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16 Lua 5.3 Reference Manual
19 by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
22 Copyright © 2015 Lua.org, PUC-Rio.
23 Freely available under the terms of the
24 <a href="http://www.lua.org/license.html">Lua license</a>.
29 <a href="contents.html#contents">contents</A>
31 <a href="contents.html#index">index</A>
33 <!-- ====================================================================== -->
36 <!-- $Id: manual.of,v 1.146 2015/01/06 11:23:01 roberto Exp $ -->
41 <h1>1 – <a name="1">Introduction</a></h1>
44 Lua is an extension programming language designed to support
45 general procedural programming with data description
47 Lua 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++.
56 As 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.
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>.
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>.
88 <h1>2 – <a name="2">Basic Concepts</a></h1>
91 This section describes the basic concepts of the language.
95 <h2>2.1 – <a name="2.1">Values and Types</a></h2>
98 Lua is a <em>dynamically typed language</em>.
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.
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.
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 both
123 integer numbers and real (floating-point) numbers.
124 <em>String</em> represents immutable sequences of bytes.
127 strings can contain any 8-bit value,
128 including embedded zeros ('<code>\0</code>').
129 Lua is also encoding-agnostic;
130 it makes no assumptions about the contents of a string.
134 The type <em>number</em> uses two internal representations,
135 one called <em>integer</em> and the other called <em>float</em>.
136 Lua has explicit rules about when each representation is used,
137 but it also converts between them automatically as needed (see <a href="#3.4.3">§3.4.3</a>).
139 the programmer may choose to mostly ignore the difference
140 between integers and floats
141 or to assume complete control over the representation of each number.
142 Standard Lua uses 64-bit integers and double-precision (64-bit) floats,
143 but you can also compile Lua so that it
144 uses 32-bit integers and/or single-precision (32-bit) floats.
145 The option with 32 bits for both integers and floats
146 is particularly attractive
147 for small machines and embedded systems.
148 (See macro <code>LUA_32BITS</code> in file <code>luaconf.h</code>.)
152 Lua can call (and manipulate) functions written in Lua and
153 functions written in C (see <a href="#3.4.10">§3.4.10</a>).
154 Both are represented by the type <em>function</em>.
158 The type <em>userdata</em> is provided to allow arbitrary C data to
159 be stored in Lua variables.
160 A userdata value represents a block of raw memory.
161 There are two kinds of userdata:
162 <em>full userdata</em>,
163 which is an object with a block of memory managed by Lua,
164 and <em>light userdata</em>,
165 which is simply a C pointer value.
166 Userdata has no predefined operations in Lua,
167 except assignment and identity test.
168 By using <em>metatables</em>,
169 the programmer can define operations for full userdata values
170 (see <a href="#2.4">§2.4</a>).
171 Userdata values cannot be created or modified in Lua,
172 only through the C API.
173 This guarantees the integrity of data owned by the host program.
177 The type <em>thread</em> represents independent threads of execution
178 and it is used to implement coroutines (see <a href="#2.6">§2.6</a>).
179 Lua threads are not related to operating-system threads.
180 Lua supports coroutines on all systems,
181 even those that do not support threads natively.
185 The type <em>table</em> implements associative arrays,
186 that is, arrays that can be indexed not only with numbers,
187 but with any Lua value except <b>nil</b> and NaN.
188 (<em>Not a Number</em> is a special numeric value used to represent
189 undefined or unrepresentable results, such as <code>0/0</code>.)
190 Tables can be <em>heterogeneous</em>;
191 that is, they can contain values of all types (except <b>nil</b>).
192 Any key with value <b>nil</b> is not considered part of the table.
193 Conversely, any key that is not part of a table has
194 an associated value <b>nil</b>.
198 Tables are the sole data-structuring mechanism in Lua;
199 they can be used to represent ordinary arrays, sequences,
200 symbol tables, sets, records, graphs, trees, etc.
201 To represent records, Lua uses the field name as an index.
202 The language supports this representation by
203 providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
204 There are several convenient ways to create tables in Lua
205 (see <a href="#3.4.9">§3.4.9</a>).
209 We use the term <em>sequence</em> to denote a table where
210 the set of all positive numeric keys is equal to {1..<em>n</em>}
211 for some non-negative integer <em>n</em>,
212 which is called the length of the sequence (see <a href="#3.4.7">§3.4.7</a>).
217 the values of table fields can be of any type.
219 because functions are first-class values,
220 table fields can contain functions.
221 Thus tables can also carry <em>methods</em> (see <a href="#3.4.11">§3.4.11</a>).
225 The indexing of tables follows
226 the definition of raw equality in the language.
227 The expressions <code>a[i]</code> and <code>a[j]</code>
228 denote the same table element
229 if and only if <code>i</code> and <code>j</code> are raw equal
230 (that is, equal without metamethods).
231 In particular, floats with integral values
232 are equal to their respective integers
233 (e.g., <code>1.0 == 1</code>).
234 To avoid ambiguities,
235 any float with integral value used as a key
236 is converted to its respective integer.
237 For instance, if you write <code>a[2.0] = true</code>,
238 the actual key inserted into the table will be the
239 integer <code>2</code>.
241 2 and "<code>2</code>" are different Lua values and therefore
242 denote different table entries.)
246 Tables, functions, threads, and (full) userdata values are <em>objects</em>:
247 variables do not actually <em>contain</em> these values,
248 only <em>references</em> to them.
249 Assignment, parameter passing, and function returns
250 always manipulate references to such values;
251 these operations do not imply any kind of copy.
255 The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
256 of a given value (see <a href="#6.1">§6.1</a>).
262 <h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2>
265 As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>,
266 any reference to a free name
267 (that is, a name not bound to any declaration) <code>var</code>
268 is syntactically translated to <code>_ENV.var</code>.
269 Moreover, every chunk is compiled in the scope of
270 an external local variable named <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>),
271 so <code>_ENV</code> itself is never a free name in a chunk.
275 Despite the existence of this external <code>_ENV</code> variable and
276 the translation of free names,
277 <code>_ENV</code> is a completely regular name.
279 you can define new variables and parameters with that name.
280 Each reference to a free name uses the <code>_ENV</code> that is
281 visible at that point in the program,
282 following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>).
286 Any table used as the value of <code>_ENV</code> is called an <em>environment</em>.
290 Lua keeps a distinguished environment called the <em>global environment</em>.
291 This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>).
292 In Lua, the global variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value.
293 (<a href="#pdf-_G"><code>_G</code></a> is never used internally.)
297 When Lua loads a chunk,
298 the default value for its <code>_ENV</code> upvalue
299 is the global environment (see <a href="#pdf-load"><code>load</code></a>).
300 Therefore, by default,
301 free names in Lua code refer to entries in the global environment
302 (and, therefore, they are also called <em>global variables</em>).
303 Moreover, all standard libraries are loaded in the global environment
304 and some functions there operate on that environment.
305 You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>)
306 to load a chunk with a different environment.
307 (In C, you have to load the chunk and then change the value
308 of its first upvalue.)
314 <h2>2.3 – <a name="2.3">Error Handling</a></h2>
317 Because Lua is an embedded extension language,
318 all Lua actions start from C code in the host program
319 calling a function from the Lua library.
320 (When you use Lua standalone,
321 the <code>lua</code> application is the host program.)
322 Whenever an error occurs during
323 the compilation or execution of a Lua chunk,
324 control returns to the host,
325 which can take appropriate measures
326 (such as printing an error message).
330 Lua code can explicitly generate an error by calling the
331 <a href="#pdf-error"><code>error</code></a> function.
332 If you need to catch errors in Lua,
333 you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a>
334 to call a given function in <em>protected mode</em>.
338 Whenever there is an error,
339 an <em>error object</em> (also called an <em>error message</em>)
340 is propagated with information about the error.
341 Lua itself only generates errors whose error object is a string,
342 but programs may generate errors with
343 any value as the error object.
344 It is up to the Lua program or its host to handle such error objects.
348 When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>,
349 you may give a <em>message handler</em>
350 to be called in case of errors.
351 This function is called with the original error message
352 and returns a new error message.
353 It is called before the error unwinds the stack,
354 so that it can gather more information about the error,
355 for instance by inspecting the stack and creating a stack traceback.
356 This message handler is still protected by the protected call;
357 so, an error inside the message handler
358 will call the message handler again.
359 If this loop goes on for too long,
360 Lua breaks it and returns an appropriate message.
366 <h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2>
369 Every value in Lua can have a <em>metatable</em>.
370 This <em>metatable</em> is an ordinary Lua table
371 that defines the behavior of the original value
372 under certain special operations.
373 You can change several aspects of the behavior
374 of operations over a value by setting specific fields in its metatable.
375 For instance, when a non-numeric value is the operand of an addition,
376 Lua checks for a function in the field "<code>__add</code>" of the value's metatable.
378 Lua calls this function to perform the addition.
382 The keys in a metatable are derived from the <em>event</em> names;
383 the corresponding values are called <em>metamethods</em>.
384 In the previous example, the event is <code>"add"</code>
385 and the metamethod is the function that performs the addition.
389 You can query the metatable of any value
390 using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
394 You can replace the metatable of tables
395 using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function.
396 You cannot change the metatable of other types from Lua
397 (except by using the debug library (<a href="#6.10">§6.10</a>));
398 you must use the C API for that.
402 Tables and full userdata have individual metatables
403 (although multiple tables and userdata can share their metatables).
404 Values of all other types share one single metatable per type;
405 that is, there is one single metatable for all numbers,
406 one for all strings, etc.
407 By default, a value has no metatable,
408 but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>).
412 A metatable controls how an object behaves in
413 arithmetic operations, bitwise operations,
414 order comparisons, concatenation, length operation, calls, and indexing.
415 A metatable also can define a function to be called
416 when a userdata or a table is garbage collected (<a href="#2.5">§2.5</a>).
420 A detailed list of events controlled by metatables is given next.
421 Each operation is identified by its corresponding event name.
422 The key for each event is a string with its name prefixed by
423 two underscores, '<code>__</code>';
424 for instance, the key for operation "add" is the
425 string "<code>__add</code>".
426 Note that queries for metamethods are always raw;
427 the access to a metamethod does not invoke other metamethods.
428 You can emulate how Lua queries a metamethod for an object <code>obj</code>
429 with the following code:
432 rawget(getmetatable(obj) or {}, "__" .. event_name)
436 For the unary operators (negation, length, and bitwise not),
437 the metamethod is computed and called with a dummy second operand,
438 equal to the first one.
439 This extra operand is only to simplify Lua's internals
440 (by making these operators behave like a binary operation)
441 and may be removed in future versions.
442 (For most uses this extra operand is irrelevant.)
449 the <code>+</code> operation.
451 If any operand for an addition is not a number
452 (nor a string coercible to a number),
453 Lua will try to call a metamethod.
454 First, Lua will check the first operand (even if it is valid).
455 If that operand does not define a metamethod for the "<code>__add</code>" event,
456 then Lua will check the second operand.
457 If Lua can find a metamethod,
458 it calls the metamethod with the two operands as arguments,
459 and the result of the call
460 (adjusted to one value)
461 is the result of the operation.
467 the <code>-</code> operation.
469 Behavior similar to the "add" operation.
473 the <code>*</code> operation.
475 Behavior similar to the "add" operation.
479 the <code>/</code> operation.
481 Behavior similar to the "add" operation.
485 the <code>%</code> operation.
487 Behavior similar to the "add" operation.
491 the <code>^</code> (exponentiation) operation.
493 Behavior similar to the "add" operation.
497 the <code>-</code> (unary minus) operation.
499 Behavior similar to the "add" operation.
503 the <code>//</code> (floor division) operation.
505 Behavior similar to the "add" operation.
509 the <code>&</code> (bitwise and) operation.
511 Behavior similar to the "add" operation,
512 except that Lua will try a metamethod
513 if any operator is neither an integer
514 nor a value coercible to an integer (see <a href="#3.4.3">§3.4.3</a>).
518 the <code>|</code> (bitwise or) operation.
520 Behavior similar to the "band" operation.
524 the <code>~</code> (bitwise exclusive or) operation.
526 Behavior similar to the "band" operation.
530 the <code>~</code> (bitwise unary not) operation.
532 Behavior similar to the "band" operation.
536 the <code><<</code> (bitwise left shift) operation.
538 Behavior similar to the "band" operation.
542 the <code>>></code> (bitwise right shift) operation.
544 Behavior similar to the "band" operation.
547 <li><b>"concat": </b>
548 the <code>..</code> (concatenation) operation.
550 Behavior similar to the "add" operation,
551 except that Lua will try a metamethod
552 if any operator is neither a string nor a number
553 (which is always coercible to a string).
557 the <code>#</code> (length) operation.
559 If the object is not a string,
560 Lua will try its metamethod.
561 If there is a metamethod,
562 Lua calls it with the object as argument,
563 and the result of the call
564 (always adjusted to one value)
565 is the result of the operation.
566 If there is no metamethod but the object is a table,
567 then Lua uses the table length operation (see <a href="#3.4.7">§3.4.7</a>).
568 Otherwise, Lua raises an error.
572 the <code>==</code> (equal) operation.
574 Behavior similar to the "add" operation,
575 except that Lua will try a metamethod only when the values
576 being compared are either both tables or both full userdata
577 and they are not primitively equal.
578 The result of the call is always converted to a boolean.
582 the <code><</code> (less than) operation.
584 Behavior similar to the "add" operation,
585 except that Lua will try a metamethod only when the values
586 being compared are neither both numbers nor both strings.
587 The result of the call is always converted to a boolean.
591 the <code><=</code> (less equal) operation.
593 Unlike other operations,
594 The less-equal operation can use two different events.
595 First, Lua looks for the "<code>__le</code>" metamethod in both operands,
596 like in the "lt" operation.
597 If it cannot find such a metamethod,
598 then it will try the "<code>__lt</code>" event,
599 assuming that <code>a <= b</code> is equivalent to <code>not (b < a)</code>.
600 As with the other comparison operators,
601 the result is always a boolean.
605 The indexing access <code>table[key]</code>.
607 This event happens when <code>table</code> is not a table or
608 when <code>key</code> is not present in <code>table</code>.
609 The metamethod is looked up in <code>table</code>.
614 the metamethod for this event can be either a function or a table.
616 it is called with <code>table</code> and <code>key</code> as arguments.
618 the final result is the result of indexing this table with <code>key</code>.
619 (This indexing is regular, not raw,
620 and therefore can trigger another metamethod.)
623 <li><b>"newindex": </b>
624 The indexing assignment <code>table[key] = value</code>.
626 Like the index event,
627 this event happens when <code>table</code> is not a table or
628 when <code>key</code> is not present in <code>table</code>.
629 The metamethod is looked up in <code>table</code>.
634 the metamethod for this event can be either a function or a table.
636 it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments.
638 Lua does an indexing assignment to this table with the same key and value.
639 (This assignment is regular, not raw,
640 and therefore can trigger another metamethod.)
644 Whenever there is a "newindex" metamethod,
645 Lua does not perform the primitive assignment.
647 the metamethod itself can call <a href="#pdf-rawset"><code>rawset</code></a>
648 to do the assignment.)
652 The call operation <code>func(args)</code>.
654 This event happens when Lua tries to call a non-function value
655 (that is, <code>func</code> is not a function).
656 The metamethod is looked up in <code>func</code>.
658 the metamethod is called with <code>func</code> as its first argument,
659 followed by the arguments of the original call (<code>args</code>).
667 <h2>2.5 – <a name="2.5">Garbage Collection</a></h2>
670 Lua performs automatic memory management.
672 you do not have to worry about allocating memory for new objects
673 or freeing it when the objects are no longer needed.
674 Lua manages memory automatically by running
675 a <em>garbage collector</em> to collect all <em>dead objects</em>
676 (that is, objects that are no longer accessible from Lua).
677 All memory used by Lua is subject to automatic management:
678 strings, tables, userdata, functions, threads, internal structures, etc.
682 Lua implements an incremental mark-and-sweep collector.
683 It uses two numbers to control its garbage-collection cycles:
684 the <em>garbage-collector pause</em> and
685 the <em>garbage-collector step multiplier</em>.
686 Both use percentage points as units
687 (e.g., a value of 100 means an internal value of 1).
691 The garbage-collector pause
692 controls how long the collector waits before starting a new cycle.
693 Larger values make the collector less aggressive.
694 Values smaller than 100 mean the collector will not wait to
696 A value of 200 means that the collector waits for the total memory in use
697 to double before starting a new cycle.
701 The garbage-collector step multiplier
702 controls the relative speed of the collector relative to
704 Larger values make the collector more aggressive but also increase
705 the size of each incremental step.
706 You should not use values smaller than 100,
707 because they make the collector too slow and
708 can result in the collector never finishing a cycle.
710 which means that the collector runs at "twice"
711 the speed of memory allocation.
715 If you set the step multiplier to a very large number
716 (larger than 10% of the maximum number of
717 bytes that the program may use),
718 the collector behaves like a stop-the-world collector.
719 If you then set the pause to 200,
720 the collector behaves as in old Lua versions,
721 doing a complete collection every time Lua doubles its
726 You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
727 or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
728 You can also use these functions to control
729 the collector directly (e.g., stop and restart it).
733 <h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3>
736 You can set garbage-collector metamethods for tables
737 and, using the C API,
738 for full userdata (see <a href="#2.4">§2.4</a>).
739 These metamethods are also called <em>finalizers</em>.
740 Finalizers allow you to coordinate Lua's garbage collection
741 with external resource management
742 (such as closing files, network or database connections,
743 or freeing your own memory).
747 For an object (table or userdata) to be finalized when collected,
748 you must <em>mark</em> it for finalization.
750 You mark an object for finalization when you set its metatable
751 and the metatable has a field indexed by the string "<code>__gc</code>".
752 Note that if you set a metatable without a <code>__gc</code> field
753 and later create that field in the metatable,
754 the object will not be marked for finalization.
755 However, after an object has been marked,
756 you can freely change the <code>__gc</code> field of its metatable.
760 When a marked object becomes garbage,
761 it is not collected immediately by the garbage collector.
762 Instead, Lua puts it in a list.
763 After the collection,
764 Lua goes through that list.
765 For each object in the list,
766 it checks the object's <code>__gc</code> metamethod:
768 Lua calls it with the object as its single argument;
769 if the metamethod is not a function,
770 Lua simply ignores it.
774 At the end of each garbage-collection cycle,
775 the finalizers for objects are called in
776 the reverse order that the objects were marked for finalization,
777 among those collected in that cycle;
778 that is, the first finalizer to be called is the one associated
779 with the object marked last in the program.
780 The execution of each finalizer may occur at any point during
781 the execution of the regular code.
785 Because the object being collected must still be used by the finalizer,
786 that object (and other objects accessible only through it)
787 must be <em>resurrected</em> by Lua.
788 Usually, this resurrection is transient,
789 and the object memory is freed in the next garbage-collection cycle.
790 However, if the finalizer stores the object in some global place
791 (e.g., a global variable),
792 then the resurrection is permanent.
793 Moreover, if the finalizer marks a finalizing object for finalization again,
794 its finalizer will be called again in the next cycle where the
795 object is unreachable.
797 the object memory is freed only in the GC cycle where
798 the object is unreachable and not marked for finalization.
802 When you close a state (see <a href="#lua_close"><code>lua_close</code></a>),
803 Lua calls the finalizers of all objects marked for finalization,
804 following the reverse order that they were marked.
805 If any finalizer marks objects for collection during that phase,
806 these marks have no effect.
812 <h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3>
815 A <em>weak table</em> is a table whose elements are
816 <em>weak references</em>.
817 A weak reference is ignored by the garbage collector.
819 if the only references to an object are weak references,
820 then the garbage collector will collect that object.
824 A weak table can have weak keys, weak values, or both.
825 A table with weak keys allows the collection of its keys,
826 but prevents the collection of its values.
827 A table with both weak keys and weak values allows the collection of
828 both keys and values.
829 In any case, if either the key or the value is collected,
830 the whole pair is removed from the table.
831 The weakness of a table is controlled by the
832 <code>__mode</code> field of its metatable.
833 If the <code>__mode</code> field is a string containing the character '<code>k</code>',
834 the keys in the table are weak.
835 If <code>__mode</code> contains '<code>v</code>',
836 the values in the table are weak.
840 A table with weak keys and strong values
841 is also called an <em>ephemeron table</em>.
842 In an ephemeron table,
843 a value is considered reachable only if its key is reachable.
845 if the only reference to a key comes through its value,
850 Any change in the weakness of a table may take effect only
851 at the next collect cycle.
852 In particular, if you change the weakness to a stronger mode,
853 Lua may still collect some items from that table
854 before the change takes effect.
858 Only objects that have an explicit construction
859 are removed from weak tables.
860 Values, such as numbers and light C functions,
861 are not subject to garbage collection,
862 and therefore are not removed from weak tables
863 (unless their associated values are collected).
864 Although strings are subject to garbage collection,
865 they do not have an explicit construction,
866 and therefore are not removed from weak tables.
871 (that is, objects being finalized
872 and objects accessible only through objects being finalized)
873 have a special behavior in weak tables.
874 They are removed from weak values before running their finalizers,
875 but are removed from weak keys only in the next collection
876 after running their finalizers, when such objects are actually freed.
877 This behavior allows the finalizer to access properties
878 associated with the object through weak tables.
882 If a weak table is among the resurrected objects in a collection cycle,
883 it may not be properly cleared until the next cycle.
891 <h2>2.6 – <a name="2.6">Coroutines</a></h2>
894 Lua supports coroutines,
895 also called <em>collaborative multithreading</em>.
896 A coroutine in Lua represents an independent thread of execution.
897 Unlike threads in multithread systems, however,
898 a coroutine only suspends its execution by explicitly calling
903 You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
904 Its sole argument is a function
905 that is the main function of the coroutine.
906 The <code>create</code> function only creates a new coroutine and
907 returns a handle to it (an object of type <em>thread</em>);
908 it does not start the coroutine.
912 You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
913 When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
914 passing as its first argument
915 a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
916 the coroutine starts its execution,
917 at the first line of its main function.
918 Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed
919 as arguments to the coroutine's main function.
920 After the coroutine starts running,
921 it runs until it terminates or <em>yields</em>.
925 A coroutine can terminate its execution in two ways:
926 normally, when its main function returns
927 (explicitly or implicitly, after the last instruction);
928 and abnormally, if there is an unprotected error.
929 In case of normal termination,
930 <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
931 plus any values returned by the coroutine main function.
932 In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
933 plus an error message.
937 A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
938 When a coroutine yields,
939 the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
940 even if the yield happens inside nested function calls
941 (that is, not in the main function,
942 but in a function directly or indirectly called by the main function).
943 In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
944 plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
945 The next time you resume the same coroutine,
946 it continues its execution from the point where it yielded,
947 with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
948 arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
952 Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
953 the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
954 but instead of returning the coroutine itself,
955 it returns a function that, when called, resumes the coroutine.
956 Any arguments passed to this function
957 go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
958 <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>,
959 except the first one (the boolean error code).
960 Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
961 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
962 any error is propagated to the caller.
966 As an example of how coroutines work,
967 consider the following code:
972 return coroutine.yield(2*a)
975 co = coroutine.create(function (a,b)
976 print("co-body", a, b)
979 local r, s = coroutine.yield(a+b, a-b)
980 print("co-body", r, s)
984 print("main", coroutine.resume(co, 1, 10))
985 print("main", coroutine.resume(co, "r"))
986 print("main", coroutine.resume(co, "x", "y"))
987 print("main", coroutine.resume(co, "x", "y"))
989 When you run it, it produces the following output:
999 main false cannot resume dead coroutine
1003 You can also create and manipulate coroutines through the C API:
1004 see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>,
1005 and <a href="#lua_yield"><code>lua_yield</code></a>.
1011 <h1>3 – <a name="3">The Language</a></h1>
1014 This section describes the lexis, the syntax, and the semantics of Lua.
1016 this section describes
1017 which tokens are valid,
1018 how they can be combined,
1019 and what their combinations mean.
1023 Language constructs will be explained using the usual extended BNF notation,
1025 {<em>a</em>} means 0 or more <em>a</em>'s, and
1026 [<em>a</em>] means an optional <em>a</em>.
1027 Non-terminals are shown like non-terminal,
1028 keywords are shown like <b>kword</b>,
1029 and other terminal symbols are shown like ‘<b>=</b>’.
1030 The complete syntax of Lua can be found in <a href="#9">§9</a>
1031 at the end of this manual.
1035 <h2>3.1 – <a name="3.1">Lexical Conventions</a></h2>
1038 Lua is a free-form language.
1039 It ignores spaces (including new lines) and comments
1040 between lexical elements (tokens),
1041 except as delimiters between names and keywords.
1046 (also called <em>identifiers</em>)
1047 in Lua can be any string of letters,
1048 digits, and underscores,
1049 not beginning with a digit.
1050 Identifiers are used to name variables, table fields, and labels.
1054 The following <em>keywords</em> are reserved
1055 and cannot be used as names:
1059 and break do else elseif end
1060 false for function goto if in
1061 local nil not or repeat return
1062 then true until while
1066 Lua is a case-sensitive language:
1067 <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
1068 are two different, valid names.
1070 programs should avoid creating
1071 names that start with an underscore followed by
1072 one or more uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>).
1076 The following strings denote other tokens:
1080 & ~ | << >> //
1081 == ~= <= >= < > =
1087 <em>Literal strings</em>
1088 can be delimited by matching single or double quotes,
1089 and can contain the following C-like escape sequences:
1090 '<code>\a</code>' (bell),
1091 '<code>\b</code>' (backspace),
1092 '<code>\f</code>' (form feed),
1093 '<code>\n</code>' (newline),
1094 '<code>\r</code>' (carriage return),
1095 '<code>\t</code>' (horizontal tab),
1096 '<code>\v</code>' (vertical tab),
1097 '<code>\\</code>' (backslash),
1098 '<code>\"</code>' (quotation mark [double quote]),
1099 and '<code>\'</code>' (apostrophe [single quote]).
1100 A backslash followed by a real newline
1101 results in a newline in the string.
1102 The escape sequence '<code>\z</code>' skips the following span
1103 of white-space characters,
1104 including line breaks;
1105 it is particularly useful to break and indent a long literal string
1106 into multiple lines without adding the newlines and spaces
1107 into the string contents.
1111 Strings in Lua can contain any 8-bit value, including embedded zeros,
1112 which can be specified as '<code>\0</code>'.
1114 we can specify any byte in a literal string by its numerical value.
1116 with the escape sequence <code>\x<em>XX</em></code>,
1117 where <em>XX</em> is a sequence of exactly two hexadecimal digits,
1118 or with the escape sequence <code>\<em>ddd</em></code>,
1119 where <em>ddd</em> is a sequence of up to three decimal digits.
1120 (Note that if a decimal escape sequence is to be followed by a digit,
1121 it must be expressed using exactly three digits.)
1125 The UTF-8 encoding of a Unicode character
1126 can be inserted in a literal string with
1127 the escape sequence <code>\u{<em>XXX</em>}</code>
1128 (note the mandatory enclosing brackets),
1129 where <em>XXX</em> is a sequence of one or more hexadecimal digits
1130 representing the character code point.
1134 Literal strings can also be defined using a long format
1135 enclosed by <em>long brackets</em>.
1136 We define an <em>opening long bracket of level <em>n</em></em> as an opening
1137 square bracket followed by <em>n</em> equal signs followed by another
1138 opening square bracket.
1139 So, an opening long bracket of level 0 is written as <code>[[</code>,
1140 an opening long bracket of level 1 is written as <code>[=[</code>,
1142 A <em>closing long bracket</em> is defined similarly;
1144 a closing long bracket of level 4 is written as <code>]====]</code>.
1145 A <em>long literal</em> starts with an opening long bracket of any level and
1146 ends at the first closing long bracket of the same level.
1147 It can contain any text except a closing bracket of the same level.
1148 Literals in this bracketed form can run for several lines,
1149 do not interpret any escape sequences,
1150 and ignore long brackets of any other level.
1151 Any kind of end-of-line sequence
1152 (carriage return, newline, carriage return followed by newline,
1153 or newline followed by carriage return)
1154 is converted to a simple newline.
1158 Any byte in a literal string not
1159 explicitly affected by the previous rules represents itself.
1160 However, Lua opens files for parsing in text mode,
1161 and the system file functions may have problems with
1162 some control characters.
1163 So, it is safer to represent
1164 non-text data as a quoted literal with
1165 explicit escape sequences for non-text characters.
1170 when the opening long bracket is immediately followed by a newline,
1171 the newline is not included in the string.
1172 As an example, in a system using ASCII
1173 (in which '<code>a</code>' is coded as 97,
1174 newline is coded as 10, and '<code>1</code>' is coded as 49),
1175 the five literal strings below denote the same string:
1180 a = '\97lo\10\04923"'
1189 A <em>numerical constant</em> (or <em>numeral</em>)
1190 can be written with an optional fractional part
1191 and an optional decimal exponent,
1192 marked by a letter '<code>e</code>' or '<code>E</code>'.
1193 Lua also accepts hexadecimal constants,
1194 which start with <code>0x</code> or <code>0X</code>.
1195 Hexadecimal constants also accept an optional fractional part
1196 plus an optional binary exponent,
1197 marked by a letter '<code>p</code>' or '<code>P</code>'.
1198 A numeric constant with a fractional dot or an exponent
1200 otherwise it denotes an integer.
1201 Examples of valid integer constants are
1206 Examples of valid float constants are
1209 3.0 3.1416 314.16e-2 0.31416E1 34e1
1210 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
1214 A <em>comment</em> starts with a double hyphen (<code>--</code>)
1215 anywhere outside a string.
1216 If the text immediately after <code>--</code> is not an opening long bracket,
1217 the comment is a <em>short comment</em>,
1218 which runs until the end of the line.
1219 Otherwise, it is a <em>long comment</em>,
1220 which runs until the corresponding closing long bracket.
1221 Long comments are frequently used to disable code temporarily.
1227 <h2>3.2 – <a name="3.2">Variables</a></h2>
1230 Variables are places that store values.
1231 There are three kinds of variables in Lua:
1232 global variables, local variables, and table fields.
1236 A single name can denote a global variable or a local variable
1237 (or a function's formal parameter,
1238 which is a particular kind of local variable):
1243 Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>.
1247 Any variable name is assumed to be global unless explicitly declared
1248 as a local (see <a href="#3.3.7">§3.3.7</a>).
1249 Local variables are <em>lexically scoped</em>:
1250 local variables can be freely accessed by functions
1251 defined inside their scope (see <a href="#3.5">§3.5</a>).
1255 Before the first assignment to a variable, its value is <b>nil</b>.
1259 Square brackets are used to index a table:
1262 var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’
1264 The meaning of accesses to table fields can be changed via metatables.
1265 An access to an indexed variable <code>t[i]</code> is equivalent to
1266 a call <code>gettable_event(t,i)</code>.
