1397
1398	<pre>
1399	block ::= {stat}
1400	</pre><p>
1401	Lua has <em>empty statements</em>
1402	that allow you to separate statements with semicolons,
1403	start a block with a semicolon
1404	or write two semicolons in sequence:
1405
1406	<pre>
1407	stat ::= ‘<b>;</b>’
1408	</pre>
1409
1410	<p>
1411	Function calls and assignments
1412	can start with an open parenthesis.
1413	This possibility leads to an ambiguity in Lua's grammar.
1414	Consider the following fragment:
1415
1416	<pre>
1417	a = b + c
1418	(print or io.write)('done')
1419	</pre><p>
1420	The grammar could see it in two ways:
1421
1422	<pre>
1423	a = b + c(print or io.write)('done')
1424
1425	a = b + c; (print or io.write)('done')
1426	</pre><p>
1427	The current parser always sees such constructions
1428	in the first way,
1429	interpreting the open parenthesis
1430	as the start of the arguments to a call.
1431	To avoid this ambiguity,
1432	it is a good practice to always precede with a semicolon
1433	statements that start with a parenthesis:
1434
1435	<pre>
1436	;(print or io.write)('done')
1437	</pre>
1438
1439	<p>
1440	A block can be explicitly delimited to produce a single statement:
1441
1442	<pre>
1443	stat ::= <b>do</b> block <b>end</b>
1444	</pre><p>
1445	Explicit blocks are useful
1446	to control the scope of variable declarations.
1447	Explicit blocks are also sometimes used to
1448	add a <b>return</b> statement in the middle
1449	of another block (see <a href="#3.3.4">§3.3.4</a>).
1450
1451
1452
1453
1454
1455	<h3>3.3.2 – <a name="3.3.2">Chunks</a></h3>
1456
1457	<p>
1458	The unit of compilation of Lua is called a <em>chunk</em>.
1459	Syntactically,
1460	a chunk is simply a block:
1461
1462	<pre>
1463	chunk ::= block
1464	</pre>
1465
1466	<p>
1467	Lua handles a chunk as the body of an anonymous function
1468	with a variable number of arguments
1469	(see <a href="#3.4.10">§3.4.10</a>).
1470	As such, chunks can define local variables,
1471	receive arguments, and return values.
1472	Moreover, such anonymous function is compiled as in the
1473	scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>).
1474	The resulting function always has <code>_ENV</code> as its only upvalue,
1475	even if it does not use that variable.
1476
1477
1478	<p>
1479	A chunk can be stored in a file or in a string inside the host program.
1480	To execute a chunk,
1481	Lua first precompiles the chunk into instructions for a virtual machine,
1482	and then it executes the compiled code
1483	with an interpreter for the virtual machine.
1484
1485
1486	<p>
1487	Chunks can also be precompiled into binary form;
1488	see program <code>luac</code> for details.
1489	Programs in source and compiled forms are interchangeable;
1490	Lua automatically detects the file type and acts accordingly.
1491
1492
1493
1494
1495
1496
1497	<h3>3.3.3 – <a name="3.3.3">Assignment</a></h3>
1498
1499	<p>
1500	Lua allows multiple assignments.
1501	Therefore, the syntax for assignment
1502	defines a list of variables on the left side
1503	and a list of expressions on the right side.
1504	The elements in both lists are separated by commas:
1505
1506	<pre>
1507	stat ::= varlist ‘<b>=</b>’ explist
1508	varlist ::= var {‘<b>,</b>’ var}
1509	explist ::= exp {‘<b>,</b>’ exp}
1510	</pre><p>
1511	Expressions are discussed in <a href="#3.4">§3.4</a>.
1512
1513
1514	<p>
1515	Before the assignment,
1516	the list of values is <em>adjusted</em> to the length of
1517	the list of variables.
1518	If there are more values than needed,
1519	the excess values are thrown away.
1520	If there are fewer values than needed,
1521	the list is extended with as many <b>nil</b>'s as needed.
1522	If the list of expressions ends with a function call,
1523	then all values returned by that call enter the list of values,
1524	before the adjustment
1525	(except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>).
1526
1527
1528	<p>
1529	The assignment statement first evaluates all its expressions
1530	and only then are the assignments performed.
1531	Thus the code
1532
1533	<pre>
1534	i = 3
1535	i, a[i] = i+1, 20
1536	</pre><p>
1537	sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
1538	because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
1539	before it is assigned 4.
1540	Similarly, the line
1541
1542	<pre>
1543	x, y = y, x
1544	</pre><p>
1545	exchanges the values of <code>x</code> and <code>y</code>,
1546	and
1547
1548	<pre>
1549	x, y, z = y, z, x
1550	</pre><p>
1551	cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
1552
1553
1554	<p>
1555	The meaning of assignments to global variables
1556	and table fields can be changed via metatables.
1557	An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
1558	<code>settable_event(t,i,val)</code>.
1559	(See <a href="#2.4">§2.4</a> for a complete description of the
1560	<code>settable_event</code> function.
1561	This function is not defined or callable in Lua.
1562	We use it here only for explanatory purposes.)
1563
1564
1565	<p>
1566	An assignment to a global variable <code>x = val</code>
1567	is equivalent to the assignment
1568	<code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>).
1569
1570
1571
1572
1573
1574	<h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p>
1575	The control structures
1576	<b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
1577	familiar syntax:
1578
1579
1580
1581
1582	<pre>
1583	stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
1584	stat ::= <b>repeat</b> block <b>until</b> exp
1585	stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
1586	</pre><p>
1587	Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>).
1588
1589
1590	<p>
1591	The condition expression of a
1592	control structure can return any value.
1593	Both <b>false</b> and <b>nil</b> are considered false.
1594	All values different from <b>nil</b> and <b>false</b> are considered true
1595	(in particular, the number 0 and the empty string are also true).
1596
1597
1598	<p>
1599	In the <b>repeat</b>–<b>until</b> loop,
1600	the inner block does not end at the <b>until</b> keyword,
1601	but only after the condition.
1602	So, the condition can refer to local variables
1603	declared inside the loop block.
1604
1605
1606	<p>
1607	The <b>goto</b> statement transfers the program control to a label.
1608	For syntactical reasons,
1609	labels in Lua are considered statements too:
1610
1611
1612
1613	<pre>
1614	stat ::= <b>goto</b> Name
1615	stat ::= label
1616	label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
1617	</pre>
1618
1619	<p>
1620	A label is visible in the entire block where it is defined,
1621	except
1622	inside nested blocks where a label with the same name is defined and
1623	inside nested functions.
1624	A goto may jump to any visible label as long as it does not
1625	enter into the scope of a local variable.
1626
1627
1628	<p>
1629	Labels and empty statements are called <em>void statements</em>,
1630	as they perform no actions.
1631
1632
1633	<p>
1634	The <b>break</b> statement terminates the execution of a
1635	<b>while</b>, <b>repeat</b>, or <b>for</b> loop,
1636	skipping to the next statement after the loop:
1637
1638
1639	<pre>
1640	stat ::= <b>break</b>
1641	</pre><p>
1642	A <b>break</b> ends the innermost enclosing loop.
1643
1644
1645	<p>
1646	The <b>return</b> statement is used to return values
1647	from a function or a chunk (which is a function in disguise).
1648
1649	Functions can return more than one value,
1650	so the syntax for the <b>return</b> statement is
1651
1652	<pre>
1653	stat ::= <b>return</b> [explist] [‘<b>;</b>’]
1654	</pre>
1655
1656	<p>
1657	The <b>return</b> statement can only be written
1658	as the last statement of a block.
1659	If it is really necessary to <b>return</b> in the middle of a block,
1660	then an explicit inner block can be used,
1661	as in the idiom <code>do return end</code>,
1662	because now <b>return</b> is the last statement in its (inner) block.
1663
1664
1665
1666
1667
1668	<h3>3.3.5 – <a name="3.3.5">For Statement</a></h3>
1669
1670	<p>
1671
1672	The <b>for</b> statement has two forms:
1673	one numeric and one generic.
1674
1675
1676	<p>
1677	The numeric <b>for</b> loop repeats a block of code while a
1678	control variable runs through an arithmetic progression.
1679	It has the following syntax:
1680
1681	<pre>
1682	stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b>
1683	</pre><p>
1684	The <em>block</em> is repeated for <em>name</em> starting at the value of
1685	the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the
1686	third <em>exp</em>.
1687	More precisely, a <b>for</b> statement like
1688
1689	<pre>
1690	for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end
1691	</pre><p>
1692	is equivalent to the code:
1693
1694	<pre>
1695	do
1696	local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
1697	if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end
1698	while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do
1699	local v = <em>var</em>
1700	<em>block</em>
1701	<em>var</em> = <em>var</em> + <em>step</em>
1702	end
1703	end
1704	</pre><p>
1705	Note the following:
1706
1707	<ul>
1708
1709	<li>
1710	All three control expressions are evaluated only once,
1711	before the loop starts.
1712	They must all result in numbers.
1713	</li>
1714
1715	<li>
1716	<code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
1717	The names shown here are for explanatory purposes only.
1718	</li>
1719
1720	<li>
1721	If the third expression (the step) is absent,
1722	then a step of 1 is used.
1723	</li>
1724
1725	<li>
1726	You can use <b>break</b> to exit a <b>for</b> loop.
1727	</li>
1728
1729	<li>
1730	The loop variable <code>v</code> is local to the loop;
1731	you cannot use its value after the <b>for</b> ends or is broken.
1732	If you need this value,
1733	assign it to another variable before breaking or exiting the loop.
1734	</li>
1735
1736	</ul>
1737
1738	<p>
1739	The generic <b>for</b> statement works over functions,
1740	called <em>iterators</em>.
1741	On each iteration, the iterator function is called to produce a new value,
1742	stopping when this new value is <b>nil</b>.
1743	The generic <b>for</b> loop has the following syntax:
1744
1745	<pre>
1746	stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
1747	namelist ::= Name {‘<b>,</b>’ Name}
1748	</pre><p>
1749	A <b>for</b> statement like
1750
1751	<pre>
1752	for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end
1753	</pre><p>
1754	is equivalent to the code:
1755
1756	<pre>
1757	do
1758	local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em>
1759	while true do
1760	local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
1761	if <em>var_1</em> == nil then break end
1762	<em>var</em> = <em>var_1</em>
1763	<em>block</em>
1764	end
1765	end
1766	</pre><p>
1767	Note the following:
1768
1769	<ul>
1770
1771	<li>
1772	<code><em>explist</em></code> is evaluated only once.
1773	Its results are an <em>iterator</em> function,
1774	a <em>state</em>,
1775	and an initial value for the first <em>iterator variable</em>.
1776	</li>
1777
1778	<li>
1779	<code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
1780	The names are here for explanatory purposes only.
1781	</li>
1782
1783	<li>
1784	You can use <b>break</b> to exit a <b>for</b> loop.
1785	</li>
1786
1787	<li>
1788	The loop variables <code><em>var_i</em></code> are local to the loop;
1789	you cannot use their values after the <b>for</b> ends.
1790	If you need these values,
1791	then assign them to other variables before breaking or exiting the loop.
1792	</li>
1793
1794	</ul>
1795
1796
1797
1798
1799	<h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p>
1800	To allow possible side-effects,
1801	function calls can be executed as statements:
1802
1803	<pre>
1804	stat ::= functioncall
1805	</pre><p>
1806	In this case, all returned values are thrown away.
1807	Function calls are explained in <a href="#3.4.9">§3.4.9</a>.
1808
1809
1810
1811
1812
1813	<h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p>
1814	Local variables can be declared anywhere inside a block.
1815	The declaration can include an initial assignment:
1816
1817	<pre>
1818	stat ::= <b>local</b> namelist [‘<b>=</b>’ explist]
1819	</pre><p>
1820	If present, an initial assignment has the same semantics
1821	of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>).
1822	Otherwise, all variables are initialized with <b>nil</b>.
1823
1824
1825	<p>
1826	A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>),
1827	and so local variables can be declared in a chunk outside any explicit block.
1828
1829
1830	<p>
1831	The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>.
1832
1833
1834
1835
1836
1837
1838
1839	<h2>3.4 – <a name="3.4">Expressions</a></h2>
1840
1841	<p>
1842	The basic expressions in Lua are the following:
1843
1844	<pre>
1845	exp ::= prefixexp
1846	exp ::= <b>nil</b> \| <b>false</b> \| <b>true</b>
1847	exp ::= Number
1848	exp ::= String
1849	exp ::= functiondef
1850	exp ::= tableconstructor
1851	exp ::= ‘<b>...</b>’
1852	exp ::= exp binop exp
1853	exp ::= unop exp
1854	prefixexp ::= var \| functioncall \| ‘<b>(</b>’ exp ‘<b>)</b>’
1855	</pre>
1856
1857	<p>
1858	Numbers and literal strings are explained in <a href="#3.1">§3.1</a>;
1859	variables are explained in <a href="#3.2">§3.2</a>;
1860	function definitions are explained in <a href="#3.4.10">§3.4.10</a>;
1861	function calls are explained in <a href="#3.4.9">§3.4.9</a>;
1862	table constructors are explained in <a href="#3.4.8">§3.4.8</a>.
1863	Vararg expressions,
1864	denoted by three dots ('<code>...</code>'), can only be used when
1865	directly inside a vararg function;
1866	they are explained in <a href="#3.4.10">§3.4.10</a>.
1867
1868
1869	<p>
1870	Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>),
1871	relational operators (see <a href="#3.4.3">§3.4.3</a>), logical operators (see <a href="#3.4.4">§3.4.4</a>),
1872	and the concatenation operator (see <a href="#3.4.5">§3.4.5</a>).
1873	Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>),
1874	the unary <b>not</b> (see <a href="#3.4.4">§3.4.4</a>),
1875	and the unary <em>length operator</em> (see <a href="#3.4.6">§3.4.6</a>).
1876
1877
1878	<p>
1879	Both function calls and vararg expressions can result in multiple values.
1880	If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>),
1881	then its return list is adjusted to zero elements,
1882	thus discarding all returned values.
1883	If an expression is used as the last (or the only) element
1884	of a list of expressions,
1885	then no adjustment is made
1886	(unless the expression is enclosed in parentheses).
1887	In all other contexts,
1888	Lua adjusts the result list to one element,
1889	either discarding all values except the first one
1890	or adding a single <b>nil</b> if there are no values.
1891
1892
1893	<p>
1894	Here are some examples:
1895
1896	<pre>
1897	f() -- adjusted to 0 results
1898	g(f(), x) -- f() is adjusted to 1 result
1899	g(x, f()) -- g gets x plus all results from f()
1900	a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
1901	a,b = ... -- a gets the first vararg parameter, b gets
1902	-- the second (both a and b can get nil if there
1903	-- is no corresponding vararg parameter)
1904
1905	a,b,c = x, f() -- f() is adjusted to 2 results
1906	a,b,c = f() -- f() is adjusted to 3 results
1907	return f() -- returns all results from f()
1908	return ... -- returns all received vararg parameters
1909	return x,y,f() -- returns x, y, and all results from f()
1910	{f()} -- creates a list with all results from f()
1911	{...} -- creates a list with all vararg parameters
1912	{f(), nil} -- f() is adjusted to 1 result
1913	</pre>
1914
1915	<p>
1916	Any expression enclosed in parentheses always results in only one value.
1917	Thus,
1918	<code>(f(x,y,z))</code> is always a single value,
1919	even if <code>f</code> returns several values.
1920	(The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
1921	or <b>nil</b> if <code>f</code> does not return any values.)
1922
1923
1924
1925	<h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p>
1926	Lua supports the usual arithmetic operators:
1927	the binary <code>+</code> (addition),
1928	<code>-</code> (subtraction), <code>*</code> (multiplication),
1929	<code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation);
1930	and unary <code>-</code> (mathematical negation).
1931	If the operands are numbers, or strings that can be converted to
1932	numbers (see <a href="#3.4.2">§3.4.2</a>),
1933	then all operations have the usual meaning.
1934	Exponentiation works for any exponent.
1935	For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>.
1936	Modulo is defined as
1937
1938	<pre>
1939	a % b == a - math.floor(a/b)*b
1940	</pre><p>
1941	That is, it is the remainder of a division that rounds
1942	the quotient towards minus infinity.
1943
1944
1945
1946
1947
1948	<h3>3.4.2 – <a name="3.4.2">Coercion</a></h3>
1949
1950	<p>
1951	Lua provides automatic conversion between
1952	string and number values at run time.
1953	Any arithmetic operation applied to a string tries to convert
1954	this string to a number, following the rules of the Lua lexer.
1955	(The string may have leading and trailing spaces and a sign.)
1956	Conversely, whenever a number is used where a string is expected,
1957	the number is converted to a string, in a reasonable format.
1958	For complete control over how numbers are converted to strings,
1959	use the <code>format</code> function from the string library
1960	(see <a href="#pdf-string.format"><code>string.format</code></a>).
1961
1962
1963
1964
1965
1966	<h3>3.4.3 – <a name="3.4.3">Relational Operators</a></h3><p>
1967	The relational operators in Lua are
1968
1969	<pre>
1970	== ~= < > <= >=
1971	</pre><p>
1972	These operators always result in <b>false</b> or <b>true</b>.
1973
1974
1975	<p>
1976	Equality (<code>==</code>) first compares the type of its operands.
1977	If the types are different, then the result is <b>false</b>.
1978	Otherwise, the values of the operands are compared.
1979	Numbers and strings are compared in the usual way.
1980	Tables, userdata, and threads
1981	are compared by reference:
1982	two objects are considered equal only if they are the same object.
1983	Every time you create a new object
1984	(a table, userdata, or thread),
1985	this new object is different from any previously existing object.
1986	Closures with the same reference are always equal.
1987	Closures with any detectable difference
1988	(different behavior, different definition) are always different.
1989
1990
1991	<p>
1992	You can change the way that Lua compares tables and userdata
1993	by using the "eq" metamethod (see <a href="#2.4">§2.4</a>).
1994
1995
1996	<p>
1997	The conversion rules of <a href="#3.4.2">§3.4.2</a>
1998	do not apply to equality comparisons.
1999	Thus, <code>"0"==0</code> evaluates to <b>false</b>,
2000	and <code>t[0]</code> and <code>t["0"]</code> denote different
2001	entries in a table.
2002
2003
2004	<p>
2005	The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
2006
2007
2008	<p>
2009	The order operators work as follows.
2010	If both arguments are numbers, then they are compared as such.
2011	Otherwise, if both arguments are strings,
2012	then their values are compared according to the current locale.
2013	Otherwise, Lua tries to call the "lt" or the "le"
2014	metamethod (see <a href="#2.4">§2.4</a>).
2015	A comparison <code>a > b</code> is translated to <code>b < a</code>
2016	and <code>a >= b</code> is translated to <code>b <= a</code>.
2017
2018
2019
2020
2021
2022	<h3>3.4.4 – <a name="3.4.4">Logical Operators</a></h3><p>
2023	The logical operators in Lua are
2024	<b>and</b>, <b>or</b>, and <b>not</b>.
2025	Like the control structures (see <a href="#3.3.4">§3.3.4</a>),
2026	all logical operators consider both <b>false</b> and <b>nil</b> as false
2027	and anything else as true.
2028
2029
2030	<p>
2031	The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
2032	The conjunction operator <b>and</b> returns its first argument
2033	if this value is <b>false</b> or <b>nil</b>;
2034	otherwise, <b>and</b> returns its second argument.
2035	The disjunction operator <b>or</b> returns its first argument
2036	if this value is different from <b>nil</b> and <b>false</b>;
2037	otherwise, <b>or</b> returns its second argument.
2038	Both <b>and</b> and <b>or</b> use short-cut evaluation;
2039	that is,
2040	the second operand is evaluated only if necessary.
2041	Here are some examples:
2042
2043	<pre>
2044	10 or 20 --> 10
2045	10 or error() --> 10
2046	nil or "a" --> "a"
2047	nil and 10 --> nil
2048	false and error() --> false
2049	false and nil --> false
2050	false or nil --> nil
2051	10 and 20 --> 20
2052	</pre><p>
2053	(In this manual,
2054	<code>--></code> indicates the result of the preceding expression.)
2055
2056
2057
2058
2059
2060	<h3>3.4.5 – <a name="3.4.5">Concatenation</a></h3><p>
2061	The string concatenation operator in Lua is
2062	denoted by two dots ('<code>..</code>').
2063	If both operands are strings or numbers, then they are converted to
2064	strings according to the rules mentioned in <a href="#3.4.2">§3.4.2</a>.
2065	Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>).
2066
2067
2068
2069
2070
2071	<h3>3.4.6 – <a name="3.4.6">The Length Operator</a></h3>
2072
2073	<p>
2074	The length operator is denoted by the unary prefix operator <code>#</code>.
2075	The length of a string is its number of bytes
2076	(that is, the usual meaning of string length when each
2077	character is one byte).
2078
2079
2080	<p>
2081	A program can modify the behavior of the length operator for
2082	any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>).
2083
2084
2085	<p>
2086	Unless a <code>__len</code> metamethod is given,
2087	the length of a table <code>t</code> is only defined if the
2088	table is a <em>sequence</em>,
2089	that is,
2090	the set of its positive numeric keys is equal to <em>{1..n}</em>
2091	for some integer <em>n</em>.
2092	In that case, <em>n</em> is its length.
2093	Note that a table like
2094
2095	<pre>
2096	{10, 20, nil, 40}
2097	</pre><p>
2098	is not a sequence, because it has the key <code>4</code>
2099	but does not have the key <code>3</code>.
2100	(So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal
2101	to the set of positive numeric keys of that table.)
2102	Note, however, that non-numeric keys do not interfere
2103	with whether a table is a sequence.
2104
2105
2106
2107
2108
2109	<h3>3.4.7 – <a name="3.4.7">Precedence</a></h3><p>
2110	Operator precedence in Lua follows the table below,
2111	from lower to higher priority:
2112
2113	<pre>
2114	or
2115	and
2116	< > <= >= ~= ==
2117	..
2118	+ -
2119	* / %
2120	not # - (unary)
2121	^
2122	</pre><p>
2123	As usual,
2124	you can use parentheses to change the precedences of an expression.
2125	The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
2126	operators are right associative.
2127	All other binary operators are left associative.
2128
2129
2130
2131
2132
2133	<h3>3.4.8 – <a name="3.4.8">Table Constructors</a></h3><p>
2134	Table constructors are expressions that create tables.
2135	Every time a constructor is evaluated, a new table is created.
2136	A constructor can be used to create an empty table
2137	or to create a table and initialize some of its fields.
2138	The general syntax for constructors is
2139
2140	<pre>
2141	tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
2142	fieldlist ::= field {fieldsep field} [fieldsep]
2143	field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp \| Name ‘<b>=</b>’ exp \| exp
2144	fieldsep ::= ‘<b>,</b>’ \| ‘<b>;</b>’
2145	</pre>
2146
2147	<p>
2148	Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
2149	with key <code>exp1</code> and value <code>exp2</code>.
2150	A field of the form <code>name = exp</code> is equivalent to
2151	<code>["name"] = exp</code>.
2152	Finally, fields of the form <code>exp</code> are equivalent to
2153	<code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers,
2154	starting with 1.
2155	Fields in the other formats do not affect this counting.
2156	For example,
2157
2158	<pre>
2159	a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
2160	</pre><p>
2161	is equivalent to
2162
2163	<pre>
2164	do
2165	local t = {}
2166	t[f(1)] = g
2167	t[1] = "x" -- 1st exp
2168	t[2] = "y" -- 2nd exp
2169	t.x = 1 -- t["x"] = 1
2170	t[3] = f(x) -- 3rd exp
2171	t[30] = 23
2172	t[4] = 45 -- 4th exp
2173	a = t
2174	end
2175	</pre>
2176
2177	<p>
2178	If the last field in the list has the form <code>exp</code>
2179	and the expression is a function call or a vararg expression,
2180	then all values returned by this expression enter the list consecutively
2181	(see <a href="#3.4.9">§3.4.9</a>).
2182
2183
2184	<p>
2185	The field list can have an optional trailing separator,
2186	as a convenience for machine-generated code.
2187
2188
2189
2190
2191
2192	<h3>3.4.9 – <a name="3.4.9">Function Calls</a></h3><p>
2193	A function call in Lua has the following syntax:
2194
2195	<pre>
2196	functioncall ::= prefixexp args
2197	</pre><p>
2198	In a function call,
2199	first prefixexp and args are evaluated.
2200	If the value of prefixexp has type <em>function</em>,
2201	then this function is called
2202	with the given arguments.
2203	Otherwise, the prefixexp "call" metamethod is called,
2204	having as first parameter the value of prefixexp,
2205	followed by the original call arguments
2206	(see <a href="#2.4">§2.4</a>).
2207
2208
2209	<p>
2210	The form
2211
2212	<pre>
2213	functioncall ::= prefixexp ‘<b>:</b>’ Name args
2214	</pre><p>
2215	can be used to call "methods".
2216	A call <code>v:name(<em>args</em>)</code>
2217	is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
2218	except that <code>v</code> is evaluated only once.
2219
2220
2221	<p>
2222	Arguments have the following syntax:
2223
2224	<pre>
2225	args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’
2226	args ::= tableconstructor
2227	args ::= String
2228	</pre><p>
2229	All argument expressions are evaluated before the call.
2230	A call of the form <code>f{<em>fields</em>}</code> is
2231	syntactic sugar for <code>f({<em>fields</em>})</code>;
2232	that is, the argument list is a single new table.
2233	A call of the form <code>f'<em>string</em>'</code>
2234	(or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
2235	is syntactic sugar for <code>f('<em>string</em>')</code>;
2236	that is, the argument list is a single literal string.
2237
2238
2239	<p>
2240	A call of the form <code>return <em>functioncall</em></code> is called
2241	a <em>tail call</em>.
2242	Lua implements <em>proper tail calls</em>
2243	(or <em>proper tail recursion</em>):
2244	in a tail call,
2245	the called function reuses the stack entry of the calling function.
2246	Therefore, there is no limit on the number of nested tail calls that
2247	a program can execute.
2248	However, a tail call erases any debug information about the
2249	calling function.
2250	Note that a tail call only happens with a particular syntax,
2251	where the <b>return</b> has one single function call as argument;
2252	this syntax makes the calling function return exactly
2253	the returns of the called function.
2254	So, none of the following examples are tail calls:
2255
2256	<pre>
2257	return (f(x)) -- results adjusted to 1
2258	return 2 * f(x)
2259	return x, f(x) -- additional results
2260	f(x); return -- results discarded
2261	return x or f(x) -- results adjusted to 1
2262	</pre>
2263
2264
2265
2266
2267	<h3>3.4.10 – <a name="3.4.10">Function Definitions</a></h3>
2268
2269	<p>
2270	The syntax for function definition is
2271
2272	<pre>
2273	functiondef ::= <b>function</b> funcbody
2274	funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
2275	</pre>
2276
2277	<p>
2278	The following syntactic sugar simplifies function definitions:
2279
2280	<pre>
2281	stat ::= <b>function</b> funcname funcbody
2282	stat ::= <b>local</b> <b>function</b> Name funcbody
2283	funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
2284	</pre><p>
2285	The statement
2286
2287	<pre>
2288	function f () <em>body</em> end
2289	</pre><p>
2290	translates to
2291
2292	<pre>
2293	f = function () <em>body</em> end
2294	</pre><p>
2295	The statement
2296
2297	<pre>
2298	function t.a.b.c.f () <em>body</em> end
2299	</pre><p>
2300	translates to
2301
2302	<pre>
2303	t.a.b.c.f = function () <em>body</em> end
2304	</pre><p>
2305	The statement
2306
2307	<pre>
2308	local function f () <em>body</em> end
2309	</pre><p>
2310	translates to
2311
2312	<pre>
2313	local f; f = function () <em>body</em> end
2314	</pre><p>
2315	not to
2316
2317	<pre>
2318	local f = function () <em>body</em> end
2319	</pre><p>
2320	(This only makes a difference when the body of the function
2321	contains references to <code>f</code>.)
2322
2323
2324	<p>
2325	A function definition is an executable expression,
2326	whose value has type <em>function</em>.
2327	When Lua precompiles a chunk,
2328	all its function bodies are precompiled too.
2329	Then, whenever Lua executes the function definition,
2330	the function is <em>instantiated</em> (or <em>closed</em>).
2331	This function instance (or <em>closure</em>)
2332	is the final value of the expression.
2333
2334
2335	<p>
2336	Parameters act as local variables that are
2337	initialized with the argument values:
2338
2339	<pre>
2340	parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] \| ‘<b>...</b>’
2341	</pre><p>
2342	When a function is called,
2343	the list of arguments is adjusted to
2344	the length of the list of parameters,
2345	unless the function is a <em>vararg function</em>,
2346	which is indicated by three dots ('<code>...</code>')
2347	at the end of its parameter list.
2348	A vararg function does not adjust its argument list;
2349	instead, it collects all extra arguments and supplies them
2350	to the function through a <em>vararg expression</em>,
2351	which is also written as three dots.
2352	The value of this expression is a list of all actual extra arguments,
2353	similar to a function with multiple results.
2354	If a vararg expression is used inside another expression
2355	or in the middle of a list of expressions,
2356	then its return list is adjusted to one element.
2357	If the expression is used as the last element of a list of expressions,
2358	then no adjustment is made
2359	(unless that last expression is enclosed in parentheses).
2360
2361
2362	<p>
2363	As an example, consider the following definitions:
2364
2365	<pre>
2366	function f(a, b) end
2367	function g(a, b, ...) end
2368	function r() return 1,2,3 end
2369	</pre><p>
2370	Then, we have the following mapping from arguments to parameters and
2371	to the vararg expression:
2372
2373	<pre>
2374	CALL PARAMETERS
2375
2376	f(3) a=3, b=nil
2377	f(3, 4) a=3, b=4
2378	f(3, 4, 5) a=3, b=4
2379	f(r(), 10) a=1, b=10
2380	f(r()) a=1, b=2
2381
2382	g(3) a=3, b=nil, ... --> (nothing)
2383	g(3, 4) a=3, b=4, ... --> (nothing)
2384	g(3, 4, 5, 8) a=3, b=4, ... --> 5 8
2385	g(5, r()) a=5, b=1, ... --> 2 3
2386	</pre>
2387
2388	<p>
2389	Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>).
2390	If control reaches the end of a function
2391	without encountering a <b>return</b> statement,
2392	then the function returns with no results.
2393
2394
2395	<p>
2396
2397	There is a system-dependent limit on the number of values
2398	that a function may return.
2399	This limit is guaranteed to be larger than 1000.
2400
2401
2402	<p>
2403	The <em>colon</em> syntax
2404	is used for defining <em>methods</em>,
2405	that is, functions that have an implicit extra parameter <code>self</code>.
2406	Thus, the statement
2407
2408	<pre>
2409	function t.a.b.c:f (<em>params</em>) <em>body</em> end
2410	</pre><p>
2411	is syntactic sugar for
2412
2413	<pre>
2414	t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
2415	</pre>
2416
2417
2418
2419
2420
2421
2422	<h2>3.5 – <a name="3.5">Visibility Rules</a></h2>
2423
2424	<p>
2425
2426	Lua is a lexically scoped language.
2427	The scope of a local variable begins at the first statement after
2428	its declaration and lasts until the last non-void statement
2429	of the innermost block that includes the declaration.
2430	Consider the following example:
2431
2432	<pre>
2433	x = 10 -- global variable
2434	do -- new block
2435	local x = x -- new 'x', with value 10
2436	print(x) --> 10
2437	x = x+1
2438	do -- another block
2439	local x = x+1 -- another 'x'
2440	print(x) --> 12
2441	end
2442	print(x) --> 11
2443	end
2444	print(x) --> 10 (the global one)
2445	</pre>
2446
2447	<p>
2448	Notice that, in a declaration like <code>local x = x</code>,
2449	the new <code>x</code> being declared is not in scope yet,
2450	and so the second <code>x</code> refers to the outside variable.
