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  15 <a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a>
  16 Lua 5.2 Reference Manual
  17 </h1>
  18
  19 by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
  20 <p>
  21 <small>
  22 Copyright &copy; 2011&ndash;2013 Lua.org, PUC-Rio.
  23 Freely available under the terms of the
  24 <a href="http://www.lua.org/license.html">Lua license</a>.
  25 </small>
  26 <hr>
  27 <p>
  28
  29 <a href="contents.html#contents">contents</A>
  30 &middot;
  31 <a href="contents.html#index">index</A>
  32
  33 <!-- ====================================================================== -->
  34 <p>
  35
  36 <!-- $Id: manual.of,v 1.103 2013/03/14 18:51:56 roberto Exp $ -->
  37
  38
  39
  40
  41 <h1>1 &ndash; <a name="1">Introduction</a></h1>
  42
  43 <p>
  44 Lua is an extension programming language designed to support
  45 general procedural programming with data description
  46 facilities.
  47 It also offers good support for object-oriented programming,
  48 functional programming, and data-driven programming.
  49 Lua is intended to be used as a powerful, lightweight,
  50 embeddable scripting language for any program that needs one.
  51 Lua is implemented as a library, written in <em>clean C</em>,
  52 the common subset of Standard&nbsp;C and C++.
  53
  54
  55 <p>
  56 Being an extension language, Lua has no notion of a "main" program:
  57 it only works <em>embedded</em> in a host client,
  58 called the <em>embedding program</em> or simply the <em>host</em>.
  59 The host program can invoke functions to execute a piece of Lua code,
  60 can write and read Lua variables,
  61 and can register C&nbsp;functions to be called by Lua code.
  62 Through the use of C&nbsp;functions, Lua can be augmented to cope with
  63 a wide range of different domains,
  64 thus creating customized programming languages sharing a syntactical framework.
  65 The Lua distribution includes a sample host program called <code>lua</code>,
  66 which uses the Lua library to offer a complete, standalone Lua interpreter,
  67 for interactive or batch use.
  68
  69
  70 <p>
  71 Lua is free software,
  72 and is provided as usual with no guarantees,
  73 as stated in its license.
  74 The implementation described in this manual is available
  75 at Lua's official web site, <code>www.lua.org</code>.
  76
  77
  78 <p>
  79 Like any other reference manual,
  80 this document is dry in places.
  81 For a discussion of the decisions behind the design of Lua,
  82 see the technical papers available at Lua's web site.
  83 For a detailed introduction to programming in Lua,
  84 see Roberto's book, <em>Programming in Lua</em>.
  85
  86
  87
  88 <h1>2 &ndash; <a name="2">Basic Concepts</a></h1>
  89
  90 <p>
  91 This section describes the basic concepts of the language.
  92
  93
  94
  95 <h2>2.1 &ndash; <a name="2.1">Values and Types</a></h2>
  96
  97 <p>
  98 Lua is a <em>dynamically typed language</em>.
  99 This means that
 100 variables do not have types; only values do.
 101 There are no type definitions in the language.
 102 All values carry their own type.
 103
 104
 105 <p>
 106 All values in Lua are <em>first-class values</em>.
 107 This means that all values can be stored in variables,
 108 passed as arguments to other functions, and returned as results.
 109
 110
 111 <p>
 112 There are eight basic types in Lua:
 113 <em>nil</em>, <em>boolean</em>, <em>number</em>,
 114 <em>string</em>, <em>function</em>, <em>userdata</em>,
 115 <em>thread</em>, and <em>table</em>.
 116 <em>Nil</em> is the type of the value <b>nil</b>,
 117 whose main property is to be different from any other value;
 118 it usually represents the absence of a useful value.
 119 <em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
 120 Both <b>nil</b> and <b>false</b> make a condition false;
 121 any other value makes it true.
 122 <em>Number</em> represents real (double-precision floating-point) numbers.
 123 Operations on numbers follow the same rules of
 124 the underlying C&nbsp;implementation,
 125 which, in turn, usually follows the IEEE 754 standard.
 126 (It is easy to build Lua interpreters that use other
 127 internal representations for numbers,
 128 such as single-precision floats or long integers;
 129 see file <code>luaconf.h</code>.)
 130 <em>String</em> represents immutable sequences of bytes.
 131
 132 Lua is 8-bit clean:
 133 strings can contain any 8-bit value,
 134 including embedded zeros ('<code>\0</code>').
 135
 136
 137 <p>
 138 Lua can call (and manipulate) functions written in Lua and
 139 functions written in C
 140 (see <a href="#3.4.9">&sect;3.4.9</a>).
 141
 142
 143 <p>
 144 The type <em>userdata</em> is provided to allow arbitrary C&nbsp;data to
 145 be stored in Lua variables.
 146 A userdata value is a pointer to a block of raw memory.
 147 There are two kinds of userdata:
 148 full userdata, where the block of memory is managed by Lua,
 149 and light userdata, where the block of memory is managed by the host.
 150 Userdata has no predefined operations in Lua,
 151 except assignment and identity test.
 152 By using <em>metatables</em>,
 153 the programmer can define operations for full userdata values
 154 (see <a href="#2.4">&sect;2.4</a>).
 155 Userdata values cannot be created or modified in Lua,
 156 only through the C&nbsp;API.
 157 This guarantees the integrity of data owned by the host program.
 158
 159
 160 <p>
 161 The type <em>thread</em> represents independent threads of execution
 162 and it is used to implement coroutines (see <a href="#2.6">&sect;2.6</a>).
 163 Do not confuse Lua threads with operating-system threads.
 164 Lua supports coroutines on all systems,
 165 even those that do not support threads.
 166
 167
 168 <p>
 169 The type <em>table</em> implements associative arrays,
 170 that is, arrays that can be indexed not only with numbers,
 171 but with any Lua value except <b>nil</b> and NaN
 172 (<em>Not a Number</em>, a special numeric value used to represent
 173 undefined or unrepresentable results, such as <code>0/0</code>).
 174 Tables can be <em>heterogeneous</em>;
 175 that is, they can contain values of all types (except <b>nil</b>).
 176 Any key with value <b>nil</b> is not considered part of the table.
 177 Conversely, any key that is not part of a table has
 178 an associated value <b>nil</b>.
 179
 180
 181 <p>
 182 Tables are the sole data structuring mechanism in Lua;
 183 they can be used to represent ordinary arrays, sequences,
 184 symbol tables, sets, records, graphs, trees, etc.
 185 To represent records, Lua uses the field name as an index.
 186 The language supports this representation by
 187 providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
 188 There are several convenient ways to create tables in Lua
 189 (see <a href="#3.4.8">&sect;3.4.8</a>).
 190
 191
 192 <p>
 193 We use the term <em>sequence</em> to denote a table where
 194 the set of all positive numeric keys is equal to <em>{1..n}</em>
 195 for some integer <em>n</em>,
 196 which is called the length of the sequence (see <a href="#3.4.6">&sect;3.4.6</a>).
 197
 198
 199 <p>
 200 Like indices,
 201 the values of table fields can be of any type.
 202 In particular,
 203 because functions are first-class values,
 204 table fields can contain functions.
 205 Thus tables can also carry <em>methods</em> (see <a href="#3.4.10">&sect;3.4.10</a>).
 206
 207
 208 <p>
 209 The indexing of tables follows
 210 the definition of raw equality in the language.
 211 The expressions <code>a[i]</code> and <code>a[j]</code>
 212 denote the same table element
 213 if and only if <code>i</code> and <code>j</code> are raw equal
 214 (that is, equal without metamethods).
 215
 216
 217 <p>
 218 Tables, functions, threads, and (full) userdata values are <em>objects</em>:
 219 variables do not actually <em>contain</em> these values,
 220 only <em>references</em> to them.
 221 Assignment, parameter passing, and function returns
 222 always manipulate references to such values;
 223 these operations do not imply any kind of copy.
 224
 225
 226 <p>
 227 The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
 228 of a given value (see <a href="#6.1">&sect;6.1</a>).
 229
 230
 231
 232
 233
 234 <h2>2.2 &ndash; <a name="2.2">Environments and the Global Environment</a></h2>
 235
 236 <p>
 237 As will be discussed in <a href="#3.2">&sect;3.2</a> and <a href="#3.3.3">&sect;3.3.3</a>,
 238 any reference to a global name <code>var</code> is syntactically translated
 239 to <code>_ENV.var</code>.
 240 Moreover, every chunk is compiled in the scope of
 241 an external local variable called <code>_ENV</code> (see <a href="#3.3.2">&sect;3.3.2</a>),
 242 so <code>_ENV</code> itself is never a global name in a chunk.
 243
 244
 245 <p>
 246 Despite the existence of this external <code>_ENV</code> variable and
 247 the translation of global names,
 248 <code>_ENV</code> is a completely regular name.
 249 In particular,
 250 you can define new variables and parameters with that name.
 251 Each reference to a global name uses the <code>_ENV</code> that is
 252 visible at that point in the program,
 253 following the usual visibility rules of Lua (see <a href="#3.5">&sect;3.5</a>).
 254
 255
 256 <p>
 257 Any table used as the value of <code>_ENV</code> is called an <em>environment</em>.
 258
 259
 260 <p>
 261 Lua keeps a distinguished environment called the <em>global environment</em>.
 262 This value is kept at a special index in the C registry (see <a href="#4.5">&sect;4.5</a>).
 263 In Lua, the variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value.
 264
 265
 266 <p>
 267 When Lua compiles a chunk,
 268 it initializes the value of its <code>_ENV</code> upvalue
 269 with the global environment (see <a href="#pdf-load"><code>load</code></a>).
 270 Therefore, by default,
 271 global variables in Lua code refer to entries in the global environment.
 272 Moreover, all standard libraries are loaded in the global environment
 273 and several functions there operate on that environment.
 274 You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>)
 275 to load a chunk with a different environment.
 276 (In C, you have to load the chunk and then change the value
 277 of its first upvalue.)
 278
 279
 280 <p>
 281 If you change the global environment in the registry
 282 (through C code or the debug library),
 283 all chunks loaded after the change will get the new environment.
 284 Previously loaded chunks are not affected, however,
 285 as each has its own reference to the environment in its <code>_ENV</code> variable.
 286 Moreover, the variable <a href="#pdf-_G"><code>_G</code></a>
 287 (which is stored in the original global environment)
 288 is never updated by Lua.
 289
 290
 291
 292
 293
 294 <h2>2.3 &ndash; <a name="2.3">Error Handling</a></h2>
 295
 296 <p>
 297 Because Lua is an embedded extension language,
 298 all Lua actions start from C&nbsp;code in the host program
 299 calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
 300 Whenever an error occurs during
 301 the compilation or execution of a Lua chunk,
 302 control returns to the host,
 303 which can take appropriate measures
 304 (such as printing an error message).
 305
 306
 307 <p>
 308 Lua code can explicitly generate an error by calling the
 309 <a href="#pdf-error"><code>error</code></a> function.
 310 If you need to catch errors in Lua,
 311 you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a>
 312 to call a given function in <em>protected mode</em>.
 313
 314
 315 <p>
 316 Whenever there is an error,
 317 an <em>error object</em> (also called an <em>error message</em>)
 318 is propagated with information about the error.
 319 Lua itself only generates errors where the error object is a string,
 320 but programs may generate errors with
 321 any value for the error object.
 322
 323
 324 <p>
 325 When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>,
 326 you may give a <em>message handler</em>
 327 to be called in case of errors.
 328 This function is called with the original error message
 329 and returns a new error message.
 330 It is called before the error unwinds the stack,
 331 so that it can gather more information about the error,
 332 for instance by inspecting the stack and creating a stack traceback.
 333 This message handler is still protected by the protected call;
 334 so, an error inside the message handler
 335 will call the message handler again.
 336 If this loop goes on, Lua breaks it and returns an appropriate message.
 337
 338
 339
 340
 341
 342 <h2>2.4 &ndash; <a name="2.4">Metatables and Metamethods</a></h2>
 343
 344 <p>
 345 Every value in Lua can have a <em>metatable</em>.
 346 This <em>metatable</em> is an ordinary Lua table
 347 that defines the behavior of the original value
 348 under certain special operations.
 349 You can change several aspects of the behavior
 350 of operations over a value by setting specific fields in its metatable.
 351 For instance, when a non-numeric value is the operand of an addition,
 352 Lua checks for a function in the field "<code>__add</code>" of the value's metatable.
 353 If it finds one,
 354 Lua calls this function to perform the addition.
 355
 356
 357 <p>
 358 The keys in a metatable are derived from the <em>event</em> names;
 359 the corresponding values are called <em>metamethods</em>.
 360 In the previous example, the event is <code>"add"</code>
 361 and the metamethod is the function that performs the addition.
 362
 363
 364 <p>
 365 You can query the metatable of any value
 366 using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function.
 367
 368
 369 <p>
 370 You can replace the metatable of tables
 371 using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function.
 372 You cannot change the metatable of other types from Lua
 373 (except by using the debug library);
 374 you must use the C&nbsp;API for that.
 375
 376
 377 <p>
 378 Tables and full userdata have individual metatables
 379 (although multiple tables and userdata can share their metatables).
 380 Values of all other types share one single metatable per type;
 381 that is, there is one single metatable for all numbers,
 382 one for all strings, etc.
 383 By default, a value has no metatable,
 384 but the string library sets a metatable for the string type (see <a href="#6.4">&sect;6.4</a>).
 385
 386
 387 <p>
 388 A metatable controls how an object behaves in arithmetic operations,
 389 order comparisons, concatenation, length operation, and indexing.
 390 A metatable also can define a function to be called
 391 when a userdata or a table is garbage collected.
 392 When Lua performs one of these operations over a value,
 393 it checks whether this value has a metatable with the corresponding event.
 394 If so, the value associated with that key (the metamethod)
 395 controls how Lua will perform the operation.
 396
 397
 398 <p>
 399 Metatables control the operations listed next.
 400 Each operation is identified by its corresponding name.
 401 The key for each operation is a string with its name prefixed by
 402 two underscores, '<code>__</code>';
 403 for instance, the key for operation "add" is the
 404 string "<code>__add</code>".
 405
 406
 407 <p>
 408 The semantics of these operations is better explained by a Lua function
 409 describing how the interpreter executes the operation.
 410 The code shown here in Lua is only illustrative;
 411 the real behavior is hard coded in the interpreter
 412 and it is much more efficient than this simulation.
 413 All functions used in these descriptions
 414 (<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.)
 415 are described in <a href="#6.1">&sect;6.1</a>.
 416 In particular, to retrieve the metamethod of a given object,
 417 we use the expression
 418
 419 <pre>
 420      metatable(obj)[event]
 421 </pre><p>
 422 This should be read as
 423
 424 <pre>
 425      rawget(getmetatable(obj) or {}, event)
 426 </pre><p>
 427 This means that the access to a metamethod does not invoke other metamethods,
 428 and access to objects with no metatables does not fail
 429 (it simply results in <b>nil</b>).
 430
 431
 432 <p>
 433 For the unary <code>-</code> and <code>#</code> operators,
 434 the metamethod is called with a dummy second argument.
 435 This extra argument is only to simplify Lua's internals;
 436 it may be removed in future versions and therefore it is not present
 437 in the following code.
 438 (For most uses this extra argument is irrelevant.)
 439
 440
 441
 442 <ul>
 443
 444 <li><b>"add": </b>
 445 the <code>+</code> operation.
 446
 447
 448
 449 <p>
 450 The function <code>getbinhandler</code> below defines how Lua chooses a handler
 451 for a binary operation.
 452 First, Lua tries the first operand.
 453 If its type does not define a handler for the operation,
 454 then Lua tries the second operand.
 455
 456 <pre>
 457      function getbinhandler (op1, op2, event)
 458        return metatable(op1)[event] or metatable(op2)[event]
 459      end
 460 </pre><p>
 461 By using this function,
 462 the behavior of the <code>op1 + op2</code> is
 463
 464 <pre>
 465      function add_event (op1, op2)
 466        local o1, o2 = tonumber(op1), tonumber(op2)
 467        if o1 and o2 then  -- both operands are numeric?
 468          return o1 + o2   -- '+' here is the primitive 'add'
 469        else  -- at least one of the operands is not numeric
 470          local h = getbinhandler(op1, op2, "__add")
 471          if h then
 472            -- call the handler with both operands
 473            return (h(op1, op2))
 474          else  -- no handler available: default behavior
 475            error(&middot;&middot;&middot;)
 476          end
 477        end
 478      end
 479 </pre><p>
 480 </li>
 481
 482 <li><b>"sub": </b>
 483 the <code>-</code> operation.
 484
 485 Behavior similar to the "add" operation.
 486 </li>
 487
 488 <li><b>"mul": </b>
 489 the <code>*</code> operation.
 490
 491 Behavior similar to the "add" operation.
 492 </li>
 493
 494 <li><b>"div": </b>
 495 the <code>/</code> operation.
 496
 497 Behavior similar to the "add" operation.
 498 </li>
 499
 500 <li><b>"mod": </b>
 501 the <code>%</code> operation.
 502
 503 Behavior similar to the "add" operation,
 504 with the operation
 505 <code>o1 - floor(o1/o2)*o2</code> as the primitive operation.
 506 </li>
 507
 508 <li><b>"pow": </b>
 509 the <code>^</code> (exponentiation) operation.
 510
 511 Behavior similar to the "add" operation,
 512 with the function <code>pow</code> (from the C&nbsp;math library)
 513 as the primitive operation.
 514 </li>
 515
 516 <li><b>"unm": </b>
 517 the unary <code>-</code> operation.
 518
 519
 520 <pre>
 521      function unm_event (op)
 522        local o = tonumber(op)
 523        if o then  -- operand is numeric?
 524          return -o  -- '-' here is the primitive 'unm'
 525        else  -- the operand is not numeric.
 526          -- Try to get a handler from the operand
 527          local h = metatable(op).__unm
 528          if h then
 529            -- call the handler with the operand
 530            return (h(op))
 531          else  -- no handler available: default behavior
 532            error(&middot;&middot;&middot;)
 533          end
 534        end
 535      end
 536 </pre><p>
 537 </li>
 538
 539 <li><b>"concat": </b>
 540 the <code>..</code> (concatenation) operation.
 541
 542
 543 <pre>
 544      function concat_event (op1, op2)
 545        if (type(op1) == "string" or type(op1) == "number") and
 546           (type(op2) == "string" or type(op2) == "number") then
 547          return op1 .. op2  -- primitive string concatenation
 548        else
 549          local h = getbinhandler(op1, op2, "__concat")
 550          if h then
 551            return (h(op1, op2))
 552          else
 553            error(&middot;&middot;&middot;)
 554          end
 555        end
 556      end
 557 </pre><p>
 558 </li>
 559
 560 <li><b>"len": </b>
 561 the <code>#</code> operation.
 562
 563
 564 <pre>
 565      function len_event (op)
 566        if type(op) == "string" then
 567          return strlen(op)      -- primitive string length
 568        else
 569          local h = metatable(op).__len
 570          if h then
 571            return (h(op))       -- call handler with the operand
 572          elseif type(op) == "table" then
 573            return #op              -- primitive table length
 574          else  -- no handler available: error
 575            error(&middot;&middot;&middot;)
 576          end
 577        end
 578      end
 579 </pre><p>
 580 See <a href="#3.4.6">&sect;3.4.6</a> for a description of the length of a table.
 581 </li>
 582
 583 <li><b>"eq": </b>
 584 the <code>==</code> operation.
 585
 586 The function <code>getequalhandler</code> defines how Lua chooses a metamethod
 587 for equality.
 588 A metamethod is selected only when both values
 589 being compared have the same type
 590 and the same metamethod for the selected operation,
 591 and the values are either tables or full userdata.
 592
 593 <pre>
 594      function getequalhandler (op1, op2)
 595        if type(op1) ~= type(op2) or
 596           (type(op1) ~= "table" and type(op1) ~= "userdata") then
 597          return nil     -- different values
 598        end
 599        local mm1 = metatable(op1).__eq
 600        local mm2 = metatable(op2).__eq
 601        if mm1 == mm2 then return mm1 else return nil end
 602      end
 603 </pre><p>
 604 The "eq" event is defined as follows:
 605
 606 <pre>
 607      function eq_event (op1, op2)
 608        if op1 == op2 then   -- primitive equal?
 609          return true   -- values are equal
 610        end
 611        -- try metamethod
 612        local h = getequalhandler(op1, op2)
 613        if h then
 614          return not not h(op1, op2)
 615        else
 616          return false
 617        end
 618      end
 619 </pre><p>
 620 Note that the result is always a boolean.
 621 </li>
 622
 623 <li><b>"lt": </b>
 624 the <code>&lt;</code> operation.
 625
 626
 627 <pre>
 628      function lt_event (op1, op2)
 629        if type(op1) == "number" and type(op2) == "number" then
 630          return op1 &lt; op2   -- numeric comparison
 631        elseif type(op1) == "string" and type(op2) == "string" then
 632          return op1 &lt; op2   -- lexicographic comparison
 633        else
 634          local h = getbinhandler(op1, op2, "__lt")
 635          if h then
 636            return not not h(op1, op2)
 637          else
 638            error(&middot;&middot;&middot;)
 639          end
 640        end
 641      end
 642 </pre><p>
 643 Note that the result is always a boolean.
 644 </li>
 645
 646 <li><b>"le": </b>
 647 the <code>&lt;=</code> operation.
 648
 649
 650 <pre>
 651      function le_event (op1, op2)
 652        if type(op1) == "number" and type(op2) == "number" then
 653          return op1 &lt;= op2   -- numeric comparison
 654        elseif type(op1) == "string" and type(op2) == "string" then
 655          return op1 &lt;= op2   -- lexicographic comparison
 656        else
 657          local h = getbinhandler(op1, op2, "__le")
 658          if h then
 659            return not not h(op1, op2)
 660          else
 661            h = getbinhandler(op1, op2, "__lt")
 662            if h then
 663              return not h(op2, op1)
 664            else
 665              error(&middot;&middot;&middot;)
 666            end
 667          end
 668        end
 669      end
 670 </pre><p>
 671 Note that, in the absence of a "le" metamethod,
 672 Lua tries the "lt", assuming that <code>a &lt;= b</code> is
 673 equivalent to <code>not (b &lt; a)</code>.
 674
 675
 676 <p>
 677 As with the other comparison operators,
 678 the result is always a boolean.
 679 </li>
 680
 681 <li><b>"index": </b>
 682 The indexing access <code>table[key]</code>.
 683 Note that the metamethod is tried only
 684 when <code>key</code> is not present in <code>table</code>.
 685 (When <code>table</code> is not a table,
 686 no key is ever present,
 687 so the metamethod is always tried.)
 688
 689
 690 <pre>
 691      function gettable_event (table, key)
 692        local h
 693        if type(table) == "table" then
 694          local v = rawget(table, key)
 695          -- if key is present, return raw value
 696          if v ~= nil then return v end
 697          h = metatable(table).__index
 698          if h == nil then return nil end
 699        else
 700          h = metatable(table).__index
 701          if h == nil then
 702            error(&middot;&middot;&middot;)
 703          end
 704        end
 705        if type(h) == "function" then
 706          return (h(table, key))     -- call the handler
 707        else return h[key]           -- or repeat operation on it
 708        end
 709      end
 710 </pre><p>
 711 </li>
 712
 713 <li><b>"newindex": </b>
 714 The indexing assignment <code>table[key] = value</code>.
 715 Note that the metamethod is tried only
 716 when <code>key</code> is not present in <code>table</code>.
 717
 718
 719 <pre>
 720      function settable_event (table, key, value)
 721        local h
 722        if type(table) == "table" then
 723          local v = rawget(table, key)
 724          -- if key is present, do raw assignment
 725          if v ~= nil then rawset(table, key, value); return end
 726          h = metatable(table).__newindex
 727          if h == nil then rawset(table, key, value); return end
 728        else
 729          h = metatable(table).__newindex
 730          if h == nil then
 731            error(&middot;&middot;&middot;)
 732          end
 733        end
 734        if type(h) == "function" then
 735          h(table, key,value)           -- call the handler
 736        else h[key] = value             -- or repeat operation on it
 737        end
 738      end
 739 </pre><p>
 740 </li>
 741
 742 <li><b>"call": </b>
 743 called when Lua calls a value.
 744
 745
 746 <pre>
 747      function function_event (func, ...)
 748        if type(func) == "function" then
 749          return func(...)   -- primitive call
 750        else
 751          local h = metatable(func).__call
 752          if h then
 753            return h(func, ...)
 754          else
 755            error(&middot;&middot;&middot;)
 756          end
 757        end
 758      end
 759 </pre><p>
 760 </li>
 761
 762 </ul>
 763
 764
 765
 766
 767 <h2>2.5 &ndash; <a name="2.5">Garbage Collection</a></h2>
 768
 769 <p>
 770 Lua performs automatic memory management.
 771 This means that
 772 you have to worry neither about allocating memory for new objects
 773 nor about freeing it when the objects are no longer needed.
 774 Lua manages memory automatically by running
 775 a <em>garbage collector</em> to collect all <em>dead objects</em>
 776 (that is, objects that are no longer accessible from Lua).
 777 All memory used by Lua is subject to automatic management:
 778 strings, tables, userdata, functions, threads, internal structures, etc.
 779
 780
 781 <p>
 782 Lua implements an incremental mark-and-sweep collector.
 783 It uses two numbers to control its garbage-collection cycles:
 784 the <em>garbage-collector pause</em> and
 785 the <em>garbage-collector step multiplier</em>.
 786 Both use percentage points as units
 787 (e.g., a value of 100 means an internal value of 1).
 788
 789
 790 <p>
 791 The garbage-collector pause
 792 controls how long the collector waits before starting a new cycle.
 793 Larger values make the collector less aggressive.
 794 Values smaller than 100 mean the collector will not wait to
 795 start a new cycle.
 796 A value of 200 means that the collector waits for the total memory in use
 797 to double before starting a new cycle.
 798
 799
 800 <p>
 801 The garbage-collector step multiplier
 802 controls the relative speed of the collector relative to
 803 memory allocation.
 804 Larger values make the collector more aggressive but also increase
 805 the size of each incremental step.
 806 Values smaller than 100 make the collector too slow and
 807 can result in the collector never finishing a cycle.
 808 The default is 200,
 809 which means that the collector runs at "twice"
 810 the speed of memory allocation.
 811
 812
 813 <p>
 814 If you set the step multiplier to a very large number
 815 (larger than 10% of the maximum number of
 816 bytes that the program may use),
 817 the collector behaves like a stop-the-world collector.
 818 If you then set the pause to 200,
 819 the collector behaves as in old Lua versions,
 820 doing a complete collection every time Lua doubles its
 821 memory usage.
 822
 823
 824 <p>
 825 You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C
 826 or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua.
 827 You can also use these functions to control
 828 the collector directly (e.g., stop and restart it).
 829
 830
 831 <p>
 832 As an experimental feature in Lua 5.2,
 833 you can change the collector's operation mode
 834 from incremental to <em>generational</em>.
 835 A <em>generational collector</em> assumes that most objects die young,
 836 and therefore it traverses only young (recently created) objects.
 837 This behavior can reduce the time used by the collector,
 838 but also increases memory usage (as old dead objects may accumulate).
 839 To mitigate this second problem,
 840 from time to time the generational collector performs a full collection.
 841 Remember that this is an experimental feature;
 842 you are welcome to try it,
 843 but check your gains.
 844
 845
 846
 847 <h3>2.5.1 &ndash; <a name="2.5.1">Garbage-Collection Metamethods</a></h3>
 848
 849 <p>
 850 You can set garbage-collector metamethods for tables
 851 and, using the C&nbsp;API,
 852 for full userdata (see <a href="#2.4">&sect;2.4</a>).
 853 These metamethods are also called <em>finalizers</em>.
 854 Finalizers allow you to coordinate Lua's garbage collection
 855 with external resource management
 856 (such as closing files, network or database connections,
 857 or freeing your own memory).
 858
 859
 860 <p>
 861 For an object (table or userdata) to be finalized when collected,
 862 you must <em>mark</em> it for finalization.
 863
 864 You mark an object for finalization when you set its metatable
 865 and the metatable has a field indexed by the string "<code>__gc</code>".
 866 Note that if you set a metatable without a <code>__gc</code> field
 867 and later create that field in the metatable,
 868 the object will not be marked for finalization.
 869 However, after an object is marked,
 870 you can freely change the <code>__gc</code> field of its metatable.
 871
 872
 873 <p>
 874 When a marked object becomes garbage,
 875 it is not collected immediately by the garbage collector.
 876 Instead, Lua puts it in a list.
 877 After the collection,
 878 Lua does the equivalent of the following function
 879 for each object in that list:
 880
 881 <pre>
 882      function gc_event (obj)
 883        local h = metatable(obj).__gc
 884        if type(h) == "function" then
 885          h(obj)
 886        end
 887      end
 888 </pre>
 889
 890 <p>
 891 At the end of each garbage-collection cycle,
 892 the finalizers for objects are called in
 893 the reverse order that they were marked for collection,
 894 among those collected in that cycle;
 895 that is, the first finalizer to be called is the one associated
 896 with the object marked last in the program.
 897 The execution of each finalizer may occur at any point during
 898 the execution of the regular code.
 899
 900
 901 <p>
 902 Because the object being collected must still be used by the finalizer,
 903 it (and other objects accessible only through it)
 904 must be <em>resurrected</em> by Lua.
 905 Usually, this resurrection is transient,
 906 and the object memory is freed in the next garbage-collection cycle.
 907 However, if the finalizer stores the object in some global place
 908 (e.g., a global variable),
 909 then there is a permanent resurrection.
 910 In any case,
 911 the object memory is freed only when it becomes completely inaccessible;
 912 its finalizer will never be called twice.
 913
 914
 915 <p>
 916 When you close a state (see <a href="#lua_close"><code>lua_close</code></a>),
 917 Lua calls the finalizers of all objects marked for finalization,
 918 following the reverse order that they were marked.
 919 If any finalizer marks new objects for collection during that phase,
 920 these new objects will not be finalized.
 921
 922
 923
 924
 925
 926 <h3>2.5.2 &ndash; <a name="2.5.2">Weak Tables</a></h3>
 927
 928 <p>
 929 A <em>weak table</em> is a table whose elements are
 930 <em>weak references</em>.
 931 A weak reference is ignored by the garbage collector.
 932 In other words,
 933 if the only references to an object are weak references,
 934 then the garbage collector will collect that object.
 935
 936
 937 <p>
 938 A weak table can have weak keys, weak values, or both.
 939 A table with weak keys allows the collection of its keys,
 940 but prevents the collection of its values.
 941 A table with both weak keys and weak values allows the collection of
 942 both keys and values.
 943 In any case, if either the key or the value is collected,
 944 the whole pair is removed from the table.
 945 The weakness of a table is controlled by the
 946 <code>__mode</code> field of its metatable.
 947 If the <code>__mode</code> field is a string containing the character&nbsp;'<code>k</code>',
 948 the keys in the table are weak.
 949 If <code>__mode</code> contains '<code>v</code>',
 950 the values in the table are weak.
 951
 952
 953 <p>
 954 A table with weak keys and strong values
 955 is also called an <em>ephemeron table</em>.
 956 In an ephemeron table,
 957 a value is considered reachable only if its key is reachable.
 958 In particular,
 959 if the only reference to a key comes through its value,
 960 the pair is removed.
 961
 962
 963 <p>
 964 Any change in the weakness of a table may take effect only
 965 at the next collect cycle.
 966 In particular, if you change the weakness to a stronger mode,
 967 Lua may still collect some items from that table
 968 before the change takes effect.
 969
 970
 971 <p>
 972 Only objects that have an explicit construction
 973 are removed from weak tables.
 974 Values, such as numbers and light C functions,
 975 are not subject to garbage collection,
 976 and therefore are not removed from weak tables
 977 (unless its associated value is collected).
 978 Although strings are subject to garbage collection,
 979 they do not have an explicit construction,
 980 and therefore are not removed from weak tables.
 981
 982
 983 <p>
 984 Resurrected objects
 985 (that is, objects being finalized
 986 and objects accessible only through objects being finalized)
 987 have a special behavior in weak tables.
 988 They are removed from weak values before running their finalizers,
 989 but are removed from weak keys only in the next collection
 990 after running their finalizers, when such objects are actually freed.
 991 This behavior allows the finalizer to access properties
 992 associated with the object through weak tables.
 993
 994
 995 <p>
 996 If a weak table is among the resurrected objects in a collection cycle,
 997 it may not be properly cleared until the next cycle.
 998
 999
1000
1001
1002
1003
1004
1005 <h2>2.6 &ndash; <a name="2.6">Coroutines</a></h2>
1006
1007 <p>
1008 Lua supports coroutines,
1009 also called <em>collaborative multithreading</em>.
1010 A coroutine in Lua represents an independent thread of execution.
1011 Unlike threads in multithread systems, however,
1012 a coroutine only suspends its execution by explicitly calling
1013 a yield function.
1014
1015
1016 <p>
1017 You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
1018 Its sole argument is a function
1019 that is the main function of the coroutine.
1020 The <code>create</code> function only creates a new coroutine and
1021 returns a handle to it (an object of type <em>thread</em>);
1022 it does not start the coroutine.
1023
1024
1025 <p>
1026 You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1027 When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
1028 passing as its first argument
1029 a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
1030 the coroutine starts its execution,
1031 at the first line of its main function.
1032 Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
1033 to the coroutine main function.
1034 After the coroutine starts running,
1035 it runs until it terminates or <em>yields</em>.
1036
1037
1038 <p>
1039 A coroutine can terminate its execution in two ways:
1040 normally, when its main function returns
1041 (explicitly or implicitly, after the last instruction);
1042 and abnormally, if there is an unprotected error.
1043 In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
1044 plus any values returned by the coroutine main function.
1045 In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
1046 plus an error message.
1047
1048
1049 <p>
1050 A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
1051 When a coroutine yields,
1052 the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
1053 even if the yield happens inside nested function calls
1054 (that is, not in the main function,
1055 but in a function directly or indirectly called by the main function).
1056 In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
1057 plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>.
1058 The next time you resume the same coroutine,
1059 it continues its execution from the point where it yielded,
1060 with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
1061 arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1062
1063
1064 <p>
1065 Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>,
1066 the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
1067 but instead of returning the coroutine itself,
1068 it returns a function that, when called, resumes the coroutine.
1069 Any arguments passed to this function
1070 go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>.
1071 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
1072 except the first one (the boolean error code).
1073 Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
1074 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors;
1075 any error is propagated to the caller.
1076
1077
1078 <p>
1079 As an example of how coroutines work,
1080 consider the following code:
1081
1082 <pre>
1083      function foo (a)
1084        print("foo", a)
1085        return coroutine.yield(2*a)
1086      end
1087
1088      co = coroutine.create(function (a,b)
1089            print("co-body", a, b)
1090            local r = foo(a+1)
1091            print("co-body", r)
1092            local r, s = coroutine.yield(a+b, a-b)
1093            print("co-body", r, s)
1094            return b, "end"
1095      end)
1096
1097      print("main", coroutine.resume(co, 1, 10))
1098      print("main", coroutine.resume(co, "r"))
1099      print("main", coroutine.resume(co, "x", "y"))
1100      print("main", coroutine.resume(co, "x", "y"))
1101 </pre><p>
1102 When you run it, it produces the following output:
1103
1104 <pre>
1105      co-body 1       10
1106      foo     2
1107      main    true    4
1108      co-body r
1109      main    true    11      -9
1110      co-body x       y
1111      main    true    10      end
1112      main    false   cannot resume dead coroutine
1113 </pre>
1114
1115 <p>
1116 You can also create and manipulate coroutines through the C API:
1117 see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>,
1118 and <a href="#lua_yield"><code>lua_yield</code></a>.
1119
1120
1121
1122
1123
1124 <h1>3 &ndash; <a name="3">The Language</a></h1>
1125
1126 <p>
1127 This section describes the lexis, the syntax, and the semantics of Lua.
1128 In other words,
1129 this section describes
1130 which tokens are valid,
1131 how they can be combined,
1132 and what their combinations mean.
1133
1134
1135 <p>
1136 Language constructs will be explained using the usual extended BNF notation,
1137 in which
1138 {<em>a</em>}&nbsp;means&nbsp;0 or more <em>a</em>'s, and
1139 [<em>a</em>]&nbsp;means an optional <em>a</em>.
1140 Non-terminals are shown like non-terminal,
1141 keywords are shown like <b>kword</b>,
1142 and other terminal symbols are shown like &lsquo;<b>=</b>&rsquo;.
1143 The complete syntax of Lua can be found in <a href="#9">&sect;9</a>
1144 at the end of this manual.
1145
1146
1147
1148 <h2>3.1 &ndash; <a name="3.1">Lexical Conventions</a></h2>
1149
1150 <p>
1151 Lua is a free-form language.
1152 It ignores spaces (including new lines) and comments
1153 between lexical elements (tokens),
1154 except as delimiters between names and keywords.
1155
1156
1157 <p>
1158 <em>Names</em>
1159 (also called <em>identifiers</em>)
1160 in Lua can be any string of letters,
1161 digits, and underscores,
1162 not beginning with a digit.
1163 Identifiers are used to name variables, table fields, and labels.
1164
1165
1166 <p>
1167 The following <em>keywords</em> are reserved
1168 and cannot be used as names:
1169
1170
1171 <pre>
1172      and       break     do        else      elseif    end
1173      false     for       function  goto      if        in
1174      local     nil       not       or        repeat    return
1175      then      true      until     while
1176 </pre>
1177
1178 <p>
1179 Lua is a case-sensitive language:
1180 <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code>
1181 are two different, valid names.
1182 As a convention, names starting with an underscore followed by
1183 uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>)
1184 are reserved for variables used by Lua.
1185
1186
1187 <p>
1188 The following strings denote other tokens:
1189
1190 <pre>
1191      +     -     *     /     %     ^     #
1192      ==    ~=    &lt;=    &gt;=    &lt;     &gt;     =
1193      (     )     {     }     [     ]     ::
1194      ;     :     ,     .     ..    ...
1195 </pre>
1196
1197 <p>
1198 <em>Literal strings</em>
1199 can be delimited by matching single or double quotes,
1200 and can contain the following C-like escape sequences:
1201 '<code>\a</code>' (bell),
1202 '<code>\b</code>' (backspace),
1203 '<code>\f</code>' (form feed),
1204 '<code>\n</code>' (newline),
1205 '<code>\r</code>' (carriage return),
1206 '<code>\t</code>' (horizontal tab),
1207 '<code>\v</code>' (vertical tab),
1208 '<code>\\</code>' (backslash),
1209 '<code>\"</code>' (quotation mark [double quote]),
1210 and '<code>\'</code>' (apostrophe [single quote]).