1267 (See <a href="#2.4">§2.4</a> for a complete description of the
1268 <code>gettable_event</code> function.
1269 This function is not defined or callable in Lua.
1270 We use it here only for explanatory purposes.)
1274 The syntax <code>var.Name</code> is just syntactic sugar for
1275 <code>var["Name"]</code>:
1278 var ::= prefixexp ‘<b>.</b>’ Name
1282 An access to a global variable <code>x</code>
1283 is equivalent to <code>_ENV.x</code>.
1284 Due to the way that chunks are compiled,
1285 <code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>).
1291 <h2>3.3 – <a name="3.3">Statements</a></h2>
1294 Lua supports an almost conventional set of statements,
1295 similar to those in Pascal or C.
1297 assignments, control structures, function calls,
1298 and variable declarations.
1302 <h3>3.3.1 – <a name="3.3.1">Blocks</a></h3>
1305 A block is a list of statements,
1306 which are executed sequentially:
1311 Lua has <em>empty statements</em>
1312 that allow you to separate statements with semicolons,
1313 start a block with a semicolon
1314 or write two semicolons in sequence:
1317 stat ::= ‘<b>;</b>’
1321 Function calls and assignments
1322 can start with an open parenthesis.
1323 This possibility leads to an ambiguity in Lua's grammar.
1324 Consider the following fragment:
1328 (print or io.write)('done')
1330 The grammar could see it in two ways:
1333 a = b + c(print or io.write)('done')
1335 a = b + c; (print or io.write)('done')
1337 The current parser always sees such constructions
1339 interpreting the open parenthesis
1340 as the start of the arguments to a call.
1341 To avoid this ambiguity,
1342 it is a good practice to always precede with a semicolon
1343 statements that start with a parenthesis:
1346 ;(print or io.write)('done')
1350 A block can be explicitly delimited to produce a single statement:
1353 stat ::= <b>do</b> block <b>end</b>
1355 Explicit blocks are useful
1356 to control the scope of variable declarations.
1357 Explicit blocks are also sometimes used to
1358 add a <b>return</b> statement in the middle
1359 of another block (see <a href="#3.3.4">§3.3.4</a>).
1365 <h3>3.3.2 – <a name="3.3.2">Chunks</a></h3>
1368 The unit of compilation of Lua is called a <em>chunk</em>.
1370 a chunk is simply a block:
1377 Lua handles a chunk as the body of an anonymous function
1378 with a variable number of arguments
1379 (see <a href="#3.4.11">§3.4.11</a>).
1380 As such, chunks can define local variables,
1381 receive arguments, and return values.
1382 Moreover, such anonymous function is compiled as in the
1383 scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>).
1384 The resulting function always has <code>_ENV</code> as its only upvalue,
1385 even if it does not use that variable.
1389 A chunk can be stored in a file or in a string inside the host program.
1391 Lua first <em>loads</em> it,
1392 precompiling the chunk's code into instructions for a virtual machine,
1393 and then Lua executes the compiled code
1394 with an interpreter for the virtual machine.
1398 Chunks can also be precompiled into binary form;
1399 see program <code>luac</code> and function <a href="#pdf-string.dump"><code>string.dump</code></a> for details.
1400 Programs in source and compiled forms are interchangeable;
1401 Lua automatically detects the file type and acts accordingly (see <a href="#pdf-load"><code>load</code></a>).
1407 <h3>3.3.3 – <a name="3.3.3">Assignment</a></h3>
1410 Lua allows multiple assignments.
1411 Therefore, the syntax for assignment
1412 defines a list of variables on the left side
1413 and a list of expressions on the right side.
1414 The elements in both lists are separated by commas:
1417 stat ::= varlist ‘<b>=</b>’ explist
1418 varlist ::= var {‘<b>,</b>’ var}
1419 explist ::= exp {‘<b>,</b>’ exp}
1421 Expressions are discussed in <a href="#3.4">§3.4</a>.
1425 Before the assignment,
1426 the list of values is <em>adjusted</em> to the length of
1427 the list of variables.
1428 If there are more values than needed,
1429 the excess values are thrown away.
1430 If there are fewer values than needed,
1431 the list is extended with as many <b>nil</b>'s as needed.
1432 If the list of expressions ends with a function call,
1433 then all values returned by that call enter the list of values,
1434 before the adjustment
1435 (except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>).
1439 The assignment statement first evaluates all its expressions
1440 and only then the assignments are performed.
1447 sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
1448 because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
1449 before it is assigned 4.
1455 exchanges the values of <code>x</code> and <code>y</code>,
1461 cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
1465 The meaning of assignments to global variables
1466 and table fields can be changed via metatables.
1467 An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
1468 <code>settable_event(t,i,val)</code>.
1469 (See <a href="#2.4">§2.4</a> for a complete description of the
1470 <code>settable_event</code> function.
1471 This function is not defined or callable in Lua.
1472 We use it here only for explanatory purposes.)
1476 An assignment to a global name <code>x = val</code>
1477 is equivalent to the assignment
1478 <code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>).
1484 <h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p>
1485 The control structures
1486 <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
1493 stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
1494 stat ::= <b>repeat</b> block <b>until</b> exp
1495 stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
1497 Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>).
1501 The condition expression of a
1502 control structure can return any value.
1503 Both <b>false</b> and <b>nil</b> are considered false.
1504 All values different from <b>nil</b> and <b>false</b> are considered true
1505 (in particular, the number 0 and the empty string are also true).
1509 In the <b>repeat</b>–<b>until</b> loop,
1510 the inner block does not end at the <b>until</b> keyword,
1511 but only after the condition.
1512 So, the condition can refer to local variables
1513 declared inside the loop block.
1517 The <b>goto</b> statement transfers the program control to a label.
1518 For syntactical reasons,
1519 labels in Lua are considered statements too:
1524 stat ::= <b>goto</b> Name
1526 label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
1530 A label is visible in the entire block where it is defined,
1532 inside nested blocks where a label with the same name is defined and
1533 inside nested functions.
1534 A goto may jump to any visible label as long as it does not
1535 enter into the scope of a local variable.
1539 Labels and empty statements are called <em>void statements</em>,
1540 as they perform no actions.
1544 The <b>break</b> statement terminates the execution of a
1545 <b>while</b>, <b>repeat</b>, or <b>for</b> loop,
1546 skipping to the next statement after the loop:
1550 stat ::= <b>break</b>
1552 A <b>break</b> ends the innermost enclosing loop.
1556 The <b>return</b> statement is used to return values
1557 from a function or a chunk
1558 (which is an anonymous function).
1560 Functions can return more than one value,
1561 so the syntax for the <b>return</b> statement is
1564 stat ::= <b>return</b> [explist] [‘<b>;</b>’]
1568 The <b>return</b> statement can only be written
1569 as the last statement of a block.
1570 If it is really necessary to <b>return</b> in the middle of a block,
1571 then an explicit inner block can be used,
1572 as in the idiom <code>do return end</code>,
1573 because now <b>return</b> is the last statement in its (inner) block.
1579 <h3>3.3.5 – <a name="3.3.5">For Statement</a></h3>
1583 The <b>for</b> statement has two forms:
1584 one numeric and one generic.
1588 The numeric <b>for</b> loop repeats a block of code while a
1589 control variable runs through an arithmetic progression.
1590 It has the following syntax:
1593 stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b>
1595 The <em>block</em> is repeated for <em>name</em> starting at the value of
1596 the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the
1598 More precisely, a <b>for</b> statement like
1601 for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end
1603 is equivalent to the code:
1607 local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
1608 if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end
1609 <em>var</em> = <em>var</em> - <em>step</em>
1611 <em>var</em> = <em>var</em> + <em>step</em>
1612 if (<em>step</em> >= 0 and <em>var</em> > <em>limit</em>) or (<em>step</em> < 0 and <em>var</em> < <em>limit</em>) then
1615 local v = <em>var</em>
1627 All three control expressions are evaluated only once,
1628 before the loop starts.
1629 They must all result in numbers.
1633 <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
1634 The names shown here are for explanatory purposes only.
1638 If the third expression (the step) is absent,
1639 then a step of 1 is used.
1643 You can use <b>break</b> and <b>goto</b> to exit a <b>for</b> loop.
1647 The loop variable <code>v</code> is local to the loop body.
1648 If you need its value after the loop,
1649 assign it to another variable before exiting the loop.
1655 The generic <b>for</b> statement works over functions,
1656 called <em>iterators</em>.
1657 On each iteration, the iterator function is called to produce a new value,
1658 stopping when this new value is <b>nil</b>.
1659 The generic <b>for</b> loop has the following syntax:
1662 stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
1663 namelist ::= Name {‘<b>,</b>’ Name}
1665 A <b>for</b> statement like
1668 for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end
1670 is equivalent to the code:
1674 local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em>
1676 local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
1677 if <em>var_1</em> == nil then break end
1678 <em>var</em> = <em>var_1</em>
1688 <code><em>explist</em></code> is evaluated only once.
1689 Its results are an <em>iterator</em> function,
1691 and an initial value for the first <em>iterator variable</em>.
1695 <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
1696 The names are here for explanatory purposes only.
1700 You can use <b>break</b> to exit a <b>for</b> loop.
1704 The loop variables <code><em>var_i</em></code> are local to the loop;
1705 you cannot use their values after the <b>for</b> ends.
1706 If you need these values,
1707 then assign them to other variables before breaking or exiting the loop.
1715 <h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p>
1716 To allow possible side-effects,
1717 function calls can be executed as statements:
1720 stat ::= functioncall
1722 In this case, all returned values are thrown away.
1723 Function calls are explained in <a href="#3.4.10">§3.4.10</a>.
1729 <h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p>
1730 Local variables can be declared anywhere inside a block.
1731 The declaration can include an initial assignment:
1734 stat ::= <b>local</b> namelist [‘<b>=</b>’ explist]
1736 If present, an initial assignment has the same semantics
1737 of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>).
1738 Otherwise, all variables are initialized with <b>nil</b>.
1742 A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>),
1743 and so local variables can be declared in a chunk outside any explicit block.
1747 The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>.
1755 <h2>3.4 – <a name="3.4">Expressions</a></h2>
1758 The basic expressions in Lua are the following:
1762 exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
1764 exp ::= LiteralString
1766 exp ::= tableconstructor
1767 exp ::= ‘<b>...</b>’
1768 exp ::= exp binop exp
1770 prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
1774 Numerals and literal strings are explained in <a href="#3.1">§3.1</a>;
1775 variables are explained in <a href="#3.2">§3.2</a>;
1776 function definitions are explained in <a href="#3.4.11">§3.4.11</a>;
1777 function calls are explained in <a href="#3.4.10">§3.4.10</a>;
1778 table constructors are explained in <a href="#3.4.9">§3.4.9</a>.
1780 denoted by three dots ('<code>...</code>'), can only be used when
1781 directly inside a vararg function;
1782 they are explained in <a href="#3.4.11">§3.4.11</a>.
1786 Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>),
1787 bitwise operators (see <a href="#3.4.2">§3.4.2</a>),
1788 relational operators (see <a href="#3.4.4">§3.4.4</a>), logical operators (see <a href="#3.4.5">§3.4.5</a>),
1789 and the concatenation operator (see <a href="#3.4.6">§3.4.6</a>).
1790 Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>),
1791 the unary bitwise not (see <a href="#3.4.2">§3.4.2</a>),
1792 the unary logical <b>not</b> (see <a href="#3.4.5">§3.4.5</a>),
1793 and the unary <em>length operator</em> (see <a href="#3.4.7">§3.4.7</a>).
1797 Both function calls and vararg expressions can result in multiple values.
1798 If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>),
1799 then its return list is adjusted to zero elements,
1800 thus discarding all returned values.
1801 If an expression is used as the last (or the only) element
1802 of a list of expressions,
1803 then no adjustment is made
1804 (unless the expression is enclosed in parentheses).
1805 In all other contexts,
1806 Lua adjusts the result list to one element,
1807 either discarding all values except the first one
1808 or adding a single <b>nil</b> if there are no values.
1812 Here are some examples:
1815 f() -- adjusted to 0 results
1816 g(f(), x) -- f() is adjusted to 1 result
1817 g(x, f()) -- g gets x plus all results from f()
1818 a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
1819 a,b = ... -- a gets the first vararg parameter, b gets
1820 -- the second (both a and b can get nil if there
1821 -- is no corresponding vararg parameter)
1823 a,b,c = x, f() -- f() is adjusted to 2 results
1824 a,b,c = f() -- f() is adjusted to 3 results
1825 return f() -- returns all results from f()
1826 return ... -- returns all received vararg parameters
1827 return x,y,f() -- returns x, y, and all results from f()
1828 {f()} -- creates a list with all results from f()
1829 {...} -- creates a list with all vararg parameters
1830 {f(), nil} -- f() is adjusted to 1 result
1834 Any expression enclosed in parentheses always results in only one value.
1836 <code>(f(x,y,z))</code> is always a single value,
1837 even if <code>f</code> returns several values.
1838 (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
1839 or <b>nil</b> if <code>f</code> does not return any values.)
1843 <h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p>
1844 Lua supports the following arithmetic operators:
1847 <li><b><code>+</code>: </b>addition</li>
1848 <li><b><code>-</code>: </b>subtraction</li>
1849 <li><b><code>*</code>: </b>multiplication</li>
1850 <li><b><code>/</code>: </b>float division</li>
1851 <li><b><code>//</code>: </b>floor division</li>
1852 <li><b><code>%</code>: </b>modulo</li>
1853 <li><b><code>^</code>: </b>exponentiation</li>
1854 <li><b><code>-</code>: </b>unary minus</li>
1858 With the exception of exponentiation and float division,
1859 the arithmetic operators work as follows:
1860 If both operands are integers,
1861 the operation is performed over integers and the result is an integer.
1862 Otherwise, if both operands are numbers
1863 or strings that can be converted to
1864 numbers (see <a href="#3.4.3">§3.4.3</a>),
1865 then they are converted to floats,
1866 the operation is performed following the usual rules
1867 for floating-point arithmetic
1868 (usually the IEEE 754 standard),
1869 and the result is a float.
1873 Exponentiation and float division (<code>/</code>)
1874 always convert their operands to floats
1875 and the result is always a float.
1876 Exponentiation uses the ISO C function <code>pow</code>,
1877 so that it works for non-integer exponents too.
1881 Floor division (<code>//</code>) is a division
1882 that rounds the quotient towards minus infinite,
1883 that is, the floor of the division of its operands.
1887 Modulo is defined as the remainder of a division
1888 that rounds the quotient towards minus infinite (floor division).
1892 In case of overflows in integer arithmetic,
1893 all operations <em>wrap around</em>,
1894 according to the usual rules of two-complement arithmetic.
1896 they return the unique representable integer
1897 that is equal modulo <em>2<sup>64</sup></em> to the mathematical result.)
1901 <h3>3.4.2 – <a name="3.4.2">Bitwise Operators</a></h3><p>
1902 Lua supports the following bitwise operators:
1905 <li><b><code>&</code>: </b>bitwise and</li>
1906 <li><b><code>|</code>: </b>bitwise or</li>
1907 <li><b><code>~</code>: </b>bitwise exclusive or</li>
1908 <li><b><code>>></code>: </b>right shift</li>
1909 <li><b><code><<</code>: </b>left shift</li>
1910 <li><b><code>~</code>: </b>unary bitwise not</li>
1914 All bitwise operations convert its operands to integers
1915 (see <a href="#3.4.3">§3.4.3</a>),
1916 operate on all bits of those integers,
1917 and result in an integer.
1921 Both right and left shifts fill the vacant bits with zeros.
1922 Negative displacements shift to the other direction;
1923 displacements with absolute values equal to or higher than
1924 the number of bits in an integer
1925 result in zero (as all bits are shifted out).
1931 <h3>3.4.3 – <a name="3.4.3">Coercions and Conversions</a></h3><p>
1932 Lua provides some automatic conversions between some
1933 types and representations at run time.
1934 Bitwise operators always convert float operands to integers.
1935 Exponentiation and float division
1936 always convert integer operands to floats.
1937 All other arithmetic operations applied to mixed numbers
1938 (integers and floats) convert the integer operand to a float;
1939 this is called the <em>usual rule</em>.
1940 The C API also converts both integers to floats and
1941 floats to integers, as needed.
1942 Moreover, string concatenation accepts numbers as arguments,
1947 Lua also converts strings to numbers,
1948 whenever a number is expected.
1952 In a conversion from integer to float,
1953 if the integer value has an exact representation as a float,
1956 the conversion gets the nearest higher or
1957 the nearest lower representable value.
1958 This kind of conversion never fails.
1962 The conversion from float to integer
1963 checks whether the float has an exact representation as an integer
1964 (that is, the float has an integral value and
1965 it is in the range of integer representation).
1966 If it does, that representation is the result.
1967 Otherwise, the conversion fails.
1971 The conversion from strings to numbers goes as follows:
1972 First, the string is converted to an integer or a float,
1973 following its syntax and the rules of the Lua lexer.
1974 (The string may have also leading and trailing spaces and a sign.)
1975 Then, the resulting number is converted to the required type
1976 (float or integer) according to the previous rules.
1980 The conversion from numbers to strings uses a
1981 non-specified human-readable format.
1982 For complete control over how numbers are converted to strings,
1983 use the <code>format</code> function from the string library
1984 (see <a href="#pdf-string.format"><code>string.format</code></a>).
1990 <h3>3.4.4 – <a name="3.4.4">Relational Operators</a></h3><p>
1991 Lua supports the following relational operators:
1994 <li><b><code>==</code>: </b>equality</li>
1995 <li><b><code>~=</code>: </b>inequality</li>
1996 <li><b><code><</code>: </b>less than</li>
1997 <li><b><code>></code>: </b>greater than</li>
1998 <li><b><code><=</code>: </b>less or equal</li>
1999 <li><b><code>>=</code>: </b>greater or equal</li>
2001 These operators always result in <b>false</b> or <b>true</b>.
2005 Equality (<code>==</code>) first compares the type of its operands.
2006 If the types are different, then the result is <b>false</b>.
2007 Otherwise, the values of the operands are compared.
2008 Strings are compared in the obvious way.
2009 Numbers follow the usual rule for binary operations:
2010 if both operands are integers,
2011 they are compared as integers;
2012 otherwise, they are converted to floats
2013 and compared as such.
2017 Tables, userdata, and threads
2018 are compared by reference:
2019 two objects are considered equal only if they are the same object.
2020 Every time you create a new object
2021 (a table, userdata, or thread),
2022 this new object is different from any previously existing object.
2023 Closures with the same reference are always equal.
2024 Closures with any detectable difference
2025 (different behavior, different definition) are always different.
2029 You can change the way that Lua compares tables and userdata
2030 by using the "eq" metamethod (see <a href="#2.4">§2.4</a>).
2034 Equality comparisons do not convert strings to numbers
2036 Thus, <code>"0"==0</code> evaluates to <b>false</b>,
2037 and <code>t[0]</code> and <code>t["0"]</code> denote different
2042 The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
2046 The order operators work as follows.
2047 If both arguments are numbers,
2048 then they are compared following
2049 the usual rule for binary operations.
2050 Otherwise, if both arguments are strings,
2051 then their values are compared according to the current locale.
2052 Otherwise, Lua tries to call the "lt" or the "le"
2053 metamethod (see <a href="#2.4">§2.4</a>).
2054 A comparison <code>a > b</code> is translated to <code>b < a</code>
2055 and <code>a >= b</code> is translated to <code>b <= a</code>.
2061 <h3>3.4.5 – <a name="3.4.5">Logical Operators</a></h3><p>
2062 The logical operators in Lua are
2063 <b>and</b>, <b>or</b>, and <b>not</b>.
2064 Like the control structures (see <a href="#3.3.4">§3.3.4</a>),
2065 all logical operators consider both <b>false</b> and <b>nil</b> as false
2066 and anything else as true.
2070 The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
2071 The conjunction operator <b>and</b> returns its first argument
2072 if this value is <b>false</b> or <b>nil</b>;
2073 otherwise, <b>and</b> returns its second argument.
2074 The disjunction operator <b>or</b> returns its first argument
2075 if this value is different from <b>nil</b> and <b>false</b>;
2076 otherwise, <b>or</b> returns its second argument.
2077 Both <b>and</b> and <b>or</b> use short-circuit evaluation;
2079 the second operand is evaluated only if necessary.
2080 Here are some examples:
2084 10 or error() --> 10
2085 nil or "a" --> "a"
2086 nil and 10 --> nil
2087 false and error() --> false
2088 false and nil --> false
2089 false or nil --> nil
2093 <code>--></code> indicates the result of the preceding expression.)
2099 <h3>3.4.6 – <a name="3.4.6">Concatenation</a></h3><p>
2100 The string concatenation operator in Lua is
2101 denoted by two dots ('<code>..</code>').
2102 If both operands are strings or numbers, then they are converted to
2103 strings according to the rules described in <a href="#3.4.3">§3.4.3</a>.
2104 Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>).
2110 <h3>3.4.7 – <a name="3.4.7">The Length Operator</a></h3>
2113 The length operator is denoted by the unary prefix operator <code>#</code>.
2114 The length of a string is its number of bytes
2115 (that is, the usual meaning of string length when each
2116 character is one byte).
2120 A program can modify the behavior of the length operator for
2121 any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>).
2125 Unless a <code>__len</code> metamethod is given,
2126 the length of a table <code>t</code> is only defined if the
2127 table is a <em>sequence</em>,
2129 the set of its positive numeric keys is equal to <em>{1..n}</em>
2130 for some non-negative integer <em>n</em>.
2131 In that case, <em>n</em> is its length.
2132 Note that a table like
2137 is not a sequence, because it has the key <code>4</code>
2138 but does not have the key <code>3</code>.
2139 (So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal
2140 to the set of positive numeric keys of that table.)
2141 Note, however, that non-numeric keys do not interfere
2142 with whether a table is a sequence.
2148 <h3>3.4.8 – <a name="3.4.8">Precedence</a></h3><p>
2149 Operator precedence in Lua follows the table below,
2150 from lower to higher priority:
2155 < > <= >= ~= ==
2163 unary operators (not # - ~)
2167 you can use parentheses to change the precedences of an expression.
2168 The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
2169 operators are right associative.
2170 All other binary operators are left associative.
2176 <h3>3.4.9 – <a name="3.4.9">Table Constructors</a></h3><p>
2177 Table constructors are expressions that create tables.
2178 Every time a constructor is evaluated, a new table is created.
2179 A constructor can be used to create an empty table
2180 or to create a table and initialize some of its fields.
2181 The general syntax for constructors is
2184 tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
2185 fieldlist ::= field {fieldsep field} [fieldsep]
2186 field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
2187 fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
2191 Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
2192 with key <code>exp1</code> and value <code>exp2</code>.
2193 A field of the form <code>name = exp</code> is equivalent to
2194 <code>["name"] = exp</code>.
2195 Finally, fields of the form <code>exp</code> are equivalent to
2196 <code>[i] = exp</code>, where <code>i</code> are consecutive integers
2198 Fields in the other formats do not affect this counting.
2202 a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
2210 t[1] = "x" -- 1st exp
2211 t[2] = "y" -- 2nd exp
2212 t.x = 1 -- t["x"] = 1
2213 t[3] = f(x) -- 3rd exp
2215 t[4] = 45 -- 4th exp
2221 The order of the assignments in a constructor is undefined.
2222 (This order would be relevant only when there are repeated keys.)
2226 If the last field in the list has the form <code>exp</code>
2227 and the expression is a function call or a vararg expression,
2228 then all values returned by this expression enter the list consecutively
2229 (see <a href="#3.4.10">§3.4.10</a>).
2233 The field list can have an optional trailing separator,
2234 as a convenience for machine-generated code.
2240 <h3>3.4.10 – <a name="3.4.10">Function Calls</a></h3><p>
2241 A function call in Lua has the following syntax:
2244 functioncall ::= prefixexp args
2247 first prefixexp and args are evaluated.
2248 If the value of prefixexp has type <em>function</em>,
2249 then this function is called
2250 with the given arguments.
2251 Otherwise, the prefixexp "call" metamethod is called,
2252 having as first parameter the value of prefixexp,
2253 followed by the original call arguments
2254 (see <a href="#2.4">§2.4</a>).
2261 functioncall ::= prefixexp ‘<b>:</b>’ Name args
2263 can be used to call "methods".
2264 A call <code>v:name(<em>args</em>)</code>
2265 is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
2266 except that <code>v</code> is evaluated only once.
2270 Arguments have the following syntax:
2273 args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’
2274 args ::= tableconstructor
2275 args ::= LiteralString
2277 All argument expressions are evaluated before the call.
2278 A call of the form <code>f{<em>fields</em>}</code> is
2279 syntactic sugar for <code>f({<em>fields</em>})</code>;
2280 that is, the argument list is a single new table.
2281 A call of the form <code>f'<em>string</em>'</code>
2282 (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
2283 is syntactic sugar for <code>f('<em>string</em>')</code>;
2284 that is, the argument list is a single literal string.
2288 A call of the form <code>return <em>functioncall</em></code> is called
2289 a <em>tail call</em>.
2290 Lua implements <em>proper tail calls</em>
2291 (or <em>proper tail recursion</em>):
2293 the called function reuses the stack entry of the calling function.
2294 Therefore, there is no limit on the number of nested tail calls that
2295 a program can execute.
2296 However, a tail call erases any debug information about the
2298 Note that a tail call only happens with a particular syntax,
2299 where the <b>return</b> has one single function call as argument;
2300 this syntax makes the calling function return exactly
2301 the returns of the called function.
2302 So, none of the following examples are tail calls:
2305 return (f(x)) -- results adjusted to 1
2307 return x, f(x) -- additional results
2308 f(x); return -- results discarded
2309 return x or f(x) -- results adjusted to 1
2315 <h3>3.4.11 – <a name="3.4.11">Function Definitions</a></h3>
2318 The syntax for function definition is
2321 functiondef ::= <b>function</b> funcbody
2322 funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
2326 The following syntactic sugar simplifies function definitions:
2329 stat ::= <b>function</b> funcname funcbody
2330 stat ::= <b>local</b> <b>function</b> Name funcbody
2331 funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
2336 function f () <em>body</em> end
2341 f = function () <em>body</em> end
2346 function t.a.b.c.f () <em>body</em> end
2351 t.a.b.c.f = function () <em>body</em> end
2356 local function f () <em>body</em> end
2361 local f; f = function () <em>body</em> end
2366 local f = function () <em>body</em> end
2368 (This only makes a difference when the body of the function
2369 contains references to <code>f</code>.)
2373 A function definition is an executable expression,
2374 whose value has type <em>function</em>.
2375 When Lua precompiles a chunk,
2376 all its function bodies are precompiled too.
2377 Then, whenever Lua executes the function definition,
2378 the function is <em>instantiated</em> (or <em>closed</em>).
2379 This function instance (or <em>closure</em>)
2380 is the final value of the expression.
2384 Parameters act as local variables that are
2385 initialized with the argument values:
2388 parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
2390 When a function is called,
2391 the list of arguments is adjusted to
2392 the length of the list of parameters,
2393 unless the function is a <em>vararg function</em>,
2394 which is indicated by three dots ('<code>...</code>')
2395 at the end of its parameter list.
2396 A vararg function does not adjust its argument list;
2397 instead, it collects all extra arguments and supplies them
2398 to the function through a <em>vararg expression</em>,
2399 which is also written as three dots.
2400 The value of this expression is a list of all actual extra arguments,
2401 similar to a function with multiple results.
2402 If a vararg expression is used inside another expression
2403 or in the middle of a list of expressions,
2404 then its return list is adjusted to one element.
2405 If the expression is used as the last element of a list of expressions,
2406 then no adjustment is made
2407 (unless that last expression is enclosed in parentheses).
2411 As an example, consider the following definitions:
2414 function f(a, b) end
2415 function g(a, b, ...) end
2416 function r() return 1,2,3 end
2418 Then, we have the following mapping from arguments to parameters and
2419 to the vararg expression:
2427 f(r(), 10) a=1, b=10
2430 g(3) a=3, b=nil, ... --> (nothing)
2431 g(3, 4) a=3, b=4, ... --> (nothing)
2432 g(3, 4, 5, 8) a=3, b=4, ... --> 5 8
2433 g(5, r()) a=5, b=1, ... --> 2 3
2437 Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>).
2438 If control reaches the end of a function
2439 without encountering a <b>return</b> statement,
2440 then the function returns with no results.
2445 There is a system-dependent limit on the number of values
2446 that a function may return.
2447 This limit is guaranteed to be larger than 1000.
2451 The <em>colon</em> syntax
2452 is used for defining <em>methods</em>,
2453 that is, functions that have an implicit extra parameter <code>self</code>.
2457 function t.a.b.c:f (<em>params</em>) <em>body</em> end
2459 is syntactic sugar for
2462 t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
2470 <h2>3.5 – <a name="3.5">Visibility Rules</a></h2>
2474 Lua is a lexically scoped language.
2475 The scope of a local variable begins at the first statement after
2476 its declaration and lasts until the last non-void statement
2477 of the innermost block that includes the declaration.
2478 Consider the following example:
2481 x = 10 -- global variable
2483 local x = x -- new 'x', with value 10
2487 local x = x+1 -- another 'x'
2492 print(x) --> 10 (the global one)
2496 Notice that, in a declaration like <code>local x = x</code>,
2497 the new <code>x</code> being declared is not in scope yet,
2498 and so the second <code>x</code> refers to the outside variable.
2502 Because of the lexical scoping rules,
2503 local variables can be freely accessed by functions
2504 defined inside their scope.
2505 A local variable used by an inner function is called
2506 an <em>upvalue</em>, or <em>external local variable</em>,
2507 inside the inner function.
2511 Notice that each execution of a <b>local</b> statement
2512 defines new local variables.
2513 Consider the following example:
2520 a[i] = function () y=y+1; return x+y end
2523 The loop creates ten closures
2524 (that is, ten instances of the anonymous function).
2525 Each of these closures uses a different <code>y</code> variable,
2526 while all of them share the same <code>x</code>.
2532 <h1>4 – <a name="4">The Application Program Interface</a></h1>
2536 This section describes the C API for Lua, that is,
2537 the set of C functions available to the host program to communicate
2539 All API functions and related types and constants
2540 are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
2544 Even when we use the term "function",
2545 any facility in the API may be provided as a macro instead.
2546 Except where stated otherwise,
2547 all such macros use each of their arguments exactly once
2548 (except for the first argument, which is always a Lua state),
2549 and so do not generate any hidden side-effects.
2553 As in most C libraries,
2554 the Lua API functions do not check their arguments for validity or consistency.
2555 However, you can change this behavior by compiling Lua
2556 with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined.
2560 <h2>4.1 – <a name="4.1">The Stack</a></h2>
2563 Lua uses a <em>virtual stack</em> to pass values to and from C.
2564 Each element in this stack represents a Lua value
2565 (<b>nil</b>, number, string, etc.).