2451
2452
2453	<p>
2454	Because of the lexical scoping rules,
2455	local variables can be freely accessed by functions
2456	defined inside their scope.
2457	A local variable used by an inner function is called
2458	an <em>upvalue</em>, or <em>external local variable</em>,
2459	inside the inner function.
2460
2461
2462	<p>
2463	Notice that each execution of a <b>local</b> statement
2464	defines new local variables.
2465	Consider the following example:
2466
2467	<pre>
2468	a = {}
2469	local x = 20
2470	for i=1,10 do
2471	local y = 0
2472	a[i] = function () y=y+1; return x+y end
2473	end
2474	</pre><p>
2475	The loop creates ten closures
2476	(that is, ten instances of the anonymous function).
2477	Each of these closures uses a different <code>y</code> variable,
2478	while all of them share the same <code>x</code>.
2479
2480
2481
2482
2483
2484	<h1>4 – <a name="4">The Application Program Interface</a></h1>
2485
2486	<p>
2487
2488	This section describes the C API for Lua, that is,
2489	the set of C functions available to the host program to communicate
2490	with Lua.
2491	All API functions and related types and constants
2492	are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
2493
2494
2495	<p>
2496	Even when we use the term "function",
2497	any facility in the API may be provided as a macro instead.
2498	Except where stated otherwise,
2499	all such macros use each of their arguments exactly once
2500	(except for the first argument, which is always a Lua state),
2501	and so do not generate any hidden side-effects.
2502
2503
2504	<p>
2505	As in most C libraries,
2506	the Lua API functions do not check their arguments for validity or consistency.
2507	However, you can change this behavior by compiling Lua
2508	with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined.
2509
2510
2511
2512	<h2>4.1 – <a name="4.1">The Stack</a></h2>
2513
2514	<p>
2515	Lua uses a <em>virtual stack</em> to pass values to and from C.
2516	Each element in this stack represents a Lua value
2517	(<b>nil</b>, number, string, etc.).
2518
2519
2520	<p>
2521	Whenever Lua calls C, the called function gets a new stack,
2522	which is independent of previous stacks and of stacks of
2523	C functions that are still active.
2524	This stack initially contains any arguments to the C function
2525	and it is where the C function pushes its results
2526	to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
2527
2528
2529	<p>
2530	For convenience,
2531	most query operations in the API do not follow a strict stack discipline.
2532	Instead, they can refer to any element in the stack
2533	by using an <em>index</em>:
2534	A positive index represents an absolute stack position
2535	(starting at 1);
2536	a negative index represents an offset relative to the top of the stack.
2537	More specifically, if the stack has <em>n</em> elements,
2538	then index 1 represents the first element
2539	(that is, the element that was pushed onto the stack first)
2540	and
2541	index <em>n</em> represents the last element;
2542	index -1 also represents the last element
2543	(that is, the element at the top)
2544	and index <em>-n</em> represents the first element.
2545
2546
2547
2548
2549
2550	<h2>4.2 – <a name="4.2">Stack Size</a></h2>
2551
2552	<p>
2553	When you interact with the Lua API,
2554	you are responsible for ensuring consistency.
2555	In particular,
2556	<em>you are responsible for controlling stack overflow</em>.
2557	You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
2558	to ensure that the stack has extra slots when pushing new elements.
2559
2560
2561	<p>
2562	Whenever Lua calls C,
2563	it ensures that the stack has at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots.
2564	<code>LUA_MINSTACK</code> is defined as 20,
2565	so that usually you do not have to worry about stack space
2566	unless your code has loops pushing elements onto the stack.
2567
2568
2569	<p>
2570	When you call a Lua function
2571	without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>),
2572	Lua ensures that the stack has enough size for all results,
2573	but it does not ensure any extra space.
2574	So, before pushing anything in the stack after such a call
2575	you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
2576
2577
2578
2579
2580
2581	<h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2>
2582
2583	<p>
2584	Any function in the API that receives stack indices
2585	works only with <em>valid indices</em> or <em>acceptable indices</em>.
2586
2587
2588	<p>
2589	A <em>valid index</em> is an index that refers to a
2590	real position within the stack, that is,
2591	its position lies between 1 and the stack top
2592	(<code>1 ≤ abs(index) ≤ top</code>).
2593
2594	Usually, functions that can modify the value at an index
2595	require valid indices.
2596
2597
2598	<p>
2599	Unless otherwise noted,
2600	any function that accepts valid indices also accepts <em>pseudo-indices</em>,
2601	which represent some Lua values that are accessible to C code
2602	but which are not in the stack.
2603	Pseudo-indices are used to access the registry
2604	and the upvalues of a C function (see <a href="#4.4">§4.4</a>).
2605
2606
2607	<p>
2608	Functions that do not need a specific stack position,
2609	but only a value in the stack (e.g., query functions),
2610	can be called with acceptable indices.
2611	An <em>acceptable index</em> can be any valid index,
2612	including the pseudo-indices,
2613	but it also can be any positive index after the stack top
2614	within the space allocated for the stack,
2615	that is, indices up to the stack size.
2616	(Note that 0 is never an acceptable index.)
2617	Except when noted otherwise,
2618	functions in the API work with acceptable indices.
2619
2620
2621	<p>
2622	Acceptable indices serve to avoid extra tests
2623	against the stack top when querying the stack.
2624	For instance, a C function can query its third argument
2625	without the need to first check whether there is a third argument,
2626	that is, without the need to check whether 3 is a valid index.
2627
2628
2629	<p>
2630	For functions that can be called with acceptable indices,
2631	any non-valid index is treated as if it
2632	contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>,
2633	which behaves like a nil value.
2634
2635
2636
2637
2638
2639	<h2>4.4 – <a name="4.4">C Closures</a></h2>
2640
2641	<p>
2642	When a C function is created,
2643	it is possible to associate some values with it,
2644	thus creating a <em>C closure</em>
2645	(see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>);
2646	these values are called <em>upvalues</em> and are
2647	accessible to the function whenever it is called.
2648
2649
2650	<p>
2651	Whenever a C function is called,
2652	its upvalues are located at specific pseudo-indices.
2653	These pseudo-indices are produced by the macro
2654	<a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>.
2655	The first value associated with a function is at position
2656	<code>lua_upvalueindex(1)</code>, and so on.
2657	Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
2658	where <em>n</em> is greater than the number of upvalues of the
2659	current function (but not greater than 256),
2660	produces an acceptable but invalid index.
2661
2662
2663
2664
2665
2666	<h2>4.5 – <a name="4.5">Registry</a></h2>
2667
2668	<p>
2669	Lua provides a <em>registry</em>,
2670	a predefined table that can be used by any C code to
2671	store whatever Lua values it needs to store.
2672	The registry table is always located at pseudo-index
2673	<a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>,
2674	which is a valid index.
2675	Any C library can store data into this table,
2676	but it should take care to choose keys
2677	that are different from those used
2678	by other libraries, to avoid collisions.
2679	Typically, you should use as key a string containing your library name,
2680	or a light userdata with the address of a C object in your code,
2681	or any Lua object created by your code.
2682	As with global names,
2683	string keys starting with an underscore followed by
2684	uppercase letters are reserved for Lua.
2685
2686
2687	<p>
2688	The integer keys in the registry are used by the reference mechanism,
2689	implemented by the auxiliary library,
2690	and by some predefined values.
2691	Therefore, integer keys should not be used for other purposes.
2692
2693
2694	<p>
2695	When you create a new Lua state,
2696	its registry comes with some predefined values.
2697	These predefined values are indexed with integer keys
2698	defined as constants in <code>lua.h</code>.
2699	The following constants are defined:
2700
2701	<ul>
2702	<li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has
2703	the main thread of the state.
2704	(The main thread is the one created together with the state.)
2705	</li>
2706
2707	<li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has
2708	the global environment.
2709	</li>
2710	</ul>
2711
2712
2713
2714
2715	<h2>4.6 – <a name="4.6">Error Handling in C</a></h2>
2716
2717	<p>
2718	Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
2719	(You can also choose to use exceptions if you compile Lua as C++;
2720	search for <code>LUAI_THROW</code> in the source code.)
2721	When Lua faces any error
2722	(such as a memory allocation error, type errors, syntax errors,
2723	and runtime errors)
2724	it <em>raises</em> an error;
2725	that is, it does a long jump.
2726	A <em>protected environment</em> uses <code>setjmp</code>
2727	to set a recovery point;
2728	any error jumps to the most recent active recovery point.
2729
2730
2731	<p>
2732	If an error happens outside any protected environment,
2733	Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>)
2734	and then calls <code>abort</code>,
2735	thus exiting the host application.
2736	Your panic function can avoid this exit by
2737	never returning
2738	(e.g., doing a long jump to your own recovery point outside Lua).
2739
2740
2741	<p>
2742	The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>);
2743	in particular, the error message is at the top of the stack.
2744	However, there is no guarantees about stack space.
2745	To push anything on the stack,
2746	the panic function should first check the available space (see <a href="#4.2">§4.2</a>).
2747
2748
2749	<p>
2750	Most functions in the API can throw an error,
2751	for instance due to a memory allocation error.
2752	The documentation for each function indicates whether
2753	it can throw errors.
2754
2755
2756	<p>
2757	Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>.
2758
2759
2760
2761
2762
2763	<h2>4.7 – <a name="4.7">Handling Yields in C</a></h2>
2764
2765	<p>
2766	Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine.
2767	Therefore, if a function <code>foo</code> calls an API function
2768	and this API function yields
2769	(directly or indirectly by calling another function that yields),
2770	Lua cannot return to <code>foo</code> any more,
2771	because the <code>longjmp</code> removes its frame from the C stack.
2772
2773
2774	<p>
2775	To avoid this kind of problem,
2776	Lua raises an error whenever it tries to yield across an API call,
2777	except for three functions:
2778	<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>.
2779	All those functions receive a <em>continuation function</em>
2780	(as a parameter called <code>k</code>) to continue execution after a yield.
2781
2782
2783	<p>
2784	We need to set some terminology to explain continuations.
2785	We have a C function called from Lua which we will call
2786	the <em>original function</em>.
2787	This original function then calls one of those three functions in the C API,
2788	which we will call the <em>callee function</em>,
2789	that then yields the current thread.
2790	(This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
2791	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>
2792	and the function called by them yields.)
2793
2794
2795	<p>
2796	Suppose the running thread yields while executing the callee function.
2797	After the thread resumes,
2798	it eventually will finish running the callee function.
2799	However,
2800	the callee function cannot return to the original function,
2801	because its frame in the C stack was destroyed by the yield.
2802	Instead, Lua calls a <em>continuation function</em>,
2803	which was given as an argument to the callee function.
2804	As the name implies,
2805	the continuation function should continue the task
2806	of the original function.
2807
2808
2809	<p>
2810	Lua treats the continuation function as if it were the original function.
2811	The continuation function receives the same Lua stack
2812	from the original function,
2813	in the same state it would be if the callee function had returned.
2814	(For instance,
2815	after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are
2816	removed from the stack and replaced by the results from the call.)
2817	It also has the same upvalues.
2818	Whatever it returns is handled by Lua as if it were the return
2819	of the original function.
2820
2821
2822	<p>
2823	The only difference in the Lua state between the original function
2824	and its continuation is the result of a call to <a href="#lua_getctx"><code>lua_getctx</code></a>.
2825
2826
2827
2828
2829
2830	<h2>4.8 – <a name="4.8">Functions and Types</a></h2>
2831
2832	<p>
2833	Here we list all functions and types from the C API in
2834	alphabetical order.
2835	Each function has an indicator like this:
2836	<span class="apii">[-o, +p, <em>x</em>]</span>
2837
2838
2839	<p>
2840	The first field, <code>o</code>,
2841	is how many elements the function pops from the stack.
2842	The second field, <code>p</code>,
2843	is how many elements the function pushes onto the stack.
2844	(Any function always pushes its results after popping its arguments.)
2845	A field in the form <code>x\|y</code> means the function can push (or pop)
2846	<code>x</code> or <code>y</code> elements,
2847	depending on the situation;
2848	an interrogation mark '<code>?</code>' means that
2849	we cannot know how many elements the function pops/pushes
2850	by looking only at its arguments
2851	(e.g., they may depend on what is on the stack).
2852	The third field, <code>x</code>,
2853	tells whether the function may throw errors:
2854	'<code>-</code>' means the function never throws any error;
2855	'<code>e</code>' means the function may throw errors;
2856	'<code>v</code>' means the function may throw an error on purpose.
2857
2858
2859
2860	<hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p>
2861	<span class="apii">[-0, +0, –]</span>
2862	<pre>int lua_absindex (lua_State *L, int idx);</pre>
2863
2864	<p>
2865	Converts the acceptable index <code>idx</code> into an absolute index
2866	(that is, one that does not depend on the stack top).
2867
2868
2869
2870
2871
2872	<hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
2873	<pre>typedef void * (lua_Alloc) (void ud,
2874	void *ptr,
2875	size_t osize,
2876	size_t nsize);</pre>
2877
2878	<p>
2879	The type of the memory-allocation function used by Lua states.
2880	The allocator function must provide a
2881	functionality similar to <code>realloc</code>,
2882	but not exactly the same.
2883	Its arguments are
2884	<code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
2885	<code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
2886	<code>osize</code>, the original size of the block or some code about what
2887	is being allocated;
2888	<code>nsize</code>, the new size of the block.
2889
2890
2891	<p>
2892	When <code>ptr</code> is not <code>NULL</code>,
2893	<code>osize</code> is the size of the block pointed by <code>ptr</code>,
2894	that is, the size given when it was allocated or reallocated.
2895
2896
2897	<p>
2898	When <code>ptr</code> is <code>NULL</code>,
2899	<code>osize</code> encodes the kind of object that Lua is allocating.
2900	<code>osize</code> is any of
2901	<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>,
2902	<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)
2903	Lua is creating a new object of that type.
2904	When <code>osize</code> is some other value,
2905	Lua is allocating memory for something else.
2906
2907
2908	<p>
2909	Lua assumes the following behavior from the allocator function:
2910
2911
2912	<p>
2913	When <code>nsize</code> is zero,
2914	the allocator should behave like <code>free</code>
2915	and return <code>NULL</code>.
2916
2917
2918	<p>
2919	When <code>nsize</code> is not zero,
2920	the allocator should behave like <code>realloc</code>.
2921	The allocator returns <code>NULL</code>
2922	if and only if it cannot fulfill the request.
2923	Lua assumes that the allocator never fails when
2924	<code>osize >= nsize</code>.
2925
2926
2927	<p>
2928	Here is a simple implementation for the allocator function.
2929	It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
2930
2931	<pre>
2932	static void l_alloc (void ud, void *ptr, size_t osize,
2933	size_t nsize) {
2934	(void)ud; (void)osize; /* not used */
2935	if (nsize == 0) {
2936	free(ptr);
2937	return NULL;
2938	}
2939	else
2940	return realloc(ptr, nsize);
2941	}
2942	</pre><p>
2943	Note that Standard C ensures
2944	that <code>free(NULL)</code> has no effect and that
2945	<code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>.
2946	This code assumes that <code>realloc</code> does not fail when shrinking a block.
2947	(Although Standard C does not ensure this behavior,
2948	it seems to be a safe assumption.)
2949
2950
2951
2952
2953
2954	<hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p>
2955	<span class="apii">[-(2\|1), +1, <em>e</em>]</span>
2956	<pre>void lua_arith (lua_State *L, int op);</pre>
2957
2958	<p>
2959	Performs an arithmetic operation over the two values
2960	(or one, in the case of negation)
2961	at the top of the stack,
2962	with the value at the top being the second operand,
2963	pops these values, and pushes the result of the operation.
2964	The function follows the semantics of the corresponding Lua operator
2965	(that is, it may call metamethods).
2966
2967
2968	<p>
2969	The value of <code>op</code> must be one of the following constants:
2970
2971	<ul>
2972
2973	<li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li>
2974	<li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li>
2975	<li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li>
2976	<li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs division (<code>/</code>)</li>
2977	<li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li>
2978	<li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li>
2979	<li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li>
2980
2981	</ul>
2982
2983
2984
2985
2986	<hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
2987	<span class="apii">[-0, +0, –]</span>
2988	<pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
2989
2990	<p>
2991	Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>).
2992
2993
2994
2995
2996
2997	<hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
2998	<span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span>
2999	<pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
3000
3001	<p>
3002	Calls a function.
3003
3004
3005	<p>
3006	To call a function you must use the following protocol:
3007	first, the function to be called is pushed onto the stack;
3008	then, the arguments to the function are pushed
3009	in direct order;
3010	that is, the first argument is pushed first.
3011	Finally you call <a href="#lua_call"><code>lua_call</code></a>;
3012	<code>nargs</code> is the number of arguments that you pushed onto the stack.
3013	All arguments and the function value are popped from the stack
3014	when the function is called.
3015	The function results are pushed onto the stack when the function returns.
3016	The number of results is adjusted to <code>nresults</code>,
3017	unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
3018	In this case, all results from the function are pushed.
3019	Lua takes care that the returned values fit into the stack space.
3020	The function results are pushed onto the stack in direct order
3021	(the first result is pushed first),
3022	so that after the call the last result is on the top of the stack.
3023
3024
3025	<p>
3026	Any error inside the called function is propagated upwards
3027	(with a <code>longjmp</code>).
3028
3029
3030	<p>
3031	The following example shows how the host program can do the
3032	equivalent to this Lua code:
3033
3034	<pre>
3035	a = f("how", t.x, 14)
3036	</pre><p>
3037	Here it is in C:
3038
3039	<pre>
3040	lua_getglobal(L, "f"); /* function to be called */
3041	lua_pushstring(L, "how"); /* 1st argument */
3042	lua_getglobal(L, "t"); /* table to be indexed */
3043	lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */
3044	lua_remove(L, -2); /* remove 't' from the stack */
3045	lua_pushinteger(L, 14); /* 3rd argument */
3046	lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */
3047	lua_setglobal(L, "a"); /* set global 'a' */
3048	</pre><p>
3049	Note that the code above is "balanced":
3050	at its end, the stack is back to its original configuration.
3051	This is considered good programming practice.
3052
3053
3054
3055
3056
3057	<hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p>
3058	<span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
3059	<pre>void lua_callk (lua_State *L, int nargs, int nresults, int ctx,
3060	lua_CFunction k);</pre>
3061
3062	<p>
3063	This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>,
3064	but allows the called function to yield (see <a href="#4.7">§4.7</a>).
3065
3066
3067
3068
3069
3070	<hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
3071	<pre>typedef int (lua_CFunction) (lua_State L);</pre>
3072
3073	<p>
3074	Type for C functions.
3075
3076
3077	<p>
3078	In order to communicate properly with Lua,
3079	a C function must use the following protocol,
3080	which defines the way parameters and results are passed:
3081	a C function receives its arguments from Lua in its stack
3082	in direct order (the first argument is pushed first).
3083	So, when the function starts,
3084	<code>lua_gettop(L)</code> returns the number of arguments received by the function.
3085	The first argument (if any) is at index 1
3086	and its last argument is at index <code>lua_gettop(L)</code>.
3087	To return values to Lua, a C function just pushes them onto the stack,
3088	in direct order (the first result is pushed first),
3089	and returns the number of results.
3090	Any other value in the stack below the results will be properly
3091	discarded by Lua.
3092	Like a Lua function, a C function called by Lua can also return
3093	many results.
3094
3095
3096	<p>
3097	As an example, the following function receives a variable number
3098	of numerical arguments and returns their average and sum:
3099
3100	<pre>
3101	static int foo (lua_State *L) {
3102	int n = lua_gettop(L); /* number of arguments */
3103	lua_Number sum = 0;
3104	int i;
3105	for (i = 1; i <= n; i++) {
3106	if (!lua_isnumber(L, i)) {
3107	lua_pushstring(L, "incorrect argument");
3108	lua_error(L);
3109	}
3110	sum += lua_tonumber(L, i);
3111	}
3112	lua_pushnumber(L, sum/n); /* first result */
3113	lua_pushnumber(L, sum); /* second result */
3114	return 2; /* number of results */
3115	}
3116	</pre>
3117
3118
3119
3120
3121	<hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
3122	<span class="apii">[-0, +0, –]</span>
3123	<pre>int lua_checkstack (lua_State *L, int extra);</pre>
3124
3125	<p>
3126	Ensures that there are at least <code>extra</code> free stack slots in the stack.
3127	It returns false if it cannot fulfill the request,
3128	because it would cause the stack to be larger than a fixed maximum size
3129	(typically at least a few thousand elements) or
3130	because it cannot allocate memory for the new stack size.
3131	This function never shrinks the stack;
3132	if the stack is already larger than the new size,
3133	it is left unchanged.
3134
3135
3136
3137
3138
3139	<hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
3140	<span class="apii">[-0, +0, –]</span>
3141	<pre>void lua_close (lua_State *L);</pre>
3142
3143	<p>
3144	Destroys all objects in the given Lua state
3145	(calling the corresponding garbage-collection metamethods, if any)
3146	and frees all dynamic memory used by this state.
3147	On several platforms, you may not need to call this function,
3148	because all resources are naturally released when the host program ends.
3149	On the other hand, long-running programs that create multiple states,
3150	such as daemons or web servers,
3151	might need to close states as soon as they are not needed.
3152
3153
3154
3155
3156
3157	<hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p>
3158	<span class="apii">[-0, +0, <em>e</em>]</span>
3159	<pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre>
3160
3161	<p>
3162	Compares two Lua values.
3163	Returns 1 if the value at index <code>index1</code> satisfies <code>op</code>
3164	when compared with the value at index <code>index2</code>,
3165	following the semantics of the corresponding Lua operator
3166	(that is, it may call metamethods).
3167	Otherwise returns 0.
3168	Also returns 0 if any of the indices is non valid.
3169
3170
3171	<p>
3172	The value of <code>op</code> must be one of the following constants:
3173
3174	<ul>
3175
3176	<li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li>
3177	<li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li>
3178	<li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li>
3179
3180	</ul>
3181
3182
3183
3184
3185	<hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
3186	<span class="apii">[-n, +1, <em>e</em>]</span>
3187	<pre>void lua_concat (lua_State *L, int n);</pre>
3188
3189	<p>
3190	Concatenates the <code>n</code> values at the top of the stack,
3191	pops them, and leaves the result at the top.
3192	If <code>n</code> is 1, the result is the single value on the stack
3193	(that is, the function does nothing);
3194	if <code>n</code> is 0, the result is the empty string.
3195	Concatenation is performed following the usual semantics of Lua
3196	(see <a href="#3.4.5">§3.4.5</a>).
3197
3198
3199
3200
3201
3202	<hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
3203	<span class="apii">[-0, +0, –]</span>
3204	<pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre>
3205
3206	<p>
3207	Moves the element at index <code>fromidx</code>
3208	into the valid index <code>toidx</code>
3209	without shifting any element
3210	(therefore replacing the value at that position).
3211
3212
3213
3214
3215
3216	<hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
3217	<span class="apii">[-0, +1, <em>e</em>]</span>
3218	<pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
3219
3220	<p>
3221	Creates a new empty table and pushes it onto the stack.
3222	Parameter <code>narr</code> is a hint for how many elements the table
3223	will have as a sequence;
3224	parameter <code>nrec</code> is a hint for how many other elements
3225	the table will have.
3226	Lua may use these hints to preallocate memory for the new table.
3227	This pre-allocation is useful for performance when you know in advance
3228	how many elements the table will have.
3229	Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
3230
3231
3232
3233
3234
3235	<hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
3236	<span class="apii">[-0, +0, <em>e</em>]</span>
3237	<pre>int lua_dump (lua_State L, lua_Writer writer, void data);</pre>
3238
3239	<p>
3240	Dumps a function as a binary chunk.
3241	Receives a Lua function on the top of the stack
3242	and produces a binary chunk that,
3243	if loaded again,
3244	results in a function equivalent to the one dumped.
3245	As it produces parts of the chunk,
3246	<a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
3247	with the given <code>data</code>
3248	to write them.
3249
3250
3251	<p>
3252	The value returned is the error code returned by the last
3253	call to the writer;
3254	0 means no errors.
3255
3256
3257	<p>
3258	This function does not pop the Lua function from the stack.
3259
3260
3261
3262
3263
3264	<hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
3265	<span class="apii">[-1, +0, <em>v</em>]</span>
3266	<pre>int lua_error (lua_State *L);</pre>
3267
3268	<p>
3269	Generates a Lua error.
3270	The error message (which can actually be a Lua value of any type)
3271	must be on the stack top.
3272	This function does a long jump,
3273	and therefore never returns
3274	(see <a href="#luaL_error"><code>luaL_error</code></a>).
3275
3276
3277
3278
3279
3280	<hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
3281	<span class="apii">[-0, +0, <em>e</em>]</span>
3282	<pre>int lua_gc (lua_State *L, int what, int data);</pre>
3283
3284	<p>
3285	Controls the garbage collector.
3286
3287
3288	<p>
3289	This function performs several tasks,
3290	according to the value of the parameter <code>what</code>:
3291
3292	<ul>
3293
3294	<li><b><code>LUA_GCSTOP</code>: </b>
3295	stops the garbage collector.
3296	</li>
3297
3298	<li><b><code>LUA_GCRESTART</code>: </b>
3299	restarts the garbage collector.
3300	</li>
3301
3302	<li><b><code>LUA_GCCOLLECT</code>: </b>
3303	performs a full garbage-collection cycle.
3304	</li>
3305
3306	<li><b><code>LUA_GCCOUNT</code>: </b>
3307	returns the current amount of memory (in Kbytes) in use by Lua.
3308	</li>
3309
3310	<li><b><code>LUA_GCCOUNTB</code>: </b>
3311	returns the remainder of dividing the current amount of bytes of
3312	memory in use by Lua by 1024.
3313	</li>
3314
3315	<li><b><code>LUA_GCSTEP</code>: </b>
3316	performs an incremental step of garbage collection.
3317	The step "size" is controlled by <code>data</code>
3318	(larger values mean more steps) in a non-specified way.
3319	If you want to control the step size
3320	you must experimentally tune the value of <code>data</code>.
3321	The function returns 1 if the step finished a
3322	garbage-collection cycle.
3323	</li>
3324
3325	<li><b><code>LUA_GCSETPAUSE</code>: </b>
3326	sets <code>data</code> as the new value
3327	for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>).
3328	The function returns the previous value of the pause.
3329	</li>
3330
3331	<li><b><code>LUA_GCSETSTEPMUL</code>: </b>
3332	sets <code>data</code> as the new value for the <em>step multiplier</em> of
3333	the collector (see <a href="#2.5">§2.5</a>).
3334	The function returns the previous value of the step multiplier.
3335	</li>
3336
3337	<li><b><code>LUA_GCISRUNNING</code>: </b>
3338	returns a boolean that tells whether the collector is running
3339	(i.e., not stopped).
3340	</li>
3341
3342	<li><b><code>LUA_GCGEN</code>: </b>
3343	changes the collector to generational mode
3344	(see <a href="#2.5">§2.5</a>).
3345	</li>
3346
3347	<li><b><code>LUA_GCINC</code>: </b>
3348	changes the collector to incremental mode.
3349	This is the default mode.
3350	</li>
3351
3352	</ul>
3353
3354	<p>
3355	For more details about these options,
3356	see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>.
3357
3358
3359
3360
3361
3362	<hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
3363	<span class="apii">[-0, +0, –]</span>
3364	<pre>lua_Alloc lua_getallocf (lua_State L, void *ud);</pre>
3365
3366	<p>
3367	Returns the memory-allocation function of a given state.
3368	If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
3369	opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>.
3370
3371
3372
3373
3374
3375	<hr><h3><a name="lua_getctx"><code>lua_getctx</code></a></h3><p>
3376	<span class="apii">[-0, +0, –]</span>
3377	<pre>int lua_getctx (lua_State L, int ctx);</pre>
3378
3379	<p>
3380	This function is called by a continuation function (see <a href="#4.7">§4.7</a>)
3381	to retrieve the status of the thread and a context information.
3382
3383
3384	<p>
3385	When called in the original function,
3386	<a href="#lua_getctx"><code>lua_getctx</code></a> always returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
3387	and does not change the value of its argument <code>ctx</code>.
3388	When called inside a continuation function,
3389	<a href="#lua_getctx"><code>lua_getctx</code></a> returns <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> and sets
3390	the value of <code>ctx</code> to be the context information
3391	(the value passed as the <code>ctx</code> argument
3392	to the callee together with the continuation function).
3393
3394
3395	<p>
3396	When the callee is <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
3397	Lua may also call its continuation function
3398	to handle errors during the call.
3399	That is, upon an error in the function called by <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
3400	Lua may not return to the original function
3401	but instead may call the continuation function.
3402	In that case, a call to <a href="#lua_getctx"><code>lua_getctx</code></a> will return the error code
3403	(the value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>);
3404	the value of <code>ctx</code> will be set to the context information,
3405	as in the case of a yield.
3406
3407
3408
3409
3410
3411	<hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
3412	<span class="apii">[-0, +1, <em>e</em>]</span>
3413	<pre>void lua_getfield (lua_State L, int index, const char k);</pre>
3414
3415	<p>
3416	Pushes onto the stack the value <code>t[k]</code>,
3417	where <code>t</code> is the value at the given index.
3418	As in Lua, this function may trigger a metamethod
3419	for the "index" event (see <a href="#2.4">§2.4</a>).
3420
3421
3422
3423
3424
3425	<hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
3426	<span class="apii">[-0, +1, <em>e</em>]</span>
3427	<pre>void lua_getglobal (lua_State L, const char name);</pre>
3428
3429	<p>
3430	Pushes onto the stack the value of the global <code>name</code>.
3431
3432
3433
3434
3435
3436	<hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
3437	<span class="apii">[-0, +(0\|1), –]</span>
3438	<pre>int lua_getmetatable (lua_State *L, int index);</pre>
3439
3440	<p>
3441	Pushes onto the stack the metatable of the value at the given index.
3442	If the value does not have a metatable,
3443	the function returns 0 and pushes nothing on the stack.
3444
3445
3446
3447
3448
3449	<hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
3450	<span class="apii">[-1, +1, <em>e</em>]</span>
3451	<pre>void lua_gettable (lua_State *L, int index);</pre>
3452
3453	<p>
3454	Pushes onto the stack the value <code>t[k]</code>,
3455	where <code>t</code> is the value at the given index
3456	and <code>k</code> is the value at the top of the stack.
3457
3458
3459	<p>
3460	This function pops the key from the stack
3461	(putting the resulting value in its place).
3462	As in Lua, this function may trigger a metamethod
3463	for the "index" event (see <a href="#2.4">§2.4</a>).
3464
3465
3466
3467
3468
3469	<hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
3470	<span class="apii">[-0, +0, –]</span>
3471	<pre>int lua_gettop (lua_State *L);</pre>
3472
3473	<p>
3474	Returns the index of the top element in the stack.
3475	Because indices start at 1,
3476	this result is equal to the number of elements in the stack
3477	(and so 0 means an empty stack).
3478
3479
3480
3481
3482
3483	<hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p>
3484	<span class="apii">[-0, +1, –]</span>
3485	<pre>void lua_getuservalue (lua_State *L, int index);</pre>
3486
3487	<p>
3488	Pushes onto the stack the Lua value associated with the userdata
3489	at the given index.
3490	This Lua value must be a table or <b>nil</b>.
3491
3492
3493
3494
3495
3496	<hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
3497	<span class="apii">[-1, +1, –]</span>
3498	<pre>void lua_insert (lua_State *L, int index);</pre>
3499
3500	<p>
3501	Moves the top element into the given valid index,
3502	shifting up the elements above this index to open space.
3503	This function cannot be called with a pseudo-index,
3504	because a pseudo-index is not an actual stack position.