1211 A backslash followed by a real newline
1212 results in a newline in the string.
1213 The escape sequence '<code>\z</code>' skips the following span
1214 of white-space characters,
1215 including line breaks;
1216 it is particularly useful to break and indent a long literal string
1217 into multiple lines without adding the newlines and spaces
1218 into the string contents.
1219
1220
1221 <p>
1222 A byte in a literal string can also be specified by its numerical value.
1223 This can be done with the escape sequence <code>\x<em>XX</em></code>,
1224 where <em>XX</em> is a sequence of exactly two hexadecimal digits,
1225 or with the escape sequence <code>\<em>ddd</em></code>,
1226 where <em>ddd</em> is a sequence of up to three decimal digits.
1227 (Note that if a decimal escape is to be followed by a digit,
1228 it must be expressed using exactly three digits.)
1229 Strings in Lua can contain any 8-bit value, including embedded zeros,
1230 which can be specified as '<code>\0</code>'.
1231
1232
1233 <p>
1234 Literal strings can also be defined using a long format
1235 enclosed by <em>long brackets</em>.
1236 We define an <em>opening long bracket of level <em>n</em></em> as an opening
1237 square bracket followed by <em>n</em> equal signs followed by another
1238 opening square bracket.
1239 So, an opening long bracket of level&nbsp;0 is written as <code>[[</code>,
1240 an opening long bracket of level&nbsp;1 is written as <code>[=[</code>,
1241 and so on.
1242 A <em>closing long bracket</em> is defined similarly;
1243 for instance, a closing long bracket of level&nbsp;4 is written as <code>]====]</code>.
1244 A <em>long literal</em> starts with an opening long bracket of any level and
1245 ends at the first closing long bracket of the same level.
1246 It can contain any text except a closing bracket of the proper level.
1247 Literals in this bracketed form can run for several lines,
1248 do not interpret any escape sequences,
1249 and ignore long brackets of any other level.
1250 Any kind of end-of-line sequence
1251 (carriage return, newline, carriage return followed by newline,
1252 or newline followed by carriage return)
1253 is converted to a simple newline.
1254
1255
1256 <p>
1257 Any byte in a literal string not
1258 explicitly affected by the previous rules represents itself.
1259 However, Lua opens files for parsing in text mode,
1260 and the system file functions may have problems with
1261 some control characters.
1262 So, it is safer to represent
1263 non-text data as a quoted literal with
1264 explicit escape sequences for non-text characters.
1265
1266
1267 <p>
1268 For convenience,
1269 when the opening long bracket is immediately followed by a newline,
1270 the newline is not included in the string.
1271 As an example, in a system using ASCII
1272 (in which '<code>a</code>' is coded as&nbsp;97,
1273 newline is coded as&nbsp;10, and '<code>1</code>' is coded as&nbsp;49),
1274 the five literal strings below denote the same string:
1275
1276 <pre>
1277      a = 'alo\n123"'
1278      a = "alo\n123\""
1279      a = '\97lo\10\04923"'
1280      a = [[alo
1281      123"]]
1282      a = [==[
1283      alo
1284      123"]==]
1285 </pre>
1286
1287 <p>
1288 A <em>numerical constant</em> can be written with an optional fractional part
1289 and an optional decimal exponent,
1290 marked by a letter '<code>e</code>' or '<code>E</code>'.
1291 Lua also accepts hexadecimal constants,
1292 which start with <code>0x</code> or <code>0X</code>.
1293 Hexadecimal constants also accept an optional fractional part
1294 plus an optional binary exponent,
1295 marked by a letter '<code>p</code>' or '<code>P</code>'.
1296 Examples of valid numerical constants are
1297
1298 <pre>
1299      3     3.0     3.1416     314.16e-2     0.31416E1
1300      0xff  0x0.1E  0xA23p-4   0X1.921FB54442D18P+1
1301 </pre>
1302
1303 <p>
1304 A <em>comment</em> starts with a double hyphen (<code>--</code>)
1305 anywhere outside a string.
1306 If the text immediately after <code>--</code> is not an opening long bracket,
1307 the comment is a <em>short comment</em>,
1308 which runs until the end of the line.
1309 Otherwise, it is a <em>long comment</em>,
1310 which runs until the corresponding closing long bracket.
1311 Long comments are frequently used to disable code temporarily.
1312
1313
1314
1315
1316
1317 <h2>3.2 &ndash; <a name="3.2">Variables</a></h2>
1318
1319 <p>
1320 Variables are places that store values.
1321 There are three kinds of variables in Lua:
1322 global variables, local variables, and table fields.
1323
1324
1325 <p>
1326 A single name can denote a global variable or a local variable
1327 (or a function's formal parameter,
1328 which is a particular kind of local variable):
1329
1330 <pre>
1331         var ::= Name
1332 </pre><p>
1333 Name denotes identifiers, as defined in <a href="#3.1">&sect;3.1</a>.
1334
1335
1336 <p>
1337 Any variable name is assumed to be global unless explicitly declared
1338 as a local (see <a href="#3.3.7">&sect;3.3.7</a>).
1339 Local variables are <em>lexically scoped</em>:
1340 local variables can be freely accessed by functions
1341 defined inside their scope (see <a href="#3.5">&sect;3.5</a>).
1342
1343
1344 <p>
1345 Before the first assignment to a variable, its value is <b>nil</b>.
1346
1347
1348 <p>
1349 Square brackets are used to index a table:
1350
1351 <pre>
1352         var ::= prefixexp &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo;
1353 </pre><p>
1354 The meaning of accesses to table fields can be changed via metatables.
1355 An access to an indexed variable <code>t[i]</code> is equivalent to
1356 a call <code>gettable_event(t,i)</code>.
1357 (See <a href="#2.4">&sect;2.4</a> for a complete description of the
1358 <code>gettable_event</code> function.
1359 This function is not defined or callable in Lua.
1360 We use it here only for explanatory purposes.)
1361
1362
1363 <p>
1364 The syntax <code>var.Name</code> is just syntactic sugar for
1365 <code>var["Name"]</code>:
1366
1367 <pre>
1368         var ::= prefixexp &lsquo;<b>.</b>&rsquo; Name
1369 </pre>
1370
1371 <p>
1372 An access to a global variable <code>x</code>
1373 is equivalent to <code>_ENV.x</code>.
1374 Due to the way that chunks are compiled,
1375 <code>_ENV</code> is never a global name (see <a href="#2.2">&sect;2.2</a>).
1376
1377
1378
1379
1380
1381 <h2>3.3 &ndash; <a name="3.3">Statements</a></h2>
1382
1383 <p>
1384 Lua supports an almost conventional set of statements,
1385 similar to those in Pascal or C.
1386 This set includes
1387 assignments, control structures, function calls,
1388 and variable declarations.
1389
1390
1391
1392 <h3>3.3.1 &ndash; <a name="3.3.1">Blocks</a></h3>
1393
1394 <p>
1395 A block is a list of statements,
1396 which are executed sequentially:
1397
1398 <pre>
1399         block ::= {stat}
1400 </pre><p>
1401 Lua has <em>empty statements</em>
1402 that allow you to separate statements with semicolons,
1403 start a block with a semicolon
1404 or write two semicolons in sequence:
1405
1406 <pre>
1407         stat ::= &lsquo;<b>;</b>&rsquo;
1408 </pre>
1409
1410 <p>
1411 Function calls and assignments
1412 can start with an open parenthesis.
1413 This possibility leads to an ambiguity in Lua's grammar.
1414 Consider the following fragment:
1415
1416 <pre>
1417      a = b + c
1418      (print or io.write)('done')
1419 </pre><p>
1420 The grammar could see it in two ways:
1421
1422 <pre>
1423      a = b + c(print or io.write)('done')
1424
1425      a = b + c; (print or io.write)('done')
1426 </pre><p>
1427 The current parser always sees such constructions
1428 in the first way,
1429 interpreting the open parenthesis
1430 as the start of the arguments to a call.
1431 To avoid this ambiguity,
1432 it is a good practice to always precede with a semicolon
1433 statements that start with a parenthesis:
1434
1435 <pre>
1436      ;(print or io.write)('done')
1437 </pre>
1438
1439 <p>
1440 A block can be explicitly delimited to produce a single statement:
1441
1442 <pre>
1443         stat ::= <b>do</b> block <b>end</b>
1444 </pre><p>
1445 Explicit blocks are useful
1446 to control the scope of variable declarations.
1447 Explicit blocks are also sometimes used to
1448 add a <b>return</b> statement in the middle
1449 of another block (see <a href="#3.3.4">&sect;3.3.4</a>).
1450
1451
1452
1453
1454
1455 <h3>3.3.2 &ndash; <a name="3.3.2">Chunks</a></h3>
1456
1457 <p>
1458 The unit of compilation of Lua is called a <em>chunk</em>.
1459 Syntactically,
1460 a chunk is simply a block:
1461
1462 <pre>
1463         chunk ::= block
1464 </pre>
1465
1466 <p>
1467 Lua handles a chunk as the body of an anonymous function
1468 with a variable number of arguments
1469 (see <a href="#3.4.10">&sect;3.4.10</a>).
1470 As such, chunks can define local variables,
1471 receive arguments, and return values.
1472 Moreover, such anonymous function is compiled as in the
1473 scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">&sect;2.2</a>).
1474 The resulting function always has <code>_ENV</code> as its only upvalue,
1475 even if it does not use that variable.
1476
1477
1478 <p>
1479 A chunk can be stored in a file or in a string inside the host program.
1480 To execute a chunk,
1481 Lua first precompiles the chunk into instructions for a virtual machine,
1482 and then it executes the compiled code
1483 with an interpreter for the virtual machine.
1484
1485
1486 <p>
1487 Chunks can also be precompiled into binary form;
1488 see program <code>luac</code> for details.
1489 Programs in source and compiled forms are interchangeable;
1490 Lua automatically detects the file type and acts accordingly.
1491
1492
1493
1494
1495
1496
1497 <h3>3.3.3 &ndash; <a name="3.3.3">Assignment</a></h3>
1498
1499 <p>
1500 Lua allows multiple assignments.
1501 Therefore, the syntax for assignment
1502 defines a list of variables on the left side
1503 and a list of expressions on the right side.
1504 The elements in both lists are separated by commas:
1505
1506 <pre>
1507         stat ::= varlist &lsquo;<b>=</b>&rsquo; explist
1508         varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
1509         explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
1510 </pre><p>
1511 Expressions are discussed in <a href="#3.4">&sect;3.4</a>.
1512
1513
1514 <p>
1515 Before the assignment,
1516 the list of values is <em>adjusted</em> to the length of
1517 the list of variables.
1518 If there are more values than needed,
1519 the excess values are thrown away.
1520 If there are fewer values than needed,
1521 the list is extended with as many  <b>nil</b>'s as needed.
1522 If the list of expressions ends with a function call,
1523 then all values returned by that call enter the list of values,
1524 before the adjustment
1525 (except when the call is enclosed in parentheses; see <a href="#3.4">&sect;3.4</a>).
1526
1527
1528 <p>
1529 The assignment statement first evaluates all its expressions
1530 and only then are the assignments performed.
1531 Thus the code
1532
1533 <pre>
1534      i = 3
1535      i, a[i] = i+1, 20
1536 </pre><p>
1537 sets <code>a[3]</code> to 20, without affecting <code>a[4]</code>
1538 because the <code>i</code> in <code>a[i]</code> is evaluated (to 3)
1539 before it is assigned&nbsp;4.
1540 Similarly, the line
1541
1542 <pre>
1543      x, y = y, x
1544 </pre><p>
1545 exchanges the values of <code>x</code> and <code>y</code>,
1546 and
1547
1548 <pre>
1549      x, y, z = y, z, x
1550 </pre><p>
1551 cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>.
1552
1553
1554 <p>
1555 The meaning of assignments to global variables
1556 and table fields can be changed via metatables.
1557 An assignment to an indexed variable <code>t[i] = val</code> is equivalent to
1558 <code>settable_event(t,i,val)</code>.
1559 (See <a href="#2.4">&sect;2.4</a> for a complete description of the
1560 <code>settable_event</code> function.
1561 This function is not defined or callable in Lua.
1562 We use it here only for explanatory purposes.)
1563
1564
1565 <p>
1566 An assignment to a global variable <code>x = val</code>
1567 is equivalent to the assignment
1568 <code>_ENV.x = val</code> (see <a href="#2.2">&sect;2.2</a>).
1569
1570
1571
1572
1573
1574 <h3>3.3.4 &ndash; <a name="3.3.4">Control Structures</a></h3><p>
1575 The control structures
1576 <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
1577 familiar syntax:
1578
1579
1580
1581
1582 <pre>
1583         stat ::= <b>while</b> exp <b>do</b> block <b>end</b>
1584         stat ::= <b>repeat</b> block <b>until</b> exp
1585         stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
1586 </pre><p>
1587 Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">&sect;3.3.5</a>).
1588
1589
1590 <p>
1591 The condition expression of a
1592 control structure can return any value.
1593 Both <b>false</b> and <b>nil</b> are considered false.
1594 All values different from <b>nil</b> and <b>false</b> are considered true
1595 (in particular, the number 0 and the empty string are also true).
1596
1597
1598 <p>
1599 In the <b>repeat</b>&ndash;<b>until</b> loop,
1600 the inner block does not end at the <b>until</b> keyword,
1601 but only after the condition.
1602 So, the condition can refer to local variables
1603 declared inside the loop block.
1604
1605
1606 <p>
1607 The <b>goto</b> statement transfers the program control to a label.
1608 For syntactical reasons,
1609 labels in Lua are considered statements too:
1610
1611
1612
1613 <pre>
1614         stat ::= <b>goto</b> Name
1615         stat ::= label
1616         label ::= &lsquo;<b>::</b>&rsquo; Name &lsquo;<b>::</b>&rsquo;
1617 </pre>
1618
1619 <p>
1620 A label is visible in the entire block where it is defined,
1621 except
1622 inside nested blocks where a label with the same name is defined and
1623 inside nested functions.
1624 A goto may jump to any visible label as long as it does not
1625 enter into the scope of a local variable.
1626
1627
1628 <p>
1629 Labels and empty statements are called <em>void statements</em>,
1630 as they perform no actions.
1631
1632
1633 <p>
1634 The <b>break</b> statement terminates the execution of a
1635 <b>while</b>, <b>repeat</b>, or <b>for</b> loop,
1636 skipping to the next statement after the loop:
1637
1638
1639 <pre>
1640         stat ::= <b>break</b>
1641 </pre><p>
1642 A <b>break</b> ends the innermost enclosing loop.
1643
1644
1645 <p>
1646 The <b>return</b> statement is used to return values
1647 from a function or a chunk (which is a function in disguise).
1648
1649 Functions can return more than one value,
1650 so the syntax for the <b>return</b> statement is
1651
1652 <pre>
1653         stat ::= <b>return</b> [explist] [&lsquo;<b>;</b>&rsquo;]
1654 </pre>
1655
1656 <p>
1657 The <b>return</b> statement can only be written
1658 as the last statement of a block.
1659 If it is really necessary to <b>return</b> in the middle of a block,
1660 then an explicit inner block can be used,
1661 as in the idiom <code>do return end</code>,
1662 because now <b>return</b> is the last statement in its (inner) block.
1663
1664
1665
1666
1667
1668 <h3>3.3.5 &ndash; <a name="3.3.5">For Statement</a></h3>
1669
1670 <p>
1671
1672 The <b>for</b> statement has two forms:
1673 one numeric and one generic.
1674
1675
1676 <p>
1677 The numeric <b>for</b> loop repeats a block of code while a
1678 control variable runs through an arithmetic progression.
1679 It has the following syntax:
1680
1681 <pre>
1682         stat ::= <b>for</b> Name &lsquo;<b>=</b>&rsquo; exp &lsquo;<b>,</b>&rsquo; exp [&lsquo;<b>,</b>&rsquo; exp] <b>do</b> block <b>end</b>
1683 </pre><p>
1684 The <em>block</em> is repeated for <em>name</em> starting at the value of
1685 the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the
1686 third <em>exp</em>.
1687 More precisely, a <b>for</b> statement like
1688
1689 <pre>
1690      for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end
1691 </pre><p>
1692 is equivalent to the code:
1693
1694 <pre>
1695      do
1696        local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
1697        if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end
1698        while (<em>step</em> &gt; 0 and <em>var</em> &lt;= <em>limit</em>) or (<em>step</em> &lt;= 0 and <em>var</em> &gt;= <em>limit</em>) do
1699          local v = <em>var</em>
1700          <em>block</em>
1701          <em>var</em> = <em>var</em> + <em>step</em>
1702        end
1703      end
1704 </pre><p>
1705 Note the following:
1706
1707 <ul>
1708
1709 <li>
1710 All three control expressions are evaluated only once,
1711 before the loop starts.
1712 They must all result in numbers.
1713 </li>
1714
1715 <li>
1716 <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
1717 The names shown here are for explanatory purposes only.
1718 </li>
1719
1720 <li>
1721 If the third expression (the step) is absent,
1722 then a step of&nbsp;1 is used.
1723 </li>
1724
1725 <li>
1726 You can use <b>break</b> to exit a <b>for</b> loop.
1727 </li>
1728
1729 <li>
1730 The loop variable <code>v</code> is local to the loop;
1731 you cannot use its value after the <b>for</b> ends or is broken.
1732 If you need this value,
1733 assign it to another variable before breaking or exiting the loop.
1734 </li>
1735
1736 </ul>
1737
1738 <p>
1739 The generic <b>for</b> statement works over functions,
1740 called <em>iterators</em>.
1741 On each iteration, the iterator function is called to produce a new value,
1742 stopping when this new value is <b>nil</b>.
1743 The generic <b>for</b> loop has the following syntax:
1744
1745 <pre>
1746         stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b>
1747         namelist ::= Name {&lsquo;<b>,</b>&rsquo; Name}
1748 </pre><p>
1749 A <b>for</b> statement like
1750
1751 <pre>
1752      for <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> in <em>explist</em> do <em>block</em> end
1753 </pre><p>
1754 is equivalent to the code:
1755
1756 <pre>
1757      do
1758        local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em>
1759        while true do
1760          local <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
1761          if <em>var_1</em> == nil then break end
1762          <em>var</em> = <em>var_1</em>
1763          <em>block</em>
1764        end
1765      end
1766 </pre><p>
1767 Note the following:
1768
1769 <ul>
1770
1771 <li>
1772 <code><em>explist</em></code> is evaluated only once.
1773 Its results are an <em>iterator</em> function,
1774 a <em>state</em>,
1775 and an initial value for the first <em>iterator variable</em>.
1776 </li>
1777
1778 <li>
1779 <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
1780 The names are here for explanatory purposes only.
1781 </li>
1782
1783 <li>
1784 You can use <b>break</b> to exit a <b>for</b> loop.
1785 </li>
1786
1787 <li>
1788 The loop variables <code><em>var_i</em></code> are local to the loop;
1789 you cannot use their values after the <b>for</b> ends.
1790 If you need these values,
1791 then assign them to other variables before breaking or exiting the loop.
1792 </li>
1793
1794 </ul>
1795
1796
1797
1798
1799 <h3>3.3.6 &ndash; <a name="3.3.6">Function Calls as Statements</a></h3><p>
1800 To allow possible side-effects,
1801 function calls can be executed as statements:
1802
1803 <pre>
1804         stat ::= functioncall
1805 </pre><p>
1806 In this case, all returned values are thrown away.
1807 Function calls are explained in <a href="#3.4.9">&sect;3.4.9</a>.
1808
1809
1810
1811
1812
1813 <h3>3.3.7 &ndash; <a name="3.3.7">Local Declarations</a></h3><p>
1814 Local variables can be declared anywhere inside a block.
1815 The declaration can include an initial assignment:
1816
1817 <pre>
1818         stat ::= <b>local</b> namelist [&lsquo;<b>=</b>&rsquo; explist]
1819 </pre><p>
1820 If present, an initial assignment has the same semantics
1821 of a multiple assignment (see <a href="#3.3.3">&sect;3.3.3</a>).
1822 Otherwise, all variables are initialized with <b>nil</b>.
1823
1824
1825 <p>
1826 A chunk is also a block (see <a href="#3.3.2">&sect;3.3.2</a>),
1827 and so local variables can be declared in a chunk outside any explicit block.
1828
1829
1830 <p>
1831 The visibility rules for local variables are explained in <a href="#3.5">&sect;3.5</a>.
1832
1833
1834
1835
1836
1837
1838
1839 <h2>3.4 &ndash; <a name="3.4">Expressions</a></h2>
1840
1841 <p>
1842 The basic expressions in Lua are the following:
1843
1844 <pre>
1845         exp ::= prefixexp
1846         exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
1847         exp ::= Number
1848         exp ::= String
1849         exp ::= functiondef
1850         exp ::= tableconstructor
1851         exp ::= &lsquo;<b>...</b>&rsquo;
1852         exp ::= exp binop exp
1853         exp ::= unop exp
1854         prefixexp ::= var | functioncall | &lsquo;<b>(</b>&rsquo; exp &lsquo;<b>)</b>&rsquo;
1855 </pre>
1856
1857 <p>
1858 Numbers and literal strings are explained in <a href="#3.1">&sect;3.1</a>;
1859 variables are explained in <a href="#3.2">&sect;3.2</a>;
1860 function definitions are explained in <a href="#3.4.10">&sect;3.4.10</a>;
1861 function calls are explained in <a href="#3.4.9">&sect;3.4.9</a>;
1862 table constructors are explained in <a href="#3.4.8">&sect;3.4.8</a>.
1863 Vararg expressions,
1864 denoted by three dots ('<code>...</code>'), can only be used when
1865 directly inside a vararg function;
1866 they are explained in <a href="#3.4.10">&sect;3.4.10</a>.
1867
1868
1869 <p>
1870 Binary operators comprise arithmetic operators (see <a href="#3.4.1">&sect;3.4.1</a>),
1871 relational operators (see <a href="#3.4.3">&sect;3.4.3</a>), logical operators (see <a href="#3.4.4">&sect;3.4.4</a>),
1872 and the concatenation operator (see <a href="#3.4.5">&sect;3.4.5</a>).
1873 Unary operators comprise the unary minus (see <a href="#3.4.1">&sect;3.4.1</a>),
1874 the unary <b>not</b> (see <a href="#3.4.4">&sect;3.4.4</a>),
1875 and the unary <em>length operator</em> (see <a href="#3.4.6">&sect;3.4.6</a>).
1876
1877
1878 <p>
1879 Both function calls and vararg expressions can result in multiple values.
1880 If a function call is used as a statement (see <a href="#3.3.6">&sect;3.3.6</a>),
1881 then its return list is adjusted to zero elements,
1882 thus discarding all returned values.
1883 If an expression is used as the last (or the only) element
1884 of a list of expressions,
1885 then no adjustment is made
1886 (unless the expression is enclosed in parentheses).
1887 In all other contexts,
1888 Lua adjusts the result list to one element,
1889 either discarding all values except the first one
1890 or adding a single <b>nil</b> if there are no values.
1891
1892
1893 <p>
1894 Here are some examples:
1895
1896 <pre>
1897      f()                -- adjusted to 0 results
1898      g(f(), x)          -- f() is adjusted to 1 result
1899      g(x, f())          -- g gets x plus all results from f()
1900      a,b,c = f(), x     -- f() is adjusted to 1 result (c gets nil)
1901      a,b = ...          -- a gets the first vararg parameter, b gets
1902                         -- the second (both a and b can get nil if there
1903                         -- is no corresponding vararg parameter)
1904
1905      a,b,c = x, f()     -- f() is adjusted to 2 results
1906      a,b,c = f()        -- f() is adjusted to 3 results
1907      return f()         -- returns all results from f()
1908      return ...         -- returns all received vararg parameters
1909      return x,y,f()     -- returns x, y, and all results from f()
1910      {f()}              -- creates a list with all results from f()
1911      {...}              -- creates a list with all vararg parameters
1912      {f(), nil}         -- f() is adjusted to 1 result
1913 </pre>
1914
1915 <p>
1916 Any expression enclosed in parentheses always results in only one value.
1917 Thus,
1918 <code>(f(x,y,z))</code> is always a single value,
1919 even if <code>f</code> returns several values.
1920 (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code>
1921 or <b>nil</b> if <code>f</code> does not return any values.)
1922
1923
1924
1925 <h3>3.4.1 &ndash; <a name="3.4.1">Arithmetic Operators</a></h3><p>
1926 Lua supports the usual arithmetic operators:
1927 the binary <code>+</code> (addition),
1928 <code>-</code> (subtraction), <code>*</code> (multiplication),
1929 <code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation);
1930 and unary <code>-</code> (mathematical negation).
1931 If the operands are numbers, or strings that can be converted to
1932 numbers (see <a href="#3.4.2">&sect;3.4.2</a>),
1933 then all operations have the usual meaning.
1934 Exponentiation works for any exponent.
1935 For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>.
1936 Modulo is defined as
1937
1938 <pre>
1939      a % b == a - math.floor(a/b)*b
1940 </pre><p>
1941 That is, it is the remainder of a division that rounds
1942 the quotient towards minus infinity.
1943
1944
1945
1946
1947
1948 <h3>3.4.2 &ndash; <a name="3.4.2">Coercion</a></h3>
1949
1950 <p>
1951 Lua provides automatic conversion between
1952 string and number values at run time.
1953 Any arithmetic operation applied to a string tries to convert
1954 this string to a number, following the rules of the Lua lexer.
1955 (The string may have leading and trailing spaces and a sign.)
1956 Conversely, whenever a number is used where a string is expected,
1957 the number is converted to a string, in a reasonable format.
1958 For complete control over how numbers are converted to strings,
1959 use the <code>format</code> function from the string library
1960 (see <a href="#pdf-string.format"><code>string.format</code></a>).
1961
1962
1963
1964
1965
1966 <h3>3.4.3 &ndash; <a name="3.4.3">Relational Operators</a></h3><p>
1967 The relational operators in Lua are
1968
1969 <pre>
1970      ==    ~=    &lt;     &gt;     &lt;=    &gt;=
1971 </pre><p>
1972 These operators always result in <b>false</b> or <b>true</b>.
1973
1974
1975 <p>
1976 Equality (<code>==</code>) first compares the type of its operands.
1977 If the types are different, then the result is <b>false</b>.
1978 Otherwise, the values of the operands are compared.
1979 Numbers and strings are compared in the usual way.
1980 Tables, userdata, and threads
1981 are compared by reference:
1982 two objects are considered equal only if they are the same object.
1983 Every time you create a new object
1984 (a table, userdata, or thread),
1985 this new object is different from any previously existing object.
1986 Closures with the same reference are always equal.
1987 Closures with any detectable difference
1988 (different behavior, different definition) are always different.
1989
1990
1991 <p>
1992 You can change the way that Lua compares tables and userdata
1993 by using the "eq" metamethod (see <a href="#2.4">&sect;2.4</a>).
1994
1995
1996 <p>
1997 The conversion rules of <a href="#3.4.2">&sect;3.4.2</a>
1998 do not apply to equality comparisons.
1999 Thus, <code>"0"==0</code> evaluates to <b>false</b>,
2000 and <code>t[0]</code> and <code>t["0"]</code> denote different
2001 entries in a table.
2002
2003
2004 <p>
2005 The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
2006
2007
2008 <p>
2009 The order operators work as follows.
2010 If both arguments are numbers, then they are compared as such.
2011 Otherwise, if both arguments are strings,
2012 then their values are compared according to the current locale.
2013 Otherwise, Lua tries to call the "lt" or the "le"
2014 metamethod (see <a href="#2.4">&sect;2.4</a>).
2015 A comparison <code>a &gt; b</code> is translated to <code>b &lt; a</code>
2016 and <code>a &gt;= b</code> is translated to <code>b &lt;= a</code>.
2017
2018
2019
2020
2021
2022 <h3>3.4.4 &ndash; <a name="3.4.4">Logical Operators</a></h3><p>
2023 The logical operators in Lua are
2024 <b>and</b>, <b>or</b>, and <b>not</b>.
2025 Like the control structures (see <a href="#3.3.4">&sect;3.3.4</a>),
2026 all logical operators consider both <b>false</b> and <b>nil</b> as false
2027 and anything else as true.
2028
2029
2030 <p>
2031 The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>.
2032 The conjunction operator <b>and</b> returns its first argument
2033 if this value is <b>false</b> or <b>nil</b>;
2034 otherwise, <b>and</b> returns its second argument.
2035 The disjunction operator <b>or</b> returns its first argument
2036 if this value is different from <b>nil</b> and <b>false</b>;
2037 otherwise, <b>or</b> returns its second argument.
2038 Both <b>and</b> and <b>or</b> use short-cut evaluation;
2039 that is,
2040 the second operand is evaluated only if necessary.
2041 Here are some examples:
2042
2043 <pre>
2044      10 or 20            --&gt; 10
2045      10 or error()       --&gt; 10
2046      nil or "a"          --&gt; "a"
2047      nil and 10          --&gt; nil
2048      false and error()   --&gt; false
2049      false and nil       --&gt; false
2050      false or nil        --&gt; nil
2051      10 and 20           --&gt; 20
2052 </pre><p>
2053 (In this manual,
2054 <code>--&gt;</code> indicates the result of the preceding expression.)
2055
2056
2057
2058
2059
2060 <h3>3.4.5 &ndash; <a name="3.4.5">Concatenation</a></h3><p>
2061 The string concatenation operator in Lua is
2062 denoted by two dots ('<code>..</code>').
2063 If both operands are strings or numbers, then they are converted to
2064 strings according to the rules mentioned in <a href="#3.4.2">&sect;3.4.2</a>.
2065 Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">&sect;2.4</a>).
2066
2067
2068
2069
2070
2071 <h3>3.4.6 &ndash; <a name="3.4.6">The Length Operator</a></h3>
2072
2073 <p>
2074 The length operator is denoted by the unary prefix operator <code>#</code>.
2075 The length of a string is its number of bytes
2076 (that is, the usual meaning of string length when each
2077 character is one byte).
2078
2079
2080 <p>
2081 A program can modify the behavior of the length operator for
2082 any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">&sect;2.4</a>).
2083
2084
2085 <p>
2086 Unless a <code>__len</code> metamethod is given,
2087 the length of a table <code>t</code> is only defined if the
2088 table is a <em>sequence</em>,
2089 that is,
2090 the set of its positive numeric keys is equal to <em>{1..n}</em>
2091 for some integer <em>n</em>.
2092 In that case, <em>n</em> is its length.
2093 Note that a table like
2094
2095 <pre>
2096      {10, 20, nil, 40}
2097 </pre><p>
2098 is not a sequence, because it has the key <code>4</code>
2099 but does not have the key <code>3</code>.
2100 (So, there is no <em>n</em> such that the set <em>{1..n}</em> is equal
2101 to the set of positive numeric keys of that table.)
2102 Note, however, that non-numeric keys do not interfere
2103 with whether a table is a sequence.
2104
2105
2106
2107
2108
2109 <h3>3.4.7 &ndash; <a name="3.4.7">Precedence</a></h3><p>
2110 Operator precedence in Lua follows the table below,
2111 from lower to higher priority:
2112
2113 <pre>
2114      or
2115      and
2116      &lt;     &gt;     &lt;=    &gt;=    ~=    ==
2117      ..
2118      +     -
2119      *     /     %
2120      not   #     - (unary)
2121      ^
2122 </pre><p>
2123 As usual,
2124 you can use parentheses to change the precedences of an expression.
2125 The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>')
2126 operators are right associative.
2127 All other binary operators are left associative.
2128
2129
2130
2131
2132
2133 <h3>3.4.8 &ndash; <a name="3.4.8">Table Constructors</a></h3><p>
2134 Table constructors are expressions that create tables.
2135 Every time a constructor is evaluated, a new table is created.
2136 A constructor can be used to create an empty table
2137 or to create a table and initialize some of its fields.
2138 The general syntax for constructors is
2139
2140 <pre>
2141         tableconstructor ::= &lsquo;<b>{</b>&rsquo; [fieldlist] &lsquo;<b>}</b>&rsquo;
2142         fieldlist ::= field {fieldsep field} [fieldsep]
2143         field ::= &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; &lsquo;<b>=</b>&rsquo; exp | Name &lsquo;<b>=</b>&rsquo; exp | exp
2144         fieldsep ::= &lsquo;<b>,</b>&rsquo; | &lsquo;<b>;</b>&rsquo;
2145 </pre>
2146
2147 <p>
2148 Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry
2149 with key <code>exp1</code> and value <code>exp2</code>.
2150 A field of the form <code>name = exp</code> is equivalent to
2151 <code>["name"] = exp</code>.
2152 Finally, fields of the form <code>exp</code> are equivalent to
2153 <code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers,
2154 starting with 1.
2155 Fields in the other formats do not affect this counting.
2156 For example,
2157
2158 <pre>
2159      a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
2160 </pre><p>
2161 is equivalent to
2162
2163 <pre>
2164      do
2165        local t = {}
2166        t[f(1)] = g
2167        t[1] = "x"         -- 1st exp
2168        t[2] = "y"         -- 2nd exp
2169        t.x = 1            -- t["x"] = 1
2170        t[3] = f(x)        -- 3rd exp
2171        t[30] = 23
2172        t[4] = 45          -- 4th exp
2173        a = t
2174      end
2175 </pre>
2176
2177 <p>
2178 If the last field in the list has the form <code>exp</code>
2179 and the expression is a function call or a vararg expression,
2180 then all values returned by this expression enter the list consecutively
2181 (see <a href="#3.4.9">&sect;3.4.9</a>).
2182
2183
2184 <p>
2185 The field list can have an optional trailing separator,
2186 as a convenience for machine-generated code.
2187
2188
2189
2190
2191
2192 <h3>3.4.9 &ndash; <a name="3.4.9">Function Calls</a></h3><p>
2193 A function call in Lua has the following syntax:
2194
2195 <pre>
2196         functioncall ::= prefixexp args
2197 </pre><p>
2198 In a function call,
2199 first prefixexp and args are evaluated.
2200 If the value of prefixexp has type <em>function</em>,
2201 then this function is called
2202 with the given arguments.
2203 Otherwise, the prefixexp "call" metamethod is called,
2204 having as first parameter the value of prefixexp,
2205 followed by the original call arguments
2206 (see <a href="#2.4">&sect;2.4</a>).
2207
2208
2209 <p>
2210 The form
2211
2212 <pre>
2213         functioncall ::= prefixexp &lsquo;<b>:</b>&rsquo; Name args
2214 </pre><p>
2215 can be used to call "methods".
2216 A call <code>v:name(<em>args</em>)</code>
2217 is syntactic sugar for <code>v.name(v,<em>args</em>)</code>,
2218 except that <code>v</code> is evaluated only once.
2219
2220
2221 <p>
2222 Arguments have the following syntax:
2223
2224 <pre>
2225         args ::= &lsquo;<b>(</b>&rsquo; [explist] &lsquo;<b>)</b>&rsquo;
2226         args ::= tableconstructor
2227         args ::= String
2228 </pre><p>
2229 All argument expressions are evaluated before the call.
2230 A call of the form <code>f{<em>fields</em>}</code> is
2231 syntactic sugar for <code>f({<em>fields</em>})</code>;
2232 that is, the argument list is a single new table.
2233 A call of the form <code>f'<em>string</em>'</code>
2234 (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>)
2235 is syntactic sugar for <code>f('<em>string</em>')</code>;
2236 that is, the argument list is a single literal string.
2237
2238
2239 <p>
2240 A call of the form <code>return <em>functioncall</em></code> is called
2241 a <em>tail call</em>.
2242 Lua implements <em>proper tail calls</em>
2243 (or <em>proper tail recursion</em>):
2244 in a tail call,
2245 the called function reuses the stack entry of the calling function.
2246 Therefore, there is no limit on the number of nested tail calls that
2247 a program can execute.
2248 However, a tail call erases any debug information about the
2249 calling function.
2250 Note that a tail call only happens with a particular syntax,
2251 where the <b>return</b> has one single function call as argument;
2252 this syntax makes the calling function return exactly
2253 the returns of the called function.
2254 So, none of the following examples are tail calls:
2255
2256 <pre>
2257      return (f(x))        -- results adjusted to 1
2258      return 2 * f(x)
2259      return x, f(x)       -- additional results
2260      f(x); return         -- results discarded
2261      return x or f(x)     -- results adjusted to 1
2262 </pre>
2263
2264
2265
2266
2267 <h3>3.4.10 &ndash; <a name="3.4.10">Function Definitions</a></h3>
2268
2269 <p>
2270 The syntax for function definition is
2271
2272 <pre>
2273         functiondef ::= <b>function</b> funcbody
2274         funcbody ::= &lsquo;<b>(</b>&rsquo; [parlist] &lsquo;<b>)</b>&rsquo; block <b>end</b>
2275 </pre>
2276
2277 <p>
2278 The following syntactic sugar simplifies function definitions:
2279
2280 <pre>
2281         stat ::= <b>function</b> funcname funcbody
2282         stat ::= <b>local</b> <b>function</b> Name funcbody
2283         funcname ::= Name {&lsquo;<b>.</b>&rsquo; Name} [&lsquo;<b>:</b>&rsquo; Name]
2284 </pre><p>
2285 The statement
2286
2287 <pre>
2288      function f () <em>body</em> end
2289 </pre><p>
2290 translates to
2291
2292 <pre>
2293      f = function () <em>body</em> end
2294 </pre><p>
2295 The statement
2296
2297 <pre>
2298      function t.a.b.c.f () <em>body</em> end
2299 </pre><p>
2300 translates to
2301
2302 <pre>
2303      t.a.b.c.f = function () <em>body</em> end
2304 </pre><p>
2305 The statement
2306
2307 <pre>
2308      local function f () <em>body</em> end
2309 </pre><p>
2310 translates to
2311
2312 <pre>
2313      local f; f = function () <em>body</em> end
2314 </pre><p>
2315 not to
2316
2317 <pre>
2318      local f = function () <em>body</em> end
2319 </pre><p>
2320 (This only makes a difference when the body of the function
2321 contains references to <code>f</code>.)
2322
2323
2324 <p>
2325 A function definition is an executable expression,
2326 whose value has type <em>function</em>.
2327 When Lua precompiles a chunk,
2328 all its function bodies are precompiled too.
2329 Then, whenever Lua executes the function definition,
2330 the function is <em>instantiated</em> (or <em>closed</em>).
2331 This function instance (or <em>closure</em>)
2332 is the final value of the expression.
2333
2334
2335 <p>
2336 Parameters act as local variables that are
2337 initialized with the argument values:
2338
2339 <pre>
2340         parlist ::= namelist [&lsquo;<b>,</b>&rsquo; &lsquo;<b>...</b>&rsquo;] | &lsquo;<b>...</b>&rsquo;
2341 </pre><p>
2342 When a function is called,
2343 the list of arguments is adjusted to
2344 the length of the list of parameters,
2345 unless the function is a <em>vararg function</em>,
2346 which is indicated by three dots ('<code>...</code>')
2347 at the end of its parameter list.
2348 A vararg function does not adjust its argument list;
2349 instead, it collects all extra arguments and supplies them
2350 to the function through a <em>vararg expression</em>,
2351 which is also written as three dots.
2352 The value of this expression is a list of all actual extra arguments,
2353 similar to a function with multiple results.
2354 If a vararg expression is used inside another expression
2355 or in the middle of a list of expressions,
2356 then its return list is adjusted to one element.
2357 If the expression is used as the last element of a list of expressions,
2358 then no adjustment is made
2359 (unless that last expression is enclosed in parentheses).
2360
2361
2362 <p>
2363 As an example, consider the following definitions:
2364
2365 <pre>
2366      function f(a, b) end
2367      function g(a, b, ...) end
2368      function r() return 1,2,3 end
2369 </pre><p>
2370 Then, we have the following mapping from arguments to parameters and
2371 to the vararg expression:
2372
2373 <pre>
2374      CALL            PARAMETERS
2375
2376      f(3)             a=3, b=nil
2377      f(3, 4)          a=3, b=4
2378      f(3, 4, 5)       a=3, b=4
2379      f(r(), 10)       a=1, b=10
2380      f(r())           a=1, b=2
2381
2382      g(3)             a=3, b=nil, ... --&gt;  (nothing)
2383      g(3, 4)          a=3, b=4,   ... --&gt;  (nothing)
2384      g(3, 4, 5, 8)    a=3, b=4,   ... --&gt;  5  8
2385      g(5, r())        a=5, b=1,   ... --&gt;  2  3
2386 </pre>
2387
2388 <p>
2389 Results are returned using the <b>return</b> statement (see <a href="#3.3.4">&sect;3.3.4</a>).
2390 If control reaches the end of a function
2391 without encountering a <b>return</b> statement,
2392 then the function returns with no results.
2393
2394
2395 <p>
2396
2397 There is a system-dependent limit on the number of values
2398 that a function may return.
2399 This limit is guaranteed to be larger than 1000.
2400
2401
2402 <p>
2403 The <em>colon</em> syntax
2404 is used for defining <em>methods</em>,
2405 that is, functions that have an implicit extra parameter <code>self</code>.
2406 Thus, the statement
2407
2408 <pre>
2409      function t.a.b.c:f (<em>params</em>) <em>body</em> end
2410 </pre><p>
2411 is syntactic sugar for
2412
2413 <pre>
2414      t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end
2415 </pre>
2416
2417
2418
2419
2420
2421
2422 <h2>3.5 &ndash; <a name="3.5">Visibility Rules</a></h2>
2423
2424 <p>
2425
2426 Lua is a lexically scoped language.
2427 The scope of a local variable begins at the first statement after
2428 its declaration and lasts until the last non-void statement
2429 of the innermost block that includes the declaration.
2430 Consider the following example:
2431
2432 <pre>
2433      x = 10                -- global variable
2434      do                    -- new block
2435        local x = x         -- new 'x', with value 10
2436        print(x)            --&gt; 10
2437        x = x+1
2438        do                  -- another block
2439          local x = x+1     -- another 'x'
2440          print(x)          --&gt; 12
2441        end
2442        print(x)            --&gt; 11
2443      end
2444      print(x)              --&gt; 10  (the global one)
2445 </pre>
2446
2447 <p>
2448 Notice that, in a declaration like <code>local x = x</code>,
2449 the new <code>x</code> being declared is not in scope yet,
2450 and so the second <code>x</code> refers to the outside variable.
2451
2452
2453 <p>
2454 Because of the lexical scoping rules,
2455 local variables can be freely accessed by functions
2456 defined inside their scope.
2457 A local variable used by an inner function is called
2458 an <em>upvalue</em>, or <em>external local variable</em>,
2459 inside the inner function.
2460
2461
2462 <p>
2463 Notice that each execution of a <b>local</b> statement
2464 defines new local variables.
2465 Consider the following example:
2466
2467 <pre>
2468      a = {}
2469      local x = 20
2470      for i=1,10 do
2471        local y = 0
2472        a[i] = function () y=y+1; return x+y end
2473      end
2474 </pre><p>
2475 The loop creates ten closures
2476 (that is, ten instances of the anonymous function).
2477 Each of these closures uses a different <code>y</code> variable,
2478 while all of them share the same <code>x</code>.
2479
2480
2481
2482
2483
2484 <h1>4 &ndash; <a name="4">The Application Program Interface</a></h1>
2485
2486 <p>
2487
2488 This section describes the C&nbsp;API for Lua, that is,
2489 the set of C&nbsp;functions available to the host program to communicate
2490 with Lua.
2491 All API functions and related types and constants
2492 are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>.
2493
2494
2495 <p>
2496 Even when we use the term "function",
2497 any facility in the API may be provided as a macro instead.
2498 Except where stated otherwise,
2499 all such macros use each of their arguments exactly once
2500 (except for the first argument, which is always a Lua state),
2501 and so do not generate any hidden side-effects.
2502
2503
2504 <p>
2505 As in most C&nbsp;libraries,
2506 the Lua API functions do not check their arguments for validity or consistency.
2507 However, you can change this behavior by compiling Lua
2508 with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined.
2509
2510
2511
2512 <h2>4.1 &ndash; <a name="4.1">The Stack</a></h2>
2513
2514 <p>
2515 Lua uses a <em>virtual stack</em> to pass values to and from C.
2516 Each element in this stack represents a Lua value
2517 (<b>nil</b>, number, string, etc.).
2518
2519
2520 <p>
2521 Whenever Lua calls C, the called function gets a new stack,
2522 which is independent of previous stacks and of stacks of
2523 C&nbsp;functions that are still active.
2524 This stack initially contains any arguments to the C&nbsp;function
2525 and it is where the C&nbsp;function pushes its results
2526 to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
2527
2528
2529 <p>
2530 For convenience,
2531 most query operations in the API do not follow a strict stack discipline.
2532 Instead, they can refer to any element in the stack
2533 by using an <em>index</em>:
2534 A positive index represents an absolute stack position
2535 (starting at&nbsp;1);
2536 a negative index represents an offset relative to the top of the stack.
2537 More specifically, if the stack has <em>n</em> elements,
2538 then index&nbsp;1 represents the first element
2539 (that is, the element that was pushed onto the stack first)
2540 and
2541 index&nbsp;<em>n</em> represents the last element;
2542 index&nbsp;-1 also represents the last element
2543 (that is, the element at the&nbsp;top)
2544 and index <em>-n</em> represents the first element.
2545
2546
2547
2548
2549
2550 <h2>4.2 &ndash; <a name="4.2">Stack Size</a></h2>
2551
2552 <p>
2553 When you interact with the Lua API,
2554 you are responsible for ensuring consistency.
2555 In particular,
2556 <em>you are responsible for controlling stack overflow</em>.
2557 You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a>
2558 to ensure that the stack has extra slots when pushing new elements.
2559
2560
2561 <p>
2562 Whenever Lua calls C,
2563 it ensures that the stack has at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots.
2564 <code>LUA_MINSTACK</code> is defined as 20,
2565 so that usually you do not have to worry about stack space
2566 unless your code has loops pushing elements onto the stack.
2567
2568
2569 <p>
2570 When you call a Lua function
2571 without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>),
2572 Lua ensures that the stack has enough size for all results,
2573 but it does not ensure any extra space.
2574 So, before pushing anything in the stack after such a call
2575 you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>.
2576
2577
2578
2579
2580
2581 <h2>4.3 &ndash; <a name="4.3">Valid and Acceptable Indices</a></h2>
2582
2583 <p>
2584 Any function in the API that receives stack indices
2585 works only with <em>valid indices</em> or <em>acceptable indices</em>.
2586
2587
2588 <p>
2589 A <em>valid index</em> is an index that refers to a
2590 real position within the stack, that is,
2591 its position lies between&nbsp;1 and the stack top
2592 (<code>1 &le; abs(index) &le; top</code>).
2593
2594 Usually, functions that can modify the value at an index
2595 require valid indices.
2596
2597
2598 <p>
2599 Unless otherwise noted,
2600 any function that accepts valid indices also accepts <em>pseudo-indices</em>,
2601 which represent some Lua values that are accessible to C&nbsp;code
2602 but which are not in the stack.
2603 Pseudo-indices are used to access the registry
2604 and the upvalues of a C&nbsp;function (see <a href="#4.4">&sect;4.4</a>).
2605
2606
2607 <p>
2608 Functions that do not need a specific stack position,
2609 but only a value in the stack (e.g., query functions),
2610 can be called with acceptable indices.
2611 An <em>acceptable index</em> can be any valid index,
2612 including the pseudo-indices,
2613 but it also can be any positive index after the stack top
2614 within the space allocated for the stack,
2615 that is, indices up to the stack size.
2616 (Note that 0 is never an acceptable index.)
2617 Except when noted otherwise,
2618 functions in the API work with acceptable indices.
2619
2620
2621 <p>
2622 Acceptable indices serve to avoid extra tests
2623 against the stack top when querying the stack.
2624 For instance, a C&nbsp;function can query its third argument
2625 without the need to first check whether there is a third argument,
2626 that is, without the need to check whether 3 is a valid index.
2627
2628
2629 <p>
2630 For functions that can be called with acceptable indices,
2631 any non-valid index is treated as if it
2632 contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>,
2633 which behaves like a nil value.
2634
2635
2636
2637
2638
2639 <h2>4.4 &ndash; <a name="4.4">C Closures</a></h2>
2640
2641 <p>
2642 When a C&nbsp;function is created,
2643 it is possible to associate some values with it,
2644 thus creating a <em>C&nbsp;closure</em>
2645 (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>);
2646 these values are called <em>upvalues</em> and are
2647 accessible to the function whenever it is called.
2648
2649
2650 <p>
2651 Whenever a C&nbsp;function is called,
2652 its upvalues are located at specific pseudo-indices.
2653 These pseudo-indices are produced by the macro
2654 <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>.
2655 The first value associated with a function is at position
2656 <code>lua_upvalueindex(1)</code>, and so on.
2657 Any access to <code>lua_upvalueindex(<em>n</em>)</code>,
2658 where <em>n</em> is greater than the number of upvalues of the
2659 current function (but not greater than 256),
2660 produces an acceptable but invalid index.
2661
2662
2663
2664
2665
2666 <h2>4.5 &ndash; <a name="4.5">Registry</a></h2>
2667
2668 <p>
2669 Lua provides a <em>registry</em>,
2670 a predefined table that can be used by any C&nbsp;code to
2671 store whatever Lua values it needs to store.
2672 The registry table is always located at pseudo-index
2673 <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>,
2674 which is a valid index.
2675 Any C&nbsp;library can store data into this table,
2676 but it should take care to choose keys
2677 that are different from those used
2678 by other libraries, to avoid collisions.
2679 Typically, you should use as key a string containing your library name,
2680 or a light userdata with the address of a C&nbsp;object in your code,
2681 or any Lua object created by your code.
2682 As with global names,
2683 string keys starting with an underscore followed by
2684 uppercase letters are reserved for Lua.
2685
2686
2687 <p>
2688 The integer keys in the registry are used by the reference mechanism,
2689 implemented by the auxiliary library,
2690 and by some predefined values.
2691 Therefore, integer keys should not be used for other purposes.
2692
2693
2694 <p>
2695 When you create a new Lua state,
2696 its registry comes with some predefined values.
2697 These predefined values are indexed with integer keys
2698 defined as constants in <code>lua.h</code>.
2699 The following constants are defined:
2700
2701 <ul>
2702 <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has
2703 the main thread of the state.
2704 (The main thread is the one created together with the state.)
2705 </li>
2706
2707 <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has
2708 the global environment.
2709 </li>
2710 </ul>
2711
2712
2713
2714
2715 <h2>4.6 &ndash; <a name="4.6">Error Handling in C</a></h2>
2716
2717 <p>
2718 Internally, Lua uses the C <code>longjmp</code> facility to handle errors.
2719 (You can also choose to use exceptions if you compile Lua as C++;
2720 search for <code>LUAI_THROW</code> in the source code.)
2721 When Lua faces any error
2722 (such as a memory allocation error, type errors, syntax errors,
2723 and runtime errors)
2724 it <em>raises</em> an error;
2725 that is, it does a long jump.
2726 A <em>protected environment</em> uses <code>setjmp</code>
2727 to set a recovery point;
2728 any error jumps to the most recent active recovery point.
2729
2730
2731 <p>
2732 If an error happens outside any protected environment,
2733 Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>)
2734 and then calls <code>abort</code>,
2735 thus exiting the host application.
2736 Your panic function can avoid this exit by
2737 never returning
2738 (e.g., doing a long jump to your own recovery point outside Lua).
2739
2740
2741 <p>
2742 The panic function runs as if it were a message handler (see <a href="#2.3">&sect;2.3</a>);
2743 in particular, the error message is at the top of the stack.
2744 However, there is no guarantees about stack space.
2745 To push anything on the stack,
2746 the panic function should first check the available space (see <a href="#4.2">&sect;4.2</a>).
2747
2748
2749 <p>
2750 Most functions in the API can throw an error,
2751 for instance due to a memory allocation error.
2752 The documentation for each function indicates whether
2753 it can throw errors.
2754
2755
2756 <p>
2757 Inside a C&nbsp;function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>.
2758
2759
2760
2761
2762
2763 <h2>4.7 &ndash; <a name="4.7">Handling Yields in C</a></h2>
2764
2765 <p>
2766 Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine.
2767 Therefore, if a function <code>foo</code> calls an API function
2768 and this API function yields
2769 (directly or indirectly by calling another function that yields),
2770 Lua cannot return to <code>foo</code> any more,
2771 because the <code>longjmp</code> removes its frame from the C stack.
2772
2773
2774 <p>
2775 To avoid this kind of problem,
2776 Lua raises an error whenever it tries to yield across an API call,
2777 except for three functions:
2778 <a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>.
2779 All those functions receive a <em>continuation function</em>
2780 (as a parameter called <code>k</code>) to continue execution after a yield.
2781
2782
2783 <p>
2784 We need to set some terminology to explain continuations.
2785 We have a C function called from Lua which we will call
2786 the <em>original function</em>.
2787 This original function then calls one of those three functions in the C API,
2788 which we will call the <em>callee function</em>,
2789 that then yields the current thread.
2790 (This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
2791 or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a>
2792 and the function called by them yields.)
2793
2794
2795 <p>
2796 Suppose the running thread yields while executing the callee function.
2797 After the thread resumes,
2798 it eventually will finish running the callee function.
2799 However,
2800 the callee function cannot return to the original function,
2801 because its frame in the C stack was destroyed by the yield.
2802 Instead, Lua calls a <em>continuation function</em>,
2803 which was given as an argument to the callee function.
2804 As the name implies,
2805 the continuation function should continue the task
2806 of the original function.
2807
2808
2809 <p>
2810 Lua treats the continuation function as if it were the original function.
2811 The continuation function receives the same Lua stack
2812 from the original function,
2813 in the same state it would be if the callee function had returned.
2814 (For instance,
2815 after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are
2816 removed from the stack and replaced by the results from the call.)
2817 It also has the same upvalues.
2818 Whatever it returns is handled by Lua as if it were the return
2819 of the original function.
2820
2821
2822 <p>
2823 The only difference in the Lua state between the original function
2824 and its continuation is the result of a call to <a href="#lua_getctx"><code>lua_getctx</code></a>.
2825
2826
2827
2828
2829
2830 <h2>4.8 &ndash; <a name="4.8">Functions and Types</a></h2>
2831
2832 <p>
2833 Here we list all functions and types from the C&nbsp;API in
2834 alphabetical order.
2835 Each function has an indicator like this:
2836 <span class="apii">[-o, +p, <em>x</em>]</span>
2837
2838
2839 <p>
2840 The first field, <code>o</code>,
2841 is how many elements the function pops from the stack.
2842 The second field, <code>p</code>,
2843 is how many elements the function pushes onto the stack.
2844 (Any function always pushes its results after popping its arguments.)
2845 A field in the form <code>x|y</code> means the function can push (or pop)
2846 <code>x</code> or <code>y</code> elements,
2847 depending on the situation;
2848 an interrogation mark '<code>?</code>' means that
2849 we cannot know how many elements the function pops/pushes
2850 by looking only at its arguments
2851 (e.g., they may depend on what is on the stack).
2852 The third field, <code>x</code>,
2853 tells whether the function may throw errors:
2854 '<code>-</code>' means the function never throws any error;
2855 '<code>e</code>' means the function may throw errors;
2856 '<code>v</code>' means the function may throw an error on purpose.
2857
2858
2859
2860 <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p>
2861 <span class="apii">[-0, +0, &ndash;]</span>
2862 <pre>int lua_absindex (lua_State *L, int idx);</pre>
2863
2864 <p>
2865 Converts the acceptable index <code>idx</code> into an absolute index
2866 (that is, one that does not depend on the stack top).
2867
2868
2869
2870
2871
2872 <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3>
2873 <pre>typedef void * (*lua_Alloc) (void *ud,
2874                              void *ptr,
2875                              size_t osize,
2876                              size_t nsize);</pre>
2877
2878 <p>
2879 The type of the memory-allocation function used by Lua states.
2880 The allocator function must provide a
2881 functionality similar to <code>realloc</code>,
2882 but not exactly the same.
2883 Its arguments are
2884 <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
2885 <code>ptr</code>, a pointer to the block being allocated/reallocated/freed;
2886 <code>osize</code>, the original size of the block or some code about what
2887 is being allocated;
2888 <code>nsize</code>, the new size of the block.
2889
2890
2891 <p>
2892 When <code>ptr</code> is not <code>NULL</code>,
2893 <code>osize</code> is the size of the block pointed by <code>ptr</code>,
2894 that is, the size given when it was allocated or reallocated.
2895
2896
2897 <p>
2898 When <code>ptr</code> is <code>NULL</code>,
2899 <code>osize</code> encodes the kind of object that Lua is allocating.
2900 <code>osize</code> is any of
2901 <a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
2902 <a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when)
2903 Lua is creating a new object of that type.
2904 When <code>osize</code> is some other value,
2905 Lua is allocating memory for something else.
2906
2907
2908 <p>
2909 Lua assumes the following behavior from the allocator function:
2910
2911
2912 <p>
2913 When <code>nsize</code> is zero,
2914 the allocator should behave like <code>free</code>
2915 and return <code>NULL</code>.
2916
2917
2918 <p>
2919 When <code>nsize</code> is not zero,
2920 the allocator should behave like <code>realloc</code>.
2921 The allocator returns <code>NULL</code>
2922 if and only if it cannot fulfill the request.
2923 Lua assumes that the allocator never fails when
2924 <code>osize &gt;= nsize</code>.
2925
2926
2927 <p>
2928 Here is a simple implementation for the allocator function.
2929 It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
2930
2931 <pre>
2932      static void *l_alloc (void *ud, void *ptr, size_t osize,
2933                                                 size_t nsize) {
2934        (void)ud;  (void)osize;  /* not used */
2935        if (nsize == 0) {
2936          free(ptr);
2937          return NULL;
2938        }
2939        else
2940          return realloc(ptr, nsize);
2941      }
2942 </pre><p>
2943 Note that Standard&nbsp;C ensures
2944 that <code>free(NULL)</code> has no effect and that
2945 <code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>.
2946 This code assumes that <code>realloc</code> does not fail when shrinking a block.
2947 (Although Standard&nbsp;C does not ensure this behavior,
2948 it seems to be a safe assumption.)
2949
2950
2951
2952
2953
2954 <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p>
2955 <span class="apii">[-(2|1), +1, <em>e</em>]</span>
2956 <pre>void lua_arith (lua_State *L, int op);</pre>
2957
2958 <p>
2959 Performs an arithmetic operation over the two values
2960 (or one, in the case of negation)
2961 at the top of the stack,
2962 with the value at the top being the second operand,
2963 pops these values, and pushes the result of the operation.
2964 The function follows the semantics of the corresponding Lua operator
2965 (that is, it may call metamethods).
2966
2967
2968 <p>
2969 The value of <code>op</code> must be one of the following constants:
2970
2971 <ul>
2972
2973 <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li>
2974 <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li>
2975 <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li>
2976 <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs division (<code>/</code>)</li>
2977 <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li>
2978 <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li>
2979 <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li>
2980
2981 </ul>
2982
2983
2984
2985
2986 <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p>
2987 <span class="apii">[-0, +0, &ndash;]</span>
2988 <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre>
2989
2990 <p>
2991 Sets a new panic function and returns the old one (see <a href="#4.6">&sect;4.6</a>).
2992
2993
2994
2995
2996
2997 <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p>
2998 <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span>
2999 <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre>
3000
3001 <p>
3002 Calls a function.
3003
3004
3005 <p>
3006 To call a function you must use the following protocol:
3007 first, the function to be called is pushed onto the stack;
3008 then, the arguments to the function are pushed
3009 in direct order;
3010 that is, the first argument is pushed first.
3011 Finally you call <a href="#lua_call"><code>lua_call</code></a>;
3012 <code>nargs</code> is the number of arguments that you pushed onto the stack.
3013 All arguments and the function value are popped from the stack
3014 when the function is called.
3015 The function results are pushed onto the stack when the function returns.
3016 The number of results is adjusted to <code>nresults</code>,
3017 unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>.
3018 In this case, all results from the function are pushed.
3019 Lua takes care that the returned values fit into the stack space.
3020 The function results are pushed onto the stack in direct order
3021 (the first result is pushed first),
3022 so that after the call the last result is on the top of the stack.
3023
3024
3025 <p>
3026 Any error inside the called function is propagated upwards
3027 (with a <code>longjmp</code>).
3028
3029
3030 <p>
3031 The following example shows how the host program can do the
3032 equivalent to this Lua code:
3033
3034 <pre>
3035      a = f("how", t.x, 14)
3036 </pre><p>
3037 Here it is in&nbsp;C:
3038
3039 <pre>
3040      lua_getglobal(L, "f");                  /* function to be called */
3041      lua_pushstring(L, "how");                        /* 1st argument */
3042      lua_getglobal(L, "t");                    /* table to be indexed */
3043      lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
3044      lua_remove(L, -2);                  /* remove 't' from the stack */
3045      lua_pushinteger(L, 14);                          /* 3rd argument */
3046      lua_call(L, 3, 1);     /* call 'f' with 3 arguments and 1 result */
3047      lua_setglobal(L, "a");                         /* set global 'a' */
3048 </pre><p>
3049 Note that the code above is "balanced":
3050 at its end, the stack is back to its original configuration.
3051 This is considered good programming practice.
3052
3053
3054
3055
3056
3057 <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p>
3058 <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span>
3059 <pre>void lua_callk (lua_State *L, int nargs, int nresults, int ctx,
3060                 lua_CFunction k);</pre>
3061
3062 <p>
3063 This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>,
3064 but allows the called function to yield (see <a href="#4.7">&sect;4.7</a>).
3065
3066
3067
3068
3069
3070 <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3>
3071 <pre>typedef int (*lua_CFunction) (lua_State *L);</pre>
3072
3073 <p>
3074 Type for C&nbsp;functions.
3075
3076
3077 <p>
3078 In order to communicate properly with Lua,
3079 a C&nbsp;function must use the following protocol,
3080 which defines the way parameters and results are passed:
3081 a C&nbsp;function receives its arguments from Lua in its stack
3082 in direct order (the first argument is pushed first).
3083 So, when the function starts,
3084 <code>lua_gettop(L)</code> returns the number of arguments received by the function.
3085 The first argument (if any) is at index 1
3086 and its last argument is at index <code>lua_gettop(L)</code>.
3087 To return values to Lua, a C&nbsp;function just pushes them onto the stack,
3088 in direct order (the first result is pushed first),
3089 and returns the number of results.
3090 Any other value in the stack below the results will be properly
3091 discarded by Lua.
3092 Like a Lua function, a C&nbsp;function called by Lua can also return
3093 many results.
3094
3095
3096 <p>
3097 As an example, the following function receives a variable number
3098 of numerical arguments and returns their average and sum:
3099
3100 <pre>
3101      static int foo (lua_State *L) {
3102        int n = lua_gettop(L);    /* number of arguments */
3103        lua_Number sum = 0;
3104        int i;
3105        for (i = 1; i &lt;= n; i++) {
3106          if (!lua_isnumber(L, i)) {
3107            lua_pushstring(L, "incorrect argument");
3108            lua_error(L);
3109          }
3110          sum += lua_tonumber(L, i);
3111        }
3112        lua_pushnumber(L, sum/n);        /* first result */
3113        lua_pushnumber(L, sum);         /* second result */
3114        return 2;                   /* number of results */
3115      }
3116 </pre>
3117
3118
3119
3120
3121 <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p>
3122 <span class="apii">[-0, +0, &ndash;]</span>
3123 <pre>int lua_checkstack (lua_State *L, int extra);</pre>
3124
3125 <p>
3126 Ensures that there are at least <code>extra</code> free stack slots in the stack.
3127 It returns false if it cannot fulfill the request,
3128 because it would cause the stack to be larger than a fixed maximum size
3129 (typically at least a few thousand elements) or
3130 because it cannot allocate memory for the new stack size.
3131 This function never shrinks the stack;
3132 if the stack is already larger than the new size,
3133 it is left unchanged.
3134
3135
3136
3137
3138
3139 <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p>
3140 <span class="apii">[-0, +0, &ndash;]</span>
3141 <pre>void lua_close (lua_State *L);</pre>
3142
3143 <p>
3144 Destroys all objects in the given Lua state
3145 (calling the corresponding garbage-collection metamethods, if any)
3146 and frees all dynamic memory used by this state.
3147 On several platforms, you may not need to call this function,
3148 because all resources are naturally released when the host program ends.
3149 On the other hand, long-running programs that create multiple states,
3150 such as daemons or web servers,
3151 might need to close states as soon as they are not needed.
3152
3153
3154
3155
3156
3157 <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p>
3158 <span class="apii">[-0, +0, <em>e</em>]</span>
3159 <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre>
3160
3161 <p>
3162 Compares two Lua values.
3163 Returns 1 if the value at index <code>index1</code> satisfies <code>op</code>
3164 when compared with the value at index <code>index2</code>,
3165 following the semantics of the corresponding Lua operator
3166 (that is, it may call metamethods).
3167 Otherwise returns&nbsp;0.
3168 Also returns&nbsp;0 if any of the indices is non valid.
3169
3170
3171 <p>
3172 The value of <code>op</code> must be one of the following constants:
3173
3174 <ul>
3175
3176 <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li>
3177 <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code>&lt;</code>)</li>
3178 <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code>&lt;=</code>)</li>
3179
3180 </ul>
3181
3182
3183
3184
3185 <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p>
3186 <span class="apii">[-n, +1, <em>e</em>]</span>
3187 <pre>void lua_concat (lua_State *L, int n);</pre>
3188
3189 <p>
3190 Concatenates the <code>n</code> values at the top of the stack,
3191 pops them, and leaves the result at the top.
3192 If <code>n</code>&nbsp;is&nbsp;1, the result is the single value on the stack
3193 (that is, the function does nothing);
3194 if <code>n</code> is 0, the result is the empty string.
3195 Concatenation is performed following the usual semantics of Lua
3196 (see <a href="#3.4.5">&sect;3.4.5</a>).
3197
3198
3199
3200
3201
3202 <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p>
3203 <span class="apii">[-0, +0, &ndash;]</span>
3204 <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre>
3205
3206 <p>
3207 Moves the element at index <code>fromidx</code>
3208 into the valid index <code>toidx</code>
3209 without shifting any element
3210 (therefore replacing the value at that position).
3211
3212
3213
3214
3215
3216 <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p>
3217 <span class="apii">[-0, +1, <em>e</em>]</span>
3218 <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre>
3219
3220 <p>
3221 Creates a new empty table and pushes it onto the stack.
3222 Parameter <code>narr</code> is a hint for how many elements the table
3223 will have as a sequence;
3224 parameter <code>nrec</code> is a hint for how many other elements
3225 the table will have.
3226 Lua may use these hints to preallocate memory for the new table.
3227 This pre-allocation is useful for performance when you know in advance
3228 how many elements the table will have.
3229 Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>.
3230
3231
3232
3233
3234
3235 <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p>
3236 <span class="apii">[-0, +0, <em>e</em>]</span>
3237 <pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre>
3238
3239 <p>
3240 Dumps a function as a binary chunk.
3241 Receives a Lua function on the top of the stack
3242 and produces a binary chunk that,
3243 if loaded again,
3244 results in a function equivalent to the one dumped.
3245 As it produces parts of the chunk,
3246 <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
3247 with the given <code>data</code>
3248 to write them.
3249
3250
3251 <p>
3252 The value returned is the error code returned by the last
3253 call to the writer;
3254 0&nbsp;means no errors.
3255
3256
3257 <p>
3258 This function does not pop the Lua function from the stack.
3259
3260
3261
3262
3263
3264 <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p>
3265 <span class="apii">[-1, +0, <em>v</em>]</span>
3266 <pre>int lua_error (lua_State *L);</pre>
3267
3268 <p>
3269 Generates a Lua error.
3270 The error message (which can actually be a Lua value of any type)
3271 must be on the stack top.
3272 This function does a long jump,
3273 and therefore never returns
3274 (see <a href="#luaL_error"><code>luaL_error</code></a>).
3275
3276
3277
3278
3279
3280 <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p>
3281 <span class="apii">[-0, +0, <em>e</em>]</span>
3282 <pre>int lua_gc (lua_State *L, int what, int data);</pre>
3283
3284 <p>
3285 Controls the garbage collector.
3286
3287
3288 <p>
3289 This function performs several tasks,
3290 according to the value of the parameter <code>what</code>:
3291
3292 <ul>
3293
3294 <li><b><code>LUA_GCSTOP</code>: </b>
3295 stops the garbage collector.
3296 </li>
3297
3298 <li><b><code>LUA_GCRESTART</code>: </b>
3299 restarts the garbage collector.
3300 </li>
3301
3302 <li><b><code>LUA_GCCOLLECT</code>: </b>
3303 performs a full garbage-collection cycle.
3304 </li>
3305
3306 <li><b><code>LUA_GCCOUNT</code>: </b>
3307 returns the current amount of memory (in Kbytes) in use by Lua.
3308 </li>
3309
3310 <li><b><code>LUA_GCCOUNTB</code>: </b>
3311 returns the remainder of dividing the current amount of bytes of
3312 memory in use by Lua by 1024.
3313 </li>
3314
3315 <li><b><code>LUA_GCSTEP</code>: </b>
3316 performs an incremental step of garbage collection.
3317 The step "size" is controlled by <code>data</code>
3318 (larger values mean more steps) in a non-specified way.
3319 If you want to control the step size
3320 you must experimentally tune the value of <code>data</code>.
3321 The function returns 1 if the step finished a
3322 garbage-collection cycle.
3323 </li>
3324
3325 <li><b><code>LUA_GCSETPAUSE</code>: </b>
3326 sets <code>data</code> as the new value
3327 for the <em>pause</em> of the collector (see <a href="#2.5">&sect;2.5</a>).
3328 The function returns the previous value of the pause.
3329 </li>
3330
3331 <li><b><code>LUA_GCSETSTEPMUL</code>: </b>
3332 sets <code>data</code> as the new value for the <em>step multiplier</em> of
3333 the collector (see <a href="#2.5">&sect;2.5</a>).
3334 The function returns the previous value of the step multiplier.
3335 </li>
3336
3337 <li><b><code>LUA_GCISRUNNING</code>: </b>
3338 returns a boolean that tells whether the collector is running
3339 (i.e., not stopped).
3340 </li>
3341
3342 <li><b><code>LUA_GCGEN</code>: </b>
3343 changes the collector to generational mode
3344 (see <a href="#2.5">&sect;2.5</a>).
3345 </li>
3346
3347 <li><b><code>LUA_GCINC</code>: </b>
3348 changes the collector to incremental mode.
3349 This is the default mode.
3350 </li>
3351
3352 </ul>
3353
3354 <p>
3355 For more details about these options,
3356 see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>.
3357
3358
3359
3360
3361
3362 <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p>
3363 <span class="apii">[-0, +0, &ndash;]</span>
3364 <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre>
3365
3366 <p>
3367 Returns the memory-allocation function of a given state.
3368 If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the
3369 opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>.
3370
3371
3372
3373
3374
3375 <hr><h3><a name="lua_getctx"><code>lua_getctx</code></a></h3><p>
3376 <span class="apii">[-0, +0, &ndash;]</span>
3377 <pre>int lua_getctx (lua_State *L, int *ctx);</pre>
3378
3379 <p>
3380 This function is called by a continuation function (see <a href="#4.7">&sect;4.7</a>)
3381 to retrieve the status of the thread and a context information.
3382
3383
3384 <p>
3385 When called in the original function,
3386 <a href="#lua_getctx"><code>lua_getctx</code></a> always returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
3387 and does not change the value of its argument <code>ctx</code>.
3388 When called inside a continuation function,
3389 <a href="#lua_getctx"><code>lua_getctx</code></a> returns <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> and sets
3390 the value of <code>ctx</code> to be the context information
3391 (the value passed as the <code>ctx</code> argument
3392 to the callee together with the continuation function).
3393
3394
3395 <p>
3396 When the callee is <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
3397 Lua may also call its continuation function
3398 to handle errors during the call.
3399 That is, upon an error in the function called by <a href="#lua_pcallk"><code>lua_pcallk</code></a>,
3400 Lua may not return to the original function
3401 but instead may call the continuation function.
3402 In that case, a call to <a href="#lua_getctx"><code>lua_getctx</code></a> will return the error code
3403 (the value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>);
3404 the value of <code>ctx</code> will be set to the context information,
3405 as in the case of a yield.
3406
3407
3408
3409
3410
3411 <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p>
3412 <span class="apii">[-0, +1, <em>e</em>]</span>
3413 <pre>void lua_getfield (lua_State *L, int index, const char *k);</pre>
3414
3415 <p>
3416 Pushes onto the stack the value <code>t[k]</code>,
3417 where <code>t</code> is the value at the given index.
3418 As in Lua, this function may trigger a metamethod
3419 for the "index" event (see <a href="#2.4">&sect;2.4</a>).
3420
3421
3422
3423
3424
3425 <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p>
3426 <span class="apii">[-0, +1, <em>e</em>]</span>
3427 <pre>void lua_getglobal (lua_State *L, const char *name);</pre>
3428
3429 <p>
3430 Pushes onto the stack the value of the global <code>name</code>.
3431
3432
3433
3434
3435
3436 <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p>
3437 <span class="apii">[-0, +(0|1), &ndash;]</span>
3438 <pre>int lua_getmetatable (lua_State *L, int index);</pre>
3439
3440 <p>
3441 Pushes onto the stack the metatable of the value at the given index.
3442 If the value does not have a metatable,
3443 the function returns&nbsp;0 and pushes nothing on the stack.
3444
3445
3446
3447
3448
3449 <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p>
3450 <span class="apii">[-1, +1, <em>e</em>]</span>
3451 <pre>void lua_gettable (lua_State *L, int index);</pre>
3452
3453 <p>
3454 Pushes onto the stack the value <code>t[k]</code>,
3455 where <code>t</code> is the value at the given index
3456 and <code>k</code> is the value at the top of the stack.
3457
3458
3459 <p>
3460 This function pops the key from the stack
3461 (putting the resulting value in its place).
3462 As in Lua, this function may trigger a metamethod
3463 for the "index" event (see <a href="#2.4">&sect;2.4</a>).
3464
3465
3466
3467
3468
3469 <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p>
3470 <span class="apii">[-0, +0, &ndash;]</span>
3471 <pre>int lua_gettop (lua_State *L);</pre>
3472
3473 <p>
3474 Returns the index of the top element in the stack.
3475 Because indices start at&nbsp;1,
3476 this result is equal to the number of elements in the stack
3477 (and so 0&nbsp;means an empty stack).
3478
3479
3480
3481
3482
3483 <hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p>
3484 <span class="apii">[-0, +1, &ndash;]</span>
3485 <pre>void lua_getuservalue (lua_State *L, int index);</pre>
3486
3487 <p>
3488 Pushes onto the stack the Lua value associated with the userdata
3489 at the given index.
3490 This Lua value must be a table or <b>nil</b>.
3491
3492
3493
3494
3495
3496 <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p>
3497 <span class="apii">[-1, +1, &ndash;]</span>
3498 <pre>void lua_insert (lua_State *L, int index);</pre>
3499
3500 <p>
3501 Moves the top element into the given valid index,
3502 shifting up the elements above this index to open space.
3503 This function cannot be called with a pseudo-index,
3504 because a pseudo-index is not an actual stack position.
3505
3506
3507
3508
3509
3510 <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3>
3511 <pre>typedef ptrdiff_t lua_Integer;</pre>
3512
3513 <p>
3514 The type used by the Lua API to represent signed integral values.
3515
3516
3517 <p>
3518 By default it is a <code>ptrdiff_t</code>,
3519 which is usually the largest signed integral type the machine handles
3520 "comfortably".
3521
3522
3523
3524
3525
3526 <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p>
3527 <span class="apii">[-0, +0, &ndash;]</span>
3528 <pre>int lua_isboolean (lua_State *L, int index);</pre>
3529
3530 <p>
3531 Returns 1 if the value at the given index is a boolean,
3532 and 0&nbsp;otherwise.
3533
3534
3535
3536
3537
3538 <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p>
3539 <span class="apii">[-0, +0, &ndash;]</span>
3540 <pre>int lua_iscfunction (lua_State *L, int index);</pre>
3541
3542 <p>
3543 Returns 1 if the value at the given index is a C&nbsp;function,
3544 and 0&nbsp;otherwise.
3545
3546
3547
3548
3549
3550 <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p>
3551 <span class="apii">[-0, +0, &ndash;]</span>
3552 <pre>int lua_isfunction (lua_State *L, int index);</pre>
3553
3554 <p>
3555 Returns 1 if the value at the given index is a function
3556 (either C or Lua), and 0&nbsp;otherwise.
3557
3558
3559
3560
3561
3562 <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p>
3563 <span class="apii">[-0, +0, &ndash;]</span>
3564 <pre>int lua_islightuserdata (lua_State *L, int index);</pre>
3565
3566 <p>
3567 Returns 1 if the value at the given index is a light userdata,
3568 and 0&nbsp;otherwise.
3569
3570
3571
3572
3573
3574 <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p>
3575 <span class="apii">[-0, +0, &ndash;]</span>
3576 <pre>int lua_isnil (lua_State *L, int index);</pre>
3577
3578 <p>
3579 Returns 1 if the value at the given index is <b>nil</b>,
3580 and 0&nbsp;otherwise.
3581
3582
3583
3584
3585
3586 <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p>
3587 <span class="apii">[-0, +0, &ndash;]</span>
3588 <pre>int lua_isnone (lua_State *L, int index);</pre>
3589
3590 <p>
3591 Returns 1 if the given index is not valid,
3592 and 0&nbsp;otherwise.
3593
3594
3595
3596
3597
3598 <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p>
3599 <span class="apii">[-0, +0, &ndash;]</span>
3600 <pre>int lua_isnoneornil (lua_State *L, int index);</pre>
3601
3602 <p>
3603 Returns 1 if the given index is not valid
3604 or if the value at this index is <b>nil</b>,
3605 and 0&nbsp;otherwise.
3606
3607
3608
3609
3610
3611 <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p>
3612 <span class="apii">[-0, +0, &ndash;]</span>
3613 <pre>int lua_isnumber (lua_State *L, int index);</pre>
3614
3615 <p>
3616 Returns 1 if the value at the given index is a number
3617 or a string convertible to a number,
3618 and 0&nbsp;otherwise.
3619
3620
3621
3622
3623
3624 <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p>
3625 <span class="apii">[-0, +0, &ndash;]</span>
3626 <pre>int lua_isstring (lua_State *L, int index);</pre>
3627
3628 <p>
3629 Returns 1 if the value at the given index is a string
3630 or a number (which is always convertible to a string),
3631 and 0&nbsp;otherwise.
3632
3633
3634
3635
3636
3637 <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p>
3638 <span class="apii">[-0, +0, &ndash;]</span>
3639 <pre>int lua_istable (lua_State *L, int index);</pre>
3640
3641 <p>
3642 Returns 1 if the value at the given index is a table,
3643 and 0&nbsp;otherwise.
3644
3645
3646
3647
3648
3649 <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p>
3650 <span class="apii">[-0, +0, &ndash;]</span>
3651 <pre>int lua_isthread (lua_State *L, int index);</pre>
3652
3653 <p>
3654 Returns 1 if the value at the given index is a thread,
3655 and 0&nbsp;otherwise.
3656
3657
3658
3659
3660
3661 <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p>
3662 <span class="apii">[-0, +0, &ndash;]</span>
3663 <pre>int lua_isuserdata (lua_State *L, int index);</pre>
3664
3665 <p>
3666 Returns 1 if the value at the given index is a userdata
3667 (either full or light), and 0&nbsp;otherwise.
3668
3669
3670
3671
3672
3673 <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p>
3674 <span class="apii">[-0, +1, <em>e</em>]</span>
3675 <pre>void lua_len (lua_State *L, int index);</pre>
3676
3677 <p>
3678 Returns the "length" of the value at the given index;
3679 it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">&sect;3.4.6</a>).
3680 The result is pushed on the stack.
3681
3682
3683
3684
3685
3686 <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p>
3687 <span class="apii">[-0, +1, &ndash;]</span>
3688 <pre>int lua_load (lua_State *L,
3689               lua_Reader reader,
3690               void *data,
3691               const char *source,
3692               const char *mode);</pre>
3693
3694 <p>
3695 Loads a Lua chunk (without running it).
3696 If there are no errors,
3697 <code>lua_load</code> pushes the compiled chunk as a Lua
3698 function on top of the stack.
3699 Otherwise, it pushes an error message.
3700
3701
3702 <p>
3703 The return values of <code>lua_load</code> are:
3704
3705 <ul>
3706
3707 <li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li>
3708
3709 <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b>
3710 syntax error during precompilation;</li>
3711
3712 <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
3713 memory allocation error;</li>
3714
3715 <li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
3716 error while running a <code>__gc</code> metamethod.
3717 (This error has no relation with the chunk being loaded.
3718 It is generated by the garbage collector.)
3719 </li>
3720
3721 </ul>
3722
3723 <p>
3724 The <code>lua_load</code> function uses a user-supplied <code>reader</code> function
3725 to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>).
3726 The <code>data</code> argument is an opaque value passed to the reader function.
3727
3728
3729 <p>
3730 The <code>source</code> argument gives a name to the chunk,
3731 which is used for error messages and in debug information (see <a href="#4.9">&sect;4.9</a>).
3732
3733
3734 <p>
3735 <code>lua_load</code> automatically detects whether the chunk is text or binary
3736 and loads it accordingly (see program <code>luac</code>).
3737 The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>,
3738 with the addition that
3739 a <code>NULL</code> value is equivalent to the string "<code>bt</code>".
3740
3741
3742 <p>
3743 <code>lua_load</code> uses the stack internally,
3744 so the reader function should always leave the stack
3745 unmodified when returning.
3746
3747
3748 <p>
3749 If the resulting function has one upvalue,
3750 this upvalue is set to the value of the global environment
3751 stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">&sect;4.5</a>).
3752 When loading main chunks,
3753 this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">&sect;2.2</a>).
3754
3755
3756
3757
3758
3759 <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p>
3760 <span class="apii">[-0, +0, &ndash;]</span>
3761 <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre>
3762
3763 <p>
3764 Creates a new thread running in a new, independent state.
3765 Returns <code>NULL</code> if cannot create the thread or the state
3766 (due to lack of memory).
3767 The argument <code>f</code> is the allocator function;
3768 Lua does all memory allocation for this state through this function.
3769 The second argument, <code>ud</code>, is an opaque pointer that Lua
3770 passes to the allocator in every call.
3771
3772
3773
3774
3775
3776 <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p>
3777 <span class="apii">[-0, +1, <em>e</em>]</span>
3778 <pre>void lua_newtable (lua_State *L);</pre>
3779
3780 <p>
3781 Creates a new empty table and pushes it onto the stack.
3782 It is equivalent to <code>lua_createtable(L, 0, 0)</code>.
3783
3784
3785
3786
3787
3788 <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p>
3789 <span class="apii">[-0, +1, <em>e</em>]</span>
3790 <pre>lua_State *lua_newthread (lua_State *L);</pre>
3791
3792 <p>
3793 Creates a new thread, pushes it on the stack,
3794 and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
3795 The new thread returned by this function shares with the original thread
3796 its global environment,
3797 but has an independent execution stack.
3798
3799
3800 <p>
3801 There is no explicit function to close or to destroy a thread.
3802 Threads are subject to garbage collection,
3803 like any Lua object.
3804
3805
3806
3807
3808
3809 <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p>
3810 <span class="apii">[-0, +1, <em>e</em>]</span>
3811 <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre>
3812
3813 <p>
3814 This function allocates a new block of memory with the given size,
3815 pushes onto the stack a new full userdata with the block address,
3816 and returns this address.
3817 The host program can freely use this memory.
3818
3819
3820
3821
3822
3823 <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p>
3824 <span class="apii">[-1, +(2|0), <em>e</em>]</span>
3825 <pre>int lua_next (lua_State *L, int index);</pre>
3826
3827 <p>
3828 Pops a key from the stack,
3829 and pushes a key&ndash;value pair from the table at the given index
3830 (the "next" pair after the given key).
3831 If there are no more elements in the table,
3832 then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing).
3833
3834
3835 <p>
3836 A typical traversal looks like this:
3837
3838 <pre>
3839      /* table is in the stack at index 't' */
3840      lua_pushnil(L);  /* first key */
3841      while (lua_next(L, t) != 0) {
3842        /* uses 'key' (at index -2) and 'value' (at index -1) */
3843        printf("%s - %s\n",
3844               lua_typename(L, lua_type(L, -2)),
3845               lua_typename(L, lua_type(L, -1)));
3846        /* removes 'value'; keeps 'key' for next iteration */
3847        lua_pop(L, 1);
3848      }
3849 </pre>
3850
3851 <p>
3852 While traversing a table,
3853 do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key,
3854 unless you know that the key is actually a string.
3855 Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change
3856 the value at the given index;
3857 this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>.
3858
3859
3860 <p>
3861 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
3862 the table during its traversal.
3863
3864
3865
3866
3867
3868 <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3>
3869 <pre>typedef double lua_Number;</pre>
3870
3871 <p>
3872 The type of numbers in Lua.
3873 By default, it is double, but that can be changed in <code>luaconf.h</code>.
3874 Through this configuration file you can change
3875 Lua to operate with another type for numbers (e.g., float or long).
3876
3877
3878
3879
3880
3881 <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p>
3882 <span class="apii">[-(nargs + 1), +(nresults|1), &ndash;]</span>
3883 <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre>
3884
3885 <p>
3886 Calls a function in protected mode.
3887
3888
3889 <p>
3890 Both <code>nargs</code> and <code>nresults</code> have the same meaning as
3891 in <a href="#lua_call"><code>lua_call</code></a>.
3892 If there are no errors during the call,
3893 <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
3894 However, if there is any error,
3895 <a href="#lua_pcall"><code>lua_pcall</code></a> catches it,
3896 pushes a single value on the stack (the error message),
3897 and returns an error code.
3898 Like <a href="#lua_call"><code>lua_call</code></a>,
3899 <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function
3900 and its arguments from the stack.
3901
3902
3903 <p>
3904 If <code>msgh</code> is 0,
3905 then the error message returned on the stack
3906 is exactly the original error message.
3907 Otherwise, <code>msgh</code> is the stack index of a
3908 <em>message handler</em>.
3909 (In the current implementation, this index cannot be a pseudo-index.)
3910 In case of runtime errors,
3911 this function will be called with the error message
3912 and its return value will be the message
3913 returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
3914
3915
3916 <p>
3917 Typically, the message handler is used to add more debug
3918 information to the error message, such as a stack traceback.
3919 Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
3920 since by then the stack has unwound.
3921
3922
3923 <p>
3924 The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following codes
3925 (defined in <code>lua.h</code>):
3926
3927 <ul>
3928
3929 <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b>
3930 success.</li>
3931
3932 <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b>
3933 a runtime error.
3934 </li>
3935
3936 <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b>
3937 memory allocation error.
3938 For such errors, Lua does not call the message handler.
3939 </li>
3940
3941 <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b>
3942 error while running the message handler.
3943 </li>
3944
3945 <li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b>
3946 error while running a <code>__gc</code> metamethod.
3947 (This error typically has no relation with the function being called.
3948 It is generated by the garbage collector.)
3949 </li>
3950
3951 </ul>
3952
3953
3954
3955
3956 <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p>
3957 <span class="apii">[-(nargs + 1), +(nresults|1), &ndash;]</span>
3958 <pre>int lua_pcallk (lua_State *L,
3959                 int nargs,
3960                 int nresults,
3961                 int errfunc,
3962                 int ctx,
3963                 lua_CFunction k);</pre>
3964
3965 <p>
3966 This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>,
3967 but allows the called function to yield (see <a href="#4.7">&sect;4.7</a>).
3968
3969
3970
3971
3972
3973 <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p>
3974 <span class="apii">[-n, +0, &ndash;]</span>
3975 <pre>void lua_pop (lua_State *L, int n);</pre>
3976
3977 <p>
3978 Pops <code>n</code> elements from the stack.
3979
3980
3981
3982
3983
3984 <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p>
3985 <span class="apii">[-0, +1, &ndash;]</span>
3986 <pre>void lua_pushboolean (lua_State *L, int b);</pre>
3987
3988 <p>
3989 Pushes a boolean value with value <code>b</code> onto the stack.
3990
3991
3992
3993
3994
3995 <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p>
3996 <span class="apii">[-n, +1, <em>e</em>]</span>
3997 <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre>
3998
3999 <p>
4000 Pushes a new C&nbsp;closure onto the stack.
4001
4002
4003 <p>
4004 When a C&nbsp;function is created,
4005 it is possible to associate some values with it,
4006 thus creating a C&nbsp;closure (see <a href="#4.4">&sect;4.4</a>);
4007 these values are then accessible to the function whenever it is called.
4008 To associate values with a C&nbsp;function,
4009 first these values should be pushed onto the stack
4010 (when there are multiple values, the first value is pushed first).
4011 Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>
4012 is called to create and push the C&nbsp;function onto the stack,
4013 with the argument <code>n</code> telling how many values should be
4014 associated with the function.
4015 <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
4016
4017
4018 <p>
4019 The maximum value for <code>n</code> is 255.
4020
4021
4022 <p>
4023 When <code>n</code> is zero,
4024 this function creates a <em>light C function</em>,
4025 which is just a pointer to the C&nbsp;function.
4026 In that case, it never throws a memory error.
4027
4028
4029
4030
4031
4032 <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p>
4033 <span class="apii">[-0, +1, &ndash;]</span>
4034 <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre>
4035
4036 <p>
4037 Pushes a C&nbsp;function onto the stack.
4038 This function receives a pointer to a C function
4039 and pushes onto the stack a Lua value of type <code>function</code> that,
4040 when called, invokes the corresponding C&nbsp;function.
4041
4042
4043 <p>
4044 Any function to be registered in Lua must
4045 follow the correct protocol to receive its parameters
4046 and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
4047
4048
4049 <p>
4050 <code>lua_pushcfunction</code> is defined as a macro:
4051
4052 <pre>
4053      #define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)
4054 </pre><p>
4055 Note that <code>f</code> is used twice.
4056
4057
4058
4059
4060
4061 <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p>
4062 <span class="apii">[-0, +1, <em>e</em>]</span>
4063 <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre>
4064
4065 <p>
4066 Pushes onto the stack a formatted string
4067 and returns a pointer to this string.
4068 It is similar to the ANSI&nbsp;C function <code>sprintf</code>,
4069 but has some important differences:
4070
4071 <ul>
4072
4073 <li>
4074 You do not have to allocate space for the result:
4075 the result is a Lua string and Lua takes care of memory allocation
4076 (and deallocation, through garbage collection).
4077 </li>
4078
4079 <li>
4080 The conversion specifiers are quite restricted.
4081 There are no flags, widths, or precisions.
4082 The conversion specifiers can only be
4083 '<code>%%</code>' (inserts a '<code>%</code>' in the string),
4084 '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions),
4085 '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>),
4086 '<code>%p</code>' (inserts a pointer as a hexadecimal numeral),
4087 '<code>%d</code>' (inserts an <code>int</code>), and
4088 '<code>%c</code>' (inserts an <code>int</code> as a byte).
4089 </li>
4090
4091 </ul>
4092
4093
4094
4095
4096 <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p>
4097 <span class="apii">[-0, +1, &ndash;]</span>
4098 <pre>void lua_pushglobaltable (lua_State *L);</pre>
4099
4100 <p>
4101 Pushes the global environment onto the stack.
4102
4103
4104
4105
4106
4107 <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p>
4108 <span class="apii">[-0, +1, &ndash;]</span>
4109 <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre>
4110
4111 <p>
4112 Pushes a number with value <code>n</code> onto the stack.
4113
4114
4115
4116
4117
4118 <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p>
4119 <span class="apii">[-0, +1, &ndash;]</span>
4120 <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre>
4121
4122 <p>
4123 Pushes a light userdata onto the stack.
4124
4125
4126 <p>
4127 Userdata represent C&nbsp;values in Lua.
4128 A <em>light userdata</em> represents a pointer, a <code>void*</code>.
4129 It is a value (like a number):
4130 you do not create it, it has no individual metatable,
4131 and it is not collected (as it was never created).
4132 A light userdata is equal to "any"
4133 light userdata with the same C&nbsp;address.
4134
4135
4136
4137
4138
4139 <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p>
4140 <span class="apii">[-0, +1, <em>e</em>]</span>
4141 <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre>
4142
4143 <p>
4144 This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>,
4145 but can be used only when <code>s</code> is a literal string.
4146 It automatically provides the string length.
4147
4148
4149
4150
4151
4152 <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p>
4153 <span class="apii">[-0, +1, <em>e</em>]</span>
4154 <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre>
4155
4156 <p>
4157 Pushes the string pointed to by <code>s</code> with size <code>len</code>
4158 onto the stack.
4159 Lua makes (or reuses) an internal copy of the given string,
4160 so the memory at <code>s</code> can be freed or reused immediately after
4161 the function returns.
4162 The string can contain any binary data,
4163 including embedded zeros.
4164
4165
4166 <p>
4167 Returns a pointer to the internal copy of the string.
4168
4169
4170
4171
4172
4173 <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p>
4174 <span class="apii">[-0, +1, &ndash;]</span>
4175 <pre>void lua_pushnil (lua_State *L);</pre>
4176
4177 <p>
4178 Pushes a nil value onto the stack.
4179
4180
4181
4182
4183
4184 <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p>
4185 <span class="apii">[-0, +1, &ndash;]</span>
4186 <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre>
4187
4188 <p>
4189 Pushes a number with value <code>n</code> onto the stack.
4190
4191
4192
4193
4194
4195 <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p>
4196 <span class="apii">[-0, +1, <em>e</em>]</span>
4197 <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre>
4198
4199 <p>
4200 Pushes the zero-terminated string pointed to by <code>s</code>
4201 onto the stack.
4202 Lua makes (or reuses) an internal copy of the given string,
4203 so the memory at <code>s</code> can be freed or reused immediately after
4204 the function returns.
4205
4206
4207 <p>
4208 Returns a pointer to the internal copy of the string.
4209
4210
4211 <p>
4212 If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>.
4213
4214
4215
4216
4217
4218 <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p>
4219 <span class="apii">[-0, +1, &ndash;]</span>
4220 <pre>int lua_pushthread (lua_State *L);</pre>
4221
4222 <p>
4223 Pushes the thread represented by <code>L</code> onto the stack.
4224 Returns 1 if this thread is the main thread of its state.
4225
4226
4227
4228
4229
4230 <hr><h3><a name="lua_pushunsigned"><code>lua_pushunsigned</code></a></h3><p>
4231 <span class="apii">[-0, +1, &ndash;]</span>
4232 <pre>void lua_pushunsigned (lua_State *L, lua_Unsigned n);</pre>
4233
4234 <p>
4235 Pushes a number with value <code>n</code> onto the stack.
4236
4237
4238
4239
4240
4241 <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p>
4242 <span class="apii">[-0, +1, &ndash;]</span>
4243 <pre>void lua_pushvalue (lua_State *L, int index);</pre>
4244
4245 <p>
4246 Pushes a copy of the element at the given index
4247 onto the stack.
4248
4249
4250
4251
4252
4253 <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p>
4254 <span class="apii">[-0, +1, <em>e</em>]</span>
4255 <pre>const char *lua_pushvfstring (lua_State *L,
4256                               const char *fmt,
4257                               va_list argp);</pre>
4258
4259 <p>
4260 Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
4261 instead of a variable number of arguments.
4262
4263
4264
4265
4266
4267 <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p>
4268 <span class="apii">[-0, +0, &ndash;]</span>
4269 <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre>
4270
4271 <p>
4272 Returns 1 if the two values in indices <code>index1</code> and
4273 <code>index2</code> are primitively equal
4274 (that is, without calling metamethods).
4275 Otherwise returns&nbsp;0.
4276 Also returns&nbsp;0 if any of the indices are non valid.
4277
4278
4279
4280
4281
4282 <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p>
4283 <span class="apii">[-1, +1, &ndash;]</span>
4284 <pre>void lua_rawget (lua_State *L, int index);</pre>
4285
4286 <p>
4287 Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access
4288 (i.e., without metamethods).
4289
4290
4291
4292
4293
4294 <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p>
4295 <span class="apii">[-0, +1, &ndash;]</span>
4296 <pre>void lua_rawgeti (lua_State *L, int index, int n);</pre>
4297
4298 <p>
4299 Pushes onto the stack the value <code>t[n]</code>,
4300 where <code>t</code> is the table at the given index.
4301 The access is raw;
4302 that is, it does not invoke metamethods.
4303
4304
4305
4306
4307
4308 <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p>
4309 <span class="apii">[-0, +1, &ndash;]</span>
4310 <pre>void lua_rawgetp (lua_State *L, int index, const void *p);</pre>
4311
4312 <p>
4313 Pushes onto the stack the value <code>t[k]</code>,
4314 where <code>t</code> is the table at the given index and
4315 <code>k</code> is the pointer <code>p</code> represented as a light userdata.
4316 The access is raw;
4317 that is, it does not invoke metamethods.
4318
4319
4320
4321
4322
4323 <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p>
4324 <span class="apii">[-0, +0, &ndash;]</span>
4325 <pre>size_t lua_rawlen (lua_State *L, int index);</pre>
4326
4327 <p>
4328 Returns the raw "length" of the value at the given index:
4329 for strings, this is the string length;
4330 for tables, this is the result of the length operator ('<code>#</code>')
4331 with no metamethods;
4332 for userdata, this is the size of the block of memory allocated
4333 for the userdata;
4334 for other values, it is&nbsp;0.
4335
4336
4337
4338
4339
4340 <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p>
4341 <span class="apii">[-2, +0, <em>e</em>]</span>
4342 <pre>void lua_rawset (lua_State *L, int index);</pre>
4343
4344 <p>
4345 Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment
4346 (i.e., without metamethods).
4347
4348
4349
4350
4351
4352 <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p>
4353 <span class="apii">[-1, +0, <em>e</em>]</span>
4354 <pre>void lua_rawseti (lua_State *L, int index, int n);</pre>
4355
4356 <p>
4357 Does the equivalent of <code>t[n] = v</code>,
4358 where <code>t</code> is the table at the given index
4359 and <code>v</code> is the value at the top of the stack.
4360
4361
4362 <p>
4363 This function pops the value from the stack.
4364 The assignment is raw;
4365 that is, it does not invoke metamethods.
4366
4367
4368
4369
4370
4371 <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p>
4372 <span class="apii">[-1, +0, <em>e</em>]</span>
4373 <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre>
4374
4375 <p>
4376 Does the equivalent of <code>t[k] = v</code>,
4377 where <code>t</code> is the table at the given index,
4378 <code>k</code> is the pointer <code>p</code> represented as a light userdata,
4379 and <code>v</code> is the value at the top of the stack.
4380
4381
4382 <p>
4383 This function pops the value from the stack.
4384 The assignment is raw;
4385 that is, it does not invoke metamethods.
4386
4387
4388
4389
4390
4391 <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3>
4392 <pre>typedef const char * (*lua_Reader) (lua_State *L,
4393                                     void *data,
4394                                     size_t *size);</pre>
4395
4396 <p>
4397 The reader function used by <a href="#lua_load"><code>lua_load</code></a>.
4398 Every time it needs another piece of the chunk,
4399 <a href="#lua_load"><code>lua_load</code></a> calls the reader,
4400 passing along its <code>data</code> parameter.
4401 The reader must return a pointer to a block of memory
4402 with a new piece of the chunk
4403 and set <code>size</code> to the block size.
4404 The block must exist until the reader function is called again.
4405 To signal the end of the chunk,
4406 the reader must return <code>NULL</code> or set <code>size</code> to zero.
4407 The reader function may return pieces of any size greater than zero.
4408
4409
4410
4411
4412
4413 <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p>
4414 <span class="apii">[-0, +0, <em>e</em>]</span>
4415 <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre>
4416
4417 <p>
4418 Sets the C function <code>f</code> as the new value of global <code>name</code>.
4419 It is defined as a macro:
4420
4421 <pre>
4422      #define lua_register(L,n,f) \
4423             (lua_pushcfunction(L, f), lua_setglobal(L, n))
4424 </pre>
4425
4426
4427
4428
4429 <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p>
4430 <span class="apii">[-1, +0, &ndash;]</span>
4431 <pre>void lua_remove (lua_State *L, int index);</pre>
4432
4433 <p>
4434 Removes the element at the given valid index,
4435 shifting down the elements above this index to fill the gap.
4436 This function cannot be called with a pseudo-index,
4437 because a pseudo-index is not an actual stack position.
4438
4439
4440
4441
4442
4443 <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p>
4444 <span class="apii">[-1, +0, &ndash;]</span>
4445 <pre>void lua_replace (lua_State *L, int index);</pre>
4446
4447 <p>
4448 Moves the top element into the given valid index
4449 without shifting any element
4450 (therefore replacing the value at the given index),
4451 and then pops the top element.
4452
4453
4454
4455
4456
4457 <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p>
4458 <span class="apii">[-?, +?, &ndash;]</span>
4459 <pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre>
4460
4461 <p>
4462 Starts and resumes a coroutine in a given thread.
4463
4464
4465 <p>
4466 To start a coroutine,
4467 you push onto the thread stack the main function plus any arguments;
4468 then you call <a href="#lua_resume"><code>lua_resume</code></a>,
4469 with <code>nargs</code> being the number of arguments.
4470 This call returns when the coroutine suspends or finishes its execution.
4471 When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
4472 or all values returned by the body function.
4473 <a href="#lua_resume"><code>lua_resume</code></a> returns
4474 <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields,
4475 <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution
4476 without errors,
4477 or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>).
4478
4479
4480 <p>
4481 In case of errors,
4482 the stack is not unwound,
4483 so you can use the debug API over it.
4484 The error message is on the top of the stack.
4485
4486
4487 <p>
4488 To resume a coroutine,
4489 you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>,
4490 put on its stack only the values to
4491 be passed as results from <code>yield</code>,
4492 and then call <a href="#lua_resume"><code>lua_resume</code></a>.
4493
4494
4495 <p>
4496 The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>.
4497 If there is no such coroutine,
4498 this parameter can be <code>NULL</code>.
4499
4500
4501
4502
4503
4504 <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p>
4505 <span class="apii">[-0, +0, &ndash;]</span>
4506 <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre>
4507
4508 <p>
4509 Changes the allocator function of a given state to <code>f</code>
4510 with user data <code>ud</code>.
4511
4512
4513
4514
4515
4516 <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p>
4517 <span class="apii">[-1, +0, <em>e</em>]</span>
4518 <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre>
4519
4520 <p>
4521 Does the equivalent to <code>t[k] = v</code>,
4522 where <code>t</code> is the value at the given index
4523 and <code>v</code> is the value at the top of the stack.
4524
4525
4526 <p>
4527 This function pops the value from the stack.
4528 As in Lua, this function may trigger a metamethod
4529 for the "newindex" event (see <a href="#2.4">&sect;2.4</a>).
4530
4531
4532
4533
4534
4535 <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p>
4536 <span class="apii">[-1, +0, <em>e</em>]</span>
4537 <pre>void lua_setglobal (lua_State *L, const char *name);</pre>
4538
4539 <p>
4540 Pops a value from the stack and
4541 sets it as the new value of global <code>name</code>.
4542
4543
4544
4545
4546
4547 <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p>
4548 <span class="apii">[-1, +0, &ndash;]</span>
4549 <pre>void lua_setmetatable (lua_State *L, int index);</pre>
4550
4551 <p>
4552 Pops a table from the stack and
4553 sets it as the new metatable for the value at the given index.
4554
4555
4556
4557
4558
4559 <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p>
4560 <span class="apii">[-2, +0, <em>e</em>]</span>
4561 <pre>void lua_settable (lua_State *L, int index);</pre>
4562
4563 <p>
4564 Does the equivalent to <code>t[k] = v</code>,
4565 where <code>t</code> is the value at the given index,
4566 <code>v</code> is the value at the top of the stack,
4567 and <code>k</code> is the value just below the top.
4568
4569
4570 <p>
4571 This function pops both the key and the value from the stack.
4572 As in Lua, this function may trigger a metamethod
4573 for the "newindex" event (see <a href="#2.4">&sect;2.4</a>).
4574
4575
4576
4577
4578
4579 <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p>
4580 <span class="apii">[-?, +?, &ndash;]</span>
4581 <pre>void lua_settop (lua_State *L, int index);</pre>
4582
4583 <p>
4584 Accepts any index, or&nbsp;0,
4585 and sets the stack top to this index.
4586 If the new top is larger than the old one,
4587 then the new elements are filled with <b>nil</b>.
4588 If <code>index</code> is&nbsp;0, then all stack elements are removed.
4589
4590
4591
4592
4593
4594 <hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p>
4595 <span class="apii">[-1, +0, &ndash;]</span>
4596 <pre>void lua_setuservalue (lua_State *L, int index);</pre>
4597
4598 <p>
4599 Pops a table or <b>nil</b> from the stack and sets it as
4600 the new value associated to the userdata at the given index.
4601
4602
4603
4604
4605
4606 <hr><h3><a name="lua_State"><code>lua_State</code></a></h3>
4607 <pre>typedef struct lua_State lua_State;</pre>
4608
4609 <p>
4610 An opaque structure that points to a thread and indirectly
4611 (through the thread) to the whole state of a Lua interpreter.
4612 The Lua library is fully reentrant:
4613 it has no global variables.
4614 All information about a state is accessible through this structure.
4615
4616
4617 <p>
4618 A pointer to this structure must be passed as the first argument to
4619 every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
4620 which creates a Lua state from scratch.
4621
4622
4623
4624
4625
4626 <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p>
4627 <span class="apii">[-0, +0, &ndash;]</span>
4628 <pre>int lua_status (lua_State *L);</pre>
4629
4630 <p>
4631 Returns the status of the thread <code>L</code>.
4632
4633
4634 <p>
4635 The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread,
4636 an error code if the thread finished the execution
4637 of a <a href="#lua_resume"><code>lua_resume</code></a> with an error,
4638 or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended.
4639
4640
4641 <p>
4642 You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>.
4643 You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>
4644 (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a>
4645 (to resume a coroutine).
4646
4647
4648
4649
4650
4651 <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p>
4652 <span class="apii">[-0, +0, &ndash;]</span>
4653 <pre>int lua_toboolean (lua_State *L, int index);</pre>
4654
4655 <p>
4656 Converts the Lua value at the given index to a C&nbsp;boolean
4657 value (0&nbsp;or&nbsp;1).
4658 Like all tests in Lua,
4659 <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value
4660 different from <b>false</b> and <b>nil</b>;
4661 otherwise it returns false.
4662 (If you want to accept only actual boolean values,
4663 use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.)
4664
4665
4666
4667
4668
4669 <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p>
4670 <span class="apii">[-0, +0, &ndash;]</span>
4671 <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre>
4672
4673 <p>
4674 Converts a value at the given index to a C&nbsp;function.
4675 That value must be a C&nbsp;function;
4676 otherwise, returns <code>NULL</code>.
4677
4678
4679
4680
4681
4682 <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p>
4683 <span class="apii">[-0, +0, &ndash;]</span>
4684 <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre>
4685
4686 <p>
4687 Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4688
4689
4690
4691
4692
4693 <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p>
4694 <span class="apii">[-0, +0, &ndash;]</span>
4695 <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre>
4696
4697 <p>
4698 Converts the Lua value at the given index
4699 to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>.
4700 The Lua value must be a number or a string convertible to a number
4701 (see <a href="#3.4.2">&sect;3.4.2</a>);
4702 otherwise, <code>lua_tointegerx</code> returns&nbsp;0.
4703
4704
4705 <p>
4706 If the number is not an integer,
4707 it is truncated in some non-specified way.
4708
4709
4710 <p>
4711 If <code>isnum</code> is not <code>NULL</code>,
4712 its referent is assigned a boolean value that
4713 indicates whether the operation succeeded.
4714
4715
4716
4717
4718
4719 <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p>
4720 <span class="apii">[-0, +0, <em>e</em>]</span>
4721 <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre>
4722
4723 <p>
4724 Converts the Lua value at the given index to a C&nbsp;string.
4725 If <code>len</code> is not <code>NULL</code>,
4726 it also sets <code>*len</code> with the string length.
4727 The Lua value must be a string or a number;
4728 otherwise, the function returns <code>NULL</code>.
4729 If the value is a number,
4730 then <code>lua_tolstring</code> also
4731 <em>changes the actual value in the stack to a string</em>.
4732 (This change confuses <a href="#lua_next"><code>lua_next</code></a>
4733 when <code>lua_tolstring</code> is applied to keys during a table traversal.)
4734
4735
4736 <p>
4737 <code>lua_tolstring</code> returns a fully aligned pointer
4738 to a string inside the Lua state.
4739 This string always has a zero ('<code>\0</code>')
4740 after its last character (as in&nbsp;C),
4741 but can contain other zeros in its body.
4742 Because Lua has garbage collection,
4743 there is no guarantee that the pointer returned by <code>lua_tolstring</code>
4744 will be valid after the corresponding value is removed from the stack.
4745
4746
4747
4748
4749
4750 <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p>
4751 <span class="apii">[-0, +0, &ndash;]</span>
4752 <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre>
4753
4754 <p>
4755 Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4756
4757
4758
4759
4760
4761 <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p>
4762 <span class="apii">[-0, +0, &ndash;]</span>
4763 <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre>
4764
4765 <p>
4766 Converts the Lua value at the given index
4767 to the C&nbsp;type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
4768 The Lua value must be a number or a string convertible to a number
4769 (see <a href="#3.4.2">&sect;3.4.2</a>);
4770 otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns&nbsp;0.
4771
4772
4773 <p>
4774 If <code>isnum</code> is not <code>NULL</code>,
4775 its referent is assigned a boolean value that
4776 indicates whether the operation succeeded.
4777
4778
4779
4780
4781
4782 <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p>
4783 <span class="apii">[-0, +0, &ndash;]</span>
4784 <pre>const void *lua_topointer (lua_State *L, int index);</pre>
4785
4786 <p>
4787 Converts the value at the given index to a generic
4788 C&nbsp;pointer (<code>void*</code>).
4789 The value can be a userdata, a table, a thread, or a function;
4790 otherwise, <code>lua_topointer</code> returns <code>NULL</code>.
4791 Different objects will give different pointers.
4792 There is no way to convert the pointer back to its original value.
4793
4794
4795 <p>
4796 Typically this function is used only for debug information.
4797
4798
4799
4800
4801
4802 <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p>
4803 <span class="apii">[-0, +0, <em>e</em>]</span>
4804 <pre>const char *lua_tostring (lua_State *L, int index);</pre>
4805
4806 <p>
4807 Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
4808
4809
4810
4811
4812
4813 <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p>
4814 <span class="apii">[-0, +0, &ndash;]</span>
4815 <pre>lua_State *lua_tothread (lua_State *L, int index);</pre>
4816
4817 <p>
4818 Converts the value at the given index to a Lua thread
4819 (represented as <code>lua_State*</code>).
4820 This value must be a thread;
4821 otherwise, the function returns <code>NULL</code>.
4822
4823
4824
4825
4826
4827 <hr><h3><a name="lua_tounsigned"><code>lua_tounsigned</code></a></h3><p>
4828 <span class="apii">[-0, +0, &ndash;]</span>
4829 <pre>lua_Unsigned lua_tounsigned (lua_State *L, int index);</pre>
4830
4831 <p>
4832 Equivalent to <a href="#lua_tounsignedx"><code>lua_tounsignedx</code></a> with <code>isnum</code> equal to <code>NULL</code>.
4833
4834
4835
4836
4837
4838 <hr><h3><a name="lua_tounsignedx"><code>lua_tounsignedx</code></a></h3><p>
4839 <span class="apii">[-0, +0, &ndash;]</span>
4840 <pre>lua_Unsigned lua_tounsignedx (lua_State *L, int index, int *isnum);</pre>
4841
4842 <p>
4843 Converts the Lua value at the given index
4844 to the unsigned integral type <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
4845 The Lua value must be a number or a string convertible to a number
4846 (see <a href="#3.4.2">&sect;3.4.2</a>);
4847 otherwise, <code>lua_tounsignedx</code> returns&nbsp;0.
4848
4849
4850 <p>
4851 If the number is not an integer,
4852 it is truncated in some non-specified way.
4853 If the number is outside the range of representable values,
4854 it is normalized to the remainder of its division by
4855 one more than the maximum representable value.
4856
4857
4858 <p>
4859 If <code>isnum</code> is not <code>NULL</code>,
4860 its referent is assigned a boolean value that
4861 indicates whether the operation succeeded.
4862
4863
4864
4865
4866
4867 <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p>
4868 <span class="apii">[-0, +0, &ndash;]</span>
4869 <pre>void *lua_touserdata (lua_State *L, int index);</pre>
4870
4871 <p>
4872 If the value at the given index is a full userdata,
4873 returns its block address.
4874 If the value is a light userdata,
4875 returns its pointer.
4876 Otherwise, returns <code>NULL</code>.
4877
4878
4879
4880
4881
4882 <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p>
4883 <span class="apii">[-0, +0, &ndash;]</span>
4884 <pre>int lua_type (lua_State *L, int index);</pre>
4885
4886 <p>
4887 Returns the type of the value in the given valid index,
4888 or <code>LUA_TNONE</code> for a non-valid (but acceptable) index.
4889 The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
4890 defined in <code>lua.h</code>:
4891 <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>,
4892 <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>,
4893 <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>,
4894 <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>,
4895 <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>,
4896 <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>,
4897 <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>,
4898 <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>,
4899 and
4900 <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>.
4901
4902
4903
4904
4905
4906 <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p>
4907 <span class="apii">[-0, +0, &ndash;]</span>
4908 <pre>const char *lua_typename (lua_State *L, int tp);</pre>
4909
4910 <p>
4911 Returns the name of the type encoded by the value <code>tp</code>,
4912 which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>.
4913
4914
4915
4916
4917
4918 <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3>
4919 <pre>typedef unsigned long lua_Unsigned;</pre>
4920
4921 <p>
4922 The type used by the Lua API to represent unsigned integral values.
4923 It must have at least 32 bits.
4924
4925
4926 <p>
4927 By default it is an <code>unsigned int</code> or an <code>unsigned long</code>,
4928 whichever can hold 32-bit values.
4929
4930
4931
4932
4933
4934 <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p>
4935 <span class="apii">[-0, +0, &ndash;]</span>
4936 <pre>int lua_upvalueindex (int i);</pre>
4937
4938 <p>
4939 Returns the pseudo-index that represents the <code>i</code>-th upvalue of
4940 the running function (see <a href="#4.4">&sect;4.4</a>).
4941
4942
4943
4944
4945
4946 <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p>
4947 <span class="apii">[-0, +0, <em>v</em>]</span>
4948 <pre>const lua_Number *lua_version (lua_State *L);</pre>
4949
4950 <p>
4951 Returns the address of the version number stored in the Lua core.
4952 When called with a valid <a href="#lua_State"><code>lua_State</code></a>,
4953 returns the address of the version used to create that state.
4954 When called with <code>NULL</code>,
4955 returns the address of the version running the call.
4956
4957
4958
4959
4960
4961 <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3>
4962 <pre>typedef int (*lua_Writer) (lua_State *L,
4963                            const void* p,
4964                            size_t sz,
4965                            void* ud);</pre>
4966
4967 <p>
4968 The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>.
4969 Every time it produces another piece of chunk,
4970 <a href="#lua_dump"><code>lua_dump</code></a> calls the writer,
4971 passing along the buffer to be written (<code>p</code>),
4972 its size (<code>sz</code>),
4973 and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>.
4974
4975
4976 <p>
4977 The writer returns an error code:
4978 0&nbsp;means no errors;
4979 any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from
4980 calling the writer again.
4981
4982
4983
4984
4985
4986 <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p>
4987 <span class="apii">[-?, +?, &ndash;]</span>
4988 <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre>
4989
4990 <p>
4991 Exchange values between different threads of the same state.
4992
4993
4994 <p>
4995 This function pops <code>n</code> values from the stack <code>from</code>,
4996 and pushes them onto the stack <code>to</code>.
4997
4998
4999
5000
5001
5002 <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p>
5003 <span class="apii">[-?, +?, &ndash;]</span>
5004 <pre>int lua_yield (lua_State *L, int nresults);</pre>
5005
5006 <p>
5007 This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5008 but it has no continuation (see <a href="#4.7">&sect;4.7</a>).
5009 Therefore, when the thread resumes,
5010 it returns to the function that called
5011 the function calling <code>lua_yield</code>.
5012
5013
5014
5015
5016
5017 <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p>
5018 <span class="apii">[-?, +?, &ndash;]</span>
5019 <pre>int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k);</pre>
5020
5021 <p>
5022 Yields a coroutine.
5023
5024
5025 <p>
5026 This function should only be called as the
5027 return expression of a C&nbsp;function, as follows:
5028
5029 <pre>
5030      return lua_yieldk (L, n, i, k);
5031 </pre><p>
5032 When a C&nbsp;function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a> in that way,
5033 the running coroutine suspends its execution,
5034 and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
5035 The parameter <code>nresults</code> is the number of values from the stack
5036 that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>.
5037
5038
5039 <p>
5040 When the coroutine is resumed again,
5041 Lua calls the given continuation function <code>k</code> to continue
5042 the execution of the C function that yielded (see <a href="#4.7">&sect;4.7</a>).
5043 This continuation function receives the same stack
5044 from the previous function,
5045 with the results removed and
5046 replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>.
5047 Moreover,
5048 the continuation function may access the value <code>ctx</code>
5049 by calling <a href="#lua_getctx"><code>lua_getctx</code></a>.
5050
5051
5052
5053
5054
5055
5056
5057 <h2>4.9 &ndash; <a name="4.9">The Debug Interface</a></h2>
5058
5059 <p>
5060 Lua has no built-in debugging facilities.
5061 Instead, it offers a special interface
5062 by means of functions and <em>hooks</em>.
5063 This interface allows the construction of different
5064 kinds of debuggers, profilers, and other tools
5065 that need "inside information" from the interpreter.
5066
5067
5068
5069 <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3>
5070 <pre>typedef struct lua_Debug {
5071   int event;
5072   const char *name;           /* (n) */
5073   const char *namewhat;       /* (n) */
5074   const char *what;           /* (S) */
5075   const char *source;         /* (S) */
5076   int currentline;            /* (l) */
5077   int linedefined;            /* (S) */
5078   int lastlinedefined;        /* (S) */
5079   unsigned char nups;         /* (u) number of upvalues */
5080   unsigned char nparams;      /* (u) number of parameters */
5081   char isvararg;              /* (u) */
5082   char istailcall;            /* (t) */
5083   char short_src[LUA_IDSIZE]; /* (S) */
5084   /* private part */
5085   <em>other fields</em>
5086 } lua_Debug;</pre>
5087
5088 <p>
5089 A structure used to carry different pieces of
5090 information about a function or an activation record.
5091 <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part
5092 of this structure, for later use.
5093 To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
5094 call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5095
5096
5097 <p>
5098 The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning:
5099
5100 <ul>
5101
5102 <li><b><code>source</code>: </b>
5103 the source of the chunk that created the function.
5104 If <code>source</code> starts with a '<code>@</code>',
5105 it means that the function was defined in a file where
5106 the file name follows the '<code>@</code>'.
5107 If <code>source</code> starts with a '<code>=</code>',
5108 the remainder of its contents describe the source in a user-dependent manner.
5109 Otherwise,
5110 the function was defined in a string where
5111 <code>source</code> is that string.
5112 </li>
5113
5114 <li><b><code>short_src</code>: </b>
5115 a "printable" version of <code>source</code>, to be used in error messages.
5116 </li>
5117
5118 <li><b><code>linedefined</code>: </b>
5119 the line number where the definition of the function starts.
5120 </li>
5121
5122 <li><b><code>lastlinedefined</code>: </b>
5123 the line number where the definition of the function ends.
5124 </li>
5125
5126 <li><b><code>what</code>: </b>
5127 the string <code>"Lua"</code> if the function is a Lua function,
5128 <code>"C"</code> if it is a C&nbsp;function,
5129 <code>"main"</code> if it is the main part of a chunk.
5130 </li>
5131
5132 <li><b><code>currentline</code>: </b>
5133 the current line where the given function is executing.
5134 When no line information is available,
5135 <code>currentline</code> is set to -1.
5136 </li>
5137
5138 <li><b><code>name</code>: </b>
5139 a reasonable name for the given function.
5140 Because functions in Lua are first-class values,
5141 they do not have a fixed name:
5142 some functions can be the value of multiple global variables,
5143 while others can be stored only in a table field.
5144 The <code>lua_getinfo</code> function checks how the function was
5145 called to find a suitable name.
5146 If it cannot find a name,
5147 then <code>name</code> is set to <code>NULL</code>.
5148 </li>
5149
5150 <li><b><code>namewhat</code>: </b>
5151 explains the <code>name</code> field.
5152 The value of <code>namewhat</code> can be
5153 <code>"global"</code>, <code>"local"</code>, <code>"method"</code>,
5154 <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string),
5155 according to how the function was called.
5156 (Lua uses the empty string when no other option seems to apply.)
5157 </li>
5158
5159 <li><b><code>istailcall</code>: </b>
5160 true if this function invocation was called by a tail call.
5161 In this case, the caller of this level is not in the stack.
5162 </li>
5163
5164 <li><b><code>nups</code>: </b>
5165 the number of upvalues of the function.
5166 </li>
5167
5168 <li><b><code>nparams</code>: </b>
5169 the number of fixed parameters of the function
5170 (always 0&nbsp;for C&nbsp;functions).
5171 </li>
5172
5173 <li><b><code>isvararg</code>: </b>
5174 true if the function is a vararg function
5175 (always true for C&nbsp;functions).
5176 </li>
5177
5178 </ul>
5179
5180
5181
5182
5183 <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p>
5184 <span class="apii">[-0, +0, &ndash;]</span>
5185 <pre>lua_Hook lua_gethook (lua_State *L);</pre>
5186
5187 <p>
5188 Returns the current hook function.
5189
5190
5191
5192
5193
5194 <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p>
5195 <span class="apii">[-0, +0, &ndash;]</span>
5196 <pre>int lua_gethookcount (lua_State *L);</pre>
5197
5198 <p>
5199 Returns the current hook count.
5200
5201
5202
5203
5204
5205 <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p>
5206 <span class="apii">[-0, +0, &ndash;]</span>
5207 <pre>int lua_gethookmask (lua_State *L);</pre>
5208
5209 <p>
5210 Returns the current hook mask.
5211
5212
5213
5214
5215
5216 <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p>
5217 <span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span>
5218 <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre>
5219
5220 <p>
5221 Gets information about a specific function or function invocation.
5222
5223
5224 <p>
5225 To get information about a function invocation,
5226 the parameter <code>ar</code> must be a valid activation record that was
5227 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5228 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5229
5230
5231 <p>
5232 To get information about a function you push it onto the stack
5233 and start the <code>what</code> string with the character '<code>&gt;</code>'.
5234 (In that case,
5235 <code>lua_getinfo</code> pops the function from the top of the stack.)
5236 For instance, to know in which line a function <code>f</code> was defined,
5237 you can write the following code:
5238
5239 <pre>
5240      lua_Debug ar;
5241      lua_getglobal(L, "f");  /* get global 'f' */
5242      lua_getinfo(L, "&gt;S", &amp;ar);
5243      printf("%d\n", ar.linedefined);
5244 </pre>
5245
5246 <p>
5247 Each character in the string <code>what</code>
5248 selects some fields of the structure <code>ar</code> to be filled or
5249 a value to be pushed on the stack:
5250
5251 <ul>
5252
5253 <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>;
5254 </li>
5255
5256 <li><b>'<code>S</code>': </b>
5257 fills in the fields <code>source</code>, <code>short_src</code>,
5258 <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>;
5259 </li>
5260
5261 <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>;
5262 </li>
5263
5264 <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>;
5265 </li>
5266
5267 <li><b>'<code>u</code>': </b> fills in the fields
5268 <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>;
5269 </li>
5270
5271 <li><b>'<code>f</code>': </b>
5272 pushes onto the stack the function that is
5273 running at the given level;
5274 </li>
5275
5276 <li><b>'<code>L</code>': </b>
5277 pushes onto the stack a table whose indices are the
5278 numbers of the lines that are valid on the function.
5279 (A <em>valid line</em> is a line with some associated code,
5280 that is, a line where you can put a break point.
5281 Non-valid lines include empty lines and comments.)
5282 </li>
5283
5284 </ul>
5285
5286 <p>
5287 This function returns 0 on error
5288 (for instance, an invalid option in <code>what</code>).
5289
5290
5291
5292
5293
5294 <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p>
5295 <span class="apii">[-0, +(0|1), &ndash;]</span>
5296 <pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre>
5297
5298 <p>
5299 Gets information about a local variable of
5300 a given activation record or a given function.
5301
5302
5303 <p>
5304 In the first case,
5305 the parameter <code>ar</code> must be a valid activation record that was
5306 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or
5307 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>).
5308 The index <code>n</code> selects which local variable to inspect;
5309 see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices
5310 and names.
5311
5312
5313 <p>
5314 <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
5315 and returns its name.
5316
5317
5318 <p>
5319 In the second case, <code>ar</code> should be <code>NULL</code> and the function
5320 to be inspected must be at the top of the stack.
5321 In this case, only parameters of Lua functions are visible
5322 (as there is no information about what variables are active)
5323 and no values are pushed onto the stack.
5324
5325
5326 <p>
5327 Returns <code>NULL</code> (and pushes nothing)
5328 when the index is greater than
5329 the number of active local variables.
5330
5331
5332
5333
5334
5335 <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p>
5336 <span class="apii">[-0, +0, &ndash;]</span>
5337 <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre>
5338
5339 <p>
5340 Gets information about the interpreter runtime stack.
5341
5342
5343 <p>
5344 This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with
5345 an identification of the <em>activation record</em>
5346 of the function executing at a given level.
5347 Level&nbsp;0 is the current running function,
5348 whereas level <em>n+1</em> is the function that has called level <em>n</em>
5349 (except for tail calls, which do not count on the stack).
5350 When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1;
5351 when called with a level greater than the stack depth,
5352 it returns 0.
5353
5354
5355
5356
5357
5358 <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p>
5359 <span class="apii">[-0, +(0|1), &ndash;]</span>
5360 <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre>
5361
5362 <p>
5363 Gets information about a closure's upvalue.
5364 (For Lua functions,
5365 upvalues are the external local variables that the function uses,
5366 and that are consequently included in its closure.)
5367 <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
5368 pushes the upvalue's value onto the stack,
5369 and returns its name.
5370 <code>funcindex</code> points to the closure in the stack.
5371 (Upvalues have no particular order,
5372 as they are active through the whole function.
5373 So, they are numbered in an arbitrary order.)
5374
5375
5376 <p>
5377 Returns <code>NULL</code> (and pushes nothing)
5378 when the index is greater than the number of upvalues.
5379 For C&nbsp;functions, this function uses the empty string <code>""</code>
5380 as a name for all upvalues.
5381
5382
5383
5384
5385
5386 <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3>
5387 <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre>
5388
5389 <p>
5390 Type for debugging hook functions.
5391
5392
5393 <p>
5394 Whenever a hook is called, its <code>ar</code> argument has its field
5395 <code>event</code> set to the specific event that triggered the hook.
5396 Lua identifies these events with the following constants:
5397 <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
5398 <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
5399 and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>.
5400 Moreover, for line events, the field <code>currentline</code> is also set.
5401 To get the value of any other field in <code>ar</code>,
5402 the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>.
5403
5404
5405 <p>
5406 For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>,
5407 the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call;
5408 in this case, there will be no corresponding return event.
5409
5410
5411 <p>
5412 While Lua is running a hook, it disables other calls to hooks.
5413 Therefore, if a hook calls back Lua to execute a function or a chunk,
5414 this execution occurs without any calls to hooks.
5415
5416
5417 <p>
5418 Hook functions cannot have continuations,
5419 that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>,
5420 <a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>.
5421
5422
5423 <p>
5424 Hook functions can yield under the following conditions:
5425 Only count and line events can yield
5426 and they cannot yield any value;
5427 to yield a hook function must finish its execution
5428 calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero.
5429
5430
5431
5432
5433
5434 <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p>
5435 <span class="apii">[-0, +0, &ndash;]</span>
5436 <pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre>
5437
5438 <p>
5439 Sets the debugging hook function.
5440
5441
5442 <p>
5443 Argument <code>f</code> is the hook function.
5444 <code>mask</code> specifies on which events the hook will be called:
5445 it is formed by a bitwise or of the constants
5446 <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>,
5447 <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>,
5448 <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>,
5449 and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>.
5450 The <code>count</code> argument is only meaningful when the mask
5451 includes <code>LUA_MASKCOUNT</code>.
5452 For each event, the hook is called as explained below:
5453
5454 <ul>
5455
5456 <li><b>The call hook: </b> is called when the interpreter calls a function.
5457 The hook is called just after Lua enters the new function,
5458 before the function gets its arguments.
5459 </li>
5460
5461 <li><b>The return hook: </b> is called when the interpreter returns from a function.
5462 The hook is called just before Lua leaves the function.
5463 There is no standard way to access the values
5464 to be returned by the function.
5465 </li>
5466
5467 <li><b>The line hook: </b> is called when the interpreter is about to
5468 start the execution of a new line of code,
5469 or when it jumps back in the code (even to the same line).
5470 (This event only happens while Lua is executing a Lua function.)
5471 </li>
5472
5473 <li><b>The count hook: </b> is called after the interpreter executes every
5474 <code>count</code> instructions.
5475 (This event only happens while Lua is executing a Lua function.)
5476 </li>
5477
5478 </ul>
5479
5480 <p>
5481 A hook is disabled by setting <code>mask</code> to zero.
5482
5483
5484
5485
5486
5487 <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p>
5488 <span class="apii">[-(0|1), +0, &ndash;]</span>
5489 <pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre>
5490
5491 <p>
5492 Sets the value of a local variable of a given activation record.
5493 Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
5494 (see <a href="#lua_getlocal"><code>lua_getlocal</code></a>).
5495 <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
5496 to the variable and returns its name.
5497 It also pops the value from the stack.
5498
5499
5500 <p>
5501 Returns <code>NULL</code> (and pops nothing)
5502 when the index is greater than
5503 the number of active local variables.
5504
5505
5506
5507
5508
5509 <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p>
5510 <span class="apii">[-(0|1), +0, &ndash;]</span>
5511 <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre>
5512
5513 <p>
5514 Sets the value of a closure's upvalue.
5515 It assigns the value at the top of the stack
5516 to the upvalue and returns its name.
5517 It also pops the value from the stack.
5518 Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5519 (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>).
5520
5521
5522 <p>
5523 Returns <code>NULL</code> (and pops nothing)
5524 when the index is greater than the number of upvalues.
5525
5526
5527
5528
5529
5530 <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p>
5531 <span class="apii">[-0, +0, &ndash;]</span>
5532 <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre>
5533
5534 <p>
5535 Returns an unique identifier for the upvalue numbered <code>n</code>
5536 from the closure at index <code>funcindex</code>.
5537 Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
5538 (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>)
5539 (but <code>n</code> cannot be greater than the number of upvalues).
5540
5541
5542 <p>
5543 These unique identifiers allow a program to check whether different
5544 closures share upvalues.
5545 Lua closures that share an upvalue
5546 (that is, that access a same external local variable)
5547 will return identical ids for those upvalue indices.
5548
5549
5550
5551
5552
5553 <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p>
5554 <span class="apii">[-0, +0, &ndash;]</span>
5555 <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
5556                                     int funcindex2, int n2);</pre>
5557
5558 <p>
5559 Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code>
5560 refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>.
5561
5562
5563
5564
5565
5566
5567
5568 <h1>5 &ndash; <a name="5">The Auxiliary Library</a></h1>
5569
5570 <p>
5571
5572 The <em>auxiliary library</em> provides several convenient functions
5573 to interface C with Lua.
5574 While the basic API provides the primitive functions for all
5575 interactions between C and Lua,
5576 the auxiliary library provides higher-level functions for some
5577 common tasks.
5578
5579
5580 <p>
5581 All functions and types from the auxiliary library
5582 are defined in header file <code>lauxlib.h</code> and
5583 have a prefix <code>luaL_</code>.
5584
5585
5586 <p>
5587 All functions in the auxiliary library are built on
5588 top of the basic API,
5589 and so they provide nothing that cannot be done with that API.
5590 Nevertheless, the use of the auxiliary library ensures
5591 more consistency to your code.
5592
5593
5594 <p>
5595 Several functions in the auxiliary library use internally some
5596 extra stack slots.
5597 When a function in the auxiliary library uses less than five slots,
5598 it does not check the stack size;
5599 it simply assumes that there are enough slots.
5600
5601
5602 <p>
5603 Several functions in the auxiliary library are used to
5604 check C&nbsp;function arguments.
5605 Because the error message is formatted for arguments
5606 (e.g., "<code>bad argument #1</code>"),
5607 you should not use these functions for other stack values.
5608
5609
5610 <p>
5611 Functions called <code>luaL_check*</code>
5612 always throw an error if the check is not satisfied.
5613
5614
5615
5616 <h2>5.1 &ndash; <a name="5.1">Functions and Types</a></h2>
5617
5618 <p>
5619 Here we list all functions and types from the auxiliary library
5620 in alphabetical order.
5621
5622
5623
5624 <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p>
5625 <span class="apii">[-?, +?, <em>e</em>]</span>
5626 <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre>
5627
5628 <p>
5629 Adds the byte <code>c</code> to the buffer <code>B</code>
5630 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5631
5632
5633
5634
5635
5636 <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p>
5637 <span class="apii">[-?, +?, <em>e</em>]</span>
5638 <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre>
5639
5640 <p>
5641 Adds the string pointed to by <code>s</code> with length <code>l</code> to
5642 the buffer <code>B</code>
5643 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5644 The string can contain embedded zeros.
5645
5646
5647
5648
5649
5650 <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p>
5651 <span class="apii">[-?, +?, <em>e</em>]</span>
5652 <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre>
5653
5654 <p>
5655 Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>)
5656 a string of length <code>n</code> previously copied to the
5657 buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>).
5658
5659
5660
5661
5662
5663 <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p>
5664 <span class="apii">[-?, +?, <em>e</em>]</span>
5665 <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre>
5666
5667 <p>
5668 Adds the zero-terminated string pointed to by <code>s</code>
5669 to the buffer <code>B</code>
5670 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5671 The string cannot contain embedded zeros.
5672
5673
5674
5675
5676
5677 <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p>
5678 <span class="apii">[-1, +?, <em>e</em>]</span>
5679 <pre>void luaL_addvalue (luaL_Buffer *B);</pre>
5680
5681 <p>
5682 Adds the value at the top of the stack
5683 to the buffer <code>B</code>
5684 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5685 Pops the value.
5686
5687
5688 <p>
5689 This is the only function on string buffers that can (and must)
5690 be called with an extra element on the stack,
5691 which is the value to be added to the buffer.
5692
5693
5694
5695
5696
5697 <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p>
5698 <span class="apii">[-0, +0, <em>v</em>]</span>
5699 <pre>void luaL_argcheck (lua_State *L,
5700                     int cond,
5701                     int arg,
5702                     const char *extramsg);</pre>
5703
5704 <p>
5705 Checks whether <code>cond</code> is true.
5706 If not, raises an error with a standard message.
5707
5708
5709
5710
5711
5712 <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p>
5713 <span class="apii">[-0, +0, <em>v</em>]</span>
5714 <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre>
5715
5716 <p>
5717 Raises an error with a standard message
5718 that includes <code>extramsg</code> as a comment.
5719
5720
5721 <p>
5722 This function never returns,
5723 but it is an idiom to use it in C&nbsp;functions
5724 as <code>return luaL_argerror(<em>args</em>)</code>.
5725
5726
5727
5728
5729
5730 <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3>
5731 <pre>typedef struct luaL_Buffer luaL_Buffer;</pre>
5732
5733 <p>
5734 Type for a <em>string buffer</em>.
5735
5736
5737 <p>
5738 A string buffer allows C&nbsp;code to build Lua strings piecemeal.
5739 Its pattern of use is as follows:
5740
5741 <ul>
5742
5743 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
5744
5745 <li>Then initialize it with a call <code>luaL_buffinit(L, &amp;b)</code>.</li>
5746
5747 <li>
5748 Then add string pieces to the buffer calling any of
5749 the <code>luaL_add*</code> functions.
5750 </li>
5751
5752 <li>
5753 Finish by calling <code>luaL_pushresult(&amp;b)</code>.
5754 This call leaves the final string on the top of the stack.
5755 </li>
5756
5757 </ul>
5758
5759 <p>
5760 If you know beforehand the total size of the resulting string,
5761 you can use the buffer like this:
5762
5763 <ul>
5764
5765 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
5766
5767 <li>Then initialize it and preallocate a space of
5768 size <code>sz</code> with a call <code>luaL_buffinitsize(L, &amp;b, sz)</code>.</li>
5769
5770 <li>Then copy the string into that space.</li>
5771
5772 <li>
5773 Finish by calling <code>luaL_pushresultsize(&amp;b, sz)</code>,
5774 where <code>sz</code> is the total size of the resulting string
5775 copied into that space.
5776 </li>
5777
5778 </ul>
5779
5780 <p>
5781 During its normal operation,
5782 a string buffer uses a variable number of stack slots.
5783 So, while using a buffer, you cannot assume that you know where
5784 the top of the stack is.
5785 You can use the stack between successive calls to buffer operations
5786 as long as that use is balanced;
5787 that is,
5788 when you call a buffer operation,
5789 the stack is at the same level
5790 it was immediately after the previous buffer operation.
5791 (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.)
5792 After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
5793 level when the buffer was initialized,
5794 plus the final string on its top.
5795
5796
5797
5798
5799
5800 <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p>
5801 <span class="apii">[-0, +0, &ndash;]</span>
5802 <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre>
5803
5804 <p>
5805 Initializes a buffer <code>B</code>.
5806 This function does not allocate any space;
5807 the buffer must be declared as a variable
5808 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
5809
5810
5811
5812
5813
5814 <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p>
5815 <span class="apii">[-?, +?, <em>e</em>]</span>
5816 <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre>
5817
5818 <p>
5819 Equivalent to the sequence
5820 <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>.
5821
5822
5823
5824
5825
5826 <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p>
5827 <span class="apii">[-0, +(0|1), <em>e</em>]</span>
5828 <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre>
5829
5830 <p>
5831 Calls a metamethod.
5832
5833
5834 <p>
5835 If the object at index <code>obj</code> has a metatable and this
5836 metatable has a field <code>e</code>,
5837 this function calls this field passing the object as its only argument.
5838 In this case this function returns true and pushes onto the
5839 stack the value returned by the call.
5840 If there is no metatable or no metamethod,
5841 this function returns false (without pushing any value on the stack).
5842
5843
5844
5845
5846
5847 <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p>
5848 <span class="apii">[-0, +0, <em>v</em>]</span>
5849 <pre>void luaL_checkany (lua_State *L, int arg);</pre>
5850
5851 <p>
5852 Checks whether the function has an argument
5853 of any type (including <b>nil</b>) at position <code>arg</code>.
5854
5855
5856
5857
5858
5859 <hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p>
5860 <span class="apii">[-0, +0, <em>v</em>]</span>
5861 <pre>int luaL_checkint (lua_State *L, int arg);</pre>
5862
5863 <p>
5864 Checks whether the function argument <code>arg</code> is a number
5865 and returns this number cast to an <code>int</code>.
5866
5867
5868
5869
5870
5871 <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p>
5872 <span class="apii">[-0, +0, <em>v</em>]</span>
5873 <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre>
5874
5875 <p>
5876 Checks whether the function argument <code>arg</code> is a number
5877 and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
5878
5879
5880
5881
5882
5883 <hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p>
5884 <span class="apii">[-0, +0, <em>v</em>]</span>
5885 <pre>long luaL_checklong (lua_State *L, int arg);</pre>
5886
5887 <p>
5888 Checks whether the function argument <code>arg</code> is a number
5889 and returns this number cast to a <code>long</code>.
5890
5891
5892
5893
5894
5895 <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p>
5896 <span class="apii">[-0, +0, <em>v</em>]</span>
5897 <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre>
5898
5899 <p>
5900 Checks whether the function argument <code>arg</code> is a string
5901 and returns this string;
5902 if <code>l</code> is not <code>NULL</code> fills <code>*l</code>
5903 with the string's length.
5904
5905
5906 <p>
5907 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
5908 so all conversions and caveats of that function apply here.
5909
5910
5911
5912
5913
5914 <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p>
5915 <span class="apii">[-0, +0, <em>v</em>]</span>
5916 <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre>
5917
5918 <p>
5919 Checks whether the function argument <code>arg</code> is a number
5920 and returns this number.
5921
5922
5923
5924
5925
5926 <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p>
5927 <span class="apii">[-0, +0, <em>v</em>]</span>
5928 <pre>int luaL_checkoption (lua_State *L,
5929                       int arg,
5930                       const char *def,
5931                       const char *const lst[]);</pre>
5932
5933 <p>
5934 Checks whether the function argument <code>arg</code> is a string and
5935 searches for this string in the array <code>lst</code>
5936 (which must be NULL-terminated).
5937 Returns the index in the array where the string was found.
5938 Raises an error if the argument is not a string or
5939 if the string cannot be found.
5940
5941
5942 <p>
5943 If <code>def</code> is not <code>NULL</code>,
5944 the function uses <code>def</code> as a default value when
5945 there is no argument <code>arg</code> or when this argument is <b>nil</b>.
5946
5947
5948 <p>
5949 This is a useful function for mapping strings to C&nbsp;enums.
5950 (The usual convention in Lua libraries is
5951 to use strings instead of numbers to select options.)
5952
5953
5954
5955
5956
5957 <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p>
5958 <span class="apii">[-0, +0, <em>v</em>]</span>
5959 <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre>
5960
5961 <p>
5962 Grows the stack size to <code>top + sz</code> elements,
5963 raising an error if the stack cannot grow to that size.
5964 <code>msg</code> is an additional text to go into the error message
5965 (or <code>NULL</code> for no additional text).
5966
5967
5968
5969
5970
5971 <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p>
5972 <span class="apii">[-0, +0, <em>v</em>]</span>
5973 <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre>
5974
5975 <p>
5976 Checks whether the function argument <code>arg</code> is a string
5977 and returns this string.
5978
5979
5980 <p>
5981 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result,
5982 so all conversions and caveats of that function apply here.
5983
5984
5985
5986
5987
5988 <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p>
5989 <span class="apii">[-0, +0, <em>v</em>]</span>
5990 <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre>
5991
5992 <p>
5993 Checks whether the function argument <code>arg</code> has type <code>t</code>.
5994 See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
5995
5996
5997
5998
5999
6000 <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p>
6001 <span class="apii">[-0, +0, <em>v</em>]</span>
6002 <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre>
6003
6004 <p>
6005 Checks whether the function argument <code>arg</code> is a userdata
6006 of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and
6007 returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>).
6008
6009
6010
6011
6012
6013 <hr><h3><a name="luaL_checkunsigned"><code>luaL_checkunsigned</code></a></h3><p>
6014 <span class="apii">[-0, +0, <em>v</em>]</span>
6015 <pre>lua_Unsigned luaL_checkunsigned (lua_State *L, int arg);</pre>
6016
6017 <p>
6018 Checks whether the function argument <code>arg</code> is a number
6019 and returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
6020
6021
6022
6023
6024
6025 <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p>
6026 <span class="apii">[-0, +0, &ndash;]</span>
6027 <pre>void luaL_checkversion (lua_State *L);</pre>
6028
6029 <p>
6030 Checks whether the core running the call,
6031 the core that created the Lua state,
6032 and the code making the call are all using the same version of Lua.
6033 Also checks whether the core running the call
6034 and the core that created the Lua state
6035 are using the same address space.
6036
6037
6038
6039
6040
6041 <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p>
6042 <span class="apii">[-0, +?, <em>e</em>]</span>
6043 <pre>int luaL_dofile (lua_State *L, const char *filename);</pre>
6044
6045 <p>
6046 Loads and runs the given file.
6047 It is defined as the following macro:
6048
6049 <pre>
6050      (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
6051 </pre><p>
6052 It returns false if there are no errors
6053 or true in case of errors.
6054
6055
6056
6057
6058
6059 <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p>
6060 <span class="apii">[-0, +?, &ndash;]</span>
6061 <pre>int luaL_dostring (lua_State *L, const char *str);</pre>
6062
6063 <p>
6064 Loads and runs the given string.
6065 It is defined as the following macro:
6066
6067 <pre>
6068      (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
6069 </pre><p>
6070 It returns false if there are no errors
6071 or true in case of errors.
6072
6073
6074
6075
6076
6077 <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p>
6078 <span class="apii">[-0, +0, <em>v</em>]</span>
6079 <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre>
6080
6081 <p>
6082 Raises an error.
6083 The error message format is given by <code>fmt</code>
6084 plus any extra arguments,
6085 following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>.
6086 It also adds at the beginning of the message the file name and
6087 the line number where the error occurred,
6088 if this information is available.
6089
6090
6091 <p>
6092 This function never returns,
6093 but it is an idiom to use it in C&nbsp;functions
6094 as <code>return luaL_error(<em>args</em>)</code>.
6095
6096
6097
6098
6099
6100 <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p>
6101 <span class="apii">[-0, +3, <em>e</em>]</span>
6102 <pre>int luaL_execresult (lua_State *L, int stat);</pre>
6103
6104 <p>
6105 This function produces the return values for
6106 process-related functions in the standard library
6107 (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>).
6108
6109
6110
6111
6112
6113 <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p>
6114 <span class="apii">[-0, +(1|3), <em>e</em>]</span>
6115 <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre>
6116
6117 <p>
6118 This function produces the return values for
6119 file-related functions in the standard library
6120 (<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.).
6121
6122
6123
6124
6125
6126 <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p>
6127 <span class="apii">[-0, +(0|1), <em>e</em>]</span>
6128 <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre>
6129
6130 <p>
6131 Pushes onto the stack the field <code>e</code> from the metatable
6132 of the object at index <code>obj</code>.
6133 If the object does not have a metatable,
6134 or if the metatable does not have this field,
6135 returns false and pushes nothing.
6136
6137
6138
6139
6140
6141 <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p>
6142 <span class="apii">[-0, +1, &ndash;]</span>
6143 <pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre>
6144
6145 <p>
6146 Pushes onto the stack the metatable associated with name <code>tname</code>
6147 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6148
6149
6150
6151
6152
6153 <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p>
6154 <span class="apii">[-0, +1, <em>e</em>]</span>
6155 <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre>
6156
6157 <p>
6158 Ensures that the value <code>t[fname]</code>,
6159 where <code>t</code> is the value at index <code>idx</code>,
6160 is a table,
6161 and pushes that table onto the stack.
6162 Returns true if it finds a previous table there
6163 and false if it creates a new table.
6164
6165
6166
6167
6168
6169 <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p>
6170 <span class="apii">[-0, +1, <em>e</em>]</span>
6171 <pre>const char *luaL_gsub (lua_State *L,
6172                        const char *s,
6173                        const char *p,
6174                        const char *r);</pre>
6175
6176 <p>
6177 Creates a copy of string <code>s</code> by replacing
6178 any occurrence of the string <code>p</code>
6179 with the string <code>r</code>.
6180 Pushes the resulting string on the stack and returns it.
6181
6182
6183
6184
6185
6186 <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p>
6187 <span class="apii">[-0, +0, <em>e</em>]</span>
6188 <pre>int luaL_len (lua_State *L, int index);</pre>
6189
6190 <p>
6191 Returns the "length" of the value at the given index
6192 as a number;
6193 it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">&sect;3.4.6</a>).
6194 Raises an error if the result of the operation is not a number.
6195 (This case only can happen through metamethods.)
6196
6197
6198
6199
6200
6201 <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p>
6202 <span class="apii">[-0, +1, &ndash;]</span>
6203 <pre>int luaL_loadbuffer (lua_State *L,
6204                      const char *buff,
6205                      size_t sz,
6206                      const char *name);</pre>
6207
6208 <p>
6209 Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>.
6210
6211
6212
6213
6214
6215 <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p>
6216 <span class="apii">[-0, +1, &ndash;]</span>
6217 <pre>int luaL_loadbufferx (lua_State *L,
6218                       const char *buff,
6219                       size_t sz,
6220                       const char *name,
6221                       const char *mode);</pre>
6222
6223 <p>
6224 Loads a buffer as a Lua chunk.
6225 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the
6226 buffer pointed to by <code>buff</code> with size <code>sz</code>.
6227
6228
6229 <p>
6230 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6231 <code>name</code> is the chunk name,
6232 used for debug information and error messages.
6233 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6234
6235
6236
6237
6238
6239 <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p>
6240 <span class="apii">[-0, +1, <em>e</em>]</span>
6241 <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre>
6242
6243 <p>
6244 Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>.
6245
6246
6247
6248
6249
6250 <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p>
6251 <span class="apii">[-0, +1, <em>e</em>]</span>
6252 <pre>int luaL_loadfilex (lua_State *L, const char *filename,
6253                                             const char *mode);</pre>
6254
6255 <p>
6256 Loads a file as a Lua chunk.
6257 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file
6258 named <code>filename</code>.
6259 If <code>filename</code> is <code>NULL</code>,
6260 then it loads from the standard input.
6261 The first line in the file is ignored if it starts with a <code>#</code>.
6262
6263
6264 <p>
6265 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>.
6266
6267
6268 <p>
6269 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>,
6270 but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a>
6271 if it cannot open/read the file or the file has a wrong mode.
6272
6273
6274 <p>
6275 As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6276 it does not run it.
6277
6278
6279
6280
6281
6282 <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p>
6283 <span class="apii">[-0, +1, &ndash;]</span>
6284 <pre>int luaL_loadstring (lua_State *L, const char *s);</pre>
6285
6286 <p>
6287 Loads a string as a Lua chunk.
6288 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in
6289 the zero-terminated string <code>s</code>.
6290
6291
6292 <p>
6293 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>.
6294
6295
6296 <p>
6297 Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk;
6298 it does not run it.
6299
6300
6301
6302
6303
6304 <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p>
6305 <span class="apii">[-0, +1, <em>e</em>]</span>
6306 <pre>void luaL_newlib (lua_State *L, const luaL_Reg *l);</pre>
6307
6308 <p>
6309 Creates a new table and registers there
6310 the functions in list <code>l</code>.
6311 It is implemented as the following macro:
6312
6313 <pre>
6314      (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
6315 </pre>
6316
6317
6318
6319
6320 <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p>
6321 <span class="apii">[-0, +1, <em>e</em>]</span>
6322 <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre>
6323
6324 <p>
6325 Creates a new table with a size optimized
6326 to store all entries in the array <code>l</code>
6327 (but does not actually store them).
6328 It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>
6329 (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>).
6330
6331
6332 <p>
6333 It is implemented as a macro.
6334 The array <code>l</code> must be the actual array,
6335 not a pointer to it.
6336
6337
6338
6339
6340
6341 <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p>
6342 <span class="apii">[-0, +1, <em>e</em>]</span>
6343 <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre>
6344
6345 <p>
6346 If the registry already has the key <code>tname</code>,
6347 returns 0.
6348 Otherwise,
6349 creates a new table to be used as a metatable for userdata,
6350 adds it to the registry with key <code>tname</code>,
6351 and returns 1.
6352
6353
6354 <p>
6355 In both cases pushes onto the stack the final value associated
6356 with <code>tname</code> in the registry.
6357
6358
6359
6360
6361
6362 <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p>
6363 <span class="apii">[-0, +0, &ndash;]</span>
6364 <pre>lua_State *luaL_newstate (void);</pre>
6365
6366 <p>
6367 Creates a new Lua state.
6368 It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an
6369 allocator based on the standard&nbsp;C <code>realloc</code> function
6370 and then sets a panic function (see <a href="#4.6">&sect;4.6</a>) that prints
6371 an error message to the standard error output in case of fatal
6372 errors.
6373
6374
6375 <p>
6376 Returns the new state,
6377 or <code>NULL</code> if there is a memory allocation error.
6378
6379
6380
6381
6382
6383 <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p>
6384 <span class="apii">[-0, +0, <em>e</em>]</span>
6385 <pre>void luaL_openlibs (lua_State *L);</pre>
6386
6387 <p>
6388 Opens all standard Lua libraries into the given state.
6389
6390
6391
6392
6393
6394 <hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p>
6395 <span class="apii">[-0, +0, <em>v</em>]</span>
6396 <pre>int luaL_optint (lua_State *L, int arg, int d);</pre>
6397
6398 <p>
6399 If the function argument <code>arg</code> is a number,
6400 returns this number cast to an <code>int</code>.
6401 If this argument is absent or is <b>nil</b>,
6402 returns <code>d</code>.
6403 Otherwise, raises an error.
6404
6405
6406
6407
6408
6409 <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p>
6410 <span class="apii">[-0, +0, <em>v</em>]</span>
6411 <pre>lua_Integer luaL_optinteger (lua_State *L,
6412                              int arg,
6413                              lua_Integer d);</pre>
6414
6415 <p>
6416 If the function argument <code>arg</code> is a number,
6417 returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>.
6418 If this argument is absent or is <b>nil</b>,
6419 returns <code>d</code>.
6420 Otherwise, raises an error.
6421
6422
6423
6424
6425
6426 <hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p>
6427 <span class="apii">[-0, +0, <em>v</em>]</span>
6428 <pre>long luaL_optlong (lua_State *L, int arg, long d);</pre>
6429
6430 <p>
6431 If the function argument <code>arg</code> is a number,
6432 returns this number cast to a <code>long</code>.
6433 If this argument is absent or is <b>nil</b>,
6434 returns <code>d</code>.
6435 Otherwise, raises an error.
6436
6437
6438
6439
6440
6441 <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p>
6442 <span class="apii">[-0, +0, <em>v</em>]</span>
6443 <pre>const char *luaL_optlstring (lua_State *L,
6444                              int arg,
6445                              const char *d,
6446                              size_t *l);</pre>
6447
6448 <p>
6449 If the function argument <code>arg</code> is a string,
6450 returns this string.
6451 If this argument is absent or is <b>nil</b>,
6452 returns <code>d</code>.
6453 Otherwise, raises an error.
6454
6455
6456 <p>
6457 If <code>l</code> is not <code>NULL</code>,
6458 fills the position <code>*l</code> with the result's length.
6459
6460
6461
6462
6463
6464 <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p>
6465 <span class="apii">[-0, +0, <em>v</em>]</span>
6466 <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre>
6467
6468 <p>
6469 If the function argument <code>arg</code> is a number,
6470 returns this number.
6471 If this argument is absent or is <b>nil</b>,
6472 returns <code>d</code>.
6473 Otherwise, raises an error.
6474
6475
6476
6477
6478
6479 <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p>
6480 <span class="apii">[-0, +0, <em>v</em>]</span>
6481 <pre>const char *luaL_optstring (lua_State *L,
6482                             int arg,
6483                             const char *d);</pre>
6484
6485 <p>
6486 If the function argument <code>arg</code> is a string,
6487 returns this string.
6488 If this argument is absent or is <b>nil</b>,
6489 returns <code>d</code>.
6490 Otherwise, raises an error.
6491
6492
6493
6494
6495
6496 <hr><h3><a name="luaL_optunsigned"><code>luaL_optunsigned</code></a></h3><p>
6497 <span class="apii">[-0, +0, <em>v</em>]</span>
6498 <pre>lua_Unsigned luaL_optunsigned (lua_State *L,
6499                                int arg,
6500                                lua_Unsigned u);</pre>
6501
6502 <p>
6503 If the function argument <code>arg</code> is a number,
6504 returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>.
6505 If this argument is absent or is <b>nil</b>,
6506 returns <code>u</code>.
6507 Otherwise, raises an error.
6508
6509
6510
6511
6512
6513 <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p>
6514 <span class="apii">[-?, +?, <em>e</em>]</span>
6515 <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre>
6516
6517 <p>
6518 Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>
6519 with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>.
6520
6521
6522
6523
6524
6525 <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p>
6526 <span class="apii">[-?, +?, <em>e</em>]</span>
6527 <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre>
6528
6529 <p>
6530 Returns an address to a space of size <code>sz</code>
6531 where you can copy a string to be added to buffer <code>B</code>
6532 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>).
6533 After copying the string into this space you must call
6534 <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
6535 it to the buffer.
6536
6537
6538
6539
6540
6541 <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p>
6542 <span class="apii">[-?, +1, <em>e</em>]</span>
6543 <pre>void luaL_pushresult (luaL_Buffer *B);</pre>
6544
6545 <p>
6546 Finishes the use of buffer <code>B</code> leaving the final string on
6547 the top of the stack.
6548
6549
6550
6551
6552
6553 <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p>
6554 <span class="apii">[-?, +1, <em>e</em>]</span>
6555 <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre>
6556
6557 <p>
6558 Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>.
6559
6560
6561
6562
6563
6564 <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p>
6565 <span class="apii">[-1, +0, <em>e</em>]</span>
6566 <pre>int luaL_ref (lua_State *L, int t);</pre>
6567
6568 <p>
6569 Creates and returns a <em>reference</em>,
6570 in the table at index <code>t</code>,
6571 for the object at the top of the stack (and pops the object).
6572
6573
6574 <p>
6575 A reference is a unique integer key.
6576 As long as you do not manually add integer keys into table <code>t</code>,
6577 <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns.
6578 You can retrieve an object referred by reference <code>r</code>
6579 by calling <code>lua_rawgeti(L, t, r)</code>.
6580 Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
6581
6582
6583 <p>
6584 If the object at the top of the stack is <b>nil</b>,
6585 <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
6586 The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different
6587 from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>.
6588
6589
6590
6591
6592
6593 <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3>
6594 <pre>typedef struct luaL_Reg {
6595   const char *name;
6596   lua_CFunction func;
6597 } luaL_Reg;</pre>
6598
6599 <p>
6600 Type for arrays of functions to be registered by
6601 <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>.
6602 <code>name</code> is the function name and <code>func</code> is a pointer to
6603 the function.
6604 Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry
6605 in which both <code>name</code> and <code>func</code> are <code>NULL</code>.
6606
6607
6608
6609
6610
6611 <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p>
6612 <span class="apii">[-0, +1, <em>e</em>]</span>
6613 <pre>void luaL_requiref (lua_State *L, const char *modname,
6614                     lua_CFunction openf, int glb);</pre>
6615
6616 <p>
6617 Calls function <code>openf</code> with string <code>modname</code> as an argument
6618 and sets the call result in <code>package.loaded[modname]</code>,
6619 as if that function has been called through <a href="#pdf-require"><code>require</code></a>.
6620
6621
6622 <p>
6623 If <code>glb</code> is true,
6624 also stores the result into global <code>modname</code>.
6625
6626
6627 <p>
6628 Leaves a copy of that result on the stack.
6629
6630
6631
6632
6633
6634 <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p>
6635 <span class="apii">[-nup, +0, <em>e</em>]</span>
6636 <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre>
6637
6638 <p>
6639 Registers all functions in the array <code>l</code>
6640 (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack
6641 (below optional upvalues, see next).
6642
6643
6644 <p>
6645 When <code>nup</code> is not zero,
6646 all functions are created sharing <code>nup</code> upvalues,
6647 which must be previously pushed on the stack
6648 on top of the library table.
6649 These values are popped from the stack after the registration.
6650
6651
6652
6653
6654
6655 <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p>
6656 <span class="apii">[-0, +0, &ndash;]</span>
6657 <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre>
6658
6659 <p>
6660 Sets the metatable of the object at the top of the stack
6661 as the metatable associated with name <code>tname</code>
6662 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
6663
6664
6665
6666
6667
6668 <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p>
6669 <span class="apii">[-0, +0, <em>e</em>]</span>
6670 <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre>
6671
6672 <p>
6673 This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>,
6674 except that, when the test fails,
6675 it returns <code>NULL</code> instead of throwing an error.
6676
6677
6678
6679
6680
6681 <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p>
6682 <span class="apii">[-0, +1, <em>e</em>]</span>
6683 <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre>
6684
6685 <p>
6686 Converts any Lua value at the given index to a C&nbsp;string
6687 in a reasonable format.
6688 The resulting string is pushed onto the stack and also
6689 returned by the function.
6690 If <code>len</code> is not <code>NULL</code>,
6691 the function also sets <code>*len</code> with the string length.
6692
6693
6694 <p>
6695 If the value has a metatable with a <code>"__tostring"</code> field,
6696 then <code>luaL_tolstring</code> calls the corresponding metamethod
6697 with the value as argument,
6698 and uses the result of the call as its result.
6699
6700
6701
6702
6703
6704 <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p>
6705 <span class="apii">[-0, +1, <em>e</em>]</span>
6706 <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
6707                      int level);</pre>
6708
6709 <p>
6710 Creates and pushes a traceback of the stack <code>L1</code>.
6711 If <code>msg</code> is not <code>NULL</code> it is appended
6712 at the beginning of the traceback.
6713 The <code>level</code> parameter tells at which level
6714 to start the traceback.
6715
6716
6717
6718
6719
6720 <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p>
6721 <span class="apii">[-0, +0, &ndash;]</span>
6722 <pre>const char *luaL_typename (lua_State *L, int index);</pre>
6723
6724 <p>
6725 Returns the name of the type of the value at the given index.
6726
6727
6728
6729
6730
6731 <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p>
6732 <span class="apii">[-0, +0, &ndash;]</span>
6733 <pre>void luaL_unref (lua_State *L, int t, int ref);</pre>
6734
6735 <p>
6736 Releases reference <code>ref</code> from the table at index <code>t</code>
6737 (see <a href="#luaL_ref"><code>luaL_ref</code></a>).
6738 The entry is removed from the table,
6739 so that the referred object can be collected.
6740 The reference <code>ref</code> is also freed to be used again.
6741
6742
6743 <p>
6744 If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>,
6745 <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing.
6746
6747
6748
6749
6750
6751 <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p>
6752 <span class="apii">[-0, +1, <em>e</em>]</span>
6753 <pre>void luaL_where (lua_State *L, int lvl);</pre>
6754
6755 <p>
6756 Pushes onto the stack a string identifying the current position
6757 of the control at level <code>lvl</code> in the call stack.
6758 Typically this string has the following format:
6759
6760 <pre>
6761      <em>chunkname</em>:<em>currentline</em>:
6762 </pre><p>
6763 Level&nbsp;0 is the running function,
6764 level&nbsp;1 is the function that called the running function,
6765 etc.
6766
6767
6768 <p>
6769 This function is used to build a prefix for error messages.
6770
6771
6772
6773
6774
6775
6776
6777 <h1>6 &ndash; <a name="6">Standard Libraries</a></h1>
6778
6779 <p>
6780 The standard Lua libraries provide useful functions
6781 that are implemented directly through the C&nbsp;API.
6782 Some of these functions provide essential services to the language
6783 (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
6784 others provide access to "outside" services (e.g., I/O);
6785 and others could be implemented in Lua itself,
6786 but are quite useful or have critical performance requirements that
6787 deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>).
6788
6789
6790 <p>
6791 All libraries are implemented through the official C&nbsp;API
6792 and are provided as separate C&nbsp;modules.
6793 Currently, Lua has the following standard libraries:
6794
6795 <ul>
6796
6797 <li>basic library (<a href="#6.1">&sect;6.1</a>);</li>
6798
6799 <li>coroutine library (<a href="#6.2">&sect;6.2</a>);</li>
6800
6801 <li>package library (<a href="#6.3">&sect;6.3</a>);</li>
6802
6803 <li>string manipulation (<a href="#6.4">&sect;6.4</a>);</li>
6804
6805 <li>table manipulation (<a href="#6.5">&sect;6.5</a>);</li>
6806
6807 <li>mathematical functions (<a href="#6.6">&sect;6.6</a>) (sin, log, etc.);</li>
6808
6809 <li>bitwise operations (<a href="#6.7">&sect;6.7</a>);</li>
6810
6811 <li>input and output (<a href="#6.8">&sect;6.8</a>);</li>
6812
6813 <li>operating system facilities (<a href="#6.9">&sect;6.9</a>);</li>
6814
6815 <li>debug facilities (<a href="#6.10">&sect;6.10</a>).</li>
6816
6817 </ul><p>
6818 Except for the basic and the package libraries,
6819 each library provides all its functions as fields of a global table
6820 or as methods of its objects.
6821
6822
6823 <p>
6824 To have access to these libraries,
6825 the C&nbsp;host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
6826 which opens all standard libraries.
6827 Alternatively,
6828 the host program can open them individually by using
6829 <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call
6830 <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library),
6831 <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library),
6832 <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library),
6833 <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library),
6834 <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library),
6835 <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library),
6836 <a name="pdf-luaopen_bit32"><code>luaopen_bit32</code></a> (for the bit library),
6837 <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library),
6838 <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library),
6839 and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library).
6840 These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>.
6841
6842
6843
6844 <h2>6.1 &ndash; <a name="6.1">Basic Functions</a></h2>
6845
6846 <p>
6847 The basic library provides core functions to Lua.
6848 If you do not include this library in your application,
6849 you should check carefully whether you need to provide
6850 implementations for some of its facilities.
6851
6852
6853 <p>
6854 <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3>
6855 Issues an  error when
6856 the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>);
6857 otherwise, returns all its arguments.
6858 <code>message</code> is an error message;
6859 when absent, it defaults to "assertion failed!"
6860
6861
6862
6863
6864 <p>
6865 <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3>
6866
6867
6868 <p>
6869 This function is a generic interface to the garbage collector.
6870 It performs different functions according to its first argument, <code>opt</code>:
6871
6872 <ul>
6873
6874 <li><b>"<code>collect</code>": </b>
6875 performs a full garbage-collection cycle.
6876 This is the default option.
6877 </li>
6878
6879 <li><b>"<code>stop</code>": </b>
6880 stops automatic execution of the garbage collector.
6881 The collector will run only when explicitly invoked,
6882 until a call to restart it.
6883 </li>
6884
6885 <li><b>"<code>restart</code>": </b>
6886 restarts automatic execution of the garbage collector.
6887 </li>
6888
6889 <li><b>"<code>count</code>": </b>
6890 returns the total memory in use by Lua (in Kbytes) and
6891 a second value with the total memory in bytes modulo 1024.
6892 The first value has a fractional part,
6893 so the following equality is always true:
6894
6895 <pre>
6896      k, b = collectgarbage("count")
6897      assert(k*1024 == math.floor(k)*1024 + b)
6898 </pre><p>
6899 (The second result is useful when Lua is compiled
6900 with a non floating-point type for numbers.)
6901 </li>
6902
6903 <li><b>"<code>step</code>": </b>
6904 performs a garbage-collection step.
6905 The step "size" is controlled by <code>arg</code>
6906 (larger values mean more steps) in a non-specified way.
6907 If you want to control the step size
6908 you must experimentally tune the value of <code>arg</code>.
6909 Returns <b>true</b> if the step finished a collection cycle.
6910 </li>
6911
6912 <li><b>"<code>setpause</code>": </b>
6913 sets <code>arg</code> as the new value for the <em>pause</em> of
6914 the collector (see <a href="#2.5">&sect;2.5</a>).
6915 Returns the previous value for <em>pause</em>.
6916 </li>
6917
6918 <li><b>"<code>setstepmul</code>": </b>
6919 sets <code>arg</code> as the new value for the <em>step multiplier</em> of
6920 the collector (see <a href="#2.5">&sect;2.5</a>).
6921 Returns the previous value for <em>step</em>.
6922 </li>
6923
6924 <li><b>"<code>isrunning</code>": </b>
6925 returns a boolean that tells whether the collector is running
6926 (i.e., not stopped).
6927 </li>
6928
6929 <li><b>"<code>generational</code>": </b>
6930 changes the collector to generational mode.
6931 This is an experimental feature (see <a href="#2.5">&sect;2.5</a>).
6932 </li>
6933
6934 <li><b>"<code>incremental</code>": </b>
6935 changes the collector to incremental mode.
6936 This is the default mode.
6937 </li>
6938
6939 </ul>
6940
6941
6942
6943 <p>
6944 <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3>
6945 Opens the named file and executes its contents as a Lua chunk.
6946 When called without arguments,
6947 <code>dofile</code> executes the contents of the standard input (<code>stdin</code>).
6948 Returns all values returned by the chunk.
6949 In case of errors, <code>dofile</code> propagates the error
6950 to its caller (that is, <code>dofile</code> does not run in protected mode).
6951
6952
6953
6954
6955 <p>
6956 <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3>
6957 Terminates the last protected function called
6958 and returns <code>message</code> as the error message.
6959 Function <code>error</code> never returns.
6960
6961
6962 <p>
6963 Usually, <code>error</code> adds some information about the error position
6964 at the beginning of the message, if the message is a string.
6965 The <code>level</code> argument specifies how to get the error position.
6966 With level&nbsp;1 (the default), the error position is where the
6967 <code>error</code> function was called.
6968 Level&nbsp;2 points the error to where the function
6969 that called <code>error</code> was called; and so on.
6970 Passing a level&nbsp;0 avoids the addition of error position information
6971 to the message.
6972
6973
6974
6975
6976 <p>
6977 <hr><h3><a name="pdf-_G"><code>_G</code></a></h3>
6978 A global variable (not a function) that
6979 holds the global environment (see <a href="#2.2">&sect;2.2</a>).
6980 Lua itself does not use this variable;
6981 changing its value does not affect any environment,
6982 nor vice-versa.
6983
6984
6985
6986
6987 <p>
6988 <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3>
6989
6990
6991 <p>
6992 If <code>object</code> does not have a metatable, returns <b>nil</b>.
6993 Otherwise,
6994 if the object's metatable has a <code>"__metatable"</code> field,
6995 returns the associated value.
6996 Otherwise, returns the metatable of the given object.
6997
6998
6999
7000
7001 <p>
7002 <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3>
7003
7004
7005 <p>
7006 If <code>t</code> has a metamethod <code>__ipairs</code>,
7007 calls it with <code>t</code> as argument and returns the first three
7008 results from the call.
7009
7010
7011 <p>
7012 Otherwise,
7013 returns three values: an iterator function, the table <code>t</code>, and 0,
7014 so that the construction
7015
7016 <pre>
7017      for i,v in ipairs(t) do <em>body</em> end
7018 </pre><p>
7019 will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ...,
7020 up to the first integer key absent from the table.
7021
7022
7023
7024
7025 <p>
7026 <hr><h3><a name="pdf-load"><code>load (ld [, source [, mode [, env]]])</code></a></h3>
7027
7028
7029 <p>
7030 Loads a chunk.
7031
7032
7033 <p>
7034 If <code>ld</code> is a string, the chunk is this string.
7035 If <code>ld</code> is a function,
7036 <code>load</code> calls it repeatedly to get the chunk pieces.
7037 Each call to <code>ld</code> must return a string that concatenates
7038 with previous results.
7039 A return of an empty string, <b>nil</b>, or no value signals the end of the chunk.
7040
7041
7042 <p>
7043 If there are no syntactic errors,
7044 returns the compiled chunk as a function;
7045 otherwise, returns <b>nil</b> plus the error message.
7046
7047
7048 <p>
7049 If the resulting function has upvalues,
7050 the first upvalue is set to the value of <code>env</code>,
7051 if that parameter is given,
7052 or to the value of the global environment.
7053 (When you load a main chunk,
7054 the resulting function will always have exactly one upvalue,
7055 the <code>_ENV</code> variable (see <a href="#2.2">&sect;2.2</a>).
7056 When you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>),
7057 the resulting function can have arbitrary upvalues.)
7058
7059
7060 <p>
7061 <code>source</code> is used as the source of the chunk for error messages
7062 and debug information (see <a href="#4.9">&sect;4.9</a>).
7063 When absent,
7064 it defaults to <code>ld</code>, if <code>ld</code> is a string,
7065 or to "<code>=(load)</code>" otherwise.
7066
7067
7068 <p>
7069 The string <code>mode</code> controls whether the chunk can be text or binary
7070 (that is, a precompiled chunk).
7071 It may be the string "<code>b</code>" (only binary chunks),
7072 "<code>t</code>" (only text chunks),
7073 or "<code>bt</code>" (both binary and text).
7074 The default is "<code>bt</code>".
7075
7076
7077
7078
7079 <p>
7080 <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3>
7081
7082
7083 <p>
7084 Similar to <a href="#pdf-load"><code>load</code></a>,
7085 but gets the chunk from file <code>filename</code>
7086 or from the standard input,
7087 if no file name is given.
7088
7089
7090
7091
7092 <p>
7093 <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3>
7094
7095
7096 <p>
7097 Allows a program to traverse all fields of a table.
7098 Its first argument is a table and its second argument
7099 is an index in this table.
7100 <code>next</code> returns the next index of the table
7101 and its associated value.
7102 When called with <b>nil</b> as its second argument,
7103 <code>next</code> returns an initial index
7104 and its associated value.
7105 When called with the last index,
7106 or with <b>nil</b> in an empty table,
7107 <code>next</code> returns <b>nil</b>.
7108 If the second argument is absent, then it is interpreted as <b>nil</b>.
7109 In particular,
7110 you can use <code>next(t)</code> to check whether a table is empty.
7111
7112
7113 <p>
7114 The order in which the indices are enumerated is not specified,
7115 <em>even for numeric indices</em>.
7116 (To traverse a table in numeric order,
7117 use a numerical <b>for</b>.)
7118
7119
7120 <p>
7121 The behavior of <code>next</code> is undefined if,
7122 during the traversal,
7123 you assign any value to a non-existent field in the table.
7124 You may however modify existing fields.
7125 In particular, you may clear existing fields.
7126
7127
7128
7129
7130 <p>
7131 <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3>
7132
7133
7134 <p>
7135 If <code>t</code> has a metamethod <code>__pairs</code>,
7136 calls it with <code>t</code> as argument and returns the first three
7137 results from the call.
7138
7139
7140 <p>
7141 Otherwise,
7142 returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
7143 so that the construction
7144
7145 <pre>
7146      for k,v in pairs(t) do <em>body</em> end
7147 </pre><p>
7148 will iterate over all key&ndash;value pairs of table <code>t</code>.
7149
7150
7151 <p>
7152 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying
7153 the table during its traversal.
7154
7155
7156
7157
7158 <p>
7159 <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, &middot;&middot;&middot;])</code></a></h3>
7160
7161
7162 <p>
7163 Calls function <code>f</code> with
7164 the given arguments in <em>protected mode</em>.
7165 This means that any error inside&nbsp;<code>f</code> is not propagated;
7166 instead, <code>pcall</code> catches the error
7167 and returns a status code.
7168 Its first result is the status code (a boolean),
7169 which is true if the call succeeds without errors.
7170 In such case, <code>pcall</code> also returns all results from the call,
7171 after this first result.
7172 In case of any error, <code>pcall</code> returns <b>false</b> plus the error message.
7173
7174
7175
7176
7177 <p>
7178 <hr><h3><a name="pdf-print"><code>print (&middot;&middot;&middot;)</code></a></h3>
7179 Receives any number of arguments
7180 and prints their values to <code>stdout</code>,
7181 using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string.
7182 <code>print</code> is not intended for formatted output,
7183 but only as a quick way to show a value,
7184 for instance for debugging.
7185 For complete control over the output,
7186 use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>.
7187
7188
7189
7190
7191 <p>
7192 <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3>
7193 Checks whether <code>v1</code> is equal to <code>v2</code>,
7194 without invoking any metamethod.
7195 Returns a boolean.
7196
7197
7198
7199
7200 <p>
7201 <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3>
7202 Gets the real value of <code>table[index]</code>,
7203 without invoking any metamethod.
7204 <code>table</code> must be a table;
7205 <code>index</code> may be any value.
7206
7207
7208
7209
7210 <p>
7211 <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3>
7212 Returns the length of the object <code>v</code>,
7213 which must be a table or a string,
7214 without invoking any metamethod.
7215 Returns an integer number.
7216
7217
7218
7219
7220 <p>
7221 <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3>
7222 Sets the real value of <code>table[index]</code> to <code>value</code>,
7223 without invoking any metamethod.
7224 <code>table</code> must be a table,
7225 <code>index</code> any value different from <b>nil</b> and NaN,
7226 and <code>value</code> any Lua value.
7227
7228
7229 <p>
7230 This function returns <code>table</code>.
7231
7232
7233
7234
7235 <p>
7236 <hr><h3><a name="pdf-select"><code>select (index, &middot;&middot;&middot;)</code></a></h3>
7237
7238
7239 <p>
7240 If <code>index</code> is a number,
7241 returns all arguments after argument number <code>index</code>;
7242 a negative number indexes from the end (-1 is the last argument).
7243 Otherwise, <code>index</code> must be the string <code>"#"</code>,
7244 and <code>select</code> returns the total number of extra arguments it received.
7245
7246
7247
7248
7249 <p>
7250 <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3>
7251
7252
7253 <p>
7254 Sets the metatable for the given table.
7255 (You cannot change the metatable of other types from Lua, only from&nbsp;C.)
7256 If <code>metatable</code> is <b>nil</b>,
7257 removes the metatable of the given table.
7258 If the original metatable has a <code>"__metatable"</code> field,
7259 raises an error.
7260
7261
7262 <p>
7263 This function returns <code>table</code>.
7264
7265
7266
7267
7268 <p>
7269 <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3>
7270
7271
7272 <p>
7273 When called with no <code>base</code>,
7274 <code>tonumber</code> tries to convert its argument to a number.
7275 If the argument is already a number or
7276 a string convertible to a number (see <a href="#3.4.2">&sect;3.4.2</a>),
7277 then <code>tonumber</code> returns this number;
7278 otherwise, it returns <b>nil</b>.
7279
7280
7281 <p>
7282 When called with <code>base</code>,
7283 then <code>e</code> should be a string to be interpreted as
7284 an integer numeral in that base.
7285 The base may be any integer between 2 and 36, inclusive.
7286 In bases above&nbsp;10, the letter '<code>A</code>' (in either upper or lower case)
7287 represents&nbsp;10, '<code>B</code>' represents&nbsp;11, and so forth,
7288 with '<code>Z</code>' representing 35.
7289 If the string <code>e</code> is not a valid numeral in the given base,
7290 the function returns <b>nil</b>.
7291
7292
7293
7294
7295 <p>
7296 <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3>
7297 Receives a value of any type and
7298 converts it to a string in a reasonable format.
7299 (For complete control of how numbers are converted,
7300 use <a href="#pdf-string.format"><code>string.format</code></a>.)
7301
7302
7303 <p>
7304 If the metatable of <code>v</code> has a <code>"__tostring"</code> field,
7305 then <code>tostring</code> calls the corresponding value
7306 with <code>v</code> as argument,
7307 and uses the result of the call as its result.
7308
7309
7310
7311
7312 <p>
7313 <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3>
7314 Returns the type of its only argument, coded as a string.
7315 The possible results of this function are
7316 "<code>nil</code>" (a string, not the value <b>nil</b>),
7317 "<code>number</code>",
7318 "<code>string</code>",
7319 "<code>boolean</code>",
7320 "<code>table</code>",
7321 "<code>function</code>",
7322 "<code>thread</code>",
7323 and "<code>userdata</code>".
7324
7325
7326
7327
7328 <p>
7329 <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3>
7330 A global variable (not a function) that
7331 holds a string containing the current interpreter version.
7332 The current contents of this variable is "<code>Lua 5.2</code>".
7333
7334
7335
7336
7337 <p>
7338 <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, &middot;&middot;&middot;])</code></a></h3>
7339
7340
7341 <p>
7342 This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>,
7343 except that it sets a new message handler <code>msgh</code>.
7344
7345
7346
7347
7348
7349
7350
7351 <h2>6.2 &ndash; <a name="6.2">Coroutine Manipulation</a></h2>
7352
7353 <p>
7354 The operations related to coroutines comprise a sub-library of
7355 the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
7356 See <a href="#2.6">&sect;2.6</a> for a general description of coroutines.
7357
7358
7359 <p>
7360 <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3>
7361
7362
7363 <p>
7364 Creates a new coroutine, with body <code>f</code>.
7365 <code>f</code> must be a Lua function.
7366 Returns this new coroutine,
7367 an object with type <code>"thread"</code>.
7368
7369
7370
7371
7372 <p>
7373 <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, &middot;&middot;&middot;])</code></a></h3>
7374
7375
7376 <p>
7377 Starts or continues the execution of coroutine <code>co</code>.
7378 The first time you resume a coroutine,
7379 it starts running its body.
7380 The values <code>val1</code>, ... are passed
7381 as the arguments to the body function.
7382 If the coroutine has yielded,
7383 <code>resume</code> restarts it;
7384 the values <code>val1</code>, ... are passed
7385 as the results from the yield.
7386
7387
7388 <p>
7389 If the coroutine runs without any errors,
7390 <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code>
7391 (if the coroutine yields) or any values returned by the body function
7392 (if the coroutine terminates).
7393 If there is any error,
7394 <code>resume</code> returns <b>false</b> plus the error message.
7395
7396
7397
7398
7399 <p>
7400 <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3>
7401
7402
7403 <p>
7404 Returns the running coroutine plus a boolean,
7405 true when the running coroutine is the main one.
7406
7407
7408
7409
7410 <p>
7411 <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3>
7412
7413
7414 <p>
7415 Returns the status of coroutine <code>co</code>, as a string:
7416 <code>"running"</code>,
7417 if the coroutine is running (that is, it called <code>status</code>);
7418 <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>,
7419 or if it has not started running yet;
7420 <code>"normal"</code> if the coroutine is active but not running
7421 (that is, it has resumed another coroutine);
7422 and <code>"dead"</code> if the coroutine has finished its body function,
7423 or if it has stopped with an error.
7424
7425
7426
7427
7428 <p>
7429 <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3>
7430
7431
7432 <p>
7433 Creates a new coroutine, with body <code>f</code>.
7434 <code>f</code> must be a Lua function.
7435 Returns a function that resumes the coroutine each time it is called.
7436 Any arguments passed to the function behave as the
7437 extra arguments to <code>resume</code>.
7438 Returns the same values returned by <code>resume</code>,
7439 except the first boolean.
7440 In case of error, propagates the error.
7441
7442
7443
7444
7445 <p>
7446 <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (&middot;&middot;&middot;)</code></a></h3>
7447
7448
7449 <p>
7450 Suspends the execution of the calling coroutine.
7451 Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>.
7452
7453
7454
7455
7456
7457
7458
7459 <h2>6.3 &ndash; <a name="6.3">Modules</a></h2>
7460
7461 <p>
7462 The package library provides basic
7463 facilities for loading modules in Lua.
7464 It exports one function directly in the global environment:
7465 <a href="#pdf-require"><code>require</code></a>.
7466 Everything else is exported in a table <a name="pdf-package"><code>package</code></a>.
7467
7468
7469 <p>
7470 <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3>
7471
7472
7473 <p>
7474 Loads the given module.
7475 The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
7476 to determine whether <code>modname</code> is already loaded.
7477 If it is, then <code>require</code> returns the value stored
7478 at <code>package.loaded[modname]</code>.
7479 Otherwise, it tries to find a <em>loader</em> for the module.
7480
7481
7482 <p>
7483 To find a loader,
7484 <code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence.
7485 By changing this sequence,
7486 we can change how <code>require</code> looks for a module.
7487 The following explanation is based on the default configuration
7488 for <a href="#pdf-package.searchers"><code>package.searchers</code></a>.
7489
7490
7491 <p>
7492 First <code>require</code> queries <code>package.preload[modname]</code>.
7493 If it has a value,
7494 this value (which should be a function) is the loader.
7495 Otherwise <code>require</code> searches for a Lua loader using the
7496 path stored in <a href="#pdf-package.path"><code>package.path</code></a>.
7497 If that also fails, it searches for a C&nbsp;loader using the
7498 path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7499 If that also fails,
7500 it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>).
7501
7502
7503 <p>
7504 Once a loader is found,
7505 <code>require</code> calls the loader with two arguments:
7506 <code>modname</code> and an extra value dependent on how it got the loader.
7507 (If the loader came from a file,
7508 this extra value is the file name.)
7509 If the loader returns any non-nil value,
7510 <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>.
7511 If the loader does not return a non-nil value and
7512 has not assigned any value to <code>package.loaded[modname]</code>,
7513 then <code>require</code> assigns <b>true</b> to this entry.
7514 In any case, <code>require</code> returns the
7515 final value of <code>package.loaded[modname]</code>.
7516
7517
7518 <p>
7519 If there is any error loading or running the module,
7520 or if it cannot find any loader for the module,
7521 then <code>require</code> raises an error.
7522
7523
7524
7525
7526 <p>
7527 <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3>
7528
7529
7530 <p>
7531 A string describing some compile-time configurations for packages.
7532 This string is a sequence of lines:
7533
7534 <ul>
7535
7536 <li>The first line is the directory separator string.
7537 Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li>
7538
7539 <li>The second line is the character that separates templates in a path.
7540 Default is '<code>;</code>'.</li>
7541
7542 <li>The third line is the string that marks the
7543 substitution points in a template.
7544 Default is '<code>?</code>'.</li>
7545
7546 <li>The fourth line is a string that, in a path in Windows,
7547 is replaced by the executable's directory.
7548 Default is '<code>!</code>'.</li>
7549
7550 <li>The fifth line is a mark to ignore all text before it
7551 when building the <code>luaopen_</code> function name.
7552 Default is '<code>-</code>'.</li>
7553
7554 </ul>
7555
7556
7557
7558 <p>
7559 <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3>
7560
7561
7562 <p>
7563 The path used by <a href="#pdf-require"><code>require</code></a> to search for a C&nbsp;loader.
7564
7565
7566 <p>
7567 Lua initializes the C&nbsp;path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
7568 it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>,
7569 using the environment variable <a name="pdf-LUA_CPATH_5_2"><code>LUA_CPATH_5_2</code></a>
7570 or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>
7571 or a default path defined in <code>luaconf.h</code>.
7572
7573
7574
7575
7576 <p>
7577 <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3>
7578
7579
7580 <p>
7581 A table used by <a href="#pdf-require"><code>require</code></a> to control which
7582 modules are already loaded.
7583 When you require a module <code>modname</code> and
7584 <code>package.loaded[modname]</code> is not false,
7585 <a href="#pdf-require"><code>require</code></a> simply returns the value stored there.
7586
7587
7588 <p>
7589 This variable is only a reference to the real table;
7590 assignments to this variable do not change the
7591 table used by <a href="#pdf-require"><code>require</code></a>.
7592
7593
7594
7595
7596 <p>
7597 <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
7598
7599
7600 <p>
7601 Dynamically links the host program with the C&nbsp;library <code>libname</code>.
7602
7603
7604 <p>
7605 If <code>funcname</code> is "<code>*</code>",
7606 then it only links with the library,
7607 making the symbols exported by the library
7608 available to other dynamically linked libraries.
7609 Otherwise,
7610 it looks for a function <code>funcname</code> inside the library
7611 and returns this function as a C&nbsp;function.
7612 So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype
7613 (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>).
7614
7615
7616 <p>
7617 This is a low-level function.
7618 It completely bypasses the package and module system.
7619 Unlike <a href="#pdf-require"><code>require</code></a>,
7620 it does not perform any path searching and
7621 does not automatically adds extensions.
7622 <code>libname</code> must be the complete file name of the C&nbsp;library,
7623 including if necessary a path and an extension.
7624 <code>funcname</code> must be the exact name exported by the C&nbsp;library
7625 (which may depend on the C&nbsp;compiler and linker used).
7626
7627
7628 <p>
7629 This function is not supported by Standard&nbsp;C.
7630 As such, it is only available on some platforms
7631 (Windows, Linux, Mac OS X, Solaris, BSD,
7632 plus other Unix systems that support the <code>dlfcn</code> standard).
7633
7634
7635
7636
7637 <p>
7638 <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3>
7639
7640
7641 <p>
7642 The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader.
7643
7644
7645 <p>
7646 At start-up, Lua initializes this variable with
7647 the value of the environment variable <a name="pdf-LUA_PATH_5_2"><code>LUA_PATH_5_2</code></a> or
7648 the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or
7649 with a default path defined in <code>luaconf.h</code>,
7650 if those environment variables are not defined.
7651 Any "<code>;;</code>" in the value of the environment variable
7652 is replaced by the default path.
7653
7654
7655
7656
7657 <p>
7658 <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3>
7659
7660
7661 <p>
7662 A table to store loaders for specific modules
7663 (see <a href="#pdf-require"><code>require</code></a>).
7664
7665
7666 <p>
7667 This variable is only a reference to the real table;
7668 assignments to this variable do not change the
7669 table used by <a href="#pdf-require"><code>require</code></a>.
7670
7671
7672
7673
7674 <p>
7675 <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3>
7676
7677
7678 <p>
7679 A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
7680
7681
7682 <p>
7683 Each entry in this table is a <em>searcher function</em>.
7684 When looking for a module,
7685 <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
7686 with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
7687 sole parameter.
7688 The function can return another function (the module <em>loader</em>)
7689 plus an extra value that will be passed to that loader,
7690 or a string explaining why it did not find that module
7691 (or <b>nil</b> if it has nothing to say).
7692
7693
7694 <p>
7695 Lua initializes this table with four searcher functions.
7696
7697
7698 <p>
7699 The first searcher simply looks for a loader in the
7700 <a href="#pdf-package.preload"><code>package.preload</code></a> table.
7701
7702
7703 <p>
7704 The second searcher looks for a loader as a Lua library,
7705 using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>.
7706 The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7707
7708
7709 <p>
7710 The third searcher looks for a loader as a C&nbsp;library,
7711 using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
7712 Again,
7713 the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7714 For instance,
7715 if the C&nbsp;path is the string
7716
7717 <pre>
7718      "./?.so;./?.dll;/usr/local/?/init.so"
7719 </pre><p>
7720 the searcher for module <code>foo</code>
7721 will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>,
7722 and <code>/usr/local/foo/init.so</code>, in that order.
7723 Once it finds a C&nbsp;library,
7724 this searcher first uses a dynamic link facility to link the
7725 application with the library.
7726 Then it tries to find a C&nbsp;function inside the library to
7727 be used as the loader.
7728 The name of this C&nbsp;function is the string "<code>luaopen_</code>"
7729 concatenated with a copy of the module name where each dot
7730 is replaced by an underscore.
7731 Moreover, if the module name has a hyphen,
7732 its prefix up to (and including) the first hyphen is removed.
7733 For instance, if the module name is <code>a.v1-b.c</code>,
7734 the function name will be <code>luaopen_b_c</code>.
7735
7736
7737 <p>
7738 The fourth searcher tries an <em>all-in-one loader</em>.
7739 It searches the C&nbsp;path for a library for
7740 the root name of the given module.
7741 For instance, when requiring <code>a.b.c</code>,
7742 it will search for a C&nbsp;library for <code>a</code>.
7743 If found, it looks into it for an open function for
7744 the submodule;
7745 in our example, that would be <code>luaopen_a_b_c</code>.
7746 With this facility, a package can pack several C&nbsp;submodules
7747 into one single library,
7748 with each submodule keeping its original open function.
7749
7750
7751 <p>
7752 All searchers except the first one (preload) return as the extra value
7753 the file name where the module was found,
7754 as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>.
7755 The first searcher returns no extra value.
7756
7757
7758
7759
7760 <p>
7761 <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3>
7762
7763
7764 <p>
7765 Searches for the given <code>name</code> in the given <code>path</code>.
7766
7767
7768 <p>
7769 A path is a string containing a sequence of
7770 <em>templates</em> separated by semicolons.
7771 For each template,
7772 the function replaces each interrogation mark (if any)
7773 in the template with a copy of <code>name</code>
7774 wherein all occurrences of <code>sep</code>
7775 (a dot, by default)
7776 were replaced by <code>rep</code>
7777 (the system's directory separator, by default),
7778 and then tries to open the resulting file name.
7779
7780
7781 <p>
7782 For instance, if the path is the string
7783
7784 <pre>
7785      "./?.lua;./?.lc;/usr/local/?/init.lua"
7786 </pre><p>
7787 the search for the name <code>foo.a</code>
7788 will try to open the files
7789 <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and
7790 <code>/usr/local/foo/a/init.lua</code>, in that order.
7791
7792
7793 <p>
7794 Returns the resulting name of the first file that it can
7795 open in read mode (after closing the file),
7796 or <b>nil</b> plus an error message if none succeeds.
7797 (This error message lists all file names it tried to open.)
7798
7799
7800
7801
7802
7803
7804
7805 <h2>6.4 &ndash; <a name="6.4">String Manipulation</a></h2>
7806
7807 <p>
7808 This library provides generic functions for string manipulation,
7809 such as finding and extracting substrings, and pattern matching.
7810 When indexing a string in Lua, the first character is at position&nbsp;1
7811 (not at&nbsp;0, as in C).
7812 Indices are allowed to be negative and are interpreted as indexing backwards,
7813 from the end of the string.