2569 Whenever Lua calls C, the called function gets a new stack,
2570 which is independent of previous stacks and of stacks of
2571 C functions that are still active.
2572 This stack initially contains any arguments to the C function
2573 and it is where the C function pushes its results
2574 to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
2579 most query operations in the API do not follow a strict stack discipline.
2580 Instead, they can refer to any element in the stack
2581 by using an <em>index</em>:
2582 A positive index represents an absolute stack position
2583 (starting at 1);
2584 a negative index represents an offset relative to the top of the stack.
2585 More specifically, if the stack has <em>n</em> elements,
2586 then index 1 represents the first element
2587 (that is, the element that was pushed onto the stack first)
2589 index <em>n</em> represents the last element;
2590 index -1 also represents the last element
2591 (that is, the element at the top)
2592 and index <em>-n</em> represents the first element.
2598 <h2>4.2 – <a name="4.2">Stack Size</a></h2>
2601 When you interact with the Lua API,
2602 you are responsible for ensuring consistency.
2604 <em>you are responsible for controlling stack overflow</em>.
2605 You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
2606 to ensure that the stack has enough space for pushing new elements.
2610 Whenever Lua calls C,
2611 it ensures that the stack has space for
2612 at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots.
2613 <code>LUA_MINSTACK</code> is defined as 20,
2614 so that usually you do not have to worry about stack space
2615 unless your code has loops pushing elements onto the stack.
2619 When you call a Lua function
2620 without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>),
2621 Lua ensures that the stack has enough space for all results,
2622 but it does not ensure any extra space.
2623 So, before pushing anything in the stack after such a call
2624 you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
2630 <h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2>
2633 Any function in the API that receives stack indices
2634 works only with <em>valid indices</em> or <em>acceptable indices</em>.
2638 A <em>valid index</em> is an index that refers to a
2639 real position within the stack, that is,
2640 its position lies between 1 and the stack top
2641 (<code>1 ≤ abs(index) ≤ top</code>).
2643 Usually, functions that can modify the value at an index
2644 require valid indices.
2648 Unless otherwise noted,
2649 any function that accepts valid indices also accepts <em>pseudo-indices</em>,
2650 which represent some Lua values that are accessible to C code
2651 but which are not in the stack.
2652 Pseudo-indices are used to access the registry
2653 and the upvalues of a C function (see <a href="#4.4">§4.4</a>).
2657 Functions that do not need a specific stack position,
2658 but only a value in the stack (e.g., query functions),
2659 can be called with acceptable indices.
2660 An <em>acceptable index</em> can be any valid index,
2661 including the pseudo-indices,
2662 but it also can be any positive index after the stack top
2663 within the space allocated for the stack,
2664 that is, indices up to the stack size.
2665 (Note that 0 is never an acceptable index.)
2666 Except when noted otherwise,
2667 functions in the API work with acceptable indices.
2671 Acceptable indices serve to avoid extra tests
2672 against the stack top when querying the stack.
2673 For instance, a C function can query its third argument
2674 without the need to first check whether there is a third argument,
2675 that is, without the need to check whether 3 is a valid index.
2679 For functions that can be called with acceptable indices,
2680 any non-valid index is treated as if it
2681 contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>,
2682 which behaves like a nil value.
2688 <h2>4.4 – <a name="4.4">C Closures</a></h2>
2691 When a C function is created,
2692 it is possible to associate some values with it,
2693 thus creating a <em>C closure</em>
2694 (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>);
2695 these values are called <em>upvalues</em> and are
2696 accessible to the function whenever it is called.
2700 Whenever a C function is called,
2701 its upvalues are located at specific pseudo-indices.
2702 These pseudo-indices are produced by the macro
2703 <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>.
2704 The first value associated with a function is at position
2705 <code>lua_upvalueindex(1)</code>, and so on.
2706 Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
2707 where <em>n</em> is greater than the number of upvalues of the
2708 current function (but not greater than 256),
2709 produces an acceptable but invalid index.
2715 <h2>4.5 – <a name="4.5">Registry</a></h2>
2718 Lua provides a <em>registry</em>,
2719 a predefined table that can be used by any C code to
2720 store whatever Lua values it needs to store.
2721 The registry table is always located at pseudo-index
2722 <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>,
2723 which is a valid index.
2724 Any C library can store data into this table,
2725 but it must take care to choose keys
2726 that are different from those used
2727 by other libraries, to avoid collisions.
2728 Typically, you should use as key a string containing your library name,
2729 or a light userdata with the address of a C object in your code,
2730 or any Lua object created by your code.
2731 As with variable names,
2732 string keys starting with an underscore followed by
2733 uppercase letters are reserved for Lua.
2737 The integer keys in the registry are used
2738 by the reference mechanism (see <a href="#luaL_ref"><code>luaL_ref</code></a>)
2739 and by some predefined values.
2740 Therefore, integer keys must not be used for other purposes.
2744 When you create a new Lua state,
2745 its registry comes with some predefined values.
2746 These predefined values are indexed with integer keys
2747 defined as constants in <code>lua.h</code>.
2748 The following constants are defined:
2751 <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has
2752 the main thread of the state.
2753 (The main thread is the one created together with the state.)
2756 <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has
2757 the global environment.
2764 <h2>4.6 – <a name="4.6">Error Handling in C</a></h2>
2767 Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
2768 (Lua will use exceptions if you compile it as C++;
2769 search for <code>LUAI_THROW</code> in the source code for details.)
2770 When Lua faces any error
2771 (such as a memory allocation error, type errors, syntax errors,
2773 it <em>raises</em> an error;
2774 that is, it does a long jump.
2775 A <em>protected environment</em> uses <code>setjmp</code>
2776 to set a recovery point;
2777 any error jumps to the most recent active recovery point.
2781 If an error happens outside any protected environment,
2782 Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>)
2783 and then calls <code>abort</code>,
2784 thus exiting the host application.
2785 Your panic function can avoid this exit by
2787 (e.g., doing a long jump to your own recovery point outside Lua).
2791 The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>);
2792 in particular, the error message is at the top of the stack.
2793 However, there is no guarantee about stack space.
2794 To push anything on the stack,
2795 the panic function must first check the available space (see <a href="#4.2">§4.2</a>).
2799 Most functions in the API can raise an error,
2800 for instance due to a memory allocation error.
2801 The documentation for each function indicates whether
2802 it can raise errors.
2806 Inside a C function you can raise an error by calling <a href="#lua_error"><code>lua_error</code></a>.
2812 <h2>4.7 – <a name="4.7">Handling Yields in C</a></h2>
2815 Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine.
2816 Therefore, if a C function <code>foo</code> calls an API function
2817 and this API function yields
2818 (directly or indirectly by calling another function that yields),
2819 Lua cannot return to <code>foo</code> any more,
2820 because the <code>longjmp</code> removes its frame from the C stack.
2824 To avoid this kind of problem,
2825 Lua raises an error whenever it tries to yield across an API call,
2826 except for three functions:
2827 <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>.
2828 All those functions receive a <em>continuation function</em>
2829 (as a parameter named <code>k</code>) to continue execution after a yield.
2833 We need to set some terminology to explain continuations.
2834 We have a C function called from Lua which we will call
2835 the <em>original function</em>.
2836 This original function then calls one of those three functions in the C API,
2837 which we will call the <em>callee function</em>,
2838 that then yields the current thread.
2839 (This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
2840 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>
2841 and the function called by them yields.)
2845 Suppose the running thread yields while executing the callee function.
2846 After the thread resumes,
2847 it eventually will finish running the callee function.
2849 the callee function cannot return to the original function,
2850 because its frame in the C stack was destroyed by the yield.
2851 Instead, Lua calls a <em>continuation function</em>,
2852 which was given as an argument to the callee function.
2853 As the name implies,
2854 the continuation function should continue the task
2855 of the original function.
2859 As an illustration, consider the following function:
2862 int original_function (lua_State *L) {
2864 status = lua_pcall(L, n, m, h); /* calls Lua */
2868 Now we want to allow
2869 the Lua code being run by <a href="#lua_pcall"><code>lua_pcall</code></a> to yield.
2870 First, we can rewrite our function like here:
2873 int k (lua_State *L, int status, lua_KContext ctx) {
2877 int original_function (lua_State *L) {
2879 return k(L, lua_pcall(L, n, m, h), ctx);
2883 the new function <code>k</code> is a
2884 <em>continuation function</em> (with type <a href="#lua_KFunction"><code>lua_KFunction</code></a>),
2885 which should do all the work that the original function
2886 was doing after calling <a href="#lua_pcall"><code>lua_pcall</code></a>.
2887 Now, we must inform Lua that it must call <code>k</code> if the Lua code
2888 being executed by <a href="#lua_pcall"><code>lua_pcall</code></a> gets interrupted in some way
2889 (errors or yielding),
2890 so we rewrite the code as here,
2891 replacing <a href="#lua_pcall"><code>lua_pcall</code></a> by <a href="#lua_pcallk"><code>lua_pcallk</code></a>:
2894 int original_function (lua_State *L) {
2896 return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
2899 Note the external, explicit call to the continuation:
2900 Lua will call the continuation only if needed, that is,
2901 in case of errors or resuming after a yield.
2902 If the called function returns normally without ever yielding,
2903 <a href="#lua_pcallk"><code>lua_pcallk</code></a> (and <a href="#lua_callk"><code>lua_callk</code></a>) will also return normally.
2904 (Of course, instead of calling the continuation in that case,
2905 you can do the equivalent work directly inside the original function.)
2909 Besides the Lua state,
2910 the continuation function has two other parameters:
2911 the final status of the call plus the context value (<code>ctx</code>) that
2912 was passed originally to <a href="#lua_pcallk"><code>lua_pcallk</code></a>.
2913 (Lua does not use this context value;
2914 it only passes this value from the original function to the
2915 continuation function.)
2916 For <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
2917 the status is the same value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
2918 except that it is <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when being executed after a yield
2919 (instead of <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>).
2920 For <a href="#lua_yieldk"><code>lua_yieldk</code></a> and <a href="#lua_callk"><code>lua_callk</code></a>,
2921 the status is always <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when Lua calls the continuation.
2922 (For these two functions,
2923 Lua will not call the continuation in case of errors,
2924 because they do not handle errors.)
2925 Similarly, when using <a href="#lua_callk"><code>lua_callk</code></a>,
2926 you should call the continuation function
2927 with <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> as the status.
2928 (For <a href="#lua_yieldk"><code>lua_yieldk</code></a>, there is not much point in calling
2929 directly the continuation function,
2930 because <a href="#lua_yieldk"><code>lua_yieldk</code></a> usually does not return.)
2934 Lua treats the continuation function as if it were the original function.
2935 The continuation function receives the same Lua stack
2936 from the original function,
2937 in the same state it would be if the callee function had returned.
2939 after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are
2940 removed from the stack and replaced by the results from the call.)
2941 It also has the same upvalues.
2942 Whatever it returns is handled by Lua as if it were the return
2943 of the original function.
2949 <h2>4.8 – <a name="4.8">Functions and Types</a></h2>
2952 Here we list all functions and types from the C API in
2954 Each function has an indicator like this:
2955 <span class="apii">[-o, +p, <em>x</em>]</span>
2959 The first field, <code>o</code>,
2960 is how many elements the function pops from the stack.
2961 The second field, <code>p</code>,
2962 is how many elements the function pushes onto the stack.
2963 (Any function always pushes its results after popping its arguments.)
2964 A field in the form <code>x|y</code> means the function can push (or pop)
2965 <code>x</code> or <code>y</code> elements,
2966 depending on the situation;
2967 an interrogation mark '<code>?</code>' means that
2968 we cannot know how many elements the function pops/pushes
2969 by looking only at its arguments
2970 (e.g., they may depend on what is on the stack).
2971 The third field, <code>x</code>,
2972 tells whether the function may raise errors:
2973 '<code>-</code>' means the function never raises any error;
2974 '<code>e</code>' means the function may raise errors;
2975 '<code>v</code>' means the function may raise an error on purpose.
2979 <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p>
2980 <span class="apii">[-0, +0, –]</span>
2981 <pre>int lua_absindex (lua_State *L, int idx);</pre>
2984 Converts the acceptable index <code>idx</code> into an absolute index
2985 (that is, one that does not depend on the stack top).
2991 <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
2992 <pre>typedef void * (*lua_Alloc) (void *ud,
2995 size_t nsize);</pre>
2998 The type of the memory-allocation function used by Lua states.
2999 The allocator function must provide a
3000 functionality similar to <code>realloc</code>,
3001 but not exactly the same.
3003 <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
3004 <code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
3005 <code>osize</code>, the original size of the block or some code about what
3007 and <code>nsize</code>, the new size of the block.
3011 When <code>ptr</code> is not <code>NULL</code>,
3012 <code>osize</code> is the size of the block pointed by <code>ptr</code>,
3013 that is, the size given when it was allocated or reallocated.
3017 When <code>ptr</code> is <code>NULL</code>,
3018 <code>osize</code> encodes the kind of object that Lua is allocating.
3019 <code>osize</code> is any of
3020 <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>,
3021 <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)
3022 Lua is creating a new object of that type.
3023 When <code>osize</code> is some other value,
3024 Lua is allocating memory for something else.
3028 Lua assumes the following behavior from the allocator function:
3032 When <code>nsize</code> is zero,
3033 the allocator must behave like <code>free</code>
3034 and return <code>NULL</code>.
3038 When <code>nsize</code> is not zero,
3039 the allocator must behave like <code>realloc</code>.
3040 The allocator returns <code>NULL</code>
3041 if and only if it cannot fulfill the request.
3042 Lua assumes that the allocator never fails when
3043 <code>osize >= nsize</code>.
3047 Here is a simple implementation for the allocator function.
3048 It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
3051 static void *l_alloc (void *ud, void *ptr, size_t osize,
3053 (void)ud; (void)osize; /* not used */
3059 return realloc(ptr, nsize);
3062 Note that Standard C ensures
3063 that <code>free(NULL)</code> has no effect and that
3064 <code>realloc(NULL,size)</code> is equivalent to <code>malloc(size)</code>.
3065 This code assumes that <code>realloc</code> does not fail when shrinking a block.
3066 (Although Standard C does not ensure this behavior,
3067 it seems to be a safe assumption.)
3073 <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p>
3074 <span class="apii">[-(2|1), +1, <em>e</em>]</span>
3075 <pre>void lua_arith (lua_State *L, int op);</pre>
3078 Performs an arithmetic or bitwise operation over the two values
3079 (or one, in the case of negations)
3080 at the top of the stack,
3081 with the value at the top being the second operand,
3082 pops these values, and pushes the result of the operation.
3083 The function follows the semantics of the corresponding Lua operator
3084 (that is, it may call metamethods).
3088 The value of <code>op</code> must be one of the following constants:
3092 <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li>
3093 <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li>
3094 <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li>
3095 <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs float division (<code>/</code>)</li>
3096 <li><b><a name="pdf-LUA_OPIDIV"><code>LUA_OPIDIV</code></a>: </b> performs floor division (<code>//</code>)</li>
3097 <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li>
3098 <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li>
3099 <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li>
3100 <li><b><a name="pdf-LUA_OPBNOT"><code>LUA_OPBNOT</code></a>: </b> performs bitwise negation (<code>~</code>)</li>
3101 <li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise and (<code>&</code>)</li>
3102 <li><b><a name="pdf-LUA_OPBOR"><code>LUA_OPBOR</code></a>: </b> performs bitwise or (<code>|</code>)</li>
3103 <li><b><a name="pdf-LUA_OPBXOR"><code>LUA_OPBXOR</code></a>: </b> performs bitwise exclusive or (<code>~</code>)</li>
3104 <li><b><a name="pdf-LUA_OPSHL"><code>LUA_OPSHL</code></a>: </b> performs left shift (<code><<</code>)</li>
3105 <li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>>></code>)</li>
3112 <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
3113 <span class="apii">[-0, +0, –]</span>
3114 <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
3117 Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>).
3123 <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
3124 <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span>
3125 <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
3132 To call a function you must use the following protocol:
3133 first, the function to be called is pushed onto the stack;
3134 then, the arguments to the function are pushed
3136 that is, the first argument is pushed first.
3137 Finally you call <a href="#lua_call"><code>lua_call</code></a>;
3138 <code>nargs</code> is the number of arguments that you pushed onto the stack.
3139 All arguments and the function value are popped from the stack
3140 when the function is called.
3141 The function results are pushed onto the stack when the function returns.
3142 The number of results is adjusted to <code>nresults</code>,
3143 unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
3144 In this case, all results from the function are pushed.
3145 Lua takes care that the returned values fit into the stack space.
3146 The function results are pushed onto the stack in direct order
3147 (the first result is pushed first),
3148 so that after the call the last result is on the top of the stack.
3152 Any error inside the called function is propagated upwards
3153 (with a <code>longjmp</code>).
3157 The following example shows how the host program can do the
3158 equivalent to this Lua code:
3161 a = f("how", t.x, 14)
3163 Here it is in C:
3166 lua_getglobal(L, "f"); /* function to be called */
3167 lua_pushliteral(L, "how"); /* 1st argument */
3168 lua_getglobal(L, "t"); /* table to be indexed */
3169 lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */
3170 lua_remove(L, -2); /* remove 't' from the stack */
3171 lua_pushinteger(L, 14); /* 3rd argument */
3172 lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */
3173 lua_setglobal(L, "a"); /* set global 'a' */
3175 Note that the code above is <em>balanced</em>:
3176 at its end, the stack is back to its original configuration.
3177 This is considered good programming practice.
3183 <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p>
3184 <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
3185 <pre>void lua_callk (lua_State *L,
3189 lua_KFunction k);</pre>
3192 This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>,
3193 but allows the called function to yield (see <a href="#4.7">§4.7</a>).
3199 <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
3200 <pre>typedef int (*lua_CFunction) (lua_State *L);</pre>
3203 Type for C functions.
3207 In order to communicate properly with Lua,
3208 a C function must use the following protocol,
3209 which defines the way parameters and results are passed:
3210 a C function receives its arguments from Lua in its stack
3211 in direct order (the first argument is pushed first).
3212 So, when the function starts,
3213 <code>lua_gettop(L)</code> returns the number of arguments received by the function.
3214 The first argument (if any) is at index 1
3215 and its last argument is at index <code>lua_gettop(L)</code>.
3216 To return values to Lua, a C function just pushes them onto the stack,
3217 in direct order (the first result is pushed first),
3218 and returns the number of results.
3219 Any other value in the stack below the results will be properly
3221 Like a Lua function, a C function called by Lua can also return
3226 As an example, the following function receives a variable number
3227 of numerical arguments and returns their average and their sum:
3230 static int foo (lua_State *L) {
3231 int n = lua_gettop(L); /* number of arguments */
3232 lua_Number sum = 0.0;
3234 for (i = 1; i <= n; i++) {
3235 if (!lua_isnumber(L, i)) {
3236 lua_pushliteral(L, "incorrect argument");
3239 sum += lua_tonumber(L, i);
3241 lua_pushnumber(L, sum/n); /* first result */
3242 lua_pushnumber(L, sum); /* second result */
3243 return 2; /* number of results */
3250 <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
3251 <span class="apii">[-0, +0, –]</span>
3252 <pre>int lua_checkstack (lua_State *L, int n);</pre>
3255 Ensures that the stack has space for at least <code>n</code> extra slots.
3256 It returns false if it cannot fulfill the request,
3257 either because it would cause the stack
3258 to be larger than a fixed maximum size
3259 (typically at least several thousand elements) or
3260 because it cannot allocate memory for the extra space.
3261 This function never shrinks the stack;
3262 if the stack is already larger than the new size,
3263 it is left unchanged.
3269 <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
3270 <span class="apii">[-0, +0, –]</span>
3271 <pre>void lua_close (lua_State *L);</pre>
3274 Destroys all objects in the given Lua state
3275 (calling the corresponding garbage-collection metamethods, if any)
3276 and frees all dynamic memory used by this state.
3277 On several platforms, you may not need to call this function,
3278 because all resources are naturally released when the host program ends.
3279 On the other hand, long-running programs that create multiple states,
3280 such as daemons or web servers,
3281 will probably need to close states as soon as they are not needed.
3287 <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p>
3288 <span class="apii">[-0, +0, <em>e</em>]</span>
3289 <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre>
3292 Compares two Lua values.
3293 Returns 1 if the value at index <code>index1</code> satisfies <code>op</code>
3294 when compared with the value at index <code>index2</code>,
3295 following the semantics of the corresponding Lua operator
3296 (that is, it may call metamethods).
3297 Otherwise returns 0.
3298 Also returns 0 if any of the indices is not valid.
3302 The value of <code>op</code> must be one of the following constants:
3306 <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li>
3307 <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li>
3308 <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li>
3315 <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
3316 <span class="apii">[-n, +1, <em>e</em>]</span>
3317 <pre>void lua_concat (lua_State *L, int n);</pre>
3320 Concatenates the <code>n</code> values at the top of the stack,
3321 pops them, and leaves the result at the top.
3322 If <code>n</code> is 1, the result is the single value on the stack
3323 (that is, the function does nothing);
3324 if <code>n</code> is 0, the result is the empty string.
3325 Concatenation is performed following the usual semantics of Lua
3326 (see <a href="#3.4.6">§3.4.6</a>).
3332 <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
3333 <span class="apii">[-0, +0, –]</span>
3334 <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre>
3337 Copies the element at index <code>fromidx</code>
3338 into the valid index <code>toidx</code>,
3339 replacing the value at that position.
3340 Values at other positions are not affected.
3346 <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
3347 <span class="apii">[-0, +1, <em>e</em>]</span>
3348 <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
3351 Creates a new empty table and pushes it onto the stack.
3352 Parameter <code>narr</code> is a hint for how many elements the table
3353 will have as a sequence;
3354 parameter <code>nrec</code> is a hint for how many other elements
3355 the table will have.
3356 Lua may use these hints to preallocate memory for the new table.
3357 This pre-allocation is useful for performance when you know in advance
3358 how many elements the table will have.
3359 Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
3365 <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
3366 <span class="apii">[-0, +0, <em>e</em>]</span>
3367 <pre>int lua_dump (lua_State *L,
3373 Dumps a function as a binary chunk.
3374 Receives a Lua function on the top of the stack
3375 and produces a binary chunk that,
3377 results in a function equivalent to the one dumped.
3378 As it produces parts of the chunk,
3379 <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
3380 with the given <code>data</code>
3385 If <code>strip</code> is true,
3386 the binary representation is created without debug information
3391 The value returned is the error code returned by the last
3393 0 means no errors.
3397 This function does not pop the Lua function from the stack.
3403 <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
3404 <span class="apii">[-1, +0, <em>v</em>]</span>
3405 <pre>int lua_error (lua_State *L);</pre>
3408 Generates a Lua error,
3409 using the value at the top of the stack as the error object.
3410 This function does a long jump,
3411 and therefore never returns
3412 (see <a href="#luaL_error"><code>luaL_error</code></a>).
3418 <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
3419 <span class="apii">[-0, +0, <em>e</em>]</span>
3420 <pre>int lua_gc (lua_State *L, int what, int data);</pre>
3423 Controls the garbage collector.
3427 This function performs several tasks,
3428 according to the value of the parameter <code>what</code>:
3432 <li><b><code>LUA_GCSTOP</code>: </b>
3433 stops the garbage collector.
3436 <li><b><code>LUA_GCRESTART</code>: </b>
3437 restarts the garbage collector.
3440 <li><b><code>LUA_GCCOLLECT</code>: </b>
3441 performs a full garbage-collection cycle.
3444 <li><b><code>LUA_GCCOUNT</code>: </b>
3445 returns the current amount of memory (in Kbytes) in use by Lua.
3448 <li><b><code>LUA_GCCOUNTB</code>: </b>
3449 returns the remainder of dividing the current amount of bytes of
3450 memory in use by Lua by 1024.
3453 <li><b><code>LUA_GCSTEP</code>: </b>
3454 performs an incremental step of garbage collection.
3457 <li><b><code>LUA_GCSETPAUSE</code>: </b>
3458 sets <code>data</code> as the new value
3459 for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>)
3460 and returns the previous value of the pause.
3463 <li><b><code>LUA_GCSETSTEPMUL</code>: </b>
3464 sets <code>data</code> as the new value for the <em>step multiplier</em> of
3465 the collector (see <a href="#2.5">§2.5</a>)
3466 and returns the previous value of the step multiplier.
3469 <li><b><code>LUA_GCISRUNNING</code>: </b>
3470 returns a boolean that tells whether the collector is running
3471 (i.e., not stopped).
3477 For more details about these options,
3478 see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>.
3484 <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
3485 <span class="apii">[-0, +0, –]</span>
3486 <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre>
3489 Returns the memory-allocation function of a given state.
3490 If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
3491 opaque pointer given when the memory-allocator function was set.
3497 <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
3498 <span class="apii">[-0, +1, <em>e</em>]</span>
3499 <pre>int lua_getfield (lua_State *L, int index, const char *k);</pre>
3502 Pushes onto the stack the value <code>t[k]</code>,
3503 where <code>t</code> is the value at the given index.
3504 As in Lua, this function may trigger a metamethod
3505 for the "index" event (see <a href="#2.4">§2.4</a>).
3509 Returns the type of the pushed value.
3515 <hr><h3><a name="lua_getextraspace"><code>lua_getextraspace</code></a></h3><p>
3516 <span class="apii">[-0, +0, –]</span>
3517 <pre>void *lua_getextraspace (lua_State *L);</pre>
3520 Returns a pointer to a raw memory area associated with the
3522 The application can use this area for any purpose;
3523 Lua does not use it for anything.
3527 Each new thread has this area initialized with a copy
3528 of the area of the main thread.
3532 By default, this area has the size of a pointer to void,
3533 but you can recompile Lua with a different size for this area.
3534 (See <code>LUA_EXTRASPACE</code> in <code>luaconf.h</code>.)
3540 <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
3541 <span class="apii">[-0, +1, <em>e</em>]</span>
3542 <pre>int lua_getglobal (lua_State *L, const char *name);</pre>
3545 Pushes onto the stack the value of the global <code>name</code>.
3546 Returns the type of that value.
3552 <hr><h3><a name="lua_geti"><code>lua_geti</code></a></h3><p>
3553 <span class="apii">[-0, +1, <em>e</em>]</span>
3554 <pre>int lua_geti (lua_State *L, int index, lua_Integer i);</pre>
3557 Pushes onto the stack the value <code>t[i]</code>,
3558 where <code>t</code> is the value at the given index.
3559 As in Lua, this function may trigger a metamethod
3560 for the "index" event (see <a href="#2.4">§2.4</a>).
3564 Returns the type of the pushed value.
3570 <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
3571 <span class="apii">[-0, +(0|1), –]</span>
3572 <pre>int lua_getmetatable (lua_State *L, int index);</pre>
3575 If the value at the given index has a metatable,
3576 the function pushes that metatable onto the stack and returns 1.
3578 the function returns 0 and pushes nothing on the stack.
3584 <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
3585 <span class="apii">[-1, +1, <em>e</em>]</span>
3586 <pre>int lua_gettable (lua_State *L, int index);</pre>
3589 Pushes onto the stack the value <code>t[k]</code>,
3590 where <code>t</code> is the value at the given index
3591 and <code>k</code> is the value at the top of the stack.
3595 This function pops the key from the stack,
3596 pushing the resulting value in its place.
3597 As in Lua, this function may trigger a metamethod
3598 for the "index" event (see <a href="#2.4">§2.4</a>).
3602 Returns the type of the pushed value.
3608 <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
3609 <span class="apii">[-0, +0, –]</span>
3610 <pre>int lua_gettop (lua_State *L);</pre>
3613 Returns the index of the top element in the stack.
3614 Because indices start at 1,
3615 this result is equal to the number of elements in the stack;
3616 in particular, 0 means an empty stack.
3622 <hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p>
3623 <span class="apii">[-0, +1, –]</span>
3624 <pre>int lua_getuservalue (lua_State *L, int index);</pre>
3627 Pushes onto the stack the Lua value associated with the userdata
3632 Returns the type of the pushed value.
3638 <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
3639 <span class="apii">[-1, +1, –]</span>
3640 <pre>void lua_insert (lua_State *L, int index);</pre>
3643 Moves the top element into the given valid index,
3644 shifting up the elements above this index to open space.
3645 This function cannot be called with a pseudo-index,
3646 because a pseudo-index is not an actual stack position.
3652 <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
3653 <pre>typedef ... lua_Integer;</pre>
3656 The type of integers in Lua.
3660 By default this type is <code>long long</code>,
3661 (usually a 64-bit two-complement integer),
3662 but that can be changed to <code>long</code> or <code>int</code>
3663 (usually a 32-bit two-complement integer).
3664 (See <code>LUA_INT</code> in <code>luaconf.h</code>.)
3668 Lua also defines the constants
3669 <a name="pdf-LUA_MININTEGER"><code>LUA_MININTEGER</code></a> and <a name="pdf-LUA_MAXINTEGER"><code>LUA_MAXINTEGER</code></a>,
3670 with the minimum and the maximum values that fit in this type.
3676 <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
3677 <span class="apii">[-0, +0, –]</span>
3678 <pre>int lua_isboolean (lua_State *L, int index);</pre>
3681 Returns 1 if the value at the given index is a boolean,
3682 and 0 otherwise.
3688 <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
3689 <span class="apii">[-0, +0, –]</span>
3690 <pre>int lua_iscfunction (lua_State *L, int index);</pre>
3693 Returns 1 if the value at the given index is a C function,
3694 and 0 otherwise.
3700 <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
3701 <span class="apii">[-0, +0, –]</span>
3702 <pre>int lua_isfunction (lua_State *L, int index);</pre>
3705 Returns 1 if the value at the given index is a function
3706 (either C or Lua), and 0 otherwise.
3712 <hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p>
3713 <span class="apii">[-0, +0, –]</span>
3714 <pre>int lua_isinteger (lua_State *L, int index);</pre>
3717 Returns 1 if the value at the given index is an integer
3718 (that is, the value is a number and is represented as an integer),
3719 and 0 otherwise.
3725 <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
3726 <span class="apii">[-0, +0, –]</span>
3727 <pre>int lua_islightuserdata (lua_State *L, int index);</pre>
3730 Returns 1 if the value at the given index is a light userdata,
3731 and 0 otherwise.
3737 <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
3738 <span class="apii">[-0, +0, –]</span>
3739 <pre>int lua_isnil (lua_State *L, int index);</pre>
3742 Returns 1 if the value at the given index is <b>nil</b>,
3743 and 0 otherwise.
3749 <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
3750 <span class="apii">[-0, +0, –]</span>
3751 <pre>int lua_isnone (lua_State *L, int index);</pre>
3754 Returns 1 if the given index is not valid,
3755 and 0 otherwise.