3505
3506
3507
3508
3509
3510	<hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
3511	<pre>typedef ptrdiff_t lua_Integer;</pre>
3512
3513	<p>
3514	The type used by the Lua API to represent signed integral values.
3515
3516
3517	<p>
3518	By default it is a <code>ptrdiff_t</code>,
3519	which is usually the largest signed integral type the machine handles
3520	"comfortably".
3521
3522
3523
3524
3525
3526	<hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
3527	<span class="apii">[-0, +0, –]</span>
3528	<pre>int lua_isboolean (lua_State *L, int index);</pre>
3529
3530	<p>
3531	Returns 1 if the value at the given index is a boolean,
3532	and 0 otherwise.
3533
3534
3535
3536
3537
3538	<hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
3539	<span class="apii">[-0, +0, –]</span>
3540	<pre>int lua_iscfunction (lua_State *L, int index);</pre>
3541
3542	<p>
3543	Returns 1 if the value at the given index is a C function,
3544	and 0 otherwise.
3545
3546
3547
3548
3549
3550	<hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
3551	<span class="apii">[-0, +0, –]</span>
3552	<pre>int lua_isfunction (lua_State *L, int index);</pre>
3553
3554	<p>
3555	Returns 1 if the value at the given index is a function
3556	(either C or Lua), and 0 otherwise.
3557
3558
3559
3560
3561
3562	<hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
3563	<span class="apii">[-0, +0, –]</span>
3564	<pre>int lua_islightuserdata (lua_State *L, int index);</pre>
3565
3566	<p>
3567	Returns 1 if the value at the given index is a light userdata,
3568	and 0 otherwise.
3569
3570
3571
3572
3573
3574	<hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
3575	<span class="apii">[-0, +0, –]</span>
3576	<pre>int lua_isnil (lua_State *L, int index);</pre>
3577
3578	<p>
3579	Returns 1 if the value at the given index is <b>nil</b>,
3580	and 0 otherwise.
3581
3582
3583
3584
3585
3586	<hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
3587	<span class="apii">[-0, +0, –]</span>
3588	<pre>int lua_isnone (lua_State *L, int index);</pre>
3589
3590	<p>
3591	Returns 1 if the given index is not valid,
3592	and 0 otherwise.
3593
3594
3595
3596
3597
3598	<hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
3599	<span class="apii">[-0, +0, –]</span>
3600	<pre>int lua_isnoneornil (lua_State *L, int index);</pre>
3601
3602	<p>
3603	Returns 1 if the given index is not valid
3604	or if the value at this index is <b>nil</b>,
3605	and 0 otherwise.
3606
3607
3608
3609
3610
3611	<hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
3612	<span class="apii">[-0, +0, –]</span>
3613	<pre>int lua_isnumber (lua_State *L, int index);</pre>
3614
3615	<p>
3616	Returns 1 if the value at the given index is a number
3617	or a string convertible to a number,
3618	and 0 otherwise.
3619
3620
3621
3622
3623
3624	<hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
3625	<span class="apii">[-0, +0, –]</span>
3626	<pre>int lua_isstring (lua_State *L, int index);</pre>
3627
3628	<p>
3629	Returns 1 if the value at the given index is a string
3630	or a number (which is always convertible to a string),
3631	and 0 otherwise.
3632
3633
3634
3635
3636
3637	<hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
3638	<span class="apii">[-0, +0, –]</span>
3639	<pre>int lua_istable (lua_State *L, int index);</pre>
3640
3641	<p>
3642	Returns 1 if the value at the given index is a table,
3643	and 0 otherwise.
3644
3645
3646
3647
3648
3649	<hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
3650	<span class="apii">[-0, +0, –]</span>
3651	<pre>int lua_isthread (lua_State *L, int index);</pre>
3652
3653	<p>
3654	Returns 1 if the value at the given index is a thread,
3655	and 0 otherwise.
3656
3657
3658
3659
3660
3661	<hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
3662	<span class="apii">[-0, +0, –]</span>
3663	<pre>int lua_isuserdata (lua_State *L, int index);</pre>
3664
3665	<p>
3666	Returns 1 if the value at the given index is a userdata
3667	(either full or light), and 0 otherwise.
3668
3669
3670
3671
3672
3673	<hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p>
3674	<span class="apii">[-0, +1, <em>e</em>]</span>
3675	<pre>void lua_len (lua_State *L, int index);</pre>
3676
3677	<p>
3678	Returns the "length" of the value at the given index;
3679	it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>).
3680	The result is pushed on the stack.
3681
3682
3683
3684
3685
3686	<hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
3687	<span class="apii">[-0, +1, –]</span>
3688	<pre>int lua_load (lua_State *L,
3689	lua_Reader reader,
3690	void *data,
3691	const char *source,
3692	const char *mode);</pre>
3693
3694	<p>
3695	Loads a Lua chunk (without running it).
3696	If there are no errors,
3697	<code>lua_load</code> pushes the compiled chunk as a Lua
3698	function on top of the stack.
3699	Otherwise, it pushes an error message.
3700
3701
3702	<p>
3703	The return values of <code>lua_load</code> are:
3704
3705	<ul>
3706
3707	<li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li>
3708
3709	<li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b>
3710	syntax error during precompilation;</li>
3711
3712	<li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
3713	memory allocation error;</li>
3714
3715	<li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
3716	error while running a <code>__gc</code> metamethod.
3717	(This error has no relation with the chunk being loaded.
3718	It is generated by the garbage collector.)
3719	</li>
3720
3721	</ul>
3722
3723	<p>
3724	The <code>lua_load</code> function uses a user-supplied <code>reader</code> function
3725	to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
3726	The <code>data</code> argument is an opaque value passed to the reader function.
3727
3728
3729	<p>
3730	The <code>source</code> argument gives a name to the chunk,
3731	which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>).
3732
3733
3734	<p>
3735	<code>lua_load</code> automatically detects whether the chunk is text or binary
3736	and loads it accordingly (see program <code>luac</code>).
3737	The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>,
3738	with the addition that
3739	a <code>NULL</code> value is equivalent to the string "<code>bt</code>".
3740
3741
3742	<p>
3743	<code>lua_load</code> uses the stack internally,
3744	so the reader function should always leave the stack
3745	unmodified when returning.
3746
3747
3748	<p>
3749	If the resulting function has one upvalue,
3750	this upvalue is set to the value of the global environment
3751	stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>).
3752	When loading main chunks,
3753	this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
3754
3755
3756
3757
3758
3759	<hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
3760	<span class="apii">[-0, +0, –]</span>
3761	<pre>lua_State lua_newstate (lua_Alloc f, void ud);</pre>
3762
3763	<p>
3764	Creates a new thread running in a new, independent state.
3765	Returns <code>NULL</code> if cannot create the thread or the state
3766	(due to lack of memory).
3767	The argument <code>f</code> is the allocator function;
3768	Lua does all memory allocation for this state through this function.
3769	The second argument, <code>ud</code>, is an opaque pointer that Lua
3770	passes to the allocator in every call.
3771
3772
3773
3774
3775
3776	<hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
3777	<span class="apii">[-0, +1, <em>e</em>]</span>
3778	<pre>void lua_newtable (lua_State *L);</pre>
3779
3780	<p>
3781	Creates a new empty table and pushes it onto the stack.
3782	It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
3783
3784
3785
3786
3787
3788	<hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
3789	<span class="apii">[-0, +1, <em>e</em>]</span>
3790	<pre>lua_State lua_newthread (lua_State L);</pre>
3791
3792	<p>
3793	Creates a new thread, pushes it on the stack,
3794	and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
3795	The new thread returned by this function shares with the original thread
3796	its global environment,
3797	but has an independent execution stack.
3798
3799
3800	<p>
3801	There is no explicit function to close or to destroy a thread.
3802	Threads are subject to garbage collection,
3803	like any Lua object.
3804
3805
3806
3807
3808
3809	<hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p>
3810	<span class="apii">[-0, +1, <em>e</em>]</span>
3811	<pre>void lua_newuserdata (lua_State L, size_t size);</pre>
3812
3813	<p>
3814	This function allocates a new block of memory with the given size,
3815	pushes onto the stack a new full userdata with the block address,
3816	and returns this address.
3817	The host program can freely use this memory.
3818
3819
3820
3821
3822
3823	<hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
3824	<span class="apii">[-1, +(2\|0), <em>e</em>]</span>
3825	<pre>int lua_next (lua_State *L, int index);</pre>
3826
3827	<p>
3828	Pops a key from the stack,
3829	and pushes a key–value pair from the table at the given index
3830	(the "next" pair after the given key).
3831	If there are no more elements in the table,
3832	then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing).
3833
3834
3835	<p>
3836	A typical traversal looks like this:
3837
3838	<pre>
3839	/* table is in the stack at index 't' */
3840	lua_pushnil(L); /* first key */
3841	while (lua_next(L, t) != 0) {
3842	/* uses 'key' (at index -2) and 'value' (at index -1) */
3843	printf("%s - %s\n",
3844	lua_typename(L, lua_type(L, -2)),
3845	lua_typename(L, lua_type(L, -1)));
3846	/* removes 'value'; keeps 'key' for next iteration */
3847	lua_pop(L, 1);
3848	}
3849	</pre>
3850
3851	<p>
3852	While traversing a table,
3853	do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
3854	unless you know that the key is actually a string.
3855	Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change
3856	the value at the given index;
3857	this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
3858
3859
3860	<p>
3861	See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
3862	the table during its traversal.
3863
3864
3865
3866
3867
3868	<hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
3869	<pre>typedef double lua_Number;</pre>
3870
3871	<p>
3872	The type of numbers in Lua.
3873	By default, it is double, but that can be changed in <code>luaconf.h</code>.
3874	Through this configuration file you can change
3875	Lua to operate with another type for numbers (e.g., float or long).
3876
3877
3878
3879
3880
3881	<hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
3882	<span class="apii">[-(nargs + 1), +(nresults\|1), –]</span>
3883	<pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre>
3884
3885	<p>
3886	Calls a function in protected mode.
3887
3888
3889	<p>
3890	Both <code>nargs</code> and <code>nresults</code> have the same meaning as
3891	in <a href="#lua_call"><code>lua_call</code></a>.
3892	If there are no errors during the call,
3893	<a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
3894	However, if there is any error,
3895	<a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
3896	pushes a single value on the stack (the error message),
3897	and returns an error code.
3898	Like <a href="#lua_call"><code>lua_call</code></a>,
3899	<a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
3900	and its arguments from the stack.
3901
3902
3903	<p>
3904	If <code>msgh</code> is 0,
3905	then the error message returned on the stack
3906	is exactly the original error message.
3907	Otherwise, <code>msgh</code> is the stack index of a
3908	<em>message handler</em>.
3909	(In the current implementation, this index cannot be a pseudo-index.)
3910	In case of runtime errors,
3911	this function will be called with the error message
3912	and its return value will be the message
3913	returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
3914
3915
3916	<p>
3917	Typically, the message handler is used to add more debug
3918	information to the error message, such as a stack traceback.
3919	Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
3920	since by then the stack has unwound.
3921
3922
3923	<p>
3924	The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following codes
3925	(defined in <code>lua.h</code>):
3926
3927	<ul>
3928
3929	<li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b>
3930	success.</li>
3931
3932	<li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b>
3933	a runtime error.
3934	</li>
3935
3936	<li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
3937	memory allocation error.
3938	For such errors, Lua does not call the message handler.
3939	</li>
3940
3941	<li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b>
3942	error while running the message handler.
3943	</li>
3944
3945	<li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
3946	error while running a <code>__gc</code> metamethod.
3947	(This error typically has no relation with the function being called.
3948	It is generated by the garbage collector.)
3949	</li>
3950
3951	</ul>
3952
3953
3954
3955
3956	<hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p>
3957	<span class="apii">[-(nargs + 1), +(nresults\|1), –]</span>
3958	<pre>int lua_pcallk (lua_State *L,
3959	int nargs,
3960	int nresults,
3961	int errfunc,
3962	int ctx,
3963	lua_CFunction k);</pre>
3964
3965	<p>
3966	This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>,
3967	but allows the called function to yield (see <a href="#4.7">§4.7</a>).
3968
3969
3970
3971
3972
3973	<hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
3974	<span class="apii">[-n, +0, –]</span>
3975	<pre>void lua_pop (lua_State *L, int n);</pre>
3976
3977	<p>
3978	Pops <code>n</code> elements from the stack.
3979
3980
3981
3982
3983
3984	<hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
3985	<span class="apii">[-0, +1, –]</span>
3986	<pre>void lua_pushboolean (lua_State *L, int b);</pre>
3987
3988	<p>
3989	Pushes a boolean value with value <code>b</code> onto the stack.
3990
3991
3992
3993
3994
3995	<hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
3996	<span class="apii">[-n, +1, <em>e</em>]</span>
3997	<pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
3998
3999	<p>
4000	Pushes a new C closure onto the stack.
4001
4002
4003	<p>
4004	When a C function is created,
4005	it is possible to associate some values with it,
4006	thus creating a C closure (see <a href="#4.4">§4.4</a>);
4007	these values are then accessible to the function whenever it is called.
4008	To associate values with a C function,
4009	first these values should be pushed onto the stack
4010	(when there are multiple values, the first value is pushed first).
4011	Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
4012	is called to create and push the C function onto the stack,
4013	with the argument <code>n</code> telling how many values should be
4014	associated with the function.
4015	<a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
4016
4017
4018	<p>
4019	The maximum value for <code>n</code> is 255.
4020
4021
4022	<p>
4023	When <code>n</code> is zero,
4024	this function creates a <em>light C function</em>,
4025	which is just a pointer to the C function.
4026	In that case, it never throws a memory error.
4027
4028
4029
4030
4031
4032	<hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
4033	<span class="apii">[-0, +1, –]</span>
4034	<pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
4035
4036	<p>
4037	Pushes a C function onto the stack.
4038	This function receives a pointer to a C function
4039	and pushes onto the stack a Lua value of type <code>function</code> that,
4040	when called, invokes the corresponding C function.
4041
4042
4043	<p>
4044	Any function to be registered in Lua must
4045	follow the correct protocol to receive its parameters
4046	and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
4047
4048
4049	<p>
4050	<code>lua_pushcfunction</code> is defined as a macro:
4051
4052	<pre>
4053	#define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
4054	</pre><p>
4055	Note that <code>f</code> is used twice.
4056
4057
4058
4059
4060
4061	<hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
4062	<span class="apii">[-0, +1, <em>e</em>]</span>
4063	<pre>const char lua_pushfstring (lua_State L, const char *fmt, ...);</pre>
4064
4065	<p>
4066	Pushes onto the stack a formatted string
4067	and returns a pointer to this string.
4068	It is similar to the ANSI C function <code>sprintf</code>,
4069	but has some important differences:
4070
4071	<ul>
4072
4073	<li>
4074	You do not have to allocate space for the result:
4075	the result is a Lua string and Lua takes care of memory allocation
4076	(and deallocation, through garbage collection).
4077	</li>
4078
4079	<li>
4080	The conversion specifiers are quite restricted.
4081	There are no flags, widths, or precisions.
4082	The conversion specifiers can only be
4083	'<code>%%</code>' (inserts a '<code>%</code>' in the string),
4084	'<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
4085	'<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
4086	'<code>%p</code>' (inserts a pointer as a hexadecimal numeral),
4087	'<code>%d</code>' (inserts an <code>int</code>), and
4088	'<code>%c</code>' (inserts an <code>int</code> as a byte).
4089	</li>
4090
4091	</ul>
4092
4093
4094
4095
4096	<hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
4097	<span class="apii">[-0, +1, –]</span>
4098	<pre>void lua_pushglobaltable (lua_State *L);</pre>
4099
4100	<p>
4101	Pushes the global environment onto the stack.
4102
4103
4104
4105
4106
4107	<hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
4108	<span class="apii">[-0, +1, –]</span>
4109	<pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
4110
4111	<p>
4112	Pushes a number with value <code>n</code> onto the stack.
4113
4114
4115
4116
4117
4118	<hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
4119	<span class="apii">[-0, +1, –]</span>
4120	<pre>void lua_pushlightuserdata (lua_State L, void p);</pre>
4121
4122	<p>
4123	Pushes a light userdata onto the stack.
4124
4125
4126	<p>
4127	Userdata represent C values in Lua.
4128	A <em>light userdata</em> represents a pointer, a <code>void*</code>.
4129	It is a value (like a number):
4130	you do not create it, it has no individual metatable,
4131	and it is not collected (as it was never created).
4132	A light userdata is equal to "any"
4133	light userdata with the same C address.
4134
4135
4136
4137
4138
4139	<hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
4140	<span class="apii">[-0, +1, <em>e</em>]</span>
4141	<pre>const char lua_pushliteral (lua_State L, const char *s);</pre>
4142
4143	<p>
4144	This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
4145	but can be used only when <code>s</code> is a literal string.
4146	It automatically provides the string length.
4147
4148
4149
4150
4151
4152	<hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
4153	<span class="apii">[-0, +1, <em>e</em>]</span>
4154	<pre>const char lua_pushlstring (lua_State L, const char *s, size_t len);</pre>
4155
4156	<p>
4157	Pushes the string pointed to by <code>s</code> with size <code>len</code>
4158	onto the stack.
4159	Lua makes (or reuses) an internal copy of the given string,
4160	so the memory at <code>s</code> can be freed or reused immediately after
4161	the function returns.
4162	The string can contain any binary data,
4163	including embedded zeros.
4164
4165
4166	<p>
4167	Returns a pointer to the internal copy of the string.
4168
4169
4170
4171
4172
4173	<hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
4174	<span class="apii">[-0, +1, –]</span>
4175	<pre>void lua_pushnil (lua_State *L);</pre>
4176
4177	<p>
4178	Pushes a nil value onto the stack.
4179
4180
4181
4182
4183
4184	<hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
4185	<span class="apii">[-0, +1, –]</span>
4186	<pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
4187
4188	<p>
4189	Pushes a number with value <code>n</code> onto the stack.
4190
4191
4192
4193
4194
4195	<hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
4196	<span class="apii">[-0, +1, <em>e</em>]</span>
4197	<pre>const char lua_pushstring (lua_State L, const char *s);</pre>
4198
4199	<p>
4200	Pushes the zero-terminated string pointed to by <code>s</code>
4201	onto the stack.
4202	Lua makes (or reuses) an internal copy of the given string,
4203	so the memory at <code>s</code> can be freed or reused immediately after
4204	the function returns.
4205
4206
4207	<p>
4208	Returns a pointer to the internal copy of the string.
4209
4210
4211	<p>
4212	If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>.
4213
4214
4215
4216
4217
4218	<hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
4219	<span class="apii">[-0, +1, –]</span>
4220	<pre>int lua_pushthread (lua_State *L);</pre>
4221
4222	<p>
4223	Pushes the thread represented by <code>L</code> onto the stack.
4224	Returns 1 if this thread is the main thread of its state.
4225
4226
4227
4228
4229
4230	<hr><h3><a name="lua_pushunsigned"><code>lua_pushunsigned</code></a></h3><p>
4231	<span class="apii">[-0, +1, –]</span>
4232	<pre>void lua_pushunsigned (lua_State *L, lua_Unsigned n);</pre>
4233
4234	<p>
4235	Pushes a number with value <code>n</code> onto the stack.
4236
4237
4238
4239
4240
4241	<hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
4242	<span class="apii">[-0, +1, –]</span>
4243	<pre>void lua_pushvalue (lua_State *L, int index);</pre>
4244
4245	<p>
4246	Pushes a copy of the element at the given index
4247	onto the stack.
4248
4249
4250
4251
4252
4253	<hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
4254	<span class="apii">[-0, +1, <em>e</em>]</span>
4255	<pre>const char lua_pushvfstring (lua_State L,
4256	const char *fmt,
4257	va_list argp);</pre>
4258
4259	<p>
4260	Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
4261	instead of a variable number of arguments.
4262
4263
4264
4265
4266
4267	<hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
4268	<span class="apii">[-0, +0, –]</span>
4269	<pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
4270
4271	<p>
4272	Returns 1 if the two values in indices <code>index1</code> and
4273	<code>index2</code> are primitively equal
4274	(that is, without calling metamethods).
4275	Otherwise returns 0.
4276	Also returns 0 if any of the indices are non valid.
4277
4278
4279
4280
4281
4282	<hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
4283	<span class="apii">[-1, +1, –]</span>
4284	<pre>void lua_rawget (lua_State *L, int index);</pre>
4285
4286	<p>
4287	Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
4288	(i.e., without metamethods).
4289
4290
4291
4292
4293
4294	<hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
4295	<span class="apii">[-0, +1, –]</span>
4296	<pre>void lua_rawgeti (lua_State *L, int index, int n);</pre>
4297
4298	<p>
4299	Pushes onto the stack the value <code>t[n]</code>,
4300	where <code>t</code> is the table at the given index.
4301	The access is raw;
4302	that is, it does not invoke metamethods.
4303
4304
4305
4306
4307
4308	<hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p>
4309	<span class="apii">[-0, +1, –]</span>
4310	<pre>void lua_rawgetp (lua_State L, int index, const void p);</pre>
4311
4312	<p>
4313	Pushes onto the stack the value <code>t[k]</code>,
4314	where <code>t</code> is the table at the given index and
4315	<code>k</code> is the pointer <code>p</code> represented as a light userdata.
4316	The access is raw;
4317	that is, it does not invoke metamethods.
4318
4319
4320
4321
4322
4323	<hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p>
4324	<span class="apii">[-0, +0, –]</span>
4325	<pre>size_t lua_rawlen (lua_State *L, int index);</pre>
4326
4327	<p>
4328	Returns the raw "length" of the value at the given index:
4329	for strings, this is the string length;
4330	for tables, this is the result of the length operator ('<code>#</code>')
4331	with no metamethods;
4332	for userdata, this is the size of the block of memory allocated
4333	for the userdata;
4334	for other values, it is 0.
4335
4336
4337
4338
4339
4340	<hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
4341	<span class="apii">[-2, +0, <em>e</em>]</span>
4342	<pre>void lua_rawset (lua_State *L, int index);</pre>
4343
4344	<p>
4345	Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
4346	(i.e., without metamethods).
4347
4348
4349
4350
4351
4352	<hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
4353	<span class="apii">[-1, +0, <em>e</em>]</span>
4354	<pre>void lua_rawseti (lua_State *L, int index, int n);</pre>
4355
4356	<p>
4357	Does the equivalent of <code>t[n] = v</code>,
4358	where <code>t</code> is the table at the given index
4359	and <code>v</code> is the value at the top of the stack.
4360
4361
4362	<p>
4363	This function pops the value from the stack.
4364	The assignment is raw;
4365	that is, it does not invoke metamethods.
4366
4367
4368
4369
4370
4371	<hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
4372	<span class="apii">[-1, +0, <em>e</em>]</span>
4373	<pre>void lua_rawsetp (lua_State L, int index, const void p);</pre>
4374
4375	<p>
4376	Does the equivalent of <code>t[k] = v</code>,
4377	where <code>t</code> is the table at the given index,
4378	<code>k</code> is the pointer <code>p</code> represented as a light userdata,
4379	and <code>v</code> is the value at the top of the stack.
4380
4381
4382	<p>
4383	This function pops the value from the stack.
4384	The assignment is raw;
4385	that is, it does not invoke metamethods.
4386
4387
4388
4389
4390
4391	<hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
4392	<pre>typedef const char * (lua_Reader) (lua_State L,
4393	void *data,
4394	size_t *size);</pre>
4395
4396	<p>
4397	The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
4398	Every time it needs another piece of the chunk,
4399	<a href="#lua_load"><code>lua_load</code></a> calls the reader,
4400	passing along its <code>data</code> parameter.
4401	The reader must return a pointer to a block of memory
4402	with a new piece of the chunk
4403	and set <code>size</code> to the block size.
4404	The block must exist until the reader function is called again.
4405	To signal the end of the chunk,
4406	the reader must return <code>NULL</code> or set <code>size</code> to zero.
4407	The reader function may return pieces of any size greater than zero.
4408
4409
4410
4411
4412
4413	<hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
4414	<span class="apii">[-0, +0, <em>e</em>]</span>
4415	<pre>void lua_register (lua_State L, const char name, lua_CFunction f);</pre>
4416
4417	<p>
4418	Sets the C function <code>f</code> as the new value of global <code>name</code>.
4419	It is defined as a macro:
4420
4421	<pre>
4422	#define lua_register(L,n,f) \
4423	(lua_pushcfunction(L, f), lua_setglobal(L, n))
4424	</pre>
4425
4426
4427
4428
4429	<hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
4430	<span class="apii">[-1, +0, –]</span>
4431	<pre>void lua_remove (lua_State *L, int index);</pre>
4432
4433	<p>
4434	Removes the element at the given valid index,
4435	shifting down the elements above this index to fill the gap.
4436	This function cannot be called with a pseudo-index,
4437	because a pseudo-index is not an actual stack position.
4438
4439
4440
4441
4442
4443	<hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
4444	<span class="apii">[-1, +0, –]</span>
4445	<pre>void lua_replace (lua_State *L, int index);</pre>
4446
4447	<p>
4448	Moves the top element into the given valid index
4449	without shifting any element
4450	(therefore replacing the value at the given index),
4451	and then pops the top element.
4452
4453
4454
4455
4456
4457	<hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
4458	<span class="apii">[-?, +?, –]</span>
4459	<pre>int lua_resume (lua_State L, lua_State from, int nargs);</pre>
4460
4461	<p>
4462	Starts and resumes a coroutine in a given thread.
4463
4464
4465	<p>
4466	To start a coroutine,
4467	you push onto the thread stack the main function plus any arguments;
4468	then you call <a href="#lua_resume"><code>lua_resume</code></a>,
4469	with <code>nargs</code> being the number of arguments.
4470	This call returns when the coroutine suspends or finishes its execution.
4471	When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
4472	or all values returned by the body function.
4473	<a href="#lua_resume"><code>lua_resume</code></a> returns
4474	<a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
4475	<a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution
4476	without errors,
4477	or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
4478
4479
4480	<p>
4481	In case of errors,
4482	the stack is not unwound,
4483	so you can use the debug API over it.
4484	The error message is on the top of the stack.
4485
4486
4487	<p>
4488	To resume a coroutine,
4489	you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>,
4490	put on its stack only the values to
4491	be passed as results from <code>yield</code>,
4492	and then call <a href="#lua_resume"><code>lua_resume</code></a>.
4493
4494
4495	<p>
4496	The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>.
4497	If there is no such coroutine,
4498	this parameter can be <code>NULL</code>.
4499
4500
4501
4502
4503
4504	<hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
4505	<span class="apii">[-0, +0, –]</span>
4506	<pre>void lua_setallocf (lua_State L, lua_Alloc f, void ud);</pre>
4507
4508	<p>
4509	Changes the allocator function of a given state to <code>f</code>
4510	with user data <code>ud</code>.
4511
4512
4513
4514
4515
4516	<hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
4517	<span class="apii">[-1, +0, <em>e</em>]</span>
4518	<pre>void lua_setfield (lua_State L, int index, const char k);</pre>
4519
4520	<p>
4521	Does the equivalent to <code>t[k] = v</code>,
4522	where <code>t</code> is the value at the given index
4523	and <code>v</code> is the value at the top of the stack.
4524
4525
4526	<p>
4527	This function pops the value from the stack.
4528	As in Lua, this function may trigger a metamethod
4529	for the "newindex" event (see <a href="#2.4">§2.4</a>).
4530
4531
4532
4533
4534
4535	<hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
4536	<span class="apii">[-1, +0, <em>e</em>]</span>
4537	<pre>void lua_setglobal (lua_State L, const char name);</pre>
4538
4539	<p>
4540	Pops a value from the stack and
4541	sets it as the new value of global <code>name</code>.
4542
4543
4544
4545
4546
4547	<hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
4548	<span class="apii">[-1, +0, –]</span>
4549	<pre>void lua_setmetatable (lua_State *L, int index);</pre>
4550
4551	<p>
4552	Pops a table from the stack and
4553	sets it as the new metatable for the value at the given index.
4554
4555
4556
4557
4558
4559	<hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
4560	<span class="apii">[-2, +0, <em>e</em>]</span>
4561	<pre>void lua_settable (lua_State *L, int index);</pre>
4562
4563	<p>
4564	Does the equivalent to <code>t[k] = v</code>,
4565	where <code>t</code> is the value at the given index,
4566	<code>v</code> is the value at the top of the stack,
4567	and <code>k</code> is the value just below the top.
4568
4569
4570	<p>
4571	This function pops both the key and the value from the stack.
4572	As in Lua, this function may trigger a metamethod
4573	for the "newindex" event (see <a href="#2.4">§2.4</a>).
4574
4575
4576
4577
4578
4579	<hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
4580	<span class="apii">[-?, +?, –]</span>
4581	<pre>void lua_settop (lua_State *L, int index);</pre>
4582
4583	<p>
4584	Accepts any index, or 0,
4585	and sets the stack top to this index.
4586	If the new top is larger than the old one,
4587	then the new elements are filled with <b>nil</b>.
4588	If <code>index</code> is 0, then all stack elements are removed.
4589
4590
4591
4592
4593
4594	<hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p>
4595	<span class="apii">[-1, +0, –]</span>
4596	<pre>void lua_setuservalue (lua_State *L, int index);</pre>
4597
4598	<p>
4599	Pops a table or <b>nil</b> from the stack and sets it as
4600	the new value associated to the userdata at the given index.
4601
4602
4603
4604
4605
4606	<hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
4607	<pre>typedef struct lua_State lua_State;</pre>
4608
4609	<p>
4610	An opaque structure that points to a thread and indirectly
4611	(through the thread) to the whole state of a Lua interpreter.
4612	The Lua library is fully reentrant:
4613	it has no global variables.
4614	All information about a state is accessible through this structure.
4615
4616
4617	<p>
4618	A pointer to this structure must be passed as the first argument to
4619	every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
4620	which creates a Lua state from scratch.
4621
4622
4623
4624
4625
4626	<hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
4627	<span class="apii">[-0, +0, –]</span>
4628	<pre>int lua_status (lua_State *L);</pre>
4629
4630	<p>
4631	Returns the status of the thread <code>L</code>.
4632
4633
4634	<p>
4635	The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread,
4636	an error code if the thread finished the execution
4637	of a <a href="#lua_resume"><code>lua_resume</code></a> with an error,
4638	or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
4639
4640
4641	<p>
4642	You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>.
4643	You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
4644	(to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a>
4645	(to resume a coroutine).
4646
4647
4648
4649
4650
4651	<hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
4652	<span class="apii">[-0, +0, –]</span>
4653	<pre>int lua_toboolean (lua_State *L, int index);</pre>
4654
4655	<p>
4656	Converts the Lua value at the given index to a C boolean
4657	value (0 or 1).
4658	Like all tests in Lua,
4659	<a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value
4660	different from <b>false</b> and <b>nil</b>;
4661	otherwise it returns false.
4662	(If you want to accept only actual boolean values,
4663	use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
4664
4665
4666
4667
4668
4669	<hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
4670	<span class="apii">[-0, +0, –]</span>
4671	<pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
4672
4673	<p>
4674	Converts a value at the given index to a C function.
4675	That value must be a C function;
4676	otherwise, returns <code>NULL</code>.
4677
4678
4679
4680
4681
4682	<hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
4683	<span class="apii">[-0, +0, –]</span>
4684	<pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
4685
4686	<p>
4687	Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4688
4689
4690
4691
4692
4693	<hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p>
4694	<span class="apii">[-0, +0, –]</span>
4695	<pre>lua_Integer lua_tointegerx (lua_State L, int index, int isnum);</pre>
4696
4697	<p>
4698	Converts the Lua value at the given index
4699	to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
4700	The Lua value must be a number or a string convertible to a number
4701	(see <a href="#3.4.2">§3.4.2</a>);
4702	otherwise, <code>lua_tointegerx</code> returns 0.