7814 Thus, the last character is at position -1, and so on.
7815
7816
7817 <p>
7818 The string library provides all its functions inside the table
7819 <a name="pdf-string"><code>string</code></a>.
7820 It also sets a metatable for strings
7821 where the <code>__index</code> field points to the <code>string</code> table.
7822 Therefore, you can use the string functions in object-oriented style.
7823 For instance, <code>string.byte(s,i)</code>
7824 can be written as <code>s:byte(i)</code>.
7825
7826
7827 <p>
7828 The string library assumes one-byte character encodings.
7829
7830
7831 <p>
7832 <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3>
7833 Returns the internal numerical codes of the characters <code>s[i]</code>,
7834 <code>s[i+1]</code>, ..., <code>s[j]</code>.
7835 The default value for <code>i</code> is&nbsp;1;
7836 the default value for <code>j</code> is&nbsp;<code>i</code>.
7837 These indices are corrected
7838 following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>.
7839
7840
7841 <p>
7842 Numerical codes are not necessarily portable across platforms.
7843
7844
7845
7846
7847 <p>
7848 <hr><h3><a name="pdf-string.char"><code>string.char (&middot;&middot;&middot;)</code></a></h3>
7849 Receives zero or more integers.
7850 Returns a string with length equal to the number of arguments,
7851 in which each character has the internal numerical code equal
7852 to its corresponding argument.
7853
7854
7855 <p>
7856 Numerical codes are not necessarily portable across platforms.
7857
7858
7859
7860
7861 <p>
7862 <hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3>
7863
7864
7865 <p>
7866 Returns a string containing a binary representation of the given function,
7867 so that a later <a href="#pdf-load"><code>load</code></a> on this string returns
7868 a copy of the function (but with new upvalues).
7869
7870
7871
7872
7873 <p>
7874 <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
7875
7876
7877 <p>
7878 Looks for the first match of
7879 <code>pattern</code> in the string <code>s</code>.
7880 If it finds a match, then <code>find</code> returns the indices of&nbsp;<code>s</code>
7881 where this occurrence starts and ends;
7882 otherwise, it returns <b>nil</b>.
7883 A third, optional numerical argument <code>init</code> specifies
7884 where to start the search;
7885 its default value is&nbsp;1 and can be negative.
7886 A value of <b>true</b> as a fourth, optional argument <code>plain</code>
7887 turns off the pattern matching facilities,
7888 so the function does a plain "find substring" operation,
7889 with no characters in <code>pattern</code> being considered magic.
7890 Note that if <code>plain</code> is given, then <code>init</code> must be given as well.
7891
7892
7893 <p>
7894 If the pattern has captures,
7895 then in a successful match
7896 the captured values are also returned,
7897 after the two indices.
7898
7899
7900
7901
7902 <p>
7903 <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, &middot;&middot;&middot;)</code></a></h3>
7904
7905
7906 <p>
7907 Returns a formatted version of its variable number of arguments
7908 following the description given in its first argument (which must be a string).
7909 The format string follows the same rules as the ANSI&nbsp;C function <code>sprintf</code>.
7910 The only differences are that the options/modifiers
7911 <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>,
7912 and <code>p</code> are not supported
7913 and that there is an extra option, <code>q</code>.
7914 The <code>q</code> option formats a string between double quotes,
7915 using escape sequences when necessary to ensure that
7916 it can safely be read back by the Lua interpreter.
7917 For instance, the call
7918
7919 <pre>
7920      string.format('%q', 'a string with "quotes" and \n new line')
7921 </pre><p>
7922 may produce the string:
7923
7924 <pre>
7925      "a string with \"quotes\" and \
7926       new line"
7927 </pre>
7928
7929 <p>
7930 Options
7931 <code>A</code> and <code>a</code> (when available),
7932 <code>E</code>, <code>e</code>, <code>f</code>,
7933 <code>G</code>, and <code>g</code> all expect a number as argument.
7934 Options <code>c</code>, <code>d</code>,
7935 <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>
7936 also expect a number,
7937 but the range of that number may be limited by
7938 the underlying C&nbsp;implementation.
7939 For options <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>,
7940 the number cannot be negative.
7941 Option <code>q</code> expects a string;
7942 option <code>s</code> expects a string without embedded zeros.
7943 If the argument to option <code>s</code> is not a string,
7944 it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>.
7945
7946
7947
7948
7949 <p>
7950 <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3>
7951 Returns an iterator function that,
7952 each time it is called,
7953 returns the next captures from <code>pattern</code> over the string <code>s</code>.
7954 If <code>pattern</code> specifies no captures,
7955 then the whole match is produced in each call.
7956
7957
7958 <p>
7959 As an example, the following loop
7960 will iterate over all the words from string <code>s</code>,
7961 printing one per line:
7962
7963 <pre>
7964      s = "hello world from Lua"
7965      for w in string.gmatch(s, "%a+") do
7966        print(w)
7967      end
7968 </pre><p>
7969 The next example collects all pairs <code>key=value</code> from the
7970 given string into a table:
7971
7972 <pre>
7973      t = {}
7974      s = "from=world, to=Lua"
7975      for k, v in string.gmatch(s, "(%w+)=(%w+)") do
7976        t[k] = v
7977      end
7978 </pre>
7979
7980 <p>
7981 For this function, a caret '<code>^</code>' at the start of a pattern does not
7982 work as an anchor, as this would prevent the iteration.
7983
7984
7985
7986
7987 <p>
7988 <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3>
7989 Returns a copy of <code>s</code>
7990 in which all (or the first <code>n</code>, if given)
7991 occurrences of the <code>pattern</code> have been
7992 replaced by a replacement string specified by <code>repl</code>,
7993 which can be a string, a table, or a function.
7994 <code>gsub</code> also returns, as its second value,
7995 the total number of matches that occurred.
7996 The name <code>gsub</code> comes from <em>Global SUBstitution</em>.
7997
7998
7999 <p>
8000 If <code>repl</code> is a string, then its value is used for replacement.
8001 The character&nbsp;<code>%</code> works as an escape character:
8002 any sequence in <code>repl</code> of the form <code>%<em>d</em></code>,
8003 with <em>d</em> between 1 and 9,
8004 stands for the value of the <em>d</em>-th captured substring.
8005 The sequence <code>%0</code> stands for the whole match.
8006 The sequence <code>%%</code> stands for a single&nbsp;<code>%</code>.
8007
8008
8009 <p>
8010 If <code>repl</code> is a table, then the table is queried for every match,
8011 using the first capture as the key.
8012
8013
8014 <p>
8015 If <code>repl</code> is a function, then this function is called every time a
8016 match occurs, with all captured substrings passed as arguments,
8017 in order.
8018
8019
8020 <p>
8021 In any case,
8022 if the pattern specifies no captures,
8023 then it behaves as if the whole pattern was inside a capture.
8024
8025
8026 <p>
8027 If the value returned by the table query or by the function call
8028 is a string or a number,
8029 then it is used as the replacement string;
8030 otherwise, if it is <b>false</b> or <b>nil</b>,
8031 then there is no replacement
8032 (that is, the original match is kept in the string).
8033
8034
8035 <p>
8036 Here are some examples:
8037
8038 <pre>
8039      x = string.gsub("hello world", "(%w+)", "%1 %1")
8040      --&gt; x="hello hello world world"
8041
8042      x = string.gsub("hello world", "%w+", "%0 %0", 1)
8043      --&gt; x="hello hello world"
8044
8045      x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
8046      --&gt; x="world hello Lua from"
8047
8048      x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
8049      --&gt; x="home = /home/roberto, user = roberto"
8050
8051      x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
8052            return load(s)()
8053          end)
8054      --&gt; x="4+5 = 9"
8055
8056      local t = {name="lua", version="5.2"}
8057      x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
8058      --&gt; x="lua-5.2.tar.gz"
8059 </pre>
8060
8061
8062
8063 <p>
8064 <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3>
8065 Receives a string and returns its length.
8066 The empty string <code>""</code> has length 0.
8067 Embedded zeros are counted,
8068 so <code>"a\000bc\000"</code> has length 5.
8069
8070
8071
8072
8073 <p>
8074 <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3>
8075 Receives a string and returns a copy of this string with all
8076 uppercase letters changed to lowercase.
8077 All other characters are left unchanged.
8078 The definition of what an uppercase letter is depends on the current locale.
8079
8080
8081
8082
8083 <p>
8084 <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3>
8085 Looks for the first <em>match</em> of
8086 <code>pattern</code> in the string <code>s</code>.
8087 If it finds one, then <code>match</code> returns
8088 the captures from the pattern;
8089 otherwise it returns <b>nil</b>.
8090 If <code>pattern</code> specifies no captures,
8091 then the whole match is returned.
8092 A third, optional numerical argument <code>init</code> specifies
8093 where to start the search;
8094 its default value is&nbsp;1 and can be negative.
8095
8096
8097
8098
8099 <p>
8100 <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3>
8101 Returns a string that is the concatenation of <code>n</code> copies of
8102 the string <code>s</code> separated by the string <code>sep</code>.
8103 The default value for <code>sep</code> is the empty string
8104 (that is, no separator).
8105
8106
8107
8108
8109 <p>
8110 <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3>
8111 Returns a string that is the string <code>s</code> reversed.
8112
8113
8114
8115
8116 <p>
8117 <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3>
8118 Returns the substring of <code>s</code> that
8119 starts at <code>i</code>  and continues until <code>j</code>;
8120 <code>i</code> and <code>j</code> can be negative.
8121 If <code>j</code> is absent, then it is assumed to be equal to -1
8122 (which is the same as the string length).
8123 In particular,
8124 the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code>
8125 with length <code>j</code>,
8126 and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code>
8127 with length <code>i</code>.
8128
8129
8130 <p>
8131 If, after the translation of negative indices,
8132 <code>i</code> is less than 1,
8133 it is corrected to 1.
8134 If <code>j</code> is greater than the string length,
8135 it is corrected to that length.
8136 If, after these corrections,
8137 <code>i</code> is greater than <code>j</code>,
8138 the function returns the empty string.
8139
8140
8141
8142
8143 <p>
8144 <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3>
8145 Receives a string and returns a copy of this string with all
8146 lowercase letters changed to uppercase.
8147 All other characters are left unchanged.
8148 The definition of what a lowercase letter is depends on the current locale.
8149
8150
8151
8152 <h3>6.4.1 &ndash; <a name="6.4.1">Patterns</a></h3>
8153
8154
8155 <h4>Character Class:</h4><p>
8156 A <em>character class</em> is used to represent a set of characters.
8157 The following combinations are allowed in describing a character class:
8158
8159 <ul>
8160
8161 <li><b><em>x</em>: </b>
8162 (where <em>x</em> is not one of the <em>magic characters</em>
8163 <code>^$()%.[]*+-?</code>)
8164 represents the character <em>x</em> itself.
8165 </li>
8166
8167 <li><b><code>.</code>: </b> (a dot) represents all characters.</li>
8168
8169 <li><b><code>%a</code>: </b> represents all letters.</li>
8170
8171 <li><b><code>%c</code>: </b> represents all control characters.</li>
8172
8173 <li><b><code>%d</code>: </b> represents all digits.</li>
8174
8175 <li><b><code>%g</code>: </b> represents all printable characters except space.</li>
8176
8177 <li><b><code>%l</code>: </b> represents all lowercase letters.</li>
8178
8179 <li><b><code>%p</code>: </b> represents all punctuation characters.</li>
8180
8181 <li><b><code>%s</code>: </b> represents all space characters.</li>
8182
8183 <li><b><code>%u</code>: </b> represents all uppercase letters.</li>
8184
8185 <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li>
8186
8187 <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li>
8188
8189 <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character)
8190 represents the character <em>x</em>.
8191 This is the standard way to escape the magic characters.
8192 Any punctuation character (even the non magic)
8193 can be preceded by a '<code>%</code>'
8194 when used to represent itself in a pattern.
8195 </li>
8196
8197 <li><b><code>[<em>set</em>]</code>: </b>
8198 represents the class which is the union of all
8199 characters in <em>set</em>.
8200 A range of characters can be specified by
8201 separating the end characters of the range,
8202 in ascending order, with a '<code>-</code>',
8203 All classes <code>%</code><em>x</em> described above can also be used as
8204 components in <em>set</em>.
8205 All other characters in <em>set</em> represent themselves.
8206 For example, <code>[%w_]</code> (or <code>[_%w]</code>)
8207 represents all alphanumeric characters plus the underscore,
8208 <code>[0-7]</code> represents the octal digits,
8209 and <code>[0-7%l%-]</code> represents the octal digits plus
8210 the lowercase letters plus the '<code>-</code>' character.
8211
8212
8213 <p>
8214 The interaction between ranges and classes is not defined.
8215 Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code>
8216 have no meaning.
8217 </li>
8218
8219 <li><b><code>[^<em>set</em>]</code>: </b>
8220 represents the complement of <em>set</em>,
8221 where <em>set</em> is interpreted as above.
8222 </li>
8223
8224 </ul><p>
8225 For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.),
8226 the corresponding uppercase letter represents the complement of the class.
8227 For instance, <code>%S</code> represents all non-space characters.
8228
8229
8230 <p>
8231 The definitions of letter, space, and other character groups
8232 depend on the current locale.
8233 In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>.
8234
8235
8236
8237
8238
8239 <h4>Pattern Item:</h4><p>
8240 A <em>pattern item</em> can be
8241
8242 <ul>
8243
8244 <li>
8245 a single character class,
8246 which matches any single character in the class;
8247 </li>
8248
8249 <li>
8250 a single character class followed by '<code>*</code>',
8251 which matches 0 or more repetitions of characters in the class.
8252 These repetition items will always match the longest possible sequence;
8253 </li>
8254
8255 <li>
8256 a single character class followed by '<code>+</code>',
8257 which matches 1 or more repetitions of characters in the class.
8258 These repetition items will always match the longest possible sequence;
8259 </li>
8260
8261 <li>
8262 a single character class followed by '<code>-</code>',
8263 which also matches 0 or more repetitions of characters in the class.
8264 Unlike '<code>*</code>',
8265 these repetition items will always match the shortest possible sequence;
8266 </li>
8267
8268 <li>
8269 a single character class followed by '<code>?</code>',
8270 which matches 0 or 1 occurrence of a character in the class;
8271 </li>
8272
8273 <li>
8274 <code>%<em>n</em></code>, for <em>n</em> between 1 and 9;
8275 such item matches a substring equal to the <em>n</em>-th captured string
8276 (see below);
8277 </li>
8278
8279 <li>
8280 <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters;
8281 such item matches strings that start with&nbsp;<em>x</em>, end with&nbsp;<em>y</em>,
8282 and where the <em>x</em> and <em>y</em> are <em>balanced</em>.
8283 This means that, if one reads the string from left to right,
8284 counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>,
8285 the ending <em>y</em> is the first <em>y</em> where the count reaches 0.
8286 For instance, the item <code>%b()</code> matches expressions with
8287 balanced parentheses.
8288 </li>
8289
8290 <li>
8291 <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>;
8292 such item matches an empty string at any position such that
8293 the next character belongs to <em>set</em>
8294 and the previous character does not belong to <em>set</em>.
8295 The set <em>set</em> is interpreted as previously described.
8296 The beginning and the end of the subject are handled as if
8297 they were the character '<code>\0</code>'.
8298 </li>
8299
8300 </ul>
8301
8302
8303
8304
8305 <h4>Pattern:</h4><p>
8306 A <em>pattern</em> is a sequence of pattern items.
8307 A caret '<code>^</code>' at the beginning of a pattern anchors the match at the
8308 beginning of the subject string.
8309 A '<code>$</code>' at the end of a pattern anchors the match at the
8310 end of the subject string.
8311 At other positions,
8312 '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves.
8313
8314
8315
8316
8317
8318 <h4>Captures:</h4><p>
8319 A pattern can contain sub-patterns enclosed in parentheses;
8320 they describe <em>captures</em>.
8321 When a match succeeds, the substrings of the subject string
8322 that match captures are stored (<em>captured</em>) for future use.
8323 Captures are numbered according to their left parentheses.
8324 For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>,
8325 the part of the string matching <code>"a*(.)%w(%s*)"</code> is
8326 stored as the first capture (and therefore has number&nbsp;1);
8327 the character matching "<code>.</code>" is captured with number&nbsp;2,
8328 and the part matching "<code>%s*</code>" has number&nbsp;3.
8329
8330
8331 <p>
8332 As a special case, the empty capture <code>()</code> captures
8333 the current string position (a number).
8334 For instance, if we apply the pattern <code>"()aa()"</code> on the
8335 string <code>"flaaap"</code>, there will be two captures: 3&nbsp;and&nbsp;5.
8336
8337
8338
8339
8340
8341
8342
8343
8344
8345
8346
8347 <h2>6.5 &ndash; <a name="6.5">Table Manipulation</a></h2>
8348
8349 <p>
8350 This library provides generic functions for table manipulation.
8351 It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>.
8352
8353
8354 <p>
8355 Remember that, whenever an operation needs the length of a table,
8356 the table should be a proper sequence
8357 or have a <code>__len</code> metamethod (see <a href="#3.4.6">&sect;3.4.6</a>).
8358 All functions ignore non-numeric keys
8359 in tables given as arguments.
8360
8361
8362 <p>
8363 For performance reasons,
8364 all table accesses (get/set) performed by these functions are raw.
8365
8366
8367 <p>
8368 <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3>
8369
8370
8371 <p>
8372 Given a list where all elements are strings or numbers,
8373 returns the string <code>list[i]..sep..list[i+1] &middot;&middot;&middot; sep..list[j]</code>.
8374 The default value for <code>sep</code> is the empty string,
8375 the default for <code>i</code> is 1,
8376 and the default for <code>j</code> is <code>#list</code>.
8377 If <code>i</code> is greater than <code>j</code>, returns the empty string.
8378
8379
8380
8381
8382 <p>
8383 <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3>
8384
8385
8386 <p>
8387 Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>,
8388 shifting up the elements
8389 <code>list[pos], list[pos+1], &middot;&middot;&middot;, list[#list]</code>.
8390 The default value for <code>pos</code> is <code>#list+1</code>,
8391 so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end
8392 of list <code>t</code>.
8393
8394
8395
8396
8397 <p>
8398 <hr><h3><a name="pdf-table.pack"><code>table.pack (&middot;&middot;&middot;)</code></a></h3>
8399
8400
8401 <p>
8402 Returns a new table with all parameters stored into keys 1, 2, etc.
8403 and with a field "<code>n</code>" with the total number of parameters.
8404 Note that the resulting table may not be a sequence.
8405
8406
8407
8408
8409 <p>
8410 <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3>
8411
8412
8413 <p>
8414 Removes from <code>list</code> the element at position <code>pos</code>,
8415 returning the value of the removed element.
8416 When <code>pos</code> is an integer between 1 and <code>#list</code>,
8417 it shifts down the elements
8418 <code>list[pos+1], list[pos+2], &middot;&middot;&middot;, list[#list]</code>
8419 and erases element <code>list[#list]</code>;
8420 The index <code>pos</code> can also be 0 when <code>#list</code> is 0,
8421 or <code>#list + 1</code>;
8422 in those cases, the function erases the element <code>list[pos]</code>.
8423
8424
8425 <p>
8426 The default value for <code>pos</code> is <code>#list</code>,
8427 so that a call <code>table.remove(t)</code> removes the last element
8428 of list <code>t</code>.
8429
8430
8431
8432
8433 <p>
8434 <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3>
8435
8436
8437 <p>
8438 Sorts list elements in a given order, <em>in-place</em>,
8439 from <code>list[1]</code> to <code>list[#list]</code>.
8440 If <code>comp</code> is given,
8441 then it must be a function that receives two list elements
8442 and returns true when the first element must come
8443 before the second in the final order
8444 (so that <code>not comp(list[i+1],list[i])</code> will be true after the sort).
8445 If <code>comp</code> is not given,
8446 then the standard Lua operator <code>&lt;</code> is used instead.
8447
8448
8449 <p>
8450 The sort algorithm is not stable;
8451 that is, elements considered equal by the given order
8452 may have their relative positions changed by the sort.
8453
8454
8455
8456
8457 <p>
8458 <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3>
8459
8460
8461 <p>
8462 Returns the elements from the given table.
8463 This function is equivalent to
8464
8465 <pre>
8466      return list[i], list[i+1], &middot;&middot;&middot;, list[j]
8467 </pre><p>
8468 By default, <code>i</code> is&nbsp;1 and <code>j</code> is <code>#list</code>.
8469
8470
8471
8472
8473
8474
8475
8476 <h2>6.6 &ndash; <a name="6.6">Mathematical Functions</a></h2>
8477
8478 <p>
8479 This library is an interface to the standard C&nbsp;math library.
8480 It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>.
8481
8482
8483 <p>
8484 <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3>
8485
8486
8487 <p>
8488 Returns the absolute value of <code>x</code>.
8489
8490
8491
8492
8493 <p>
8494 <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3>
8495
8496
8497 <p>
8498 Returns the arc cosine of <code>x</code> (in radians).
8499
8500
8501
8502
8503 <p>
8504 <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3>
8505
8506
8507 <p>
8508 Returns the arc sine of <code>x</code> (in radians).
8509
8510
8511
8512
8513 <p>
8514 <hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3>
8515
8516
8517 <p>
8518 Returns the arc tangent of <code>x</code> (in radians).
8519
8520
8521
8522
8523 <p>
8524 <hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3>
8525
8526
8527 <p>
8528 Returns the arc tangent of <code>y/x</code> (in radians),
8529 but uses the signs of both parameters to find the
8530 quadrant of the result.
8531 (It also handles correctly the case of <code>x</code> being zero.)
8532
8533
8534
8535
8536 <p>
8537 <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3>
8538
8539
8540 <p>
8541 Returns the smallest integer larger than or equal to <code>x</code>.
8542
8543
8544
8545
8546 <p>
8547 <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3>
8548
8549
8550 <p>
8551 Returns the cosine of <code>x</code> (assumed to be in radians).
8552
8553
8554
8555
8556 <p>
8557 <hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3>
8558
8559
8560 <p>
8561 Returns the hyperbolic cosine of <code>x</code>.
8562
8563
8564
8565
8566 <p>
8567 <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3>
8568
8569
8570 <p>
8571 Returns the angle <code>x</code> (given in radians) in degrees.
8572
8573
8574
8575
8576 <p>
8577 <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3>
8578
8579
8580 <p>
8581 Returns the value <em>e<sup>x</sup></em>.
8582
8583
8584
8585
8586 <p>
8587 <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3>
8588
8589
8590 <p>
8591 Returns the largest integer smaller than or equal to <code>x</code>.
8592
8593
8594
8595
8596 <p>
8597 <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3>
8598
8599
8600 <p>
8601 Returns the remainder of the division of <code>x</code> by <code>y</code>
8602 that rounds the quotient towards zero.
8603
8604
8605
8606
8607 <p>
8608 <hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3>
8609
8610
8611 <p>
8612 Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>,
8613 <code>e</code> is an integer and the absolute value of <code>m</code> is
8614 in the range <em>[0.5, 1)</em>
8615 (or zero when <code>x</code> is zero).
8616
8617
8618
8619
8620 <p>
8621 <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3>
8622
8623
8624 <p>
8625 The value <code>HUGE_VAL</code>,
8626 a value larger than or equal to any other numerical value.
8627
8628
8629
8630
8631 <p>
8632 <hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3>
8633
8634
8635 <p>
8636 Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer).
8637
8638
8639
8640
8641 <p>
8642 <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3>
8643
8644
8645 <p>
8646 Returns the logarithm of <code>x</code> in the given base.
8647 The default for <code>base</code> is <em>e</em>
8648 (so that the function returns the natural logarithm of <code>x</code>).
8649
8650
8651
8652
8653 <p>
8654 <hr><h3><a name="pdf-math.max"><code>math.max (x, &middot;&middot;&middot;)</code></a></h3>
8655
8656
8657 <p>
8658 Returns the maximum value among its arguments.
8659
8660
8661
8662
8663 <p>
8664 <hr><h3><a name="pdf-math.min"><code>math.min (x, &middot;&middot;&middot;)</code></a></h3>
8665
8666
8667 <p>
8668 Returns the minimum value among its arguments.
8669
8670
8671
8672
8673 <p>
8674 <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3>
8675
8676
8677 <p>
8678 Returns two numbers,
8679 the integral part of <code>x</code> and the fractional part of <code>x</code>.
8680
8681
8682
8683
8684 <p>
8685 <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3>
8686
8687
8688 <p>
8689 The value of <em>&pi;</em>.
8690
8691
8692
8693
8694 <p>
8695 <hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3>
8696
8697
8698 <p>
8699 Returns <em>x<sup>y</sup></em>.
8700 (You can also use the expression <code>x^y</code> to compute this value.)
8701
8702
8703
8704
8705 <p>
8706 <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3>
8707
8708
8709 <p>
8710 Returns the angle <code>x</code> (given in degrees) in radians.
8711
8712
8713
8714
8715 <p>
8716 <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3>
8717
8718
8719 <p>
8720 This function is an interface to the simple
8721 pseudo-random generator function <code>rand</code> provided by Standard&nbsp;C.
8722 (No guarantees can be given for its statistical properties.)
8723
8724
8725 <p>
8726 When called without arguments,
8727 returns a uniform pseudo-random real number
8728 in the range <em>[0,1)</em>.
8729 When called with an integer number <code>m</code>,
8730 <code>math.random</code> returns
8731 a uniform pseudo-random integer in the range <em>[1, m]</em>.
8732 When called with two integer numbers <code>m</code> and <code>n</code>,
8733 <code>math.random</code> returns a uniform pseudo-random
8734 integer in the range <em>[m, n]</em>.
8735
8736
8737
8738
8739 <p>
8740 <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3>
8741
8742
8743 <p>
8744 Sets <code>x</code> as the "seed"
8745 for the pseudo-random generator:
8746 equal seeds produce equal sequences of numbers.
8747
8748
8749
8750
8751 <p>
8752 <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3>
8753
8754
8755 <p>
8756 Returns the sine of <code>x</code> (assumed to be in radians).
8757
8758
8759
8760
8761 <p>
8762 <hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3>
8763
8764
8765 <p>
8766 Returns the hyperbolic sine of <code>x</code>.
8767
8768
8769
8770
8771 <p>
8772 <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3>
8773
8774
8775 <p>
8776 Returns the square root of <code>x</code>.
8777 (You can also use the expression <code>x^0.5</code> to compute this value.)
8778
8779
8780
8781
8782 <p>
8783 <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3>
8784
8785
8786 <p>
8787 Returns the tangent of <code>x</code> (assumed to be in radians).
8788
8789
8790
8791
8792 <p>
8793 <hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3>
8794
8795
8796 <p>
8797 Returns the hyperbolic tangent of <code>x</code>.
8798
8799
8800
8801
8802
8803
8804
8805 <h2>6.7 &ndash; <a name="6.7">Bitwise Operations</a></h2>
8806
8807 <p>
8808 This library provides bitwise operations.
8809 It provides all its functions inside the table <a name="pdf-bit32"><code>bit32</code></a>.
8810
8811
8812 <p>
8813 Unless otherwise stated,
8814 all functions accept numeric arguments in the range
8815 <em>(-2<sup>51</sup>,+2<sup>51</sup>)</em>;
8816 each argument is normalized to
8817 the remainder of its division by <em>2<sup>32</sup></em>
8818 and truncated to an integer (in some unspecified way),
8819 so that its final value falls in the range <em>[0,2<sup>32</sup> - 1]</em>.
8820 Similarly, all results are in the range <em>[0,2<sup>32</sup> - 1]</em>.
8821 Note that <code>bit32.bnot(0)</code> is <code>0xFFFFFFFF</code>,
8822 which is different from <code>-1</code>.
8823
8824
8825 <p>
8826 <hr><h3><a name="pdf-bit32.arshift"><code>bit32.arshift (x, disp)</code></a></h3>
8827
8828
8829 <p>
8830 Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
8831 The number <code>disp</code> may be any representable integer.
8832 Negative displacements shift to the left.
8833
8834
8835 <p>
8836 This shift operation is what is called arithmetic shift.
8837 Vacant bits on the left are filled
8838 with copies of the higher bit of <code>x</code>;
8839 vacant bits on the right are filled with zeros.
8840 In particular,
8841 displacements with absolute values higher than 31
8842 result in zero or <code>0xFFFFFFFF</code> (all original bits are shifted out).
8843
8844
8845
8846
8847 <p>
8848 <hr><h3><a name="pdf-bit32.band"><code>bit32.band (&middot;&middot;&middot;)</code></a></h3>
8849
8850
8851 <p>
8852 Returns the bitwise <em>and</em> of its operands.
8853
8854
8855
8856
8857 <p>
8858 <hr><h3><a name="pdf-bit32.bnot"><code>bit32.bnot (x)</code></a></h3>
8859
8860
8861 <p>
8862 Returns the bitwise negation of <code>x</code>.
8863 For any integer <code>x</code>,
8864 the following identity holds:
8865
8866 <pre>
8867      assert(bit32.bnot(x) == (-1 - x) % 2^32)
8868 </pre>
8869
8870
8871
8872 <p>
8873 <hr><h3><a name="pdf-bit32.bor"><code>bit32.bor (&middot;&middot;&middot;)</code></a></h3>
8874
8875
8876 <p>
8877 Returns the bitwise <em>or</em> of its operands.
8878
8879
8880
8881
8882 <p>
8883 <hr><h3><a name="pdf-bit32.btest"><code>bit32.btest (&middot;&middot;&middot;)</code></a></h3>
8884
8885
8886 <p>
8887 Returns a boolean signaling
8888 whether the bitwise <em>and</em> of its operands is different from zero.
8889
8890
8891
8892
8893 <p>
8894 <hr><h3><a name="pdf-bit32.bxor"><code>bit32.bxor (&middot;&middot;&middot;)</code></a></h3>
8895
8896
8897 <p>
8898 Returns the bitwise <em>exclusive or</em> of its operands.
8899
8900
8901
8902
8903 <p>
8904 <hr><h3><a name="pdf-bit32.extract"><code>bit32.extract (n, field [, width])</code></a></h3>
8905
8906
8907 <p>
8908 Returns the unsigned number formed by the bits
8909 <code>field</code> to <code>field + width - 1</code> from <code>n</code>.
8910 Bits are numbered from 0 (least significant) to 31 (most significant).
8911 All accessed bits must be in the range <em>[0, 31]</em>.
8912
8913
8914 <p>
8915 The default for <code>width</code> is 1.
8916
8917
8918
8919
8920 <p>
8921 <hr><h3><a name="pdf-bit32.replace"><code>bit32.replace (n, v, field [, width])</code></a></h3>
8922
8923
8924 <p>
8925 Returns a copy of <code>n</code> with
8926 the bits <code>field</code> to <code>field + width - 1</code>
8927 replaced by the value <code>v</code>.
8928 See <a href="#pdf-bit32.extract"><code>bit32.extract</code></a> for details about <code>field</code> and <code>width</code>.
8929
8930
8931
8932
8933 <p>
8934 <hr><h3><a name="pdf-bit32.lrotate"><code>bit32.lrotate (x, disp)</code></a></h3>
8935
8936
8937 <p>
8938 Returns the number <code>x</code> rotated <code>disp</code> bits to the left.
8939 The number <code>disp</code> may be any representable integer.
8940
8941
8942 <p>
8943 For any valid displacement,
8944 the following identity holds:
8945
8946 <pre>
8947      assert(bit32.lrotate(x, disp) == bit32.lrotate(x, disp % 32))
8948 </pre><p>
8949 In particular,
8950 negative displacements rotate to the right.
8951
8952
8953
8954
8955 <p>
8956 <hr><h3><a name="pdf-bit32.lshift"><code>bit32.lshift (x, disp)</code></a></h3>
8957
8958
8959 <p>
8960 Returns the number <code>x</code> shifted <code>disp</code> bits to the left.
8961 The number <code>disp</code> may be any representable integer.
8962 Negative displacements shift to the right.
8963 In any direction, vacant bits are filled with zeros.
8964 In particular,
8965 displacements with absolute values higher than 31
8966 result in zero (all bits are shifted out).
8967
8968
8969 <p>
8970 For positive displacements,
8971 the following equality holds:
8972
8973 <pre>
8974      assert(bit32.lshift(b, disp) == (b * 2^disp) % 2^32)
8975 </pre>
8976
8977
8978
8979 <p>
8980 <hr><h3><a name="pdf-bit32.rrotate"><code>bit32.rrotate (x, disp)</code></a></h3>
8981
8982
8983 <p>
8984 Returns the number <code>x</code> rotated <code>disp</code> bits to the right.
8985 The number <code>disp</code> may be any representable integer.
8986
8987
8988 <p>
8989 For any valid displacement,
8990 the following identity holds:
8991
8992 <pre>
8993      assert(bit32.rrotate(x, disp) == bit32.rrotate(x, disp % 32))
8994 </pre><p>
8995 In particular,
8996 negative displacements rotate to the left.
8997
8998
8999
9000
9001 <p>
9002 <hr><h3><a name="pdf-bit32.rshift"><code>bit32.rshift (x, disp)</code></a></h3>
9003
9004
9005 <p>
9006 Returns the number <code>x</code> shifted <code>disp</code> bits to the right.
9007 The number <code>disp</code> may be any representable integer.
9008 Negative displacements shift to the left.
9009 In any direction, vacant bits are filled with zeros.
9010 In particular,
9011 displacements with absolute values higher than 31
9012 result in zero (all bits are shifted out).
9013
9014
9015 <p>
9016 For positive displacements,
9017 the following equality holds:
9018
9019 <pre>
9020      assert(bit32.rshift(b, disp) == math.floor(b % 2^32 / 2^disp))
9021 </pre>
9022
9023 <p>
9024 This shift operation is what is called logical shift.
9025
9026
9027
9028
9029
9030
9031
9032 <h2>6.8 &ndash; <a name="6.8">Input and Output Facilities</a></h2>
9033
9034 <p>
9035 The I/O library provides two different styles for file manipulation.
9036 The first one uses implicit file descriptors;
9037 that is, there are operations to set a default input file and a
9038 default output file,
9039 and all input/output operations are over these default files.
9040 The second style uses explicit file descriptors.
9041
9042
9043 <p>
9044 When using implicit file descriptors,
9045 all operations are supplied by table <a name="pdf-io"><code>io</code></a>.
9046 When using explicit file descriptors,
9047 the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor
9048 and then all operations are supplied as methods of the file descriptor.
9049
9050
9051 <p>
9052 The table <code>io</code> also provides
9053 three predefined file descriptors with their usual meanings from C:
9054 <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>.
9055 The I/O library never closes these files.
9056
9057
9058 <p>
9059 Unless otherwise stated,
9060 all I/O functions return <b>nil</b> on failure
9061 (plus an error message as a second result and
9062 a system-dependent error code as a third result)
9063 and some value different from <b>nil</b> on success.
9064 On non-Posix systems,
9065 the computation of the error message and error code
9066 in case of errors
9067 may be not thread safe,
9068 because they rely on the global C variable <code>errno</code>.
9069
9070
9071 <p>
9072 <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3>
9073
9074
9075 <p>
9076 Equivalent to <code>file:close()</code>.
9077 Without a <code>file</code>, closes the default output file.
9078
9079
9080
9081
9082 <p>
9083 <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3>
9084
9085
9086 <p>
9087 Equivalent to <code>io.output():flush()</code>.
9088
9089
9090
9091
9092 <p>
9093 <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3>
9094
9095
9096 <p>
9097 When called with a file name, it opens the named file (in text mode),
9098 and sets its handle as the default input file.
9099 When called with a file handle,
9100 it simply sets this file handle as the default input file.
9101 When called without parameters,
9102 it returns the current default input file.
9103
9104
9105 <p>
9106 In case of errors this function raises the error,
9107 instead of returning an error code.
9108
9109
9110
9111
9112 <p>
9113 <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename &middot;&middot;&middot;])</code></a></h3>
9114
9115
9116 <p>
9117 Opens the given file name in read mode
9118 and returns an iterator function that
9119 works like <code>file:lines(&middot;&middot;&middot;)</code> over the opened file.
9120 When the iterator function detects the end of file,
9121 it returns <b>nil</b> (to finish the loop) and automatically closes the file.
9122
9123
9124 <p>
9125 The call <code>io.lines()</code> (with no file name) is equivalent
9126 to <code>io.input():lines()</code>;
9127 that is, it iterates over the lines of the default input file.
9128 In this case it does not close the file when the loop ends.
9129
9130
9131 <p>
9132 In case of errors this function raises the error,
9133 instead of returning an error code.
9134
9135
9136
9137
9138 <p>
9139 <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3>
9140
9141
9142 <p>
9143 This function opens a file,
9144 in the mode specified in the string <code>mode</code>.
9145 It returns a new file handle,
9146 or, in case of errors, <b>nil</b> plus an error message.
9147
9148
9149 <p>
9150 The <code>mode</code> string can be any of the following:
9151
9152 <ul>
9153 <li><b>"<code>r</code>": </b> read mode (the default);</li>
9154 <li><b>"<code>w</code>": </b> write mode;</li>
9155 <li><b>"<code>a</code>": </b> append mode;</li>
9156 <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li>
9157 <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li>
9158 <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved,
9159   writing is only allowed at the end of file.</li>
9160 </ul><p>
9161 The <code>mode</code> string can also have a '<code>b</code>' at the end,
9162 which is needed in some systems to open the file in binary mode.
9163
9164
9165
9166
9167 <p>
9168 <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3>
9169
9170
9171 <p>
9172 Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
9173
9174
9175
9176
9177 <p>
9178 <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3>
9179
9180
9181 <p>
9182 This function is system dependent and is not available
9183 on all platforms.
9184
9185
9186 <p>
9187 Starts program <code>prog</code> in a separated process and returns
9188 a file handle that you can use to read data from this program
9189 (if <code>mode</code> is <code>"r"</code>, the default)
9190 or to write data to this program
9191 (if <code>mode</code> is <code>"w"</code>).
9192
9193
9194
9195
9196 <p>
9197 <hr><h3><a name="pdf-io.read"><code>io.read (&middot;&middot;&middot;)</code></a></h3>
9198
9199
9200 <p>
9201 Equivalent to <code>io.input():read(&middot;&middot;&middot;)</code>.
9202
9203
9204
9205
9206 <p>
9207 <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3>
9208
9209
9210 <p>
9211 Returns a handle for a temporary file.
9212 This file is opened in update mode
9213 and it is automatically removed when the program ends.
9214
9215
9216
9217
9218 <p>
9219 <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3>
9220
9221
9222 <p>
9223 Checks whether <code>obj</code> is a valid file handle.
9224 Returns the string <code>"file"</code> if <code>obj</code> is an open file handle,
9225 <code>"closed file"</code> if <code>obj</code> is a closed file handle,
9226 or <b>nil</b> if <code>obj</code> is not a file handle.
9227
9228
9229
9230
9231 <p>
9232 <hr><h3><a name="pdf-io.write"><code>io.write (&middot;&middot;&middot;)</code></a></h3>
9233
9234
9235 <p>
9236 Equivalent to <code>io.output():write(&middot;&middot;&middot;)</code>.
9237
9238
9239
9240
9241 <p>
9242 <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3>
9243
9244
9245 <p>
9246 Closes <code>file</code>.
9247 Note that files are automatically closed when
9248 their handles are garbage collected,
9249 but that takes an unpredictable amount of time to happen.
9250
9251
9252 <p>
9253 When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>,
9254 <a href="#pdf-file:close"><code>file:close</code></a> returns the same values
9255 returned by <a href="#pdf-os.execute"><code>os.execute</code></a>.
9256
9257
9258
9259
9260 <p>
9261 <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3>
9262
9263
9264 <p>
9265 Saves any written data to <code>file</code>.
9266
9267
9268
9269
9270 <p>
9271 <hr><h3><a name="pdf-file:lines"><code>file:lines (&middot;&middot;&middot;)</code></a></h3>
9272
9273
9274 <p>
9275 Returns an iterator function that,
9276 each time it is called,
9277 reads the file according to the given formats.
9278 When no format is given,
9279 uses "*l" as a default.
9280 As an example, the construction
9281
9282 <pre>
9283      for c in file:lines(1) do <em>body</em> end
9284 </pre><p>
9285 will iterate over all characters of the file,
9286 starting at the current position.
9287 Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
9288 when the loop ends.
9289
9290
9291 <p>
9292 In case of errors this function raises the error,
9293 instead of returning an error code.
9294
9295
9296
9297
9298 <p>
9299 <hr><h3><a name="pdf-file:read"><code>file:read (&middot;&middot;&middot;)</code></a></h3>
9300
9301
9302 <p>
9303 Reads the file <code>file</code>,
9304 according to the given formats, which specify what to read.
9305 For each format,
9306 the function returns a string (or a number) with the characters read,
9307 or <b>nil</b> if it cannot read data with the specified format.
9308 When called without formats,
9309 it uses a default format that reads the next line
9310 (see below).
9311
9312
9313 <p>
9314 The available formats are
9315
9316 <ul>
9317
9318 <li><b>"<code>*n</code>": </b>
9319 reads a number;
9320 this is the only format that returns a number instead of a string.
9321 </li>
9322
9323 <li><b>"<code>*a</code>": </b>
9324 reads the whole file, starting at the current position.
9325 On end of file, it returns the empty string.
9326 </li>
9327
9328 <li><b>"<code>*l</code>": </b>
9329 reads the next line skipping the end of line,
9330 returning <b>nil</b> on end of file.
9331 This is the default format.
9332 </li>
9333
9334 <li><b>"<code>*L</code>": </b>
9335 reads the next line keeping the end of line (if present),
9336 returning <b>nil</b> on end of file.
9337 </li>
9338
9339 <li><b><em>number</em>: </b>
9340 reads a string with up to this number of bytes,
9341 returning <b>nil</b> on end of file.
9342 If number is zero,
9343 it reads nothing and returns an empty string,
9344 or <b>nil</b> on end of file.
9345 </li>
9346
9347 </ul>
9348
9349
9350
9351 <p>
9352 <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3>
9353
9354
9355 <p>
9356 Sets and gets the file position,
9357 measured from the beginning of the file,
9358 to the position given by <code>offset</code> plus a base
9359 specified by the string <code>whence</code>, as follows:
9360
9361 <ul>
9362 <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li>
9363 <li><b>"<code>cur</code>": </b> base is current position;</li>
9364 <li><b>"<code>end</code>": </b> base is end of file;</li>
9365 </ul><p>
9366 In case of success, <code>seek</code> returns the final file position,
9367 measured in bytes from the beginning of the file.
9368 If <code>seek</code> fails, it returns <b>nil</b>,
9369 plus a string describing the error.
9370
9371
9372 <p>
9373 The default value for <code>whence</code> is <code>"cur"</code>,
9374 and for <code>offset</code> is 0.
9375 Therefore, the call <code>file:seek()</code> returns the current
9376 file position, without changing it;
9377 the call <code>file:seek("set")</code> sets the position to the
9378 beginning of the file (and returns 0);
9379 and the call <code>file:seek("end")</code> sets the position to the
9380 end of the file, and returns its size.
9381
9382
9383
9384
9385 <p>
9386 <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3>
9387
9388
9389 <p>
9390 Sets the buffering mode for an output file.
9391 There are three available modes:
9392
9393 <ul>
9394
9395 <li><b>"<code>no</code>": </b>
9396 no buffering; the result of any output operation appears immediately.
9397 </li>
9398
9399 <li><b>"<code>full</code>": </b>
9400 full buffering; output operation is performed only
9401 when the buffer is full or when
9402 you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>).
9403 </li>
9404
9405 <li><b>"<code>line</code>": </b>
9406 line buffering; output is buffered until a newline is output
9407 or there is any input from some special files
9408 (such as a terminal device).
9409 </li>
9410
9411 </ul><p>
9412 For the last two cases, <code>size</code>
9413 specifies the size of the buffer, in bytes.
9414 The default is an appropriate size.
9415
9416
9417
9418
9419 <p>
9420 <hr><h3><a name="pdf-file:write"><code>file:write (&middot;&middot;&middot;)</code></a></h3>
9421
9422
9423 <p>
9424 Writes the value of each of its arguments to <code>file</code>.
9425 The arguments must be strings or numbers.
9426
9427
9428 <p>
9429 In case of success, this function returns <code>file</code>.
9430 Otherwise it returns <b>nil</b> plus a string describing the error.
9431
9432
9433
9434
9435
9436
9437
9438 <h2>6.9 &ndash; <a name="6.9">Operating System Facilities</a></h2>
9439
9440 <p>
9441 This library is implemented through table <a name="pdf-os"><code>os</code></a>.
9442
9443
9444 <p>
9445 <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3>
9446
9447
9448 <p>
9449 Returns an approximation of the amount in seconds of CPU time
9450 used by the program.
9451
9452
9453
9454
9455 <p>
9456 <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3>
9457
9458
9459 <p>
9460 Returns a string or a table containing date and time,
9461 formatted according to the given string <code>format</code>.
9462
9463
9464 <p>
9465 If the <code>time</code> argument is present,
9466 this is the time to be formatted
9467 (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
9468 Otherwise, <code>date</code> formats the current time.
9469
9470
9471 <p>
9472 If <code>format</code> starts with '<code>!</code>',
9473 then the date is formatted in Coordinated Universal Time.
9474 After this optional character,
9475 if <code>format</code> is the string "<code>*t</code>",
9476 then <code>date</code> returns a table with the following fields:
9477 <code>year</code> (four digits), <code>month</code> (1&ndash;12), <code>day</code> (1&ndash;31),
9478 <code>hour</code> (0&ndash;23), <code>min</code> (0&ndash;59), <code>sec</code> (0&ndash;61),
9479 <code>wday</code> (weekday, Sunday is&nbsp;1),
9480 <code>yday</code> (day of the year),
9481 and <code>isdst</code> (daylight saving flag, a boolean).
9482 This last field may be absent
9483 if the information is not available.
9484
9485
9486 <p>
9487 If <code>format</code> is not "<code>*t</code>",
9488 then <code>date</code> returns the date as a string,
9489 formatted according to the same rules as the ANSI&nbsp;C function <code>strftime</code>.
9490
9491
9492 <p>
9493 When called without arguments,
9494 <code>date</code> returns a reasonable date and time representation that depends on
9495 the host system and on the current locale
9496 (that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>).
9497
9498
9499 <p>
9500 On non-Posix systems,
9501 this function may be not thread safe
9502 because of its reliance on C&nbsp;function <code>gmtime</code> and C&nbsp;function <code>localtime</code>.
9503
9504
9505
9506
9507 <p>
9508 <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3>
9509
9510
9511 <p>
9512 Returns the number of seconds from time <code>t1</code> to time <code>t2</code>.
9513 In POSIX, Windows, and some other systems,
9514 this value is exactly <code>t2</code><em>-</em><code>t1</code>.
9515
9516
9517
9518
9519 <p>
9520 <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3>
9521
9522
9523 <p>
9524 This function is equivalent to the ANSI&nbsp;C function <code>system</code>.
9525 It passes <code>command</code> to be executed by an operating system shell.
9526 Its first result is <b>true</b>
9527 if the command terminated successfully,
9528 or <b>nil</b> otherwise.
9529 After this first result
9530 the function returns a string and a number,
9531 as follows:
9532
9533 <ul>
9534
9535 <li><b>"<code>exit</code>": </b>
9536 the command terminated normally;
9537 the following number is the exit status of the command.
9538 </li>
9539
9540 <li><b>"<code>signal</code>": </b>
9541 the command was terminated by a signal;
9542 the following number is the signal that terminated the command.
9543 </li>
9544
9545 </ul>
9546
9547 <p>
9548 When called without a <code>command</code>,
9549 <code>os.execute</code> returns a boolean that is true if a shell is available.
9550
9551
9552
9553
9554 <p>
9555 <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close])</code></a></h3>
9556
9557
9558 <p>
9559 Calls the ANSI&nbsp;C function <code>exit</code> to terminate the host program.
9560 If <code>code</code> is <b>true</b>,
9561 the returned status is <code>EXIT_SUCCESS</code>;
9562 if <code>code</code> is <b>false</b>,
9563 the returned status is <code>EXIT_FAILURE</code>;
9564 if <code>code</code> is a number,
9565 the returned status is this number.
9566 The default value for <code>code</code> is <b>true</b>.
9567
9568
9569 <p>
9570 If the optional second argument <code>close</code> is true,
9571 closes the Lua state before exiting.
9572
9573
9574
9575
9576 <p>
9577 <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3>
9578
9579
9580 <p>
9581 Returns the value of the process environment variable <code>varname</code>,
9582 or <b>nil</b> if the variable is not defined.
9583
9584
9585
9586
9587 <p>
9588 <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3>
9589
9590
9591 <p>
9592 Deletes the file (or empty directory, on POSIX systems)
9593 with the given name.
9594 If this function fails, it returns <b>nil</b>,
9595 plus a string describing the error and the error code.
9596
9597
9598
9599
9600 <p>
9601 <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3>
9602
9603
9604 <p>
9605 Renames file or directory named <code>oldname</code> to <code>newname</code>.
9606 If this function fails, it returns <b>nil</b>,
9607 plus a string describing the error and the error code.
9608
9609
9610
9611
9612 <p>
9613 <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3>
9614
9615
9616 <p>
9617 Sets the current locale of the program.
9618 <code>locale</code> is a system-dependent string specifying a locale;
9619 <code>category</code> is an optional string describing which category to change:
9620 <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>,
9621 <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>;
9622 the default category is <code>"all"</code>.
9623 The function returns the name of the new locale,
9624 or <b>nil</b> if the request cannot be honored.
9625
9626
9627 <p>
9628 If <code>locale</code> is the empty string,
9629 the current locale is set to an implementation-defined native locale.
9630 If <code>locale</code> is the string "<code>C</code>",
9631 the current locale is set to the standard C locale.
9632
9633
9634 <p>
9635 When called with <b>nil</b> as the first argument,
9636 this function only returns the name of the current locale
9637 for the given category.
9638
9639
9640 <p>
9641 This function may be not thread safe
9642 because of its reliance on C&nbsp;function <code>setlocale</code>.
9643
9644
9645
9646
9647 <p>
9648 <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3>
9649
9650
9651 <p>
9652 Returns the current time when called without arguments,
9653 or a time representing the date and time specified by the given table.
9654 This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>,
9655 and may have fields
9656 <code>hour</code> (default is 12),
9657 <code>min</code> (default is 0),
9658 <code>sec</code> (default is 0),
9659 and <code>isdst</code> (default is <b>nil</b>).
9660 For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function.
9661
9662
9663 <p>
9664 The returned value is a number, whose meaning depends on your system.
9665 In POSIX, Windows, and some other systems,
9666 this number counts the number
9667 of seconds since some given start time (the "epoch").
9668 In other systems, the meaning is not specified,
9669 and the number returned by <code>time</code> can be used only as an argument to
9670 <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>.
9671
9672
9673
9674
9675 <p>
9676 <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3>
9677
9678
9679 <p>
9680 Returns a string with a file name that can
9681 be used for a temporary file.
9682 The file must be explicitly opened before its use
9683 and explicitly removed when no longer needed.
9684
9685
9686 <p>
9687 On POSIX systems,
9688 this function also creates a file with that name,
9689 to avoid security risks.
9690 (Someone else might create the file with wrong permissions
9691 in the time between getting the name and creating the file.)
9692 You still have to open the file to use it
9693 and to remove it (even if you do not use it).
9694
9695
9696 <p>
9697 When possible,
9698 you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>,
9699 which automatically removes the file when the program ends.
9700
9701
9702
9703
9704
9705
9706
9707 <h2>6.10 &ndash; <a name="6.10">The Debug Library</a></h2>
9708
9709 <p>
9710 This library provides
9711 the functionality of the debug interface (<a href="#4.9">&sect;4.9</a>) to Lua programs.
9712 You should exert care when using this library.
9713 Several of its functions
9714 violate basic assumptions about Lua code
9715 (e.g., that variables local to a function
9716 cannot be accessed from outside;
9717 that userdata metatables cannot be changed by Lua code;
9718 that Lua programs do not crash)
9719 and therefore can compromise otherwise secure code.
9720 Moreover, some functions in this library may be slow.
9721
9722
9723 <p>
9724 All functions in this library are provided
9725 inside the <a name="pdf-debug"><code>debug</code></a> table.
9726 All functions that operate over a thread
9727 have an optional first argument which is the
9728 thread to operate over.
9729 The default is always the current thread.
9730
9731
9732 <p>
9733 <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3>
9734
9735
9736 <p>
9737 Enters an interactive mode with the user,
9738 running each string that the user enters.
9739 Using simple commands and other debug facilities,
9740 the user can inspect global and local variables,
9741 change their values, evaluate expressions, and so on.
9742 A line containing only the word <code>cont</code> finishes this function,
9743 so that the caller continues its execution.
9744
9745
9746 <p>
9747 Note that commands for <code>debug.debug</code> are not lexically nested
9748 within any function and so have no direct access to local variables.
9749
9750
9751
9752
9753 <p>
9754 <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3>
9755
9756
9757 <p>
9758 Returns the current hook settings of the thread, as three values:
9759 the current hook function, the current hook mask,
9760 and the current hook count
9761 (as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function).
9762
9763
9764
9765
9766 <p>
9767 <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3>
9768
9769
9770 <p>
9771 Returns a table with information about a function.
9772 You can give the function directly
9773 or you can give a number as the value of <code>f</code>,
9774 which means the function running at level <code>f</code> of the call stack
9775 of the given thread:
9776 level&nbsp;0 is the current function (<code>getinfo</code> itself);
9777 level&nbsp;1 is the function that called <code>getinfo</code>
9778 (except for tail calls, which do not count on the stack);
9779 and so on.
9780 If <code>f</code> is a number larger than the number of active functions,
9781 then <code>getinfo</code> returns <b>nil</b>.
9782
9783
9784 <p>
9785 The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
9786 with the string <code>what</code> describing which fields to fill in.
9787 The default for <code>what</code> is to get all information available,
9788 except the table of valid lines.
9789 If present,
9790 the option '<code>f</code>'
9791 adds a field named <code>func</code> with the function itself.
9792 If present,
9793 the option '<code>L</code>'
9794 adds a field named <code>activelines</code> with the table of
9795 valid lines.
9796
9797
9798 <p>
9799 For instance, the expression <code>debug.getinfo(1,"n").name</code> returns
9800 a table with a name for the current function,
9801 if a reasonable name can be found,
9802 and the expression <code>debug.getinfo(print)</code>
9803 returns a table with all available information
9804 about the <a href="#pdf-print"><code>print</code></a> function.
9805
9806
9807
9808
9809 <p>
9810 <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3>
9811
9812
9813 <p>
9814 This function returns the name and the value of the local variable
9815 with index <code>local</code> of the function at level <code>f</code> of the stack.
9816 This function accesses not only explicit local variables,
9817 but also parameters, temporaries, etc.
9818
9819
9820 <p>
9821 The first parameter or local variable has index&nbsp;1, and so on,
9822 until the last active variable.
9823 Negative indices refer to vararg parameters;
9824 -1 is the first vararg parameter.
9825 The function returns <b>nil</b> if there is no variable with the given index,
9826 and raises an error when called with a level out of range.
9827 (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
9828
9829
9830 <p>
9831 Variable names starting with '<code>(</code>' (open parenthesis)
9832 represent internal variables
9833 (loop control variables, temporaries, varargs, and C&nbsp;function locals).
9834
9835
9836 <p>
9837 The parameter <code>f</code> may also be a function.
9838 In that case, <code>getlocal</code> returns only the name of function parameters.
9839
9840
9841
9842
9843 <p>
9844 <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3>
9845
9846
9847 <p>
9848 Returns the metatable of the given <code>value</code>
9849 or <b>nil</b> if it does not have a metatable.
9850
9851
9852
9853
9854 <p>
9855 <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3>
9856
9857
9858 <p>
9859 Returns the registry table (see <a href="#4.5">&sect;4.5</a>).
9860
9861
9862
9863
9864 <p>
9865 <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3>
9866
9867
9868 <p>
9869 This function returns the name and the value of the upvalue
9870 with index <code>up</code> of the function <code>f</code>.
9871 The function returns <b>nil</b> if there is no upvalue with the given index.
9872
9873
9874
9875
9876 <p>
9877 <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3>
9878
9879
9880 <p>
9881 Returns the Lua value associated to <code>u</code>.
9882 If <code>u</code> is not a userdata,
9883 returns <b>nil</b>.
9884
9885
9886
9887
9888 <p>
9889 <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
9890
9891
9892 <p>
9893 Sets the given function as a hook.
9894 The string <code>mask</code> and the number <code>count</code> describe
9895 when the hook will be called.
9896 The string mask may have the following characters,
9897 with the given meaning:
9898
9899 <ul>
9900 <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li>
9901 <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li>
9902 <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li>
9903 </ul><p>
9904 With a <code>count</code> different from zero,
9905 the hook is called after every <code>count</code> instructions.
9906
9907
9908 <p>
9909 When called without arguments,
9910 <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook.
9911
9912
9913 <p>
9914 When the hook is called, its first parameter is a string
9915 describing the event that has triggered its call:
9916 <code>"call"</code> (or <code>"tail call"</code>),
9917 <code>"return"</code>,
9918 <code>"line"</code>, and <code>"count"</code>.
9919 For line events,
9920 the hook also gets the new line number as its second parameter.
9921 Inside a hook,
9922 you can call <code>getinfo</code> with level&nbsp;2 to get more information about
9923 the running function
9924 (level&nbsp;0 is the <code>getinfo</code> function,
9925 and level&nbsp;1 is the hook function).
9926
9927
9928
9929
9930 <p>
9931 <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
9932
9933
9934 <p>
9935 This function assigns the value <code>value</code> to the local variable
9936 with index <code>local</code> of the function at level <code>level</code> of the stack.
9937 The function returns <b>nil</b> if there is no local
9938 variable with the given index,
9939 and raises an error when called with a <code>level</code> out of range.
9940 (You can call <code>getinfo</code> to check whether the level is valid.)
9941 Otherwise, it returns the name of the local variable.
9942
9943
9944 <p>
9945 See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about
9946 variable indices and names.
9947
9948
9949
9950
9951 <p>
9952 <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3>
9953
9954
9955 <p>
9956 Sets the metatable for the given <code>value</code> to the given <code>table</code>
9957 (which can be <b>nil</b>).
9958 Returns <code>value</code>.
9959
9960
9961
9962
9963 <p>
9964 <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3>
9965
9966
9967 <p>
9968 This function assigns the value <code>value</code> to the upvalue
9969 with index <code>up</code> of the function <code>f</code>.
9970 The function returns <b>nil</b> if there is no upvalue
9971 with the given index.
9972 Otherwise, it returns the name of the upvalue.
9973
9974
9975
9976
9977 <p>
9978 <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3>
9979
9980
9981 <p>
9982 Sets the given <code>value</code> as
9983 the Lua value associated to the given <code>udata</code>.
9984 <code>value</code> must be a table or <b>nil</b>;
9985 <code>udata</code> must be a full userdata.
9986
9987
9988 <p>
9989 Returns <code>udata</code>.
9990
9991
9992
9993
9994 <p>
9995 <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
9996
9997
9998 <p>
9999 If <code>message</code> is present but is neither a string nor <b>nil</b>,
10000 this function returns <code>message</code> without further processing.
10001 Otherwise,
10002 it returns a string with a traceback of the call stack.
10003 An optional <code>message</code> string is appended
10004 at the beginning of the traceback.
10005 An optional <code>level</code> number tells at which level
10006 to start the traceback
10007 (default is 1, the function calling <code>traceback</code>).
10008
10009
10010
10011
10012 <p>
10013 <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3>
10014
10015
10016 <p>
10017 Returns an unique identifier (as a light userdata)
10018 for the upvalue numbered <code>n</code>
10019 from the given function.
10020
10021
10022 <p>
10023 These unique identifiers allow a program to check whether different
10024 closures share upvalues.
10025 Lua closures that share an upvalue
10026 (that is, that access a same external local variable)
10027 will return identical ids for those upvalue indices.
10028
10029
10030
10031
10032 <p>
10033 <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3>
10034
10035
10036 <p>
10037 Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code>
10038 refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>.
10039
10040
10041
10042
10043
10044
10045
10046 <h1>7 &ndash; <a name="7">Lua Standalone</a></h1>
10047
10048 <p>
10049 Although Lua has been designed as an extension language,
10050 to be embedded in a host C&nbsp;program,
10051 it is also frequently used as a standalone language.
10052 An interpreter for Lua as a standalone language,
10053 called simply <code>lua</code>,
10054 is provided with the standard distribution.
10055 The standalone interpreter includes
10056 all standard libraries, including the debug library.
10057 Its usage is:
10058
10059 <pre>
10060      lua [options] [script [args]]
10061 </pre><p>
10062 The options are:
10063
10064 <ul>
10065 <li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li>
10066 <li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li>
10067 <li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li>
10068 <li><b><code>-v</code>: </b> prints version information;</li>
10069 <li><b><code>-E</code>: </b> ignores environment variables;</li>
10070 <li><b><code>--</code>: </b> stops handling options;</li>
10071 <li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li>
10072 </ul><p>
10073 After handling its options, <code>lua</code> runs the given <em>script</em>,
10074 passing to it the given <em>args</em> as string arguments.
10075 When called without arguments,
10076 <code>lua</code> behaves as <code>lua -v -i</code>
10077 when the standard input (<code>stdin</code>) is a terminal,
10078 and as <code>lua -</code> otherwise.
10079
10080
10081 <p>
10082 When called without option <code>-E</code>,
10083 the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_2"><code>LUA_INIT_5_2</code></a>
10084 (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if it is not defined)
10085 before running any argument.
10086 If the variable content has the format <code>@<em>filename</em></code>,
10087 then <code>lua</code> executes the file.
10088 Otherwise, <code>lua</code> executes the string itself.
10089
10090
10091 <p>
10092 When called with option <code>-E</code>,
10093 besides ignoring <code>LUA_INIT</code>,
10094 Lua also ignores
10095 the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>,
10096 setting the values of
10097 <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a>
10098 with the default paths defined in <code>luaconf.h</code>.
10099
10100
10101 <p>
10102 All options are handled in order, except <code>-i</code> and <code>-E</code>.
10103 For instance, an invocation like
10104
10105 <pre>
10106      $ lua -e'a=1' -e 'print(a)' script.lua
10107 </pre><p>
10108 will first set <code>a</code> to 1, then print the value of <code>a</code>,
10109 and finally run the file <code>script.lua</code> with no arguments.
10110 (Here <code>$</code> is the shell prompt. Your prompt may be different.)
10111
10112
10113 <p>
10114 Before starting to run the script,
10115 <code>lua</code> collects all arguments in the command line
10116 in a global table called <code>arg</code>.
10117 The script name is stored at index 0,
10118 the first argument after the script name goes to index 1,
10119 and so on.
10120 Any arguments before the script name
10121 (that is, the interpreter name plus the options)
10122 go to negative indices.
10123 For instance, in the call
10124
10125 <pre>
10126      $ lua -la b.lua t1 t2
10127 </pre><p>
10128 the interpreter first runs the file <code>a.lua</code>,
10129 then creates a table
10130
10131 <pre>
10132      arg = { [-2] = "lua", [-1] = "-la",
10133              [0] = "b.lua",
10134              [1] = "t1", [2] = "t2" }
10135 </pre><p>
10136 and finally runs the file <code>b.lua</code>.
10137 The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ...
10138 as arguments;
10139 it can also access these arguments with the vararg expression '<code>...</code>'.
10140
10141
10142 <p>
10143 In interactive mode,
10144 if you write an incomplete statement,
10145 the interpreter waits for its completion
10146 by issuing a different prompt.
10147
10148
10149 <p>
10150 In case of unprotected errors in the script,
10151 the interpreter reports the error to the standard error stream.
10152 If the error object is a string,
10153 the interpreter adds a stack traceback to it.
10154 Otherwise, if the error object has a metamethod <code>__tostring</code>,
10155 the interpreter calls this metamethod to produce the final message.
10156 Finally, if the error object is <b>nil</b>,
10157 the interpreter does not report the error.
10158
10159
10160 <p>
10161 When finishing normally,
10162 the interpreter closes its main Lua state
10163 (see <a href="#lua_close"><code>lua_close</code></a>).
10164 The script can avoid this step by
10165 calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate.
10166
10167
10168 <p>
10169 To allow the use of Lua as a
10170 script interpreter in Unix systems,
10171 the standalone interpreter skips
10172 the first line of a chunk if it starts with <code>#</code>.
10173 Therefore, Lua scripts can be made into executable programs
10174 by using <code>chmod +x</code> and the&nbsp;<code>#!</code> form,
10175 as in
10176
10177 <pre>
10178      #!/usr/local/bin/lua
10179 </pre><p>
10180 (Of course,
10181 the location of the Lua interpreter may be different in your machine.
10182 If <code>lua</code> is in your <code>PATH</code>,
10183 then
10184
10185 <pre>
10186      #!/usr/bin/env lua
10187 </pre><p>
10188 is a more portable solution.)
10189
10190
10191
10192 <h1>8 &ndash; <a name="8">Incompatibilities with the Previous Version</a></h1>
10193
10194 <p>
10195 Here we list the incompatibilities that you may find when moving a program
10196 from Lua&nbsp;5.1 to Lua&nbsp;5.2.
10197 You can avoid some incompatibilities by compiling Lua with
10198 appropriate options (see file <code>luaconf.h</code>).
10199 However,
10200 all these compatibility options will be removed in the next version of Lua.
10201 Similarly,
10202 all features marked as deprecated in Lua&nbsp;5.1
10203 have been removed in Lua&nbsp;5.2.
10204
10205
10206
10207 <h2>8.1 &ndash; <a name="8.1">Changes in the Language</a></h2>
10208 <ul>
10209
10210 <li>
10211 The concept of <em>environment</em> changed.
10212 Only Lua functions have environments.
10213 To set the environment of a Lua function,
10214 use the variable <code>_ENV</code> or the function <a href="#pdf-load"><code>load</code></a>.
10215
10216
10217 <p>
10218 C functions no longer have environments.
10219 Use an upvalue with a shared table if you need to keep
10220 shared state among several C functions.
10221 (You may use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> to open a C library
10222 with all functions sharing a common upvalue.)
10223
10224
10225 <p>
10226 To manipulate the "environment" of a userdata
10227 (which is now called user value),
10228 use the new functions
10229 <a href="#lua_getuservalue"><code>lua_getuservalue</code></a> and <a href="#lua_setuservalue"><code>lua_setuservalue</code></a>.
10230 </li>
10231
10232 <li>
10233 Lua identifiers cannot use locale-dependent letters.
10234 </li>
10235
10236 <li>
10237 Doing a step or a full collection in the garbage collector
10238 does not restart the collector if it has been stopped.
10239 </li>
10240
10241 <li>
10242 Weak tables with weak keys now perform like <em>ephemeron tables</em>.
10243 </li>
10244
10245 <li>
10246 The event <em>tail return</em> in debug hooks was removed.
10247 Instead, tail calls generate a special new event,
10248 <em>tail call</em>, so that the debugger can know that
10249 there will not be a corresponding return event.
10250 </li>
10251
10252 <li>
10253 Equality between function values has changed.
10254 Now, a function definition may not create a new value;
10255 it may reuse some previous value if there is no
10256 observable difference to the new function.
10257 </li>
10258
10259 </ul>
10260
10261
10262
10263
10264 <h2>8.2 &ndash; <a name="8.2">Changes in the Libraries</a></h2>
10265 <ul>
10266
10267 <li>
10268 Function <code>module</code> is deprecated.
10269 It is easy to set up a module with regular Lua code.
10270 Modules are not expected to set global variables.
10271 </li>
10272
10273 <li>
10274 Functions <code>setfenv</code> and <code>getfenv</code> were removed,
10275 because of the changes in environments.
10276 </li>
10277
10278 <li>
10279 Function <code>math.log10</code> is deprecated.
10280 Use <a href="#pdf-math.log"><code>math.log</code></a> with 10 as its second argument, instead.
10281 </li>
10282
10283 <li>
10284 Function <code>loadstring</code> is deprecated.
10285 Use <code>load</code> instead; it now accepts string arguments
10286 and are exactly equivalent to <code>loadstring</code>.
10287 </li>
10288
10289 <li>
10290 Function <code>table.maxn</code> is deprecated.
10291 Write it in Lua if you really need it.
10292 </li>
10293
10294 <li>
10295 Function <code>os.execute</code> now returns <b>true</b> when command
10296 terminates successfully and <b>nil</b> plus error information
10297 otherwise.
10298 </li>
10299
10300 <li>
10301 Function <code>unpack</code> was moved into the table library
10302 and therefore must be called as <a href="#pdf-table.unpack"><code>table.unpack</code></a>.
10303 </li>
10304
10305 <li>
10306 Character class <code>%z</code> in patterns is deprecated,
10307 as now patterns may contain '<code>\0</code>' as a regular character.
10308 </li>
10309
10310 <li>
10311 The table <code>package.loaders</code> was renamed <code>package.searchers</code>.
10312 </li>
10313
10314 <li>
10315 Lua does not have bytecode verification anymore.
10316 So, all functions that load code
10317 (<a href="#pdf-load"><code>load</code></a> and <a href="#pdf-loadfile"><code>loadfile</code></a>)
10318 are potentially insecure when loading untrusted binary data.
10319 (Actually, those functions were already insecure because
10320 of flaws in the verification algorithm.)
10321 When in doubt,
10322 use the <code>mode</code> argument of those functions
10323 to restrict them to loading textual chunks.
10324 </li>
10325
10326 <li>
10327 The standard paths in the official distribution may
10328 change between versions.
10329 </li>
10330
10331 </ul>
10332
10333
10334
10335
10336 <h2>8.3 &ndash; <a name="8.3">Changes in the API</a></h2>
10337 <ul>
10338
10339 <li>
10340 Pseudoindex <code>LUA_GLOBALSINDEX</code> was removed.
10341 You must get the global environment from the registry
10342 (see <a href="#4.5">&sect;4.5</a>).
10343 </li>
10344
10345 <li>
10346 Pseudoindex <code>LUA_ENVIRONINDEX</code>
10347 and functions <code>lua_getfenv</code>/<code>lua_setfenv</code>
10348 were removed,
10349 as C&nbsp;functions no longer have environments.
10350 </li>
10351
10352 <li>
10353 Function <code>luaL_register</code> is deprecated.
10354 Use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> so that your module does not create globals.
10355 (Modules are not expected to set global variables anymore.)
10356 </li>
10357
10358 <li>
10359 The <code>osize</code> argument to the allocation function
10360 may not be zero when creating a new block,
10361 that is, when <code>ptr</code> is <code>NULL</code>
10362 (see <a href="#lua_Alloc"><code>lua_Alloc</code></a>).
10363 Use only the test <code>ptr == NULL</code> to check whether
10364 the block is new.
10365 </li>
10366
10367 <li>
10368 Finalizers (<code>__gc</code> metamethods) for userdata are called in the
10369 reverse order that they were marked for finalization,
10370 not that they were created (see <a href="#2.5.1">&sect;2.5.1</a>).
10371 (Most userdata are marked immediately after they are created.)
10372 Moreover,
10373 if the metatable does not have a <code>__gc</code> field when set,
10374 the finalizer will not be called,
10375 even if it is set later.
10376 </li>
10377
10378 <li>
10379 <code>luaL_typerror</code> was removed.
10380 Write your own version if you need it.
10381 </li>
10382
10383 <li>
10384 Function <code>lua_cpcall</code> is deprecated.
10385 You can simply push the function with <a href="#lua_pushcfunction"><code>lua_pushcfunction</code></a>
10386 and call it with <a href="#lua_pcall"><code>lua_pcall</code></a>.
10387 </li>
10388
10389 <li>
10390 Functions <code>lua_equal</code> and <code>lua_lessthan</code> are deprecated.
10391 Use the new <a href="#lua_compare"><code>lua_compare</code></a> with appropriate options instead.
10392 </li>
10393
10394 <li>
10395 Function <code>lua_objlen</code> was renamed <a href="#lua_rawlen"><code>lua_rawlen</code></a>.
10396 </li>
10397
10398 <li>
10399 Function <a href="#lua_load"><code>lua_load</code></a> has an extra parameter, <code>mode</code>.
10400 Pass <code>NULL</code> to simulate the old behavior.
10401 </li>
10402
10403 <li>
10404 Function <a href="#lua_resume"><code>lua_resume</code></a> has an extra parameter, <code>from</code>.
10405 Pass <code>NULL</code> or the thread doing the call.
10406 </li>
10407
10408 </ul>
10409
10410
10411
10412
10413 <h1>9 &ndash; <a name="9">The Complete Syntax of Lua</a></h1>
10414
10415 <p>
10416 Here is the complete syntax of Lua in extended BNF.
10417 (It does not describe operator precedences.)
10418
10419
10420
10421
10422 <pre>
10423
10424         chunk ::= block
10425
10426         block ::= {stat} [retstat]
10427
10428         stat ::=  &lsquo;<b>;</b>&rsquo; |
10429                  varlist &lsquo;<b>=</b>&rsquo; explist |
10430                  functioncall |
10431                  label |
10432                  <b>break</b> |
10433                  <b>goto</b> Name |
10434                  <b>do</b> block <b>end</b> |
10435                  <b>while</b> exp <b>do</b> block <b>end</b> |
10436                  <b>repeat</b> block <b>until</b> exp |
10437                  <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
10438                  <b>for</b> Name &lsquo;<b>=</b>&rsquo; exp &lsquo;<b>,</b>&rsquo; exp [&lsquo;<b>,</b>&rsquo; exp] <b>do</b> block <b>end</b> |
10439                  <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> |
10440                  <b>function</b> funcname funcbody |
10441                  <b>local</b> <b>function</b> Name funcbody |
10442                  <b>local</b> namelist [&lsquo;<b>=</b>&rsquo; explist]
10443
10444         retstat ::= <b>return</b> [explist] [&lsquo;<b>;</b>&rsquo;]
10445
10446         label ::= &lsquo;<b>::</b>&rsquo; Name &lsquo;<b>::</b>&rsquo;
10447
10448         funcname ::= Name {&lsquo;<b>.</b>&rsquo; Name} [&lsquo;<b>:</b>&rsquo; Name]
10449
10450         varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
10451
10452         var ::=  Name | prefixexp &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; | prefixexp &lsquo;<b>.</b>&rsquo; Name
10453
10454         namelist ::= Name {&lsquo;<b>,</b>&rsquo; Name}
10455
10456         explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
10457
10458         exp ::=  <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | &lsquo;<b>...</b>&rsquo; | functiondef |
10459                  prefixexp | tableconstructor | exp binop exp | unop exp
10460
10461         prefixexp ::= var | functioncall | &lsquo;<b>(</b>&rsquo; exp &lsquo;<b>)</b>&rsquo;
10462
10463         functioncall ::=  prefixexp args | prefixexp &lsquo;<b>:</b>&rsquo; Name args
10464
10465         args ::=  &lsquo;<b>(</b>&rsquo; [explist] &lsquo;<b>)</b>&rsquo; | tableconstructor | String
10466
10467         functiondef ::= <b>function</b> funcbody
10468
10469         funcbody ::= &lsquo;<b>(</b>&rsquo; [parlist] &lsquo;<b>)</b>&rsquo; block <b>end</b>
10470
10471         parlist ::= namelist [&lsquo;<b>,</b>&rsquo; &lsquo;<b>...</b>&rsquo;] | &lsquo;<b>...</b>&rsquo;
10472
10473         tableconstructor ::= &lsquo;<b>{</b>&rsquo; [fieldlist] &lsquo;<b>}</b>&rsquo;
10474
10475         fieldlist ::= field {fieldsep field} [fieldsep]
10476
10477         field ::= &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo; &lsquo;<b>=</b>&rsquo; exp | Name &lsquo;<b>=</b>&rsquo; exp | exp
10478
10479         fieldsep ::= &lsquo;<b>,</b>&rsquo; | &lsquo;<b>;</b>&rsquo;
10480
10481         binop ::= &lsquo;<b>+</b>&rsquo; | &lsquo;<b>-</b>&rsquo; | &lsquo;<b>*</b>&rsquo; | &lsquo;<b>/</b>&rsquo; | &lsquo;<b>^</b>&rsquo; | &lsquo;<b>%</b>&rsquo; | &lsquo;<b>..</b>&rsquo; |
10482                  &lsquo;<b>&lt;</b>&rsquo; | &lsquo;<b>&lt;=</b>&rsquo; | &lsquo;<b>&gt;</b>&rsquo; | &lsquo;<b>&gt;=</b>&rsquo; | &lsquo;<b>==</b>&rsquo; | &lsquo;<b>~=</b>&rsquo; |
10483                  <b>and</b> | <b>or</b>
10484
10485         unop ::= &lsquo;<b>-</b>&rsquo; | <b>not</b> | &lsquo;<b>#</b>&rsquo;
10486
10487 </pre>
10488
10489 <p>
10490
10491
10492
10493
10494
10495
10496
10497 <HR>
10498 <SMALL CLASS="footer">
10499 Last update:
10500 Thu Mar 21 12:58:59 BRT 2013
10501 </SMALL>
10502 <!--
10503 Last change: revised for Lua 5.2.2
10504 -->
10505
10506 </body></html>
10507