3761 <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
3762 <span class="apii">[-0, +0, –]</span>
3763 <pre>int lua_isnoneornil (lua_State *L, int index);</pre>
3766 Returns 1 if the given index is not valid
3767 or if the value at this index is <b>nil</b>,
3768 and 0 otherwise.
3774 <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
3775 <span class="apii">[-0, +0, –]</span>
3776 <pre>int lua_isnumber (lua_State *L, int index);</pre>
3779 Returns 1 if the value at the given index is a number
3780 or a string convertible to a number,
3781 and 0 otherwise.
3787 <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
3788 <span class="apii">[-0, +0, –]</span>
3789 <pre>int lua_isstring (lua_State *L, int index);</pre>
3792 Returns 1 if the value at the given index is a string
3793 or a number (which is always convertible to a string),
3794 and 0 otherwise.
3800 <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
3801 <span class="apii">[-0, +0, –]</span>
3802 <pre>int lua_istable (lua_State *L, int index);</pre>
3805 Returns 1 if the value at the given index is a table,
3806 and 0 otherwise.
3812 <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
3813 <span class="apii">[-0, +0, –]</span>
3814 <pre>int lua_isthread (lua_State *L, int index);</pre>
3817 Returns 1 if the value at the given index is a thread,
3818 and 0 otherwise.
3824 <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
3825 <span class="apii">[-0, +0, –]</span>
3826 <pre>int lua_isuserdata (lua_State *L, int index);</pre>
3829 Returns 1 if the value at the given index is a userdata
3830 (either full or light), and 0 otherwise.
3836 <hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p>
3837 <span class="apii">[-0, +0, –]</span>
3838 <pre>int lua_isyieldable (lua_State *L);</pre>
3841 Returns 1 if the given coroutine can yield,
3842 and 0 otherwise.
3848 <hr><h3><a name="lua_KContext"><code>lua_KContext</code></a></h3>
3849 <pre>typedef ... lua_KContext;</pre>
3852 The type for continuation-function contexts.
3853 It must be a numerical type.
3854 This type is defined as <code>intptr_t</code>
3855 when <code>intptr_t</code> is available,
3856 so that it can store pointers too.
3857 Otherwise, it is defined as <code>ptrdiff_t</code>.
3863 <hr><h3><a name="lua_KFunction"><code>lua_KFunction</code></a></h3>
3864 <pre>typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);</pre>
3867 Type for continuation functions (see <a href="#4.7">§4.7</a>).
3873 <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p>
3874 <span class="apii">[-0, +1, <em>e</em>]</span>
3875 <pre>void lua_len (lua_State *L, int index);</pre>
3878 Returns the length of the value at the given index.
3879 It is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>) and
3880 may trigger a metamethod for the "length" event (see <a href="#2.4">§2.4</a>).
3881 The result is pushed on the stack.
3887 <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
3888 <span class="apii">[-0, +1, –]</span>
3889 <pre>int lua_load (lua_State *L,
3892 const char *chunkname,
3893 const char *mode);</pre>
3896 Loads a Lua chunk without running it.
3897 If there are no errors,
3898 <code>lua_load</code> pushes the compiled chunk as a Lua
3899 function on top of the stack.
3900 Otherwise, it pushes an error message.
3904 The return values of <code>lua_load</code> are:
3908 <li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li>
3910 <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b>
3911 syntax error during precompilation;</li>
3913 <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
3914 memory allocation error;</li>
3916 <li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
3917 error while running a <code>__gc</code> metamethod.
3918 (This error has no relation with the chunk being loaded.
3919 It is generated by the garbage collector.)
3925 The <code>lua_load</code> function uses a user-supplied <code>reader</code> function
3926 to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
3927 The <code>data</code> argument is an opaque value passed to the reader function.
3931 The <code>chunkname</code> argument gives a name to the chunk,
3932 which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>).
3936 <code>lua_load</code> automatically detects whether the chunk is text or binary
3937 and loads it accordingly (see program <code>luac</code>).
3938 The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>,
3939 with the addition that
3940 a <code>NULL</code> value is equivalent to the string "<code>bt</code>".
3944 <code>lua_load</code> uses the stack internally,
3945 so the reader function must always leave the stack
3946 unmodified when returning.
3950 If the resulting function has upvalues,
3951 its first upvalue is set to the value of the global environment
3952 stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>).
3953 When loading main chunks,
3954 this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
3955 Other upvalues are initialized with <b>nil</b>.
3961 <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
3962 <span class="apii">[-0, +0, –]</span>
3963 <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre>
3966 Creates a new thread running in a new, independent state.
3967 Returns <code>NULL</code> if it cannot create the thread or the state
3968 (due to lack of memory).
3969 The argument <code>f</code> is the allocator function;
3970 Lua does all memory allocation for this state through this function.
3971 The second argument, <code>ud</code>, is an opaque pointer that Lua
3972 passes to the allocator in every call.
3978 <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
3979 <span class="apii">[-0, +1, <em>e</em>]</span>
3980 <pre>void lua_newtable (lua_State *L);</pre>
3983 Creates a new empty table and pushes it onto the stack.
3984 It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
3990 <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
3991 <span class="apii">[-0, +1, <em>e</em>]</span>
3992 <pre>lua_State *lua_newthread (lua_State *L);</pre>
3995 Creates a new thread, pushes it on the stack,
3996 and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
3997 The new thread returned by this function shares with the original thread
3998 its global environment,
3999 but has an independent execution stack.
4003 There is no explicit function to close or to destroy a thread.
4004 Threads are subject to garbage collection,
4005 like any Lua object.
4011 <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p>
4012 <span class="apii">[-0, +1, <em>e</em>]</span>
4013 <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre>
4016 This function allocates a new block of memory with the given size,
4017 pushes onto the stack a new full userdata with the block address,
4018 and returns this address.
4019 The host program can freely use this memory.
4025 <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
4026 <span class="apii">[-1, +(2|0), <em>e</em>]</span>
4027 <pre>int lua_next (lua_State *L, int index);</pre>
4030 Pops a key from the stack,
4031 and pushes a key–value pair from the table at the given index
4032 (the "next" pair after the given key).
4033 If there are no more elements in the table,
4034 then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing).
4038 A typical traversal looks like this:
4041 /* table is in the stack at index 't' */
4042 lua_pushnil(L); /* first key */
4043 while (lua_next(L, t) != 0) {
4044 /* uses 'key' (at index -2) and 'value' (at index -1) */
4046 lua_typename(L, lua_type(L, -2)),
4047 lua_typename(L, lua_type(L, -1)));
4048 /* removes 'value'; keeps 'key' for next iteration */
4054 While traversing a table,
4055 do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
4056 unless you know that the key is actually a string.
4057 Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change
4058 the value at the given index;
4059 this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
4063 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
4064 the table during its traversal.
4070 <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
4071 <pre>typedef double lua_Number;</pre>
4074 The type of floats in Lua.
4078 By default this type is double,
4079 but that can be changed to a single float.
4080 (See <code>LUA_REAL</code> in <code>luaconf.h</code>.)
4086 <hr><h3><a name="lua_numbertointeger"><code>lua_numbertointeger</code></a></h3>
4087 <pre>int lua_numbertointeger (lua_Number n, lua_Integer *p);</pre>
4090 Converts a Lua float to a Lua integer.
4091 This macro assumes that <code>n</code> has an integral value.
4092 If that value is within the range of Lua integers,
4093 it is converted to an integer and assigned to <code>*p</code>.
4094 The macro results in a boolean indicating whether the
4095 conversion was successful.
4096 (Note that this range test can be tricky to do
4097 correctly without this macro,
4102 This macro may evaluate its arguments more than once.
4108 <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
4109 <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
4110 <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre>
4113 Calls a function in protected mode.
4117 Both <code>nargs</code> and <code>nresults</code> have the same meaning as
4118 in <a href="#lua_call"><code>lua_call</code></a>.
4119 If there are no errors during the call,
4120 <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
4121 However, if there is any error,
4122 <a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
4123 pushes a single value on the stack (the error message),
4124 and returns an error code.
4125 Like <a href="#lua_call"><code>lua_call</code></a>,
4126 <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
4127 and its arguments from the stack.
4131 If <code>msgh</code> is 0,
4132 then the error message returned on the stack
4133 is exactly the original error message.
4134 Otherwise, <code>msgh</code> is the stack index of a
4135 <em>message handler</em>.
4136 (In the current implementation, this index cannot be a pseudo-index.)
4137 In case of runtime errors,
4138 this function will be called with the error message
4139 and its return value will be the message
4140 returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
4144 Typically, the message handler is used to add more debug
4145 information to the error message, such as a stack traceback.
4146 Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
4147 since by then the stack has unwound.
4151 The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following constants
4152 (defined in <code>lua.h</code>):
4156 <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b>
4159 <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b>
4163 <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
4164 memory allocation error.
4165 For such errors, Lua does not call the message handler.
4168 <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b>
4169 error while running the message handler.
4172 <li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
4173 error while running a <code>__gc</code> metamethod.
4174 (This error typically has no relation with the function being called.)
4182 <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p>
4183 <span class="apii">[-(nargs + 1), +(nresults|1), –]</span>
4184 <pre>int lua_pcallk (lua_State *L,
4189 lua_KFunction k);</pre>
4192 This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>,
4193 but allows the called function to yield (see <a href="#4.7">§4.7</a>).
4199 <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
4200 <span class="apii">[-n, +0, –]</span>
4201 <pre>void lua_pop (lua_State *L, int n);</pre>
4204 Pops <code>n</code> elements from the stack.
4210 <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
4211 <span class="apii">[-0, +1, –]</span>
4212 <pre>void lua_pushboolean (lua_State *L, int b);</pre>
4215 Pushes a boolean value with value <code>b</code> onto the stack.
4221 <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
4222 <span class="apii">[-n, +1, <em>e</em>]</span>
4223 <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
4226 Pushes a new C closure onto the stack.
4230 When a C function is created,
4231 it is possible to associate some values with it,
4232 thus creating a C closure (see <a href="#4.4">§4.4</a>);
4233 these values are then accessible to the function whenever it is called.
4234 To associate values with a C function,
4235 first these values must be pushed onto the stack
4236 (when there are multiple values, the first value is pushed first).
4237 Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
4238 is called to create and push the C function onto the stack,
4239 with the argument <code>n</code> telling how many values will be
4240 associated with the function.
4241 <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
4245 The maximum value for <code>n</code> is 255.
4249 When <code>n</code> is zero,
4250 this function creates a <em>light C function</em>,
4251 which is just a pointer to the C function.
4252 In that case, it never raises a memory error.
4258 <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
4259 <span class="apii">[-0, +1, –]</span>
4260 <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
4263 Pushes a C function onto the stack.
4264 This function receives a pointer to a C function
4265 and pushes onto the stack a Lua value of type <code>function</code> that,
4266 when called, invokes the corresponding C function.
4270 Any function to be registered in Lua must
4271 follow the correct protocol to receive its parameters
4272 and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
4276 <code>lua_pushcfunction</code> is defined as a macro:
4279 #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
4281 Note that <code>f</code> is used twice.
4287 <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
4288 <span class="apii">[-0, +1, <em>e</em>]</span>
4289 <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre>
4292 Pushes onto the stack a formatted string
4293 and returns a pointer to this string.
4294 It is similar to the ISO C function <code>sprintf</code>,
4295 but has some important differences:
4300 You do not have to allocate space for the result:
4301 the result is a Lua string and Lua takes care of memory allocation
4302 (and deallocation, through garbage collection).
4306 The conversion specifiers are quite restricted.
4307 There are no flags, widths, or precisions.
4308 The conversion specifiers can only be
4309 '<code>%%</code>' (inserts the character '<code>%</code>'),
4310 '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
4311 '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
4312 '<code>%L</code>' (inserts a <a href="#lua_Integer"><code>lua_Integer</code></a>),
4313 '<code>%p</code>' (inserts a pointer as a hexadecimal numeral),
4314 '<code>%d</code>' (inserts an <code>int</code>),
4315 '<code>%c</code>' (inserts an <code>int</code> as a one-byte character), and
4316 '<code>%U</code>' (inserts a <code>long int</code> as a UTF-8 byte sequence).
4324 <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
4325 <span class="apii">[-0, +1, –]</span>
4326 <pre>void lua_pushglobaltable (lua_State *L);</pre>
4329 Pushes the global environment onto the stack.
4335 <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
4336 <span class="apii">[-0, +1, –]</span>
4337 <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
4340 Pushes an integer with value <code>n</code> onto the stack.
4346 <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
4347 <span class="apii">[-0, +1, –]</span>
4348 <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
4351 Pushes a light userdata onto the stack.
4355 Userdata represent C values in Lua.
4356 A <em>light userdata</em> represents a pointer, a <code>void*</code>.
4357 It is a value (like a number):
4358 you do not create it, it has no individual metatable,
4359 and it is not collected (as it was never created).
4360 A light userdata is equal to "any"
4361 light userdata with the same C address.
4367 <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
4368 <span class="apii">[-0, +1, <em>e</em>]</span>
4369 <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre>
4372 This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
4373 but can be used only when <code>s</code> is a literal string.
4374 It automatically provides the string length.
4380 <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
4381 <span class="apii">[-0, +1, <em>e</em>]</span>
4382 <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre>
4385 Pushes the string pointed to by <code>s</code> with size <code>len</code>
4387 Lua makes (or reuses) an internal copy of the given string,
4388 so the memory at <code>s</code> can be freed or reused immediately after
4389 the function returns.
4390 The string can contain any binary data,
4391 including embedded zeros.
4395 Returns a pointer to the internal copy of the string.
4401 <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
4402 <span class="apii">[-0, +1, –]</span>
4403 <pre>void lua_pushnil (lua_State *L);</pre>
4406 Pushes a nil value onto the stack.
4412 <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
4413 <span class="apii">[-0, +1, –]</span>
4414 <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
4417 Pushes a float with value <code>n</code> onto the stack.
4423 <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
4424 <span class="apii">[-0, +1, <em>e</em>]</span>
4425 <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre>
4428 Pushes the zero-terminated string pointed to by <code>s</code>
4430 Lua makes (or reuses) an internal copy of the given string,
4431 so the memory at <code>s</code> can be freed or reused immediately after
4432 the function returns.
4436 Returns a pointer to the internal copy of the string.
4440 If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>.
4446 <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
4447 <span class="apii">[-0, +1, –]</span>
4448 <pre>int lua_pushthread (lua_State *L);</pre>
4451 Pushes the thread represented by <code>L</code> onto the stack.
4452 Returns 1 if this thread is the main thread of its state.
4458 <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
4459 <span class="apii">[-0, +1, –]</span>
4460 <pre>void lua_pushvalue (lua_State *L, int index);</pre>
4463 Pushes a copy of the element at the given index
4470 <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
4471 <span class="apii">[-0, +1, <em>e</em>]</span>
4472 <pre>const char *lua_pushvfstring (lua_State *L,
4474 va_list argp);</pre>
4477 Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
4478 instead of a variable number of arguments.
4484 <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
4485 <span class="apii">[-0, +0, –]</span>
4486 <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
4489 Returns 1 if the two values in indices <code>index1</code> and
4490 <code>index2</code> are primitively equal
4491 (that is, without calling metamethods).
4492 Otherwise returns 0.
4493 Also returns 0 if any of the indices are not valid.
4499 <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
4500 <span class="apii">[-1, +1, –]</span>
4501 <pre>int lua_rawget (lua_State *L, int index);</pre>
4504 Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
4505 (i.e., without metamethods).
4511 <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
4512 <span class="apii">[-0, +1, –]</span>
4513 <pre>int lua_rawgeti (lua_State *L, int index, lua_Integer n);</pre>
4516 Pushes onto the stack the value <code>t[n]</code>,
4517 where <code>t</code> is the table at the given index.
4519 that is, it does not invoke metamethods.
4523 Returns the type of the pushed value.
4529 <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p>
4530 <span class="apii">[-0, +1, –]</span>
4531 <pre>int lua_rawgetp (lua_State *L, int index, const void *p);</pre>
4534 Pushes onto the stack the value <code>t[k]</code>,
4535 where <code>t</code> is the table at the given index and
4536 <code>k</code> is the pointer <code>p</code> represented as a light userdata.
4538 that is, it does not invoke metamethods.
4542 Returns the type of the pushed value.
4548 <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p>
4549 <span class="apii">[-0, +0, –]</span>
4550 <pre>size_t lua_rawlen (lua_State *L, int index);</pre>
4553 Returns the raw "length" of the value at the given index:
4554 for strings, this is the string length;
4555 for tables, this is the result of the length operator ('<code>#</code>')
4556 with no metamethods;
4557 for userdata, this is the size of the block of memory allocated
4559 for other values, it is 0.
4565 <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
4566 <span class="apii">[-2, +0, <em>e</em>]</span>
4567 <pre>void lua_rawset (lua_State *L, int index);</pre>
4570 Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
4571 (i.e., without metamethods).
4577 <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
4578 <span class="apii">[-1, +0, <em>e</em>]</span>
4579 <pre>void lua_rawseti (lua_State *L, int index, lua_Integer i);</pre>
4582 Does the equivalent of <code>t[i] = v</code>,
4583 where <code>t</code> is the table at the given index
4584 and <code>v</code> is the value at the top of the stack.
4588 This function pops the value from the stack.
4589 The assignment is raw;
4590 that is, it does not invoke metamethods.
4596 <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
4597 <span class="apii">[-1, +0, <em>e</em>]</span>
4598 <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre>
4601 Does the equivalent of <code>t[k] = v</code>,
4602 where <code>t</code> is the table at the given index,
4603 <code>k</code> is the pointer <code>p</code> represented as a light userdata,
4604 and <code>v</code> is the value at the top of the stack.
4608 This function pops the value from the stack.
4609 The assignment is raw;
4610 that is, it does not invoke metamethods.
4616 <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
4617 <pre>typedef const char * (*lua_Reader) (lua_State *L,
4619 size_t *size);</pre>
4622 The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
4623 Every time it needs another piece of the chunk,
4624 <a href="#lua_load"><code>lua_load</code></a> calls the reader,
4625 passing along its <code>data</code> parameter.
4626 The reader must return a pointer to a block of memory
4627 with a new piece of the chunk
4628 and set <code>size</code> to the block size.
4629 The block must exist until the reader function is called again.
4630 To signal the end of the chunk,
4631 the reader must return <code>NULL</code> or set <code>size</code> to zero.
4632 The reader function may return pieces of any size greater than zero.
4638 <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
4639 <span class="apii">[-0, +0, <em>e</em>]</span>
4640 <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre>
4643 Sets the C function <code>f</code> as the new value of global <code>name</code>.
4644 It is defined as a macro:
4647 #define lua_register(L,n,f) \
4648 (lua_pushcfunction(L, f), lua_setglobal(L, n))
4654 <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
4655 <span class="apii">[-1, +0, –]</span>
4656 <pre>void lua_remove (lua_State *L, int index);</pre>
4659 Removes the element at the given valid index,
4660 shifting down the elements above this index to fill the gap.
4661 This function cannot be called with a pseudo-index,
4662 because a pseudo-index is not an actual stack position.
4668 <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
4669 <span class="apii">[-1, +0, –]</span>
4670 <pre>void lua_replace (lua_State *L, int index);</pre>
4673 Moves the top element into the given valid index
4674 without shifting any element
4675 (therefore replacing the value at the given index),
4676 and then pops the top element.
4682 <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
4683 <span class="apii">[-?, +?, –]</span>
4684 <pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre>
4687 Starts and resumes a coroutine in a given thread.
4691 To start a coroutine,
4692 you push onto the thread stack the main function plus any arguments;
4693 then you call <a href="#lua_resume"><code>lua_resume</code></a>,
4694 with <code>nargs</code> being the number of arguments.
4695 This call returns when the coroutine suspends or finishes its execution.
4696 When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
4697 or all values returned by the body function.
4698 <a href="#lua_resume"><code>lua_resume</code></a> returns
4699 <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
4700 <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution
4702 or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
4707 the stack is not unwound,
4708 so you can use the debug API over it.
4709 The error message is on the top of the stack.
4713 To resume a coroutine,
4714 you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>,
4715 put on its stack only the values to
4716 be passed as results from <code>yield</code>,
4717 and then call <a href="#lua_resume"><code>lua_resume</code></a>.
4721 The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>.
4722 If there is no such coroutine,
4723 this parameter can be <code>NULL</code>.
4729 <hr><h3><a name="lua_rotate"><code>lua_rotate</code></a></h3><p>
4730 <span class="apii">[-0, +0, –]</span>
4731 <pre>void lua_rotate (lua_State *L, int idx, int n);</pre>
4734 Rotates the stack elements from <code>idx</code> to the top <code>n</code> positions
4735 in the direction of the top, for a positive <code>n</code>,
4736 or <code>-n</code> positions in the direction of the bottom,
4737 for a negative <code>n</code>.
4738 The absolute value of <code>n</code> must not be greater than the size
4739 of the slice being rotated.
4745 <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
4746 <span class="apii">[-0, +0, –]</span>
4747 <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre>
4750 Changes the allocator function of a given state to <code>f</code>
4751 with user data <code>ud</code>.
4757 <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
4758 <span class="apii">[-1, +0, <em>e</em>]</span>
4759 <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
4762 Does the equivalent to <code>t[k] = v</code>,
4763 where <code>t</code> is the value at the given index
4764 and <code>v</code> is the value at the top of the stack.
4768 This function pops the value from the stack.
4769 As in Lua, this function may trigger a metamethod
4770 for the "newindex" event (see <a href="#2.4">§2.4</a>).
4776 <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
4777 <span class="apii">[-1, +0, <em>e</em>]</span>
4778 <pre>void lua_setglobal (lua_State *L, const char *name);</pre>
4781 Pops a value from the stack and
4782 sets it as the new value of global <code>name</code>.
4788 <hr><h3><a name="lua_seti"><code>lua_seti</code></a></h3><p>
4789 <span class="apii">[-1, +0, <em>e</em>]</span>
4790 <pre>void lua_seti (lua_State *L, int index, lua_Integer n);</pre>
4793 Does the equivalent to <code>t[n] = v</code>,
4794 where <code>t</code> is the value at the given index
4795 and <code>v</code> is the value at the top of the stack.
4799 This function pops the value from the stack.
4800 As in Lua, this function may trigger a metamethod
4801 for the "newindex" event (see <a href="#2.4">§2.4</a>).
4807 <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
4808 <span class="apii">[-1, +0, –]</span>
4809 <pre>void lua_setmetatable (lua_State *L, int index);</pre>
4812 Pops a table from the stack and
4813 sets it as the new metatable for the value at the given index.
4819 <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
4820 <span class="apii">[-2, +0, <em>e</em>]</span>
4821 <pre>void lua_settable (lua_State *L, int index);</pre>
4824 Does the equivalent to <code>t[k] = v</code>,
4825 where <code>t</code> is the value at the given index,
4826 <code>v</code> is the value at the top of the stack,
4827 and <code>k</code> is the value just below the top.
4831 This function pops both the key and the value from the stack.
4832 As in Lua, this function may trigger a metamethod
4833 for the "newindex" event (see <a href="#2.4">§2.4</a>).
4839 <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
4840 <span class="apii">[-?, +?, –]</span>
4841 <pre>void lua_settop (lua_State *L, int index);</pre>
4844 Accepts any index, or 0,
4845 and sets the stack top to this index.
4846 If the new top is larger than the old one,
4847 then the new elements are filled with <b>nil</b>.
4848 If <code>index</code> is 0, then all stack elements are removed.
4854 <hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p>
4855 <span class="apii">[-1, +0, –]</span>
4856 <pre>void lua_setuservalue (lua_State *L, int index);</pre>
4859 Pops a value from the stack and sets it as
4860 the new value associated to the userdata at the given index.
4866 <hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
4867 <pre>typedef struct lua_State lua_State;</pre>
4870 An opaque structure that points to a thread and indirectly
4871 (through the thread) to the whole state of a Lua interpreter.
4872 The Lua library is fully reentrant:
4873 it has no global variables.
4874 All information about a state is accessible through this structure.
4878 A pointer to this structure must be passed as the first argument to
4879 every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
4880 which creates a Lua state from scratch.
4886 <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
4887 <span class="apii">[-0, +0, –]</span>
4888 <pre>int lua_status (lua_State *L);</pre>
4891 Returns the status of the thread <code>L</code>.
4895 The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread,
4896 an error code if the thread finished the execution
4897 of a <a href="#lua_resume"><code>lua_resume</code></a> with an error,
4898 or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
4902 You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>.
4903 You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
4904 (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a>
4905 (to resume a coroutine).
4911 <hr><h3><a name="lua_stringtonumber"><code>lua_stringtonumber</code></a></h3><p>
4912 <span class="apii">[-0, +1, –]</span>
4913 <pre>size_t lua_stringtonumber (lua_State *L, const char *s);</pre>
4916 Converts the zero-terminated string <code>s</code> to a number,
4917 pushes that number into the stack,
4918 and returns the total size of the string,
4919 that is, its length plus one.
4920 The conversion can result in an integer or a float,
4921 according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>).
4922 The string may have leading and trailing spaces and a sign.
4923 If the string is not a valid numeral,
4924 returns 0 and pushes nothing.
4925 (Note that the result can be used as a boolean,
4926 true if the conversion succeeds.)
4932 <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
4933 <span class="apii">[-0, +0, –]</span>
4934 <pre>int lua_toboolean (lua_State *L, int index);</pre>
4937 Converts the Lua value at the given index to a C boolean
4938 value (0 or 1).
4939 Like all tests in Lua,
4940 <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value
4941 different from <b>false</b> and <b>nil</b>;
4942 otherwise it returns false.
4943 (If you want to accept only actual boolean values,
4944 use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
4950 <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
4951 <span class="apii">[-0, +0, –]</span>
4952 <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
4955 Converts a value at the given index to a C function.
4956 That value must be a C function;
4957 otherwise, returns <code>NULL</code>.
4963 <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
4964 <span class="apii">[-0, +0, –]</span>
4965 <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
4968 Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4974 <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p>
4975 <span class="apii">[-0, +0, –]</span>
4976 <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre>
4979 Converts the Lua value at the given index
4980 to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
4981 The Lua value must be an integer,
4982 or a number or string convertible to an integer (see <a href="#3.4.3">§3.4.3</a>);
4983 otherwise, <code>lua_tointegerx</code> returns 0.
4987 If <code>isnum</code> is not <code>NULL</code>,
4988 its referent is assigned a boolean value that
4989 indicates whether the operation succeeded.
4995 <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
4996 <span class="apii">[-0, +0, <em>e</em>]</span>
4997 <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre>
5000 Converts the Lua value at the given index to a C string.
5001 If <code>len</code> is not <code>NULL</code>,
5002 it also sets <code>*len</code> with the string length.
5003 The Lua value must be a string or a number;
5004 otherwise, the function returns <code>NULL</code>.
5005 If the value is a number,
5006 then <code>lua_tolstring</code> also
5007 <em>changes the actual value in the stack to a string</em>.
5008 (This change confuses <a href="#lua_next"><code>lua_next</code></a>
5009 when <code>lua_tolstring</code> is applied to keys during a table traversal.)
5013 <code>lua_tolstring</code> returns a fully aligned pointer
5014 to a string inside the Lua state.
5015 This string always has a zero ('<code>\0</code>')
5016 after its last character (as in C),
5017 but can contain other zeros in its body.
5021 Because Lua has garbage collection,
5022 there is no guarantee that the pointer returned by <code>lua_tolstring</code>
5023 will be valid after the corresponding Lua value is removed from the stack.
5029 <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
5030 <span class="apii">[-0, +0, –]</span>
5031 <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
5034 Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
5040 <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p>
5041 <span class="apii">[-0, +0, –]</span>
5042 <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre>
5045 Converts the Lua value at the given index
5046 to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
5047 The Lua value must be a number or a string convertible to a number
5048 (see <a href="#3.4.3">§3.4.3</a>);
5049 otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0.
5053 If <code>isnum</code> is not <code>NULL</code>,
5054 its referent is assigned a boolean value that
5055 indicates whether the operation succeeded.
5061 <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
5062 <span class="apii">[-0, +0, –]</span>
5063 <pre>const void *lua_topointer (lua_State *L, int index);</pre>
5066 Converts the value at the given index to a generic
5067 C pointer (<code>void*</code>).
5068 The value can be a userdata, a table, a thread, or a function;
5069 otherwise, <code>lua_topointer</code> returns <code>NULL</code>.
5070 Different objects will give different pointers.
5071 There is no way to convert the pointer back to its original value.
5075 Typically this function is used only for debug information.
5081 <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
5082 <span class="apii">[-0, +0, <em>e</em>]</span>
5083 <pre>const char *lua_tostring (lua_State *L, int index);</pre>
5086 Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
5092 <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
5093 <span class="apii">[-0, +0, –]</span>
5094 <pre>lua_State *lua_tothread (lua_State *L, int index);</pre>
5097 Converts the value at the given index to a Lua thread
5098 (represented as <code>lua_State*</code>).
5099 This value must be a thread;
5100 otherwise, the function returns <code>NULL</code>.
5106 <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
5107 <span class="apii">[-0, +0, –]</span>
5108 <pre>void *lua_touserdata (lua_State *L, int index);</pre>
5111 If the value at the given index is a full userdata,
5112 returns its block address.
5113 If the value is a light userdata,
5114 returns its pointer.
5115 Otherwise, returns <code>NULL</code>.
5121 <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
5122 <span class="apii">[-0, +0, –]</span>
5123 <pre>int lua_type (lua_State *L, int index);</pre>
5126 Returns the type of the value in the given valid index,
5127 or <code>LUA_TNONE</code> for a non-valid (but acceptable) index.
5128 The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
5129 defined in <code>lua.h</code>:
5130 <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>,
5131 <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>,
5132 <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>,
5133 <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>,
5134 <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>,
5135 <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
5136 <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>,
5137 <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>,
5139 <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>.
5145 <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
5146 <span class="apii">[-0, +0, –]</span>
5147 <pre>const char *lua_typename (lua_State *L, int tp);</pre>
5150 Returns the name of the type encoded by the value <code>tp</code>,
5151 which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
5157 <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3>
5158 <pre>typedef ... lua_Unsigned;</pre>
5161 The unsigned version of <a href="#lua_Integer"><code>lua_Integer</code></a>.
5167 <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p>
5168 <span class="apii">[-0, +0, –]</span>
5169 <pre>int lua_upvalueindex (int i);</pre>
5172 Returns the pseudo-index that represents the <code>i</code>-th upvalue of
5173 the running function (see <a href="#4.4">§4.4</a>).
5179 <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
5180 <span class="apii">[-0, +0, <em>v</em>]</span>
5181 <pre>const lua_Number *lua_version (lua_State *L);</pre>
5184 Returns the address of the version number stored in the Lua core.
5185 When called with a valid <a href="#lua_State"><code>lua_State</code></a>,
5186 returns the address of the version used to create that state.