4703
4704
4705	<p>
4706	If the number is not an integer,
4707	it is truncated in some non-specified way.
4708
4709
4710	<p>
4711	If <code>isnum</code> is not <code>NULL</code>,
4712	its referent is assigned a boolean value that
4713	indicates whether the operation succeeded.
4714
4715
4716
4717
4718
4719	<hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
4720	<span class="apii">[-0, +0, <em>e</em>]</span>
4721	<pre>const char lua_tolstring (lua_State L, int index, size_t *len);</pre>
4722
4723	<p>
4724	Converts the Lua value at the given index to a C string.
4725	If <code>len</code> is not <code>NULL</code>,
4726	it also sets <code>*len</code> with the string length.
4727	The Lua value must be a string or a number;
4728	otherwise, the function returns <code>NULL</code>.
4729	If the value is a number,
4730	then <code>lua_tolstring</code> also
4731	<em>changes the actual value in the stack to a string</em>.
4732	(This change confuses <a href="#lua_next"><code>lua_next</code></a>
4733	when <code>lua_tolstring</code> is applied to keys during a table traversal.)
4734
4735
4736	<p>
4737	<code>lua_tolstring</code> returns a fully aligned pointer
4738	to a string inside the Lua state.
4739	This string always has a zero ('<code>\0</code>')
4740	after its last character (as in C),
4741	but can contain other zeros in its body.
4742	Because Lua has garbage collection,
4743	there is no guarantee that the pointer returned by <code>lua_tolstring</code>
4744	will be valid after the corresponding value is removed from the stack.
4745
4746
4747
4748
4749
4750	<hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
4751	<span class="apii">[-0, +0, –]</span>
4752	<pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
4753
4754	<p>
4755	Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4756
4757
4758
4759
4760
4761	<hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p>
4762	<span class="apii">[-0, +0, –]</span>
4763	<pre>lua_Number lua_tonumberx (lua_State L, int index, int isnum);</pre>
4764
4765	<p>
4766	Converts the Lua value at the given index
4767	to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
4768	The Lua value must be a number or a string convertible to a number
4769	(see <a href="#3.4.2">§3.4.2</a>);
4770	otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0.
4771
4772
4773	<p>
4774	If <code>isnum</code> is not <code>NULL</code>,
4775	its referent is assigned a boolean value that
4776	indicates whether the operation succeeded.
4777
4778
4779
4780
4781
4782	<hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
4783	<span class="apii">[-0, +0, –]</span>
4784	<pre>const void lua_topointer (lua_State L, int index);</pre>
4785
4786	<p>
4787	Converts the value at the given index to a generic
4788	C pointer (<code>void*</code>).
4789	The value can be a userdata, a table, a thread, or a function;
4790	otherwise, <code>lua_topointer</code> returns <code>NULL</code>.
4791	Different objects will give different pointers.
4792	There is no way to convert the pointer back to its original value.
4793
4794
4795	<p>
4796	Typically this function is used only for debug information.
4797
4798
4799
4800
4801
4802	<hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
4803	<span class="apii">[-0, +0, <em>e</em>]</span>
4804	<pre>const char lua_tostring (lua_State L, int index);</pre>
4805
4806	<p>
4807	Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
4808
4809
4810
4811
4812
4813	<hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
4814	<span class="apii">[-0, +0, –]</span>
4815	<pre>lua_State lua_tothread (lua_State L, int index);</pre>
4816
4817	<p>
4818	Converts the value at the given index to a Lua thread
4819	(represented as <code>lua_State*</code>).
4820	This value must be a thread;
4821	otherwise, the function returns <code>NULL</code>.
4822
4823
4824
4825
4826
4827	<hr><h3><a name="lua_tounsigned"><code>lua_tounsigned</code></a></h3><p>
4828	<span class="apii">[-0, +0, –]</span>
4829	<pre>lua_Unsigned lua_tounsigned (lua_State *L, int index);</pre>
4830
4831	<p>
4832	Equivalent to <a href="#lua_tounsignedx"><code>lua_tounsignedx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4833
4834
4835
4836
4837
4838	<hr><h3><a name="lua_tounsignedx"><code>lua_tounsignedx</code></a></h3><p>
4839	<span class="apii">[-0, +0, –]</span>
4840	<pre>lua_Unsigned lua_tounsignedx (lua_State L, int index, int isnum);</pre>
4841
4842	<p>
4843	Converts the Lua value at the given index
4844	to the unsigned integral type <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
4845	The Lua value must be a number or a string convertible to a number
4846	(see <a href="#3.4.2">§3.4.2</a>);
4847	otherwise, <code>lua_tounsignedx</code> returns 0.
4848
4849
4850	<p>
4851	If the number is not an integer,
4852	it is truncated in some non-specified way.
4853	If the number is outside the range of representable values,
4854	it is normalized to the remainder of its division by
4855	one more than the maximum representable value.
4856
4857
4858	<p>
4859	If <code>isnum</code> is not <code>NULL</code>,
4860	its referent is assigned a boolean value that
4861	indicates whether the operation succeeded.
4862
4863
4864
4865
4866
4867	<hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
4868	<span class="apii">[-0, +0, –]</span>
4869	<pre>void lua_touserdata (lua_State L, int index);</pre>
4870
4871	<p>
4872	If the value at the given index is a full userdata,
4873	returns its block address.
4874	If the value is a light userdata,
4875	returns its pointer.
4876	Otherwise, returns <code>NULL</code>.
4877
4878
4879
4880
4881
4882	<hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
4883	<span class="apii">[-0, +0, –]</span>
4884	<pre>int lua_type (lua_State *L, int index);</pre>
4885
4886	<p>
4887	Returns the type of the value in the given valid index,
4888	or <code>LUA_TNONE</code> for a non-valid (but acceptable) index.
4889	The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
4890	defined in <code>lua.h</code>:
4891	<a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>,
4892	<a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>,
4893	<a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>,
4894	<a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>,
4895	<a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>,
4896	<a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
4897	<a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>,
4898	<a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>,
4899	and
4900	<a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>.
4901
4902
4903
4904
4905
4906	<hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
4907	<span class="apii">[-0, +0, –]</span>
4908	<pre>const char lua_typename (lua_State L, int tp);</pre>
4909
4910	<p>
4911	Returns the name of the type encoded by the value <code>tp</code>,
4912	which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
4913
4914
4915
4916
4917
4918	<hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3>
4919	<pre>typedef unsigned long lua_Unsigned;</pre>
4920
4921	<p>
4922	The type used by the Lua API to represent unsigned integral values.
4923	It must have at least 32 bits.
4924
4925
4926	<p>
4927	By default it is an <code>unsigned int</code> or an <code>unsigned long</code>,
4928	whichever can hold 32-bit values.
4929
4930
4931
4932
4933
4934	<hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p>
4935	<span class="apii">[-0, +0, –]</span>
4936	<pre>int lua_upvalueindex (int i);</pre>
4937
4938	<p>
4939	Returns the pseudo-index that represents the <code>i</code>-th upvalue of
4940	the running function (see <a href="#4.4">§4.4</a>).
4941
4942
4943
4944
4945
4946	<hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
4947	<span class="apii">[-0, +0, <em>v</em>]</span>
4948	<pre>const lua_Number lua_version (lua_State L);</pre>
4949
4950	<p>
4951	Returns the address of the version number stored in the Lua core.
4952	When called with a valid <a href="#lua_State"><code>lua_State</code></a>,
4953	returns the address of the version used to create that state.
4954	When called with <code>NULL</code>,
4955	returns the address of the version running the call.
4956
4957
4958
4959
4960
4961	<hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
4962	<pre>typedef int (lua_Writer) (lua_State L,
4963	const void* p,
4964	size_t sz,
4965	void* ud);</pre>
4966
4967	<p>
4968	The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
4969	Every time it produces another piece of chunk,
4970	<a href="#lua_dump"><code>lua_dump</code></a> calls the writer,
4971	passing along the buffer to be written (<code>p</code>),
4972	its size (<code>sz</code>),
4973	and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
4974
4975
4976	<p>
4977	The writer returns an error code:
4978	0 means no errors;
4979	any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
4980	calling the writer again.
4981
4982
4983
4984
4985
4986	<hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
4987	<span class="apii">[-?, +?, –]</span>
4988	<pre>void lua_xmove (lua_State from, lua_State to, int n);</pre>
4989
4990	<p>
4991	Exchange values between different threads of the same state.
4992
4993
4994	<p>
4995	This function pops <code>n</code> values from the stack <code>from</code>,
4996	and pushes them onto the stack <code>to</code>.
4997
4998
4999
5000
5001
5002	<hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
5003	<span class="apii">[-?, +?, –]</span>
5004	<pre>int lua_yield (lua_State *L, int nresults);</pre>
5005
5006	<p>
5007	This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5008	but it has no continuation (see <a href="#4.7">§4.7</a>).
5009	Therefore, when the thread resumes,
5010	it returns to the function that called
5011	the function calling <code>lua_yield</code>.
5012
5013
5014
5015
5016
5017	<hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p>
5018	<span class="apii">[-?, +?, –]</span>
5019	<pre>int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k);</pre>
5020
5021	<p>
5022	Yields a coroutine.
5023
5024
5025	<p>
5026	This function should only be called as the
5027	return expression of a C function, as follows:
5028
5029	<pre>
5030	return lua_yieldk (L, n, i, k);
5031	</pre><p>
5032	When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a> in that way,
5033	the running coroutine suspends its execution,
5034	and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
5035	The parameter <code>nresults</code> is the number of values from the stack
5036	that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
5037
5038
5039	<p>
5040	When the coroutine is resumed again,
5041	Lua calls the given continuation function <code>k</code> to continue
5042	the execution of the C function that yielded (see <a href="#4.7">§4.7</a>).
5043	This continuation function receives the same stack
5044	from the previous function,
5045	with the results removed and
5046	replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>.
5047	Moreover,
5048	the continuation function may access the value <code>ctx</code>
5049	by calling <a href="#lua_getctx"><code>lua_getctx</code></a>.
5050
5051
5052
5053
5054
5055
5056
5057	<h2>4.9 – <a name="4.9">The Debug Interface</a></h2>
5058
5059	<p>
5060	Lua has no built-in debugging facilities.
5061	Instead, it offers a special interface
5062	by means of functions and <em>hooks</em>.
5063	This interface allows the construction of different
5064	kinds of debuggers, profilers, and other tools
5065	that need "inside information" from the interpreter.
5066
5067
5068
5069	<hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
5070	<pre>typedef struct lua_Debug {
5071	int event;
5072	const char name; / (n) */
5073	const char namewhat; / (n) */
5074	const char what; / (S) */
5075	const char source; / (S) */
5076	int currentline; /* (l) */
5077	int linedefined; /* (S) */
5078	int lastlinedefined; /* (S) */
5079	unsigned char nups; /* (u) number of upvalues */
5080	unsigned char nparams; /* (u) number of parameters */
5081	char isvararg; /* (u) */
5082	char istailcall; /* (t) */
5083	char short_src[LUA_IDSIZE]; /* (S) */
5084	/* private part */
5085	<em>other fields</em>
5086	} lua_Debug;</pre>
5087
5088	<p>
5089	A structure used to carry different pieces of
5090	information about a function or an activation record.
5091	<a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
5092	of this structure, for later use.
5093	To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
5094	call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5095
5096
5097	<p>
5098	The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
5099
5100	<ul>
5101
5102	<li><b><code>source</code>: </b>
5103	the source of the chunk that created the function.
5104	If <code>source</code> starts with a '<code>@</code>',
5105	it means that the function was defined in a file where
5106	the file name follows the '<code>@</code>'.
5107	If <code>source</code> starts with a '<code>=</code>',
5108	the remainder of its contents describe the source in a user-dependent manner.
5109	Otherwise,
5110	the function was defined in a string where
5111	<code>source</code> is that string.
5112	</li>
5113
5114	<li><b><code>short_src</code>: </b>
5115	a "printable" version of <code>source</code>, to be used in error messages.
5116	</li>
5117
5118	<li><b><code>linedefined</code>: </b>
5119	the line number where the definition of the function starts.
5120	</li>
5121
5122	<li><b><code>lastlinedefined</code>: </b>
5123	the line number where the definition of the function ends.
5124	</li>
5125
5126	<li><b><code>what</code>: </b>
5127	the string <code>"Lua"</code> if the function is a Lua function,
5128	<code>"C"</code> if it is a C function,
5129	<code>"main"</code> if it is the main part of a chunk.
5130	</li>
5131
5132	<li><b><code>currentline</code>: </b>
5133	the current line where the given function is executing.
5134	When no line information is available,
5135	<code>currentline</code> is set to -1.
5136	</li>
5137
5138	<li><b><code>name</code>: </b>
5139	a reasonable name for the given function.
5140	Because functions in Lua are first-class values,
5141	they do not have a fixed name:
5142	some functions can be the value of multiple global variables,
5143	while others can be stored only in a table field.
5144	The <code>lua_getinfo</code> function checks how the function was
5145	called to find a suitable name.
5146	If it cannot find a name,
5147	then <code>name</code> is set to <code>NULL</code>.
5148	</li>
5149
5150	<li><b><code>namewhat</code>: </b>
5151	explains the <code>name</code> field.
5152	The value of <code>namewhat</code> can be
5153	<code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
5154	<code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
5155	according to how the function was called.
5156	(Lua uses the empty string when no other option seems to apply.)
5157	</li>
5158
5159	<li><b><code>istailcall</code>: </b>
5160	true if this function invocation was called by a tail call.
5161	In this case, the caller of this level is not in the stack.
5162	</li>
5163
5164	<li><b><code>nups</code>: </b>
5165	the number of upvalues of the function.
5166	</li>
5167
5168	<li><b><code>nparams</code>: </b>
5169	the number of fixed parameters of the function
5170	(always 0 for C functions).
5171	</li>
5172
5173	<li><b><code>isvararg</code>: </b>
5174	true if the function is a vararg function
5175	(always true for C functions).
5176	</li>
5177
5178	</ul>
5179
5180
5181
5182
5183	<hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
5184	<span class="apii">[-0, +0, –]</span>
5185	<pre>lua_Hook lua_gethook (lua_State *L);</pre>
5186
5187	<p>
5188	Returns the current hook function.
5189
5190
5191
5192
5193
5194	<hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
5195	<span class="apii">[-0, +0, –]</span>
5196	<pre>int lua_gethookcount (lua_State *L);</pre>
5197
5198	<p>
5199	Returns the current hook count.
5200
5201
5202
5203
5204
5205	<hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
5206	<span class="apii">[-0, +0, –]</span>
5207	<pre>int lua_gethookmask (lua_State *L);</pre>
5208
5209	<p>
5210	Returns the current hook mask.
5211
5212
5213
5214
5215
5216	<hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
5217	<span class="apii">[-(0\|1), +(0\|1\|2), <em>e</em>]</span>
5218	<pre>int lua_getinfo (lua_State L, const char what, lua_Debug *ar);</pre>
5219
5220	<p>
5221	Gets information about a specific function or function invocation.
5222
5223
5224	<p>
5225	To get information about a function invocation,
5226	the parameter <code>ar</code> must be a valid activation record that was
5227	filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5228	given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5229
5230
5231	<p>
5232	To get information about a function you push it onto the stack
5233	and start the <code>what</code> string with the character '<code>></code>'.
5234	(In that case,
5235	<code>lua_getinfo</code> pops the function from the top of the stack.)
5236	For instance, to know in which line a function <code>f</code> was defined,
5237	you can write the following code:
5238
5239	<pre>
5240	lua_Debug ar;
5241	lua_getglobal(L, "f"); /* get global 'f' */
5242	lua_getinfo(L, ">S", &ar);
5243	printf("%d\n", ar.linedefined);
5244	</pre>
5245
5246	<p>
5247	Each character in the string <code>what</code>
5248	selects some fields of the structure <code>ar</code> to be filled or
5249	a value to be pushed on the stack:
5250
5251	<ul>
5252
5253	<li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>;
5254	</li>
5255
5256	<li><b>'<code>S</code>': </b>
5257	fills in the fields <code>source</code>, <code>short_src</code>,
5258	<code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
5259	</li>
5260
5261	<li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>;
5262	</li>
5263
5264	<li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>;
5265	</li>
5266
5267	<li><b>'<code>u</code>': </b> fills in the fields
5268	<code>nups</code>, <code>nparams</code>, and <code>isvararg</code>;
5269	</li>
5270
5271	<li><b>'<code>f</code>': </b>
5272	pushes onto the stack the function that is
5273	running at the given level;
5274	</li>
5275
5276	<li><b>'<code>L</code>': </b>
5277	pushes onto the stack a table whose indices are the
5278	numbers of the lines that are valid on the function.
5279	(A <em>valid line</em> is a line with some associated code,
5280	that is, a line where you can put a break point.
5281	Non-valid lines include empty lines and comments.)
5282	</li>
5283
5284	</ul>
5285
5286	<p>
5287	This function returns 0 on error
5288	(for instance, an invalid option in <code>what</code>).
5289
5290
5291
5292
5293
5294	<hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
5295	<span class="apii">[-0, +(0\|1), –]</span>
5296	<pre>const char lua_getlocal (lua_State L, lua_Debug *ar, int n);</pre>
5297
5298	<p>
5299	Gets information about a local variable of
5300	a given activation record or a given function.
5301
5302
5303	<p>
5304	In the first case,
5305	the parameter <code>ar</code> must be a valid activation record that was
5306	filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5307	given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5308	The index <code>n</code> selects which local variable to inspect;
5309	see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices
5310	and names.
5311
5312
5313	<p>
5314	<a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
5315	and returns its name.
5316
5317
5318	<p>
5319	In the second case, <code>ar</code> should be <code>NULL</code> and the function
5320	to be inspected must be at the top of the stack.
5321	In this case, only parameters of Lua functions are visible
5322	(as there is no information about what variables are active)
5323	and no values are pushed onto the stack.
5324
5325
5326	<p>
5327	Returns <code>NULL</code> (and pushes nothing)
5328	when the index is greater than
5329	the number of active local variables.
5330
5331
5332
5333
5334
5335	<hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
5336	<span class="apii">[-0, +0, –]</span>
5337	<pre>int lua_getstack (lua_State L, int level, lua_Debug ar);</pre>
5338
5339	<p>
5340	Gets information about the interpreter runtime stack.
5341
5342
5343	<p>
5344	This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
5345	an identification of the <em>activation record</em>
5346	of the function executing at a given level.
5347	Level 0 is the current running function,
5348	whereas level <em>n+1</em> is the function that has called level <em>n</em>
5349	(except for tail calls, which do not count on the stack).
5350	When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1;
5351	when called with a level greater than the stack depth,
5352	it returns 0.
5353
5354
5355
5356
5357
5358	<hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
5359	<span class="apii">[-0, +(0\|1), –]</span>
5360	<pre>const char lua_getupvalue (lua_State L, int funcindex, int n);</pre>
5361
5362	<p>
5363	Gets information about a closure's upvalue.
5364	(For Lua functions,
5365	upvalues are the external local variables that the function uses,
5366	and that are consequently included in its closure.)
5367	<a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
5368	pushes the upvalue's value onto the stack,
5369	and returns its name.
5370	<code>funcindex</code> points to the closure in the stack.
5371	(Upvalues have no particular order,
5372	as they are active through the whole function.
5373	So, they are numbered in an arbitrary order.)
5374
5375
5376	<p>
5377	Returns <code>NULL</code> (and pushes nothing)
5378	when the index is greater than the number of upvalues.
5379	For C functions, this function uses the empty string <code>""</code>
5380	as a name for all upvalues.
5381
5382
5383
5384
5385
5386	<hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
5387	<pre>typedef void (lua_Hook) (lua_State L, lua_Debug *ar);</pre>
5388
5389	<p>
5390	Type for debugging hook functions.
5391
5392
5393	<p>
5394	Whenever a hook is called, its <code>ar</code> argument has its field
5395	<code>event</code> set to the specific event that triggered the hook.
5396	Lua identifies these events with the following constants:
5397	<a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
5398	<a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
5399	and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
5400	Moreover, for line events, the field <code>currentline</code> is also set.
5401	To get the value of any other field in <code>ar</code>,
5402	the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5403
5404
5405	<p>
5406	For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>,
5407	the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call;
5408	in this case, there will be no corresponding return event.
5409
5410
5411	<p>
5412	While Lua is running a hook, it disables other calls to hooks.
5413	Therefore, if a hook calls back Lua to execute a function or a chunk,
5414	this execution occurs without any calls to hooks.
5415
5416
5417	<p>
5418	Hook functions cannot have continuations,
5419	that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5420	<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>.
5421
5422
5423	<p>
5424	Hook functions can yield under the following conditions:
5425	Only count and line events can yield
5426	and they cannot yield any value;
5427	to yield a hook function must finish its execution
5428	calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero.
5429
5430
5431
5432
5433
5434	<hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
5435	<span class="apii">[-0, +0, –]</span>
5436	<pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
5437
5438	<p>
5439	Sets the debugging hook function.
5440
5441
5442	<p>
5443	Argument <code>f</code> is the hook function.
5444	<code>mask</code> specifies on which events the hook will be called:
5445	it is formed by a bitwise or of the constants
5446	<a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
5447	<a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
5448	<a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
5449	and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
5450	The <code>count</code> argument is only meaningful when the mask
5451	includes <code>LUA_MASKCOUNT</code>.
5452	For each event, the hook is called as explained below:
5453
5454	<ul>
5455
5456	<li><b>The call hook: </b> is called when the interpreter calls a function.
5457	The hook is called just after Lua enters the new function,
5458	before the function gets its arguments.
5459	</li>
5460
5461	<li><b>The return hook: </b> is called when the interpreter returns from a function.
5462	The hook is called just before Lua leaves the function.
5463	There is no standard way to access the values
5464	to be returned by the function.
5465	</li>
5466
5467	<li><b>The line hook: </b> is called when the interpreter is about to
5468	start the execution of a new line of code,
5469	or when it jumps back in the code (even to the same line).
5470	(This event only happens while Lua is executing a Lua function.)
5471	</li>
5472
5473	<li><b>The count hook: </b> is called after the interpreter executes every
5474	<code>count</code> instructions.
5475	(This event only happens while Lua is executing a Lua function.)
5476	</li>
5477
5478	</ul>
5479
5480	<p>
5481	A hook is disabled by setting <code>mask</code> to zero.
5482
5483
5484
5485
5486
5487	<hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
5488	<span class="apii">[-(0\|1), +0, –]</span>
5489	<pre>const char lua_setlocal (lua_State L, lua_Debug *ar, int n);</pre>
5490
5491	<p>
5492	Sets the value of a local variable of a given activation record.
5493	Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
5494	(see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
5495	<a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
5496	to the variable and returns its name.
5497	It also pops the value from the stack.
5498
5499
5500	<p>
5501	Returns <code>NULL</code> (and pops nothing)
5502	when the index is greater than
5503	the number of active local variables.
5504
5505
5506
5507
5508
5509	<hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
5510	<span class="apii">[-(0\|1), +0, –]</span>
5511	<pre>const char lua_setupvalue (lua_State L, int funcindex, int n);</pre>
5512
5513	<p>
5514	Sets the value of a closure's upvalue.
5515	It assigns the value at the top of the stack
5516	to the upvalue and returns its name.
5517	It also pops the value from the stack.
5518	Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5519	(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
5520
5521
5522	<p>
5523	Returns <code>NULL</code> (and pops nothing)
5524	when the index is greater than the number of upvalues.
5525
5526
5527
5528
5529
5530	<hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
5531	<span class="apii">[-0, +0, –]</span>
5532	<pre>void lua_upvalueid (lua_State L, int funcindex, int n);</pre>
5533
5534	<p>
5535	Returns an unique identifier for the upvalue numbered <code>n</code>
5536	from the closure at index <code>funcindex</code>.
5537	Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5538	(see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>)
5539	(but <code>n</code> cannot be greater than the number of upvalues).
5540
5541
5542	<p>
5543	These unique identifiers allow a program to check whether different
5544	closures share upvalues.
5545	Lua closures that share an upvalue
5546	(that is, that access a same external local variable)
5547	will return identical ids for those upvalue indices.
5548
5549
5550
5551
5552
5553	<hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
5554	<span class="apii">[-0, +0, –]</span>
5555	<pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
5556	int funcindex2, int n2);</pre>
5557
5558	<p>
5559	Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code>
5560	refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>.
5561
5562
5563
5564
5565
5566
5567
5568	<h1>5 – <a name="5">The Auxiliary Library</a></h1>
5569
5570	<p>
5571
5572	The <em>auxiliary library</em> provides several convenient functions
5573	to interface C with Lua.
5574	While the basic API provides the primitive functions for all
5575	interactions between C and Lua,
5576	the auxiliary library provides higher-level functions for some
5577	common tasks.
5578
5579
5580	<p>
5581	All functions and types from the auxiliary library
5582	are defined in header file <code>lauxlib.h</code> and
5583	have a prefix <code>luaL_</code>.
5584
5585
5586	<p>
5587	All functions in the auxiliary library are built on
5588	top of the basic API,
5589	and so they provide nothing that cannot be done with that API.
5590	Nevertheless, the use of the auxiliary library ensures
5591	more consistency to your code.
5592
5593
5594	<p>
5595	Several functions in the auxiliary library use internally some
5596	extra stack slots.
5597	When a function in the auxiliary library uses less than five slots,
5598	it does not check the stack size;
5599	it simply assumes that there are enough slots.
5600
5601
5602	<p>
5603	Several functions in the auxiliary library are used to
5604	check C function arguments.
5605	Because the error message is formatted for arguments
5606	(e.g., "<code>bad argument #1</code>"),
5607	you should not use these functions for other stack values.
5608
5609
5610	<p>
5611	Functions called <code>luaL_check*</code>
5612	always throw an error if the check is not satisfied.
5613
5614
5615
5616	<h2>5.1 – <a name="5.1">Functions and Types</a></h2>
5617
5618	<p>
5619	Here we list all functions and types from the auxiliary library
5620	in alphabetical order.
5621
5622
5623
5624	<hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
5625	<span class="apii">[-?, +?, <em>e</em>]</span>
5626	<pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
5627
5628	<p>
5629	Adds the byte <code>c</code> to the buffer <code>B</code>
5630	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5631
5632
5633
5634
5635
5636	<hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
5637	<span class="apii">[-?, +?, <em>e</em>]</span>
5638	<pre>void luaL_addlstring (luaL_Buffer B, const char s, size_t l);</pre>
5639
5640	<p>
5641	Adds the string pointed to by <code>s</code> with length <code>l</code> to
5642	the buffer <code>B</code>
5643	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5644	The string can contain embedded zeros.
5645
5646
5647
5648
5649
5650	<hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
5651	<span class="apii">[-?, +?, <em>e</em>]</span>
5652	<pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
5653
5654	<p>
5655	Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
5656	a string of length <code>n</code> previously copied to the
5657	buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
5658
5659
5660
5661
5662
5663	<hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
5664	<span class="apii">[-?, +?, <em>e</em>]</span>
5665	<pre>void luaL_addstring (luaL_Buffer B, const char s);</pre>
5666
5667	<p>
5668	Adds the zero-terminated string pointed to by <code>s</code>
5669	to the buffer <code>B</code>
5670	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5671	The string cannot contain embedded zeros.
5672
5673
5674
5675
5676
5677	<hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
5678	<span class="apii">[-1, +?, <em>e</em>]</span>
5679	<pre>void luaL_addvalue (luaL_Buffer *B);</pre>
5680
5681	<p>
5682	Adds the value at the top of the stack
5683	to the buffer <code>B</code>
5684	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5685	Pops the value.
5686
5687
5688	<p>
5689	This is the only function on string buffers that can (and must)
5690	be called with an extra element on the stack,
5691	which is the value to be added to the buffer.
5692
5693
5694
5695
5696
5697	<hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
5698	<span class="apii">[-0, +0, <em>v</em>]</span>
5699	<pre>void luaL_argcheck (lua_State *L,
5700	int cond,
5701	int arg,
5702	const char *extramsg);</pre>
5703
5704	<p>
5705	Checks whether <code>cond</code> is true.
5706	If not, raises an error with a standard message.
5707
5708
5709
5710
5711
5712	<hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
5713	<span class="apii">[-0, +0, <em>v</em>]</span>
5714	<pre>int luaL_argerror (lua_State L, int arg, const char extramsg);</pre>
5715
5716	<p>
5717	Raises an error with a standard message
5718	that includes <code>extramsg</code> as a comment.
5719
5720
5721	<p>
5722	This function never returns,
5723	but it is an idiom to use it in C functions
5724	as <code>return luaL_argerror(<em>args</em>)</code>.
5725
5726
5727
5728
5729
5730	<hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
5731	<pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
5732
5733	<p>
5734	Type for a <em>string buffer</em>.
5735
5736
5737	<p>
5738	A string buffer allows C code to build Lua strings piecemeal.
5739	Its pattern of use is as follows:
5740
5741	<ul>
5742
5743	<li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
5744
5745	<li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li>
5746
5747	<li>
5748	Then add string pieces to the buffer calling any of
5749	the <code>luaL_add*</code> functions.
5750	</li>
5751
5752	<li>
5753	Finish by calling <code>luaL_pushresult(&b)</code>.
5754	This call leaves the final string on the top of the stack.
5755	</li>
5756
5757	</ul>
5758
5759	<p>
5760	If you know beforehand the total size of the resulting string,
5761	you can use the buffer like this:
5762
5763	<ul>
5764
5765	<li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
5766
5767	<li>Then initialize it and preallocate a space of
5768	size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li>
5769
5770	<li>Then copy the string into that space.</li>
5771
5772	<li>
5773	Finish by calling <code>luaL_pushresultsize(&b, sz)</code>,
5774	where <code>sz</code> is the total size of the resulting string
5775	copied into that space.
5776	</li>
5777
5778	</ul>
5779
5780	<p>
5781	During its normal operation,
5782	a string buffer uses a variable number of stack slots.
5783	So, while using a buffer, you cannot assume that you know where
5784	the top of the stack is.
5785	You can use the stack between successive calls to buffer operations
5786	as long as that use is balanced;
5787	that is,
5788	when you call a buffer operation,
5789	the stack is at the same level
5790	it was immediately after the previous buffer operation.
5791	(The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
5792	After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
5793	level when the buffer was initialized,
5794	plus the final string on its top.
5795
5796
5797
5798
5799
5800	<hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
5801	<span class="apii">[-0, +0, –]</span>
5802	<pre>void luaL_buffinit (lua_State L, luaL_Buffer B);</pre>
5803
5804	<p>
5805	Initializes a buffer <code>B</code>.
5806	This function does not allocate any space;
5807	the buffer must be declared as a variable
5808	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5809
5810
5811
5812
5813
5814	<hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p>
5815	<span class="apii">[-?, +?, <em>e</em>]</span>
5816	<pre>char luaL_buffinitsize (lua_State L, luaL_Buffer *B, size_t sz);</pre>
5817
5818	<p>
5819	Equivalent to the sequence
5820	<a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>.
5821
5822
5823
5824
5825
5826	<hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
5827	<span class="apii">[-0, +(0\|1), <em>e</em>]</span>
5828	<pre>int luaL_callmeta (lua_State L, int obj, const char e);</pre>
5829
5830	<p>
5831	Calls a metamethod.
5832
5833
5834	<p>
5835	If the object at index <code>obj</code> has a metatable and this
5836	metatable has a field <code>e</code>,
5837	this function calls this field passing the object as its only argument.
5838	In this case this function returns true and pushes onto the
5839	stack the value returned by the call.
5840	If there is no metatable or no metamethod,
5841	this function returns false (without pushing any value on the stack).
5842
5843
5844
5845
5846
5847	<hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
5848	<span class="apii">[-0, +0, <em>v</em>]</span>
5849	<pre>void luaL_checkany (lua_State *L, int arg);</pre>
5850
5851	<p>
5852	Checks whether the function has an argument
5853	of any type (including <b>nil</b>) at position <code>arg</code>.
5854
5855
5856
5857
5858
5859	<hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p>
5860	<span class="apii">[-0, +0, <em>v</em>]</span>
5861	<pre>int luaL_checkint (lua_State *L, int arg);</pre>
5862
5863	<p>
5864	Checks whether the function argument <code>arg</code> is a number
5865	and returns this number cast to an <code>int</code>.
5866
5867
5868
5869
5870
5871	<hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
5872	<span class="apii">[-0, +0, <em>v</em>]</span>
5873	<pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre>
5874
5875	<p>
5876	Checks whether the function argument <code>arg</code> is a number
5877	and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
5878
5879
5880
5881
5882
5883	<hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p>
5884	<span class="apii">[-0, +0, <em>v</em>]</span>
5885	<pre>long luaL_checklong (lua_State *L, int arg);</pre>
5886
5887	<p>
5888	Checks whether the function argument <code>arg</code> is a number
5889	and returns this number cast to a <code>long</code>.
5890
5891
5892
5893
5894
5895	<hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
5896	<span class="apii">[-0, +0, <em>v</em>]</span>
5897	<pre>const char luaL_checklstring (lua_State L, int arg, size_t *l);</pre>
5898
5899	<p>
5900	Checks whether the function argument <code>arg</code> is a string
5901	and returns this string;
5902	if <code>l</code> is not <code>NULL</code> fills <code>*l</code>
5903	with the string's length.
5904
5905
5906	<p>
5907	This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
5908	so all conversions and caveats of that function apply here.
5909
5910
5911
5912
5913
5914	<hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
5915	<span class="apii">[-0, +0, <em>v</em>]</span>
5916	<pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre>
5917
5918	<p>
5919	Checks whether the function argument <code>arg</code> is a number
5920	and returns this number.
5921
5922
5923
5924
5925
5926	<hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
5927	<span class="apii">[-0, +0, <em>v</em>]</span>
5928	<pre>int luaL_checkoption (lua_State *L,
5929	int arg,
5930	const char *def,
5931	const char *const lst[]);</pre>
5932
5933	<p>
5934	Checks whether the function argument <code>arg</code> is a string and
5935	searches for this string in the array <code>lst</code>
5936	(which must be NULL-terminated).
5937	Returns the index in the array where the string was found.
5938	Raises an error if the argument is not a string or
5939	if the string cannot be found.
5940
5941
5942	<p>
5943	If <code>def</code> is not <code>NULL</code>,
5944	the function uses <code>def</code> as a default value when
5945	there is no argument <code>arg</code> or when this argument is <b>nil</b>.
5946
5947
5948	<p>
5949	This is a useful function for mapping strings to C enums.
5950	(The usual convention in Lua libraries is
5951	to use strings instead of numbers to select options.)
5952
5953
5954
5955
5956
5957	<hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
5958	<span class="apii">[-0, +0, <em>v</em>]</span>
5959	<pre>void luaL_checkstack (lua_State L, int sz, const char msg);</pre>
5960
5961	<p>
5962	Grows the stack size to <code>top + sz</code> elements,
5963	raising an error if the stack cannot grow to that size.
5964	<code>msg</code> is an additional text to go into the error message
5965	(or <code>NULL</code> for no additional text).
5966
5967
5968
5969
5970
5971	<hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
5972	<span class="apii">[-0, +0, <em>v</em>]</span>
5973	<pre>const char luaL_checkstring (lua_State L, int arg);</pre>
5974
5975	<p>
5976	Checks whether the function argument <code>arg</code> is a string
5977	and returns this string.
5978
5979
5980	<p>
5981	This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
5982	so all conversions and caveats of that function apply here.
5983
5984
5985
5986
5987
5988	<hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
5989	<span class="apii">[-0, +0, <em>v</em>]</span>
5990	<pre>void luaL_checktype (lua_State *L, int arg, int t);</pre>
5991
5992	<p>
5993	Checks whether the function argument <code>arg</code> has type <code>t</code>.
5994	See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
5995
5996
5997
5998
5999
6000	<hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
6001	<span class="apii">[-0, +0, <em>v</em>]</span>
6002	<pre>void luaL_checkudata (lua_State L, int arg, const char *tname);</pre>
6003
6004	<p>
6005	Checks whether the function argument <code>arg</code> is a userdata
6006	of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and
6007	returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>).
6008
6009
6010
6011
6012
6013	<hr><h3><a name="luaL_checkunsigned"><code>luaL_checkunsigned</code></a></h3><p>
6014	<span class="apii">[-0, +0, <em>v</em>]</span>
6015	<pre>lua_Unsigned luaL_checkunsigned (lua_State *L, int arg);</pre>
6016
6017	<p>
6018	Checks whether the function argument <code>arg</code> is a number
6019	and returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
6020
6021
6022
6023
6024
6025	<hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p>
6026	<span class="apii">[-0, +0, –]</span>
6027	<pre>void luaL_checkversion (lua_State *L);</pre>
6028
6029	<p>
6030	Checks whether the core running the call,
6031	the core that created the Lua state,
6032	and the code making the call are all using the same version of Lua.
6033	Also checks whether the core running the call
6034	and the core that created the Lua state
6035	are using the same address space.
6036
6037
6038
6039
6040
6041	<hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
6042	<span class="apii">[-0, +?, <em>e</em>]</span>
6043	<pre>int luaL_dofile (lua_State L, const char filename);</pre>
6044
6045	<p>
6046	Loads and runs the given file.
6047	It is defined as the following macro:
6048
6049	<pre>
6050	(luaL_loadfile(L, filename) \|\| lua_pcall(L, 0, LUA_MULTRET, 0))
6051	</pre><p>
6052	It returns false if there are no errors
6053	or true in case of errors.
6054
6055
6056
6057
6058
6059	<hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
6060	<span class="apii">[-0, +?, –]</span>
6061	<pre>int luaL_dostring (lua_State L, const char str);</pre>
6062
6063	<p>
6064	Loads and runs the given string.
6065	It is defined as the following macro:
6066
6067	<pre>
6068	(luaL_loadstring(L, str) \|\| lua_pcall(L, 0, LUA_MULTRET, 0))
6069	</pre><p>
6070	It returns false if there are no errors
6071	or true in case of errors.
6072
6073
6074
6075
6076
6077	<hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
6078	<span class="apii">[-0, +0, <em>v</em>]</span>
6079	<pre>int luaL_error (lua_State L, const char fmt, ...);</pre>
6080
6081	<p>
6082	Raises an error.
6083	The error message format is given by <code>fmt</code>
6084	plus any extra arguments,
6085	following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
6086	It also adds at the beginning of the message the file name and
6087	the line number where the error occurred,
6088	if this information is available.
6089
6090
6091	<p>
6092	This function never returns,
6093	but it is an idiom to use it in C functions
6094	as <code>return luaL_error(<em>args</em>)</code>.
6095
6096
6097
6098
6099
6100	<hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p>
6101	<span class="apii">[-0, +3, <em>e</em>]</span>
6102	<pre>int luaL_execresult (lua_State *L, int stat);</pre>
6103
6104	<p>
6105	This function produces the return values for
6106	process-related functions in the standard library
6107	(<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>).
6108
6109
6110
6111
6112
6113	<hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p>
6114	<span class="apii">[-0, +(1\|3), <em>e</em>]</span>
6115	<pre>int luaL_fileresult (lua_State L, int stat, const char fname);</pre>
6116
6117	<p>
6118	This function produces the return values for
6119	file-related functions in the standard library
6120	(<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.).
6121
6122
6123
6124
6125
6126	<hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
6127	<span class="apii">[-0, +(0\|1), <em>e</em>]</span>
6128	<pre>int luaL_getmetafield (lua_State L, int obj, const char e);</pre>
6129
6130	<p>
6131	Pushes onto the stack the field <code>e</code> from the metatable
6132	of the object at index <code>obj</code>.
6133	If the object does not have a metatable,
6134	or if the metatable does not have this field,
6135	returns false and pushes nothing.
6136
6137
6138
6139
6140
6141	<hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
6142	<span class="apii">[-0, +1, –]</span>
6143	<pre>void luaL_getmetatable (lua_State L, const char tname);</pre>
6144
6145	<p>
6146	Pushes onto the stack the metatable associated with name <code>tname</code>
6147	in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6148
6149
6150
6151
6152
6153	<hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p>
6154	<span class="apii">[-0, +1, <em>e</em>]</span>
6155	<pre>int luaL_getsubtable (lua_State L, int idx, const char fname);</pre>
6156
6157	<p>
6158	Ensures that the value <code>t[fname]</code>,
6159	where <code>t</code> is the value at index <code>idx</code>,
6160	is a table,
6161	and pushes that table onto the stack.
6162	Returns true if it finds a previous table there
6163	and false if it creates a new table.
6164
6165
6166
6167
6168
6169	<hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
6170	<span class="apii">[-0, +1, <em>e</em>]</span>
6171	<pre>const char luaL_gsub (lua_State L,
6172	const char *s,
6173	const char *p,
6174	const char *r);</pre>
6175
6176	<p>
6177	Creates a copy of string <code>s</code> by replacing
6178	any occurrence of the string <code>p</code>
6179	with the string <code>r</code>.
6180	Pushes the resulting string on the stack and returns it.
6181
6182
6183
6184
6185
6186	<hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p>
6187	<span class="apii">[-0, +0, <em>e</em>]</span>
6188	<pre>int luaL_len (lua_State *L, int index);</pre>
6189
6190	<p>
6191	Returns the "length" of the value at the given index
6192	as a number;
6193	it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>).
6194	Raises an error if the result of the operation is not a number.
6195	(This case only can happen through metamethods.)
6196
6197
6198
6199
6200
6201	<hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
6202	<span class="apii">[-0, +1, –]</span>
6203	<pre>int luaL_loadbuffer (lua_State *L,
6204	const char *buff,
6205	size_t sz,
6206	const char *name);</pre>
6207
6208	<p>
6209	Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>.
6210
6211
6212
6213
6214
6215	<hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p>
6216	<span class="apii">[-0, +1, –]</span>
6217	<pre>int luaL_loadbufferx (lua_State *L,
6218	const char *buff,
6219	size_t sz,
6220	const char *name,
6221	const char *mode);</pre>
6222
6223	<p>
6224	Loads a buffer as a Lua chunk.
6225	This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
6226	buffer pointed to by <code>buff</code> with size <code>sz</code>.
6227
6228
6229	<p>
6230	This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6231	<code>name</code> is the chunk name,
6232	used for debug information and error messages.
6233	The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6234
6235
6236
6237
6238
6239	<hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
6240	<span class="apii">[-0, +1, <em>e</em>]</span>
6241	<pre>int luaL_loadfile (lua_State L, const char filename);</pre>
6242
6243	<p>
6244	Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>.
6245
6246
6247
6248
6249
6250	<hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p>
6251	<span class="apii">[-0, +1, <em>e</em>]</span>
6252	<pre>int luaL_loadfilex (lua_State L, const char filename,
6253	const char *mode);</pre>
6254
6255	<p>
6256	Loads a file as a Lua chunk.
6257	This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
6258	named <code>filename</code>.
6259	If <code>filename</code> is <code>NULL</code>,
6260	then it loads from the standard input.
6261	The first line in the file is ignored if it starts with a <code>#</code>.
6262
6263
6264	<p>
6265	The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6266
6267
6268	<p>
6269	This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>,
6270	but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>
6271	if it cannot open/read the file or the file has a wrong mode.
6272
6273
6274	<p>
6275	As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6276	it does not run it.
6277
6278
6279
6280
6281
6282	<hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
6283	<span class="apii">[-0, +1, –]</span>
6284	<pre>int luaL_loadstring (lua_State L, const char s);</pre>
6285
6286	<p>
6287	Loads a string as a Lua chunk.
6288	This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
6289	the zero-terminated string <code>s</code>.
6290
6291
6292	<p>
6293	This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6294
6295
6296	<p>
6297	Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6298	it does not run it.
6299
6300
6301
6302
6303
6304	<hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p>
6305	<span class="apii">[-0, +1, <em>e</em>]</span>
6306	<pre>void luaL_newlib (lua_State L, const luaL_Reg l);</pre>
6307
6308	<p>
6309	Creates a new table and registers there
6310	the functions in list <code>l</code>.
6311	It is implemented as the following macro:
6312
6313	<pre>
6314	(luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
6315	</pre>
6316
6317
6318
6319
6320	<hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p>
6321	<span class="apii">[-0, +1, <em>e</em>]</span>
6322	<pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre>
6323
6324	<p>
6325	Creates a new table with a size optimized
6326	to store all entries in the array <code>l</code>
6327	(but does not actually store them).
6328	It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>
6329	(see <a href="#luaL_newlib"><code>luaL_newlib</code></a>).
6330
6331
6332	<p>
6333	It is implemented as a macro.
6334	The array <code>l</code> must be the actual array,
6335	not a pointer to it.
6336
6337
6338
6339
6340
6341	<hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
6342	<span class="apii">[-0, +1, <em>e</em>]</span>
6343	<pre>int luaL_newmetatable (lua_State L, const char tname);</pre>
6344
6345	<p>
6346	If the registry already has the key <code>tname</code>,
6347	returns 0.
6348	Otherwise,
6349	creates a new table to be used as a metatable for userdata,
6350	adds it to the registry with key <code>tname</code>,
6351	and returns 1.
6352
6353
6354	<p>
6355	In both cases pushes onto the stack the final value associated
6356	with <code>tname</code> in the registry.
6357
6358
6359
6360
6361
6362	<hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
6363	<span class="apii">[-0, +0, –]</span>
6364	<pre>lua_State *luaL_newstate (void);</pre>
6365
6366	<p>
6367	Creates a new Lua state.
6368	It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
6369	allocator based on the standard C <code>realloc</code> function
6370	and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints
6371	an error message to the standard error output in case of fatal
6372	errors.
6373
6374
6375	<p>
6376	Returns the new state,
6377	or <code>NULL</code> if there is a memory allocation error.
6378
6379
6380
6381
6382
6383	<hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
6384	<span class="apii">[-0, +0, <em>e</em>]</span>
6385	<pre>void luaL_openlibs (lua_State *L);</pre>
6386
6387	<p>
6388	Opens all standard Lua libraries into the given state.
6389
6390
6391
6392
6393
6394	<hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p>
6395	<span class="apii">[-0, +0, <em>v</em>]</span>
6396	<pre>int luaL_optint (lua_State *L, int arg, int d);</pre>
6397
6398	<p>
6399	If the function argument <code>arg</code> is a number,
6400	returns this number cast to an <code>int</code>.
6401	If this argument is absent or is <b>nil</b>,
6402	returns <code>d</code>.
6403	Otherwise, raises an error.
6404
6405
6406
6407
6408
6409	<hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
6410	<span class="apii">[-0, +0, <em>v</em>]</span>
6411	<pre>lua_Integer luaL_optinteger (lua_State *L,
6412	int arg,
6413	lua_Integer d);</pre>
6414
6415	<p>
6416	If the function argument <code>arg</code> is a number,
6417	returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
6418	If this argument is absent or is <b>nil</b>,
6419	returns <code>d</code>.
6420	Otherwise, raises an error.
6421
6422
6423
6424
6425
6426	<hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p>
6427	<span class="apii">[-0, +0, <em>v</em>]</span>
6428	<pre>long luaL_optlong (lua_State *L, int arg, long d);</pre>
6429
6430	<p>
6431	If the function argument <code>arg</code> is a number,
6432	returns this number cast to a <code>long</code>.
6433	If this argument is absent or is <b>nil</b>,
6434	returns <code>d</code>.
6435	Otherwise, raises an error.
6436
6437
6438
6439
6440
6441	<hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
6442	<span class="apii">[-0, +0, <em>v</em>]</span>
6443	<pre>const char luaL_optlstring (lua_State L,
6444	int arg,
6445	const char *d,
6446	size_t *l);</pre>
6447
6448	<p>
6449	If the function argument <code>arg</code> is a string,
6450	returns this string.
6451	If this argument is absent or is <b>nil</b>,
6452	returns <code>d</code>.
6453	Otherwise, raises an error.
6454
6455
6456	<p>
6457	If <code>l</code> is not <code>NULL</code>,
6458	fills the position <code>*l</code> with the result's length.
6459
6460
6461
6462
6463
6464	<hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
6465	<span class="apii">[-0, +0, <em>v</em>]</span>
6466	<pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre>
6467
6468	<p>
6469	If the function argument <code>arg</code> is a number,
6470	returns this number.
6471	If this argument is absent or is <b>nil</b>,
6472	returns <code>d</code>.
6473	Otherwise, raises an error.
6474
6475
6476
6477
6478
6479	<hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
6480	<span class="apii">[-0, +0, <em>v</em>]</span>
6481	<pre>const char luaL_optstring (lua_State L,
6482	int arg,
6483	const char *d);</pre>
6484
6485	<p>
6486	If the function argument <code>arg</code> is a string,
6487	returns this string.
6488	If this argument is absent or is <b>nil</b>,
6489	returns <code>d</code>.
6490	Otherwise, raises an error.
6491
6492
6493
6494
6495
6496	<hr><h3><a name="luaL_optunsigned"><code>luaL_optunsigned</code></a></h3><p>
6497	<span class="apii">[-0, +0, <em>v</em>]</span>
6498	<pre>lua_Unsigned luaL_optunsigned (lua_State *L,
6499	int arg,
6500	lua_Unsigned u);</pre>
6501
6502	<p>
6503	If the function argument <code>arg</code> is a number,
6504	returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
6505	If this argument is absent or is <b>nil</b>,
6506	returns <code>u</code>.
6507	Otherwise, raises an error.
6508
6509
6510
6511
6512
6513	<hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
6514	<span class="apii">[-?, +?, <em>e</em>]</span>
6515	<pre>char luaL_prepbuffer (luaL_Buffer B);</pre>
6516
6517	<p>
6518	Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>
6519	with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>.
6520
6521
6522
6523
6524
6525	<hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p>
6526	<span class="apii">[-?, +?, <em>e</em>]</span>
6527	<pre>char luaL_prepbuffsize (luaL_Buffer B, size_t sz);</pre>
6528
6529	<p>
6530	Returns an address to a space of size <code>sz</code>
6531	where you can copy a string to be added to buffer <code>B</code>
6532	(see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
6533	After copying the string into this space you must call
6534	<a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
6535	it to the buffer.
6536
6537
6538
6539
6540
6541	<hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
6542	<span class="apii">[-?, +1, <em>e</em>]</span>
6543	<pre>void luaL_pushresult (luaL_Buffer *B);</pre>
6544
6545	<p>
6546	Finishes the use of buffer <code>B</code> leaving the final string on
6547	the top of the stack.
6548
6549
6550
6551
6552
6553	<hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p>
6554	<span class="apii">[-?, +1, <em>e</em>]</span>
6555	<pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre>
6556
6557	<p>
6558	Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>.
6559
6560
6561
6562
6563
6564	<hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
6565	<span class="apii">[-1, +0, <em>e</em>]</span>
6566	<pre>int luaL_ref (lua_State *L, int t);</pre>
6567
6568	<p>
6569	Creates and returns a <em>reference</em>,
6570	in the table at index <code>t</code>,
6571	for the object at the top of the stack (and pops the object).
6572
6573
6574	<p>
6575	A reference is a unique integer key.
6576	As long as you do not manually add integer keys into table <code>t</code>,
6577	<a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
6578	You can retrieve an object referred by reference <code>r</code>
6579	by calling <code>lua_rawgeti(L, t, r)</code>.
6580	Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
6581
6582
6583	<p>
6584	If the object at the top of the stack is <b>nil</b>,
6585	<a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
6586	The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
6587	from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
6588
6589
6590
6591
6592
6593	<hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
6594	<pre>typedef struct luaL_Reg {
6595	const char *name;
6596	lua_CFunction func;
6597	} luaL_Reg;</pre>
6598
6599	<p>
6600	Type for arrays of functions to be registered by
6601	<a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>.
6602	<code>name</code> is the function name and <code>func</code> is a pointer to
6603	the function.
6604	Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry
6605	in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
6606
6607
6608
6609
6610
6611	<hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p>
6612	<span class="apii">[-0, +1, <em>e</em>]</span>
6613	<pre>void luaL_requiref (lua_State L, const char modname,
6614	lua_CFunction openf, int glb);</pre>
6615
6616	<p>
6617	Calls function <code>openf</code> with string <code>modname</code> as an argument
6618	and sets the call result in <code>package.loaded[modname]</code>,
6619	as if that function has been called through <a href="#pdf-require"><code>require</code></a>.
6620
6621
6622	<p>
6623	If <code>glb</code> is true,
6624	also stores the result into global <code>modname</code>.
6625
6626
6627	<p>
6628	Leaves a copy of that result on the stack.
6629
6630
6631
6632
6633
6634	<hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p>
6635	<span class="apii">[-nup, +0, <em>e</em>]</span>
6636	<pre>void luaL_setfuncs (lua_State L, const luaL_Reg l, int nup);</pre>
6637
6638	<p>
6639	Registers all functions in the array <code>l</code>
6640	(see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack
6641	(below optional upvalues, see next).
6642
6643
6644	<p>
6645	When <code>nup</code> is not zero,
6646	all functions are created sharing <code>nup</code> upvalues,
6647	which must be previously pushed on the stack
6648	on top of the library table.
6649	These values are popped from the stack after the registration.
6650
6651
6652
6653
6654
6655	<hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p>
6656	<span class="apii">[-0, +0, –]</span>
6657	<pre>void luaL_setmetatable (lua_State L, const char tname);</pre>
6658
6659	<p>
6660	Sets the metatable of the object at the top of the stack
6661	as the metatable associated with name <code>tname</code>
6662	in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6663
6664
6665
6666
6667
6668	<hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p>
6669	<span class="apii">[-0, +0, <em>e</em>]</span>
6670	<pre>void luaL_testudata (lua_State L, int arg, const char *tname);</pre>
6671
6672	<p>
6673	This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>,
6674	except that, when the test fails,
6675	it returns <code>NULL</code> instead of throwing an error.
6676
6677
6678
6679
6680
6681	<hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p>
6682	<span class="apii">[-0, +1, <em>e</em>]</span>
6683	<pre>const char luaL_tolstring (lua_State L, int idx, size_t *len);</pre>
6684
6685	<p>
6686	Converts any Lua value at the given index to a C string
6687	in a reasonable format.
6688	The resulting string is pushed onto the stack and also
6689	returned by the function.
6690	If <code>len</code> is not <code>NULL</code>,
6691	the function also sets <code>*len</code> with the string length.
6692
6693
6694	<p>
6695	If the value has a metatable with a <code>"__tostring"</code> field,
6696	then <code>luaL_tolstring</code> calls the corresponding metamethod
6697	with the value as argument,
6698	and uses the result of the call as its result.
6699
6700
6701
6702
6703
6704	<hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p>
6705	<span class="apii">[-0, +1, <em>e</em>]</span>
6706	<pre>void luaL_traceback (lua_State L, lua_State L1, const char *msg,
6707	int level);</pre>
6708
6709	<p>
6710	Creates and pushes a traceback of the stack <code>L1</code>.
6711	If <code>msg</code> is not <code>NULL</code> it is appended
6712	at the beginning of the traceback.
6713	The <code>level</code> parameter tells at which level
6714	to start the traceback.
6715
6716
6717
6718
6719
6720	<hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
6721	<span class="apii">[-0, +0, –]</span>
6722	<pre>const char luaL_typename (lua_State L, int index);</pre>
6723
6724	<p>
6725	Returns the name of the type of the value at the given index.
6726
6727
6728
6729
6730
6731	<hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
6732	<span class="apii">[-0, +0, –]</span>
6733	<pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
6734
6735	<p>
6736	Releases reference <code>ref</code> from the table at index <code>t</code>
6737	(see <a href="#luaL_ref"><code>luaL_ref</code></a>).
6738	The entry is removed from the table,
6739	so that the referred object can be collected.
6740	The reference <code>ref</code> is also freed to be used again.
6741
6742
6743	<p>
6744	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>,
6745	<a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
6746
6747
6748
6749
6750
6751	<hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
6752	<span class="apii">[-0, +1, <em>e</em>]</span>
6753	<pre>void luaL_where (lua_State *L, int lvl);</pre>
6754
6755	<p>
6756	Pushes onto the stack a string identifying the current position
6757	of the control at level <code>lvl</code> in the call stack.
6758	Typically this string has the following format:
6759
6760	<pre>
6761	<em>chunkname</em>:<em>currentline</em>:
6762	</pre><p>
6763	Level 0 is the running function,
6764	level 1 is the function that called the running function,
6765	etc.
6766
6767
6768	<p>
6769	This function is used to build a prefix for error messages.
6770
6771
6772
6773
6774
6775
6776
6777	<h1>6 – <a name="6">Standard Libraries</a></h1>
6778
6779	<p>
6780	The standard Lua libraries provide useful functions
6781	that are implemented directly through the C API.
6782	Some of these functions provide essential services to the language
6783	(e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
6784	others provide access to "outside" services (e.g., I/O);
6785	and others could be implemented in Lua itself,
6786	but are quite useful or have critical performance requirements that
6787	deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
6788
6789
6790	<p>
6791	All libraries are implemented through the official C API
6792	and are provided as separate C modules.
6793	Currently, Lua has the following standard libraries:
6794
6795	<ul>
6796
6797	<li>basic library (<a href="#6.1">§6.1</a>);</li>
6798
6799	<li>coroutine library (<a href="#6.2">§6.2</a>);</li>
6800
6801	<li>package library (<a href="#6.3">§6.3</a>);</li>
6802
6803	<li>string manipulation (<a href="#6.4">§6.4</a>);</li>
6804
6805	<li>table manipulation (<a href="#6.5">§6.5</a>);</li>
6806
6807	<li>mathematical functions (<a href="#6.6">§6.6</a>) (sin, log, etc.);</li>
6808
6809	<li>bitwise operations (<a href="#6.7">§6.7</a>);</li>
6810
6811	<li>input and output (<a href="#6.8">§6.8</a>);</li>
6812
6813	<li>operating system facilities (<a href="#6.9">§6.9</a>);</li>
6814
6815	<li>debug facilities (<a href="#6.10">§6.10</a>).</li>
6816
6817	</ul><p>
6818	Except for the basic and the package libraries,
6819	each library provides all its functions as fields of a global table
6820	or as methods of its objects.
6821
6822
6823	<p>
6824	To have access to these libraries,
6825	the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
6826	which opens all standard libraries.
6827	Alternatively,
6828	the host program can open them individually by using
6829	<a href="#luaL_requiref"><code>luaL_requiref</code></a> to call
6830	<a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
6831	<a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
6832	<a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library),
6833	<a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
6834	<a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
6835	<a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
6836	<a name="pdf-luaopen_bit32"><code>luaopen_bit32</code></a> (for the bit library),
6837	<a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
6838	<a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library),
6839	and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
6840	These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>.
6841
6842
6843
6844	<h2>6.1 – <a name="6.1">Basic Functions</a></h2>
6845
6846	<p>
6847	The basic library provides core functions to Lua.
6848	If you do not include this library in your application,
6849	you should check carefully whether you need to provide
6850	implementations for some of its facilities.
6851
6852
6853	<p>
6854	<hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
6855	Issues an error when
6856	the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
6857	otherwise, returns all its arguments.
6858	<code>message</code> is an error message;
6859	when absent, it defaults to "assertion failed!"
6860
6861
6862
6863
6864	<p>
6865	<hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3>
6866
6867
6868	<p>
6869	This function is a generic interface to the garbage collector.
6870	It performs different functions according to its first argument, <code>opt</code>:
6871
6872	<ul>
6873
6874	<li><b>"<code>collect</code>": </b>
6875	performs a full garbage-collection cycle.
6876	This is the default option.
6877	</li>
6878
6879	<li><b>"<code>stop</code>": </b>
6880	stops automatic execution of the garbage collector.
6881	The collector will run only when explicitly invoked,
6882	until a call to restart it.
6883	</li>
6884
6885	<li><b>"<code>restart</code>": </b>
6886	restarts automatic execution of the garbage collector.
6887	</li>
6888
6889	<li><b>"<code>count</code>": </b>
6890	returns the total memory in use by Lua (in Kbytes) and
6891	a second value with the total memory in bytes modulo 1024.
6892	The first value has a fractional part,
6893	so the following equality is always true:
6894
6895	<pre>
6896	k, b = collectgarbage("count")
6897	assert(k1024 == math.floor(k)1024 + b)
6898	</pre><p>
6899	(The second result is useful when Lua is compiled
6900	with a non floating-point type for numbers.)
6901	</li>
6902
6903	<li><b>"<code>step</code>": </b>
6904	performs a garbage-collection step.
6905	The step "size" is controlled by <code>arg</code>
6906	(larger values mean more steps) in a non-specified way.
6907	If you want to control the step size
6908	you must experimentally tune the value of <code>arg</code>.
6909	Returns <b>true</b> if the step finished a collection cycle.
6910	</li>
6911
6912	<li><b>"<code>setpause</code>": </b>
6913	sets <code>arg</code> as the new value for the <em>pause</em> of
6914	the collector (see <a href="#2.5">§2.5</a>).
6915	Returns the previous value for <em>pause</em>.
6916	</li>
6917
6918	<li><b>"<code>setstepmul</code>": </b>
6919	sets <code>arg</code> as the new value for the <em>step multiplier</em> of
6920	the collector (see <a href="#2.5">§2.5</a>).
6921	Returns the previous value for <em>step</em>.
6922	</li>
6923
6924	<li><b>"<code>isrunning</code>": </b>
6925	returns a boolean that tells whether the collector is running
6926	(i.e., not stopped).
6927	</li>
6928
6929	<li><b>"<code>generational</code>": </b>
6930	changes the collector to generational mode.
6931	This is an experimental feature (see <a href="#2.5">§2.5</a>).
6932	</li>
6933
6934	<li><b>"<code>incremental</code>": </b>
6935	changes the collector to incremental mode.
6936	This is the default mode.
6937	</li>
6938
6939	</ul>
6940
6941
6942
6943	<p>
6944	<hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3>
6945	Opens the named file and executes its contents as a Lua chunk.
6946	When called without arguments,
6947	<code>dofile</code> executes the contents of the standard input (<code>stdin</code>).
6948	Returns all values returned by the chunk.
6949	In case of errors, <code>dofile</code> propagates the error
6950	to its caller (that is, <code>dofile</code> does not run in protected mode).
6951
6952
6953
6954
6955	<p>
6956	<hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
6957	Terminates the last protected function called
6958	and returns <code>message</code> as the error message.
6959	Function <code>error</code> never returns.
6960
6961
6962	<p>
6963	Usually, <code>error</code> adds some information about the error position
6964	at the beginning of the message, if the message is a string.
6965	The <code>level</code> argument specifies how to get the error position.
6966	With level 1 (the default), the error position is where the
6967	<code>error</code> function was called.
6968	Level 2 points the error to where the function
6969	that called <code>error</code> was called; and so on.
6970	Passing a level 0 avoids the addition of error position information
6971	to the message.
6972
6973
6974
6975
6976	<p>
6977	<hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
6978	A global variable (not a function) that
6979	holds the global environment (see <a href="#2.2">§2.2</a>).
6980	Lua itself does not use this variable;
6981	changing its value does not affect any environment,
6982	nor vice-versa.
6983
6984
6985
6986
6987	<p>
6988	<hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
6989
6990
6991	<p>
6992	If <code>object</code> does not have a metatable, returns <b>nil</b>.
6993	Otherwise,
6994	if the object's metatable has a <code>"__metatable"</code> field,
6995	returns the associated value.