5187 When called with <code>NULL</code>,
5188 returns the address of the version running the call.
5194 <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
5195 <pre>typedef int (*lua_Writer) (lua_State *L,
5201 The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
5202 Every time it produces another piece of chunk,
5203 <a href="#lua_dump"><code>lua_dump</code></a> calls the writer,
5204 passing along the buffer to be written (<code>p</code>),
5205 its size (<code>sz</code>),
5206 and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
5210 The writer returns an error code:
5211 0 means no errors;
5212 any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
5213 calling the writer again.
5219 <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
5220 <span class="apii">[-?, +?, –]</span>
5221 <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre>
5224 Exchange values between different threads of the same state.
5228 This function pops <code>n</code> values from the stack <code>from</code>,
5229 and pushes them onto the stack <code>to</code>.
5235 <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
5236 <span class="apii">[-?, +?, <em>e</em>]</span>
5237 <pre>int lua_yield (lua_State *L, int nresults);</pre>
5240 This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5241 but it has no continuation (see <a href="#4.7">§4.7</a>).
5242 Therefore, when the thread resumes,
5243 it continues the function that called
5244 the function calling <code>lua_yield</code>.
5250 <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p>
5251 <span class="apii">[-?, +?, <em>e</em>]</span>
5252 <pre>int lua_yieldk (lua_State *L,
5255 lua_KFunction k);</pre>
5258 Yields a coroutine (thread).
5262 When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5263 the running coroutine suspends its execution,
5264 and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
5265 The parameter <code>nresults</code> is the number of values from the stack
5266 that will be passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
5270 When the coroutine is resumed again,
5271 Lua calls the given continuation function <code>k</code> to continue
5272 the execution of the C function that yielded (see <a href="#4.7">§4.7</a>).
5273 This continuation function receives the same stack
5274 from the previous function,
5275 with the <code>n</code> results removed and
5276 replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>.
5278 the continuation function receives the value <code>ctx</code>
5279 that was passed to <a href="#lua_yieldk"><code>lua_yieldk</code></a>.
5283 Usually, this function does not return;
5284 when the coroutine eventually resumes,
5285 it continues executing the continuation function.
5286 However, there is one special case,
5287 which is when this function is called
5288 from inside a line hook (see <a href="#4.9">§4.9</a>).
5289 In that case, <code>lua_yieldk</code> should be called with no continuation
5290 (probably in the form of <a href="#lua_yield"><code>lua_yield</code></a>),
5291 and the hook should return immediately after the call.
5293 when the coroutine resumes again,
5294 it will continue the normal execution
5295 of the (Lua) function that triggered the hook.
5299 This function can raise an error if it is called from a thread
5300 with a pending C call with no continuation function,
5301 or it is called from a thread that is not running inside a resume
5302 (e.g., the main thread).
5310 <h2>4.9 – <a name="4.9">The Debug Interface</a></h2>
5313 Lua has no built-in debugging facilities.
5314 Instead, it offers a special interface
5315 by means of functions and <em>hooks</em>.
5316 This interface allows the construction of different
5317 kinds of debuggers, profilers, and other tools
5318 that need "inside information" from the interpreter.
5322 <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
5323 <pre>typedef struct lua_Debug {
5325 const char *name; /* (n) */
5326 const char *namewhat; /* (n) */
5327 const char *what; /* (S) */
5328 const char *source; /* (S) */
5329 int currentline; /* (l) */
5330 int linedefined; /* (S) */
5331 int lastlinedefined; /* (S) */
5332 unsigned char nups; /* (u) number of upvalues */
5333 unsigned char nparams; /* (u) number of parameters */
5334 char isvararg; /* (u) */
5335 char istailcall; /* (t) */
5336 char short_src[LUA_IDSIZE]; /* (S) */
5338 <em>other fields</em>
5342 A structure used to carry different pieces of
5343 information about a function or an activation record.
5344 <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
5345 of this structure, for later use.
5346 To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
5347 call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5351 The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
5355 <li><b><code>source</code>: </b>
5356 the name of the chunk that created the function.
5357 If <code>source</code> starts with a '<code>@</code>',
5358 it means that the function was defined in a file where
5359 the file name follows the '<code>@</code>'.
5360 If <code>source</code> starts with a '<code>=</code>',
5361 the remainder of its contents describe the source in a user-dependent manner.
5363 the function was defined in a string where
5364 <code>source</code> is that string.
5367 <li><b><code>short_src</code>: </b>
5368 a "printable" version of <code>source</code>, to be used in error messages.
5371 <li><b><code>linedefined</code>: </b>
5372 the line number where the definition of the function starts.
5375 <li><b><code>lastlinedefined</code>: </b>
5376 the line number where the definition of the function ends.
5379 <li><b><code>what</code>: </b>
5380 the string <code>"Lua"</code> if the function is a Lua function,
5381 <code>"C"</code> if it is a C function,
5382 <code>"main"</code> if it is the main part of a chunk.
5385 <li><b><code>currentline</code>: </b>
5386 the current line where the given function is executing.
5387 When no line information is available,
5388 <code>currentline</code> is set to -1.
5391 <li><b><code>name</code>: </b>
5392 a reasonable name for the given function.
5393 Because functions in Lua are first-class values,
5394 they do not have a fixed name:
5395 some functions can be the value of multiple global variables,
5396 while others can be stored only in a table field.
5397 The <code>lua_getinfo</code> function checks how the function was
5398 called to find a suitable name.
5399 If it cannot find a name,
5400 then <code>name</code> is set to <code>NULL</code>.
5403 <li><b><code>namewhat</code>: </b>
5404 explains the <code>name</code> field.
5405 The value of <code>namewhat</code> can be
5406 <code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
5407 <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
5408 according to how the function was called.
5409 (Lua uses the empty string when no other option seems to apply.)
5412 <li><b><code>istailcall</code>: </b>
5413 true if this function invocation was called by a tail call.
5414 In this case, the caller of this level is not in the stack.
5417 <li><b><code>nups</code>: </b>
5418 the number of upvalues of the function.
5421 <li><b><code>nparams</code>: </b>
5422 the number of fixed parameters of the function
5423 (always 0 for C functions).
5426 <li><b><code>isvararg</code>: </b>
5427 true if the function is a vararg function
5428 (always true for C functions).
5436 <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
5437 <span class="apii">[-0, +0, –]</span>
5438 <pre>lua_Hook lua_gethook (lua_State *L);</pre>
5441 Returns the current hook function.
5447 <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
5448 <span class="apii">[-0, +0, –]</span>
5449 <pre>int lua_gethookcount (lua_State *L);</pre>
5452 Returns the current hook count.
5458 <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
5459 <span class="apii">[-0, +0, –]</span>
5460 <pre>int lua_gethookmask (lua_State *L);</pre>
5463 Returns the current hook mask.
5469 <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
5470 <span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span>
5471 <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre>
5474 Gets information about a specific function or function invocation.
5478 To get information about a function invocation,
5479 the parameter <code>ar</code> must be a valid activation record that was
5480 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5481 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5485 To get information about a function you push it onto the stack
5486 and start the <code>what</code> string with the character '<code>></code>'.
5488 <code>lua_getinfo</code> pops the function from the top of the stack.)
5489 For instance, to know in which line a function <code>f</code> was defined,
5490 you can write the following code:
5494 lua_getglobal(L, "f"); /* get global 'f' */
5495 lua_getinfo(L, ">S", &ar);
5496 printf("%d\n", ar.linedefined);
5500 Each character in the string <code>what</code>
5501 selects some fields of the structure <code>ar</code> to be filled or
5502 a value to be pushed on the stack:
5506 <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>;
5509 <li><b>'<code>S</code>': </b>
5510 fills in the fields <code>source</code>, <code>short_src</code>,
5511 <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
5514 <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>;
5517 <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>;
5520 <li><b>'<code>u</code>': </b> fills in the fields
5521 <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>;
5524 <li><b>'<code>f</code>': </b>
5525 pushes onto the stack the function that is
5526 running at the given level;
5529 <li><b>'<code>L</code>': </b>
5530 pushes onto the stack a table whose indices are the
5531 numbers of the lines that are valid on the function.
5532 (A <em>valid line</em> is a line with some associated code,
5533 that is, a line where you can put a break point.
5534 Non-valid lines include empty lines and comments.)
5538 If this option is given together with option '<code>f</code>',
5539 its table is pushed after the function.
5545 This function returns 0 on error
5546 (for instance, an invalid option in <code>what</code>).
5552 <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
5553 <span class="apii">[-0, +(0|1), –]</span>
5554 <pre>const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);</pre>
5557 Gets information about a local variable of
5558 a given activation record or a given function.
5563 the parameter <code>ar</code> must be a valid activation record that was
5564 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5565 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5566 The index <code>n</code> selects which local variable to inspect;
5567 see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices
5572 <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
5573 and returns its name.
5577 In the second case, <code>ar</code> must be <code>NULL</code> and the function
5578 to be inspected must be at the top of the stack.
5579 In this case, only parameters of Lua functions are visible
5580 (as there is no information about what variables are active)
5581 and no values are pushed onto the stack.
5585 Returns <code>NULL</code> (and pushes nothing)
5586 when the index is greater than
5587 the number of active local variables.
5593 <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
5594 <span class="apii">[-0, +0, –]</span>
5595 <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre>
5598 Gets information about the interpreter runtime stack.
5602 This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
5603 an identification of the <em>activation record</em>
5604 of the function executing at a given level.
5605 Level 0 is the current running function,
5606 whereas level <em>n+1</em> is the function that has called level <em>n</em>
5607 (except for tail calls, which do not count on the stack).
5608 When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1;
5609 when called with a level greater than the stack depth,
5616 <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
5617 <span class="apii">[-0, +(0|1), –]</span>
5618 <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
5621 Gets information about a closure's upvalue.
5623 upvalues are the external local variables that the function uses,
5624 and that are consequently included in its closure.)
5625 <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
5626 pushes the upvalue's value onto the stack,
5627 and returns its name.
5628 <code>funcindex</code> points to the closure in the stack.
5629 (Upvalues have no particular order,
5630 as they are active through the whole function.
5631 So, they are numbered in an arbitrary order.)
5635 Returns <code>NULL</code> (and pushes nothing)
5636 when the index is greater than the number of upvalues.
5637 For C functions, this function uses the empty string <code>""</code>
5638 as a name for all upvalues.
5644 <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
5645 <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
5648 Type for debugging hook functions.
5652 Whenever a hook is called, its <code>ar</code> argument has its field
5653 <code>event</code> set to the specific event that triggered the hook.
5654 Lua identifies these events with the following constants:
5655 <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
5656 <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
5657 and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
5658 Moreover, for line events, the field <code>currentline</code> is also set.
5659 To get the value of any other field in <code>ar</code>,
5660 the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5664 For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>,
5665 the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call;
5666 in this case, there will be no corresponding return event.
5670 While Lua is running a hook, it disables other calls to hooks.
5671 Therefore, if a hook calls back Lua to execute a function or a chunk,
5672 this execution occurs without any calls to hooks.
5676 Hook functions cannot have continuations,
5677 that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5678 <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>.
5682 Hook functions can yield under the following conditions:
5683 Only count and line events can yield
5684 and they cannot yield any value;
5685 to yield a hook function must finish its execution
5686 calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero.
5692 <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
5693 <span class="apii">[-0, +0, –]</span>
5694 <pre>void lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
5697 Sets the debugging hook function.
5701 Argument <code>f</code> is the hook function.
5702 <code>mask</code> specifies on which events the hook will be called:
5703 it is formed by a bitwise or of the constants
5704 <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
5705 <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
5706 <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
5707 and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
5708 The <code>count</code> argument is only meaningful when the mask
5709 includes <code>LUA_MASKCOUNT</code>.
5710 For each event, the hook is called as explained below:
5714 <li><b>The call hook: </b> is called when the interpreter calls a function.
5715 The hook is called just after Lua enters the new function,
5716 before the function gets its arguments.
5719 <li><b>The return hook: </b> is called when the interpreter returns from a function.
5720 The hook is called just before Lua leaves the function.
5721 There is no standard way to access the values
5722 to be returned by the function.
5725 <li><b>The line hook: </b> is called when the interpreter is about to
5726 start the execution of a new line of code,
5727 or when it jumps back in the code (even to the same line).
5728 (This event only happens while Lua is executing a Lua function.)
5731 <li><b>The count hook: </b> is called after the interpreter executes every
5732 <code>count</code> instructions.
5733 (This event only happens while Lua is executing a Lua function.)
5739 A hook is disabled by setting <code>mask</code> to zero.
5745 <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
5746 <span class="apii">[-(0|1), +0, –]</span>
5747 <pre>const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);</pre>
5750 Sets the value of a local variable of a given activation record.
5751 Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
5752 (see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
5753 <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
5754 to the variable and returns its name.
5755 It also pops the value from the stack.
5759 Returns <code>NULL</code> (and pops nothing)
5760 when the index is greater than
5761 the number of active local variables.
5767 <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
5768 <span class="apii">[-(0|1), +0, –]</span>
5769 <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
5772 Sets the value of a closure's upvalue.
5773 It assigns the value at the top of the stack
5774 to the upvalue and returns its name.
5775 It also pops the value from the stack.
5776 Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5777 (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
5781 Returns <code>NULL</code> (and pops nothing)
5782 when the index is greater than the number of upvalues.
5788 <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
5789 <span class="apii">[-0, +0, –]</span>
5790 <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre>
5793 Returns a unique identifier for the upvalue numbered <code>n</code>
5794 from the closure at index <code>funcindex</code>.
5795 Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5796 (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>)
5797 (but <code>n</code> cannot be greater than the number of upvalues).
5801 These unique identifiers allow a program to check whether different
5802 closures share upvalues.
5803 Lua closures that share an upvalue
5804 (that is, that access a same external local variable)
5805 will return identical ids for those upvalue indices.
5811 <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
5812 <span class="apii">[-0, +0, –]</span>
5813 <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
5814 int funcindex2, int n2);</pre>
5817 Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code>
5818 refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>.
5826 <h1>5 – <a name="5">The Auxiliary Library</a></h1>
5830 The <em>auxiliary library</em> provides several convenient functions
5831 to interface C with Lua.
5832 While the basic API provides the primitive functions for all
5833 interactions between C and Lua,
5834 the auxiliary library provides higher-level functions for some
5839 All functions and types from the auxiliary library
5840 are defined in header file <code>lauxlib.h</code> and
5841 have a prefix <code>luaL_</code>.
5845 All functions in the auxiliary library are built on
5846 top of the basic API,
5847 and so they provide nothing that cannot be done with that API.
5848 Nevertheless, the use of the auxiliary library ensures
5849 more consistency to your code.
5853 Several functions in the auxiliary library use internally some
5855 When a function in the auxiliary library uses less than five slots,
5856 it does not check the stack size;
5857 it simply assumes that there are enough slots.
5861 Several functions in the auxiliary library are used to
5862 check C function arguments.
5863 Because the error message is formatted for arguments
5864 (e.g., "<code>bad argument #1</code>"),
5865 you should not use these functions for other stack values.
5869 Functions called <code>luaL_check*</code>
5870 always raise an error if the check is not satisfied.
5874 <h2>5.1 – <a name="5.1">Functions and Types</a></h2>
5877 Here we list all functions and types from the auxiliary library
5878 in alphabetical order.
5882 <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
5883 <span class="apii">[-?, +?, <em>e</em>]</span>
5884 <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
5887 Adds the byte <code>c</code> to the buffer <code>B</code>
5888 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5894 <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
5895 <span class="apii">[-?, +?, <em>e</em>]</span>
5896 <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre>
5899 Adds the string pointed to by <code>s</code> with length <code>l</code> to
5900 the buffer <code>B</code>
5901 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5902 The string can contain embedded zeros.
5908 <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
5909 <span class="apii">[-?, +?, <em>e</em>]</span>
5910 <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
5913 Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
5914 a string of length <code>n</code> previously copied to the
5915 buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
5921 <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
5922 <span class="apii">[-?, +?, <em>e</em>]</span>
5923 <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre>
5926 Adds the zero-terminated string pointed to by <code>s</code>
5927 to the buffer <code>B</code>
5928 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5934 <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
5935 <span class="apii">[-1, +?, <em>e</em>]</span>
5936 <pre>void luaL_addvalue (luaL_Buffer *B);</pre>
5939 Adds the value at the top of the stack
5940 to the buffer <code>B</code>
5941 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5946 This is the only function on string buffers that can (and must)
5947 be called with an extra element on the stack,
5948 which is the value to be added to the buffer.
5954 <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
5955 <span class="apii">[-0, +0, <em>v</em>]</span>
5956 <pre>void luaL_argcheck (lua_State *L,
5959 const char *extramsg);</pre>
5962 Checks whether <code>cond</code> is true.
5963 If it is not, raises an error with a standard message (see <a href="#luaL_argerror"><code>luaL_argerror</code></a>).
5969 <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
5970 <span class="apii">[-0, +0, <em>v</em>]</span>
5971 <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre>
5974 Raises an error reporting a problem with argument <code>arg</code>
5975 of the C function that called it,
5976 using a standard message
5977 that includes <code>extramsg</code> as a comment:
5980 bad argument #<em>arg</em> to '<em>funcname</em>' (<em>extramsg</em>)
5982 This function never returns.
5988 <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
5989 <pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
5992 Type for a <em>string buffer</em>.
5996 A string buffer allows C code to build Lua strings piecemeal.
5997 Its pattern of use is as follows:
6001 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
6003 <li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li>
6006 Then add string pieces to the buffer calling any of
6007 the <code>luaL_add*</code> functions.
6011 Finish by calling <code>luaL_pushresult(&b)</code>.
6012 This call leaves the final string on the top of the stack.
6018 If you know beforehand the total size of the resulting string,
6019 you can use the buffer like this:
6023 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
6025 <li>Then initialize it and preallocate a space of
6026 size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li>
6028 <li>Then copy the string into that space.</li>
6031 Finish by calling <code>luaL_pushresultsize(&b, sz)</code>,
6032 where <code>sz</code> is the total size of the resulting string
6033 copied into that space.
6039 During its normal operation,
6040 a string buffer uses a variable number of stack slots.
6041 So, while using a buffer, you cannot assume that you know where
6042 the top of the stack is.
6043 You can use the stack between successive calls to buffer operations
6044 as long as that use is balanced;
6046 when you call a buffer operation,
6047 the stack is at the same level
6048 it was immediately after the previous buffer operation.
6049 (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
6050 After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
6051 level when the buffer was initialized,
6052 plus the final string on its top.
6058 <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
6059 <span class="apii">[-0, +0, –]</span>
6060 <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre>
6063 Initializes a buffer <code>B</code>.
6064 This function does not allocate any space;
6065 the buffer must be declared as a variable
6066 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
6072 <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p>
6073 <span class="apii">[-?, +?, <em>e</em>]</span>
6074 <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre>
6077 Equivalent to the sequence
6078 <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>.
6084 <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
6085 <span class="apii">[-0, +(0|1), <em>e</em>]</span>
6086 <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre>
6093 If the object at index <code>obj</code> has a metatable and this
6094 metatable has a field <code>e</code>,
6095 this function calls this field passing the object as its only argument.
6096 In this case this function returns true and pushes onto the
6097 stack the value returned by the call.
6098 If there is no metatable or no metamethod,
6099 this function returns false (without pushing any value on the stack).
6105 <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
6106 <span class="apii">[-0, +0, <em>v</em>]</span>
6107 <pre>void luaL_checkany (lua_State *L, int arg);</pre>
6110 Checks whether the function has an argument
6111 of any type (including <b>nil</b>) at position <code>arg</code>.
6117 <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
6118 <span class="apii">[-0, +0, <em>v</em>]</span>
6119 <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre>
6122 Checks whether the function argument <code>arg</code> is an integer
6123 (or can be converted to an integer)
6124 and returns this integer cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
6130 <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
6131 <span class="apii">[-0, +0, <em>v</em>]</span>
6132 <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre>
6135 Checks whether the function argument <code>arg</code> is a string
6136 and returns this string;
6137 if <code>l</code> is not <code>NULL</code> fills <code>*l</code>
6138 with the string's length.
6142 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
6143 so all conversions and caveats of that function apply here.
6149 <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
6150 <span class="apii">[-0, +0, <em>v</em>]</span>
6151 <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre>
6154 Checks whether the function argument <code>arg</code> is a number
6155 and returns this number.
6161 <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
6162 <span class="apii">[-0, +0, <em>v</em>]</span>
6163 <pre>int luaL_checkoption (lua_State *L,
6166 const char *const lst[]);</pre>
6169 Checks whether the function argument <code>arg</code> is a string and
6170 searches for this string in the array <code>lst</code>
6171 (which must be NULL-terminated).
6172 Returns the index in the array where the string was found.
6173 Raises an error if the argument is not a string or
6174 if the string cannot be found.
6178 If <code>def</code> is not <code>NULL</code>,
6179 the function uses <code>def</code> as a default value when
6180 there is no argument <code>arg</code> or when this argument is <b>nil</b>.
6184 This is a useful function for mapping strings to C enums.
6185 (The usual convention in Lua libraries is
6186 to use strings instead of numbers to select options.)
6192 <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
6193 <span class="apii">[-0, +0, <em>v</em>]</span>
6194 <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre>
6197 Grows the stack size to <code>top + sz</code> elements,
6198 raising an error if the stack cannot grow to that size.
6199 <code>msg</code> is an additional text to go into the error message
6200 (or <code>NULL</code> for no additional text).
6206 <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
6207 <span class="apii">[-0, +0, <em>v</em>]</span>
6208 <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre>
6211 Checks whether the function argument <code>arg</code> is a string
6212 and returns this string.
6216 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
6217 so all conversions and caveats of that function apply here.
6223 <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
6224 <span class="apii">[-0, +0, <em>v</em>]</span>
6225 <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre>
6228 Checks whether the function argument <code>arg</code> has type <code>t</code>.
6229 See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
6235 <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
6236 <span class="apii">[-0, +0, <em>v</em>]</span>
6237 <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre>
6240 Checks whether the function argument <code>arg</code> is a userdata
6241 of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and
6242 returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>).
6248 <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p>
6249 <span class="apii">[-0, +0, –]</span>
6250 <pre>void luaL_checkversion (lua_State *L);</pre>
6253 Checks whether the core running the call,
6254 the core that created the Lua state,
6255 and the code making the call are all using the same version of Lua.
6256 Also checks whether the core running the call
6257 and the core that created the Lua state
6258 are using the same address space.
6264 <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
6265 <span class="apii">[-0, +?, <em>e</em>]</span>
6266 <pre>int luaL_dofile (lua_State *L, const char *filename);</pre>
6269 Loads and runs the given file.
6270 It is defined as the following macro:
6273 (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
6275 It returns false if there are no errors
6276 or true in case of errors.
6282 <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
6283 <span class="apii">[-0, +?, –]</span>
6284 <pre>int luaL_dostring (lua_State *L, const char *str);</pre>
6287 Loads and runs the given string.
6288 It is defined as the following macro:
6291 (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
6293 It returns false if there are no errors
6294 or true in case of errors.
6300 <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
6301 <span class="apii">[-0, +0, <em>v</em>]</span>
6302 <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre>
6306 The error message format is given by <code>fmt</code>
6307 plus any extra arguments,
6308 following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
6309 It also adds at the beginning of the message the file name and
6310 the line number where the error occurred,
6311 if this information is available.
6315 This function never returns,
6316 but it is an idiom to use it in C functions
6317 as <code>return luaL_error(<em>args</em>)</code>.
6323 <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p>
6324 <span class="apii">[-0, +3, <em>e</em>]</span>
6325 <pre>int luaL_execresult (lua_State *L, int stat);</pre>
6328 This function produces the return values for
6329 process-related functions in the standard library
6330 (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>).
6336 <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p>
6337 <span class="apii">[-0, +(1|3), <em>e</em>]</span>
6338 <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre>
6341 This function produces the return values for
6342 file-related functions in the standard library
6343 (<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.).
6349 <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
6350 <span class="apii">[-0, +(0|1), <em>e</em>]</span>
6351 <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre>
6354 Pushes onto the stack the field <code>e</code> from the metatable
6355 of the object at index <code>obj</code> and returns the type of pushed value.
6356 If the object does not have a metatable,
6357 or if the metatable does not have this field,
6358 pushes nothing and returns <code>LUA_TNIL</code>.
6364 <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
6365 <span class="apii">[-0, +1, –]</span>
6366 <pre>int luaL_getmetatable (lua_State *L, const char *tname);</pre>
6369 Pushes onto the stack the metatable associated with name <code>tname</code>
6370 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6371 If there is no metatable associated with <code>tname</code>,
6372 returns false and pushes <b>nil</b>.
6378 <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p>
6379 <span class="apii">[-0, +1, <em>e</em>]</span>
6380 <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre>
6383 Ensures that the value <code>t[fname]</code>,
6384 where <code>t</code> is the value at index <code>idx</code>,
6386 and pushes that table onto the stack.
6387 Returns true if it finds a previous table there
6388 and false if it creates a new table.
6394 <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
6395 <span class="apii">[-0, +1, <em>e</em>]</span>
6396 <pre>const char *luaL_gsub (lua_State *L,
6399 const char *r);</pre>
6402 Creates a copy of string <code>s</code> by replacing
6403 any occurrence of the string <code>p</code>
6404 with the string <code>r</code>.
6405 Pushes the resulting string on the stack and returns it.
6411 <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p>
6412 <span class="apii">[-0, +0, <em>e</em>]</span>
6413 <pre>lua_Integer luaL_len (lua_State *L, int index);</pre>
6416 Returns the "length" of the value at the given index
6418 it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>).
6419 Raises an error if the result of the operation is not an integer.
6420 (This case only can happen through metamethods.)
6426 <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
6427 <span class="apii">[-0, +1, –]</span>
6428 <pre>int luaL_loadbuffer (lua_State *L,
6431 const char *name);</pre>
6434 Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>.
6440 <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p>
6441 <span class="apii">[-0, +1, –]</span>
6442 <pre>int luaL_loadbufferx (lua_State *L,
6446 const char *mode);</pre>
6449 Loads a buffer as a Lua chunk.
6450 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
6451 buffer pointed to by <code>buff</code> with size <code>sz</code>.
6455 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6456 <code>name</code> is the chunk name,
6457 used for debug information and error messages.
6458 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6464 <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
6465 <span class="apii">[-0, +1, <em>e</em>]</span>
6466 <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre>
6469 Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>.
6475 <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p>
6476 <span class="apii">[-0, +1, <em>e</em>]</span>
6477 <pre>int luaL_loadfilex (lua_State *L, const char *filename,
6478 const char *mode);</pre>
6481 Loads a file as a Lua chunk.
6482 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
6483 named <code>filename</code>.
6484 If <code>filename</code> is <code>NULL</code>,
6485 then it loads from the standard input.
6486 The first line in the file is ignored if it starts with a <code>#</code>.
6490 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6494 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>,
6495 but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>
6496 if it cannot open/read the file or the file has a wrong mode.
6500 As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6507 <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
6508 <span class="apii">[-0, +1, –]</span>
6509 <pre>int luaL_loadstring (lua_State *L, const char *s);</pre>
6512 Loads a string as a Lua chunk.
6513 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
6514 the zero-terminated string <code>s</code>.
6518 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6522 Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6529 <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p>
6530 <span class="apii">[-0, +1, <em>e</em>]</span>
6531 <pre>void luaL_newlib (lua_State *L, const luaL_Reg l[]);</pre>
6534 Creates a new table and registers there
6535 the functions in list <code>l</code>.
6539 It is implemented as the following macro:
6542 (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
6544 The array <code>l</code> must be the actual array,
6545 not a pointer to it.
6551 <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p>
6552 <span class="apii">[-0, +1, <em>e</em>]</span>
6553 <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre>
6556 Creates a new table with a size optimized
6557 to store all entries in the array <code>l</code>
6558 (but does not actually store them).
6559 It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>
6560 (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>).
6564 It is implemented as a macro.
6565 The array <code>l</code> must be the actual array,
6566 not a pointer to it.
6572 <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
6573 <span class="apii">[-0, +1, <em>e</em>]</span>
6574 <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre>
6577 If the registry already has the key <code>tname</code>,
6580 creates a new table to be used as a metatable for userdata,
6581 adds to this new table the pair <code>__name = tname</code>,
6582 adds to the registry the pair <code>[tname] = new table</code>,
6584 (The entry <code>__name</code> is used by some error-reporting functions.)
6588 In both cases pushes onto the stack the final value associated
6589 with <code>tname</code> in the registry.
6595 <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
6596 <span class="apii">[-0, +0, –]</span>
6597 <pre>lua_State *luaL_newstate (void);</pre>
6600 Creates a new Lua state.
6601 It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
6602 allocator based on the standard C <code>realloc</code> function
6603 and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints
6604 an error message to the standard error output in case of fatal
6609 Returns the new state,
6610 or <code>NULL</code> if there is a memory allocation error.
6616 <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
6617 <span class="apii">[-0, +0, <em>e</em>]</span>
6618 <pre>void luaL_openlibs (lua_State *L);</pre>
6621 Opens all standard Lua libraries into the given state.
6627 <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
6628 <span class="apii">[-0, +0, <em>v</em>]</span>
6629 <pre>lua_Integer luaL_optinteger (lua_State *L,
6631 lua_Integer d);</pre>
6634 If the function argument <code>arg</code> is an integer
6635 (or convertible to an integer),
6636 returns this integer.
6637 If this argument is absent or is <b>nil</b>,
6638 returns <code>d</code>.
6639 Otherwise, raises an error.
6645 <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
6646 <span class="apii">[-0, +0, <em>v</em>]</span>
6647 <pre>const char *luaL_optlstring (lua_State *L,
6653 If the function argument <code>arg</code> is a string,
6654 returns this string.
6655 If this argument is absent or is <b>nil</b>,
6656 returns <code>d</code>.
6657 Otherwise, raises an error.
6661 If <code>l</code> is not <code>NULL</code>,
6662 fills the position <code>*l</code> with the result's length.
6668 <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
6669 <span class="apii">[-0, +0, <em>v</em>]</span>
6670 <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre>
6673 If the function argument <code>arg</code> is a number,
6674 returns this number.
6675 If this argument is absent or is <b>nil</b>,
6676 returns <code>d</code>.
6677 Otherwise, raises an error.
6683 <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
6684 <span class="apii">[-0, +0, <em>v</em>]</span>
6685 <pre>const char *luaL_optstring (lua_State *L,
6687 const char *d);</pre>
6690 If the function argument <code>arg</code> is a string,
6691 returns this string.
6692 If this argument is absent or is <b>nil</b>,
6693 returns <code>d</code>.
6694 Otherwise, raises an error.
6700 <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
6701 <span class="apii">[-?, +?, <em>e</em>]</span>
6702 <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre>
6705 Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>
6706 with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>.