6996	Otherwise, returns the metatable of the given object.
6997
6998
6999
7000
7001	<p>
7002	<hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
7003
7004
7005	<p>
7006	If <code>t</code> has a metamethod <code>__ipairs</code>,
7007	calls it with <code>t</code> as argument and returns the first three
7008	results from the call.
7009
7010
7011	<p>
7012	Otherwise,
7013	returns three values: an iterator function, the table <code>t</code>, and 0,
7014	so that the construction
7015
7016	<pre>
7017	for i,v in ipairs(t) do <em>body</em> end
7018	</pre><p>
7019	will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ...,
7020	up to the first integer key absent from the table.
7021
7022
7023
7024
7025	<p>
7026	<hr><h3><a name="pdf-load"><code>load (ld [, source [, mode [, env]]])</code></a></h3>
7027
7028
7029	<p>
7030	Loads a chunk.
7031
7032
7033	<p>
7034	If <code>ld</code> is a string, the chunk is this string.
7035	If <code>ld</code> is a function,
7036	<code>load</code> calls it repeatedly to get the chunk pieces.
7037	Each call to <code>ld</code> must return a string that concatenates
7038	with previous results.
7039	A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
7040
7041
7042	<p>
7043	If there are no syntactic errors,
7044	returns the compiled chunk as a function;
7045	otherwise, returns <b>nil</b> plus the error message.
7046
7047
7048	<p>
7049	If the resulting function has upvalues,
7050	the first upvalue is set to the value of <code>env</code>,
7051	if that parameter is given,
7052	or to the value of the global environment.
7053	(When you load a main chunk,
7054	the resulting function will always have exactly one upvalue,
7055	the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
7056	When you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>),
7057	the resulting function can have arbitrary upvalues.)
7058
7059
7060	<p>
7061	<code>source</code> is used as the source of the chunk for error messages
7062	and debug information (see <a href="#4.9">§4.9</a>).
7063	When absent,
7064	it defaults to <code>ld</code>, if <code>ld</code> is a string,
7065	or to "<code>=(load)</code>" otherwise.
7066
7067
7068	<p>
7069	The string <code>mode</code> controls whether the chunk can be text or binary
7070	(that is, a precompiled chunk).
7071	It may be the string "<code>b</code>" (only binary chunks),
7072	"<code>t</code>" (only text chunks),
7073	or "<code>bt</code>" (both binary and text).
7074	The default is "<code>bt</code>".
7075
7076
7077
7078
7079	<p>
7080	<hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3>
7081
7082
7083	<p>
7084	Similar to <a href="#pdf-load"><code>load</code></a>,
7085	but gets the chunk from file <code>filename</code>
7086	or from the standard input,
7087	if no file name is given.
7088
7089
7090
7091
7092	<p>
7093	<hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
7094
7095
7096	<p>
7097	Allows a program to traverse all fields of a table.
7098	Its first argument is a table and its second argument
7099	is an index in this table.
7100	<code>next</code> returns the next index of the table
7101	and its associated value.
7102	When called with <b>nil</b> as its second argument,
7103	<code>next</code> returns an initial index
7104	and its associated value.
7105	When called with the last index,
7106	or with <b>nil</b> in an empty table,
7107	<code>next</code> returns <b>nil</b>.
7108	If the second argument is absent, then it is interpreted as <b>nil</b>.
7109	In particular,
7110	you can use <code>next(t)</code> to check whether a table is empty.
7111
7112
7113	<p>
7114	The order in which the indices are enumerated is not specified,
7115	<em>even for numeric indices</em>.
7116	(To traverse a table in numeric order,
7117	use a numerical <b>for</b>.)
7118
7119
7120	<p>
7121	The behavior of <code>next</code> is undefined if,
7122	during the traversal,
7123	you assign any value to a non-existent field in the table.
7124	You may however modify existing fields.
7125	In particular, you may clear existing fields.
7126
7127
7128
7129
7130	<p>
7131	<hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
7132
7133
7134	<p>
7135	If <code>t</code> has a metamethod <code>__pairs</code>,
7136	calls it with <code>t</code> as argument and returns the first three
7137	results from the call.
7138
7139
7140	<p>
7141	Otherwise,
7142	returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
7143	so that the construction
7144
7145	<pre>
7146	for k,v in pairs(t) do <em>body</em> end
7147	</pre><p>
7148	will iterate over all key–value pairs of table <code>t</code>.
7149
7150
7151	<p>
7152	See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
7153	the table during its traversal.
7154
7155
7156
7157
7158	<p>
7159	<hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3>
7160
7161
7162	<p>
7163	Calls function <code>f</code> with
7164	the given arguments in <em>protected mode</em>.
7165	This means that any error inside <code>f</code> is not propagated;
7166	instead, <code>pcall</code> catches the error
7167	and returns a status code.
7168	Its first result is the status code (a boolean),
7169	which is true if the call succeeds without errors.
7170	In such case, <code>pcall</code> also returns all results from the call,
7171	after this first result.
7172	In case of any error, <code>pcall</code> returns <b>false</b> plus the error message.
7173
7174
7175
7176
7177	<p>
7178	<hr><h3><a name="pdf-print"><code>print (···)</code></a></h3>
7179	Receives any number of arguments
7180	and prints their values to <code>stdout</code>,
7181	using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string.
7182	<code>print</code> is not intended for formatted output,
7183	but only as a quick way to show a value,
7184	for instance for debugging.
7185	For complete control over the output,
7186	use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>.
7187
7188
7189
7190
7191	<p>
7192	<hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
7193	Checks whether <code>v1</code> is equal to <code>v2</code>,
7194	without invoking any metamethod.
7195	Returns a boolean.
7196
7197
7198
7199
7200	<p>
7201	<hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
7202	Gets the real value of <code>table[index]</code>,
7203	without invoking any metamethod.
7204	<code>table</code> must be a table;
7205	<code>index</code> may be any value.
7206
7207
7208
7209
7210	<p>
7211	<hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3>
7212	Returns the length of the object <code>v</code>,
7213	which must be a table or a string,
7214	without invoking any metamethod.
7215	Returns an integer number.
7216
7217
7218
7219
7220	<p>
7221	<hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
7222	Sets the real value of <code>table[index]</code> to <code>value</code>,
7223	without invoking any metamethod.
7224	<code>table</code> must be a table,
7225	<code>index</code> any value different from <b>nil</b> and NaN,
7226	and <code>value</code> any Lua value.
7227
7228
7229	<p>
7230	This function returns <code>table</code>.
7231
7232
7233
7234
7235	<p>
7236	<hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3>
7237
7238
7239	<p>
7240	If <code>index</code> is a number,
7241	returns all arguments after argument number <code>index</code>;
7242	a negative number indexes from the end (-1 is the last argument).
7243	Otherwise, <code>index</code> must be the string <code>"#"</code>,
7244	and <code>select</code> returns the total number of extra arguments it received.
7245
7246
7247
7248
7249	<p>
7250	<hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
7251
7252
7253	<p>
7254	Sets the metatable for the given table.
7255	(You cannot change the metatable of other types from Lua, only from C.)
7256	If <code>metatable</code> is <b>nil</b>,
7257	removes the metatable of the given table.
7258	If the original metatable has a <code>"__metatable"</code> field,
7259	raises an error.
7260
7261
7262	<p>
7263	This function returns <code>table</code>.
7264
7265
7266
7267
7268	<p>
7269	<hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
7270
7271
7272	<p>
7273	When called with no <code>base</code>,
7274	<code>tonumber</code> tries to convert its argument to a number.
7275	If the argument is already a number or
7276	a string convertible to a number (see <a href="#3.4.2">§3.4.2</a>),
7277	then <code>tonumber</code> returns this number;
7278	otherwise, it returns <b>nil</b>.
7279
7280
7281	<p>
7282	When called with <code>base</code>,
7283	then <code>e</code> should be a string to be interpreted as
7284	an integer numeral in that base.
7285	The base may be any integer between 2 and 36, inclusive.
7286	In bases above 10, the letter '<code>A</code>' (in either upper or lower case)
7287	represents 10, '<code>B</code>' represents 11, and so forth,
7288	with '<code>Z</code>' representing 35.
7289	If the string <code>e</code> is not a valid numeral in the given base,
7290	the function returns <b>nil</b>.
7291
7292
7293
7294
7295	<p>
7296	<hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3>
7297	Receives a value of any type and
7298	converts it to a string in a reasonable format.
7299	(For complete control of how numbers are converted,
7300	use <a href="#pdf-string.format"><code>string.format</code></a>.)
7301
7302
7303	<p>
7304	If the metatable of <code>v</code> has a <code>"__tostring"</code> field,
7305	then <code>tostring</code> calls the corresponding value
7306	with <code>v</code> as argument,
7307	and uses the result of the call as its result.
7308
7309
7310
7311
7312	<p>
7313	<hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
7314	Returns the type of its only argument, coded as a string.
7315	The possible results of this function are
7316	"<code>nil</code>" (a string, not the value <b>nil</b>),
7317	"<code>number</code>",
7318	"<code>string</code>",
7319	"<code>boolean</code>",
7320	"<code>table</code>",
7321	"<code>function</code>",
7322	"<code>thread</code>",
7323	and "<code>userdata</code>".
7324
7325
7326
7327
7328	<p>
7329	<hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
7330	A global variable (not a function) that
7331	holds a string containing the current interpreter version.
7332	The current contents of this variable is "<code>Lua 5.2</code>".
7333
7334
7335
7336
7337	<p>
7338	<hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3>
7339
7340
7341	<p>
7342	This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
7343	except that it sets a new message handler <code>msgh</code>.
7344
7345
7346
7347
7348
7349
7350
7351	<h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2>
7352
7353	<p>
7354	The operations related to coroutines comprise a sub-library of
7355	the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
7356	See <a href="#2.6">§2.6</a> for a general description of coroutines.
7357
7358
7359	<p>
7360	<hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
7361
7362
7363	<p>
7364	Creates a new coroutine, with body <code>f</code>.
7365	<code>f</code> must be a Lua function.
7366	Returns this new coroutine,
7367	an object with type <code>"thread"</code>.
7368
7369
7370
7371
7372	<p>
7373	<hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3>
7374
7375
7376	<p>
7377	Starts or continues the execution of coroutine <code>co</code>.
7378	The first time you resume a coroutine,
7379	it starts running its body.
7380	The values <code>val1</code>, ... are passed
7381	as the arguments to the body function.
7382	If the coroutine has yielded,
7383	<code>resume</code> restarts it;
7384	the values <code>val1</code>, ... are passed
7385	as the results from the yield.
7386
7387
7388	<p>
7389	If the coroutine runs without any errors,
7390	<code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
7391	(if the coroutine yields) or any values returned by the body function
7392	(if the coroutine terminates).
7393	If there is any error,
7394	<code>resume</code> returns <b>false</b> plus the error message.
7395
7396
7397
7398
7399	<p>
7400	<hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
7401
7402
7403	<p>
7404	Returns the running coroutine plus a boolean,
7405	true when the running coroutine is the main one.
7406
7407
7408
7409
7410	<p>
7411	<hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
7412
7413
7414	<p>
7415	Returns the status of coroutine <code>co</code>, as a string:
7416	<code>"running"</code>,
7417	if the coroutine is running (that is, it called <code>status</code>);
7418	<code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
7419	or if it has not started running yet;
7420	<code>"normal"</code> if the coroutine is active but not running
7421	(that is, it has resumed another coroutine);
7422	and <code>"dead"</code> if the coroutine has finished its body function,
7423	or if it has stopped with an error.
7424
7425
7426
7427
7428	<p>
7429	<hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
7430
7431
7432	<p>
7433	Creates a new coroutine, with body <code>f</code>.
7434	<code>f</code> must be a Lua function.
7435	Returns a function that resumes the coroutine each time it is called.
7436	Any arguments passed to the function behave as the
7437	extra arguments to <code>resume</code>.
7438	Returns the same values returned by <code>resume</code>,
7439	except the first boolean.
7440	In case of error, propagates the error.
7441
7442
7443
7444
7445	<p>
7446	<hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3>
7447
7448
7449	<p>
7450	Suspends the execution of the calling coroutine.
7451	Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
7452
7453
7454
7455
7456
7457
7458
7459	<h2>6.3 – <a name="6.3">Modules</a></h2>
7460
7461	<p>
7462	The package library provides basic
7463	facilities for loading modules in Lua.
7464	It exports one function directly in the global environment:
7465	<a href="#pdf-require"><code>require</code></a>.
7466	Everything else is exported in a table <a name="pdf-package"><code>package</code></a>.
7467
7468
7469	<p>
7470	<hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
7471
7472
7473	<p>
7474	Loads the given module.
7475	The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
7476	to determine whether <code>modname</code> is already loaded.
7477	If it is, then <code>require</code> returns the value stored
7478	at <code>package.loaded[modname]</code>.
7479	Otherwise, it tries to find a <em>loader</em> for the module.
7480
7481
7482	<p>
7483	To find a loader,
7484	<code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence.
7485	By changing this sequence,
7486	we can change how <code>require</code> looks for a module.
7487	The following explanation is based on the default configuration
7488	for <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
7489
7490
7491	<p>
7492	First <code>require</code> queries <code>package.preload[modname]</code>.
7493	If it has a value,
7494	this value (which should be a function) is the loader.
7495	Otherwise <code>require</code> searches for a Lua loader using the
7496	path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
7497	If that also fails, it searches for a C loader using the
7498	path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7499	If that also fails,
7500	it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>).
7501
7502
7503	<p>
7504	Once a loader is found,
7505	<code>require</code> calls the loader with two arguments:
7506	<code>modname</code> and an extra value dependent on how it got the loader.
7507	(If the loader came from a file,
7508	this extra value is the file name.)
7509	If the loader returns any non-nil value,
7510	<code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
7511	If the loader does not return a non-nil value and
7512	has not assigned any value to <code>package.loaded[modname]</code>,
7513	then <code>require</code> assigns <b>true</b> to this entry.
7514	In any case, <code>require</code> returns the
7515	final value of <code>package.loaded[modname]</code>.
7516
7517
7518	<p>
7519	If there is any error loading or running the module,
7520	or if it cannot find any loader for the module,
7521	then <code>require</code> raises an error.
7522
7523
7524
7525
7526	<p>
7527	<hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3>
7528
7529
7530	<p>
7531	A string describing some compile-time configurations for packages.
7532	This string is a sequence of lines:
7533
7534	<ul>
7535
7536	<li>The first line is the directory separator string.
7537	Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li>
7538
7539	<li>The second line is the character that separates templates in a path.
7540	Default is '<code>;</code>'.</li>
7541
7542	<li>The third line is the string that marks the
7543	substitution points in a template.
7544	Default is '<code>?</code>'.</li>
7545
7546	<li>The fourth line is a string that, in a path in Windows,
7547	is replaced by the executable's directory.
7548	Default is '<code>!</code>'.</li>
7549
7550	<li>The fifth line is a mark to ignore all text before it
7551	when building the <code>luaopen_</code> function name.
7552	Default is '<code>-</code>'.</li>
7553
7554	</ul>
7555
7556
7557
7558	<p>
7559	<hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
7560
7561
7562	<p>
7563	The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader.
7564
7565
7566	<p>
7567	Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
7568	it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
7569	using the environment variable <a name="pdf-LUA_CPATH_5_2"><code>LUA_CPATH_5_2</code></a>
7570	or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>
7571	or a default path defined in <code>luaconf.h</code>.
7572
7573
7574
7575
7576	<p>
7577	<hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
7578
7579
7580	<p>
7581	A table used by <a href="#pdf-require"><code>require</code></a> to control which
7582	modules are already loaded.
7583	When you require a module <code>modname</code> and
7584	<code>package.loaded[modname]</code> is not false,
7585	<a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
7586
7587
7588	<p>
7589	This variable is only a reference to the real table;
7590	assignments to this variable do not change the
7591	table used by <a href="#pdf-require"><code>require</code></a>.
7592
7593
7594
7595
7596	<p>
7597	<hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
7598
7599
7600	<p>
7601	Dynamically links the host program with the C library <code>libname</code>.
7602
7603
7604	<p>
7605	If <code>funcname</code> is "<code>*</code>",
7606	then it only links with the library,
7607	making the symbols exported by the library
7608	available to other dynamically linked libraries.
7609	Otherwise,
7610	it looks for a function <code>funcname</code> inside the library
7611	and returns this function as a C function.
7612	So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype
7613	(see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
7614
7615
7616	<p>
7617	This is a low-level function.
7618	It completely bypasses the package and module system.
7619	Unlike <a href="#pdf-require"><code>require</code></a>,
7620	it does not perform any path searching and
7621	does not automatically adds extensions.
7622	<code>libname</code> must be the complete file name of the C library,
7623	including if necessary a path and an extension.
7624	<code>funcname</code> must be the exact name exported by the C library
7625	(which may depend on the C compiler and linker used).
7626
7627
7628	<p>
7629	This function is not supported by Standard C.
7630	As such, it is only available on some platforms
7631	(Windows, Linux, Mac OS X, Solaris, BSD,
7632	plus other Unix systems that support the <code>dlfcn</code> standard).
7633
7634
7635
7636
7637	<p>
7638	<hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
7639
7640
7641	<p>
7642	The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader.
7643
7644
7645	<p>
7646	At start-up, Lua initializes this variable with
7647	the value of the environment variable <a name="pdf-LUA_PATH_5_2"><code>LUA_PATH_5_2</code></a> or
7648	the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
7649	with a default path defined in <code>luaconf.h</code>,
7650	if those environment variables are not defined.
7651	Any "<code>;;</code>" in the value of the environment variable
7652	is replaced by the default path.
7653
7654
7655
7656
7657	<p>
7658	<hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
7659
7660
7661	<p>
7662	A table to store loaders for specific modules
7663	(see <a href="#pdf-require"><code>require</code></a>).
7664
7665
7666	<p>
7667	This variable is only a reference to the real table;
7668	assignments to this variable do not change the
7669	table used by <a href="#pdf-require"><code>require</code></a>.
7670
7671
7672
7673
7674	<p>
7675	<hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3>
7676
7677
7678	<p>
7679	A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
7680
7681
7682	<p>
7683	Each entry in this table is a <em>searcher function</em>.
7684	When looking for a module,
7685	<a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
7686	with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
7687	sole parameter.
7688	The function can return another function (the module <em>loader</em>)
7689	plus an extra value that will be passed to that loader,
7690	or a string explaining why it did not find that module
7691	(or <b>nil</b> if it has nothing to say).
7692
7693
7694	<p>
7695	Lua initializes this table with four searcher functions.
7696
7697
7698	<p>
7699	The first searcher simply looks for a loader in the
7700	<a href="#pdf-package.preload"><code>package.preload</code></a> table.
7701
7702
7703	<p>
7704	The second searcher looks for a loader as a Lua library,
7705	using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
7706	The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7707
7708
7709	<p>
7710	The third searcher looks for a loader as a C library,
7711	using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7712	Again,
7713	the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7714	For instance,
7715	if the C path is the string
7716
7717	<pre>
7718	"./?.so;./?.dll;/usr/local/?/init.so"
7719	</pre><p>
7720	the searcher for module <code>foo</code>
7721	will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
7722	and <code>/usr/local/foo/init.so</code>, in that order.
7723	Once it finds a C library,
7724	this searcher first uses a dynamic link facility to link the
7725	application with the library.
7726	Then it tries to find a C function inside the library to
7727	be used as the loader.
7728	The name of this C function is the string "<code>luaopen_</code>"
7729	concatenated with a copy of the module name where each dot
7730	is replaced by an underscore.
7731	Moreover, if the module name has a hyphen,
7732	its prefix up to (and including) the first hyphen is removed.
7733	For instance, if the module name is <code>a.v1-b.c</code>,
7734	the function name will be <code>luaopen_b_c</code>.
7735
7736
7737	<p>
7738	The fourth searcher tries an <em>all-in-one loader</em>.
7739	It searches the C path for a library for
7740	the root name of the given module.
7741	For instance, when requiring <code>a.b.c</code>,
7742	it will search for a C library for <code>a</code>.
7743	If found, it looks into it for an open function for
7744	the submodule;
7745	in our example, that would be <code>luaopen_a_b_c</code>.
7746	With this facility, a package can pack several C submodules
7747	into one single library,
7748	with each submodule keeping its original open function.
7749
7750
7751	<p>
7752	All searchers except the first one (preload) return as the extra value
7753	the file name where the module was found,
7754	as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7755	The first searcher returns no extra value.
7756
7757
7758
7759
7760	<p>
7761	<hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3>
7762
7763
7764	<p>
7765	Searches for the given <code>name</code> in the given <code>path</code>.
7766
7767
7768	<p>
7769	A path is a string containing a sequence of
7770	<em>templates</em> separated by semicolons.
7771	For each template,
7772	the function replaces each interrogation mark (if any)
7773	in the template with a copy of <code>name</code>
7774	wherein all occurrences of <code>sep</code>
7775	(a dot, by default)
7776	were replaced by <code>rep</code>
7777	(the system's directory separator, by default),
7778	and then tries to open the resulting file name.
7779
7780
7781	<p>
7782	For instance, if the path is the string
7783
7784	<pre>
7785	"./?.lua;./?.lc;/usr/local/?/init.lua"
7786	</pre><p>
7787	the search for the name <code>foo.a</code>
7788	will try to open the files
7789	<code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and
7790	<code>/usr/local/foo/a/init.lua</code>, in that order.
7791
7792
7793	<p>
7794	Returns the resulting name of the first file that it can
7795	open in read mode (after closing the file),
7796	or <b>nil</b> plus an error message if none succeeds.
7797	(This error message lists all file names it tried to open.)
7798
7799
7800
7801
7802
7803
7804
7805	<h2>6.4 – <a name="6.4">String Manipulation</a></h2>
7806
7807	<p>
7808	This library provides generic functions for string manipulation,
7809	such as finding and extracting substrings, and pattern matching.
7810	When indexing a string in Lua, the first character is at position 1
7811	(not at 0, as in C).
7812	Indices are allowed to be negative and are interpreted as indexing backwards,
7813	from the end of the string.
7814	Thus, the last character is at position -1, and so on.
7815
7816
7817	<p>
7818	The string library provides all its functions inside the table
7819	<a name="pdf-string"><code>string</code></a>.
7820	It also sets a metatable for strings
7821	where the <code>__index</code> field points to the <code>string</code> table.
7822	Therefore, you can use the string functions in object-oriented style.
7823	For instance, <code>string.byte(s,i)</code>
7824	can be written as <code>s:byte(i)</code>.
7825
7826
7827	<p>
7828	The string library assumes one-byte character encodings.
7829
7830
7831	<p>
7832	<hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
7833	Returns the internal numerical codes of the characters <code>s[i]</code>,
7834	<code>s[i+1]</code>, ..., <code>s[j]</code>.
7835	The default value for <code>i</code> is 1;
7836	the default value for <code>j</code> is <code>i</code>.
7837	These indices are corrected
7838	following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
7839
7840
7841	<p>
7842	Numerical codes are not necessarily portable across platforms.
7843
7844
7845
7846
7847	<p>
7848	<hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3>
7849	Receives zero or more integers.
7850	Returns a string with length equal to the number of arguments,
7851	in which each character has the internal numerical code equal
7852	to its corresponding argument.
7853
7854
7855	<p>
7856	Numerical codes are not necessarily portable across platforms.
7857
7858
7859
7860
7861	<p>
7862	<hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3>
7863
7864
7865	<p>
7866	Returns a string containing a binary representation of the given function,
7867	so that a later <a href="#pdf-load"><code>load</code></a> on this string returns
7868	a copy of the function (but with new upvalues).
7869
7870
7871
7872
7873	<p>
7874	<hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
7875
7876
7877	<p>
7878	Looks for the first match of
7879	<code>pattern</code> in the string <code>s</code>.
7880	If it finds a match, then <code>find</code> returns the indices of <code>s</code>
7881	where this occurrence starts and ends;
7882	otherwise, it returns <b>nil</b>.
7883	A third, optional numerical argument <code>init</code> specifies
7884	where to start the search;
7885	its default value is 1 and can be negative.
7886	A value of <b>true</b> as a fourth, optional argument <code>plain</code>
7887	turns off the pattern matching facilities,
7888	so the function does a plain "find substring" operation,
7889	with no characters in <code>pattern</code> being considered magic.
7890	Note that if <code>plain</code> is given, then <code>init</code> must be given as well.
7891
7892
7893	<p>
7894	If the pattern has captures,
7895	then in a successful match
7896	the captured values are also returned,
7897	after the two indices.
7898
7899
7900
7901
7902	<p>
7903	<hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3>
7904
7905
7906	<p>
7907	Returns a formatted version of its variable number of arguments
7908	following the description given in its first argument (which must be a string).
7909	The format string follows the same rules as the ANSI C function <code>sprintf</code>.
7910	The only differences are that the options/modifiers
7911	<code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>,
7912	and <code>p</code> are not supported
7913	and that there is an extra option, <code>q</code>.
7914	The <code>q</code> option formats a string between double quotes,
7915	using escape sequences when necessary to ensure that
7916	it can safely be read back by the Lua interpreter.
7917	For instance, the call
7918
7919	<pre>
7920	string.format('%q', 'a string with "quotes" and \n new line')
7921	</pre><p>
7922	may produce the string:
7923
7924	<pre>
7925	"a string with \"quotes\" and \
7926	new line"
7927	</pre>
7928
7929	<p>
7930	Options
7931	<code>A</code> and <code>a</code> (when available),
7932	<code>E</code>, <code>e</code>, <code>f</code>,
7933	<code>G</code>, and <code>g</code> all expect a number as argument.
7934	Options <code>c</code>, <code>d</code>,
7935	<code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>
7936	also expect a number,
7937	but the range of that number may be limited by
7938	the underlying C implementation.
7939	For options <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>,
7940	the number cannot be negative.
7941	Option <code>q</code> expects a string;
7942	option <code>s</code> expects a string without embedded zeros.
7943	If the argument to option <code>s</code> is not a string,
7944	it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
7945
7946
7947
7948
7949	<p>
7950	<hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3>
7951	Returns an iterator function that,
7952	each time it is called,
7953	returns the next captures from <code>pattern</code> over the string <code>s</code>.
7954	If <code>pattern</code> specifies no captures,
7955	then the whole match is produced in each call.
7956
7957
7958	<p>
7959	As an example, the following loop
7960	will iterate over all the words from string <code>s</code>,
7961	printing one per line:
7962
7963	<pre>
7964	s = "hello world from Lua"
7965	for w in string.gmatch(s, "%a+") do
7966	print(w)
7967	end
7968	</pre><p>
7969	The next example collects all pairs <code>key=value</code> from the
7970	given string into a table:
7971
7972	<pre>
7973	t = {}
7974	s = "from=world, to=Lua"
7975	for k, v in string.gmatch(s, "(%w+)=(%w+)") do
7976	t[k] = v
7977	end
7978	</pre>
7979
7980	<p>
7981	For this function, a caret '<code>^</code>' at the start of a pattern does not
7982	work as an anchor, as this would prevent the iteration.
7983
7984
7985
7986
7987	<p>
7988	<hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
7989	Returns a copy of <code>s</code>
7990	in which all (or the first <code>n</code>, if given)
7991	occurrences of the <code>pattern</code> have been
7992	replaced by a replacement string specified by <code>repl</code>,
7993	which can be a string, a table, or a function.
7994	<code>gsub</code> also returns, as its second value,
7995	the total number of matches that occurred.
7996	The name <code>gsub</code> comes from <em>Global SUBstitution</em>.
7997
7998
7999	<p>
8000	If <code>repl</code> is a string, then its value is used for replacement.
8001	The character <code>%</code> works as an escape character:
8002	any sequence in <code>repl</code> of the form <code>%<em>d</em></code>,
8003	with <em>d</em> between 1 and 9,
8004	stands for the value of the <em>d</em>-th captured substring.
8005	The sequence <code>%0</code> stands for the whole match.
8006	The sequence <code>%%</code> stands for a single <code>%</code>.
8007
8008
8009	<p>
8010	If <code>repl</code> is a table, then the table is queried for every match,
8011	using the first capture as the key.
8012
8013
8014	<p>
8015	If <code>repl</code> is a function, then this function is called every time a
8016	match occurs, with all captured substrings passed as arguments,
8017	in order.
8018
8019
8020	<p>
8021	In any case,
8022	if the pattern specifies no captures,
8023	then it behaves as if the whole pattern was inside a capture.
8024
8025
8026	<p>
8027	If the value returned by the table query or by the function call
8028	is a string or a number,
8029	then it is used as the replacement string;
8030	otherwise, if it is <b>false</b> or <b>nil</b>,
8031	then there is no replacement
8032	(that is, the original match is kept in the string).
8033
8034
8035	<p>
8036	Here are some examples:
8037
8038	<pre>
8039	x = string.gsub("hello world", "(%w+)", "%1 %1")
8040	--> x="hello hello world world"
8041
8042	x = string.gsub("hello world", "%w+", "%0 %0", 1)
8043	--> x="hello hello world"
8044
8045	x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
8046	--> x="world hello Lua from"
8047
8048	x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
8049	--> x="home = /home/roberto, user = roberto"
8050
8051	x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
8052	return load(s)()
8053	end)
8054	--> x="4+5 = 9"
8055
8056	local t = {name="lua", version="5.2"}
8057	x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
8058	--> x="lua-5.2.tar.gz"
8059	</pre>
8060
8061
8062
8063	<p>
8064	<hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
8065	Receives a string and returns its length.
8066	The empty string <code>""</code> has length 0.
8067	Embedded zeros are counted,
8068	so <code>"a\000bc\000"</code> has length 5.
8069
8070
8071
8072
8073	<p>
8074	<hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
8075	Receives a string and returns a copy of this string with all
8076	uppercase letters changed to lowercase.
8077	All other characters are left unchanged.
8078	The definition of what an uppercase letter is depends on the current locale.
8079
8080
8081
8082
8083	<p>
8084	<hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
8085	Looks for the first <em>match</em> of
8086	<code>pattern</code> in the string <code>s</code>.
8087	If it finds one, then <code>match</code> returns
8088	the captures from the pattern;
8089	otherwise it returns <b>nil</b>.
8090	If <code>pattern</code> specifies no captures,
8091	then the whole match is returned.
8092	A third, optional numerical argument <code>init</code> specifies
8093	where to start the search;
8094	its default value is 1 and can be negative.
8095
8096
8097
8098
8099	<p>
8100	<hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3>
8101	Returns a string that is the concatenation of <code>n</code> copies of
8102	the string <code>s</code> separated by the string <code>sep</code>.
8103	The default value for <code>sep</code> is the empty string
8104	(that is, no separator).
8105
8106
8107
8108
8109	<p>
8110	<hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
8111	Returns a string that is the string <code>s</code> reversed.
8112
8113
8114
8115
8116	<p>
8117	<hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
8118	Returns the substring of <code>s</code> that
8119	starts at <code>i</code> and continues until <code>j</code>;
8120	<code>i</code> and <code>j</code> can be negative.
8121	If <code>j</code> is absent, then it is assumed to be equal to -1
8122	(which is the same as the string length).
8123	In particular,
8124	the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
8125	with length <code>j</code>,
8126	and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code>
8127	with length <code>i</code>.
8128
8129
8130	<p>
8131	If, after the translation of negative indices,
8132	<code>i</code> is less than 1,
8133	it is corrected to 1.
8134	If <code>j</code> is greater than the string length,
8135	it is corrected to that length.
8136	If, after these corrections,
8137	<code>i</code> is greater than <code>j</code>,
8138	the function returns the empty string.
8139
8140
8141
8142
8143	<p>
8144	<hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
8145	Receives a string and returns a copy of this string with all
8146	lowercase letters changed to uppercase.