6712 <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p>
6713 <span class="apii">[-?, +?, <em>e</em>]</span>
6714 <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre>
6717 Returns an address to a space of size <code>sz</code>
6718 where you can copy a string to be added to buffer <code>B</code>
6719 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
6720 After copying the string into this space you must call
6721 <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
6728 <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
6729 <span class="apii">[-?, +1, <em>e</em>]</span>
6730 <pre>void luaL_pushresult (luaL_Buffer *B);</pre>
6733 Finishes the use of buffer <code>B</code> leaving the final string on
6734 the top of the stack.
6740 <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p>
6741 <span class="apii">[-?, +1, <em>e</em>]</span>
6742 <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre>
6745 Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>.
6751 <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
6752 <span class="apii">[-1, +0, <em>e</em>]</span>
6753 <pre>int luaL_ref (lua_State *L, int t);</pre>
6756 Creates and returns a <em>reference</em>,
6757 in the table at index <code>t</code>,
6758 for the object at the top of the stack (and pops the object).
6762 A reference is a unique integer key.
6763 As long as you do not manually add integer keys into table <code>t</code>,
6764 <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
6765 You can retrieve an object referred by reference <code>r</code>
6766 by calling <code>lua_rawgeti(L, t, r)</code>.
6767 Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
6771 If the object at the top of the stack is <b>nil</b>,
6772 <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
6773 The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
6774 from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
6780 <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
6781 <pre>typedef struct luaL_Reg {
6787 Type for arrays of functions to be registered by
6788 <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>.
6789 <code>name</code> is the function name and <code>func</code> is a pointer to
6791 Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with a sentinel entry
6792 in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
6798 <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p>
6799 <span class="apii">[-0, +1, <em>e</em>]</span>
6800 <pre>void luaL_requiref (lua_State *L, const char *modname,
6801 lua_CFunction openf, int glb);</pre>
6804 If <code>modname</code> is not already present in <a href="#pdf-package.loaded"><code>package.loaded</code></a>,
6805 calls function <code>openf</code> with string <code>modname</code> as an argument
6806 and sets the call result in <code>package.loaded[modname]</code>,
6807 as if that function has been called through <a href="#pdf-require"><code>require</code></a>.
6811 If <code>glb</code> is true,
6812 also stores the module into global <code>modname</code>.
6816 Leaves a copy of the module on the stack.
6822 <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p>
6823 <span class="apii">[-nup, +0, <em>e</em>]</span>
6824 <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre>
6827 Registers all functions in the array <code>l</code>
6828 (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack
6829 (below optional upvalues, see next).
6833 When <code>nup</code> is not zero,
6834 all functions are created sharing <code>nup</code> upvalues,
6835 which must be previously pushed on the stack
6836 on top of the library table.
6837 These values are popped from the stack after the registration.
6843 <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p>
6844 <span class="apii">[-0, +0, –]</span>
6845 <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre>
6848 Sets the metatable of the object at the top of the stack
6849 as the metatable associated with name <code>tname</code>
6850 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6856 <hr><h3><a name="luaL_Stream"><code>luaL_Stream</code></a></h3>
6857 <pre>typedef struct luaL_Stream {
6859 lua_CFunction closef;
6860 } luaL_Stream;</pre>
6863 The standard representation for file handles,
6864 which is used by the standard I/O library.
6868 A file handle is implemented as a full userdata,
6869 with a metatable called <code>LUA_FILEHANDLE</code>
6870 (where <code>LUA_FILEHANDLE</code> is a macro with the actual metatable's name).
6871 The metatable is created by the I/O library
6872 (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6876 This userdata must start with the structure <code>luaL_Stream</code>;
6877 it can contain other data after this initial structure.
6878 Field <code>f</code> points to the corresponding C stream
6879 (or it can be <code>NULL</code> to indicate an incompletely created handle).
6880 Field <code>closef</code> points to a Lua function
6881 that will be called to close the stream
6882 when the handle is closed or collected;
6883 this function receives the file handle as its sole argument and
6884 must return either <b>true</b> (in case of success)
6885 or <b>nil</b> plus an error message (in case of error).
6886 Once Lua calls this field,
6887 the field value is changed to <code>NULL</code>
6888 to signal that the handle is closed.
6894 <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p>
6895 <span class="apii">[-0, +0, <em>e</em>]</span>
6896 <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre>
6899 This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>,
6900 except that, when the test fails,
6901 it returns <code>NULL</code> instead of raising an error.
6907 <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p>
6908 <span class="apii">[-0, +1, <em>e</em>]</span>
6909 <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre>
6912 Converts any Lua value at the given index to a C string
6913 in a reasonable format.
6914 The resulting string is pushed onto the stack and also
6915 returned by the function.
6916 If <code>len</code> is not <code>NULL</code>,
6917 the function also sets <code>*len</code> with the string length.
6921 If the value has a metatable with a <code>"__tostring"</code> field,
6922 then <code>luaL_tolstring</code> calls the corresponding metamethod
6923 with the value as argument,
6924 and uses the result of the call as its result.
6930 <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p>
6931 <span class="apii">[-0, +1, <em>e</em>]</span>
6932 <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
6936 Creates and pushes a traceback of the stack <code>L1</code>.
6937 If <code>msg</code> is not <code>NULL</code> it is appended
6938 at the beginning of the traceback.
6939 The <code>level</code> parameter tells at which level
6940 to start the traceback.
6946 <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
6947 <span class="apii">[-0, +0, –]</span>
6948 <pre>const char *luaL_typename (lua_State *L, int index);</pre>
6951 Returns the name of the type of the value at the given index.
6957 <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
6958 <span class="apii">[-0, +0, –]</span>
6959 <pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
6962 Releases reference <code>ref</code> from the table at index <code>t</code>
6963 (see <a href="#luaL_ref"><code>luaL_ref</code></a>).
6964 The entry is removed from the table,
6965 so that the referred object can be collected.
6966 The reference <code>ref</code> is also freed to be used again.
6970 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>,
6971 <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
6977 <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
6978 <span class="apii">[-0, +1, <em>e</em>]</span>
6979 <pre>void luaL_where (lua_State *L, int lvl);</pre>
6982 Pushes onto the stack a string identifying the current position
6983 of the control at level <code>lvl</code> in the call stack.
6984 Typically this string has the following format:
6987 <em>chunkname</em>:<em>currentline</em>:
6989 Level 0 is the running function,
6990 level 1 is the function that called the running function,
6995 This function is used to build a prefix for error messages.
7003 <h1>6 – <a name="6">Standard Libraries</a></h1>
7006 The standard Lua libraries provide useful functions
7007 that are implemented directly through the C API.
7008 Some of these functions provide essential services to the language
7009 (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
7010 others provide access to "outside" services (e.g., I/O);
7011 and others could be implemented in Lua itself,
7012 but are quite useful or have critical performance requirements that
7013 deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
7017 All libraries are implemented through the official C API
7018 and are provided as separate C modules.
7019 Currently, Lua has the following standard libraries:
7023 <li>basic library (<a href="#6.1">§6.1</a>);</li>
7025 <li>coroutine library (<a href="#6.2">§6.2</a>);</li>
7027 <li>package library (<a href="#6.3">§6.3</a>);</li>
7029 <li>string manipulation (<a href="#6.4">§6.4</a>);</li>
7031 <li>basic UTF-8 support (<a href="#6.5">§6.5</a>);</li>
7033 <li>table manipulation (<a href="#6.6">§6.6</a>);</li>
7035 <li>mathematical functions (<a href="#6.7">§6.7</a>) (sin, log, etc.);</li>
7037 <li>input and output (<a href="#6.8">§6.8</a>);</li>
7039 <li>operating system facilities (<a href="#6.9">§6.9</a>);</li>
7041 <li>debug facilities (<a href="#6.10">§6.10</a>).</li>
7044 Except for the basic and the package libraries,
7045 each library provides all its functions as fields of a global table
7046 or as methods of its objects.
7050 To have access to these libraries,
7051 the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
7052 which opens all standard libraries.
7054 the host program can open them individually by using
7055 <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call
7056 <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
7057 <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
7058 <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library),
7059 <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
7060 <a name="pdf-luaopen_utf8"><code>luaopen_utf8</code></a> (for the UTF8 library),
7061 <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
7062 <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
7063 <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
7064 <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the operating system library),
7065 and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
7066 These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>.
7070 <h2>6.1 – <a name="6.1">Basic Functions</a></h2>
7073 The basic library provides core functions to Lua.
7074 If you do not include this library in your application,
7075 you should check carefully whether you need to provide
7076 implementations for some of its facilities.
7080 <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
7084 Calls <a href="#pdf-error"><code>error</code></a> if
7085 the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
7086 otherwise, returns all its arguments.
7088 <code>message</code> is the error object;
7089 when absent, it defaults to "<code>assertion failed!</code>"
7095 <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3>
7099 This function is a generic interface to the garbage collector.
7100 It performs different functions according to its first argument, <code>opt</code>:
7104 <li><b>"<code>collect</code>": </b>
7105 performs a full garbage-collection cycle.
7106 This is the default option.
7109 <li><b>"<code>stop</code>": </b>
7110 stops automatic execution of the garbage collector.
7111 The collector will run only when explicitly invoked,
7112 until a call to restart it.
7115 <li><b>"<code>restart</code>": </b>
7116 restarts automatic execution of the garbage collector.
7119 <li><b>"<code>count</code>": </b>
7120 returns the total memory in use by Lua in Kbytes.
7121 The value has a fractional part,
7122 so that it multiplied by 1024
7123 gives the exact number of bytes in use by Lua
7124 (except for overflows).
7127 <li><b>"<code>step</code>": </b>
7128 performs a garbage-collection step.
7129 The step "size" is controlled by <code>arg</code>.
7131 the collector will perform one basic (indivisible) step.
7132 For non-zero values,
7133 the collector will perform as if that amount of memory
7134 (in KBytes) had been allocated by Lua.
7135 Returns <b>true</b> if the step finished a collection cycle.
7138 <li><b>"<code>setpause</code>": </b>
7139 sets <code>arg</code> as the new value for the <em>pause</em> of
7140 the collector (see <a href="#2.5">§2.5</a>).
7141 Returns the previous value for <em>pause</em>.
7144 <li><b>"<code>setstepmul</code>": </b>
7145 sets <code>arg</code> as the new value for the <em>step multiplier</em> of
7146 the collector (see <a href="#2.5">§2.5</a>).
7147 Returns the previous value for <em>step</em>.
7150 <li><b>"<code>isrunning</code>": </b>
7151 returns a boolean that tells whether the collector is running
7152 (i.e., not stopped).
7160 <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3>
7161 Opens the named file and executes its contents as a Lua chunk.
7162 When called without arguments,
7163 <code>dofile</code> executes the contents of the standard input (<code>stdin</code>).
7164 Returns all values returned by the chunk.
7165 In case of errors, <code>dofile</code> propagates the error
7166 to its caller (that is, <code>dofile</code> does not run in protected mode).
7172 <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
7173 Terminates the last protected function called
7174 and returns <code>message</code> as the error object.
7175 Function <code>error</code> never returns.
7179 Usually, <code>error</code> adds some information about the error position
7180 at the beginning of the message, if the message is a string.
7181 The <code>level</code> argument specifies how to get the error position.
7182 With level 1 (the default), the error position is where the
7183 <code>error</code> function was called.
7184 Level 2 points the error to where the function
7185 that called <code>error</code> was called; and so on.
7186 Passing a level 0 avoids the addition of error position information
7193 <hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
7194 A global variable (not a function) that
7195 holds the global environment (see <a href="#2.2">§2.2</a>).
7196 Lua itself does not use this variable;
7197 changing its value does not affect any environment,
7204 <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
7208 If <code>object</code> does not have a metatable, returns <b>nil</b>.
7210 if the object's metatable has a <code>"__metatable"</code> field,
7211 returns the associated value.
7212 Otherwise, returns the metatable of the given object.
7218 <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
7222 Returns three values (an iterator function, the table <code>t</code>, and 0)
7223 so that the construction
7226 for i,v in ipairs(t) do <em>body</em> end
7228 will iterate over the key–value pairs
7229 (<code>1,t[1]</code>), (<code>2,t[2]</code>), ...,
7230 up to the first nil value.
7236 <hr><h3><a name="pdf-load"><code>load (chunk [, chunkname [, mode [, env]]])</code></a></h3>
7244 If <code>chunk</code> is a string, the chunk is this string.
7245 If <code>chunk</code> is a function,
7246 <code>load</code> calls it repeatedly to get the chunk pieces.
7247 Each call to <code>chunk</code> must return a string that concatenates
7248 with previous results.
7249 A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
7253 If there are no syntactic errors,
7254 returns the compiled chunk as a function;
7255 otherwise, returns <b>nil</b> plus the error message.
7259 If the resulting function has upvalues,
7260 the first upvalue is set to the value of <code>env</code>,
7261 if that parameter is given,
7262 or to the value of the global environment.
7263 Other upvalues are initialized with <b>nil</b>.
7264 (When you load a main chunk,
7265 the resulting function will always have exactly one upvalue,
7266 the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>).
7268 when you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>),
7269 the resulting function can have an arbitrary number of upvalues.)
7270 All upvalues are fresh, that is,
7271 they are not shared with any other function.
7275 <code>chunkname</code> is used as the name of the chunk for error messages
7276 and debug information (see <a href="#4.9">§4.9</a>).
7278 it defaults to <code>chunk</code>, if <code>chunk</code> is a string,
7279 or to "<code>=(load)</code>" otherwise.
7283 The string <code>mode</code> controls whether the chunk can be text or binary
7284 (that is, a precompiled chunk).
7285 It may be the string "<code>b</code>" (only binary chunks),
7286 "<code>t</code>" (only text chunks),
7287 or "<code>bt</code>" (both binary and text).
7288 The default is "<code>bt</code>".
7292 Lua does not check the consistency of binary chunks.
7293 Maliciously crafted binary chunks can crash
7300 <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3>
7304 Similar to <a href="#pdf-load"><code>load</code></a>,
7305 but gets the chunk from file <code>filename</code>
7306 or from the standard input,
7307 if no file name is given.
7313 <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
7317 Allows a program to traverse all fields of a table.
7318 Its first argument is a table and its second argument
7319 is an index in this table.
7320 <code>next</code> returns the next index of the table
7321 and its associated value.
7322 When called with <b>nil</b> as its second argument,
7323 <code>next</code> returns an initial index
7324 and its associated value.
7325 When called with the last index,
7326 or with <b>nil</b> in an empty table,
7327 <code>next</code> returns <b>nil</b>.
7328 If the second argument is absent, then it is interpreted as <b>nil</b>.
7330 you can use <code>next(t)</code> to check whether a table is empty.
7334 The order in which the indices are enumerated is not specified,
7335 <em>even for numeric indices</em>.
7336 (To traverse a table in numeric order,
7337 use a numerical <b>for</b>.)
7341 The behavior of <code>next</code> is undefined if,
7342 during the traversal,
7343 you assign any value to a non-existent field in the table.
7344 You may however modify existing fields.
7345 In particular, you may clear existing fields.
7351 <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
7355 If <code>t</code> has a metamethod <code>__pairs</code>,
7356 calls it with <code>t</code> as argument and returns the first three
7357 results from the call.
7362 returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
7363 so that the construction
7366 for k,v in pairs(t) do <em>body</em> end
7368 will iterate over all key–value pairs of table <code>t</code>.
7372 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
7373 the table during its traversal.
7379 <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3>
7383 Calls function <code>f</code> with
7384 the given arguments in <em>protected mode</em>.
7385 This means that any error inside <code>f</code> is not propagated;
7386 instead, <code>pcall</code> catches the error
7387 and returns a status code.
7388 Its first result is the status code (a boolean),
7389 which is true if the call succeeds without errors.
7390 In such case, <code>pcall</code> also returns all results from the call,
7391 after this first result.
7392 In case of any error, <code>pcall</code> returns <b>false</b> plus the error message.
7398 <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3>
7399 Receives any number of arguments
7400 and prints their values to <code>stdout</code>,
7401 using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string.
7402 <code>print</code> is not intended for formatted output,
7403 but only as a quick way to show a value,
7404 for instance for debugging.
7405 For complete control over the output,
7406 use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>.
7412 <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
7413 Checks whether <code>v1</code> is equal to <code>v2</code>,
7414 without invoking any metamethod.
7421 <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
7422 Gets the real value of <code>table[index]</code>,
7423 without invoking any metamethod.
7424 <code>table</code> must be a table;
7425 <code>index</code> may be any value.
7431 <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3>
7432 Returns the length of the object <code>v</code>,
7433 which must be a table or a string,
7434 without invoking any metamethod.
7441 <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
7442 Sets the real value of <code>table[index]</code> to <code>value</code>,
7443 without invoking any metamethod.
7444 <code>table</code> must be a table,
7445 <code>index</code> any value different from <b>nil</b> and NaN,
7446 and <code>value</code> any Lua value.
7450 This function returns <code>table</code>.
7456 <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3>
7460 If <code>index</code> is a number,
7461 returns all arguments after argument number <code>index</code>;
7462 a negative number indexes from the end (-1 is the last argument).
7463 Otherwise, <code>index</code> must be the string <code>"#"</code>,
7464 and <code>select</code> returns the total number of extra arguments it received.
7470 <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
7474 Sets the metatable for the given table.
7475 (You cannot change the metatable of other types from Lua, only from C.)
7476 If <code>metatable</code> is <b>nil</b>,
7477 removes the metatable of the given table.
7478 If the original metatable has a <code>"__metatable"</code> field,
7483 This function returns <code>table</code>.
7489 <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
7493 When called with no <code>base</code>,
7494 <code>tonumber</code> tries to convert its argument to a number.
7495 If the argument is already a number or
7496 a string convertible to a number,
7497 then <code>tonumber</code> returns this number;
7498 otherwise, it returns <b>nil</b>.
7502 The conversion of strings can result in integers or floats,
7503 according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>).
7504 (The string may have leading and trailing spaces and a sign.)
7508 When called with <code>base</code>,
7509 then <code>e</code> must be a string to be interpreted as
7510 an integer numeral in that base.
7511 The base may be any integer between 2 and 36, inclusive.
7512 In bases above 10, the letter '<code>A</code>' (in either upper or lower case)
7513 represents 10, '<code>B</code>' represents 11, and so forth,
7514 with '<code>Z</code>' representing 35.
7515 If the string <code>e</code> is not a valid numeral in the given base,
7516 the function returns <b>nil</b>.
7522 <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3>
7523 Receives a value of any type and
7524 converts it to a string in a human-readable format.
7525 Floats always produce strings with some
7526 floating-point indication (either a decimal dot or an exponent).
7527 (For complete control of how numbers are converted,
7528 use <a href="#pdf-string.format"><code>string.format</code></a>.)
7532 If the metatable of <code>v</code> has a <code>"__tostring"</code> field,
7533 then <code>tostring</code> calls the corresponding value
7534 with <code>v</code> as argument,
7535 and uses the result of the call as its result.
7541 <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
7542 Returns the type of its only argument, coded as a string.
7543 The possible results of this function are
7544 "<code>nil</code>" (a string, not the value <b>nil</b>),
7545 "<code>number</code>",
7546 "<code>string</code>",
7547 "<code>boolean</code>",
7548 "<code>table</code>",
7549 "<code>function</code>",
7550 "<code>thread</code>",
7551 and "<code>userdata</code>".
7557 <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
7558 A global variable (not a function) that
7559 holds a string containing the current interpreter version.
7560 The current value of this variable is "<code>Lua 5.3</code>".
7566 <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3>
7570 This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
7571 except that it sets a new message handler <code>msgh</code>.
7579 <h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2>
7582 The operations related to coroutines comprise a sub-library of
7583 the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
7584 See <a href="#2.6">§2.6</a> for a general description of coroutines.
7588 <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
7592 Creates a new coroutine, with body <code>f</code>.
7593 <code>f</code> must be a Lua function.
7594 Returns this new coroutine,
7595 an object with type <code>"thread"</code>.
7601 <hr><h3><a name="pdf-coroutine.isyieldable"><code>coroutine.isyieldable ()</code></a></h3>
7605 Returns true when the running coroutine can yield.
7609 A running coroutine is yieldable if it is not the main thread and
7610 it is not inside a non-yieldable C function.
7616 <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3>
7620 Starts or continues the execution of coroutine <code>co</code>.
7621 The first time you resume a coroutine,
7622 it starts running its body.
7623 The values <code>val1</code>, ... are passed
7624 as the arguments to the body function.
7625 If the coroutine has yielded,
7626 <code>resume</code> restarts it;
7627 the values <code>val1</code>, ... are passed
7628 as the results from the yield.
7632 If the coroutine runs without any errors,
7633 <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
7634 (when the coroutine yields) or any values returned by the body function
7635 (when the coroutine terminates).
7636 If there is any error,
7637 <code>resume</code> returns <b>false</b> plus the error message.
7643 <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
7647 Returns the running coroutine plus a boolean,
7648 true when the running coroutine is the main one.
7654 <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
7658 Returns the status of coroutine <code>co</code>, as a string:
7659 <code>"running"</code>,
7660 if the coroutine is running (that is, it called <code>status</code>);
7661 <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
7662 or if it has not started running yet;
7663 <code>"normal"</code> if the coroutine is active but not running
7664 (that is, it has resumed another coroutine);
7665 and <code>"dead"</code> if the coroutine has finished its body function,
7666 or if it has stopped with an error.
7672 <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
7676 Creates a new coroutine, with body <code>f</code>.
7677 <code>f</code> must be a Lua function.
7678 Returns a function that resumes the coroutine each time it is called.
7679 Any arguments passed to the function behave as the
7680 extra arguments to <code>resume</code>.
7681 Returns the same values returned by <code>resume</code>,
7682 except the first boolean.
7683 In case of error, propagates the error.
7689 <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3>
7693 Suspends the execution of the calling coroutine.
7694 Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
7702 <h2>6.3 – <a name="6.3">Modules</a></h2>
7705 The package library provides basic
7706 facilities for loading modules in Lua.
7707 It exports one function directly in the global environment:
7708 <a href="#pdf-require"><code>require</code></a>.
7709 Everything else is exported in a table <a name="pdf-package"><code>package</code></a>.
7713 <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
7717 Loads the given module.
7718 The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
7719 to determine whether <code>modname</code> is already loaded.
7720 If it is, then <code>require</code> returns the value stored
7721 at <code>package.loaded[modname]</code>.
7722 Otherwise, it tries to find a <em>loader</em> for the module.
7727 <code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence.
7728 By changing this sequence,
7729 we can change how <code>require</code> looks for a module.
7730 The following explanation is based on the default configuration
7731 for <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
7735 First <code>require</code> queries <code>package.preload[modname]</code>.
7737 this value (which must be a function) is the loader.
7738 Otherwise <code>require</code> searches for a Lua loader using the
7739 path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
7740 If that also fails, it searches for a C loader using the
7741 path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7743 it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>).
7747 Once a loader is found,
7748 <code>require</code> calls the loader with two arguments:
7749 <code>modname</code> and an extra value dependent on how it got the loader.
7750 (If the loader came from a file,
7751 this extra value is the file name.)
7752 If the loader returns any non-nil value,
7753 <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
7754 If the loader does not return a non-nil value and
7755 has not assigned any value to <code>package.loaded[modname]</code>,
7756 then <code>require</code> assigns <b>true</b> to this entry.
7757 In any case, <code>require</code> returns the
7758 final value of <code>package.loaded[modname]</code>.
7762 If there is any error loading or running the module,
7763 or if it cannot find any loader for the module,
7764 then <code>require</code> raises an error.
7770 <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3>
7774 A string describing some compile-time configurations for packages.
7775 This string is a sequence of lines:
7779 <li>The first line is the directory separator string.
7780 Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li>
7782 <li>The second line is the character that separates templates in a path.
7783 Default is '<code>;</code>'.</li>
7785 <li>The third line is the string that marks the
7786 substitution points in a template.
7787 Default is '<code>?</code>'.</li>
7789 <li>The fourth line is a string that, in a path in Windows,
7790 is replaced by the executable's directory.
7791 Default is '<code>!</code>'.</li>
7793 <li>The fifth line is a mark to ignore all text after it
7794 when building the <code>luaopen_</code> function name.
7795 Default is '<code>-</code>'.</li>
7802 <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
7806 The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader.
7810 Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
7811 it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
7812 using the environment variable <a name="pdf-LUA_CPATH_5_3"><code>LUA_CPATH_5_3</code></a>
7813 or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>
7814 or a default path defined in <code>luaconf.h</code>.
7820 <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
7824 A table used by <a href="#pdf-require"><code>require</code></a> to control which
7825 modules are already loaded.
7826 When you require a module <code>modname</code> and
7827 <code>package.loaded[modname]</code> is not false,
7828 <a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
7832 This variable is only a reference to the real table;
7833 assignments to this variable do not change the
7834 table used by <a href="#pdf-require"><code>require</code></a>.
7840 <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
7844 Dynamically links the host program with the C library <code>libname</code>.
7848 If <code>funcname</code> is "<code>*</code>",
7849 then it only links with the library,
7850 making the symbols exported by the library
7851 available to other dynamically linked libraries.
7853 it looks for a function <code>funcname</code> inside the library
7854 and returns this function as a C function.
7855 So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype
7856 (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
7860 This is a low-level function.
7861 It completely bypasses the package and module system.
7862 Unlike <a href="#pdf-require"><code>require</code></a>,
7863 it does not perform any path searching and
7864 does not automatically adds extensions.
7865 <code>libname</code> must be the complete file name of the C library,
7866 including if necessary a path and an extension.
7867 <code>funcname</code> must be the exact name exported by the C library
7868 (which may depend on the C compiler and linker used).
7872 This function is not supported by Standard C.
7873 As such, it is only available on some platforms
7874 (Windows, Linux, Mac OS X, Solaris, BSD,
7875 plus other Unix systems that support the <code>dlfcn</code> standard).
7881 <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
7885 The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader.
7889 At start-up, Lua initializes this variable with
7890 the value of the environment variable <a name="pdf-LUA_PATH_5_3"><code>LUA_PATH_5_3</code></a> or
7891 the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
7892 with a default path defined in <code>luaconf.h</code>,
7893 if those environment variables are not defined.
7894 Any "<code>;;</code>" in the value of the environment variable
7895 is replaced by the default path.
7901 <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
7905 A table to store loaders for specific modules
7906 (see <a href="#pdf-require"><code>require</code></a>).
7910 This variable is only a reference to the real table;
7911 assignments to this variable do not change the
7912 table used by <a href="#pdf-require"><code>require</code></a>.
7918 <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3>
7922 A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
7926 Each entry in this table is a <em>searcher function</em>.
7927 When looking for a module,
7928 <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
7929 with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
7931 The function can return another function (the module <em>loader</em>)
7932 plus an extra value that will be passed to that loader,
7933 or a string explaining why it did not find that module
7934 (or <b>nil</b> if it has nothing to say).
7938 Lua initializes this table with four searcher functions.
7942 The first searcher simply looks for a loader in the
7943 <a href="#pdf-package.preload"><code>package.preload</code></a> table.
7947 The second searcher looks for a loader as a Lua library,
7948 using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
7949 The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7953 The third searcher looks for a loader as a C library,
7954 using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7956 the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7958 if the C path is the string
7961 "./?.so;./?.dll;/usr/local/?/init.so"
7963 the searcher for module <code>foo</code>
7964 will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
7965 and <code>/usr/local/foo/init.so</code>, in that order.
7966 Once it finds a C library,
7967 this searcher first uses a dynamic link facility to link the
7968 application with the library.
7969 Then it tries to find a C function inside the library to
7970 be used as the loader.
7971 The name of this C function is the string "<code>luaopen_</code>"
7972 concatenated with a copy of the module name where each dot
7973 is replaced by an underscore.
7974 Moreover, if the module name has a hyphen,
7975 its suffix after (and including) the first hyphen is removed.
7976 For instance, if the module name is <code>a.b.c-v2.1</code>,
7977 the function name will be <code>luaopen_a_b_c</code>.
7981 The fourth searcher tries an <em>all-in-one loader</em>.
7982 It searches the C path for a library for
7983 the root name of the given module.
7984 For instance, when requiring <code>a.b.c</code>,
7985 it will search for a C library for <code>a</code>.
7986 If found, it looks into it for an open function for
7988 in our example, that would be <code>luaopen_a_b_c</code>.
7989 With this facility, a package can pack several C submodules
7990 into one single library,
7991 with each submodule keeping its original open function.
7995 All searchers except the first one (preload) return as the extra value
7996 the file name where the module was found,
7997 as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7998 The first searcher returns no extra value.
8004 <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3>
8008 Searches for the given <code>name</code> in the given <code>path</code>.
8012 A path is a string containing a sequence of
8013 <em>templates</em> separated by semicolons.
8015 the function replaces each interrogation mark (if any)
8016 in the template with a copy of <code>name</code>
8017 wherein all occurrences of <code>sep</code>
8019 were replaced by <code>rep</code>
8020 (the system's directory separator, by default),
8021 and then tries to open the resulting file name.
8025 For instance, if the path is the string
8028 "./?.lua;./?.lc;/usr/local/?/init.lua"
8030 the search for the name <code>foo.a</code>
8031 will try to open the files
8032 <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and
8033 <code>/usr/local/foo/a/init.lua</code>, in that order.
8037 Returns the resulting name of the first file that it can
8038 open in read mode (after closing the file),
8039 or <b>nil</b> plus an error message if none succeeds.
8040 (This error message lists all file names it tried to open.)
8048 <h2>6.4 – <a name="6.4">String Manipulation</a></h2>
8051 This library provides generic functions for string manipulation,
8052 such as finding and extracting substrings, and pattern matching.
8053 When indexing a string in Lua, the first character is at position 1
8054 (not at 0, as in C).
8055 Indices are allowed to be negative and are interpreted as indexing backwards,
8056 from the end of the string.
8057 Thus, the last character is at position -1, and so on.
8061 The string library provides all its functions inside the table
8062 <a name="pdf-string"><code>string</code></a>.
8063 It also sets a metatable for strings
8064 where the <code>__index</code> field points to the <code>string</code> table.
8065 Therefore, you can use the string functions in object-oriented style.
8066 For instance, <code>string.byte(s,i)</code>
8067 can be written as <code>s:byte(i)</code>.
8071 The string library assumes one-byte character encodings.
8075 <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
8076 Returns the internal numerical codes of the characters <code>s[i]</code>,
8077 <code>s[i+1]</code>, ..., <code>s[j]</code>.
8078 The default value for <code>i</code> is 1;
8079 the default value for <code>j</code> is <code>i</code>.
8080 These indices are corrected
8081 following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
8085 Numerical codes are not necessarily portable across platforms.
8091 <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3>
8092 Receives zero or more integers.
8093 Returns a string with length equal to the number of arguments,
8094 in which each character has the internal numerical code equal
8095 to its corresponding argument.