8147	All other characters are left unchanged.
8148	The definition of what a lowercase letter is depends on the current locale.
8149
8150
8151
8152	<h3>6.4.1 – <a name="6.4.1">Patterns</a></h3>
8153
8154
8155	<h4>Character Class:</h4><p>
8156	A <em>character class</em> is used to represent a set of characters.
8157	The following combinations are allowed in describing a character class:
8158
8159	<ul>
8160
8161	<li><b><em>x</em>: </b>
8162	(where <em>x</em> is not one of the <em>magic characters</em>
8163	<code>^$()%.[]*+-?</code>)
8164	represents the character <em>x</em> itself.
8165	</li>
8166
8167	<li><b><code>.</code>: </b> (a dot) represents all characters.</li>
8168
8169	<li><b><code>%a</code>: </b> represents all letters.</li>
8170
8171	<li><b><code>%c</code>: </b> represents all control characters.</li>
8172
8173	<li><b><code>%d</code>: </b> represents all digits.</li>
8174
8175	<li><b><code>%g</code>: </b> represents all printable characters except space.</li>
8176
8177	<li><b><code>%l</code>: </b> represents all lowercase letters.</li>
8178
8179	<li><b><code>%p</code>: </b> represents all punctuation characters.</li>
8180
8181	<li><b><code>%s</code>: </b> represents all space characters.</li>
8182
8183	<li><b><code>%u</code>: </b> represents all uppercase letters.</li>
8184
8185	<li><b><code>%w</code>: </b> represents all alphanumeric characters.</li>
8186
8187	<li><b><code>%x</code>: </b> represents all hexadecimal digits.</li>
8188
8189	<li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character)
8190	represents the character <em>x</em>.
8191	This is the standard way to escape the magic characters.
8192	Any punctuation character (even the non magic)
8193	can be preceded by a '<code>%</code>'
8194	when used to represent itself in a pattern.
8195	</li>
8196
8197	<li><b><code>[<em>set</em>]</code>: </b>
8198	represents the class which is the union of all
8199	characters in <em>set</em>.
8200	A range of characters can be specified by
8201	separating the end characters of the range,
8202	in ascending order, with a '<code>-</code>',
8203	All classes <code>%</code><em>x</em> described above can also be used as
8204	components in <em>set</em>.
8205	All other characters in <em>set</em> represent themselves.
8206	For example, <code>[%w_]</code> (or <code>[_%w]</code>)
8207	represents all alphanumeric characters plus the underscore,
8208	<code>[0-7]</code> represents the octal digits,
8209	and <code>[0-7%l%-]</code> represents the octal digits plus
8210	the lowercase letters plus the '<code>-</code>' character.
8211
8212
8213	<p>
8214	The interaction between ranges and classes is not defined.
8215	Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
8216	have no meaning.
8217	</li>
8218
8219	<li><b><code>[^<em>set</em>]</code>: </b>
8220	represents the complement of <em>set</em>,
8221	where <em>set</em> is interpreted as above.
8222	</li>
8223
8224	</ul><p>
8225	For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
8226	the corresponding uppercase letter represents the complement of the class.
8227	For instance, <code>%S</code> represents all non-space characters.
8228
8229
8230	<p>
8231	The definitions of letter, space, and other character groups
8232	depend on the current locale.
8233	In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
8234
8235
8236
8237
8238
8239	<h4>Pattern Item:</h4><p>
8240	A <em>pattern item</em> can be
8241
8242	<ul>
8243
8244	<li>
8245	a single character class,
8246	which matches any single character in the class;
8247	</li>
8248
8249	<li>
8250	a single character class followed by '<code>*</code>',
8251	which matches 0 or more repetitions of characters in the class.
8252	These repetition items will always match the longest possible sequence;
8253	</li>
8254
8255	<li>
8256	a single character class followed by '<code>+</code>',
8257	which matches 1 or more repetitions of characters in the class.
8258	These repetition items will always match the longest possible sequence;
8259	</li>
8260
8261	<li>
8262	a single character class followed by '<code>-</code>',
8263	which also matches 0 or more repetitions of characters in the class.
8264	Unlike '<code>*</code>',
8265	these repetition items will always match the shortest possible sequence;
8266	</li>
8267
8268	<li>
8269	a single character class followed by '<code>?</code>',
8270	which matches 0 or 1 occurrence of a character in the class;
8271	</li>
8272
8273	<li>
8274	<code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
8275	such item matches a substring equal to the <em>n</em>-th captured string
8276	(see below);
8277	</li>
8278
8279	<li>
8280	<code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
8281	such item matches strings that start with <em>x</em>, end with <em>y</em>,
8282	and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
8283	This means that, if one reads the string from left to right,
8284	counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
8285	the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
8286	For instance, the item <code>%b()</code> matches expressions with
8287	balanced parentheses.
8288	</li>
8289
8290	<li>
8291	<code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>;
8292	such item matches an empty string at any position such that
8293	the next character belongs to <em>set</em>
8294	and the previous character does not belong to <em>set</em>.
8295	The set <em>set</em> is interpreted as previously described.
8296	The beginning and the end of the subject are handled as if
8297	they were the character '<code>\0</code>'.
8298	</li>
8299
8300	</ul>
8301
8302
8303
8304
8305	<h4>Pattern:</h4><p>
8306	A <em>pattern</em> is a sequence of pattern items.
8307	A caret '<code>^</code>' at the beginning of a pattern anchors the match at the
8308	beginning of the subject string.
8309	A '<code>$</code>' at the end of a pattern anchors the match at the
8310	end of the subject string.
8311	At other positions,
8312	'<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
8313
8314
8315
8316
8317
8318	<h4>Captures:</h4><p>
8319	A pattern can contain sub-patterns enclosed in parentheses;
8320	they describe <em>captures</em>.
8321	When a match succeeds, the substrings of the subject string
8322	that match captures are stored (<em>captured</em>) for future use.
8323	Captures are numbered according to their left parentheses.
8324	For instance, in the pattern <code>"(a(.)%w(%s))"</code>,
8325	the part of the string matching <code>"a(.)%w(%s)"</code> is
8326	stored as the first capture (and therefore has number 1);
8327	the character matching "<code>.</code>" is captured with number 2,
8328	and the part matching "<code>%s*</code>" has number 3.
8329
8330
8331	<p>
8332	As a special case, the empty capture <code>()</code> captures
8333	the current string position (a number).
8334	For instance, if we apply the pattern <code>"()aa()"</code> on the
8335	string <code>"flaaap"</code>, there will be two captures: 3 and 5.
8336
8337
8338
8339
8340
8341
8342
8343
8344
8345
8346
8347	<h2>6.5 – <a name="6.5">Table Manipulation</a></h2>
8348
8349	<p>
8350	This library provides generic functions for table manipulation.
8351	It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
8352
8353
8354	<p>
8355	Remember that, whenever an operation needs the length of a table,
8356	the table should be a proper sequence
8357	or have a <code>__len</code> metamethod (see <a href="#3.4.6">§3.4.6</a>).
8358	All functions ignore non-numeric keys
8359	in tables given as arguments.
8360
8361
8362	<p>
8363	For performance reasons,
8364	all table accesses (get/set) performed by these functions are raw.
8365
8366
8367	<p>
8368	<hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3>
8369
8370
8371	<p>
8372	Given a list where all elements are strings or numbers,
8373	returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>.
8374	The default value for <code>sep</code> is the empty string,
8375	the default for <code>i</code> is 1,
8376	and the default for <code>j</code> is <code>#list</code>.
8377	If <code>i</code> is greater than <code>j</code>, returns the empty string.
8378
8379
8380
8381
8382	<p>
8383	<hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3>
8384
8385
8386	<p>
8387	Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>,
8388	shifting up the elements
8389	<code>list[pos], list[pos+1], ···, list[#list]</code>.
8390	The default value for <code>pos</code> is <code>#list+1</code>,
8391	so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
8392	of list <code>t</code>.
8393
8394
8395
8396
8397	<p>
8398	<hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3>
8399
8400
8401	<p>
8402	Returns a new table with all parameters stored into keys 1, 2, etc.
8403	and with a field "<code>n</code>" with the total number of parameters.
8404	Note that the resulting table may not be a sequence.
8405
8406
8407
8408
8409	<p>
8410	<hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3>
8411
8412
8413	<p>
8414	Removes from <code>list</code> the element at position <code>pos</code>,
8415	returning the value of the removed element.
8416	When <code>pos</code> is an integer between 1 and <code>#list</code>,
8417	it shifts down the elements
8418	<code>list[pos+1], list[pos+2], ···, list[#list]</code>
8419	and erases element <code>list[#list]</code>;
8420	The index <code>pos</code> can also be 0 when <code>#list</code> is 0,
8421	or <code>#list + 1</code>;
8422	in those cases, the function erases the element <code>list[pos]</code>.
8423
8424
8425	<p>
8426	The default value for <code>pos</code> is <code>#list</code>,
8427	so that a call <code>table.remove(t)</code> removes the last element
8428	of list <code>t</code>.
8429
8430
8431
8432
8433	<p>
8434	<hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3>
8435
8436
8437	<p>
8438	Sorts list elements in a given order, <em>in-place</em>,
8439	from <code>list[1]</code> to <code>list[#list]</code>.
8440	If <code>comp</code> is given,
8441	then it must be a function that receives two list elements
8442	and returns true when the first element must come
8443	before the second in the final order
8444	(so that <code>not comp(list[i+1],list[i])</code> will be true after the sort).
8445	If <code>comp</code> is not given,
8446	then the standard Lua operator <code><</code> is used instead.
8447
8448
8449	<p>
8450	The sort algorithm is not stable;
8451	that is, elements considered equal by the given order
8452	may have their relative positions changed by the sort.
8453
8454
8455
8456
8457	<p>
8458	<hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3>
8459
8460
8461	<p>
8462	Returns the elements from the given table.
8463	This function is equivalent to
8464
8465	<pre>
8466	return list[i], list[i+1], ···, list[j]
8467	</pre><p>
8468	By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>.
8469
8470
8471
8472
8473
8474
8475
8476	<h2>6.6 – <a name="6.6">Mathematical Functions</a></h2>
8477
8478	<p>
8479	This library is an interface to the standard C math library.
8480	It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>.
8481
8482
8483	<p>
8484	<hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
8485
8486
8487	<p>
8488	Returns the absolute value of <code>x</code>.
8489
8490
8491
8492
8493	<p>
8494	<hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
8495
8496
8497	<p>
8498	Returns the arc cosine of <code>x</code> (in radians).
8499
8500
8501
8502
8503	<p>
8504	<hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
8505
8506
8507	<p>
8508	Returns the arc sine of <code>x</code> (in radians).
8509
8510
8511
8512
8513	<p>
8514	<hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3>
8515
8516
8517	<p>
8518	Returns the arc tangent of <code>x</code> (in radians).
8519
8520
8521
8522
8523	<p>
8524	<hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3>
8525
8526
8527	<p>
8528	Returns the arc tangent of <code>y/x</code> (in radians),
8529	but uses the signs of both parameters to find the
8530	quadrant of the result.
8531	(It also handles correctly the case of <code>x</code> being zero.)
8532
8533
8534
8535
8536	<p>
8537	<hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
8538
8539
8540	<p>
8541	Returns the smallest integer larger than or equal to <code>x</code>.
8542
8543
8544
8545
8546	<p>
8547	<hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
8548
8549
8550	<p>
8551	Returns the cosine of <code>x</code> (assumed to be in radians).
8552
8553
8554
8555
8556	<p>
8557	<hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3>
8558
8559
8560	<p>
8561	Returns the hyperbolic cosine of <code>x</code>.
8562
8563
8564
8565
8566	<p>
8567	<hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
8568
8569
8570	<p>
8571	Returns the angle <code>x</code> (given in radians) in degrees.
8572
8573
8574
8575
8576	<p>
8577	<hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
8578
8579
8580	<p>
8581	Returns the value <em>e<sup>x</sup></em>.
8582
8583
8584
8585
8586	<p>
8587	<hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
8588
8589
8590	<p>
8591	Returns the largest integer smaller than or equal to <code>x</code>.
8592
8593
8594
8595
8596	<p>
8597	<hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
8598
8599
8600	<p>
8601	Returns the remainder of the division of <code>x</code> by <code>y</code>
8602	that rounds the quotient towards zero.
8603
8604
8605
8606
8607	<p>
8608	<hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3>
8609
8610
8611	<p>
8612	Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>,
8613	<code>e</code> is an integer and the absolute value of <code>m</code> is
8614	in the range <em>[0.5, 1)</em>
8615	(or zero when <code>x</code> is zero).
8616
8617
8618
8619
8620	<p>
8621	<hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
8622
8623
8624	<p>
8625	The value <code>HUGE_VAL</code>,
8626	a value larger than or equal to any other numerical value.
8627
8628
8629
8630
8631	<p>
8632	<hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3>
8633
8634
8635	<p>
8636	Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer).
8637
8638
8639
8640
8641	<p>
8642	<hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3>
8643
8644
8645	<p>
8646	Returns the logarithm of <code>x</code> in the given base.
8647	The default for <code>base</code> is <em>e</em>
8648	(so that the function returns the natural logarithm of <code>x</code>).
8649
8650
8651
8652
8653	<p>
8654	<hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3>
8655
8656
8657	<p>
8658	Returns the maximum value among its arguments.
8659
8660
8661
8662
8663	<p>
8664	<hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3>
8665
8666
8667	<p>
8668	Returns the minimum value among its arguments.
8669
8670
8671
8672
8673	<p>
8674	<hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
8675
8676
8677	<p>
8678	Returns two numbers,
8679	the integral part of <code>x</code> and the fractional part of <code>x</code>.
8680
8681
8682
8683
8684	<p>
8685	<hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
8686
8687
8688	<p>
8689	The value of <em>π</em>.
8690
8691
8692
8693
8694	<p>
8695	<hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3>
8696
8697
8698	<p>
8699	Returns <em>x<sup>y</sup></em>.
8700	(You can also use the expression <code>x^y</code> to compute this value.)
8701
8702
8703
8704
8705	<p>
8706	<hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
8707
8708
8709	<p>
8710	Returns the angle <code>x</code> (given in degrees) in radians.
8711
8712
8713
8714
8715	<p>
8716	<hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
8717
8718
8719	<p>
8720	This function is an interface to the simple
8721	pseudo-random generator function <code>rand</code> provided by Standard C.
8722	(No guarantees can be given for its statistical properties.)
8723
8724
8725	<p>
8726	When called without arguments,
8727	returns a uniform pseudo-random real number
8728	in the range <em>[0,1)</em>.
8729	When called with an integer number <code>m</code>,
8730	<code>math.random</code> returns
8731	a uniform pseudo-random integer in the range <em>[1, m]</em>.
8732	When called with two integer numbers <code>m</code> and <code>n</code>,
8733	<code>math.random</code> returns a uniform pseudo-random
8734	integer in the range <em>[m, n]</em>.
8735
8736
8737
8738
8739	<p>
8740	<hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3>
8741
8742
8743	<p>
8744	Sets <code>x</code> as the "seed"
8745	for the pseudo-random generator:
8746	equal seeds produce equal sequences of numbers.
8747
8748
8749
8750
8751	<p>
8752	<hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
8753
8754
8755	<p>
8756	Returns the sine of <code>x</code> (assumed to be in radians).
8757
8758
8759
8760
8761	<p>
8762	<hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3>
8763
8764
8765	<p>
8766	Returns the hyperbolic sine of <code>x</code>.
8767
8768
8769
8770
8771	<p>
8772	<hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
8773
8774
8775	<p>
8776	Returns the square root of <code>x</code>.
8777	(You can also use the expression <code>x^0.5</code> to compute this value.)
8778
8779
8780
8781
8782	<p>
8783	<hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
8784
8785
8786	<p>
8787	Returns the tangent of <code>x</code> (assumed to be in radians).
8788
8789
8790
8791
8792	<p>
8793	<hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3>
8794
8795
8796	<p>
8797	Returns the hyperbolic tangent of <code>x</code>.
8798
8799
8800
8801
8802
8803
8804
8805	<h2>6.7 – <a name="6.7">Bitwise Operations</a></h2>
8806
8807	<p>
8808	This library provides bitwise operations.
8809	It provides all its functions inside the table <a name="pdf-bit32"><code>bit32</code></a>.
8810
8811
8812	<p>
8813	Unless otherwise stated,
8814	all functions accept numeric arguments in the range
8815	<em>(-2<sup>51</sup>,+2<sup>51</sup>)</em>;
8816	each argument is normalized to
8817	the remainder of its division by <em>2<sup>32</sup></em>
8818	and truncated to an integer (in some unspecified way),
8819	so that its final value falls in the range <em>[0,2<sup>32</sup> - 1]</em>.
8820	Similarly, all results are in the range <em>[0,2<sup>32</sup> - 1]</em>.
8821	Note that <code>bit32.bnot(0)</code> is <code>0xFFFFFFFF</code>,
8822	which is different from <code>-1</code>.
8823
8824
8825	<p>
8826	<hr><h3><a name="pdf-bit32.arshift"><code>bit32.arshift (x, disp)</code></a></h3>
8827
8828
8829	<p>
8830	Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
8831	The number <code>disp</code> may be any representable integer.
8832	Negative displacements shift to the left.
8833
8834
8835	<p>
8836	This shift operation is what is called arithmetic shift.
8837	Vacant bits on the left are filled
8838	with copies of the higher bit of <code>x</code>;
8839	vacant bits on the right are filled with zeros.
8840	In particular,
8841	displacements with absolute values higher than 31
8842	result in zero or <code>0xFFFFFFFF</code> (all original bits are shifted out).
8843
8844
8845
8846
8847	<p>
8848	<hr><h3><a name="pdf-bit32.band"><code>bit32.band (···)</code></a></h3>
8849
8850
8851	<p>
8852	Returns the bitwise <em>and</em> of its operands.
8853
8854
8855
8856
8857	<p>
8858	<hr><h3><a name="pdf-bit32.bnot"><code>bit32.bnot (x)</code></a></h3>
8859
8860
8861	<p>
8862	Returns the bitwise negation of <code>x</code>.
8863	For any integer <code>x</code>,
8864	the following identity holds:
8865
8866	<pre>
8867	assert(bit32.bnot(x) == (-1 - x) % 2^32)
8868	</pre>
8869
8870
8871
8872	<p>
8873	<hr><h3><a name="pdf-bit32.bor"><code>bit32.bor (···)</code></a></h3>
8874
8875
8876	<p>
8877	Returns the bitwise <em>or</em> of its operands.
8878
8879
8880
8881
8882	<p>
8883	<hr><h3><a name="pdf-bit32.btest"><code>bit32.btest (···)</code></a></h3>
8884
8885
8886	<p>
8887	Returns a boolean signaling
8888	whether the bitwise <em>and</em> of its operands is different from zero.
8889
8890
8891
8892
8893	<p>
8894	<hr><h3><a name="pdf-bit32.bxor"><code>bit32.bxor (···)</code></a></h3>
8895
8896
8897	<p>
8898	Returns the bitwise <em>exclusive or</em> of its operands.
8899
8900
8901
8902
8903	<p>
8904	<hr><h3><a name="pdf-bit32.extract"><code>bit32.extract (n, field [, width])</code></a></h3>
8905
8906
8907	<p>
8908	Returns the unsigned number formed by the bits
8909	<code>field</code> to <code>field + width - 1</code> from <code>n</code>.
8910	Bits are numbered from 0 (least significant) to 31 (most significant).
8911	All accessed bits must be in the range <em>[0, 31]</em>.
8912
8913
8914	<p>
8915	The default for <code>width</code> is 1.
8916
8917
8918
8919
8920	<p>
8921	<hr><h3><a name="pdf-bit32.replace"><code>bit32.replace (n, v, field [, width])</code></a></h3>
8922
8923
8924	<p>
8925	Returns a copy of <code>n</code> with
8926	the bits <code>field</code> to <code>field + width - 1</code>
8927	replaced by the value <code>v</code>.
8928	See <a href="#pdf-bit32.extract"><code>bit32.extract</code></a> for details about <code>field</code> and <code>width</code>.
8929
8930
8931
8932
8933	<p>
8934	<hr><h3><a name="pdf-bit32.lrotate"><code>bit32.lrotate (x, disp)</code></a></h3>
8935
8936
8937	<p>
8938	Returns the number <code>x</code> rotated <code>disp</code> bits to the left.
8939	The number <code>disp</code> may be any representable integer.
8940
8941
8942	<p>
8943	For any valid displacement,
8944	the following identity holds:
8945
8946	<pre>
8947	assert(bit32.lrotate(x, disp) == bit32.lrotate(x, disp % 32))
8948	</pre><p>
8949	In particular,
8950	negative displacements rotate to the right.
8951
8952
8953
8954
8955	<p>
8956	<hr><h3><a name="pdf-bit32.lshift"><code>bit32.lshift (x, disp)</code></a></h3>
8957
8958
8959	<p>
8960	Returns the number <code>x</code> shifted <code>disp</code> bits to the left.
8961	The number <code>disp</code> may be any representable integer.
8962	Negative displacements shift to the right.
8963	In any direction, vacant bits are filled with zeros.
8964	In particular,
8965	displacements with absolute values higher than 31
8966	result in zero (all bits are shifted out).
8967
8968
8969	<p>
8970	For positive displacements,
8971	the following equality holds:
8972
8973	<pre>
8974	assert(bit32.lshift(b, disp) == (b * 2^disp) % 2^32)
8975	</pre>
8976
8977
8978
8979	<p>
8980	<hr><h3><a name="pdf-bit32.rrotate"><code>bit32.rrotate (x, disp)</code></a></h3>
8981
8982
8983	<p>
8984	Returns the number <code>x</code> rotated <code>disp</code> bits to the right.
8985	The number <code>disp</code> may be any representable integer.
8986
8987
8988	<p>
8989	For any valid displacement,
8990	the following identity holds:
8991
8992	<pre>
8993	assert(bit32.rrotate(x, disp) == bit32.rrotate(x, disp % 32))
8994	</pre><p>
8995	In particular,
8996	negative displacements rotate to the left.
8997
8998
8999
9000
9001	<p>
9002	<hr><h3><a name="pdf-bit32.rshift"><code>bit32.rshift (x, disp)</code></a></h3>
9003
9004
9005	<p>
9006	Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
9007	The number <code>disp</code> may be any representable integer.
9008	Negative displacements shift to the left.
9009	In any direction, vacant bits are filled with zeros.
9010	In particular,
9011	displacements with absolute values higher than 31
9012	result in zero (all bits are shifted out).
9013
9014
9015	<p>
9016	For positive displacements,
9017	the following equality holds:
9018
9019	<pre>
9020	assert(bit32.rshift(b, disp) == math.floor(b % 2^32 / 2^disp))
9021	</pre>
9022
9023	<p>
9024	This shift operation is what is called logical shift.
9025
9026
9027
9028
9029
9030
9031
9032	<h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2>
9033
9034	<p>
9035	The I/O library provides two different styles for file manipulation.
9036	The first one uses implicit file descriptors;
9037	that is, there are operations to set a default input file and a
9038	default output file,
9039	and all input/output operations are over these default files.
9040	The second style uses explicit file descriptors.
9041
9042
9043	<p>
9044	When using implicit file descriptors,
9045	all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
9046	When using explicit file descriptors,
9047	the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor
9048	and then all operations are supplied as methods of the file descriptor.
9049
9050
9051	<p>
9052	The table <code>io</code> also provides
9053	three predefined file descriptors with their usual meanings from C:
9054	<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>.
9055	The I/O library never closes these files.
9056
9057
9058	<p>
9059	Unless otherwise stated,
9060	all I/O functions return <b>nil</b> on failure
9061	(plus an error message as a second result and
9062	a system-dependent error code as a third result)
9063	and some value different from <b>nil</b> on success.
9064	On non-Posix systems,
9065	the computation of the error message and error code
9066	in case of errors
9067	may be not thread safe,
9068	because they rely on the global C variable <code>errno</code>.
9069
9070
9071	<p>
9072	<hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
9073
9074
9075	<p>
9076	Equivalent to <code>file:close()</code>.
9077	Without a <code>file</code>, closes the default output file.
9078
9079
9080
9081
9082	<p>
9083	<hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
9084
9085
9086	<p>
9087	Equivalent to <code>io.output():flush()</code>.
9088
9089
9090
9091
9092	<p>
9093	<hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
9094
9095
9096	<p>
9097	When called with a file name, it opens the named file (in text mode),
9098	and sets its handle as the default input file.
9099	When called with a file handle,
9100	it simply sets this file handle as the default input file.
9101	When called without parameters,
9102	it returns the current default input file.
9103
9104
9105	<p>
9106	In case of errors this function raises the error,
9107	instead of returning an error code.
9108
9109
9110
9111
9112	<p>
9113	<hr><h3><a name="pdf-io.lines"><code>io.lines ([filename ···])</code></a></h3>
9114
9115
9116	<p>
9117	Opens the given file name in read mode
9118	and returns an iterator function that
9119	works like <code>file:lines(···)</code> over the opened file.
9120	When the iterator function detects the end of file,
9121	it returns <b>nil</b> (to finish the loop) and automatically closes the file.
9122
9123
9124	<p>
9125	The call <code>io.lines()</code> (with no file name) is equivalent
9126	to <code>io.input():lines()</code>;
9127	that is, it iterates over the lines of the default input file.
9128	In this case it does not close the file when the loop ends.
9129
9130
9131	<p>
9132	In case of errors this function raises the error,
9133	instead of returning an error code.
9134
9135
9136
9137
9138	<p>
9139	<hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
9140
9141
9142	<p>
9143	This function opens a file,
9144	in the mode specified in the string <code>mode</code>.
9145	It returns a new file handle,
9146	or, in case of errors, <b>nil</b> plus an error message.
9147
9148
9149	<p>
9150	The <code>mode</code> string can be any of the following:
9151
9152	<ul>
9153	<li><b>"<code>r</code>": </b> read mode (the default);</li>
9154	<li><b>"<code>w</code>": </b> write mode;</li>
9155	<li><b>"<code>a</code>": </b> append mode;</li>
9156	<li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li>
9157	<li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li>
9158	<li><b>"<code>a+</code>": </b> append update mode, previous data is preserved,
9159	writing is only allowed at the end of file.</li>
9160	</ul><p>
9161	The <code>mode</code> string can also have a '<code>b</code>' at the end,
9162	which is needed in some systems to open the file in binary mode.
9163
9164
9165
9166
9167	<p>
9168	<hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
9169
9170
9171	<p>
9172	Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
9173
9174
9175
9176
9177	<p>
9178	<hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
9179
9180
9181	<p>
9182	This function is system dependent and is not available
9183	on all platforms.
9184
9185
9186	<p>
9187	Starts program <code>prog</code> in a separated process and returns
9188	a file handle that you can use to read data from this program
9189	(if <code>mode</code> is <code>"r"</code>, the default)
9190	or to write data to this program
9191	(if <code>mode</code> is <code>"w"</code>).
9192
9193
9194
9195
9196	<p>
9197	<hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3>
9198
9199
9200	<p>
9201	Equivalent to <code>io.input():read(···)</code>.
9202
9203
9204
9205
9206	<p>
9207	<hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
9208
9209
9210	<p>
9211	Returns a handle for a temporary file.
9212	This file is opened in update mode
9213	and it is automatically removed when the program ends.
9214
9215
9216
9217
9218	<p>
9219	<hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
9220
9221
9222	<p>
9223	Checks whether <code>obj</code> is a valid file handle.
9224	Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
9225	<code>"closed file"</code> if <code>obj</code> is a closed file handle,
9226	or <b>nil</b> if <code>obj</code> is not a file handle.
9227
9228
9229
9230
9231	<p>
9232	<hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3>
9233
9234
9235	<p>
9236	Equivalent to <code>io.output():write(···)</code>.
9237
9238
9239
9240
9241	<p>
9242	<hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
9243
9244
9245	<p>
9246	Closes <code>file</code>.
9247	Note that files are automatically closed when
9248	their handles are garbage collected,
9249	but that takes an unpredictable amount of time to happen.
9250
9251
9252	<p>
9253	When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>,
9254	<a href="#pdf-file:close"><code>file:close</code></a> returns the same values
9255	returned by <a href="#pdf-os.execute"><code>os.execute</code></a>.
9256
9257
9258
9259
9260	<p>
9261	<hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
9262
9263
9264	<p>
9265	Saves any written data to <code>file</code>.
9266
9267
9268
9269
9270	<p>
9271	<hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3>
9272
9273
9274	<p>
9275	Returns an iterator function that,
9276	each time it is called,
9277	reads the file according to the given formats.
9278	When no format is given,
9279	uses "*l" as a default.
9280	As an example, the construction
9281
9282	<pre>
9283	for c in file:lines(1) do <em>body</em> end
9284	</pre><p>
9285	will iterate over all characters of the file,
9286	starting at the current position.
9287	Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
9288	when the loop ends.
9289
9290
9291	<p>
9292	In case of errors this function raises the error,
9293	instead of returning an error code.
9294
9295
9296
9297
9298	<p>
9299	<hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3>
9300
9301
9302	<p>
9303	Reads the file <code>file</code>,
9304	according to the given formats, which specify what to read.
9305	For each format,
9306	the function returns a string (or a number) with the characters read,
9307	or <b>nil</b> if it cannot read data with the specified format.
9308	When called without formats,
9309	it uses a default format that reads the next line
9310	(see below).
9311
9312
9313	<p>
9314	The available formats are
9315
9316	<ul>
9317
9318	<li><b>"<code>*n</code>": </b>
9319	reads a number;
9320	this is the only format that returns a number instead of a string.
9321	</li>
9322
9323	<li><b>"<code>*a</code>": </b>
9324	reads the whole file, starting at the current position.
9325	On end of file, it returns the empty string.
9326	</li>
9327
9328	<li><b>"<code>*l</code>": </b>
9329	reads the next line skipping the end of line,
9330	returning <b>nil</b> on end of file.
9331	This is the default format.
9332	</li>
9333
9334	<li><b>"<code>*L</code>": </b>
9335	reads the next line keeping the end of line (if present),
9336	returning <b>nil</b> on end of file.
9337	</li>
9338
9339	<li><b><em>number</em>: </b>
9340	reads a string with up to this number of bytes,
9341	returning <b>nil</b> on end of file.
9342	If number is zero,
9343	it reads nothing and returns an empty string,
9344	or <b>nil</b> on end of file.
9345	</li>
9346
9347	</ul>
9348
9349
9350
9351	<p>
9352	<hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3>
9353
9354
9355	<p>
9356	Sets and gets the file position,
9357	measured from the beginning of the file,
9358	to the position given by <code>offset</code> plus a base
9359	specified by the string <code>whence</code>, as follows:
9360
9361	<ul>
9362	<li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li>
9363	<li><b>"<code>cur</code>": </b> base is current position;</li>
9364	<li><b>"<code>end</code>": </b> base is end of file;</li>
9365	</ul><p>
9366	In case of success, <code>seek</code> returns the final file position,
9367	measured in bytes from the beginning of the file.
9368	If <code>seek</code> fails, it returns <b>nil</b>,
9369	plus a string describing the error.
9370
9371
9372	<p>
9373	The default value for <code>whence</code> is <code>"cur"</code>,
9374	and for <code>offset</code> is 0.
9375	Therefore, the call <code>file:seek()</code> returns the current
9376	file position, without changing it;
9377	the call <code>file:seek("set")</code> sets the position to the
9378	beginning of the file (and returns 0);
9379	and the call <code>file:seek("end")</code> sets the position to the
9380	end of the file, and returns its size.
9381
9382
9383
9384
9385	<p>
9386	<hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
9387
9388
9389	<p>
9390	Sets the buffering mode for an output file.
9391	There are three available modes:
9392
9393	<ul>
9394
9395	<li><b>"<code>no</code>": </b>
9396	no buffering; the result of any output operation appears immediately.
9397	</li>
9398
9399	<li><b>"<code>full</code>": </b>
9400	full buffering; output operation is performed only
9401	when the buffer is full or when
9402	you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>).