8099 Numerical codes are not necessarily portable across platforms.
8105 <hr><h3><a name="pdf-string.dump"><code>string.dump (function [, strip])</code></a></h3>
8109 Returns a string containing a binary representation
8110 (a <em>binary chunk</em>)
8111 of the given function,
8112 so that a later <a href="#pdf-load"><code>load</code></a> on this string returns
8113 a copy of the function (but with new upvalues).
8114 If <code>strip</code> is a true value,
8115 the binary representation is created without debug information
8117 (local variable names, lines, etc.).
8121 Functions with upvalues have only their number of upvalues saved.
8123 those upvalues receive fresh instances containing <b>nil</b>.
8124 (You can use the debug library to serialize
8125 and reload the upvalues of a function
8126 in a way adequate to your needs.)
8132 <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
8136 Looks for the first match of
8137 <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>.
8138 If it finds a match, then <code>find</code> returns the indices of <code>s</code>
8139 where this occurrence starts and ends;
8140 otherwise, it returns <b>nil</b>.
8141 A third, optional numerical argument <code>init</code> specifies
8142 where to start the search;
8143 its default value is 1 and can be negative.
8144 A value of <b>true</b> as a fourth, optional argument <code>plain</code>
8145 turns off the pattern matching facilities,
8146 so the function does a plain "find substring" operation,
8147 with no characters in <code>pattern</code> being considered magic.
8148 Note that if <code>plain</code> is given, then <code>init</code> must be given as well.
8152 If the pattern has captures,
8153 then in a successful match
8154 the captured values are also returned,
8155 after the two indices.
8161 <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3>
8165 Returns a formatted version of its variable number of arguments
8166 following the description given in its first argument (which must be a string).
8167 The format string follows the same rules as the ISO C function <code>sprintf</code>.
8168 The only differences are that the options/modifiers
8169 <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>,
8170 and <code>p</code> are not supported
8171 and that there is an extra option, <code>q</code>.
8172 The <code>q</code> option formats a string between double quotes,
8173 using escape sequences when necessary to ensure that
8174 it can safely be read back by the Lua interpreter.
8175 For instance, the call
8178 string.format('%q', 'a string with "quotes" and \n new line')
8180 may produce the string:
8183 "a string with \"quotes\" and \
8189 <code>A</code> and <code>a</code> (when available),
8190 <code>E</code>, <code>e</code>, <code>f</code>,
8191 <code>G</code>, and <code>g</code> all expect a number as argument.
8192 Options <code>c</code>, <code>d</code>,
8193 <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>
8195 Option <code>q</code> expects a string;
8196 option <code>s</code> expects a string without embedded zeros.
8197 If the argument to option <code>s</code> is not a string,
8198 it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
8204 <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3>
8205 Returns an iterator function that,
8206 each time it is called,
8207 returns the next captures from <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>)
8208 over the string <code>s</code>.
8209 If <code>pattern</code> specifies no captures,
8210 then the whole match is produced in each call.
8214 As an example, the following loop
8215 will iterate over all the words from string <code>s</code>,
8216 printing one per line:
8219 s = "hello world from Lua"
8220 for w in string.gmatch(s, "%a+") do
8224 The next example collects all pairs <code>key=value</code> from the
8225 given string into a table:
8229 s = "from=world, to=Lua"
8230 for k, v in string.gmatch(s, "(%w+)=(%w+)") do
8236 For this function, a caret '<code>^</code>' at the start of a pattern does not
8237 work as an anchor, as this would prevent the iteration.
8243 <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
8244 Returns a copy of <code>s</code>
8245 in which all (or the first <code>n</code>, if given)
8246 occurrences of the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) have been
8247 replaced by a replacement string specified by <code>repl</code>,
8248 which can be a string, a table, or a function.
8249 <code>gsub</code> also returns, as its second value,
8250 the total number of matches that occurred.
8251 The name <code>gsub</code> comes from <em>Global SUBstitution</em>.
8255 If <code>repl</code> is a string, then its value is used for replacement.
8256 The character <code>%</code> works as an escape character:
8257 any sequence in <code>repl</code> of the form <code>%<em>d</em></code>,
8258 with <em>d</em> between 1 and 9,
8259 stands for the value of the <em>d</em>-th captured substring.
8260 The sequence <code>%0</code> stands for the whole match.
8261 The sequence <code>%%</code> stands for a single <code>%</code>.
8265 If <code>repl</code> is a table, then the table is queried for every match,
8266 using the first capture as the key.
8270 If <code>repl</code> is a function, then this function is called every time a
8271 match occurs, with all captured substrings passed as arguments,
8277 if the pattern specifies no captures,
8278 then it behaves as if the whole pattern was inside a capture.
8282 If the value returned by the table query or by the function call
8283 is a string or a number,
8284 then it is used as the replacement string;
8285 otherwise, if it is <b>false</b> or <b>nil</b>,
8286 then there is no replacement
8287 (that is, the original match is kept in the string).
8291 Here are some examples:
8294 x = string.gsub("hello world", "(%w+)", "%1 %1")
8295 --> x="hello hello world world"
8297 x = string.gsub("hello world", "%w+", "%0 %0", 1)
8298 --> x="hello hello world"
8300 x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
8301 --> x="world hello Lua from"
8303 x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
8304 --> x="home = /home/roberto, user = roberto"
8306 x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
8311 local t = {name="lua", version="5.3"}
8312 x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
8313 --> x="lua-5.3.tar.gz"
8319 <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
8320 Receives a string and returns its length.
8321 The empty string <code>""</code> has length 0.
8322 Embedded zeros are counted,
8323 so <code>"a\000bc\000"</code> has length 5.
8329 <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
8330 Receives a string and returns a copy of this string with all
8331 uppercase letters changed to lowercase.
8332 All other characters are left unchanged.
8333 The definition of what an uppercase letter is depends on the current locale.
8339 <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
8340 Looks for the first <em>match</em> of
8341 <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>.
8342 If it finds one, then <code>match</code> returns
8343 the captures from the pattern;
8344 otherwise it returns <b>nil</b>.
8345 If <code>pattern</code> specifies no captures,
8346 then the whole match is returned.
8347 A third, optional numerical argument <code>init</code> specifies
8348 where to start the search;
8349 its default value is 1 and can be negative.
8355 <hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, ···)</code></a></h3>
8359 Returns a binary string containing the values <code>v1</code>, <code>v2</code>, etc.
8360 packed (that is, serialized in binary form)
8361 according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>).
8367 <hr><h3><a name="pdf-string.packsize"><code>string.packsize (fmt)</code></a></h3>
8371 Returns the size of a string resulting from <a href="#pdf-string.pack"><code>string.pack</code></a>
8372 with the given format.
8373 The format string cannot have the variable-length options
8374 '<code>s</code>' or '<code>z</code>' (see <a href="#6.4.2">§6.4.2</a>).
8380 <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3>
8381 Returns a string that is the concatenation of <code>n</code> copies of
8382 the string <code>s</code> separated by the string <code>sep</code>.
8383 The default value for <code>sep</code> is the empty string
8384 (that is, no separator).
8385 Returns the empty string if <code>n</code> is not positive.
8391 <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
8392 Returns a string that is the string <code>s</code> reversed.
8398 <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
8399 Returns the substring of <code>s</code> that
8400 starts at <code>i</code> and continues until <code>j</code>;
8401 <code>i</code> and <code>j</code> can be negative.
8402 If <code>j</code> is absent, then it is assumed to be equal to -1
8403 (which is the same as the string length).
8405 the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
8406 with length <code>j</code>,
8407 and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code>
8408 with length <code>i</code>.
8412 If, after the translation of negative indices,
8413 <code>i</code> is less than 1,
8414 it is corrected to 1.
8415 If <code>j</code> is greater than the string length,
8416 it is corrected to that length.
8417 If, after these corrections,
8418 <code>i</code> is greater than <code>j</code>,
8419 the function returns the empty string.
8425 <hr><h3><a name="pdf-string.unpack"><code>string.unpack (fmt, s [, pos])</code></a></h3>
8429 Returns the values packed in string <code>s</code> (see <a href="#pdf-string.pack"><code>string.pack</code></a>)
8430 according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>).
8431 An optional <code>pos</code> marks where
8432 to start reading in <code>s</code> (default is 1).
8433 After the read values,
8434 this function also returns the index of the first unread byte in <code>s</code>.
8440 <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
8441 Receives a string and returns a copy of this string with all
8442 lowercase letters changed to uppercase.
8443 All other characters are left unchanged.
8444 The definition of what a lowercase letter is depends on the current locale.
8450 <h3>6.4.1 – <a name="6.4.1">Patterns</a></h3>
8453 Patterns in Lua are described by regular strings,
8454 which are interpreted as patterns by the pattern-matching functions
8455 <a href="#pdf-string.find"><code>string.find</code></a>,
8456 <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>,
8457 <a href="#pdf-string.gsub"><code>string.gsub</code></a>,
8458 and <a href="#pdf-string.match"><code>string.match</code></a>.
8459 This section describes the syntax and the meaning
8460 (that is, what they match) of these strings.
8464 <h4>Character Class:</h4><p>
8465 A <em>character class</em> is used to represent a set of characters.
8466 The following combinations are allowed in describing a character class:
8470 <li><b><em>x</em>: </b>
8471 (where <em>x</em> is not one of the <em>magic characters</em>
8472 <code>^$()%.[]*+-?</code>)
8473 represents the character <em>x</em> itself.
8476 <li><b><code>.</code>: </b> (a dot) represents all characters.</li>
8478 <li><b><code>%a</code>: </b> represents all letters.</li>
8480 <li><b><code>%c</code>: </b> represents all control characters.</li>
8482 <li><b><code>%d</code>: </b> represents all digits.</li>
8484 <li><b><code>%g</code>: </b> represents all printable characters except space.</li>
8486 <li><b><code>%l</code>: </b> represents all lowercase letters.</li>
8488 <li><b><code>%p</code>: </b> represents all punctuation characters.</li>
8490 <li><b><code>%s</code>: </b> represents all space characters.</li>
8492 <li><b><code>%u</code>: </b> represents all uppercase letters.</li>
8494 <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li>
8496 <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li>
8498 <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character)
8499 represents the character <em>x</em>.
8500 This is the standard way to escape the magic characters.
8501 Any non-alphanumeric character
8502 (including all punctuations, even the non-magical)
8503 can be preceded by a '<code>%</code>'
8504 when used to represent itself in a pattern.
8507 <li><b><code>[<em>set</em>]</code>: </b>
8508 represents the class which is the union of all
8509 characters in <em>set</em>.
8510 A range of characters can be specified by
8511 separating the end characters of the range,
8512 in ascending order, with a '<code>-</code>'.
8513 All classes <code>%</code><em>x</em> described above can also be used as
8514 components in <em>set</em>.
8515 All other characters in <em>set</em> represent themselves.
8516 For example, <code>[%w_]</code> (or <code>[_%w]</code>)
8517 represents all alphanumeric characters plus the underscore,
8518 <code>[0-7]</code> represents the octal digits,
8519 and <code>[0-7%l%-]</code> represents the octal digits plus
8520 the lowercase letters plus the '<code>-</code>' character.
8524 The interaction between ranges and classes is not defined.
8525 Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
8529 <li><b><code>[^<em>set</em>]</code>: </b>
8530 represents the complement of <em>set</em>,
8531 where <em>set</em> is interpreted as above.
8535 For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
8536 the corresponding uppercase letter represents the complement of the class.
8537 For instance, <code>%S</code> represents all non-space characters.
8541 The definitions of letter, space, and other character groups
8542 depend on the current locale.
8543 In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
8549 <h4>Pattern Item:</h4><p>
8550 A <em>pattern item</em> can be
8555 a single character class,
8556 which matches any single character in the class;
8560 a single character class followed by '<code>*</code>',
8561 which matches zero or more repetitions of characters in the class.
8562 These repetition items will always match the longest possible sequence;
8566 a single character class followed by '<code>+</code>',
8567 which matches one or more repetitions of characters in the class.
8568 These repetition items will always match the longest possible sequence;
8572 a single character class followed by '<code>-</code>',
8573 which also matches zero or more repetitions of characters in the class.
8574 Unlike '<code>*</code>',
8575 these repetition items will always match the shortest possible sequence;
8579 a single character class followed by '<code>?</code>',
8580 which matches zero or one occurrence of a character in the class.
8581 It always matches one occurrence if possible;
8585 <code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
8586 such item matches a substring equal to the <em>n</em>-th captured string
8591 <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
8592 such item matches strings that start with <em>x</em>, end with <em>y</em>,
8593 and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
8594 This means that, if one reads the string from left to right,
8595 counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
8596 the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
8597 For instance, the item <code>%b()</code> matches expressions with
8598 balanced parentheses.
8602 <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>;
8603 such item matches an empty string at any position such that
8604 the next character belongs to <em>set</em>
8605 and the previous character does not belong to <em>set</em>.
8606 The set <em>set</em> is interpreted as previously described.
8607 The beginning and the end of the subject are handled as if
8608 they were the character '<code>\0</code>'.
8616 <h4>Pattern:</h4><p>
8617 A <em>pattern</em> is a sequence of pattern items.
8618 A caret '<code>^</code>' at the beginning of a pattern anchors the match at the
8619 beginning of the subject string.
8620 A '<code>$</code>' at the end of a pattern anchors the match at the
8621 end of the subject string.
8623 '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
8629 <h4>Captures:</h4><p>
8630 A pattern can contain sub-patterns enclosed in parentheses;
8631 they describe <em>captures</em>.
8632 When a match succeeds, the substrings of the subject string
8633 that match captures are stored (<em>captured</em>) for future use.
8634 Captures are numbered according to their left parentheses.
8635 For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
8636 the part of the string matching <code>"a*(.)%w(%s*)"</code> is
8637 stored as the first capture (and therefore has number 1);
8638 the character matching "<code>.</code>" is captured with number 2,
8639 and the part matching "<code>%s*</code>" has number 3.
8643 As a special case, the empty capture <code>()</code> captures
8644 the current string position (a number).
8645 For instance, if we apply the pattern <code>"()aa()"</code> on the
8646 string <code>"flaaap"</code>, there will be two captures: 3 and 5.
8654 <h3>6.4.2 – <a name="6.4.2">Format Strings for Pack and Unpack</a></h3>
8657 The first argument to <a href="#pdf-string.pack"><code>string.pack</code></a>,
8658 <a href="#pdf-string.packsize"><code>string.packsize</code></a>, and <a href="#pdf-string.unpack"><code>string.unpack</code></a>
8660 which describes the layout of the structure being created or read.
8664 A format string is a sequence of conversion options.
8665 The conversion options are as follows:
8668 <li><b><code><</code>: </b>sets little endian</li>
8669 <li><b><code>></code>: </b>sets big endian</li>
8670 <li><b><code>=</code>: </b>sets native endian</li>
8671 <li><b><code>![<em>n</em>]</code>: </b>sets maximum alignment to <code>n</code>
8672 (default is native alignment)</li>
8673 <li><b><code>b</code>: </b>a signed byte (<code>char</code>)</li>
8674 <li><b><code>B</code>: </b>an unsigned byte (<code>char</code>)</li>
8675 <li><b><code>h</code>: </b>a signed <code>short</code> (native size)</li>
8676 <li><b><code>H</code>: </b>an unsigned <code>short</code> (native size)</li>
8677 <li><b><code>l</code>: </b>a signed <code>long</code> (native size)</li>
8678 <li><b><code>L</code>: </b>an unsigned <code>long</code> (native size)</li>
8679 <li><b><code>j</code>: </b>a <code>lua_Integer</code></li>
8680 <li><b><code>J</code>: </b>a <code>lua_Unsigned</code></li>
8681 <li><b><code>T</code>: </b>a <code>size_t</code> (native size)</li>
8682 <li><b><code>i[<em>n</em>]</code>: </b>a signed <code>int</code> with <code>n</code> bytes
8683 (default is native size)</li>
8684 <li><b><code>I[<em>n</em>]</code>: </b>an unsigned <code>int</code> with <code>n</code> bytes
8685 (default is native size)</li>
8686 <li><b><code>f</code>: </b>a <code>float</code> (native size)</li>
8687 <li><b><code>d</code>: </b>a <code>double</code> (native size)</li>
8688 <li><b><code>n</code>: </b>a <code>lua_Number</code></li>
8689 <li><b><code>c<em>n</em></code>: </b>a fixed-sized string with <code>n</code> bytes</li>
8690 <li><b><code>z</code>: </b>a zero-terminated string</li>
8691 <li><b><code>s[<em>n</em>]</code>: </b>a string preceded by its length
8692 coded as an unsigned integer with <code>n</code> bytes
8693 (default is a <code>size_t</code>)</li>
8694 <li><b><code>x</code>: </b>one byte of padding</li>
8695 <li><b><code>X<em>op</em></code>: </b>an empty item that aligns
8696 according to option <code>op</code>
8697 (which is otherwise ignored)</li>
8698 <li><b>'<code> </code>': </b>(empty space) ignored</li>
8700 (A "<code>[<em>n</em>]</code>" means an optional integral numeral.)
8701 Except for padding, spaces, and configurations
8702 (options "<code>xX <=>!</code>"),
8703 each option corresponds to an argument (in <a href="#pdf-string.pack"><code>string.pack</code></a>)
8704 or a result (in <a href="#pdf-string.unpack"><code>string.unpack</code></a>).
8708 For options "<code>!<em>n</em></code>", "<code>s<em>n</em></code>", "<code>i<em>n</em></code>", and "<code>I<em>n</em></code>",
8709 <code>n</code> can be any integer between 1 and 16.
8710 All integral options check overflows;
8711 <a href="#pdf-string.pack"><code>string.pack</code></a> checks whether the given value fits in the given size;
8712 <a href="#pdf-string.unpack"><code>string.unpack</code></a> checks whether the read value fits in a Lua integer.
8716 Any format string starts as if prefixed by "<code>!1=</code>",
8718 with maximum alignment of 1 (no alignment)
8719 and native endianness.
8723 Alignment works as follows:
8725 the format gets extra padding until the data starts
8726 at an offset that is a multiple of the minimum between the
8727 option size and the maximum alignment;
8728 this minimum must be a power of 2.
8729 Options "<code>c</code>" and "<code>z</code>" are not aligned;
8730 option "<code>s</code>" follows the alignment of its starting integer.
8734 All padding is filled with zeros by <a href="#pdf-string.pack"><code>string.pack</code></a>
8735 (and ignored by <a href="#pdf-string.unpack"><code>string.unpack</code></a>).
8743 <h2>6.5 – <a name="6.5">UTF-8 Support</a></h2>
8746 This library provides basic support for UTF-8 encoding.
8747 It provides all its functions inside the table <a name="pdf-utf8"><code>utf8</code></a>.
8748 This library does not provide any support for Unicode other
8749 than the handling of the encoding.
8750 Any operation that needs the meaning of a character,
8751 such as character classification, is outside its scope.
8755 Unless stated otherwise,
8756 all functions that expect a byte position as a parameter
8757 assume that the given position is either the start of a byte sequence
8758 or one plus the length of the subject string.
8759 As in the string library,
8760 negative indices count from the end of the string.
8764 <hr><h3><a name="pdf-utf8.char"><code>utf8.char (···)</code></a></h3>
8765 Receives zero or more integers,
8766 converts each one to its corresponding UTF-8 byte sequence
8767 and returns a string with the concatenation of all these sequences.
8773 <hr><h3><a name="pdf-utf8.charpattern"><code>utf8.charpattern</code></a></h3>
8774 The pattern (a string, not a function) "<code>[\0-\x7F\xC2-\xF4][\x80-\xBF]*</code>"
8775 (see <a href="#6.4.1">§6.4.1</a>),
8776 which matches exactly one UTF-8 byte sequence,
8777 assuming that the subject is a valid UTF-8 string.
8783 <hr><h3><a name="pdf-utf8.codes"><code>utf8.codes (s)</code></a></h3>
8787 Returns values so that the construction
8790 for p, c in utf8.codes(s) do <em>body</em> end
8792 will iterate over all characters in string <code>s</code>,
8793 with <code>p</code> being the position (in bytes) and <code>c</code> the code point
8795 It raises an error if it meets any invalid byte sequence.
8801 <hr><h3><a name="pdf-utf8.codepoint"><code>utf8.codepoint (s [, i [, j]])</code></a></h3>
8802 Returns the codepoints (as integers) from all characters in <code>s</code>
8803 that start between byte position <code>i</code> and <code>j</code> (both included).
8804 The default for <code>i</code> is 1 and for <code>j</code> is <code>i</code>.
8805 It raises an error if it meets any invalid byte sequence.
8811 <hr><h3><a name="pdf-utf8.len"><code>utf8.len (s [, i [, j]])</code></a></h3>
8812 Returns the number of UTF-8 characters in string <code>s</code>
8813 that start between positions <code>i</code> and <code>j</code> (both inclusive).
8814 The default for <code>i</code> is 1 and for <code>j</code> is -1.
8815 If it finds any invalid byte sequence,
8816 returns a false value plus the position of the first invalid byte.
8822 <hr><h3><a name="pdf-utf8.offset"><code>utf8.offset (s, n [, i])</code></a></h3>
8823 Returns the position (in bytes) where the encoding of the
8824 <code>n</code>-th character of <code>s</code>
8825 (counting from position <code>i</code>) starts.
8826 A negative <code>n</code> gets characters before position <code>i</code>.
8827 The default for <code>i</code> is 1 when <code>n</code> is non-negative
8828 and <code>#s + 1</code> otherwise,
8829 so that <code>utf8.offset(s, -n)</code> gets the offset of the
8830 <code>n</code>-th character from the end of the string.
8831 If the specified character is neither in the subject
8832 nor right after its end,
8833 the function returns <b>nil</b>.
8838 when <code>n</code> is 0 the function returns the start of the encoding
8839 of the character that contains the <code>i</code>-th byte of <code>s</code>.
8843 This function assumes that <code>s</code> is a valid UTF-8 string.
8851 <h2>6.6 – <a name="6.6">Table Manipulation</a></h2>
8854 This library provides generic functions for table manipulation.
8855 It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
8859 Remember that, whenever an operation needs the length of a table,
8860 the table must be a proper sequence
8861 or have a <code>__len</code> metamethod (see <a href="#3.4.7">§3.4.7</a>).
8862 All functions ignore non-numeric keys
8863 in the tables given as arguments.
8867 <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3>
8871 Given a list where all elements are strings or numbers,
8872 returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>.
8873 The default value for <code>sep</code> is the empty string,
8874 the default for <code>i</code> is 1,
8875 and the default for <code>j</code> is <code>#list</code>.
8876 If <code>i</code> is greater than <code>j</code>, returns the empty string.
8882 <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3>
8886 Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>,
8887 shifting up the elements
8888 <code>list[pos], list[pos+1], ···, list[#list]</code>.
8889 The default value for <code>pos</code> is <code>#list+1</code>,
8890 so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
8891 of list <code>t</code>.
8897 <hr><h3><a name="pdf-table.move"><code>table.move (a1, f, e, t [,a2])</code></a></h3>
8901 Moves elements from table <code>a1</code> to table <code>a2</code>.
8902 This function performs the equivalent to the following
8903 multiple assignment:
8904 <code>a2[t],··· = a1[f],···,a1[e]</code>.
8905 The default for <code>a2</code> is <code>a1</code>.
8906 The destination range can overlap with the source range.
8907 Index <code>f</code> must be positive.
8913 <hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3>
8917 Returns a new table with all parameters stored into keys 1, 2, etc.
8918 and with a field "<code>n</code>" with the total number of parameters.
8919 Note that the resulting table may not be a sequence.
8925 <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3>
8929 Removes from <code>list</code> the element at position <code>pos</code>,
8930 returning the value of the removed element.
8931 When <code>pos</code> is an integer between 1 and <code>#list</code>,
8932 it shifts down the elements
8933 <code>list[pos+1], list[pos+2], ···, list[#list]</code>
8934 and erases element <code>list[#list]</code>;
8935 The index <code>pos</code> can also be 0 when <code>#list</code> is 0,
8936 or <code>#list + 1</code>;
8937 in those cases, the function erases the element <code>list[pos]</code>.
8941 The default value for <code>pos</code> is <code>#list</code>,
8942 so that a call <code>table.remove(l)</code> removes the last element
8943 of list <code>l</code>.
8949 <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3>
8953 Sorts list elements in a given order, <em>in-place</em>,
8954 from <code>list[1]</code> to <code>list[#list]</code>.
8955 If <code>comp</code> is given,
8956 then it must be a function that receives two list elements
8957 and returns true when the first element must come
8958 before the second in the final order
8959 (so that <code>not comp(list[i+1],list[i])</code> will be true after the sort).
8960 If <code>comp</code> is not given,
8961 then the standard Lua operator <code><</code> is used instead.
8965 The sort algorithm is not stable;
8966 that is, elements considered equal by the given order
8967 may have their relative positions changed by the sort.
8973 <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3>
8977 Returns the elements from the given list.
8978 This function is equivalent to
8981 return list[i], list[i+1], ···, list[j]
8983 By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>.
8991 <h2>6.7 – <a name="6.7">Mathematical Functions</a></h2>
8994 This library provides basic mathematical functions.
8995 It provides all its functions and constants inside the table <a name="pdf-math"><code>math</code></a>.
8996 Functions with the annotation "<code>integer/float</code>" give
8997 integer results for integer arguments
8998 and float results for float (or mixed) arguments.
9000 (<a href="#pdf-math.ceil"><code>math.ceil</code></a>, <a href="#pdf-math.floor"><code>math.floor</code></a>, and <a href="#pdf-math.modf"><code>math.modf</code></a>)
9001 return an integer when the result fits in the range of an integer,
9002 or a float otherwise.
9006 <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
9010 Returns the absolute value of <code>x</code>. (integer/float)
9016 <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
9020 Returns the arc cosine of <code>x</code> (in radians).
9026 <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
9030 Returns the arc sine of <code>x</code> (in radians).
9036 <hr><h3><a name="pdf-math.atan"><code>math.atan (y [, x])</code></a></h3>
9041 Returns the arc tangent of <code>y/x</code> (in radians),
9042 but uses the signs of both parameters to find the
9043 quadrant of the result.
9044 (It also handles correctly the case of <code>x</code> being zero.)
9048 The default value for <code>x</code> is 1,
9049 so that the call <code>math.atan(y)</code>
9050 returns the arc tangent of <code>y</code>.
9056 <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
9060 Returns the smallest integral value larger than or equal to <code>x</code>.
9066 <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
9070 Returns the cosine of <code>x</code> (assumed to be in radians).
9076 <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
9080 Converts the angle <code>x</code> from radians to degrees.
9086 <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
9090 Returns the value <em>e<sup>x</sup></em>
9091 (where <code>e</code> is the base of natural logarithms).
9097 <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
9101 Returns the largest integral value smaller than or equal to <code>x</code>.
9107 <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
9111 Returns the remainder of the division of <code>x</code> by <code>y</code>
9112 that rounds the quotient towards zero. (integer/float)
9118 <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
9122 The float value <code>HUGE_VAL</code>,
9123 a value larger than any other numerical value.
9129 <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3>
9133 Returns the logarithm of <code>x</code> in the given base.
9134 The default for <code>base</code> is <em>e</em>
9135 (so that the function returns the natural logarithm of <code>x</code>).
9141 <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3>
9145 Returns the argument with the maximum value,
9146 according to the Lua operator <code><</code>. (integer/float)
9152 <hr><h3><a name="pdf-math.maxinteger"><code>math.maxinteger</code></a></h3>
9153 An integer with the maximum value for an integer.
9159 <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3>
9163 Returns the argument with the minimum value,
9164 according to the Lua operator <code><</code>. (integer/float)
9170 <hr><h3><a name="pdf-math.mininteger"><code>math.mininteger</code></a></h3>
9171 An integer with the minimum value for an integer.
9177 <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
9181 Returns the integral part of <code>x</code> and the fractional part of <code>x</code>.
9182 Its second result is always a float.
9188 <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
9192 The value of <em>π</em>.
9198 <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
9202 Converts the angle <code>x</code> from degrees to radians.
9208 <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
9212 When called without arguments,
9213 returns a pseudo-random float with uniform distribution
9214 in the range <em>[0,1)</em>.
9215 When called with two integers <code>m</code> and <code>n</code>,
9216 <code>math.random</code> returns a pseudo-random integer
9217 with uniform distribution in the range <em>[m, n]</em>.
9218 (The value <em>m-n</em> cannot be negative and must fit in a Lua integer.)
9219 The call <code>math.random(n)</code> is equivalent to <code>math.random(1,n)</code>.
9223 This function is an interface to the underling
9224 pseudo-random generator function provided by C.
9225 No guarantees can be given for its statistical properties.
9231 <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3>
9235 Sets <code>x</code> as the "seed"
9236 for the pseudo-random generator:
9237 equal seeds produce equal sequences of numbers.
9243 <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
9247 Returns the sine of <code>x</code> (assumed to be in radians).
9253 <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
9257 Returns the square root of <code>x</code>.
9258 (You can also use the expression <code>x^0.5</code> to compute this value.)
9264 <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
9268 Returns the tangent of <code>x</code> (assumed to be in radians).
9274 <hr><h3><a name="pdf-math.tointeger"><code>math.tointeger (x)</code></a></h3>
9278 If the value <code>x</code> is convertible to an integer,
9279 returns that integer.
9280 Otherwise, returns <b>nil</b>.
9286 <hr><h3><a name="pdf-math.type"><code>math.type (x)</code></a></h3>
9290 Returns "<code>integer</code>" if <code>x</code> is an integer,
9291 "<code>float</code>" if it is a float,
9292 or <b>nil</b> if <code>x</code> is not a number.
9298 <hr><h3><a name="pdf-math.ult"><code>math.ult (m, n)</code></a></h3>
9303 true if integer <code>m</code> is below integer <code>n</code> when
9304 they are compared as unsigned integers.
9312 <h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2>
9315 The I/O library provides two different styles for file manipulation.
9316 The first one uses implicit file handles;
9317 that is, there are operations to set a default input file and a
9318 default output file,
9319 and all input/output operations are over these default files.
9320 The second style uses explicit file handles.
9324 When using implicit file handles,
9325 all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
9326 When using explicit file handles,
9327 the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file handle
9328 and then all operations are supplied as methods of the file handle.
9332 The table <code>io</code> also provides
9333 three predefined file handles with their usual meanings from C:
9334 <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>.
9335 The I/O library never closes these files.
9339 Unless otherwise stated,
9340 all I/O functions return <b>nil</b> on failure
9341 (plus an error message as a second result and
9342 a system-dependent error code as a third result)
9343 and some value different from <b>nil</b> on success.
9344 On non-POSIX systems,
9345 the computation of the error message and error code
9347 may be not thread safe,
9348 because they rely on the global C variable <code>errno</code>.
9352 <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
9356 Equivalent to <code>file:close()</code>.
9357 Without a <code>file</code>, closes the default output file.
9363 <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
9367 Equivalent to <code>io.output():flush()</code>.
9373 <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
9377 When called with a file name, it opens the named file (in text mode),
9378 and sets its handle as the default input file.
9379 When called with a file handle,
9380 it simply sets this file handle as the default input file.
9381 When called without parameters,
9382 it returns the current default input file.
9386 In case of errors this function raises the error,
9387 instead of returning an error code.
9393 <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename ···])</code></a></h3>
9397 Opens the given file name in read mode
9398 and returns an iterator function that
9399 works like <code>file:lines(···)</code> over the opened file.
9400 When the iterator function detects the end of file,
9401 it returns no values (to finish the loop) and automatically closes the file.
9405 The call <code>io.lines()</code> (with no file name) is equivalent
9406 to <code>io.input():lines("*l")</code>;
9407 that is, it iterates over the lines of the default input file.
9408 In this case it does not close the file when the loop ends.
9412 In case of errors this function raises the error,
9413 instead of returning an error code.
9419 <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
9423 This function opens a file,
9424 in the mode specified in the string <code>mode</code>.
9425 It returns a new file handle,
9426 or, in case of errors, <b>nil</b> plus an error message.
9430 The <code>mode</code> string can be any of the following:
9433 <li><b>"<code>r</code>": </b> read mode (the default);</li>
9434 <li><b>"<code>w</code>": </b> write mode;</li>
9435 <li><b>"<code>a</code>": </b> append mode;</li>
9436 <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li>
9437 <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li>
9438 <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved,
9439 writing is only allowed at the end of file.</li>
9441 The <code>mode</code> string can also have a '<code>b</code>' at the end,
9442 which is needed in some systems to open the file in binary mode.
9448 <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
9452 Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
9458 <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
9462 This function is system dependent and is not available
9467 Starts program <code>prog</code> in a separated process and returns
9468 a file handle that you can use to read data from this program
9469 (if <code>mode</code> is <code>"r"</code>, the default)
9470 or to write data to this program
9471 (if <code>mode</code> is <code>"w"</code>).
9477 <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3>
9481 Equivalent to <code>io.input():read(···)</code>.
9487 <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
9491 Returns a handle for a temporary file.
9492 This file is opened in update mode
9493 and it is automatically removed when the program ends.
9499 <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
9503 Checks whether <code>obj</code> is a valid file handle.
9504 Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
9505 <code>"closed file"</code> if <code>obj</code> is a closed file handle,
9506 or <b>nil</b> if <code>obj</code> is not a file handle.
9512 <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3>
9516 Equivalent to <code>io.output():write(···)</code>.
9522 <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
9526 Closes <code>file</code>.
9527 Note that files are automatically closed when
9528 their handles are garbage collected,
9529 but that takes an unpredictable amount of time to happen.
9533 When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>,
9534 <a href="#pdf-file:close"><code>file:close</code></a> returns the same values
9535 returned by <a href="#pdf-os.execute"><code>os.execute</code></a>.
9541 <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
9545 Saves any written data to <code>file</code>.
9551 <hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3>
9555 Returns an iterator function that,
9556 each time it is called,
9557 reads the file according to the given formats.
9558 When no format is given,
9559 uses "<code>l</code>" as a default.
9560 As an example, the construction
9563 for c in file:lines(1) do <em>body</em> end
9565 will iterate over all characters of the file,
9566 starting at the current position.
9567 Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
9572 In case of errors this function raises the error,
9573 instead of returning an error code.
9579 <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3>
9583 Reads the file <code>file</code>,
9584 according to the given formats, which specify what to read.
9586 the function returns a string or a number with the characters read,
9587 or <b>nil</b> if it cannot read data with the specified format.
9588 (In this latter case,
9589 the function does not read subsequent formats.)
9590 When called without formats,
9591 it uses a default format that reads the next line
9596 The available formats are
9600 <li><b>"<code>n</code>": </b>
9601 reads a numeral and returns it as a float or an integer,
9602 following the lexical conventions of Lua.
9603 (The numeral may have leading spaces and a sign.)
9604 This format always reads the longest input sequence that
9605 is a valid prefix for a number;
9606 if that prefix does not form a valid number
9607 (e.g., an empty string, "<code>0x</code>", or "<code>3.4e-</code>"),
9608 it is discarded and the function returns <b>nil</b>.
9611 <li><b>"<code>i</code>": </b>
9612 reads an integral number and returns it as an integer.
9615 <li><b>"<code>a</code>": </b>
9616 reads the whole file, starting at the current position.
9617 On end of file, it returns the empty string.
9620 <li><b>"<code>l</code>": </b>
9621 reads the next line skipping the end of line,
9622 returning <b>nil</b> on end of file.
9623 This is the default format.
9626 <li><b>"<code>L</code>": </b>
9627 reads the next line keeping the end-of-line character (if present),
9628 returning <b>nil</b> on end of file.
9631 <li><b><em>number</em>: </b>
9632 reads a string with up to this number of bytes,
9633 returning <b>nil</b> on end of file.
9634 If <code>number</code> is zero,
9635 it reads nothing and returns an empty string,
9636 or <b>nil</b> on end of file.
9640 The formats "<code>l</code>" and "<code>L</code>" should be used only for text files.
9646 <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3>
9650 Sets and gets the file position,
9651 measured from the beginning of the file,
9652 to the position given by <code>offset</code> plus a base
9653 specified by the string <code>whence</code>, as follows:
9656 <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li>
9657 <li><b>"<code>cur</code>": </b> base is current position;</li>
9658 <li><b>"<code>end</code>": </b> base is end of file;</li>
9660 In case of success, <code>seek</code> returns the final file position,
9661 measured in bytes from the beginning of the file.
9662 If <code>seek</code> fails, it returns <b>nil</b>,
9663 plus a string describing the error.
9667 The default value for <code>whence</code> is <code>"cur"</code>,
9668 and for <code>offset</code> is 0.
9669 Therefore, the call <code>file:seek()</code> returns the current
9670 file position, without changing it;
9671 the call <code>file:seek("set")</code> sets the position to the
9672 beginning of the file (and returns 0);
9673 and the call <code>file:seek("end")</code> sets the position to the
9674 end of the file, and returns its size.
9680 <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
9684 Sets the buffering mode for an output file.
9685 There are three available modes:
9689 <li><b>"<code>no</code>": </b>
9690 no buffering; the result of any output operation appears immediately.
9693 <li><b>"<code>full</code>": </b>
9694 full buffering; output operation is performed only
9695 when the buffer is full or when
9696 you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>).
9699 <li><b>"<code>line</code>": </b>
9700 line buffering; output is buffered until a newline is output
9701 or there is any input from some special files
9702 (such as a terminal device).
9706 For the last two cases, <code>size</code>
9707 specifies the size of the buffer, in bytes.
9708 The default is an appropriate size.
9714 <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3>
9718 Writes the value of each of its arguments to <code>file</code>.
9719 The arguments must be strings or numbers.
9723 In case of success, this function returns <code>file</code>.
9724 Otherwise it returns <b>nil</b> plus a string describing the error.
9732 <h2>6.9 – <a name="6.9">Operating System Facilities</a></h2>
9735 This library is implemented through table <a name="pdf-os"><code>os</code></a>.
9739 <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
9743 Returns an approximation of the amount in seconds of CPU time
9744 used by the program.
9750 <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
9754 Returns a string or a table containing date and time,
9755 formatted according to the given string <code>format</code>.
9759 If the <code>time</code> argument is present,
9760 this is the time to be formatted
9761 (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
9762 Otherwise, <code>date</code> formats the current time.
9766 If <code>format</code> starts with '<code>!</code>',
9767 then the date is formatted in Coordinated Universal Time.
9768 After this optional character,
9769 if <code>format</code> is the string "<code>*t</code>",
9770 then <code>date</code> returns a table with the following fields:
9771 <code>year</code> (four digits), <code>month</code> (1–12), <code>day</code> (1–31),
9772 <code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61),
9773 <code>wday</code> (weekday, Sunday is 1),
9774 <code>yday</code> (day of the year),
9775 and <code>isdst</code> (daylight saving flag, a boolean).
9776 This last field may be absent
9777 if the information is not available.
9781 If <code>format</code> is not "<code>*t</code>",
9782 then <code>date</code> returns the date as a string,
9783 formatted according to the same rules as the ISO C function <code>strftime</code>.
9787 When called without arguments,
9788 <code>date</code> returns a reasonable date and time representation that depends on
9789 the host system and on the current locale
9790 (that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
9794 On non-POSIX systems,
9795 this function may be not thread safe
9796 because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>.
9802 <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
9806 Returns the difference, in seconds,
9807 from time <code>t1</code> to time <code>t2</code>
9808 (where the times are values returned by <a href="#pdf-os.time"><code>os.time</code></a>).
9809 In POSIX, Windows, and some other systems,
9810 this value is exactly <code>t2</code><em>-</em><code>t1</code>.
9816 <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
9820 This function is equivalent to the ISO C function <code>system</code>.
9821 It passes <code>command</code> to be executed by an operating system shell.
9822 Its first result is <b>true</b>
9823 if the command terminated successfully,
9824 or <b>nil</b> otherwise.
9825 After this first result
9826 the function returns a string plus a number,
9831 <li><b>"<code>exit</code>": </b>
9832 the command terminated normally;
9833 the following number is the exit status of the command.
9836 <li><b>"<code>signal</code>": </b>
9837 the command was terminated by a signal;
9838 the following number is the signal that terminated the command.
9844 When called without a <code>command</code>,
9845 <code>os.execute</code> returns a boolean that is true if a shell is available.
9851 <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close]])</code></a></h3>
9855 Calls the ISO C function <code>exit</code> to terminate the host program.
9856 If <code>code</code> is <b>true</b>,
9857 the returned status is <code>EXIT_SUCCESS</code>;
9858 if <code>code</code> is <b>false</b>,
9859 the returned status is <code>EXIT_FAILURE</code>;
9860 if <code>code</code> is a number,
9861 the returned status is this number.
9862 The default value for <code>code</code> is <b>true</b>.
9866 If the optional second argument <code>close</code> is true,
9867 closes the Lua state before exiting.
9873 <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
9877 Returns the value of the process environment variable <code>varname</code>,
9878 or <b>nil</b> if the variable is not defined.
9884 <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
9888 Deletes the file (or empty directory, on POSIX systems)
9889 with the given name.
9890 If this function fails, it returns <b>nil</b>,
9891 plus a string describing the error and the error code.
9897 <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
9901 Renames file or directory named <code>oldname</code> to <code>newname</code>.
9902 If this function fails, it returns <b>nil</b>,
9903 plus a string describing the error and the error code.
9909 <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
9913 Sets the current locale of the program.
9914 <code>locale</code> is a system-dependent string specifying a locale;
9915 <code>category</code> is an optional string describing which category to change:
9916 <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
9917 <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
9918 the default category is <code>"all"</code>.
9919 The function returns the name of the new locale,
9920 or <b>nil</b> if the request cannot be honored.
9924 If <code>locale</code> is the empty string,
9925 the current locale is set to an implementation-defined native locale.
9926 If <code>locale</code> is the string "<code>C</code>",
9927 the current locale is set to the standard C locale.
9931 When called with <b>nil</b> as the first argument,
9932 this function only returns the name of the current locale
9933 for the given category.
9937 This function may be not thread safe
9938 because of its reliance on C function <code>setlocale</code>.
9944 <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
9948 Returns the current time when called without arguments,
9949 or a time representing the date and time specified by the given table.
9950 This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
9952 <code>hour</code> (default is 12),
9953 <code>min</code> (default is 0),
9954 <code>sec</code> (default is 0),
9955 and <code>isdst</code> (default is <b>nil</b>).
9956 For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
9960 The returned value is a number, whose meaning depends on your system.
9961 In POSIX, Windows, and some other systems,
9962 this number counts the number
9963 of seconds since some given start time (the "epoch").
9964 In other systems, the meaning is not specified,
9965 and the number returned by <code>time</code> can be used only as an argument to
9966 <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>.
9972 <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
9976 Returns a string with a file name that can
9977 be used for a temporary file.
9978 The file must be explicitly opened before its use
9979 and explicitly removed when no longer needed.
9984 this function also creates a file with that name,
9985 to avoid security risks.
9986 (Someone else might create the file with wrong permissions
9987 in the time between getting the name and creating the file.)
9988 You still have to open the file to use it
9989 and to remove it (even if you do not use it).
9994 you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
9995 which automatically removes the file when the program ends.
10003 <h2>6.10 – <a name="6.10">The Debug Library</a></h2>
10006 This library provides
10007 the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs.
10008 You should exert care when using this library.
10009 Several of its functions
10010 violate basic assumptions about Lua code
10011 (e.g., that variables local to a function
10012 cannot be accessed from outside;
10013 that userdata metatables cannot be changed by Lua code;
10014 that Lua programs do not crash)
10015 and therefore can compromise otherwise secure code.
10016 Moreover, some functions in this library may be slow.
10020 All functions in this library are provided
10021 inside the <a name="pdf-debug"><code>debug</code></a> table.
10022 All functions that operate over a thread
10023 have an optional first argument which is the
10024 thread to operate over.
10025 The default is always the current thread.
10029 <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
10033 Enters an interactive mode with the user,
10034 running each string that the user enters.
10035 Using simple commands and other debug facilities,
10036 the user can inspect global and local variables,
10037 change their values, evaluate expressions, and so on.
10038 A line containing only the word <code>cont</code> finishes this function,
10039 so that the caller continues its execution.
10043 Note that commands for <code>debug.debug</code> are not lexically nested
10044 within any function and so have no direct access to local variables.
10050 <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
10054 Returns the current hook settings of the thread, as three values:
10055 the current hook function, the current hook mask,
10056 and the current hook count
10057 (as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function).
10063 <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3>
10067 Returns a table with information about a function.
10068 You can give the function directly
10069 or you can give a number as the value of <code>f</code>,
10070 which means the function running at level <code>f</code> of the call stack
10071 of the given thread:
10072 level 0 is the current function (<code>getinfo</code> itself);
10073 level 1 is the function that called <code>getinfo</code>
10074 (except for tail calls, which do not count on the stack);
10076 If <code>f</code> is a number larger than the number of active functions,
10077 then <code>getinfo</code> returns <b>nil</b>.
10081 The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
10082 with the string <code>what</code> describing which fields to fill in.
10083 The default for <code>what</code> is to get all information available,
10084 except the table of valid lines.
10086 the option '<code>f</code>'
10087 adds a field named <code>func</code> with the function itself.
10089 the option '<code>L</code>'
10090 adds a field named <code>activelines</code> with the table of
10095 For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
10096 a table with a name for the current function,
10097 if a reasonable name can be found,
10098 and the expression <code>debug.getinfo(print)</code>
10099 returns a table with all available information
10100 about the <a href="#pdf-print"><code>print</code></a> function.
10106 <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3>
10110 This function returns the name and the value of the local variable
10111 with index <code>local</code> of the function at level <code>f</code> of the stack.
10112 This function accesses not only explicit local variables,
10113 but also parameters, temporaries, etc.
10117 The first parameter or local variable has index 1, and so on,
10118 following the order that they are declared in the code,
10119 counting only the variables that are active
10120 in the current scope of the function.
10121 Negative indices refer to vararg parameters;
10122 -1 is the first vararg parameter.
10123 The function returns <b>nil</b> if there is no variable with the given index,
10124 and raises an error when called with a level out of range.
10125 (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
10129 Variable names starting with '<code>(</code>' (open parenthesis)
10130 represent variables with no known names
10131 (internal variables such as loop control variables,
10132 and variables from chunks saved without debug information).
10136 The parameter <code>f</code> may also be a function.
10137 In that case, <code>getlocal</code> returns only the name of function parameters.
10143 <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3>
10147 Returns the metatable of the given <code>value</code>
10148 or <b>nil</b> if it does not have a metatable.
10154 <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
10158 Returns the registry table (see <a href="#4.5">§4.5</a>).
10164 <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3>
10168 This function returns the name and the value of the upvalue
10169 with index <code>up</code> of the function <code>f</code>.
10170 The function returns <b>nil</b> if there is no upvalue with the given index.
10174 Variable names starting with '<code>(</code>' (open parenthesis)
10175 represent variables with no known names
10176 (variables from chunks saved without debug information).
10182 <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3>
10186 Returns the Lua value associated to <code>u</code>.
10187 If <code>u</code> is not a userdata,
10188 returns <b>nil</b>.
10194 <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
10198 Sets the given function as a hook.
10199 The string <code>mask</code> and the number <code>count</code> describe
10200 when the hook will be called.
10201 The string mask may have any combination of the following characters,
10202 with the given meaning:
10205 <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li>
10206 <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li>
10207 <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li>
10210 with a <code>count</code> different from zero,
10211 the hook is called also after every <code>count</code> instructions.
10215 When called without arguments,
10216 <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
10220 When the hook is called, its first parameter is a string
10221 describing the event that has triggered its call:
10222 <code>"call"</code> (or <code>"tail call"</code>),
10223 <code>"return"</code>,
10224 <code>"line"</code>, and <code>"count"</code>.
10226 the hook also gets the new line number as its second parameter.
10228 you can call <code>getinfo</code> with level 2 to get more information about
10229 the running function
10230 (level 0 is the <code>getinfo</code> function,
10231 and level 1 is the hook function).
10237 <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
10241 This function assigns the value <code>value</code> to the local variable
10242 with index <code>local</code> of the function at level <code>level</code> of the stack.
10243 The function returns <b>nil</b> if there is no local
10244 variable with the given index,
10245 and raises an error when called with a <code>level</code> out of range.
10246 (You can call <code>getinfo</code> to check whether the level is valid.)
10247 Otherwise, it returns the name of the local variable.
10251 See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about
10252 variable indices and names.
10258 <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3>
10262 Sets the metatable for the given <code>value</code> to the given <code>table</code>
10263 (which can be <b>nil</b>).
10264 Returns <code>value</code>.
10270 <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3>
10274 This function assigns the value <code>value</code> to the upvalue
10275 with index <code>up</code> of the function <code>f</code>.
10276 The function returns <b>nil</b> if there is no upvalue
10277 with the given index.
10278 Otherwise, it returns the name of the upvalue.
10284 <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3>
10288 Sets the given <code>value</code> as
10289 the Lua value associated to the given <code>udata</code>.
10290 <code>udata</code> must be a full userdata.
10294 Returns <code>udata</code>.
10300 <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
10304 If <code>message</code> is present but is neither a string nor <b>nil</b>,
10305 this function returns <code>message</code> without further processing.
10307 it returns a string with a traceback of the call stack.
10308 The optional <code>message</code> string is appended
10309 at the beginning of the traceback.
10310 An optional <code>level</code> number tells at which level
10311 to start the traceback
10312 (default is 1, the function calling <code>traceback</code>).
10318 <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3>
10322 Returns a unique identifier (as a light userdata)
10323 for the upvalue numbered <code>n</code>
10324 from the given function.
10328 These unique identifiers allow a program to check whether different
10329 closures share upvalues.
10330 Lua closures that share an upvalue
10331 (that is, that access a same external local variable)
10332 will return identical ids for those upvalue indices.
10338 <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3>
10342 Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code>
10343 refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>.
10351 <h1>7 – <a name="7">Lua Standalone</a></h1>
10354 Although Lua has been designed as an extension language,
10355 to be embedded in a host C program,
10356 it is also frequently used as a standalone language.
10357 An interpreter for Lua as a standalone language,
10358 called simply <code>lua</code>,
10359 is provided with the standard distribution.
10360 The standalone interpreter includes
10361 all standard libraries, including the debug library.
10365 lua [options] [script [args]]
10370 <li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li>
10371 <li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li>
10372 <li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li>
10373 <li><b><code>-v</code>: </b> prints version information;</li>
10374 <li><b><code>-E</code>: </b> ignores environment variables;</li>
10375 <li><b><code>--</code>: </b> stops handling options;</li>
10376 <li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li>
10378 After handling its options, <code>lua</code> runs the given <em>script</em>.
10379 When called without arguments,
10380 <code>lua</code> behaves as <code>lua -v -i</code>
10381 when the standard input (<code>stdin</code>) is a terminal,
10382 and as <code>lua -</code> otherwise.
10386 When called without option <code>-E</code>,
10387 the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_3"><code>LUA_INIT_5_3</code></a>
10388 (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if the versioned name is not defined)
10389 before running any argument.
10390 If the variable content has the format <code>@<em>filename</em></code>,
10391 then <code>lua</code> executes the file.
10392 Otherwise, <code>lua</code> executes the string itself.
10396 When called with option <code>-E</code>,
10397 besides ignoring <code>LUA_INIT</code>,
10399 the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>,
10400 setting the values of
10401 <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a>
10402 with the default paths defined in <code>luaconf.h</code>.
10406 All options are handled in order, except <code>-i</code> and <code>-E</code>.
10407 For instance, an invocation like
10410 $ lua -e'a=1' -e 'print(a)' script.lua
10412 will first set <code>a</code> to 1, then print the value of <code>a</code>,
10413 and finally run the file <code>script.lua</code> with no arguments.
10414 (Here <code>$</code> is the shell prompt. Your prompt may be different.)
10418 Before running any code,
10419 <code>lua</code> collects all command-line arguments
10420 in a global table called <code>arg</code>.
10421 The script name goes to index 0,
10422 the first argument after the script name goes to index 1,
10424 Any arguments before the script name
10425 (that is, the interpreter name plus its options)
10426 go to negative indices.
10427 For instance, in the call
10430 $ lua -la b.lua t1 t2
10432 the table is like this:
10435 arg = { [-2] = "lua", [-1] = "-la",
10437 [1] = "t1", [2] = "t2" }
10439 If there is no script in the call,
10440 the interpreter name goes to index 0,
10441 followed by the other arguments.
10442 For instance, the call
10445 $ lua -e "print(arg[1])"
10447 will print "<code>-e</code>".
10448 If there is a script,
10449 the script is called with parameters
10450 <code>arg[1]</code>, ···, <code>arg[#arg]</code>.
10451 (Like all chunks in Lua,
10452 the script is compiled as a vararg function.)
10456 In interactive mode,
10457 Lua repeatedly prompts and waits for a line.
10458 After reading a line,
10459 Lua first try to interpret the line as an expression.
10460 If it succeeds, it prints its value.
10461 Otherwise, it interprets the line as a statement.
10462 If you write an incomplete statement,
10463 the interpreter waits for its completion
10464 by issuing a different prompt.
10468 In case of unprotected errors in the script,
10469 the interpreter reports the error to the standard error stream.
10470 If the error object is not a string but
10471 has a metamethod <code>__tostring</code>,
10472 the interpreter calls this metamethod to produce the final message.
10473 Otherwise, the interpreter converts the error object to a string
10474 and adds a stack traceback to it.
10478 When finishing normally,
10479 the interpreter closes its main Lua state
10480 (see <a href="#lua_close"><code>lua_close</code></a>).
10481 The script can avoid this step by
10482 calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate.
10486 To allow the use of Lua as a
10487 script interpreter in Unix systems,
10488 the standalone interpreter skips
10489 the first line of a chunk if it starts with <code>#</code>.
10490 Therefore, Lua scripts can be made into executable programs
10491 by using <code>chmod +x</code> and the <code>#!</code> form,
10495 #!/usr/local/bin/lua
10498 the location of the Lua interpreter may be different in your machine.
10499 If <code>lua</code> is in your <code>PATH</code>,
10505 is a more portable solution.)
10509 <h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1>
10512 Here we list the incompatibilities that you may find when moving a program
10513 from Lua 5.2 to Lua 5.3.
10514 You can avoid some incompatibilities by compiling Lua with
10515 appropriate options (see file <code>luaconf.h</code>).
10517 all these compatibility options will be removed in the future.
10521 Lua versions can always change the C API in ways that
10522 do not imply source-code changes in a program,
10523 such as the numeric values for constants
10524 or the implementation of functions as macros.
10526 you should not assume that binaries are compatible between
10527 different Lua versions.
10528 Always recompile clients of the Lua API when
10529 using a new version.
10533 Similarly, Lua versions can always change the internal representation
10534 of precompiled chunks;
10535 precompiled chunks are not compatible between different Lua versions.
10539 The standard paths in the official distribution may
10540 change between versions.
10544 <h2>8.1 – <a name="8.1">Changes in the Language</a></h2>
10548 The main difference between Lua 5.2 and Lua 5.3 is the
10549 introduction of an integer subtype for numbers.
10550 Although this change should not affect "normal" computations,
10552 (mainly those that involve some kind of overflow)
10553 can give different results.
10557 You can fix these differences by forcing a number to be a float
10558 (in Lua 5.2 all numbers were float),
10559 in particular writing constants with an ending <code>.0</code>
10560 or using <code>x = x + 0.0</code> to convert a variable.
10561 (This recommendation is only for a quick fix
10562 for an occasional incompatibility;
10563 it is not a general guideline for good programming.
10564 For good programming,
10565 use floats where you need floats
10566 and integers where you need integers.)
10570 The conversion of a float to a string now adds a <code>.0</code> suffix
10571 to the result if it looks like an integer.
10572 (For instance, the float 2.0 will be printed as <code>2.0</code>,
10573 not as <code>2</code>.)
10574 You should always use an explicit format
10575 when you need a specific format for numbers.
10579 (Formally this is not an incompatibility,
10580 because Lua does not specify how numbers are formatted as strings,
10581 but some programs assumed a specific format.)
10585 The generational mode for the garbage collector was removed.
10586 (It was an experimental feature in Lua 5.2.)
10594 <h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2>
10598 The <code>bit32</code> library has been deprecated.
10599 It is easy to require a compatible external library or,
10600 better yet, to replace its functions with appropriate bitwise operations.
10601 (Keep in mind that <code>bit32</code> operates on 32-bit integers,
10602 while the bitwise operators in standard Lua operate on 64-bit integers.)
10606 The Table library now respects metamethods
10607 for setting and getting elements.
10611 The <a href="#pdf-ipairs"><code>ipairs</code></a> iterator now respects metamethods and
10612 its <code>__ipairs</code> metamethod has been deprecated.
10616 Option names in <a href="#pdf-io.read"><code>io.read</code></a> do not have a starting '<code>*</code>' anymore.
10617 For compatibility, Lua will continue to ignore this character.
10621 The following functions were deprecated in the mathematical library:
10622 <code>atan2</code>, <code>cosh</code>, <code>sinh</code>, <code>tanh</code>, <code>pow</code>,
10623 <code>frexp</code>, and <code>ldexp</code>.
10624 You can replace <code>math.pow(x,y)</code> with <code>x^y</code>;
10625 you can replace <code>math.atan2</code> with <code>math.atan</code>,
10626 which now accepts one or two parameters;
10627 you can replace <code>math.ldexp(x,exp)</code> with <code>x * 2.0^exp</code>.
10628 For the other operations,
10629 you can either use an external library or
10630 implement them in Lua.
10634 The searcher for C loaders used by <a href="#pdf-require"><code>require</code></a>
10635 changed the way it handles versioned names.
10636 Now, the version should come after the module name
10637 (as is usual in most other tools).
10638 For compatibility, that searcher still tries the old format
10639 if it cannot find an open function according to the new style.
10640 (Lua 5.2 already worked that way,
10641 but it did not document the change.)
10649 <h2>8.3 – <a name="8.3">Changes in the API</a></h2>
10655 Continuation functions now receive as parameters what they needed
10656 to get through <code>lua_getctx</code>,
10657 so <code>lua_getctx</code> has been removed.
10658 Adapt your code accordingly.
10662 Function <a href="#lua_dump"><code>lua_dump</code></a> has an extra parameter, <code>strip</code>.
10663 Use 0 as the value of this parameter to get the old behavior.
10667 Functions to inject/project unsigned integers
10668 (<code>lua_pushunsigned</code>, <code>lua_tounsigned</code>, <code>lua_tounsignedx</code>,
10669 <code>luaL_checkunsigned</code>, <code>luaL_optunsigned</code>)
10671 Use their signed equivalents with a type cast.
10675 Macros to project non-default integer types
10676 (<code>luaL_checkint</code>, <code>luaL_optint</code>, <code>luaL_checklong</code>, <code>luaL_optlong</code>)
10678 Use their equivalent over <a href="#lua_Integer"><code>lua_Integer</code></a> with a type cast
10679 (or, when possible, use <a href="#lua_Integer"><code>lua_Integer</code></a> in your code).
10687 <h1>9 – <a name="9">The Complete Syntax of Lua</a></h1>
10690 Here is the complete syntax of Lua in extended BNF.
10691 As usual in extended BNF,
10692 {A} means 0 or more As,
10693 and [A] means an optional A.
10694 (For operator precedences, see <a href="#3.4.8">§3.4.8</a>;
10695 for a description of the terminals
10697 and LiteralString, see <a href="#3.1">§3.1</a>.)
10706 block ::= {stat} [retstat]
10708 stat ::= ‘<b>;</b>’ |
10709 varlist ‘<b>=</b>’ explist |
10714 <b>do</b> block <b>end</b> |
10715 <b>while</b> exp <b>do</b> block <b>end</b> |
10716 <b>repeat</b> block <b>until</b> exp |
10717 <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
10718 <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> |
10719 <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> |
10720 <b>function</b> funcname funcbody |
10721 <b>local</b> <b>function</b> Name funcbody |
10722 <b>local</b> namelist [‘<b>=</b>’ explist]
10724 retstat ::= <b>return</b> [explist] [‘<b>;</b>’]
10726 label ::= ‘<b>::</b>’ Name ‘<b>::</b>’
10728 funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name]
10730 varlist ::= var {‘<b>,</b>’ var}
10732 var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name
10734 namelist ::= Name {‘<b>,</b>’ Name}
10736 explist ::= exp {‘<b>,</b>’ exp}
10738 exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | ‘<b>...</b>’ | functiondef |
10739 prefixexp | tableconstructor | exp binop exp | unop exp
10741 prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’
10743 functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args
10745 args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | LiteralString
10747 functiondef ::= <b>function</b> funcbody
10749 funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b>
10751 parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’
10753 tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’
10755 fieldlist ::= field {fieldsep field} [fieldsep]
10757 field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp
10759 fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’
10761 binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>//</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ |
10762 ‘<b>&</b>’ | ‘<b>~</b>’ | ‘<b>|</b>’ | ‘<b>>></b>’ | ‘<b><<</b>’ | ‘<b>..</b>’ |
10763 ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ |
10764 <b>and</b> | <b>or</b>
10766 unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’ | ‘<b>~</b>’
10780 <SMALL CLASS="footer">
10782 Tue Jan 6 10:10:50 BRST 2015
10785 Last change: revised for Lua 5.3.0 (final)
projects / FreeBSD / FreeBSD.git / blob