9403	</li>
9404
9405	<li><b>"<code>line</code>": </b>
9406	line buffering; output is buffered until a newline is output
9407	or there is any input from some special files
9408	(such as a terminal device).
9409	</li>
9410
9411	</ul><p>
9412	For the last two cases, <code>size</code>
9413	specifies the size of the buffer, in bytes.
9414	The default is an appropriate size.
9415
9416
9417
9418
9419	<p>
9420	<hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3>
9421
9422
9423	<p>
9424	Writes the value of each of its arguments to <code>file</code>.
9425	The arguments must be strings or numbers.
9426
9427
9428	<p>
9429	In case of success, this function returns <code>file</code>.
9430	Otherwise it returns <b>nil</b> plus a string describing the error.
9431
9432
9433
9434
9435
9436
9437
9438	<h2>6.9 – <a name="6.9">Operating System Facilities</a></h2>
9439
9440	<p>
9441	This library is implemented through table <a name="pdf-os"><code>os</code></a>.
9442
9443
9444	<p>
9445	<hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
9446
9447
9448	<p>
9449	Returns an approximation of the amount in seconds of CPU time
9450	used by the program.
9451
9452
9453
9454
9455	<p>
9456	<hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
9457
9458
9459	<p>
9460	Returns a string or a table containing date and time,
9461	formatted according to the given string <code>format</code>.
9462
9463
9464	<p>
9465	If the <code>time</code> argument is present,
9466	this is the time to be formatted
9467	(see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
9468	Otherwise, <code>date</code> formats the current time.
9469
9470
9471	<p>
9472	If <code>format</code> starts with '<code>!</code>',
9473	then the date is formatted in Coordinated Universal Time.
9474	After this optional character,
9475	if <code>format</code> is the string "<code>*t</code>",
9476	then <code>date</code> returns a table with the following fields:
9477	<code>year</code> (four digits), <code>month</code> (1–12), <code>day</code> (1–31),
9478	<code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61),
9479	<code>wday</code> (weekday, Sunday is 1),
9480	<code>yday</code> (day of the year),
9481	and <code>isdst</code> (daylight saving flag, a boolean).
9482	This last field may be absent
9483	if the information is not available.
9484
9485
9486	<p>
9487	If <code>format</code> is not "<code>*t</code>",
9488	then <code>date</code> returns the date as a string,
9489	formatted according to the same rules as the ANSI C function <code>strftime</code>.
9490
9491
9492	<p>
9493	When called without arguments,
9494	<code>date</code> returns a reasonable date and time representation that depends on
9495	the host system and on the current locale
9496	(that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
9497
9498
9499	<p>
9500	On non-Posix systems,
9501	this function may be not thread safe
9502	because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>.
9503
9504
9505
9506
9507	<p>
9508	<hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
9509
9510
9511	<p>
9512	Returns the number of seconds from time <code>t1</code> to time <code>t2</code>.
9513	In POSIX, Windows, and some other systems,
9514	this value is exactly <code>t2</code><em>-</em><code>t1</code>.
9515
9516
9517
9518
9519	<p>
9520	<hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
9521
9522
9523	<p>
9524	This function is equivalent to the ANSI C function <code>system</code>.
9525	It passes <code>command</code> to be executed by an operating system shell.
9526	Its first result is <b>true</b>
9527	if the command terminated successfully,
9528	or <b>nil</b> otherwise.
9529	After this first result
9530	the function returns a string and a number,
9531	as follows:
9532
9533	<ul>
9534
9535	<li><b>"<code>exit</code>": </b>
9536	the command terminated normally;
9537	the following number is the exit status of the command.
9538	</li>
9539
9540	<li><b>"<code>signal</code>": </b>
9541	the command was terminated by a signal;
9542	the following number is the signal that terminated the command.
9543	</li>
9544
9545	</ul>
9546
9547	<p>
9548	When called without a <code>command</code>,
9549	<code>os.execute</code> returns a boolean that is true if a shell is available.
9550
9551
9552
9553
9554	<p>
9555	<hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close])</code></a></h3>
9556
9557
9558	<p>
9559	Calls the ANSI C function <code>exit</code> to terminate the host program.
9560	If <code>code</code> is <b>true</b>,
9561	the returned status is <code>EXIT_SUCCESS</code>;
9562	if <code>code</code> is <b>false</b>,
9563	the returned status is <code>EXIT_FAILURE</code>;
9564	if <code>code</code> is a number,
9565	the returned status is this number.
9566	The default value for <code>code</code> is <b>true</b>.
9567
9568
9569	<p>
9570	If the optional second argument <code>close</code> is true,
9571	closes the Lua state before exiting.
9572
9573
9574
9575
9576	<p>
9577	<hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
9578
9579
9580	<p>
9581	Returns the value of the process environment variable <code>varname</code>,
9582	or <b>nil</b> if the variable is not defined.
9583
9584
9585
9586
9587	<p>
9588	<hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
9589
9590
9591	<p>
9592	Deletes the file (or empty directory, on POSIX systems)
9593	with the given name.
9594	If this function fails, it returns <b>nil</b>,
9595	plus a string describing the error and the error code.
9596
9597
9598
9599
9600	<p>
9601	<hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
9602
9603
9604	<p>
9605	Renames file or directory named <code>oldname</code> to <code>newname</code>.
9606	If this function fails, it returns <b>nil</b>,
9607	plus a string describing the error and the error code.
9608
9609
9610
9611
9612	<p>
9613	<hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
9614
9615
9616	<p>
9617	Sets the current locale of the program.
9618	<code>locale</code> is a system-dependent string specifying a locale;
9619	<code>category</code> is an optional string describing which category to change:
9620	<code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
9621	<code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
9622	the default category is <code>"all"</code>.
9623	The function returns the name of the new locale,
9624	or <b>nil</b> if the request cannot be honored.
9625
9626
9627	<p>
9628	If <code>locale</code> is the empty string,
9629	the current locale is set to an implementation-defined native locale.
9630	If <code>locale</code> is the string "<code>C</code>",
9631	the current locale is set to the standard C locale.
9632
9633
9634	<p>
9635	When called with <b>nil</b> as the first argument,
9636	this function only returns the name of the current locale
9637	for the given category.
9638
9639
9640	<p>
9641	This function may be not thread safe
9642	because of its reliance on C function <code>setlocale</code>.
9643
9644
9645
9646
9647	<p>
9648	<hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
9649
9650
9651	<p>
9652	Returns the current time when called without arguments,
9653	or a time representing the date and time specified by the given table.
9654	This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
9655	and may have fields
9656	<code>hour</code> (default is 12),
9657	<code>min</code> (default is 0),
9658	<code>sec</code> (default is 0),
9659	and <code>isdst</code> (default is <b>nil</b>).
9660	For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
9661
9662
9663	<p>
9664	The returned value is a number, whose meaning depends on your system.
9665	In POSIX, Windows, and some other systems,
9666	this number counts the number
9667	of seconds since some given start time (the "epoch").
9668	In other systems, the meaning is not specified,
9669	and the number returned by <code>time</code> can be used only as an argument to
9670	<a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>.
9671
9672
9673
9674
9675	<p>
9676	<hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
9677
9678
9679	<p>
9680	Returns a string with a file name that can
9681	be used for a temporary file.
9682	The file must be explicitly opened before its use
9683	and explicitly removed when no longer needed.
9684
9685
9686	<p>
9687	On POSIX systems,
9688	this function also creates a file with that name,
9689	to avoid security risks.
9690	(Someone else might create the file with wrong permissions
9691	in the time between getting the name and creating the file.)
9692	You still have to open the file to use it
9693	and to remove it (even if you do not use it).
9694
9695
9696	<p>
9697	When possible,
9698	you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
9699	which automatically removes the file when the program ends.
9700
9701
9702
9703
9704
9705
9706
9707	<h2>6.10 – <a name="6.10">The Debug Library</a></h2>
9708
9709	<p>
9710	This library provides
9711	the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs.
9712	You should exert care when using this library.
9713	Several of its functions
9714	violate basic assumptions about Lua code
9715	(e.g., that variables local to a function
9716	cannot be accessed from outside;
9717	that userdata metatables cannot be changed by Lua code;
9718	that Lua programs do not crash)
9719	and therefore can compromise otherwise secure code.
9720	Moreover, some functions in this library may be slow.
9721
9722
9723	<p>
9724	All functions in this library are provided
9725	inside the <a name="pdf-debug"><code>debug</code></a> table.
9726	All functions that operate over a thread
9727	have an optional first argument which is the
9728	thread to operate over.
9729	The default is always the current thread.
9730
9731
9732	<p>
9733	<hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
9734
9735
9736	<p>
9737	Enters an interactive mode with the user,
9738	running each string that the user enters.
9739	Using simple commands and other debug facilities,
9740	the user can inspect global and local variables,
9741	change their values, evaluate expressions, and so on.
9742	A line containing only the word <code>cont</code> finishes this function,
9743	so that the caller continues its execution.
9744
9745
9746	<p>
9747	Note that commands for <code>debug.debug</code> are not lexically nested
9748	within any function and so have no direct access to local variables.
9749
9750
9751
9752
9753	<p>
9754	<hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
9755
9756
9757	<p>
9758	Returns the current hook settings of the thread, as three values:
9759	the current hook function, the current hook mask,
9760	and the current hook count
9761	(as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function).
9762
9763
9764
9765
9766	<p>
9767	<hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3>
9768
9769
9770	<p>
9771	Returns a table with information about a function.
9772	You can give the function directly
9773	or you can give a number as the value of <code>f</code>,
9774	which means the function running at level <code>f</code> of the call stack
9775	of the given thread:
9776	level 0 is the current function (<code>getinfo</code> itself);
9777	level 1 is the function that called <code>getinfo</code>
9778	(except for tail calls, which do not count on the stack);
9779	and so on.
9780	If <code>f</code> is a number larger than the number of active functions,
9781	then <code>getinfo</code> returns <b>nil</b>.
9782
9783
9784	<p>
9785	The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
9786	with the string <code>what</code> describing which fields to fill in.
9787	The default for <code>what</code> is to get all information available,
9788	except the table of valid lines.
9789	If present,
9790	the option '<code>f</code>'
9791	adds a field named <code>func</code> with the function itself.
9792	If present,
9793	the option '<code>L</code>'
9794	adds a field named <code>activelines</code> with the table of
9795	valid lines.
9796
9797
9798	<p>
9799	For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
9800	a table with a name for the current function,
9801	if a reasonable name can be found,
9802	and the expression <code>debug.getinfo(print)</code>
9803	returns a table with all available information
9804	about the <a href="#pdf-print"><code>print</code></a> function.
9805
9806
9807
9808
9809	<p>
9810	<hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3>
9811
9812
9813	<p>
9814	This function returns the name and the value of the local variable
9815	with index <code>local</code> of the function at level <code>f</code> of the stack.
9816	This function accesses not only explicit local variables,
9817	but also parameters, temporaries, etc.
9818
9819
9820	<p>
9821	The first parameter or local variable has index 1, and so on,
9822	until the last active variable.
9823	Negative indices refer to vararg parameters;
9824	-1 is the first vararg parameter.
9825	The function returns <b>nil</b> if there is no variable with the given index,
9826	and raises an error when called with a level out of range.
9827	(You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
9828
9829
9830	<p>
9831	Variable names starting with '<code>(</code>' (open parenthesis)
9832	represent internal variables
9833	(loop control variables, temporaries, varargs, and C function locals).
9834
9835
9836	<p>
9837	The parameter <code>f</code> may also be a function.
9838	In that case, <code>getlocal</code> returns only the name of function parameters.
9839
9840
9841
9842
9843	<p>
9844	<hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3>
9845
9846
9847	<p>
9848	Returns the metatable of the given <code>value</code>
9849	or <b>nil</b> if it does not have a metatable.
9850
9851
9852
9853
9854	<p>
9855	<hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
9856
9857
9858	<p>
9859	Returns the registry table (see <a href="#4.5">§4.5</a>).
9860
9861
9862
9863
9864	<p>
9865	<hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3>
9866
9867
9868	<p>
9869	This function returns the name and the value of the upvalue
9870	with index <code>up</code> of the function <code>f</code>.
9871	The function returns <b>nil</b> if there is no upvalue with the given index.
9872
9873
9874
9875
9876	<p>
9877	<hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3>
9878
9879
9880	<p>
9881	Returns the Lua value associated to <code>u</code>.
9882	If <code>u</code> is not a userdata,
9883	returns <b>nil</b>.
9884
9885
9886
9887
9888	<p>
9889	<hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
9890
9891
9892	<p>
9893	Sets the given function as a hook.
9894	The string <code>mask</code> and the number <code>count</code> describe
9895	when the hook will be called.
9896	The string mask may have the following characters,
9897	with the given meaning:
9898
9899	<ul>
9900	<li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li>
9901	<li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li>
9902	<li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li>
9903	</ul><p>
9904	With a <code>count</code> different from zero,
9905	the hook is called after every <code>count</code> instructions.
9906
9907
9908	<p>
9909	When called without arguments,
9910	<a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
9911
9912
9913	<p>
9914	When the hook is called, its first parameter is a string
9915	describing the event that has triggered its call:
9916	<code>"call"</code> (or <code>"tail call"</code>),
9917	<code>"return"</code>,
9918	<code>"line"</code>, and <code>"count"</code>.
9919	For line events,
9920	the hook also gets the new line number as its second parameter.
9921	Inside a hook,
9922	you can call <code>getinfo</code> with level 2 to get more information about
9923	the running function
9924	(level 0 is the <code>getinfo</code> function,
9925	and level 1 is the hook function).
9926
9927
9928
9929
9930	<p>
9931	<hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
9932
9933
9934	<p>
9935	This function assigns the value <code>value</code> to the local variable
9936	with index <code>local</code> of the function at level <code>level</code> of the stack.
9937	The function returns <b>nil</b> if there is no local
9938	variable with the given index,
9939	and raises an error when called with a <code>level</code> out of range.
9940	(You can call <code>getinfo</code> to check whether the level is valid.)
9941	Otherwise, it returns the name of the local variable.
9942
9943
9944	<p>
9945	See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about
9946	variable indices and names.
9947
9948
9949
9950
9951	<p>
9952	<hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3>
9953
9954
9955	<p>
9956	Sets the metatable for the given <code>value</code> to the given <code>table</code>
9957	(which can be <b>nil</b>).
9958	Returns <code>value</code>.
9959
9960
9961
9962
9963	<p>
9964	<hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3>
9965
9966
9967	<p>
9968	This function assigns the value <code>value</code> to the upvalue
9969	with index <code>up</code> of the function <code>f</code>.
9970	The function returns <b>nil</b> if there is no upvalue
9971	with the given index.
9972	Otherwise, it returns the name of the upvalue.
9973
9974
9975
9976
9977	<p>
9978	<hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3>
9979
9980
9981	<p>
9982	Sets the given <code>value</code> as
9983	the Lua value associated to the given <code>udata</code>.
9984	<code>value</code> must be a table or <b>nil</b>;
9985	<code>udata</code> must be a full userdata.
9986
9987
9988	<p>
9989	Returns <code>udata</code>.
9990
9991
9992
9993
9994	<p>
9995	<hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
9996
9997
9998	<p>
9999	If <code>message</code> is present but is neither a string nor <b>nil</b>,
10000	this function returns <code>message</code> without further processing.
10001	Otherwise,
10002	it returns a string with a traceback of the call stack.
10003	An optional <code>message</code> string is appended
10004	at the beginning of the traceback.
10005	An optional <code>level</code> number tells at which level
10006	to start the traceback
10007	(default is 1, the function calling <code>traceback</code>).
10008
10009
10010
10011
10012	<p>
10013	<hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3>
10014
10015
10016	<p>
10017	Returns an unique identifier (as a light userdata)
10018	for the upvalue numbered <code>n</code>
10019	from the given function.
10020
10021
10022	<p>
10023	These unique identifiers allow a program to check whether different
10024	closures share upvalues.
10025	Lua closures that share an upvalue
10026	(that is, that access a same external local variable)
10027	will return identical ids for those upvalue indices.
10028
10029
10030
10031
10032	<p>
10033	<hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3>
10034
10035
10036	<p>
10037	Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code>
10038	refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>.
10039
10040
10041
10042
10043
10044
10045
10046	<h1>7 – <a name="7">Lua Standalone</a></h1>
10047
10048	<p>
10049	Although Lua has been designed as an extension language,
10050	to be embedded in a host C program,
10051	it is also frequently used as a standalone language.
10052	An interpreter for Lua as a standalone language,
10053	called simply <code>lua</code>,
10054	is provided with the standard distribution.
10055	The standalone interpreter includes
10056	all standard libraries, including the debug library.
10057	Its usage is:
10058
10059	<pre>
10060	lua [options] [script [args]]
10061	</pre><p>
10062	The options are:
10063
10064	<ul>
10065	<li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li>
10066	<li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li>
10067	<li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li>
10068	<li><b><code>-v</code>: </b> prints version information;</li>
10069	<li><b><code>-E</code>: </b> ignores environment variables;</li>
10070	<li><b><code>--</code>: </b> stops handling options;</li>
10071	<li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li>
10072	</ul><p>
10073	After handling its options, <code>lua</code> runs the given <em>script</em>,
10074	passing to it the given <em>args</em> as string arguments.
10075	When called without arguments,
10076	<code>lua</code> behaves as <code>lua -v -i</code>
10077	when the standard input (<code>stdin</code>) is a terminal,
10078	and as <code>lua -</code> otherwise.
10079
10080
10081	<p>
10082	When called without option <code>-E</code>,
10083	the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_2"><code>LUA_INIT_5_2</code></a>
10084	(or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if it is not defined)
10085	before running any argument.
10086	If the variable content has the format <code>@<em>filename</em></code>,
10087	then <code>lua</code> executes the file.
10088	Otherwise, <code>lua</code> executes the string itself.
10089
10090
10091	<p>
10092	When called with option <code>-E</code>,
10093	besides ignoring <code>LUA_INIT</code>,
10094	Lua also ignores
10095	the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>,
10096	setting the values of
10097	<a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a>
10098	with the default paths defined in <code>luaconf.h</code>.
10099
10100
10101	<p>
10102	All options are handled in order, except <code>-i</code> and <code>-E</code>.
10103	For instance, an invocation like
10104
10105	<pre>
10106	$ lua -e'a=1' -e 'print(a)' script.lua
10107	</pre><p>
10108	will first set <code>a</code> to 1, then print the value of <code>a</code>,
10109	and finally run the file <code>script.lua</code> with no arguments.
10110	(Here <code>$</code> is the shell prompt. Your prompt may be different.)
10111
10112
10113	<p>
10114	Before starting to run the script,
10115	<code>lua</code> collects all arguments in the command line
10116	in a global table called <code>arg</code>.
10117	The script name is stored at index 0,
10118	the first argument after the script name goes to index 1,
10119	and so on.
10120	Any arguments before the script name
10121	(that is, the interpreter name plus the options)
10122	go to negative indices.
10123	For instance, in the call
10124
10125	<pre>
10126	$ lua -la b.lua t1 t2
10127	</pre><p>
10128	the interpreter first runs the file <code>a.lua</code>,
10129	then creates a table
10130
10131	<pre>
10132	arg = { [-2] = "lua", [-1] = "-la",
10133	[0] = "b.lua",
10134	[1] = "t1", [2] = "t2" }
10135	</pre><p>
10136	and finally runs the file <code>b.lua</code>.
10137	The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ...
10138	as arguments;
10139	it can also access these arguments with the vararg expression '<code>...</code>'.
10140
10141
10142	<p>
10143	In interactive mode,
10144	if you write an incomplete statement,
10145	the interpreter waits for its completion
10146	by issuing a different prompt.
10147
10148
10149	<p>
10150	In case of unprotected errors in the script,
10151	the interpreter reports the error to the standard error stream.
10152	If the error object is a string,
10153	the interpreter adds a stack traceback to it.
10154	Otherwise, if the error object has a metamethod <code>__tostring</code>,
10155	the interpreter calls this metamethod to produce the final message.
10156	Finally, if the error object is <b>nil</b>,
10157	the interpreter does not report the error.
10158
10159
10160	<p>
10161	When finishing normally,
10162	the interpreter closes its main Lua state
10163	(see <a href="#lua_close"><code>lua_close</code></a>).
10164	The script can avoid this step by
10165	calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate.
10166
10167
10168	<p>
10169	To allow the use of Lua as a
10170	script interpreter in Unix systems,
10171	the standalone interpreter skips
10172	the first line of a chunk if it starts with <code>#</code>.
10173	Therefore, Lua scripts can be made into executable programs
10174	by using <code>chmod +x</code> and the <code>#!</code> form,
10175	as in
10176
10177	<pre>
10178	#!/usr/local/bin/lua
10179	</pre><p>
10180	(Of course,
10181	the location of the Lua interpreter may be different in your machine.
10182	If <code>lua</code> is in your <code>PATH</code>,
10183	then
10184
10185	<pre>
10186	#!/usr/bin/env lua
10187	</pre><p>
10188	is a more portable solution.)
10189
10190
10191
10192	<h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1>
10193
10194	<p>
10195	Here we list the incompatibilities that you may find when moving a program
10196	from Lua 5.1 to Lua 5.2.
10197	You can avoid some incompatibilities by compiling Lua with
10198	appropriate options (see file <code>luaconf.h</code>).
10199	However,
10200	all these compatibility options will be removed in the next version of Lua.
10201	Similarly,
10202	all features marked as deprecated in Lua 5.1
10203	have been removed in Lua 5.2.
10204
10205
10206
10207	<h2>8.1 – <a name="8.1">Changes in the Language</a></h2>
10208	<ul>
10209
10210	<li>
10211	The concept of <em>environment</em> changed.
10212	Only Lua functions have environments.
10213	To set the environment of a Lua function,
10214	use the variable <code>_ENV</code> or the function <a href="#pdf-load"><code>load</code></a>.
10215
10216
10217	<p>
10218	C functions no longer have environments.
10219	Use an upvalue with a shared table if you need to keep
10220	shared state among several C functions.
10221	(You may use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> to open a C library
10222	with all functions sharing a common upvalue.)
10223
10224
10225	<p>
10226	To manipulate the "environment" of a userdata
10227	(which is now called user value),
10228	use the new functions
10229	<a href="#lua_getuservalue"><code>lua_getuservalue</code></a> and <a href="#lua_setuservalue"><code>lua_setuservalue</code></a>.
10230	</li>
10231
10232	<li>
10233	Lua identifiers cannot use locale-dependent letters.
10234	</li>
10235
10236	<li>
10237	Doing a step or a full collection in the garbage collector
10238	does not restart the collector if it has been stopped.
10239	</li>
10240
10241	<li>
10242	Weak tables with weak keys now perform like <em>ephemeron tables</em>.
10243	</li>
10244
10245	<li>
10246	The event <em>tail return</em> in debug hooks was removed.
10247	Instead, tail calls generate a special new event,
10248	<em>tail call</em>, so that the debugger can know that
10249	there will not be a corresponding return event.
10250	</li>
10251
10252	<li>
10253	Equality between function values has changed.
10254	Now, a function definition may not create a new value;
10255	it may reuse some previous value if there is no
10256	observable difference to the new function.
10257	</li>
10258
10259	</ul>
10260
10261
10262
10263
10264	<h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2>
10265	<ul>
10266
10267	<li>
10268	Function <code>module</code> is deprecated.
10269	It is easy to set up a module with regular Lua code.
10270	Modules are not expected to set global variables.
10271	</li>
10272
10273	<li>
10274	Functions <code>setfenv</code> and <code>getfenv</code> were removed,
10275	because of the changes in environments.
10276	</li>
10277
10278	<li>
10279	Function <code>math.log10</code> is deprecated.
10280	Use <a href="#pdf-math.log"><code>math.log</code></a> with 10 as its second argument, instead.
10281	</li>
10282
10283	<li>
10284	Function <code>loadstring</code> is deprecated.
10285	Use <code>load</code> instead; it now accepts string arguments
10286	and are exactly equivalent to <code>loadstring</code>.
10287	</li>
10288
10289	<li>
10290	Function <code>table.maxn</code> is deprecated.
10291	Write it in Lua if you really need it.
10292	</li>
10293
10294	<li>
10295	Function <code>os.execute</code> now returns <b>true</b> when command
10296	terminates successfully and <b>nil</b> plus error information
10297	otherwise.
10298	</li>
10299
10300	<li>
10301	Function <code>unpack</code> was moved into the table library
10302	and therefore must be called as <a href="#pdf-table.unpack"><code>table.unpack</code></a>.
10303	</li>
10304
10305	<li>
10306	Character class <code>%z</code> in patterns is deprecated,
10307	as now patterns may contain '<code>\0</code>' as a regular character.
10308	</li>
10309
10310	<li>
10311	The table <code>package.loaders</code> was renamed <code>package.searchers</code>.
10312	</li>
10313
10314	<li>
10315	Lua does not have bytecode verification anymore.
10316	So, all functions that load code
10317	(<a href="#pdf-load"><code>load</code></a> and <a href="#pdf-loadfile"><code>loadfile</code></a>)
10318	are potentially insecure when loading untrusted binary data.
10319	(Actually, those functions were already insecure because
10320	of flaws in the verification algorithm.)
10321	When in doubt,
10322	use the <code>mode</code> argument of those functions
10323	to restrict them to loading textual chunks.
10324	</li>
10325
10326	<li>
10327	The standard paths in the official distribution may
10328	change between versions.
10329	</li>
10330
10331	</ul>
10332
10333
10334
10335
10336	<h2>8.3 – <a name="8.3">Changes in the API</a></h2>
10337	<ul>
10338
10339	<li>
10340	Pseudoindex <code>LUA_GLOBALSINDEX</code> was removed.
10341	You must get the global environment from the registry
10342	(see <a href="#4.5">§4.5</a>).
10343	</li>
10344
10345	<li>
10346	Pseudoindex <code>LUA_ENVIRONINDEX</code>
10347	and functions <code>lua_getfenv</code>/<code>lua_setfenv</code>
10348	were removed,
10349	as C functions no longer have environments.
10350	</li>
10351
10352	<li>
10353	Function <code>luaL_register</code> is deprecated.
10354	Use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> so that your module does not create globals.
10355	(Modules are not expected to set global variables anymore.)
10356	</li>
10357
10358	<li>
10359	The <code>osize</code> argument to the allocation function
10360	may not be zero when creating a new block,
10361	that is, when <code>ptr</code> is <code>NULL</code>
10362	(see <a href="#lua_Alloc"><code>lua_Alloc</code></a>).
10363	Use only the test <code>ptr == NULL</code> to check whether
10364	the block is new.
10365	</li>
10366
10367	<li>
10368	Finalizers (<code>__gc</code> metamethods) for userdata are called in the
10369	reverse order that they were marked for finalization,
10370	not that they were created (see <a href="#2.5.1">§2.5.1</a>).
10371	(Most userdata are marked immediately after they are created.)
10372	Moreover,
10373	if the metatable does not have a <code>__gc</code> field when set,
10374	the finalizer will not be called,
10375	even if it is set later.
10376	</li>
10377
10378	<li>
10379	<code>luaL_typerror</code> was removed.
10380	Write your own version if you need it.
10381	</li>
10382
10383	<li>
10384	Function <code>lua_cpcall</code> is deprecated.
10385	You can simply push the function with <a href="#lua_pushcfunction"><code>lua_pushcfunction</code></a>
10386	and call it with <a href="#lua_pcall"><code>lua_pcall</code></a>.
10387	</li>
10388
10389	<li>
10390	Functions <code>lua_equal</code> and <code>lua_lessthan</code> are deprecated.
10391	Use the new <a href="#lua_compare"><code>lua_compare</code></a> with appropriate options instead.
10392	</li>
10393
10394	<li>
10395	Function <code>lua_objlen</code> was renamed <a href="#lua_rawlen"><code>lua_rawlen</code></a>.
10396	</li>
10397
10398	<li>
10399	Function <a href="#lua_load"><code>lua_load</code></a> has an extra parameter, <code>mode</code>.
10400	Pass <code>NULL</code> to simulate the old behavior.
10401	</li>
10402
10403	<li>
10404	Function <a href="#lua_resume"><code>lua_resume</code></a> has an extra parameter, <code>from</code>.
10405	Pass <code>NULL</code> or the thread doing the call.
10406	</li>
10407
10408	</ul>
10409
10410
10411
10412
10413	<h1>9 – <a name="9">The Complete Syntax of Lua</a></h1>
10414
10415	<p>
10416	Here is the complete syntax of Lua in extended BNF.
10417	(It does not describe operator precedences.)
10418
10419
10420
10421
10422	<pre>
10423
10424	chunk ::= block
10425
10426	block ::= {stat} [retstat]
10427
10428	stat ::= ‘<b>;</b>’ \|
10429	varlist ‘<b>=</b>’ explist \|
10430	functioncall \|
10431	label \|
10432	<b>break</b> \|
10433	<b>goto</b> Name \|
10434	<b>do</b> block <b>end</b> \|
10435	<b>while</b> exp <b>do</b> block <b>end</b> \|
10436	<b>repeat</b> block <b>until</b> exp \|
10437	<b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> \|
10438	<b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> \|
10439	<b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> \|
10440	<b>function</b> funcname funcbody \|
10441	<b>local</b> <b>function</b> Name funcbody \|
10442	<b>local</b> namelist [‘<b>=</b>’ explist]
10443
10444	retstat ::= <b>return</b> [explist] [‘<b>;</b>’]
10445
10446	label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
10447
10448	funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
10449
10450	varlist ::= var {‘<b>,</b>’ var}
10451
10452	var ::= Name \| prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ \| prefixexp ‘<b>.</b>’ Name
10453
10454	namelist ::= Name {‘<b>,</b>’ Name}
10455
10456	explist ::= exp {‘<b>,</b>’ exp}
10457
10458	exp ::= <b>nil</b> \| <b>false</b> \| <b>true</b> \| Number \| String \| ‘<b>...</b>’ \| functiondef \|
10459	prefixexp \| tableconstructor \| exp binop exp \| unop exp
10460
10461	prefixexp ::= var \| functioncall \| ‘<b>(</b>’ exp ‘<b>)</b>’
10462
10463	functioncall ::= prefixexp args \| prefixexp ‘<b>:</b>’ Name args
10464
10465	args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ \| tableconstructor \| String
10466
10467	functiondef ::= <b>function</b> funcbody
10468
10469	funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
10470
10471	parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] \| ‘<b>...</b>’
10472
10473	tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
10474
10475	fieldlist ::= field {fieldsep field} [fieldsep]
10476
10477	field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp \| Name ‘<b>=</b>’ exp \| exp
10478
10479	fieldsep ::= ‘<b>,</b>’ \| ‘<b>;</b>’
10480
10481	binop ::= ‘<b>+</b>’ \| ‘<b>-</b>’ \| ‘<b>*</b>’ \| ‘<b>/</b>’ \| ‘<b>^</b>’ \| ‘<b>%</b>’ \| ‘<b>..</b>’ \|
10482	‘<b><</b>’ \| ‘<b><=</b>’ \| ‘<b>></b>’ \| ‘<b>>=</b>’ \| ‘<b>==</b>’ \| ‘<b>~=</b>’ \|
10483	<b>and</b> \| <b>or</b>
10484
10485	unop ::= ‘<b>-</b>’ \| <b>not</b> \| ‘<b>#</b>’
10486
10487	</pre>
10488
10489	<p>
10490
10491
10492
10493
10494
10495
10496
10497	<HR>
10498	<SMALL CLASS="footer">
10499	Last update:
10500	Thu Mar 21 12:58:59 BRT 2013
10501	</SMALL>
10502	<!--
10503	Last change: revised for Lua 5.2.2
10504	-->
10505
10506	</body></html>
10507

Note: See TracBrowser for help on using the repository browser.

Download in other formats: