From 483eb2f56657e8e7f419ab1a4fab8dce9ade8609 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 27 Apr 2024 20:24:20 +0200 Subject: Adding upstream version 14.2.21. Signed-off-by: Daniel Baumann --- src/lua/doc/contents.html | 618 ++ src/lua/doc/index.css | 21 + src/lua/doc/logo.gif | Bin 0 -> 4232 bytes src/lua/doc/lua.1 | 111 + src/lua/doc/lua.css | 159 + src/lua/doc/luac.1 | 118 + src/lua/doc/manual.css | 21 + src/lua/doc/manual.html | 10835 ++++++++++++++++++++++++++++++++++ src/lua/doc/osi-certified-72x60.png | Bin 0 -> 3774 bytes src/lua/doc/readme.html | 365 ++ 10 files changed, 12248 insertions(+) create mode 100644 src/lua/doc/contents.html create mode 100644 src/lua/doc/index.css create mode 100644 src/lua/doc/logo.gif create mode 100644 src/lua/doc/lua.1 create mode 100644 src/lua/doc/lua.css create mode 100644 src/lua/doc/luac.1 create mode 100644 src/lua/doc/manual.css create mode 100644 src/lua/doc/manual.html create mode 100644 src/lua/doc/osi-certified-72x60.png create mode 100644 src/lua/doc/readme.html (limited to 'src/lua/doc') diff --git a/src/lua/doc/contents.html b/src/lua/doc/contents.html new file mode 100644 index 00000000..1272c59c --- /dev/null +++ b/src/lua/doc/contents.html @@ -0,0 +1,618 @@ + + + +Lua 5.3 Reference Manual - contents + + + + + + + +

+ +Lua 5.3 Reference Manual +

+ +

+The reference manual is the official definition of the Lua language. +
+For a complete introduction to Lua programming, see the book +Programming in Lua. + +

+start +· +contents +· +index +· +other versions +

+ +

Index

+ + + + + + + +

+ + + + + + diff --git a/src/lua/doc/index.css b/src/lua/doc/index.css new file mode 100644 index 00000000..c9618357 --- /dev/null +++ b/src/lua/doc/index.css @@ -0,0 +1,21 @@ +ul { + list-style-type: none ; +} + +ul.contents { + padding: 0 ; +} + +table { + border: none ; + border-spacing: 0 ; + border-collapse: collapse ; +} + +td { + vertical-align: top ; + padding: 0 ; + text-align: left ; + line-height: 1.25 ; + width: 15% ; +} diff --git a/src/lua/doc/logo.gif b/src/lua/doc/logo.gif new file mode 100644 index 00000000..2f5e4ac2 Binary files /dev/null and b/src/lua/doc/logo.gif differ diff --git a/src/lua/doc/lua.1 b/src/lua/doc/lua.1 new file mode 100644 index 00000000..411531b9 --- /dev/null +++ b/src/lua/doc/lua.1 @@ -0,0 +1,111 @@ +.TH LUA 1 "$Date: 2014/12/10 15:55:45 $" +.SH NAME +lua \- Lua interpreter +.SH SYNOPSIS +.B lua +[ +.I options +] +[ +.I script +[ +.I args +] +] +.SH DESCRIPTION +.B lua +is the standalone Lua interpreter. +It loads and executes Lua programs, +either in textual source form or +in precompiled binary form. +(Precompiled binaries are output by +.BR luac , +the Lua compiler.) +.B lua +can be used as a batch interpreter and also interactively. +.LP +The given +.I options +are handled in order and then +the Lua program in file +.I script +is loaded and executed. +The given +.I args +are available to +.I script +as strings in a global table named +.BR arg . +If no options or arguments are given, +then +.B "\-v \-i" +is assumed when the standard input is a terminal; +otherwise, +.B "\-" +is assumed. +.LP +In interactive mode, +.B lua +prompts the user, +reads lines from the standard input, +and executes them as they are read. +If the line contains an expression or list of expressions, +then the line is evaluated and the results are printed. +If a line does not contain a complete statement, +then a secondary prompt is displayed and +lines are read until a complete statement is formed or +a syntax error is found. +.LP +At the very start, +before even handling the command line, +.B lua +checks the contents of the environment variables +.B LUA_INIT_5_3 +or +.BR LUA_INIT , +in that order. +If the contents is of the form +.RI '@ filename ', +then +.I filename +is executed. +Otherwise, the string is assumed to be a Lua statement and is executed. +.SH OPTIONS +.TP +.BI \-e " stat" +execute statement +.IR stat . +.TP +.B \-i +enter interactive mode after executing +.IR script . +.TP +.BI \-l " name" +execute the equivalent of +.IB name =require(' name ') +before executing +.IR script . +.TP +.B \-v +show version information. +.TP +.B \-E +ignore environment variables. +.TP +.B \-\- +stop handling options. +.TP +.B \- +stop handling options and execute the standard input as a file. +.SH "SEE ALSO" +.BR luac (1) +.br +The documentation at lua.org, +especially section 7 of the reference manual. +.SH DIAGNOSTICS +Error messages should be self explanatory. +.SH AUTHORS +R. Ierusalimschy, +L. H. de Figueiredo, +W. Celes +.\" EOF diff --git a/src/lua/doc/lua.css b/src/lua/doc/lua.css new file mode 100644 index 00000000..eb20fecd --- /dev/null +++ b/src/lua/doc/lua.css @@ -0,0 +1,159 @@ +html { + background-color: #F8F8F8 ; +} + +body { + background-color: #FFFFFF ; + color: #000000 ; + font-family: Helvetica, Arial, sans-serif ; + text-align: justify ; + line-height: 1.25 ; + margin: 16px auto ; + padding: 32px ; + border: solid #a0a0a0 1px ; + border-radius: 20px ; + max-width: 70em ; + width: 90% ; +} + +h1, h2, h3, h4 { + color: #000080 ; + font-family: Verdana, Geneva, sans-serif ; + font-weight: normal ; + font-style: normal ; + text-align: left ; +} + +h1 { + font-size: 28pt ; +} + +h1 img { + vertical-align: text-bottom ; +} + +h2:before { + content: "\2756" ; + padding-right: 0.5em ; +} + +a { + text-decoration: none ; +} + +a:link { + color: #000080 ; +} + +a:link:hover, a:visited:hover { + background-color: #D0D0FF ; + color: #000080 ; + border-radius: 4px ; +} + +a:link:active, a:visited:active { + color: #FF0000 ; +} + +div.menubar { + padding-bottom: 0.5em ; +} + +p.menubar { + margin-left: 2.5em ; +} + +.menubar a:hover { + margin: -3px -3px -3px -3px ; + padding: 3px 3px 3px 3px ; + border-radius: 4px ; +} + +:target { + background-color: #F0F0F0 ; + margin: -8px ; + padding: 8px ; + border-radius: 8px ; + outline: none ; +} + +hr { + display: none ; +} + +table hr { + background-color: #a0a0a0 ; + color: #a0a0a0 ; + border: 0 ; + height: 1px ; + display: block ; +} + +.footer { + color: gray ; + font-size: x-small ; +} + +input[type=text] { + border: solid #a0a0a0 2px ; + border-radius: 2em ; + background-image: url('images/search.png') ; + background-repeat: no-repeat ; + background-position: 4px center ; + padding-left: 20px ; + height: 2em ; +} + +pre.session { + background-color: #F8F8F8 ; + padding: 1em ; + border-radius: 8px ; +} + +td.gutter { + width: 4% ; +} + +table.columns { + border: none ; + border-spacing: 0 ; + border-collapse: collapse ; +} + +table.columns td { + vertical-align: top ; + padding: 0 ; + padding-bottom: 1em ; + text-align: justify ; + line-height: 1.25 ; +} + +p.logos a:link:hover, p.logos a:visited:hover { + background-color: inherit ; +} + +table.book { + border: none ; + border-spacing: 0 ; + border-collapse: collapse ; +} + +table.book td { + padding: 0 ; + vertical-align: top ; +} + +table.book td.cover { + padding-right: 1em ; +} + +table.book img { + border: solid #000080 1px ; +} + +table.book span { + font-size: small ; + text-align: left ; + display: block ; + margin-top: 0.25em ; +} diff --git a/src/lua/doc/luac.1 b/src/lua/doc/luac.1 new file mode 100644 index 00000000..33a4ed00 --- /dev/null +++ b/src/lua/doc/luac.1 @@ -0,0 +1,118 @@ +.\" $Id: luac.man,v 1.29 2011/11/16 13:53:40 lhf Exp $ +.TH LUAC 1 "$Date: 2011/11/16 13:53:40 $" +.SH NAME +luac \- Lua compiler +.SH SYNOPSIS +.B luac +[ +.I options +] [ +.I filenames +] +.SH DESCRIPTION +.B luac +is the Lua compiler. +It translates programs written in the Lua programming language +into binary files containing precompiled chunks +that can be later loaded and executed. +.LP +The main advantages of precompiling chunks are: +faster loading, +protecting source code from accidental user changes, +and +off-line syntax checking. +Precompiling does not imply faster execution +because in Lua chunks are always compiled into bytecodes before being executed. +.B luac +simply allows those bytecodes to be saved in a file for later execution. +Precompiled chunks are not necessarily smaller than the corresponding source. +The main goal in precompiling is faster loading. +.LP +In the command line, +you can mix +text files containing Lua source and +binary files containing precompiled chunks. +.B luac +produces a single output file containing the combined bytecodes +for all files given. +Executing the combined file is equivalent to executing the given files. +By default, +the output file is named +.BR luac.out , +but you can change this with the +.B \-o +option. +.LP +Precompiled chunks are +.I not +portable across different architectures. +Moreover, +the internal format of precompiled chunks +is likely to change when a new version of Lua is released. +Make sure you save the source files of all Lua programs that you precompile. +.LP +.SH OPTIONS +.TP +.B \-l +produce a listing of the compiled bytecode for Lua's virtual machine. +Listing bytecodes is useful to learn about Lua's virtual machine. +If no files are given, then +.B luac +loads +.B luac.out +and lists its contents. +Use +.B \-l \-l +for a full listing. +.TP +.BI \-o " file" +output to +.IR file , +instead of the default +.BR luac.out . +(You can use +.B "'\-'" +for standard output, +but not on platforms that open standard output in text mode.) +The output file may be one of the given files because +all files are loaded before the output file is written. +Be careful not to overwrite precious files. +.TP +.B \-p +load files but do not generate any output file. +Used mainly for syntax checking and for testing precompiled chunks: +corrupted files will probably generate errors when loaded. +If no files are given, then +.B luac +loads +.B luac.out +and tests its contents. +No messages are displayed if the file loads without errors. +.TP +.B \-s +strip debug information before writing the output file. +This saves some space in very large chunks, +but if errors occur when running a stripped chunk, +then the error messages may not contain the full information they usually do. +In particular, +line numbers and names of local variables are lost. +.TP +.B \-v +show version information. +.TP +.B \-\- +stop handling options. +.TP +.B \- +stop handling options and process standard input. +.SH "SEE ALSO" +.BR lua (1) +.br +The documentation at lua.org. +.SH DIAGNOSTICS +Error messages should be self explanatory. +.SH AUTHORS +R. Ierusalimschy, +L. H. de Figueiredo, +W. Celes +.\" EOF diff --git a/src/lua/doc/manual.css b/src/lua/doc/manual.css new file mode 100644 index 00000000..aa0e677d --- /dev/null +++ b/src/lua/doc/manual.css @@ -0,0 +1,21 @@ +h3 code { + font-family: inherit ; + font-size: inherit ; +} + +pre, code { + font-size: 12pt ; +} + +span.apii { + color: gray ; + float: right ; + font-family: inherit ; + font-style: normal ; + font-size: small ; +} + +h2:before { + content: "" ; + padding-right: 0em ; +} diff --git a/src/lua/doc/manual.html b/src/lua/doc/manual.html new file mode 100644 index 00000000..60c4c98b --- /dev/null +++ b/src/lua/doc/manual.html @@ -0,0 +1,10835 @@ + + + +Lua 5.3 Reference Manual + + + + + + + +

+ +Lua 5.3 Reference Manual +

+ +

+by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes + +

+contents +· +index +· +other versions +

+ + +

+ + + + + + +

1 – Introduction

+ +

+Lua is an extension programming language designed to support +general procedural programming with data description +facilities. +Lua also offers good support for object-oriented programming, +functional programming, and data-driven programming. +Lua is intended to be used as a powerful, lightweight, +embeddable scripting language for any program that needs one. +Lua is implemented as a library, written in clean C, +the common subset of Standard C and C++. + + +

+As an extension language, Lua has no notion of a "main" program: +it only works embedded in a host client, +called the embedding program or simply the host. +The host program can invoke functions to execute a piece of Lua code, +can write and read Lua variables, +and can register C functions to be called by Lua code. +Through the use of C functions, Lua can be augmented to cope with +a wide range of different domains, +thus creating customized programming languages sharing a syntactical framework. +The Lua distribution includes a sample host program called lua, +which uses the Lua library to offer a complete, standalone Lua interpreter, +for interactive or batch use. + + +

+Lua is free software, +and is provided as usual with no guarantees, +as stated in its license. +The implementation described in this manual is available +at Lua's official web site, www.lua.org. + + +

+Like any other reference manual, +this document is dry in places. +For a discussion of the decisions behind the design of Lua, +see the technical papers available at Lua's web site. +For a detailed introduction to programming in Lua, +see Roberto's book, Programming in Lua. + + + +

2 – Basic Concepts

+ +

+This section describes the basic concepts of the language. + + + +

2.1 – Values and Types

+ +

+Lua is a dynamically typed language. +This means that +variables do not have types; only values do. +There are no type definitions in the language. +All values carry their own type. + + +

+All values in Lua are first-class values. +This means that all values can be stored in variables, +passed as arguments to other functions, and returned as results. + + +

+There are eight basic types in Lua: +nil, boolean, number, +string, function, userdata, +thread, and table. +The type nil has one single value, nil, +whose main property is to be different from any other value; +it usually represents the absence of a useful value. +The type boolean has two values, false and true. +Both nil and false make a condition false; +any other value makes it true. +The type number represents both +integer numbers and real (floating-point) numbers. +The type string represents immutable sequences of bytes. + +Lua is 8-bit clean: +strings can contain any 8-bit value, +including embedded zeros ('\0'). +Lua is also encoding-agnostic; +it makes no assumptions about the contents of a string. + + +

+The type number uses two internal representations, +or two subtypes, +one called integer and the other called float. +Lua has explicit rules about when each representation is used, +but it also converts between them automatically as needed (see §3.4.3). +Therefore, +the programmer may choose to mostly ignore the difference +between integers and floats +or to assume complete control over the representation of each number. +Standard Lua uses 64-bit integers and double-precision (64-bit) floats, +but you can also compile Lua so that it +uses 32-bit integers and/or single-precision (32-bit) floats. +The option with 32 bits for both integers and floats +is particularly attractive +for small machines and embedded systems. +(See macro LUA_32BITS in file luaconf.h.) + + +

+Lua can call (and manipulate) functions written in Lua and +functions written in C (see §3.4.10). +Both are represented by the type function. + + +

+The type userdata is provided to allow arbitrary C data to +be stored in Lua variables. +A userdata value represents a block of raw memory. +There are two kinds of userdata: +full userdata, +which is an object with a block of memory managed by Lua, +and light userdata, +which is simply a C pointer value. +Userdata has no predefined operations in Lua, +except assignment and identity test. +By using metatables, +the programmer can define operations for full userdata values +(see §2.4). +Userdata values cannot be created or modified in Lua, +only through the C API. +This guarantees the integrity of data owned by the host program. + + +

+The type thread represents independent threads of execution +and it is used to implement coroutines (see §2.6). +Lua threads are not related to operating-system threads. +Lua supports coroutines on all systems, +even those that do not support threads natively. + + +

+The type table implements associative arrays, +that is, arrays that can be indexed not only with numbers, +but with any Lua value except nil and NaN. +(Not a Number is a special value used to represent +undefined or unrepresentable numerical results, such as 0/0.) +Tables can be heterogeneous; +that is, they can contain values of all types (except nil). +Any key with value nil is not considered part of the table. +Conversely, any key that is not part of a table has +an associated value nil. + + +

+Tables are the sole data-structuring mechanism in Lua; +they can be used to represent ordinary arrays, sequences, +symbol tables, sets, records, graphs, trees, etc. +To represent records, Lua uses the field name as an index. +The language supports this representation by +providing a.name as syntactic sugar for a["name"]. +There are several convenient ways to create tables in Lua +(see §3.4.9). + + +

+We use the term sequence to denote a table where +the set of all positive numeric keys is equal to {1..n} +for some non-negative integer n, +which is called the length of the sequence (see §3.4.7). + + +

+Like indices, +the values of table fields can be of any type. +In particular, +because functions are first-class values, +table fields can contain functions. +Thus tables can also carry methods (see §3.4.11). + + +

+The indexing of tables follows +the definition of raw equality in the language. +The expressions a[i] and a[j] +denote the same table element +if and only if i and j are raw equal +(that is, equal without metamethods). +In particular, floats with integral values +are equal to their respective integers +(e.g., 1.0 == 1). +To avoid ambiguities, +any float with integral value used as a key +is converted to its respective integer. +For instance, if you write a[2.0] = true, +the actual key inserted into the table will be the +integer 2. +(On the other hand, +2 and "2" are different Lua values and therefore +denote different table entries.) + + +

+Tables, functions, threads, and (full) userdata values are objects: +variables do not actually contain these values, +only references to them. +Assignment, parameter passing, and function returns +always manipulate references to such values; +these operations do not imply any kind of copy. + + +

+The library function type returns a string describing the type +of a given value (see §6.1). + + + + + +

2.2 – Environments and the Global Environment

+ +

+As will be discussed in §3.2 and §3.3.3, +any reference to a free name +(that is, a name not bound to any declaration) var +is syntactically translated to _ENV.var. +Moreover, every chunk is compiled in the scope of +an external local variable named _ENV (see §3.3.2), +so _ENV itself is never a free name in a chunk. + + +

+Despite the existence of this external _ENV variable and +the translation of free names, +_ENV is a completely regular name. +In particular, +you can define new variables and parameters with that name. +Each reference to a free name uses the _ENV that is +visible at that point in the program, +following the usual visibility rules of Lua (see §3.5). + + +

+Any table used as the value of _ENV is called an environment. + + +

+Lua keeps a distinguished environment called the global environment. +This value is kept at a special index in the C registry (see §4.5). +In Lua, the global variable _G is initialized with this same value. +(_G is never used internally.) + + +

+When Lua loads a chunk, +the default value for its _ENV upvalue +is the global environment (see load). +Therefore, by default, +free names in Lua code refer to entries in the global environment +(and, therefore, they are also called global variables). +Moreover, all standard libraries are loaded in the global environment +and some functions there operate on that environment. +You can use load (or loadfile) +to load a chunk with a different environment. +(In C, you have to load the chunk and then change the value +of its first upvalue.) + + + + + +

2.3 – Error Handling

+ +

+Because Lua is an embedded extension language, +all Lua actions start from C code in the host program +calling a function from the Lua library. +(When you use Lua standalone, +the lua application is the host program.) +Whenever an error occurs during +the compilation or execution of a Lua chunk, +control returns to the host, +which can take appropriate measures +(such as printing an error message). + + +

+Lua code can explicitly generate an error by calling the +error function. +If you need to catch errors in Lua, +you can use pcall or xpcall +to call a given function in protected mode. + + +

+Whenever there is an error, +an error object (also called an error message) +is propagated with information about the error. +Lua itself only generates errors whose error object is a string, +but programs may generate errors with +any value as the error object. +It is up to the Lua program or its host to handle such error objects. + + +

+When you use xpcall or lua_pcall, +you may give a message handler +to be called in case of errors. +This function is called with the original error message +and returns a new error message. +It is called before the error unwinds the stack, +so that it can gather more information about the error, +for instance by inspecting the stack and creating a stack traceback. +This message handler is still protected by the protected call; +so, an error inside the message handler +will call the message handler again. +If this loop goes on for too long, +Lua breaks it and returns an appropriate message. + + + + + +

2.4 – Metatables and Metamethods

+ +

+Every value in Lua can have a metatable. +This metatable is an ordinary Lua table +that defines the behavior of the original value +under certain special operations. +You can change several aspects of the behavior +of operations over a value by setting specific fields in its metatable. +For instance, when a non-numeric value is the operand of an addition, +Lua checks for a function in the field "__add" of the value's metatable. +If it finds one, +Lua calls this function to perform the addition. + + +

+The keys in a metatable are derived from the event names; +the corresponding values are called metamethods. +In the previous example, the event is "add" +and the metamethod is the function that performs the addition. + + +

+You can query the metatable of any value +using the getmetatable function. + + +

+You can replace the metatable of tables +using the setmetatable function. +You cannot change the metatable of other types from Lua code +(except by using the debug library (§6.10)); +you should use the C API for that. + + +

+Tables and full userdata have individual metatables +(although multiple tables and userdata can share their metatables). +Values of all other types share one single metatable per type; +that is, there is one single metatable for all numbers, +one for all strings, etc. +By default, a value has no metatable, +but the string library sets a metatable for the string type (see §6.4). + + +

+A metatable controls how an object behaves in +arithmetic operations, bitwise operations, +order comparisons, concatenation, length operation, calls, and indexing. +A metatable also can define a function to be called +when a userdata or a table is garbage collected (§2.5). + + +

+A detailed list of events controlled by metatables is given next. +Each operation is identified by its corresponding event name. +The key for each event is a string with its name prefixed by +two underscores, '__'; +for instance, the key for operation "add" is the +string "__add". +Note that queries for metamethods are always raw; +the access to a metamethod does not invoke other metamethods. + + +

+For the unary operators (negation, length, and bitwise not), +the metamethod is computed and called with a dummy second operand, +equal to the first one. +This extra operand is only to simplify Lua's internals +(by making these operators behave like a binary operation) +and may be removed in future versions. +(For most uses this extra operand is irrelevant.) + + + +

"add": +the + operation. + +If any operand for an addition is not a number +(nor a string coercible to a number), +Lua will try to call a metamethod. +First, Lua will check the first operand (even if it is valid). +If that operand does not define a metamethod for the "__add" event, +then Lua will check the second operand. +If Lua can find a metamethod, +it calls the metamethod with the two operands as arguments, +and the result of the call +(adjusted to one value) +is the result of the operation. +Otherwise, +it raises an error. +
"sub": +the - operation. + +Behavior similar to the "add" operation. +
"mul": +the * operation. + +Behavior similar to the "add" operation. +
"div": +the / operation. + +Behavior similar to the "add" operation. +
"mod": +the % operation. + +Behavior similar to the "add" operation. +
"pow": +the ^ (exponentiation) operation. + +Behavior similar to the "add" operation. +
"unm": +the - (unary minus) operation. + +Behavior similar to the "add" operation. +
"idiv": +the // (floor division) operation. + +Behavior similar to the "add" operation. +
"band": +the & (bitwise and) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod +if any operand is neither an integer +nor a value coercible to an integer (see §3.4.3). +
"bor": +the | (bitwise or) operation. + +Behavior similar to the "band" operation. +
"bxor": +the ~ (bitwise exclusive or) operation. + +Behavior similar to the "band" operation. +
"bnot": +the ~ (bitwise unary not) operation. + +Behavior similar to the "band" operation. +
"shl": +the << (bitwise left shift) operation. + +Behavior similar to the "band" operation. +
"shr": +the >> (bitwise right shift) operation. + +Behavior similar to the "band" operation. +
"concat": +the .. (concatenation) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod +if any operand is neither a string nor a number +(which is always coercible to a string). +
"len": +the # (length) operation. + +If the object is not a string, +Lua will try its metamethod. +If there is a metamethod, +Lua calls it with the object as argument, +and the result of the call +(always adjusted to one value) +is the result of the operation. +If there is no metamethod but the object is a table, +then Lua uses the table length operation (see §3.4.7). +Otherwise, Lua raises an error. +
"eq": +the == (equal) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod only when the values +being compared are either both tables or both full userdata +and they are not primitively equal. +The result of the call is always converted to a boolean. +
"lt": +the < (less than) operation. + +Behavior similar to the "add" operation, +except that Lua will try a metamethod only when the values +being compared are neither both numbers nor both strings. +The result of the call is always converted to a boolean. +
"le": +the <= (less equal) operation. + +Unlike other operations, +the less-equal operation can use two different events. +First, Lua looks for the "__le" metamethod in both operands, +like in the "lt" operation. +If it cannot find such a metamethod, +then it will try the "__lt" event, +assuming that a <= b is equivalent to not (b < a). +As with the other comparison operators, +the result is always a boolean. +(This use of the "__lt" event can be removed in future versions; +it is also slower than a real "__le" metamethod.) +
"index": +The indexing access table[key]. + +This event happens when table is not a table or +when key is not present in table. +The metamethod is looked up in table. + + +
+Despite the name, +the metamethod for this event can be either a function or a table. +If it is a function, +it is called with table and key as arguments. +If it is a table, +the final result is the result of indexing this table with key. +(This indexing is regular, not raw, +and therefore can trigger another metamethod.) +
"newindex": +The indexing assignment table[key] = value. + +Like the index event, +this event happens when table is not a table or +when key is not present in table. +The metamethod is looked up in table. + + +
+Like with indexing, +the metamethod for this event can be either a function or a table. +If it is a function, +it is called with table, key, and value as arguments. +If it is a table, +Lua does an indexing assignment to this table with the same key and value. +(This assignment is regular, not raw, +and therefore can trigger another metamethod.) + + +
+Whenever there is a "newindex" metamethod, +Lua does not perform the primitive assignment. +(If necessary, +the metamethod itself can call rawset +to do the assignment.) +
"call": +The call operation func(args). + +This event happens when Lua tries to call a non-function value +(that is, func is not a function). +The metamethod is looked up in func. +If present, +the metamethod is called with func as its first argument, +followed by the arguments of the original call (args). +

+ +

+It is a good practice to add all needed metamethods to a table +before setting it as a metatable of some object. +In particular, the "__gc" metamethod works only when this order +is followed (see §2.5.1). + + + + + +

2.5 – Garbage Collection

+ +

+Lua performs automatic memory management. +This means that +you do not have to worry about allocating memory for new objects +or freeing it when the objects are no longer needed. +Lua manages memory automatically by running +a garbage collector to collect all dead objects +(that is, objects that are no longer accessible from Lua). +All memory used by Lua is subject to automatic management: +strings, tables, userdata, functions, threads, internal structures, etc. + + +

+Lua implements an incremental mark-and-sweep collector. +It uses two numbers to control its garbage-collection cycles: +the garbage-collector pause and +the garbage-collector step multiplier. +Both use percentage points as units +(e.g., a value of 100 means an internal value of 1). + + +

+The garbage-collector pause +controls how long the collector waits before starting a new cycle. +Larger values make the collector less aggressive. +Values smaller than 100 mean the collector will not wait to +start a new cycle. +A value of 200 means that the collector waits for the total memory in use +to double before starting a new cycle. + + +

+The garbage-collector step multiplier +controls the relative speed of the collector relative to +memory allocation. +Larger values make the collector more aggressive but also increase +the size of each incremental step. +You should not use values smaller than 100, +because they make the collector too slow and +can result in the collector never finishing a cycle. +The default is 200, +which means that the collector runs at "twice" +the speed of memory allocation. + + +

+If you set the step multiplier to a very large number +(larger than 10% of the maximum number of +bytes that the program may use), +the collector behaves like a stop-the-world collector. +If you then set the pause to 200, +the collector behaves as in old Lua versions, +doing a complete collection every time Lua doubles its +memory usage. + + +

+You can change these numbers by calling lua_gc in C +or collectgarbage in Lua. +You can also use these functions to control +the collector directly (e.g., stop and restart it). + + + +

2.5.1 – Garbage-Collection Metamethods

+ +

+You can set garbage-collector metamethods for tables +and, using the C API, +for full userdata (see §2.4). +These metamethods are also called finalizers. +Finalizers allow you to coordinate Lua's garbage collection +with external resource management +(such as closing files, network or database connections, +or freeing your own memory). + + +

+For an object (table or userdata) to be finalized when collected, +you must mark it for finalization. + +You mark an object for finalization when you set its metatable +and the metatable has a field indexed by the string "__gc". +Note that if you set a metatable without a __gc field +and later create that field in the metatable, +the object will not be marked for finalization. + + +

+When a marked object becomes garbage, +it is not collected immediately by the garbage collector. +Instead, Lua puts it in a list. +After the collection, +Lua goes through that list. +For each object in the list, +it checks the object's __gc metamethod: +If it is a function, +Lua calls it with the object as its single argument; +if the metamethod is not a function, +Lua simply ignores it. + + +

+At the end of each garbage-collection cycle, +the finalizers for objects are called in +the reverse order that the objects were marked for finalization, +among those collected in that cycle; +that is, the first finalizer to be called is the one associated +with the object marked last in the program. +The execution of each finalizer may occur at any point during +the execution of the regular code. + + +

+Because the object being collected must still be used by the finalizer, +that object (and other objects accessible only through it) +must be resurrected by Lua. +Usually, this resurrection is transient, +and the object memory is freed in the next garbage-collection cycle. +However, if the finalizer stores the object in some global place +(e.g., a global variable), +then the resurrection is permanent. +Moreover, if the finalizer marks a finalizing object for finalization again, +its finalizer will be called again in the next cycle where the +object is unreachable. +In any case, +the object memory is freed only in a GC cycle where +the object is unreachable and not marked for finalization. + + +

+When you close a state (see lua_close), +Lua calls the finalizers of all objects marked for finalization, +following the reverse order that they were marked. +If any finalizer marks objects for collection during that phase, +these marks have no effect. + + + + + +

2.5.2 – Weak Tables

+ +

+A weak table is a table whose elements are +weak references. +A weak reference is ignored by the garbage collector. +In other words, +if the only references to an object are weak references, +then the garbage collector will collect that object. + + +

+A weak table can have weak keys, weak values, or both. +A table with weak values allows the collection of its values, +but prevents the collection of its keys. +A table with both weak keys and weak values allows the collection of +both keys and values. +In any case, if either the key or the value is collected, +the whole pair is removed from the table. +The weakness of a table is controlled by the +__mode field of its metatable. +If the __mode field is a string containing the character 'k', +the keys in the table are weak. +If __mode contains 'v', +the values in the table are weak. + + +

+A table with weak keys and strong values +is also called an ephemeron table. +In an ephemeron table, +a value is considered reachable only if its key is reachable. +In particular, +if the only reference to a key comes through its value, +the pair is removed. + + +

+Any change in the weakness of a table may take effect only +at the next collect cycle. +In particular, if you change the weakness to a stronger mode, +Lua may still collect some items from that table +before the change takes effect. + + +

+Only objects that have an explicit construction +are removed from weak tables. +Values, such as numbers and light C functions, +are not subject to garbage collection, +and therefore are not removed from weak tables +(unless their associated values are collected). +Although strings are subject to garbage collection, +they do not have an explicit construction, +and therefore are not removed from weak tables. + + +

+Resurrected objects +(that is, objects being finalized +and objects accessible only through objects being finalized) +have a special behavior in weak tables. +They are removed from weak values before running their finalizers, +but are removed from weak keys only in the next collection +after running their finalizers, when such objects are actually freed. +This behavior allows the finalizer to access properties +associated with the object through weak tables. + + +

+If a weak table is among the resurrected objects in a collection cycle, +it may not be properly cleared until the next cycle. + + + + + + + +

2.6 – Coroutines

+ +

+Lua supports coroutines, +also called collaborative multithreading. +A coroutine in Lua represents an independent thread of execution. +Unlike threads in multithread systems, however, +a coroutine only suspends its execution by explicitly calling +a yield function. + + +

+You create a coroutine by calling coroutine.create. +Its sole argument is a function +that is the main function of the coroutine. +The create function only creates a new coroutine and +returns a handle to it (an object of type thread); +it does not start the coroutine. + + +

+You execute a coroutine by calling coroutine.resume. +When you first call coroutine.resume, +passing as its first argument +a thread returned by coroutine.create, +the coroutine starts its execution by +calling its main function. +Extra arguments passed to coroutine.resume are passed +as arguments to that function. +After the coroutine starts running, +it runs until it terminates or yields. + + +

+A coroutine can terminate its execution in two ways: +normally, when its main function returns +(explicitly or implicitly, after the last instruction); +and abnormally, if there is an unprotected error. +In case of normal termination, +coroutine.resume returns true, +plus any values returned by the coroutine main function. +In case of errors, coroutine.resume returns false +plus an error message. + + +

+A coroutine yields by calling coroutine.yield. +When a coroutine yields, +the corresponding coroutine.resume returns immediately, +even if the yield happens inside nested function calls +(that is, not in the main function, +but in a function directly or indirectly called by the main function). +In the case of a yield, coroutine.resume also returns true, +plus any values passed to coroutine.yield. +The next time you resume the same coroutine, +it continues its execution from the point where it yielded, +with the call to coroutine.yield returning any extra +arguments passed to coroutine.resume. + + +

+Like coroutine.create, +the coroutine.wrap function also creates a coroutine, +but instead of returning the coroutine itself, +it returns a function that, when called, resumes the coroutine. +Any arguments passed to this function +go as extra arguments to coroutine.resume. +coroutine.wrap returns all the values returned by coroutine.resume, +except the first one (the boolean error code). +Unlike coroutine.resume, +coroutine.wrap does not catch errors; +any error is propagated to the caller. + + +

+As an example of how coroutines work, +consider the following code: + +

+     function foo (a)
+       print("foo", a)
+       return coroutine.yield(2*a)
+     end
+     
+     co = coroutine.create(function (a,b)
+           print("co-body", a, b)
+           local r = foo(a+1)
+           print("co-body", r)
+           local r, s = coroutine.yield(a+b, a-b)
+           print("co-body", r, s)
+           return b, "end"
+     end)
+     
+     print("main", coroutine.resume(co, 1, 10))
+     print("main", coroutine.resume(co, "r"))
+     print("main", coroutine.resume(co, "x", "y"))
+     print("main", coroutine.resume(co, "x", "y"))
+

+When you run it, it produces the following output: + +

+     co-body 1       10
+     foo     2
+     main    true    4
+     co-body r
+     main    true    11      -9
+     co-body x       y
+     main    true    10      end
+     main    false   cannot resume dead coroutine
+

+ +

+You can also create and manipulate coroutines through the C API: +see functions lua_newthread, lua_resume, +and lua_yield. + + + + + +

3 – The Language

+ +

+This section describes the lexis, the syntax, and the semantics of Lua. +In other words, +this section describes +which tokens are valid, +how they can be combined, +and what their combinations mean. + + +

+Language constructs will be explained using the usual extended BNF notation, +in which +{a} means 0 or more a's, and +[a] means an optional a. +Non-terminals are shown like non-terminal, +keywords are shown like kword, +and other terminal symbols are shown like ‘=’. +The complete syntax of Lua can be found in §9 +at the end of this manual. + + + +

3.1 – Lexical Conventions

+ +

+Lua is a free-form language. +It ignores spaces (including new lines) and comments +between lexical elements (tokens), +except as delimiters between names and keywords. + + +

+Names +(also called identifiers) +in Lua can be any string of letters, +digits, and underscores, +not beginning with a digit and +not being a reserved word. +Identifiers are used to name variables, table fields, and labels. + + +

+The following keywords are reserved +and cannot be used as names: + + +

+     and       break     do        else      elseif    end
+     false     for       function  goto      if        in
+     local     nil       not       or        repeat    return
+     then      true      until     while
+

+ +

+Lua is a case-sensitive language: +and is a reserved word, but And and AND +are two different, valid names. +As a convention, +programs should avoid creating +names that start with an underscore followed by +one or more uppercase letters (such as _VERSION). + + +

+The following strings denote other tokens: + +

+     +     -     *     /     %     ^     #
+     &     ~     |     <<    >>    //
+     ==    ~=    <=    >=    <     >     =
+     (     )     {     }     [     ]     ::
+     ;     :     ,     .     ..    ...
+

+ +

+Literal strings +can be delimited by matching single or double quotes, +and can contain the following C-like escape sequences: +'\a' (bell), +'\b' (backspace), +'\f' (form feed), +'\n' (newline), +'\r' (carriage return), +'\t' (horizontal tab), +'\v' (vertical tab), +'\\' (backslash), +'\"' (quotation mark [double quote]), +and '\'' (apostrophe [single quote]). +A backslash followed by a real newline +results in a newline in the string. +The escape sequence '\z' skips the following span +of white-space characters, +including line breaks; +it is particularly useful to break and indent a long literal string +into multiple lines without adding the newlines and spaces +into the string contents. + + +

+Strings in Lua can contain any 8-bit value, including embedded zeros, +which can be specified as '\0'. +More generally, +we can specify any byte in a literal string by its numeric value. +This can be done +with the escape sequence \xXX, +where XX is a sequence of exactly two hexadecimal digits, +or with the escape sequence \ddd, +where ddd is a sequence of up to three decimal digits. +(Note that if a decimal escape sequence is to be followed by a digit, +it must be expressed using exactly three digits.) + + +

+The UTF-8 encoding of a Unicode character +can be inserted in a literal string with +the escape sequence \u{XXX} +(note the mandatory enclosing brackets), +where XXX is a sequence of one or more hexadecimal digits +representing the character code point. + + +

+Literal strings can also be defined using a long format +enclosed by long brackets. +We define an opening long bracket of level n as an opening +square bracket followed by n equal signs followed by another +opening square bracket. +So, an opening long bracket of level 0 is written as [[, +an opening long bracket of level 1 is written as [=[, +and so on. +A closing long bracket is defined similarly; +for instance, +a closing long bracket of level 4 is written as ]====]. +A long literal starts with an opening long bracket of any level and +ends at the first closing long bracket of the same level. +It can contain any text except a closing bracket of the same level. +Literals in this bracketed form can run for several lines, +do not interpret any escape sequences, +and ignore long brackets of any other level. +Any kind of end-of-line sequence +(carriage return, newline, carriage return followed by newline, +or newline followed by carriage return) +is converted to a simple newline. + + +

+Any byte in a literal string not +explicitly affected by the previous rules represents itself. +However, Lua opens files for parsing in text mode, +and the system file functions may have problems with +some control characters. +So, it is safer to represent +non-text data as a quoted literal with +explicit escape sequences for non-text characters. + + +

+For convenience, +when the opening long bracket is immediately followed by a newline, +the newline is not included in the string. +As an example, in a system using ASCII +(in which 'a' is coded as 97, +newline is coded as 10, and '1' is coded as 49), +the five literal strings below denote the same string: + +

+     a = 'alo\n123"'
+     a = "alo\n123\""
+     a = '\97lo\10\04923"'
+     a = [[alo
+     123"]]
+     a = [==[
+     alo
+     123"]==]
+

+ +

+A numeric constant (or numeral) +can be written with an optional fractional part +and an optional decimal exponent, +marked by a letter 'e' or 'E'. +Lua also accepts hexadecimal constants, +which start with 0x or 0X. +Hexadecimal constants also accept an optional fractional part +plus an optional binary exponent, +marked by a letter 'p' or 'P'. +A numeric constant with a fractional dot or an exponent +denotes a float; +otherwise it denotes an integer. +Examples of valid integer constants are + +

+     3   345   0xff   0xBEBADA
+

+Examples of valid float constants are + +

+     3.0     3.1416     314.16e-2     0.31416E1     34e1
+     0x0.1E  0xA23p-4   0X1.921FB54442D18P+1
+

+ +

+A comment starts with a double hyphen (--) +anywhere outside a string. +If the text immediately after -- is not an opening long bracket, +the comment is a short comment, +which runs until the end of the line. +Otherwise, it is a long comment, +which runs until the corresponding closing long bracket. +Long comments are frequently used to disable code temporarily. + + + + + +

3.2 – Variables

+ +

+Variables are places that store values. +There are three kinds of variables in Lua: +global variables, local variables, and table fields. + + +

+A single name can denote a global variable or a local variable +(or a function's formal parameter, +which is a particular kind of local variable): + +

+	var ::= Name
+

+Name denotes identifiers, as defined in §3.1. + + +

+Any variable name is assumed to be global unless explicitly declared +as a local (see §3.3.7). +Local variables are lexically scoped: +local variables can be freely accessed by functions +defined inside their scope (see §3.5). + + +

+Before the first assignment to a variable, its value is nil. + + +

+Square brackets are used to index a table: + +

+	var ::= prefixexp ‘[’ exp ‘]’
+

+The meaning of accesses to table fields can be changed via metatables. +An access to an indexed variable t[i] is equivalent to +a call gettable_event(t,i). +(See §2.4 for a complete description of the +gettable_event function. +This function is not defined or callable in Lua. +We use it here only for explanatory purposes.) + + +

+The syntax var.Name is just syntactic sugar for +var["Name"]: + +

+	var ::= prefixexp ‘.’ Name
+

+ +

+An access to a global variable x +is equivalent to _ENV.x. +Due to the way that chunks are compiled, +_ENV is never a global name (see §2.2). + + + + + +

3.3 – Statements

+ +

+Lua supports an almost conventional set of statements, +similar to those in Pascal or C. +This set includes +assignments, control structures, function calls, +and variable declarations. + + + +

3.3.1 – Blocks

+ +

+A block is a list of statements, +which are executed sequentially: + +

+	block ::= {stat}
+

+Lua has empty statements +that allow you to separate statements with semicolons, +start a block with a semicolon +or write two semicolons in sequence: + +

+	stat ::= ‘;’
+

+ +

+Function calls and assignments +can start with an open parenthesis. +This possibility leads to an ambiguity in Lua's grammar. +Consider the following fragment: + +

+     a = b + c
+     (print or io.write)('done')
+

+The grammar could see it in two ways: + +

+     a = b + c(print or io.write)('done')
+     
+     a = b + c; (print or io.write)('done')
+

+The current parser always sees such constructions +in the first way, +interpreting the open parenthesis +as the start of the arguments to a call. +To avoid this ambiguity, +it is a good practice to always precede with a semicolon +statements that start with a parenthesis: + +

+     ;(print or io.write)('done')
+

+ +

+A block can be explicitly delimited to produce a single statement: + +

+	stat ::= do block end
+

+Explicit blocks are useful +to control the scope of variable declarations. +Explicit blocks are also sometimes used to +add a return statement in the middle +of another block (see §3.3.4). + + + + + +

3.3.2 – Chunks

+ +

+The unit of compilation of Lua is called a chunk. +Syntactically, +a chunk is simply a block: + +

+	chunk ::= block
+

+ +

+Lua handles a chunk as the body of an anonymous function +with a variable number of arguments +(see §3.4.11). +As such, chunks can define local variables, +receive arguments, and return values. +Moreover, such anonymous function is compiled as in the +scope of an external local variable called _ENV (see §2.2). +The resulting function always has _ENV as its only upvalue, +even if it does not use that variable. + + +

+A chunk can be stored in a file or in a string inside the host program. +To execute a chunk, +Lua first loads it, +precompiling the chunk's code into instructions for a virtual machine, +and then Lua executes the compiled code +with an interpreter for the virtual machine. + + +

+Chunks can also be precompiled into binary form; +see program luac and function string.dump for details. +Programs in source and compiled forms are interchangeable; +Lua automatically detects the file type and acts accordingly (see load). + + + + + +

3.3.3 – Assignment

+ +

+Lua allows multiple assignments. +Therefore, the syntax for assignment +defines a list of variables on the left side +and a list of expressions on the right side. +The elements in both lists are separated by commas: + +

+	stat ::= varlist ‘=’ explist
+	varlist ::= var {‘,’ var}
+	explist ::= exp {‘,’ exp}
+

+Expressions are discussed in §3.4. + + +

+Before the assignment, +the list of values is adjusted to the length of +the list of variables. +If there are more values than needed, +the excess values are thrown away. +If there are fewer values than needed, +the list is extended with as many nil's as needed. +If the list of expressions ends with a function call, +then all values returned by that call enter the list of values, +before the adjustment +(except when the call is enclosed in parentheses; see §3.4). + + +

+The assignment statement first evaluates all its expressions +and only then the assignments are performed. +Thus the code + +

+     i = 3
+     i, a[i] = i+1, 20
+

+sets a[3] to 20, without affecting a[4] +because the i in a[i] is evaluated (to 3) +before it is assigned 4. +Similarly, the line + +

+     x, y = y, x
+

+exchanges the values of x and y, +and + +

+     x, y, z = y, z, x
+

+cyclically permutes the values of x, y, and z. + + +

+The meaning of assignments to global variables +and table fields can be changed via metatables. +An assignment to an indexed variable t[i] = val is equivalent to +settable_event(t,i,val). +(See §2.4 for a complete description of the +settable_event function. +This function is not defined or callable in Lua. +We use it here only for explanatory purposes.) + + +

+An assignment to a global name x = val +is equivalent to the assignment +_ENV.x = val (see §2.2). + + + + + +

3.3.4 – Control Structures

+The control structures +if, while, and repeat have the usual meaning and +familiar syntax: + + + + +

+	stat ::= while exp do block end
+	stat ::= repeat block until exp
+	stat ::= if exp then block {elseif exp then block} [else block] end
+

+Lua also has a for statement, in two flavors (see §3.3.5). + + +

+The condition expression of a +control structure can return any value. +Both false and nil are considered false. +All values different from nil and false are considered true +(in particular, the number 0 and the empty string are also true). + + +

+In the repeat–until loop, +the inner block does not end at the until keyword, +but only after the condition. +So, the condition can refer to local variables +declared inside the loop block. + + +

+The goto statement transfers the program control to a label. +For syntactical reasons, +labels in Lua are considered statements too: + + + +

+	stat ::= goto Name
+	stat ::= label
+	label ::= ‘::’ Name ‘::’
+

+ +

+A label is visible in the entire block where it is defined, +except +inside nested blocks where a label with the same name is defined and +inside nested functions. +A goto may jump to any visible label as long as it does not +enter into the scope of a local variable. + + +

+Labels and empty statements are called void statements, +as they perform no actions. + + +

+The break statement terminates the execution of a +while, repeat, or for loop, +skipping to the next statement after the loop: + + +

+	stat ::= break
+

+A break ends the innermost enclosing loop. + + +

+The return statement is used to return values +from a function or a chunk +(which is an anonymous function). + +Functions can return more than one value, +so the syntax for the return statement is + +

+	stat ::= return [explist] [‘;’]
+

+ +

+The return statement can only be written +as the last statement of a block. +If it is really necessary to return in the middle of a block, +then an explicit inner block can be used, +as in the idiom do return end, +because now return is the last statement in its (inner) block. + + + + + +

3.3.5 – For Statement

+ +

+ +The for statement has two forms: +one numerical and one generic. + + +

+The numerical for loop repeats a block of code while a +control variable runs through an arithmetic progression. +It has the following syntax: + +

+	stat ::= for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end
+

+The block is repeated for name starting at the value of +the first exp, until it passes the second exp by steps of the +third exp. +More precisely, a for statement like + +

+     for v = e1, e2, e3 do block end
+

+is equivalent to the code: + +

+     do
+       local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
+       if not (var and limit and step) then error() end
+       var = var - step
+       while true do
+         var = var + step
+         if (step >= 0 and var > limit) or (step < 0 and var < limit) then
+           break
+         end
+         local v = var
+         block
+       end
+     end
+

+ +

+Note the following: + +

+All three control expressions are evaluated only once, +before the loop starts. +They must all result in numbers. +
+var, limit, and step are invisible variables. +The names shown here are for explanatory purposes only. +
+If the third expression (the step) is absent, +then a step of 1 is used. +
+You can use break and goto to exit a for loop. +
+The loop variable v is local to the loop body. +If you need its value after the loop, +assign it to another variable before exiting the loop. +

+ +

+The generic for statement works over functions, +called iterators. +On each iteration, the iterator function is called to produce a new value, +stopping when this new value is nil. +The generic for loop has the following syntax: + +

+	stat ::= for namelist in explist do block end
+	namelist ::= Name {‘,’ Name}
+

+A for statement like + +

+     for var_1, ···, var_n in explist do block end
+

+is equivalent to the code: + +

+     do
+       local f, s, var = explist
+       while true do
+         local var_1, ···, var_n = f(s, var)
+         if var_1 == nil then break end
+         var = var_1
+         block
+       end
+     end
+

+Note the following: + +

+explist is evaluated only once. +Its results are an iterator function, +a state, +and an initial value for the first iterator variable. +
+f, s, and var are invisible variables. +The names are here for explanatory purposes only. +
+You can use break to exit a for loop. +
+The loop variables var_i are local to the loop; +you cannot use their values after the for ends. +If you need these values, +then assign them to other variables before breaking or exiting the loop. +

+ + + + +

3.3.6 – Function Calls as Statements

+To allow possible side-effects, +function calls can be executed as statements: + +

+	stat ::= functioncall
+

+In this case, all returned values are thrown away. +Function calls are explained in §3.4.10. + + + + + +

3.3.7 – Local Declarations

+Local variables can be declared anywhere inside a block. +The declaration can include an initial assignment: + +

+	stat ::= local namelist [‘=’ explist]
+

+If present, an initial assignment has the same semantics +of a multiple assignment (see §3.3.3). +Otherwise, all variables are initialized with nil. + + +

+A chunk is also a block (see §3.3.2), +and so local variables can be declared in a chunk outside any explicit block. + + +

+The visibility rules for local variables are explained in §3.5. + + + + + + + +

3.4 – Expressions

+ +

+The basic expressions in Lua are the following: + +

+	exp ::= prefixexp
+	exp ::= nil | false | true
+	exp ::= Numeral
+	exp ::= LiteralString
+	exp ::= functiondef
+	exp ::= tableconstructor
+	exp ::= ‘...’
+	exp ::= exp binop exp
+	exp ::= unop exp
+	prefixexp ::= var | functioncall | ‘(’ exp ‘)’
+

+ +

+Numerals and literal strings are explained in §3.1; +variables are explained in §3.2; +function definitions are explained in §3.4.11; +function calls are explained in §3.4.10; +table constructors are explained in §3.4.9. +Vararg expressions, +denoted by three dots ('...'), can only be used when +directly inside a vararg function; +they are explained in §3.4.11. + + +

+Binary operators comprise arithmetic operators (see §3.4.1), +bitwise operators (see §3.4.2), +relational operators (see §3.4.4), logical operators (see §3.4.5), +and the concatenation operator (see §3.4.6). +Unary operators comprise the unary minus (see §3.4.1), +the unary bitwise not (see §3.4.2), +the unary logical not (see §3.4.5), +and the unary length operator (see §3.4.7). + + +

+Both function calls and vararg expressions can result in multiple values. +If a function call is used as a statement (see §3.3.6), +then its return list is adjusted to zero elements, +thus discarding all returned values. +If an expression is used as the last (or the only) element +of a list of expressions, +then no adjustment is made +(unless the expression is enclosed in parentheses). +In all other contexts, +Lua adjusts the result list to one element, +either discarding all values except the first one +or adding a single nil if there are no values. + + +

+Here are some examples: + +

+     f()                -- adjusted to 0 results
+     g(f(), x)          -- f() is adjusted to 1 result
+     g(x, f())          -- g gets x plus all results from f()
+     a,b,c = f(), x     -- f() is adjusted to 1 result (c gets nil)
+     a,b = ...          -- a gets the first vararg parameter, b gets
+                        -- the second (both a and b can get nil if there
+                        -- is no corresponding vararg parameter)
+     
+     a,b,c = x, f()     -- f() is adjusted to 2 results
+     a,b,c = f()        -- f() is adjusted to 3 results
+     return f()         -- returns all results from f()
+     return ...         -- returns all received vararg parameters
+     return x,y,f()     -- returns x, y, and all results from f()
+     {f()}              -- creates a list with all results from f()
+     {...}              -- creates a list with all vararg parameters
+     {f(), nil}         -- f() is adjusted to 1 result
+

+ +

+Any expression enclosed in parentheses always results in only one value. +Thus, +(f(x,y,z)) is always a single value, +even if f returns several values. +(The value of (f(x,y,z)) is the first value returned by f +or nil if f does not return any values.) + + + +

3.4.1 – Arithmetic Operators

+Lua supports the following arithmetic operators: + +

+: addition
-: subtraction
*: multiplication
/: float division
//: floor division
%: modulo
^: exponentiation
-: unary minus

+ +

+With the exception of exponentiation and float division, +the arithmetic operators work as follows: +If both operands are integers, +the operation is performed over integers and the result is an integer. +Otherwise, if both operands are numbers +or strings that can be converted to +numbers (see §3.4.3), +then they are converted to floats, +the operation is performed following the usual rules +for floating-point arithmetic +(usually the IEEE 754 standard), +and the result is a float. + + +

+Exponentiation and float division (/) +always convert their operands to floats +and the result is always a float. +Exponentiation uses the ISO C function pow, +so that it works for non-integer exponents too. + + +

+Floor division (//) is a division +that rounds the quotient towards minus infinity, +that is, the floor of the division of its operands. + + +

+Modulo is defined as the remainder of a division +that rounds the quotient towards minus infinity (floor division). + + +

+In case of overflows in integer arithmetic, +all operations wrap around, +according to the usual rules of two-complement arithmetic. +(In other words, +they return the unique representable integer +that is equal modulo 2⁶⁴ to the mathematical result.) + + + +

3.4.2 – Bitwise Operators

+Lua supports the following bitwise operators: + +

&: bitwise and
|: bitwise or
~: bitwise exclusive or
>>: right shift
<<: left shift
~: unary bitwise not

+ +

+All bitwise operations convert its operands to integers +(see §3.4.3), +operate on all bits of those integers, +and result in an integer. + + +

+Both right and left shifts fill the vacant bits with zeros. +Negative displacements shift to the other direction; +displacements with absolute values equal to or higher than +the number of bits in an integer +result in zero (as all bits are shifted out). + + + + + +

3.4.3 – Coercions and Conversions

+Lua provides some automatic conversions between some +types and representations at run time. +Bitwise operators always convert float operands to integers. +Exponentiation and float division +always convert integer operands to floats. +All other arithmetic operations applied to mixed numbers +(integers and floats) convert the integer operand to a float; +this is called the usual rule. +The C API also converts both integers to floats and +floats to integers, as needed. +Moreover, string concatenation accepts numbers as arguments, +besides strings. + + +

+Lua also converts strings to numbers, +whenever a number is expected. + + +

+In a conversion from integer to float, +if the integer value has an exact representation as a float, +that is the result. +Otherwise, +the conversion gets the nearest higher or +the nearest lower representable value. +This kind of conversion never fails. + + +

+The conversion from float to integer +checks whether the float has an exact representation as an integer +(that is, the float has an integral value and +it is in the range of integer representation). +If it does, that representation is the result. +Otherwise, the conversion fails. + + +

+The conversion from strings to numbers goes as follows: +First, the string is converted to an integer or a float, +following its syntax and the rules of the Lua lexer. +(The string may have also leading and trailing spaces and a sign.) +Then, the resulting number (float or integer) +is converted to the type (float or integer) required by the context +(e.g., the operation that forced the conversion). + + +

+The conversion from numbers to strings uses a +non-specified human-readable format. +For complete control over how numbers are converted to strings, +use the format function from the string library +(see string.format). + + + + + +

3.4.4 – Relational Operators

+Lua supports the following relational operators: + +

==: equality
~=: inequality
<: less than
>: greater than
<=: less or equal
>=: greater or equal

+These operators always result in false or true. + + +

+Equality (==) first compares the type of its operands. +If the types are different, then the result is false. +Otherwise, the values of the operands are compared. +Strings are compared in the obvious way. +Numbers are equal if they denote the same mathematical value. + + +

+Tables, userdata, and threads +are compared by reference: +two objects are considered equal only if they are the same object. +Every time you create a new object +(a table, userdata, or thread), +this new object is different from any previously existing object. +Closures with the same reference are always equal. +Closures with any detectable difference +(different behavior, different definition) are always different. + + +

+You can change the way that Lua compares tables and userdata +by using the "eq" metamethod (see §2.4). + + +

+Equality comparisons do not convert strings to numbers +or vice versa. +Thus, "0"==0 evaluates to false, +and t[0] and t["0"] denote different +entries in a table. + + +

+The operator ~= is exactly the negation of equality (==). + + +

+The order operators work as follows. +If both arguments are numbers, +then they are compared according to their mathematical values +(regardless of their subtypes). +Otherwise, if both arguments are strings, +then their values are compared according to the current locale. +Otherwise, Lua tries to call the "lt" or the "le" +metamethod (see §2.4). +A comparison a > b is translated to b < a +and a >= b is translated to b <= a. + + +

+Following the IEEE 754 standard, +NaN is considered neither smaller than, +nor equal to, nor greater than any value (including itself). + + + + + +

3.4.5 – Logical Operators

+The logical operators in Lua are +and, or, and not. +Like the control structures (see §3.3.4), +all logical operators consider both false and nil as false +and anything else as true. + + +

+The negation operator not always returns false or true. +The conjunction operator and returns its first argument +if this value is false or nil; +otherwise, and returns its second argument. +The disjunction operator or returns its first argument +if this value is different from nil and false; +otherwise, or returns its second argument. +Both and and or use short-circuit evaluation; +that is, +the second operand is evaluated only if necessary. +Here are some examples: + +

+     10 or 20            --> 10
+     10 or error()       --> 10
+     nil or "a"          --> "a"
+     nil and 10          --> nil
+     false and error()   --> false
+     false and nil       --> false
+     false or nil        --> nil
+     10 and 20           --> 20
+

+(In this manual, +--> indicates the result of the preceding expression.) + + + + + +

3.4.6 – Concatenation

+The string concatenation operator in Lua is +denoted by two dots ('..'). +If both operands are strings or numbers, then they are converted to +strings according to the rules described in §3.4.3. +Otherwise, the __concat metamethod is called (see §2.4). + + + + + +

3.4.7 – The Length Operator

+ +

+The length operator is denoted by the unary prefix operator #. +The length of a string is its number of bytes +(that is, the usual meaning of string length when each +character is one byte). + + +

+A program can modify the behavior of the length operator for +any value but strings through the __len metamethod (see §2.4). + + +

+Unless a __len metamethod is given, +the length of a table t is only defined if the +table is a sequence, +that is, +the set of its positive numeric keys is equal to {1..n} +for some non-negative integer n. +In that case, n is its length. +Note that a table like + +

+     {10, 20, nil, 40}
+

+is not a sequence, because it has the key 4 +but does not have the key 3. +(So, there is no n such that the set {1..n} is equal +to the set of positive numeric keys of that table.) +Note, however, that non-numeric keys do not interfere +with whether a table is a sequence. + + + + + +

3.4.8 – Precedence

+Operator precedence in Lua follows the table below, +from lower to higher priority: + +

+     or
+     and
+     <     >     <=    >=    ~=    ==
+     |
+     ~
+     &
+     <<    >>
+     ..
+     +     -
+     *     /     //    %
+     unary operators (not   #     -     ~)
+     ^
+

+As usual, +you can use parentheses to change the precedences of an expression. +The concatenation ('..') and exponentiation ('^') +operators are right associative. +All other binary operators are left associative. + + + + + +

3.4.9 – Table Constructors

+Table constructors are expressions that create tables. +Every time a constructor is evaluated, a new table is created. +A constructor can be used to create an empty table +or to create a table and initialize some of its fields. +The general syntax for constructors is + +

+	tableconstructor ::= ‘{’ [fieldlist] ‘}’
+	fieldlist ::= field {fieldsep field} [fieldsep]
+	field ::= ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp
+	fieldsep ::= ‘,’ | ‘;’
+

+ +

+Each field of the form [exp1] = exp2 adds to the new table an entry +with key exp1 and value exp2. +A field of the form name = exp is equivalent to +["name"] = exp. +Finally, fields of the form exp are equivalent to +[i] = exp, where i are consecutive integers +starting with 1. +Fields in the other formats do not affect this counting. +For example, + +

+     a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
+

+is equivalent to + +

+     do
+       local t = {}
+       t[f(1)] = g
+       t[1] = "x"         -- 1st exp
+       t[2] = "y"         -- 2nd exp
+       t.x = 1            -- t["x"] = 1
+       t[3] = f(x)        -- 3rd exp
+       t[30] = 23
+       t[4] = 45          -- 4th exp
+       a = t
+     end
+

+ +

+The order of the assignments in a constructor is undefined. +(This order would be relevant only when there are repeated keys.) + + +

+If the last field in the list has the form exp +and the expression is a function call or a vararg expression, +then all values returned by this expression enter the list consecutively +(see §3.4.10). + + +

+The field list can have an optional trailing separator, +as a convenience for machine-generated code. + + + + + +

3.4.10 – Function Calls

+A function call in Lua has the following syntax: + +

+	functioncall ::= prefixexp args
+

+In a function call, +first prefixexp and args are evaluated. +If the value of prefixexp has type function, +then this function is called +with the given arguments. +Otherwise, the prefixexp "call" metamethod is called, +having as first parameter the value of prefixexp, +followed by the original call arguments +(see §2.4). + + +

+The form + +

+	functioncall ::= prefixexp ‘:’ Name args
+

+can be used to call "methods". +A call v:name(args) +is syntactic sugar for v.name(v,args), +except that v is evaluated only once. + + +

+Arguments have the following syntax: + +

+	args ::= ‘(’ [explist] ‘)’
+	args ::= tableconstructor
+	args ::= LiteralString
+

+All argument expressions are evaluated before the call. +A call of the form f{fields} is +syntactic sugar for f({fields}); +that is, the argument list is a single new table. +A call of the form f'string' +(or f"string" or f[[string]]) +is syntactic sugar for f('string'); +that is, the argument list is a single literal string. + + +

+A call of the form return functioncall is called +a tail call. +Lua implements proper tail calls +(or proper tail recursion): +in a tail call, +the called function reuses the stack entry of the calling function. +Therefore, there is no limit on the number of nested tail calls that +a program can execute. +However, a tail call erases any debug information about the +calling function. +Note that a tail call only happens with a particular syntax, +where the return has one single function call as argument; +this syntax makes the calling function return exactly +the returns of the called function. +So, none of the following examples are tail calls: + +

+     return (f(x))        -- results adjusted to 1
+     return 2 * f(x)
+     return x, f(x)       -- additional results
+     f(x); return         -- results discarded
+     return x or f(x)     -- results adjusted to 1
+

+ + + + +

3.4.11 – Function Definitions

+ +

+The syntax for function definition is + +

+	functiondef ::= function funcbody
+	funcbody ::= ‘(’ [parlist] ‘)’ block end
+

+ +

+The following syntactic sugar simplifies function definitions: + +

+	stat ::= function funcname funcbody
+	stat ::= local function Name funcbody
+	funcname ::= Name {‘.’ Name} [‘:’ Name]
+

+The statement + +

+     function f () body end
+

+translates to + +

+     f = function () body end
+

+The statement + +

+     function t.a.b.c.f () body end
+

+translates to + +

+     t.a.b.c.f = function () body end
+

+The statement + +

+     local function f () body end
+

+translates to + +

+     local f; f = function () body end
+

+not to + +

+     local f = function () body end
+

+(This only makes a difference when the body of the function +contains references to f.) + + +

+A function definition is an executable expression, +whose value has type function. +When Lua precompiles a chunk, +all its function bodies are precompiled too. +Then, whenever Lua executes the function definition, +the function is instantiated (or closed). +This function instance (or closure) +is the final value of the expression. + + +

+Parameters act as local variables that are +initialized with the argument values: + +

+	parlist ::= namelist [‘,’ ‘...’] | ‘...’
+

+When a function is called, +the list of arguments is adjusted to +the length of the list of parameters, +unless the function is a vararg function, +which is indicated by three dots ('...') +at the end of its parameter list. +A vararg function does not adjust its argument list; +instead, it collects all extra arguments and supplies them +to the function through a vararg expression, +which is also written as three dots. +The value of this expression is a list of all actual extra arguments, +similar to a function with multiple results. +If a vararg expression is used inside another expression +or in the middle of a list of expressions, +then its return list is adjusted to one element. +If the expression is used as the last element of a list of expressions, +then no adjustment is made +(unless that last expression is enclosed in parentheses). + + +

+As an example, consider the following definitions: + +

+     function f(a, b) end
+     function g(a, b, ...) end
+     function r() return 1,2,3 end
+

+Then, we have the following mapping from arguments to parameters and +to the vararg expression: + +

+     CALL            PARAMETERS
+     
+     f(3)             a=3, b=nil
+     f(3, 4)          a=3, b=4
+     f(3, 4, 5)       a=3, b=4
+     f(r(), 10)       a=1, b=10
+     f(r())           a=1, b=2
+     
+     g(3)             a=3, b=nil, ... -->  (nothing)
+     g(3, 4)          a=3, b=4,   ... -->  (nothing)
+     g(3, 4, 5, 8)    a=3, b=4,   ... -->  5  8
+     g(5, r())        a=5, b=1,   ... -->  2  3
+

+ +

+Results are returned using the return statement (see §3.3.4). +If control reaches the end of a function +without encountering a return statement, +then the function returns with no results. + + +

+ +There is a system-dependent limit on the number of values +that a function may return. +This limit is guaranteed to be larger than 1000. + + +

+The colon syntax +is used for defining methods, +that is, functions that have an implicit extra parameter self. +Thus, the statement + +

+     function t.a.b.c:f (params) body end
+

+is syntactic sugar for + +

+     t.a.b.c.f = function (self, params) body end
+

+ + + + + + +

3.5 – Visibility Rules

+ +

+ +Lua is a lexically scoped language. +The scope of a local variable begins at the first statement after +its declaration and lasts until the last non-void statement +of the innermost block that includes the declaration. +Consider the following example: + +

+     x = 10                -- global variable
+     do                    -- new block
+       local x = x         -- new 'x', with value 10
+       print(x)            --> 10
+       x = x+1
+       do                  -- another block
+         local x = x+1     -- another 'x'
+         print(x)          --> 12
+       end
+       print(x)            --> 11
+     end
+     print(x)              --> 10  (the global one)
+

+ +

+Notice that, in a declaration like local x = x, +the new x being declared is not in scope yet, +and so the second x refers to the outside variable. + + +

+Because of the lexical scoping rules, +local variables can be freely accessed by functions +defined inside their scope. +A local variable used by an inner function is called +an upvalue, or external local variable, +inside the inner function. + + +

+Notice that each execution of a local statement +defines new local variables. +Consider the following example: + +

+     a = {}
+     local x = 20
+     for i=1,10 do
+       local y = 0
+       a[i] = function () y=y+1; return x+y end
+     end
+

+The loop creates ten closures +(that is, ten instances of the anonymous function). +Each of these closures uses a different y variable, +while all of them share the same x. + + + + + +

4 – The Application Program Interface

+ +

+ +This section describes the C API for Lua, that is, +the set of C functions available to the host program to communicate +with Lua. +All API functions and related types and constants +are declared in the header file lua.h. + + +

+Even when we use the term "function", +any facility in the API may be provided as a macro instead. +Except where stated otherwise, +all such macros use each of their arguments exactly once +(except for the first argument, which is always a Lua state), +and so do not generate any hidden side-effects. + + +

+As in most C libraries, +the Lua API functions do not check their arguments for validity or consistency. +However, you can change this behavior by compiling Lua +with the macro LUA_USE_APICHECK defined. + + + +

4.1 – The Stack

+ +

+Lua uses a virtual stack to pass values to and from C. +Each element in this stack represents a Lua value +(nil, number, string, etc.). + + +

+Whenever Lua calls C, the called function gets a new stack, +which is independent of previous stacks and of stacks of +C functions that are still active. +This stack initially contains any arguments to the C function +and it is where the C function pushes its results +to be returned to the caller (see lua_CFunction). + + +

+For convenience, +most query operations in the API do not follow a strict stack discipline. +Instead, they can refer to any element in the stack +by using an index: +A positive index represents an absolute stack position +(starting at 1); +a negative index represents an offset relative to the top of the stack. +More specifically, if the stack has n elements, +then index 1 represents the first element +(that is, the element that was pushed onto the stack first) +and +index n represents the last element; +index -1 also represents the last element +(that is, the element at the top) +and index -n represents the first element. + + + + + +

4.2 – Stack Size

+ +

+When you interact with the Lua API, +you are responsible for ensuring consistency. +In particular, +you are responsible for controlling stack overflow. +You can use the function lua_checkstack +to ensure that the stack has enough space for pushing new elements. + + +

+Whenever Lua calls C, +it ensures that the stack has space for +at least LUA_MINSTACK extra slots. +LUA_MINSTACK is defined as 20, +so that usually you do not have to worry about stack space +unless your code has loops pushing elements onto the stack. + + +

+When you call a Lua function +without a fixed number of results (see lua_call), +Lua ensures that the stack has enough space for all results, +but it does not ensure any extra space. +So, before pushing anything in the stack after such a call +you should use lua_checkstack. + + + + + +

4.3 – Valid and Acceptable Indices

+ +

+Any function in the API that receives stack indices +works only with valid indices or acceptable indices. + + +

+A valid index is an index that refers to a +position that stores a modifiable Lua value. +It comprises stack indices between 1 and the stack top +(1 ≤ abs(index) ≤ top) + +plus pseudo-indices, +which represent some positions that are accessible to C code +but that are not in the stack. +Pseudo-indices are used to access the registry (see §4.5) +and the upvalues of a C function (see §4.4). + + +

+Functions that do not need a specific mutable position, +but only a value (e.g., query functions), +can be called with acceptable indices. +An acceptable index can be any valid index, +but it also can be any positive index after the stack top +within the space allocated for the stack, +that is, indices up to the stack size. +(Note that 0 is never an acceptable index.) +Except when noted otherwise, +functions in the API work with acceptable indices. + + +

+Acceptable indices serve to avoid extra tests +against the stack top when querying the stack. +For instance, a C function can query its third argument +without the need to first check whether there is a third argument, +that is, without the need to check whether 3 is a valid index. + + +

+For functions that can be called with acceptable indices, +any non-valid index is treated as if it +contains a value of a virtual type LUA_TNONE, +which behaves like a nil value. + + + + + +

4.4 – C Closures

+ +

+When a C function is created, +it is possible to associate some values with it, +thus creating a C closure +(see lua_pushcclosure); +these values are called upvalues and are +accessible to the function whenever it is called. + + +

+Whenever a C function is called, +its upvalues are located at specific pseudo-indices. +These pseudo-indices are produced by the macro +lua_upvalueindex. +The first upvalue associated with a function is at index +lua_upvalueindex(1), and so on. +Any access to lua_upvalueindex(n), +where n is greater than the number of upvalues of the +current function +(but not greater than 256, +which is one plus the maximum number of upvalues in a closure), +produces an acceptable but invalid index. + + + + + +

4.5 – Registry

+ +

+Lua provides a registry, +a predefined table that can be used by any C code to +store whatever Lua values it needs to store. +The registry table is always located at pseudo-index +LUA_REGISTRYINDEX. +Any C library can store data into this table, +but it must take care to choose keys +that are different from those used +by other libraries, to avoid collisions. +Typically, you should use as key a string containing your library name, +or a light userdata with the address of a C object in your code, +or any Lua object created by your code. +As with variable names, +string keys starting with an underscore followed by +uppercase letters are reserved for Lua. + + +

+The integer keys in the registry are used +by the reference mechanism (see luaL_ref) +and by some predefined values. +Therefore, integer keys must not be used for other purposes. + + +

+When you create a new Lua state, +its registry comes with some predefined values. +These predefined values are indexed with integer keys +defined as constants in lua.h. +The following constants are defined: + +

LUA_RIDX_MAINTHREAD: At this index the registry has +the main thread of the state. +(The main thread is the one created together with the state.) +
LUA_RIDX_GLOBALS: At this index the registry has +the global environment. +

+ + + + +

4.6 – Error Handling in C

+ +

+Internally, Lua uses the C longjmp facility to handle errors. +(Lua will use exceptions if you compile it as C++; +search for LUAI_THROW in the source code for details.) +When Lua faces any error +(such as a memory allocation error, type errors, syntax errors, +and runtime errors) +it raises an error; +that is, it does a long jump. +A protected environment uses setjmp +to set a recovery point; +any error jumps to the most recent active recovery point. + + +

+If an error happens outside any protected environment, +Lua calls a panic function (see lua_atpanic) +and then calls abort, +thus exiting the host application. +Your panic function can avoid this exit by +never returning +(e.g., doing a long jump to your own recovery point outside Lua). + + +

+The panic function runs as if it were a message handler (see §2.3); +in particular, the error message is at the top of the stack. +However, there is no guarantee about stack space. +To push anything on the stack, +the panic function must first check the available space (see §4.2). + + +

+Most functions in the API can raise an error, +for instance due to a memory allocation error. +The documentation for each function indicates whether +it can raise errors. + + +

+Inside a C function you can raise an error by calling lua_error. + + + + + +

4.7 – Handling Yields in C

+ +

+Internally, Lua uses the C longjmp facility to yield a coroutine. +Therefore, if a C function foo calls an API function +and this API function yields +(directly or indirectly by calling another function that yields), +Lua cannot return to foo any more, +because the longjmp removes its frame from the C stack. + + +

+To avoid this kind of problem, +Lua raises an error whenever it tries to yield across an API call, +except for three functions: +lua_yieldk, lua_callk, and lua_pcallk. +All those functions receive a continuation function +(as a parameter named k) to continue execution after a yield. + + +

+We need to set some terminology to explain continuations. +We have a C function called from Lua which we will call +the original function. +This original function then calls one of those three functions in the C API, +which we will call the callee function, +that then yields the current thread. +(This can happen when the callee function is lua_yieldk, +or when the callee function is either lua_callk or lua_pcallk +and the function called by them yields.) + + +

+Suppose the running thread yields while executing the callee function. +After the thread resumes, +it eventually will finish running the callee function. +However, +the callee function cannot return to the original function, +because its frame in the C stack was destroyed by the yield. +Instead, Lua calls a continuation function, +which was given as an argument to the callee function. +As the name implies, +the continuation function should continue the task +of the original function. + + +

+As an illustration, consider the following function: + +

+     int original_function (lua_State *L) {
+       ...     /* code 1 */
+       status = lua_pcall(L, n, m, h);  /* calls Lua */
+       ...     /* code 2 */
+     }
+

+Now we want to allow +the Lua code being run by lua_pcall to yield. +First, we can rewrite our function like here: + +

+     int k (lua_State *L, int status, lua_KContext ctx) {
+       ...  /* code 2 */
+     }
+     
+     int original_function (lua_State *L) {
+       ...     /* code 1 */
+       return k(L, lua_pcall(L, n, m, h), ctx);
+     }
+

+In the above code, +the new function k is a +continuation function (with type lua_KFunction), +which should do all the work that the original function +was doing after calling lua_pcall. +Now, we must inform Lua that it must call k if the Lua code +being executed by lua_pcall gets interrupted in some way +(errors or yielding), +so we rewrite the code as here, +replacing lua_pcall by lua_pcallk: + +

+     int original_function (lua_State *L) {
+       ...     /* code 1 */
+       return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
+     }
+

+Note the external, explicit call to the continuation: +Lua will call the continuation only if needed, that is, +in case of errors or resuming after a yield. +If the called function returns normally without ever yielding, +lua_pcallk (and lua_callk) will also return normally. +(Of course, instead of calling the continuation in that case, +you can do the equivalent work directly inside the original function.) + + +

+Besides the Lua state, +the continuation function has two other parameters: +the final status of the call plus the context value (ctx) that +was passed originally to lua_pcallk. +(Lua does not use this context value; +it only passes this value from the original function to the +continuation function.) +For lua_pcallk, +the status is the same value that would be returned by lua_pcallk, +except that it is LUA_YIELD when being executed after a yield +(instead of LUA_OK). +For lua_yieldk and lua_callk, +the status is always LUA_YIELD when Lua calls the continuation. +(For these two functions, +Lua will not call the continuation in case of errors, +because they do not handle errors.) +Similarly, when using lua_callk, +you should call the continuation function +with LUA_OK as the status. +(For lua_yieldk, there is not much point in calling +directly the continuation function, +because lua_yieldk usually does not return.) + + +

+Lua treats the continuation function as if it were the original function. +The continuation function receives the same Lua stack +from the original function, +in the same state it would be if the callee function had returned. +(For instance, +after a lua_callk the function and its arguments are +removed from the stack and replaced by the results from the call.) +It also has the same upvalues. +Whatever it returns is handled by Lua as if it were the return +of the original function. + + + + + +

4.8 – Functions and Types

+ +

+Here we list all functions and types from the C API in +alphabetical order. +Each function has an indicator like this: +[-o, +p, x] + + +

+The first field, o, +is how many elements the function pops from the stack. +The second field, p, +is how many elements the function pushes onto the stack. +(Any function always pushes its results after popping its arguments.) +A field in the form x|y means the function can push (or pop) +x or y elements, +depending on the situation; +an interrogation mark '?' means that +we cannot know how many elements the function pops/pushes +by looking only at its arguments +(e.g., they may depend on what is on the stack). +The third field, x, +tells whether the function may raise errors: +'-' means the function never raises any error; +'m' means the function may raise memory errors; +'e' means the function may raise errors; +'v' means the function may raise an error on purpose. + + + +

`lua_absindex`

+[-0, +0, –] +

int lua_absindex (lua_State *L, int idx);

+ +

+Converts the acceptable index idx +into an equivalent absolute index +(that is, one that does not depend on the stack top). + + + + + +

`lua_Alloc`

typedef void * (*lua_Alloc) (void *ud,
+                             void *ptr,
+                             size_t osize,
+                             size_t nsize);

+ +

+The type of the memory-allocation function used by Lua states. +The allocator function must provide a +functionality similar to realloc, +but not exactly the same. +Its arguments are +ud, an opaque pointer passed to lua_newstate; +ptr, a pointer to the block being allocated/reallocated/freed; +osize, the original size of the block or some code about what +is being allocated; +and nsize, the new size of the block. + + +

+When ptr is not NULL, +osize is the size of the block pointed by ptr, +that is, the size given when it was allocated or reallocated. + + +

+When ptr is NULL, +osize encodes the kind of object that Lua is allocating. +osize is any of +LUA_TSTRING, LUA_TTABLE, LUA_TFUNCTION, +LUA_TUSERDATA, or LUA_TTHREAD when (and only when) +Lua is creating a new object of that type. +When osize is some other value, +Lua is allocating memory for something else. + + +

+Lua assumes the following behavior from the allocator function: + + +

+When nsize is zero, +the allocator must behave like free +and return NULL. + + +

+When nsize is not zero, +the allocator must behave like realloc. +The allocator returns NULL +if and only if it cannot fulfill the request. +Lua assumes that the allocator never fails when +osize >= nsize. + + +

+Here is a simple implementation for the allocator function. +It is used in the auxiliary library by luaL_newstate. + +

+     static void *l_alloc (void *ud, void *ptr, size_t osize,
+                                                size_t nsize) {
+       (void)ud;  (void)osize;  /* not used */
+       if (nsize == 0) {
+         free(ptr);
+         return NULL;
+       }
+       else
+         return realloc(ptr, nsize);
+     }
+

+Note that Standard C ensures +that free(NULL) has no effect and that +realloc(NULL,size) is equivalent to malloc(size). +This code assumes that realloc does not fail when shrinking a block. +(Although Standard C does not ensure this behavior, +it seems to be a safe assumption.) + + + + + +

`lua_arith`

+[-(2|1), +1, e] +

void lua_arith (lua_State *L, int op);

+ +

+Performs an arithmetic or bitwise operation over the two values +(or one, in the case of negations) +at the top of the stack, +with the value at the top being the second operand, +pops these values, and pushes the result of the operation. +The function follows the semantics of the corresponding Lua operator +(that is, it may call metamethods). + + +

+The value of op must be one of the following constants: + +

LUA_OPADD: performs addition (+)
LUA_OPSUB: performs subtraction (-)
LUA_OPMUL: performs multiplication (*)
LUA_OPDIV: performs float division (/)
LUA_OPIDIV: performs floor division (//)
LUA_OPMOD: performs modulo (%)
LUA_OPPOW: performs exponentiation (^)
LUA_OPUNM: performs mathematical negation (unary -)
LUA_OPBNOT: performs bitwise negation (~)
LUA_OPBAND: performs bitwise and (&)
LUA_OPBOR: performs bitwise or (|)
LUA_OPBXOR: performs bitwise exclusive or (~)
LUA_OPSHL: performs left shift (<<)
LUA_OPSHR: performs right shift (>>)

+ + + + +

`lua_atpanic`

+[-0, +0, –] +

lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);

+ +

+Sets a new panic function and returns the old one (see §4.6). + + + + + +

`lua_call`

+[-(nargs+1), +nresults, e] +

void lua_call (lua_State *L, int nargs, int nresults);

+ +

+Calls a function. + + +

+To call a function you must use the following protocol: +first, the function to be called is pushed onto the stack; +then, the arguments to the function are pushed +in direct order; +that is, the first argument is pushed first. +Finally you call lua_call; +nargs is the number of arguments that you pushed onto the stack. +All arguments and the function value are popped from the stack +when the function is called. +The function results are pushed onto the stack when the function returns. +The number of results is adjusted to nresults, +unless nresults is LUA_MULTRET. +In this case, all results from the function are pushed. +Lua takes care that the returned values fit into the stack space, +but it does not ensure any extra space in the stack. +The function results are pushed onto the stack in direct order +(the first result is pushed first), +so that after the call the last result is on the top of the stack. + + +

+Any error inside the called function is propagated upwards +(with a longjmp). + + +

+The following example shows how the host program can do the +equivalent to this Lua code: + +

+     a = f("how", t.x, 14)
+

+Here it is in C: + +

+     lua_getglobal(L, "f");                  /* function to be called */
+     lua_pushliteral(L, "how");                       /* 1st argument */
+     lua_getglobal(L, "t");                    /* table to be indexed */
+     lua_getfield(L, -1, "x");        /* push result of t.x (2nd arg) */
+     lua_remove(L, -2);                  /* remove 't' from the stack */
+     lua_pushinteger(L, 14);                          /* 3rd argument */
+     lua_call(L, 3, 1);     /* call 'f' with 3 arguments and 1 result */
+     lua_setglobal(L, "a");                         /* set global 'a' */
+

+Note that the code above is balanced: +at its end, the stack is back to its original configuration. +This is considered good programming practice. + + + + + +

`lua_callk`

+[-(nargs + 1), +nresults, e] +

void lua_callk (lua_State *L,
+                int nargs,
+                int nresults,
+                lua_KContext ctx,
+                lua_KFunction k);

+ +

+This function behaves exactly like lua_call, +but allows the called function to yield (see §4.7). + + + + + +

`lua_CFunction`

typedef int (*lua_CFunction) (lua_State *L);

+ +

+Type for C functions. + + +

+In order to communicate properly with Lua, +a C function must use the following protocol, +which defines the way parameters and results are passed: +a C function receives its arguments from Lua in its stack +in direct order (the first argument is pushed first). +So, when the function starts, +lua_gettop(L) returns the number of arguments received by the function. +The first argument (if any) is at index 1 +and its last argument is at index lua_gettop(L). +To return values to Lua, a C function just pushes them onto the stack, +in direct order (the first result is pushed first), +and returns the number of results. +Any other value in the stack below the results will be properly +discarded by Lua. +Like a Lua function, a C function called by Lua can also return +many results. + + +

+As an example, the following function receives a variable number +of numeric arguments and returns their average and their sum: + +

+     static int foo (lua_State *L) {
+       int n = lua_gettop(L);    /* number of arguments */
+       lua_Number sum = 0.0;
+       int i;
+       for (i = 1; i <= n; i++) {
+         if (!lua_isnumber(L, i)) {
+           lua_pushliteral(L, "incorrect argument");
+           lua_error(L);
+         }
+         sum += lua_tonumber(L, i);
+       }
+       lua_pushnumber(L, sum/n);        /* first result */
+       lua_pushnumber(L, sum);         /* second result */
+       return 2;                   /* number of results */
+     }
+

+ + + + +

`lua_checkstack`

+[-0, +0, –] +

int lua_checkstack (lua_State *L, int n);

+ +

+Ensures that the stack has space for at least n extra slots +(that is, that you can safely push up to n values into it). +It returns false if it cannot fulfill the request, +either because it would cause the stack +to be larger than a fixed maximum size +(typically at least several thousand elements) or +because it cannot allocate memory for the extra space. +This function never shrinks the stack; +if the stack already has space for the extra slots, +it is left unchanged. + + + + + +

`lua_close`

+[-0, +0, –] +

void lua_close (lua_State *L);

+ +

+Destroys all objects in the given Lua state +(calling the corresponding garbage-collection metamethods, if any) +and frees all dynamic memory used by this state. +On several platforms, you may not need to call this function, +because all resources are naturally released when the host program ends. +On the other hand, long-running programs that create multiple states, +such as daemons or web servers, +will probably need to close states as soon as they are not needed. + + + + + +

`lua_compare`

+[-0, +0, e] +

int lua_compare (lua_State *L, int index1, int index2, int op);

+ +

+Compares two Lua values. +Returns 1 if the value at index index1 satisfies op +when compared with the value at index index2, +following the semantics of the corresponding Lua operator +(that is, it may call metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices is not valid. + + +

+The value of op must be one of the following constants: + +

LUA_OPEQ: compares for equality (==)
LUA_OPLT: compares for less than (<)
LUA_OPLE: compares for less or equal (<=)

+ + + + +

`lua_concat`

+[-n, +1, e] +

void lua_concat (lua_State *L, int n);

+ +

+Concatenates the n values at the top of the stack, +pops them, and leaves the result at the top. +If n is 1, the result is the single value on the stack +(that is, the function does nothing); +if n is 0, the result is the empty string. +Concatenation is performed following the usual semantics of Lua +(see §3.4.6). + + + + + +

`lua_copy`

+[-0, +0, –] +

void lua_copy (lua_State *L, int fromidx, int toidx);

+ +

+Copies the element at index fromidx +into the valid index toidx, +replacing the value at that position. +Values at other positions are not affected. + + + + + +

`lua_createtable`

+[-0, +1, m] +

void lua_createtable (lua_State *L, int narr, int nrec);

+ +

+Creates a new empty table and pushes it onto the stack. +Parameter narr is a hint for how many elements the table +will have as a sequence; +parameter nrec is a hint for how many other elements +the table will have. +Lua may use these hints to preallocate memory for the new table. +This preallocation is useful for performance when you know in advance +how many elements the table will have. +Otherwise you can use the function lua_newtable. + + + + + +

`lua_dump`

+[-0, +0, –] +

int lua_dump (lua_State *L,
+                        lua_Writer writer,
+                        void *data,
+                        int strip);

+ +

+Dumps a function as a binary chunk. +Receives a Lua function on the top of the stack +and produces a binary chunk that, +if loaded again, +results in a function equivalent to the one dumped. +As it produces parts of the chunk, +lua_dump calls function writer (see lua_Writer) +with the given data +to write them. + + +

+If strip is true, +the binary representation may not include all debug information +about the function, +to save space. + + +

+The value returned is the error code returned by the last +call to the writer; +0 means no errors. + + +

+This function does not pop the Lua function from the stack. + + + + + +

`lua_error`

+[-1, +0, v] +

int lua_error (lua_State *L);

+ +

+Generates a Lua error, +using the value at the top of the stack as the error object. +This function does a long jump, +and therefore never returns +(see luaL_error). + + + + + +

`lua_gc`

+[-0, +0, e] +

int lua_gc (lua_State *L, int what, int data);

+ +

+Controls the garbage collector. + + +

+This function performs several tasks, +according to the value of the parameter what: + +

LUA_GCSTOP: +stops the garbage collector. +
LUA_GCRESTART: +restarts the garbage collector. +
LUA_GCCOLLECT: +performs a full garbage-collection cycle. +
LUA_GCCOUNT: +returns the current amount of memory (in Kbytes) in use by Lua. +
LUA_GCCOUNTB: +returns the remainder of dividing the current amount of bytes of +memory in use by Lua by 1024. +
LUA_GCSTEP: +performs an incremental step of garbage collection. +
LUA_GCSETPAUSE: +sets data as the new value +for the pause of the collector (see §2.5) +and returns the previous value of the pause. +
LUA_GCSETSTEPMUL: +sets data as the new value for the step multiplier of +the collector (see §2.5) +and returns the previous value of the step multiplier. +
LUA_GCISRUNNING: +returns a boolean that tells whether the collector is running +(i.e., not stopped). +

+ +

+For more details about these options, +see collectgarbage. + + + + + +

`lua_getallocf`

+[-0, +0, –] +

lua_Alloc lua_getallocf (lua_State *L, void **ud);

+ +

+Returns the memory-allocation function of a given state. +If ud is not NULL, Lua stores in *ud the +opaque pointer given when the memory-allocator function was set. + + + + + +

`lua_getfield`

+[-0, +1, e] +

int lua_getfield (lua_State *L, int index, const char *k);

+ +

+Pushes onto the stack the value t[k], +where t is the value at the given index. +As in Lua, this function may trigger a metamethod +for the "index" event (see §2.4). + + +

+Returns the type of the pushed value. + + + + + +

`lua_getextraspace`

+[-0, +0, –] +

void *lua_getextraspace (lua_State *L);

+ +

+Returns a pointer to a raw memory area associated with the +given Lua state. +The application can use this area for any purpose; +Lua does not use it for anything. + + +

+Each new thread has this area initialized with a copy +of the area of the main thread. + + +

+By default, this area has the size of a pointer to void, +but you can recompile Lua with a different size for this area. +(See LUA_EXTRASPACE in luaconf.h.) + + + + + +

`lua_getglobal`

+[-0, +1, e] +

int lua_getglobal (lua_State *L, const char *name);

+ +

+Pushes onto the stack the value of the global name. +Returns the type of that value. + + + + + +

`lua_geti`

+[-0, +1, e] +

int lua_geti (lua_State *L, int index, lua_Integer i);

+ +

+Pushes onto the stack the value t[i], +where t is the value at the given index. +As in Lua, this function may trigger a metamethod +for the "index" event (see §2.4). + + +

+Returns the type of the pushed value. + + + + + +

`lua_getmetatable`

+[-0, +(0|1), –] +

int lua_getmetatable (lua_State *L, int index);

+ +

+If the value at the given index has a metatable, +the function pushes that metatable onto the stack and returns 1. +Otherwise, +the function returns 0 and pushes nothing on the stack. + + + + + +

`lua_gettable`

+[-1, +1, e] +

int lua_gettable (lua_State *L, int index);

+ +

+Pushes onto the stack the value t[k], +where t is the value at the given index +and k is the value at the top of the stack. + + +

+This function pops the key from the stack, +pushing the resulting value in its place. +As in Lua, this function may trigger a metamethod +for the "index" event (see §2.4). + + +

+Returns the type of the pushed value. + + + + + +

`lua_gettop`

+[-0, +0, –] +

int lua_gettop (lua_State *L);

+ +

+Returns the index of the top element in the stack. +Because indices start at 1, +this result is equal to the number of elements in the stack; +in particular, 0 means an empty stack. + + + + + +

`lua_getuservalue`

+[-0, +1, –] +

int lua_getuservalue (lua_State *L, int index);

+ +

+Pushes onto the stack the Lua value associated with the userdata +at the given index. + + +

+Returns the type of the pushed value. + + + + + +

`lua_insert`

+[-1, +1, –] +

void lua_insert (lua_State *L, int index);

+ +

+Moves the top element into the given valid index, +shifting up the elements above this index to open space. +This function cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +

`lua_Integer`

typedef ... lua_Integer;

+ +

+The type of integers in Lua. + + +

+By default this type is long long, +(usually a 64-bit two-complement integer), +but that can be changed to long or int +(usually a 32-bit two-complement integer). +(See LUA_INT_TYPE in luaconf.h.) + + +

+Lua also defines the constants +LUA_MININTEGER and LUA_MAXINTEGER, +with the minimum and the maximum values that fit in this type. + + + + + +

`lua_isboolean`

+[-0, +0, –] +

int lua_isboolean (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a boolean, +and 0 otherwise. + + + + + +

`lua_iscfunction`

+[-0, +0, –] +

int lua_iscfunction (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a C function, +and 0 otherwise. + + + + + +

`lua_isfunction`

+[-0, +0, –] +

int lua_isfunction (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a function +(either C or Lua), and 0 otherwise. + + + + + +

`lua_isinteger`

+[-0, +0, –] +

int lua_isinteger (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is an integer +(that is, the value is a number and is represented as an integer), +and 0 otherwise. + + + + + +

`lua_islightuserdata`

+[-0, +0, –] +

int lua_islightuserdata (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a light userdata, +and 0 otherwise. + + + + + +

`lua_isnil`

+[-0, +0, –] +

int lua_isnil (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is nil, +and 0 otherwise. + + + + + +

`lua_isnone`

+[-0, +0, –] +

int lua_isnone (lua_State *L, int index);

+ +

+Returns 1 if the given index is not valid, +and 0 otherwise. + + + + + +

`lua_isnoneornil`

+[-0, +0, –] +

int lua_isnoneornil (lua_State *L, int index);

+ +

+Returns 1 if the given index is not valid +or if the value at this index is nil, +and 0 otherwise. + + + + + +

`lua_isnumber`

+[-0, +0, –] +

int lua_isnumber (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a number +or a string convertible to a number, +and 0 otherwise. + + + + + +

`lua_isstring`

+[-0, +0, –] +

int lua_isstring (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a string +or a number (which is always convertible to a string), +and 0 otherwise. + + + + + +

`lua_istable`

+[-0, +0, –] +

int lua_istable (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a table, +and 0 otherwise. + + + + + +

`lua_isthread`

+[-0, +0, –] +

int lua_isthread (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a thread, +and 0 otherwise. + + + + + +

`lua_isuserdata`

+[-0, +0, –] +

int lua_isuserdata (lua_State *L, int index);

+ +

+Returns 1 if the value at the given index is a userdata +(either full or light), and 0 otherwise. + + + + + +

`lua_isyieldable`

+[-0, +0, –] +

int lua_isyieldable (lua_State *L);

+ +

+Returns 1 if the given coroutine can yield, +and 0 otherwise. + + + + + +

`lua_KContext`

typedef ... lua_KContext;

+ +

+The type for continuation-function contexts. +It must be a numeric type. +This type is defined as intptr_t +when intptr_t is available, +so that it can store pointers too. +Otherwise, it is defined as ptrdiff_t. + + + + + +

`lua_KFunction`

typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);

+ +

+Type for continuation functions (see §4.7). + + + + + +

`lua_len`

+[-0, +1, e] +

void lua_len (lua_State *L, int index);

+ +

+Returns the length of the value at the given index. +It is equivalent to the '#' operator in Lua (see §3.4.7) and +may trigger a metamethod for the "length" event (see §2.4). +The result is pushed on the stack. + + + + + +

`lua_load`

+[-0, +1, –] +

int lua_load (lua_State *L,
+              lua_Reader reader,
+              void *data,
+              const char *chunkname,
+              const char *mode);

+ +

+Loads a Lua chunk without running it. +If there are no errors, +lua_load pushes the compiled chunk as a Lua +function on top of the stack. +Otherwise, it pushes an error message. + + +

+The return values of lua_load are: + +

LUA_OK: no errors;
LUA_ERRSYNTAX: +syntax error during precompilation;
LUA_ERRMEM: +memory allocation error;
LUA_ERRGCMM: +error while running a __gc metamethod. +(This error has no relation with the chunk being loaded. +It is generated by the garbage collector.) +

+ +

+The lua_load function uses a user-supplied reader function +to read the chunk (see lua_Reader). +The data argument is an opaque value passed to the reader function. + + +

+The chunkname argument gives a name to the chunk, +which is used for error messages and in debug information (see §4.9). + + +

+lua_load automatically detects whether the chunk is text or binary +and loads it accordingly (see program luac). +The string mode works as in function load, +with the addition that +a NULL value is equivalent to the string "bt". + + +

+lua_load uses the stack internally, +so the reader function must always leave the stack +unmodified when returning. + + +

+If the resulting function has upvalues, +its first upvalue is set to the value of the global environment +stored at index LUA_RIDX_GLOBALS in the registry (see §4.5). +When loading main chunks, +this upvalue will be the _ENV variable (see §2.2). +Other upvalues are initialized with nil. + + + + + +

`lua_newstate`

+[-0, +0, –] +

lua_State *lua_newstate (lua_Alloc f, void *ud);

+ +

+Creates a new thread running in a new, independent state. +Returns NULL if it cannot create the thread or the state +(due to lack of memory). +The argument f is the allocator function; +Lua does all memory allocation for this state through this function. +The second argument, ud, is an opaque pointer that Lua +passes to the allocator in every call. + + + + + +

`lua_newtable`

+[-0, +1, m] +

void lua_newtable (lua_State *L);

+ +

+Creates a new empty table and pushes it onto the stack. +It is equivalent to lua_createtable(L, 0, 0). + + + + + +

`lua_newthread`

+[-0, +1, m] +

lua_State *lua_newthread (lua_State *L);

+ +

+Creates a new thread, pushes it on the stack, +and returns a pointer to a lua_State that represents this new thread. +The new thread returned by this function shares with the original thread +its global environment, +but has an independent execution stack. + + +

+There is no explicit function to close or to destroy a thread. +Threads are subject to garbage collection, +like any Lua object. + + + + + +

`lua_newuserdata`

+[-0, +1, m] +

void *lua_newuserdata (lua_State *L, size_t size);

+ +

+This function allocates a new block of memory with the given size, +pushes onto the stack a new full userdata with the block address, +and returns this address. +The host program can freely use this memory. + + + + + +

`lua_next`

+[-1, +(2|0), e] +

int lua_next (lua_State *L, int index);

+ +

+Pops a key from the stack, +and pushes a key–value pair from the table at the given index +(the "next" pair after the given key). +If there are no more elements in the table, +then lua_next returns 0 (and pushes nothing). + + +

+A typical traversal looks like this: + +

+     /* table is in the stack at index 't' */
+     lua_pushnil(L);  /* first key */
+     while (lua_next(L, t) != 0) {
+       /* uses 'key' (at index -2) and 'value' (at index -1) */
+       printf("%s - %s\n",
+              lua_typename(L, lua_type(L, -2)),
+              lua_typename(L, lua_type(L, -1)));
+       /* removes 'value'; keeps 'key' for next iteration */
+       lua_pop(L, 1);
+     }
+

+ +

+While traversing a table, +do not call lua_tolstring directly on a key, +unless you know that the key is actually a string. +Recall that lua_tolstring may change +the value at the given index; +this confuses the next call to lua_next. + + +

+See function next for the caveats of modifying +the table during its traversal. + + + + + +

`lua_Number`

typedef ... lua_Number;

+ +

+The type of floats in Lua. + + +

+By default this type is double, +but that can be changed to a single float or a long double. +(See LUA_FLOAT_TYPE in luaconf.h.) + + + + + +

`lua_numbertointeger`

int lua_numbertointeger (lua_Number n, lua_Integer *p);

+ +

+Converts a Lua float to a Lua integer. +This macro assumes that n has an integral value. +If that value is within the range of Lua integers, +it is converted to an integer and assigned to *p. +The macro results in a boolean indicating whether the +conversion was successful. +(Note that this range test can be tricky to do +correctly without this macro, +due to roundings.) + + +

+This macro may evaluate its arguments more than once. + + + + + +

`lua_pcall`

+[-(nargs + 1), +(nresults|1), –] +

int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);

+ +

+Calls a function in protected mode. + + +

+Both nargs and nresults have the same meaning as +in lua_call. +If there are no errors during the call, +lua_pcall behaves exactly like lua_call. +However, if there is any error, +lua_pcall catches it, +pushes a single value on the stack (the error message), +and returns an error code. +Like lua_call, +lua_pcall always removes the function +and its arguments from the stack. + + +

+If msgh is 0, +then the error message returned on the stack +is exactly the original error message. +Otherwise, msgh is the stack index of a +message handler. +(This index cannot be a pseudo-index.) +In case of runtime errors, +this function will be called with the error message +and its return value will be the message +returned on the stack by lua_pcall. + + +

+Typically, the message handler is used to add more debug +information to the error message, such as a stack traceback. +Such information cannot be gathered after the return of lua_pcall, +since by then the stack has unwound. + + +

+The lua_pcall function returns one of the following constants +(defined in lua.h): + +

LUA_OK (0): +success.
LUA_ERRRUN: +a runtime error. +
LUA_ERRMEM: +memory allocation error. +For such errors, Lua does not call the message handler. +
LUA_ERRERR: +error while running the message handler. +
LUA_ERRGCMM: +error while running a __gc metamethod. +(This error typically has no relation with the function being called.) +

+ + + + +

`lua_pcallk`

+[-(nargs + 1), +(nresults|1), –] +

int lua_pcallk (lua_State *L,
+                int nargs,
+                int nresults,
+                int msgh,
+                lua_KContext ctx,
+                lua_KFunction k);

+ +

+This function behaves exactly like lua_pcall, +but allows the called function to yield (see §4.7). + + + + + +

`lua_pop`

+[-n, +0, –] +

void lua_pop (lua_State *L, int n);

+ +

+Pops n elements from the stack. + + + + + +

`lua_pushboolean`

+[-0, +1, –] +

void lua_pushboolean (lua_State *L, int b);

+ +

+Pushes a boolean value with value b onto the stack. + + + + + +

`lua_pushcclosure`

+[-n, +1, m] +

void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);

+ +

+Pushes a new C closure onto the stack. + + +

+When a C function is created, +it is possible to associate some values with it, +thus creating a C closure (see §4.4); +these values are then accessible to the function whenever it is called. +To associate values with a C function, +first these values must be pushed onto the stack +(when there are multiple values, the first value is pushed first). +Then lua_pushcclosure +is called to create and push the C function onto the stack, +with the argument n telling how many values will be +associated with the function. +lua_pushcclosure also pops these values from the stack. + + +

+The maximum value for n is 255. + + +

+When n is zero, +this function creates a light C function, +which is just a pointer to the C function. +In that case, it never raises a memory error. + + + + + +

`lua_pushcfunction`

+[-0, +1, –] +

void lua_pushcfunction (lua_State *L, lua_CFunction f);

+ +

+Pushes a C function onto the stack. +This function receives a pointer to a C function +and pushes onto the stack a Lua value of type function that, +when called, invokes the corresponding C function. + + +

+Any function to be callable by Lua must +follow the correct protocol to receive its parameters +and return its results (see lua_CFunction). + + + + + +

`lua_pushfstring`

+[-0, +1, m] +

const char *lua_pushfstring (lua_State *L, const char *fmt, ...);

+ +

+Pushes onto the stack a formatted string +and returns a pointer to this string. +It is similar to the ISO C function sprintf, +but has some important differences: + +

+You do not have to allocate space for the result: +the result is a Lua string and Lua takes care of memory allocation +(and deallocation, through garbage collection). +
+The conversion specifiers are quite restricted. +There are no flags, widths, or precisions. +The conversion specifiers can only be +'%%' (inserts the character '%'), +'%s' (inserts a zero-terminated string, with no size restrictions), +'%f' (inserts a lua_Number), +'%I' (inserts a lua_Integer), +'%p' (inserts a pointer as a hexadecimal numeral), +'%d' (inserts an int), +'%c' (inserts an int as a one-byte character), and +'%U' (inserts a long int as a UTF-8 byte sequence). +

+ + + + +

`lua_pushglobaltable`

+[-0, +1, –] +

void lua_pushglobaltable (lua_State *L);

+ +

+Pushes the global environment onto the stack. + + + + + +

`lua_pushinteger`

+[-0, +1, –] +

void lua_pushinteger (lua_State *L, lua_Integer n);

+ +

+Pushes an integer with value n onto the stack. + + + + + +

`lua_pushlightuserdata`

+[-0, +1, –] +

void lua_pushlightuserdata (lua_State *L, void *p);

+ +

+Pushes a light userdata onto the stack. + + +

+Userdata represent C values in Lua. +A light userdata represents a pointer, a void*. +It is a value (like a number): +you do not create it, it has no individual metatable, +and it is not collected (as it was never created). +A light userdata is equal to "any" +light userdata with the same C address. + + + + + +

`lua_pushliteral`

+[-0, +1, m] +

const char *lua_pushliteral (lua_State *L, const char *s);

+ +

+This macro is equivalent to lua_pushstring, +but should be used only when s is a literal string. + + + + + +

`lua_pushlstring`

+[-0, +1, m] +

const char *lua_pushlstring (lua_State *L, const char *s, size_t len);

+ +

+Pushes the string pointed to by s with size len +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at s can be freed or reused immediately after +the function returns. +The string can contain any binary data, +including embedded zeros. + + +

+Returns a pointer to the internal copy of the string. + + + + + +

`lua_pushnil`

+[-0, +1, –] +

void lua_pushnil (lua_State *L);

+ +

+Pushes a nil value onto the stack. + + + + + +

`lua_pushnumber`

+[-0, +1, –] +

void lua_pushnumber (lua_State *L, lua_Number n);

+ +

+Pushes a float with value n onto the stack. + + + + + +

`lua_pushstring`

+[-0, +1, m] +

const char *lua_pushstring (lua_State *L, const char *s);

+ +

+Pushes the zero-terminated string pointed to by s +onto the stack. +Lua makes (or reuses) an internal copy of the given string, +so the memory at s can be freed or reused immediately after +the function returns. + + +

+Returns a pointer to the internal copy of the string. + + +

+If s is NULL, pushes nil and returns NULL. + + + + + +

`lua_pushthread`

+[-0, +1, –] +

int lua_pushthread (lua_State *L);

+ +

+Pushes the thread represented by L onto the stack. +Returns 1 if this thread is the main thread of its state. + + + + + +

`lua_pushvalue`

+[-0, +1, –] +

void lua_pushvalue (lua_State *L, int index);

+ +

+Pushes a copy of the element at the given index +onto the stack. + + + + + +

`lua_pushvfstring`

+[-0, +1, m] +

const char *lua_pushvfstring (lua_State *L,
+                              const char *fmt,
+                              va_list argp);

+ +

+Equivalent to lua_pushfstring, except that it receives a va_list +instead of a variable number of arguments. + + + + + +

`lua_rawequal`

+[-0, +0, –] +

int lua_rawequal (lua_State *L, int index1, int index2);

+ +

+Returns 1 if the two values in indices index1 and +index2 are primitively equal +(that is, without calling metamethods). +Otherwise returns 0. +Also returns 0 if any of the indices are not valid. + + + + + +

`lua_rawget`

+[-1, +1, –] +

int lua_rawget (lua_State *L, int index);

+ +

+Similar to lua_gettable, but does a raw access +(i.e., without metamethods). + + + + + +

`lua_rawgeti`

+[-0, +1, –] +

int lua_rawgeti (lua_State *L, int index, lua_Integer n);

+ +

+Pushes onto the stack the value t[n], +where t is the table at the given index. +The access is raw; +that is, it does not invoke metamethods. + + +

+Returns the type of the pushed value. + + + + + +

`lua_rawgetp`

+[-0, +1, –] +

int lua_rawgetp (lua_State *L, int index, const void *p);

+ +

+Pushes onto the stack the value t[k], +where t is the table at the given index and +k is the pointer p represented as a light userdata. +The access is raw; +that is, it does not invoke metamethods. + + +

+Returns the type of the pushed value. + + + + + +

`lua_rawlen`

+[-0, +0, –] +

size_t lua_rawlen (lua_State *L, int index);

+ +

+Returns the raw "length" of the value at the given index: +for strings, this is the string length; +for tables, this is the result of the length operator ('#') +with no metamethods; +for userdata, this is the size of the block of memory allocated +for the userdata; +for other values, it is 0. + + + + + +

`lua_rawset`

+[-2, +0, m] +

void lua_rawset (lua_State *L, int index);

+ +

+Similar to lua_settable, but does a raw assignment +(i.e., without metamethods). + + + + + +

`lua_rawseti`

+[-1, +0, m] +

void lua_rawseti (lua_State *L, int index, lua_Integer i);

+ +

+Does the equivalent of t[i] = v, +where t is the table at the given index +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +The assignment is raw; +that is, it does not invoke metamethods. + + + + + +

`lua_rawsetp`

+[-1, +0, m] +

void lua_rawsetp (lua_State *L, int index, const void *p);

+ +

+Does the equivalent of t[p] = v, +where t is the table at the given index, +p is encoded as a light userdata, +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +The assignment is raw; +that is, it does not invoke metamethods. + + + + + +

`lua_Reader`

typedef const char * (*lua_Reader) (lua_State *L,
+                                    void *data,
+                                    size_t *size);

+ +

+The reader function used by lua_load. +Every time it needs another piece of the chunk, +lua_load calls the reader, +passing along its data parameter. +The reader must return a pointer to a block of memory +with a new piece of the chunk +and set size to the block size. +The block must exist until the reader function is called again. +To signal the end of the chunk, +the reader must return NULL or set size to zero. +The reader function may return pieces of any size greater than zero. + + + + + +

`lua_register`

+[-0, +0, e] +

void lua_register (lua_State *L, const char *name, lua_CFunction f);

+ +

+Sets the C function f as the new value of global name. +It is defined as a macro: + +

+     #define lua_register(L,n,f) \
+            (lua_pushcfunction(L, f), lua_setglobal(L, n))
+

+ + + + +

`lua_remove`

+[-1, +0, –] +

void lua_remove (lua_State *L, int index);

+ +

+Removes the element at the given valid index, +shifting down the elements above this index to fill the gap. +This function cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +

`lua_replace`

+[-1, +0, –] +

void lua_replace (lua_State *L, int index);

+ +

+Moves the top element into the given valid index +without shifting any element +(therefore replacing the value at that given index), +and then pops the top element. + + + + + +

`lua_resume`

+[-?, +?, –] +

int lua_resume (lua_State *L, lua_State *from, int nargs);

+ +

+Starts and resumes a coroutine in the given thread L. + + +

+To start a coroutine, +you push onto the thread stack the main function plus any arguments; +then you call lua_resume, +with nargs being the number of arguments. +This call returns when the coroutine suspends or finishes its execution. +When it returns, the stack contains all values passed to lua_yield, +or all values returned by the body function. +lua_resume returns +LUA_YIELD if the coroutine yields, +LUA_OK if the coroutine finishes its execution +without errors, +or an error code in case of errors (see lua_pcall). + + +

+In case of errors, +the stack is not unwound, +so you can use the debug API over it. +The error message is on the top of the stack. + + +

+To resume a coroutine, +you remove any results from the last lua_yield, +put on its stack only the values to +be passed as results from yield, +and then call lua_resume. + + +

+The parameter from represents the coroutine that is resuming L. +If there is no such coroutine, +this parameter can be NULL. + + + + + +

`lua_rotate`

+[-0, +0, –] +

void lua_rotate (lua_State *L, int idx, int n);

+ +

+Rotates the stack elements between the valid index idx +and the top of the stack. +The elements are rotated n positions in the direction of the top, +for a positive n, +or -n positions in the direction of the bottom, +for a negative n. +The absolute value of n must not be greater than the size +of the slice being rotated. +This function cannot be called with a pseudo-index, +because a pseudo-index is not an actual stack position. + + + + + +

`lua_setallocf`

+[-0, +0, –] +

void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);

+ +

+Changes the allocator function of a given state to f +with user data ud. + + + + + +

`lua_setfield`

+[-1, +0, e] +

void lua_setfield (lua_State *L, int index, const char *k);

+ +

+Does the equivalent to t[k] = v, +where t is the value at the given index +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see §2.4). + + + + + +

`lua_setglobal`

+[-1, +0, e] +

void lua_setglobal (lua_State *L, const char *name);

+ +

+Pops a value from the stack and +sets it as the new value of global name. + + + + + +

`lua_seti`

+[-1, +0, e] +

void lua_seti (lua_State *L, int index, lua_Integer n);

+ +

+Does the equivalent to t[n] = v, +where t is the value at the given index +and v is the value at the top of the stack. + + +

+This function pops the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see §2.4). + + + + + +

`lua_setmetatable`

+[-1, +0, –] +

void lua_setmetatable (lua_State *L, int index);

+ +

+Pops a table from the stack and +sets it as the new metatable for the value at the given index. + + + + + +

`lua_settable`

+[-2, +0, e] +

void lua_settable (lua_State *L, int index);

+ +

+Does the equivalent to t[k] = v, +where t is the value at the given index, +v is the value at the top of the stack, +and k is the value just below the top. + + +

+This function pops both the key and the value from the stack. +As in Lua, this function may trigger a metamethod +for the "newindex" event (see §2.4). + + + + + +

`lua_settop`

+[-?, +?, –] +

void lua_settop (lua_State *L, int index);

+ +

+Accepts any index, or 0, +and sets the stack top to this index. +If the new top is larger than the old one, +then the new elements are filled with nil. +If index is 0, then all stack elements are removed. + + + + + +

`lua_setuservalue`

+[-1, +0, –] +

void lua_setuservalue (lua_State *L, int index);

+ +

+Pops a value from the stack and sets it as +the new value associated to the userdata at the given index. + + + + + +

`lua_State`

typedef struct lua_State lua_State;

+ +

+An opaque structure that points to a thread and indirectly +(through the thread) to the whole state of a Lua interpreter. +The Lua library is fully reentrant: +it has no global variables. +All information about a state is accessible through this structure. + + +

+A pointer to this structure must be passed as the first argument to +every function in the library, except to lua_newstate, +which creates a Lua state from scratch. + + + + + +

`lua_status`

+[-0, +0, –] +

int lua_status (lua_State *L);

+ +

+Returns the status of the thread L. + + +

+The status can be 0 (LUA_OK) for a normal thread, +an error code if the thread finished the execution +of a lua_resume with an error, +or LUA_YIELD if the thread is suspended. + + +

+You can only call functions in threads with status LUA_OK. +You can resume threads with status LUA_OK +(to start a new coroutine) or LUA_YIELD +(to resume a coroutine). + + + + + +

`lua_stringtonumber`

+[-0, +1, –] +

size_t lua_stringtonumber (lua_State *L, const char *s);

+ +

+Converts the zero-terminated string s to a number, +pushes that number into the stack, +and returns the total size of the string, +that is, its length plus one. +The conversion can result in an integer or a float, +according to the lexical conventions of Lua (see §3.1). +The string may have leading and trailing spaces and a sign. +If the string is not a valid numeral, +returns 0 and pushes nothing. +(Note that the result can be used as a boolean, +true if the conversion succeeds.) + + + + + +

`lua_toboolean`

+[-0, +0, –] +

int lua_toboolean (lua_State *L, int index);

+ +

+Converts the Lua value at the given index to a C boolean +value (0 or 1). +Like all tests in Lua, +lua_toboolean returns true for any Lua value +different from false and nil; +otherwise it returns false. +(If you want to accept only actual boolean values, +use lua_isboolean to test the value's type.) + + + + + +

`lua_tocfunction`

+[-0, +0, –] +

lua_CFunction lua_tocfunction (lua_State *L, int index);

+ +

+Converts a value at the given index to a C function. +That value must be a C function; +otherwise, returns NULL. + + + + + +

`lua_tointeger`

+[-0, +0, –] +

lua_Integer lua_tointeger (lua_State *L, int index);

+ +

+Equivalent to lua_tointegerx with isnum equal to NULL. + + + + + +

`lua_tointegerx`

+[-0, +0, –] +

lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);

+ +

+Converts the Lua value at the given index +to the signed integral type lua_Integer. +The Lua value must be an integer, +or a number or string convertible to an integer (see §3.4.3); +otherwise, lua_tointegerx returns 0. + + +

+If isnum is not NULL, +its referent is assigned a boolean value that +indicates whether the operation succeeded. + + + + + +

`lua_tolstring`

+[-0, +0, m] +

const char *lua_tolstring (lua_State *L, int index, size_t *len);

+ +

+Converts the Lua value at the given index to a C string. +If len is not NULL, +it sets *len with the string length. +The Lua value must be a string or a number; +otherwise, the function returns NULL. +If the value is a number, +then lua_tolstring also +changes the actual value in the stack to a string. +(This change confuses lua_next +when lua_tolstring is applied to keys during a table traversal.) + + +

+lua_tolstring returns a pointer +to a string inside the Lua state. +This string always has a zero ('\0') +after its last character (as in C), +but can contain other zeros in its body. + + +

+Because Lua has garbage collection, +there is no guarantee that the pointer returned by lua_tolstring +will be valid after the corresponding Lua value is removed from the stack. + + + + + +

`lua_tonumber`

+[-0, +0, –] +

lua_Number lua_tonumber (lua_State *L, int index);

+ +

+Equivalent to lua_tonumberx with isnum equal to NULL. + + + + + +

`lua_tonumberx`

+[-0, +0, –] +

lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);

+ +

+Converts the Lua value at the given index +to the C type lua_Number (see lua_Number). +The Lua value must be a number or a string convertible to a number +(see §3.4.3); +otherwise, lua_tonumberx returns 0. + + +

+If isnum is not NULL, +its referent is assigned a boolean value that +indicates whether the operation succeeded. + + + + + +

`lua_topointer`

+[-0, +0, –] +

const void *lua_topointer (lua_State *L, int index);

+ +

+Converts the value at the given index to a generic +C pointer (void*). +The value can be a userdata, a table, a thread, or a function; +otherwise, lua_topointer returns NULL. +Different objects will give different pointers. +There is no way to convert the pointer back to its original value. + + +

+Typically this function is used only for hashing and debug information. + + + + + +

`lua_tostring`

+[-0, +0, m] +

const char *lua_tostring (lua_State *L, int index);

+ +

+Equivalent to lua_tolstring with len equal to NULL. + + + + + +

`lua_tothread`

+[-0, +0, –] +

lua_State *lua_tothread (lua_State *L, int index);

+ +

+Converts the value at the given index to a Lua thread +(represented as lua_State*). +This value must be a thread; +otherwise, the function returns NULL. + + + + + +

`lua_touserdata`

+[-0, +0, –] +

void *lua_touserdata (lua_State *L, int index);

+ +

+If the value at the given index is a full userdata, +returns its block address. +If the value is a light userdata, +returns its pointer. +Otherwise, returns NULL. + + + + + +

`lua_type`

+[-0, +0, –] +

int lua_type (lua_State *L, int index);

+ +

+Returns the type of the value in the given valid index, +or LUA_TNONE for a non-valid (but acceptable) index. +The types returned by lua_type are coded by the following constants +defined in lua.h: +LUA_TNIL (0), +LUA_TNUMBER, +LUA_TBOOLEAN, +LUA_TSTRING, +LUA_TTABLE, +LUA_TFUNCTION, +LUA_TUSERDATA, +LUA_TTHREAD, +and +LUA_TLIGHTUSERDATA. + + + + + +

`lua_typename`

+[-0, +0, –] +

const char *lua_typename (lua_State *L, int tp);

+ +

+Returns the name of the type encoded by the value tp, +which must be one the values returned by lua_type. + + + + + +

`lua_Unsigned`

typedef ... lua_Unsigned;

+ +

+The unsigned version of lua_Integer. + + + + + +

`lua_upvalueindex`

+[-0, +0, –] +

int lua_upvalueindex (int i);

+ +

+Returns the pseudo-index that represents the i-th upvalue of +the running function (see §4.4). + + + + + +

`lua_version`

+[-0, +0, v] +

const lua_Number *lua_version (lua_State *L);

+ +

+Returns the address of the version number stored in the Lua core. +When called with a valid lua_State, +returns the address of the version used to create that state. +When called with NULL, +returns the address of the version running the call. + + + + + +

`lua_Writer`

typedef int (*lua_Writer) (lua_State *L,
+                           const void* p,
+                           size_t sz,
+                           void* ud);

+ +

+The type of the writer function used by lua_dump. +Every time it produces another piece of chunk, +lua_dump calls the writer, +passing along the buffer to be written (p), +its size (sz), +and the data parameter supplied to lua_dump. + + +

+The writer returns an error code: +0 means no errors; +any other value means an error and stops lua_dump from +calling the writer again. + + + + + +

`lua_xmove`

+[-?, +?, –] +

void lua_xmove (lua_State *from, lua_State *to, int n);

+ +

+Exchange values between different threads of the same state. + + +

+This function pops n values from the stack from, +and pushes them onto the stack to. + + + + + +

`lua_yield`

+[-?, +?, e] +

int lua_yield (lua_State *L, int nresults);

+ +

+This function is equivalent to lua_yieldk, +but it has no continuation (see §4.7). +Therefore, when the thread resumes, +it continues the function that called +the function calling lua_yield. + + + + + +

`lua_yieldk`

+[-?, +?, e] +

int lua_yieldk (lua_State *L,
+                int nresults,
+                lua_KContext ctx,
+                lua_KFunction k);

+ +

+Yields a coroutine (thread). + + +

+When a C function calls lua_yieldk, +the running coroutine suspends its execution, +and the call to lua_resume that started this coroutine returns. +The parameter nresults is the number of values from the stack +that will be passed as results to lua_resume. + + +

+When the coroutine is resumed again, +Lua calls the given continuation function k to continue +the execution of the C function that yielded (see §4.7). +This continuation function receives the same stack +from the previous function, +with the n results removed and +replaced by the arguments passed to lua_resume. +Moreover, +the continuation function receives the value ctx +that was passed to lua_yieldk. + + +

+Usually, this function does not return; +when the coroutine eventually resumes, +it continues executing the continuation function. +However, there is one special case, +which is when this function is called +from inside a line hook (see §4.9). +In that case, lua_yieldk should be called with no continuation +(probably in the form of lua_yield), +and the hook should return immediately after the call. +Lua will yield and, +when the coroutine resumes again, +it will continue the normal execution +of the (Lua) function that triggered the hook. + + +

+This function can raise an error if it is called from a thread +with a pending C call with no continuation function, +or it is called from a thread that is not running inside a resume +(e.g., the main thread). + + + + + + + +

4.9 – The Debug Interface

+ +

+Lua has no built-in debugging facilities. +Instead, it offers a special interface +by means of functions and hooks. +This interface allows the construction of different +kinds of debuggers, profilers, and other tools +that need "inside information" from the interpreter. + + + +

`lua_Debug`

typedef struct lua_Debug {
+  int event;
+  const char *name;           /* (n) */
+  const char *namewhat;       /* (n) */
+  const char *what;           /* (S) */
+  const char *source;         /* (S) */
+  int currentline;            /* (l) */
+  int linedefined;            /* (S) */
+  int lastlinedefined;        /* (S) */
+  unsigned char nups;         /* (u) number of upvalues */
+  unsigned char nparams;      /* (u) number of parameters */
+  char isvararg;              /* (u) */
+  char istailcall;            /* (t) */
+  char short_src[LUA_IDSIZE]; /* (S) */
+  /* private part */
+  other fields
+} lua_Debug;

+ +

+A structure used to carry different pieces of +information about a function or an activation record. +lua_getstack fills only the private part +of this structure, for later use. +To fill the other fields of lua_Debug with useful information, +call lua_getinfo. + + +

+The fields of lua_Debug have the following meaning: + +

source: +the name of the chunk that created the function. +If source starts with a '@', +it means that the function was defined in a file where +the file name follows the '@'. +If source starts with a '=', +the remainder of its contents describe the source in a user-dependent manner. +Otherwise, +the function was defined in a string where +source is that string. +
short_src: +a "printable" version of source, to be used in error messages. +
linedefined: +the line number where the definition of the function starts. +
lastlinedefined: +the line number where the definition of the function ends. +
what: +the string "Lua" if the function is a Lua function, +"C" if it is a C function, +"main" if it is the main part of a chunk. +
currentline: +the current line where the given function is executing. +When no line information is available, +currentline is set to -1. +
name: +a reasonable name for the given function. +Because functions in Lua are first-class values, +they do not have a fixed name: +some functions can be the value of multiple global variables, +while others can be stored only in a table field. +The lua_getinfo function checks how the function was +called to find a suitable name. +If it cannot find a name, +then name is set to NULL. +
namewhat: +explains the name field. +The value of namewhat can be +"global", "local", "method", +"field", "upvalue", or "" (the empty string), +according to how the function was called. +(Lua uses the empty string when no other option seems to apply.) +
istailcall: +true if this function invocation was called by a tail call. +In this case, the caller of this level is not in the stack. +
nups: +the number of upvalues of the function. +
nparams: +the number of fixed parameters of the function +(always 0 for C functions). +
isvararg: +true if the function is a vararg function +(always true for C functions). +

+ + + + +

`lua_gethook`

+[-0, +0, –] +

lua_Hook lua_gethook (lua_State *L);

+ +

+Returns the current hook function. + + + + + +

`lua_gethookcount`

+[-0, +0, –] +

int lua_gethookcount (lua_State *L);

+ +

+Returns the current hook count. + + + + + +

`lua_gethookmask`

+[-0, +0, –] +

int lua_gethookmask (lua_State *L);

+ +

+Returns the current hook mask. + + + + + +

`lua_getinfo`

+[-(0|1), +(0|1|2), e] +

int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);

+ +

+Gets information about a specific function or function invocation. + + +

+To get information about a function invocation, +the parameter ar must be a valid activation record that was +filled by a previous call to lua_getstack or +given as argument to a hook (see lua_Hook). + + +

+To get information about a function you push it onto the stack +and start the what string with the character '>'. +(In that case, +lua_getinfo pops the function from the top of the stack.) +For instance, to know in which line a function f was defined, +you can write the following code: + +

+     lua_Debug ar;
+     lua_getglobal(L, "f");  /* get global 'f' */
+     lua_getinfo(L, ">S", &ar);
+     printf("%d\n", ar.linedefined);
+

+ +

+Each character in the string what +selects some fields of the structure ar to be filled or +a value to be pushed on the stack: + +

'n': fills in the field name and namewhat; +
'S': +fills in the fields source, short_src, +linedefined, lastlinedefined, and what; +
'l': fills in the field currentline; +
't': fills in the field istailcall; +
'u': fills in the fields +nups, nparams, and isvararg; +
'f': +pushes onto the stack the function that is +running at the given level; +
'L': +pushes onto the stack a table whose indices are the +numbers of the lines that are valid on the function. +(A valid line is a line with some associated code, +that is, a line where you can put a break point. +Non-valid lines include empty lines and comments.) + + +
+If this option is given together with option 'f', +its table is pushed after the function. +

+ +

+This function returns 0 on error +(for instance, an invalid option in what). + + + + + +

`lua_getlocal`

+[-0, +(0|1), –] +

const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);

+ +

+Gets information about a local variable of +a given activation record or a given function. + + +

+In the first case, +the parameter ar must be a valid activation record that was +filled by a previous call to lua_getstack or +given as argument to a hook (see lua_Hook). +The index n selects which local variable to inspect; +see debug.getlocal for details about variable indices +and names. + + +

+lua_getlocal pushes the variable's value onto the stack +and returns its name. + + +

+In the second case, ar must be NULL and the function +to be inspected must be at the top of the stack. +In this case, only parameters of Lua functions are visible +(as there is no information about what variables are active) +and no values are pushed onto the stack. + + +

+Returns NULL (and pushes nothing) +when the index is greater than +the number of active local variables. + + + + + +

`lua_getstack`

+[-0, +0, –] +

int lua_getstack (lua_State *L, int level, lua_Debug *ar);

+ +

+Gets information about the interpreter runtime stack. + + +

+This function fills parts of a lua_Debug structure with +an identification of the activation record +of the function executing at a given level. +Level 0 is the current running function, +whereas level n+1 is the function that has called level n +(except for tail calls, which do not count on the stack). +When there are no errors, lua_getstack returns 1; +when called with a level greater than the stack depth, +it returns 0. + + + + + +

`lua_getupvalue`

+[-0, +(0|1), –] +

const char *lua_getupvalue (lua_State *L, int funcindex, int n);

+ +

+Gets information about the n-th upvalue +of the closure at index funcindex. +It pushes the upvalue's value onto the stack +and returns its name. +Returns NULL (and pushes nothing) +when the index n is greater than the number of upvalues. + + +

+For C functions, this function uses the empty string "" +as a name for all upvalues. +(For Lua functions, +upvalues are the external local variables that the function uses, +and that are consequently included in its closure.) + + +

+Upvalues have no particular order, +as they are active through the whole function. +They are numbered in an arbitrary order. + + + + + +

`lua_Hook`

typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);

+ +

+Type for debugging hook functions. + + +

+Whenever a hook is called, its ar argument has its field +event set to the specific event that triggered the hook. +Lua identifies these events with the following constants: +LUA_HOOKCALL, LUA_HOOKRET, +LUA_HOOKTAILCALL, LUA_HOOKLINE, +and LUA_HOOKCOUNT. +Moreover, for line events, the field currentline is also set. +To get the value of any other field in ar, +the hook must call lua_getinfo. + + +

+For call events, event can be LUA_HOOKCALL, +the normal value, or LUA_HOOKTAILCALL, for a tail call; +in this case, there will be no corresponding return event. + + +

+While Lua is running a hook, it disables other calls to hooks. +Therefore, if a hook calls back Lua to execute a function or a chunk, +this execution occurs without any calls to hooks. + + +

+Hook functions cannot have continuations, +that is, they cannot call lua_yieldk, +lua_pcallk, or lua_callk with a non-null k. + + +

+Hook functions can yield under the following conditions: +Only count and line events can yield; +to yield, a hook function must finish its execution +calling lua_yield with nresults equal to zero +(that is, with no values). + + + + + +

`lua_sethook`

+[-0, +0, –] +

void lua_sethook (lua_State *L, lua_Hook f, int mask, int count);

+ +

+Sets the debugging hook function. + + +

+Argument f is the hook function. +mask specifies on which events the hook will be called: +it is formed by a bitwise or of the constants +LUA_MASKCALL, +LUA_MASKRET, +LUA_MASKLINE, +and LUA_MASKCOUNT. +The count argument is only meaningful when the mask +includes LUA_MASKCOUNT. +For each event, the hook is called as explained below: + +

The call hook: is called when the interpreter calls a function. +The hook is called just after Lua enters the new function, +before the function gets its arguments. +
The return hook: is called when the interpreter returns from a function. +The hook is called just before Lua leaves the function. +There is no standard way to access the values +to be returned by the function. +
The line hook: is called when the interpreter is about to +start the execution of a new line of code, +or when it jumps back in the code (even to the same line). +(This event only happens while Lua is executing a Lua function.) +
The count hook: is called after the interpreter executes every +count instructions. +(This event only happens while Lua is executing a Lua function.) +

+ +

+A hook is disabled by setting mask to zero. + + + + + +

`lua_setlocal`

+[-(0|1), +0, –] +

const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);

+ +

+Sets the value of a local variable of a given activation record. +It assigns the value at the top of the stack +to the variable and returns its name. +It also pops the value from the stack. + + +

+Returns NULL (and pops nothing) +when the index is greater than +the number of active local variables. + + +

+Parameters ar and n are as in function lua_getlocal. + + + + + +

`lua_setupvalue`

+[-(0|1), +0, –] +

const char *lua_setupvalue (lua_State *L, int funcindex, int n);

+ +

+Sets the value of a closure's upvalue. +It assigns the value at the top of the stack +to the upvalue and returns its name. +It also pops the value from the stack. + + +

+Returns NULL (and pops nothing) +when the index n is greater than the number of upvalues. + + +

+Parameters funcindex and n are as in function lua_getupvalue. + + + + + +

`lua_upvalueid`

+[-0, +0, –] +

void *lua_upvalueid (lua_State *L, int funcindex, int n);

+ +

+Returns a unique identifier for the upvalue numbered n +from the closure at index funcindex. + + +

+These unique identifiers allow a program to check whether different +closures share upvalues. +Lua closures that share an upvalue +(that is, that access a same external local variable) +will return identical ids for those upvalue indices. + + +

+Parameters funcindex and n are as in function lua_getupvalue, +but n cannot be greater than the number of upvalues. + + + + + +

`lua_upvaluejoin`

+[-0, +0, –] +

void lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
+                                    int funcindex2, int n2);

+ +

+Make the n1-th upvalue of the Lua closure at index funcindex1 +refer to the n2-th upvalue of the Lua closure at index funcindex2. + + + + + + + +

5 – The Auxiliary Library

+ +

+ +The auxiliary library provides several convenient functions +to interface C with Lua. +While the basic API provides the primitive functions for all +interactions between C and Lua, +the auxiliary library provides higher-level functions for some +common tasks. + + +

+All functions and types from the auxiliary library +are defined in header file lauxlib.h and +have a prefix luaL_. + + +

+All functions in the auxiliary library are built on +top of the basic API, +and so they provide nothing that cannot be done with that API. +Nevertheless, the use of the auxiliary library ensures +more consistency to your code. + + +

+Several functions in the auxiliary library use internally some +extra stack slots. +When a function in the auxiliary library uses less than five slots, +it does not check the stack size; +it simply assumes that there are enough slots. + + +

+Several functions in the auxiliary library are used to +check C function arguments. +Because the error message is formatted for arguments +(e.g., "bad argument #1"), +you should not use these functions for other stack values. + + +

+Functions called luaL_check* +always raise an error if the check is not satisfied. + + + +

5.1 – Functions and Types

+ +

+Here we list all functions and types from the auxiliary library +in alphabetical order. + + + +

`luaL_addchar`

+[-?, +?, m] +

void luaL_addchar (luaL_Buffer *B, char c);

+ +

+Adds the byte c to the buffer B +(see luaL_Buffer). + + + + + +

`luaL_addlstring`

+[-?, +?, m] +

void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);

+ +

+Adds the string pointed to by s with length l to +the buffer B +(see luaL_Buffer). +The string can contain embedded zeros. + + + + + +

`luaL_addsize`

+[-?, +?, –] +

void luaL_addsize (luaL_Buffer *B, size_t n);

+ +

+Adds to the buffer B (see luaL_Buffer) +a string of length n previously copied to the +buffer area (see luaL_prepbuffer). + + + + + +

`luaL_addstring`

+[-?, +?, m] +

void luaL_addstring (luaL_Buffer *B, const char *s);

+ +

+Adds the zero-terminated string pointed to by s +to the buffer B +(see luaL_Buffer). + + + + + +

`luaL_addvalue`

+[-1, +?, m] +

void luaL_addvalue (luaL_Buffer *B);

+ +

+Adds the value at the top of the stack +to the buffer B +(see luaL_Buffer). +Pops the value. + + +

+This is the only function on string buffers that can (and must) +be called with an extra element on the stack, +which is the value to be added to the buffer. + + + + + +

`luaL_argcheck`

+[-0, +0, v] +

void luaL_argcheck (lua_State *L,
+                    int cond,
+                    int arg,
+                    const char *extramsg);

+ +

+Checks whether cond is true. +If it is not, raises an error with a standard message (see luaL_argerror). + + + + + +

`luaL_argerror`

+[-0, +0, v] +

int luaL_argerror (lua_State *L, int arg, const char *extramsg);

+ +

+Raises an error reporting a problem with argument arg +of the C function that called it, +using a standard message +that includes extramsg as a comment: + +

+     bad argument #arg to 'funcname' (extramsg)
+

+This function never returns. + + + + + +

`luaL_Buffer`

typedef struct luaL_Buffer luaL_Buffer;

+ +

+Type for a string buffer. + + +

+A string buffer allows C code to build Lua strings piecemeal. +Its pattern of use is as follows: + +

First declare a variable b of type luaL_Buffer.
Then initialize it with a call luaL_buffinit(L, &b).
+Then add string pieces to the buffer calling any of +the luaL_add* functions. +
+Finish by calling luaL_pushresult(&b). +This call leaves the final string on the top of the stack. +

+ +

+If you know beforehand the total size of the resulting string, +you can use the buffer like this: + +

First declare a variable b of type luaL_Buffer.
Then initialize it and preallocate a space of +size sz with a call luaL_buffinitsize(L, &b, sz).
Then copy the string into that space.
+Finish by calling luaL_pushresultsize(&b, sz), +where sz is the total size of the resulting string +copied into that space. +

+ +

+During its normal operation, +a string buffer uses a variable number of stack slots. +So, while using a buffer, you cannot assume that you know where +the top of the stack is. +You can use the stack between successive calls to buffer operations +as long as that use is balanced; +that is, +when you call a buffer operation, +the stack is at the same level +it was immediately after the previous buffer operation. +(The only exception to this rule is luaL_addvalue.) +After calling luaL_pushresult the stack is back to its +level when the buffer was initialized, +plus the final string on its top. + + + + + +

`luaL_buffinit`

+[-0, +0, –] +

void luaL_buffinit (lua_State *L, luaL_Buffer *B);

+ +

+Initializes a buffer B. +This function does not allocate any space; +the buffer must be declared as a variable +(see luaL_Buffer). + + + + + +

`luaL_buffinitsize`

+[-?, +?, m] +

char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);

+ +

+Equivalent to the sequence +luaL_buffinit, luaL_prepbuffsize. + + + + + +

`luaL_callmeta`

+[-0, +(0|1), e] +

int luaL_callmeta (lua_State *L, int obj, const char *e);

+ +

+Calls a metamethod. + + +

+If the object at index obj has a metatable and this +metatable has a field e, +this function calls this field passing the object as its only argument. +In this case this function returns true and pushes onto the +stack the value returned by the call. +If there is no metatable or no metamethod, +this function returns false (without pushing any value on the stack). + + + + + +

`luaL_checkany`

+[-0, +0, v] +

void luaL_checkany (lua_State *L, int arg);

+ +

+Checks whether the function has an argument +of any type (including nil) at position arg. + + + + + +

`luaL_checkinteger`

+[-0, +0, v] +

lua_Integer luaL_checkinteger (lua_State *L, int arg);

+ +

+Checks whether the function argument arg is an integer +(or can be converted to an integer) +and returns this integer cast to a lua_Integer. + + + + + +

`luaL_checklstring`

+[-0, +0, v] +

const char *luaL_checklstring (lua_State *L, int arg, size_t *l);

+ +

+Checks whether the function argument arg is a string +and returns this string; +if l is not NULL fills *l +with the string's length. + + +

+This function uses lua_tolstring to get its result, +so all conversions and caveats of that function apply here. + + + + + +

`luaL_checknumber`

+[-0, +0, v] +

lua_Number luaL_checknumber (lua_State *L, int arg);

+ +

+Checks whether the function argument arg is a number +and returns this number. + + + + + +

`luaL_checkoption`

+[-0, +0, v] +

int luaL_checkoption (lua_State *L,
+                      int arg,
+                      const char *def,
+                      const char *const lst[]);

+ +

+Checks whether the function argument arg is a string and +searches for this string in the array lst +(which must be NULL-terminated). +Returns the index in the array where the string was found. +Raises an error if the argument is not a string or +if the string cannot be found. + + +

+If def is not NULL, +the function uses def as a default value when +there is no argument arg or when this argument is nil. + + +

+This is a useful function for mapping strings to C enums. +(The usual convention in Lua libraries is +to use strings instead of numbers to select options.) + + + + + +

`luaL_checkstack`

+[-0, +0, v] +

void luaL_checkstack (lua_State *L, int sz, const char *msg);

+ +

+Grows the stack size to top + sz elements, +raising an error if the stack cannot grow to that size. +msg is an additional text to go into the error message +(or NULL for no additional text). + + + + + +

`luaL_checkstring`

+[-0, +0, v] +

const char *luaL_checkstring (lua_State *L, int arg);

+ +

+Checks whether the function argument arg is a string +and returns this string. + + +

+This function uses lua_tolstring to get its result, +so all conversions and caveats of that function apply here. + + + + + +

`luaL_checktype`

+[-0, +0, v] +

void luaL_checktype (lua_State *L, int arg, int t);

+ +

+Checks whether the function argument arg has type t. +See lua_type for the encoding of types for t. + + + + + +

`luaL_checkudata`

+[-0, +0, v] +

void *luaL_checkudata (lua_State *L, int arg, const char *tname);

+ +

+Checks whether the function argument arg is a userdata +of the type tname (see luaL_newmetatable) and +returns the userdata address (see lua_touserdata). + + + + + +

`luaL_checkversion`

+[-0, +0, –] +

void luaL_checkversion (lua_State *L);

+ +

+Checks whether the core running the call, +the core that created the Lua state, +and the code making the call are all using the same version of Lua. +Also checks whether the core running the call +and the core that created the Lua state +are using the same address space. + + + + + +

`luaL_dofile`

+[-0, +?, e] +

int luaL_dofile (lua_State *L, const char *filename);

+ +

+Loads and runs the given file. +It is defined as the following macro: + +

+     (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
+

+It returns false if there are no errors +or true in case of errors. + + + + + +

`luaL_dostring`

+[-0, +?, –] +

int luaL_dostring (lua_State *L, const char *str);

+ +

+Loads and runs the given string. +It is defined as the following macro: + +

+     (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
+

+It returns false if there are no errors +or true in case of errors. + + + + + +

`luaL_error`

+[-0, +0, v] +

int luaL_error (lua_State *L, const char *fmt, ...);

+ +

+Raises an error. +The error message format is given by fmt +plus any extra arguments, +following the same rules of lua_pushfstring. +It also adds at the beginning of the message the file name and +the line number where the error occurred, +if this information is available. + + +

+This function never returns, +but it is an idiom to use it in C functions +as return luaL_error(args). + + + + + +

`luaL_execresult`

+[-0, +3, m] +

int luaL_execresult (lua_State *L, int stat);

+ +

+This function produces the return values for +process-related functions in the standard library +(os.execute and io.close). + + + + + +

`luaL_fileresult`

+[-0, +(1|3), m] +

int luaL_fileresult (lua_State *L, int stat, const char *fname);

+ +

+This function produces the return values for +file-related functions in the standard library +(io.open, os.rename, file:seek, etc.). + + + + + +

`luaL_getmetafield`

+[-0, +(0|1), m] +

int luaL_getmetafield (lua_State *L, int obj, const char *e);

+ +

+Pushes onto the stack the field e from the metatable +of the object at index obj and returns the type of pushed value. +If the object does not have a metatable, +or if the metatable does not have this field, +pushes nothing and returns LUA_TNIL. + + + + + +

`luaL_getmetatable`

+[-0, +1, m] +

int luaL_getmetatable (lua_State *L, const char *tname);

+ +

+Pushes onto the stack the metatable associated with name tname +in the registry (see luaL_newmetatable) +(nil if there is no metatable associated with that name). +Returns the type of the pushed value. + + + + + +

`luaL_getsubtable`

+[-0, +1, e] +

int luaL_getsubtable (lua_State *L, int idx, const char *fname);

+ +

+Ensures that the value t[fname], +where t is the value at index idx, +is a table, +and pushes that table onto the stack. +Returns true if it finds a previous table there +and false if it creates a new table. + + + + + +

`luaL_gsub`

+[-0, +1, m] +

const char *luaL_gsub (lua_State *L,
+                       const char *s,
+                       const char *p,
+                       const char *r);

+ +

+Creates a copy of string s by replacing +any occurrence of the string p +with the string r. +Pushes the resulting string on the stack and returns it. + + + + + +

`luaL_len`

+[-0, +0, e] +

lua_Integer luaL_len (lua_State *L, int index);

+ +

+Returns the "length" of the value at the given index +as a number; +it is equivalent to the '#' operator in Lua (see §3.4.7). +Raises an error if the result of the operation is not an integer. +(This case only can happen through metamethods.) + + + + + +

`luaL_loadbuffer`

+[-0, +1, –] +

int luaL_loadbuffer (lua_State *L,
+                     const char *buff,
+                     size_t sz,
+                     const char *name);

+ +

+Equivalent to luaL_loadbufferx with mode equal to NULL. + + + + + +

`luaL_loadbufferx`

+[-0, +1, –] +

int luaL_loadbufferx (lua_State *L,
+                      const char *buff,
+                      size_t sz,
+                      const char *name,
+                      const char *mode);

+ +

+Loads a buffer as a Lua chunk. +This function uses lua_load to load the chunk in the +buffer pointed to by buff with size sz. + + +

+This function returns the same results as lua_load. +name is the chunk name, +used for debug information and error messages. +The string mode works as in function lua_load. + + + + + +

`luaL_loadfile`

+[-0, +1, e] +

int luaL_loadfile (lua_State *L, const char *filename);

+ +

+Equivalent to luaL_loadfilex with mode equal to NULL. + + + + + +

`luaL_loadfilex`

+[-0, +1, e] +

int luaL_loadfilex (lua_State *L, const char *filename,
+                                            const char *mode);

+ +

+Loads a file as a Lua chunk. +This function uses lua_load to load the chunk in the file +named filename. +If filename is NULL, +then it loads from the standard input. +The first line in the file is ignored if it starts with a #. + + +

+The string mode works as in function lua_load. + + +

+This function returns the same results as lua_load, +but it has an extra error code LUA_ERRFILE +if it cannot open/read the file or the file has a wrong mode. + + +

+As lua_load, this function only loads the chunk; +it does not run it. + + + + + +

`luaL_loadstring`

+[-0, +1, –] +

int luaL_loadstring (lua_State *L, const char *s);

+ +

+Loads a string as a Lua chunk. +This function uses lua_load to load the chunk in +the zero-terminated string s. + + +

+This function returns the same results as lua_load. + + +

+Also as lua_load, this function only loads the chunk; +it does not run it. + + + + + +

`luaL_newlib`

+[-0, +1, m] +

void luaL_newlib (lua_State *L, const luaL_Reg l[]);

+ +

+Creates a new table and registers there +the functions in list l. + + +

+It is implemented as the following macro: + +

+     (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
+

+The array l must be the actual array, +not a pointer to it. + + + + + +

`luaL_newlibtable`

+[-0, +1, m] +

void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);

+ +

+Creates a new table with a size optimized +to store all entries in the array l +(but does not actually store them). +It is intended to be used in conjunction with luaL_setfuncs +(see luaL_newlib). + + +

+It is implemented as a macro. +The array l must be the actual array, +not a pointer to it. + + + + + +

`luaL_newmetatable`

+[-0, +1, m] +

int luaL_newmetatable (lua_State *L, const char *tname);

+ +

+If the registry already has the key tname, +returns 0. +Otherwise, +creates a new table to be used as a metatable for userdata, +adds to this new table the pair __name = tname, +adds to the registry the pair [tname] = new table, +and returns 1. +(The entry __name is used by some error-reporting functions.) + + +

+In both cases pushes onto the stack the final value associated +with tname in the registry. + + + + + +

`luaL_newstate`

+[-0, +0, –] +

lua_State *luaL_newstate (void);

+ +

+Creates a new Lua state. +It calls lua_newstate with an +allocator based on the standard C realloc function +and then sets a panic function (see §4.6) that prints +an error message to the standard error output in case of fatal +errors. + + +

+Returns the new state, +or NULL if there is a memory allocation error. + + + + + +

`luaL_openlibs`

+[-0, +0, e] +

void luaL_openlibs (lua_State *L);

+ +

+Opens all standard Lua libraries into the given state. + + + + + +

`luaL_optinteger`

+[-0, +0, v] +

lua_Integer luaL_optinteger (lua_State *L,
+                             int arg,
+                             lua_Integer d);

+ +

+If the function argument arg is an integer +(or convertible to an integer), +returns this integer. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

`luaL_optlstring`

+[-0, +0, v] +

const char *luaL_optlstring (lua_State *L,
+                             int arg,
+                             const char *d,
+                             size_t *l);

+ +

+If the function argument arg is a string, +returns this string. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + +

+If l is not NULL, +fills the position *l with the result's length. +If the result is NULL +(only possible when returning d and d == NULL), +its length is considered zero. + + + + + +

`luaL_optnumber`

+[-0, +0, v] +

lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);

+ +

+If the function argument arg is a number, +returns this number. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

`luaL_optstring`

+[-0, +0, v] +

const char *luaL_optstring (lua_State *L,
+                            int arg,
+                            const char *d);

+ +

+If the function argument arg is a string, +returns this string. +If this argument is absent or is nil, +returns d. +Otherwise, raises an error. + + + + + +

`luaL_prepbuffer`

+[-?, +?, m] +

char *luaL_prepbuffer (luaL_Buffer *B);

+ +

+Equivalent to luaL_prepbuffsize +with the predefined size LUAL_BUFFERSIZE. + + + + + +

`luaL_prepbuffsize`

+[-?, +?, m] +

char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);

+ +

+Returns an address to a space of size sz +where you can copy a string to be added to buffer B +(see luaL_Buffer). +After copying the string into this space you must call +luaL_addsize with the size of the string to actually add +it to the buffer. + + + + + +

`luaL_pushresult`

+[-?, +1, m] +

void luaL_pushresult (luaL_Buffer *B);

+ +

+Finishes the use of buffer B leaving the final string on +the top of the stack. + + + + + +

`luaL_pushresultsize`

+[-?, +1, m] +

void luaL_pushresultsize (luaL_Buffer *B, size_t sz);

+ +

+Equivalent to the sequence luaL_addsize, luaL_pushresult. + + + + + +

`luaL_ref`

+[-1, +0, m] +

int luaL_ref (lua_State *L, int t);

+ +

+Creates and returns a reference, +in the table at index t, +for the object at the top of the stack (and pops the object). + + +

+A reference is a unique integer key. +As long as you do not manually add integer keys into table t, +luaL_ref ensures the uniqueness of the key it returns. +You can retrieve an object referred by reference r +by calling lua_rawgeti(L, t, r). +Function luaL_unref frees a reference and its associated object. + + +

+If the object at the top of the stack is nil, +luaL_ref returns the constant LUA_REFNIL. +The constant LUA_NOREF is guaranteed to be different +from any reference returned by luaL_ref. + + + + + +

`luaL_Reg`

typedef struct luaL_Reg {
+  const char *name;
+  lua_CFunction func;
+} luaL_Reg;

+ +

+Type for arrays of functions to be registered by +luaL_setfuncs. +name is the function name and func is a pointer to +the function. +Any array of luaL_Reg must end with a sentinel entry +in which both name and func are NULL. + + + + + +

`luaL_requiref`

+[-0, +1, e] +

void luaL_requiref (lua_State *L, const char *modname,
+                    lua_CFunction openf, int glb);

+ +

+If modname is not already present in package.loaded, +calls function openf with string modname as an argument +and sets the call result in package.loaded[modname], +as if that function has been called through require. + + +

+If glb is true, +also stores the module into global modname. + + +

+Leaves a copy of the module on the stack. + + + + + +

`luaL_setfuncs`

+[-nup, +0, m] +

void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);

+ +

+Registers all functions in the array l +(see luaL_Reg) into the table on the top of the stack +(below optional upvalues, see next). + + +

+When nup is not zero, +all functions are created sharing nup upvalues, +which must be previously pushed on the stack +on top of the library table. +These values are popped from the stack after the registration. + + + + + +

`luaL_setmetatable`

+[-0, +0, –] +

void luaL_setmetatable (lua_State *L, const char *tname);

+ +

+Sets the metatable of the object at the top of the stack +as the metatable associated with name tname +in the registry (see luaL_newmetatable). + + + + + +

`luaL_Stream`

typedef struct luaL_Stream {
+  FILE *f;
+  lua_CFunction closef;
+} luaL_Stream;

+ +

+The standard representation for file handles, +which is used by the standard I/O library. + + +

+A file handle is implemented as a full userdata, +with a metatable called LUA_FILEHANDLE +(where LUA_FILEHANDLE is a macro with the actual metatable's name). +The metatable is created by the I/O library +(see luaL_newmetatable). + + +

+This userdata must start with the structure luaL_Stream; +it can contain other data after this initial structure. +Field f points to the corresponding C stream +(or it can be NULL to indicate an incompletely created handle). +Field closef points to a Lua function +that will be called to close the stream +when the handle is closed or collected; +this function receives the file handle as its sole argument and +must return either true (in case of success) +or nil plus an error message (in case of error). +Once Lua calls this field, +it changes the field value to NULL +to signal that the handle is closed. + + + + + +

`luaL_testudata`

+[-0, +0, m] +

void *luaL_testudata (lua_State *L, int arg, const char *tname);

+ +

+This function works like luaL_checkudata, +except that, when the test fails, +it returns NULL instead of raising an error. + + + + + +

`luaL_tolstring`

+[-0, +1, e] +

const char *luaL_tolstring (lua_State *L, int idx, size_t *len);

+ +

+Converts any Lua value at the given index to a C string +in a reasonable format. +The resulting string is pushed onto the stack and also +returned by the function. +If len is not NULL, +the function also sets *len with the string length. + + +

+If the value has a metatable with a "__tostring" field, +then luaL_tolstring calls the corresponding metamethod +with the value as argument, +and uses the result of the call as its result. + + + + + +

`luaL_traceback`

+[-0, +1, m] +

void luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
+                     int level);

+ +

+Creates and pushes a traceback of the stack L1. +If msg is not NULL it is appended +at the beginning of the traceback. +The level parameter tells at which level +to start the traceback. + + + + + +

`luaL_typename`

+[-0, +0, –] +

const char *luaL_typename (lua_State *L, int index);

+ +

+Returns the name of the type of the value at the given index. + + + + + +

`luaL_unref`

+[-0, +0, –] +

void luaL_unref (lua_State *L, int t, int ref);

+ +

+Releases reference ref from the table at index t +(see luaL_ref). +The entry is removed from the table, +so that the referred object can be collected. +The reference ref is also freed to be used again. + + +

+If ref is LUA_NOREF or LUA_REFNIL, +luaL_unref does nothing. + + + + + +

`luaL_where`

+[-0, +1, m] +

void luaL_where (lua_State *L, int lvl);

+ +

+Pushes onto the stack a string identifying the current position +of the control at level lvl in the call stack. +Typically this string has the following format: + +

+     chunkname:currentline:
+

+Level 0 is the running function, +level 1 is the function that called the running function, +etc. + + +

+This function is used to build a prefix for error messages. + + + + + + + +

6 – Standard Libraries

+ +

+The standard Lua libraries provide useful functions +that are implemented directly through the C API. +Some of these functions provide essential services to the language +(e.g., type and getmetatable); +others provide access to "outside" services (e.g., I/O); +and others could be implemented in Lua itself, +but are quite useful or have critical performance requirements that +deserve an implementation in C (e.g., table.sort). + + +

+All libraries are implemented through the official C API +and are provided as separate C modules. +Currently, Lua has the following standard libraries: + +

basic library (§6.1);
coroutine library (§6.2);
package library (§6.3);
string manipulation (§6.4);
basic UTF-8 support (§6.5);
table manipulation (§6.6);
mathematical functions (§6.7) (sin, log, etc.);
input and output (§6.8);
operating system facilities (§6.9);
debug facilities (§6.10).

+Except for the basic and the package libraries, +each library provides all its functions as fields of a global table +or as methods of its objects. + + +

+To have access to these libraries, +the C host program should call the luaL_openlibs function, +which opens all standard libraries. +Alternatively, +the host program can open them individually by using +luaL_requiref to call +luaopen_base (for the basic library), +luaopen_package (for the package library), +luaopen_coroutine (for the coroutine library), +luaopen_string (for the string library), +luaopen_utf8 (for the UTF8 library), +luaopen_table (for the table library), +luaopen_math (for the mathematical library), +luaopen_io (for the I/O library), +luaopen_os (for the operating system library), +and luaopen_debug (for the debug library). +These functions are declared in lualib.h. + + + +

6.1 – Basic Functions

+ +

+The basic library provides core functions to Lua. +If you do not include this library in your application, +you should check carefully whether you need to provide +implementations for some of its facilities. + + +

`assert (v [, message])`

+ + +

+Calls error if +the value of its argument v is false (i.e., nil or false); +otherwise, returns all its arguments. +In case of error, +message is the error object; +when absent, it defaults to "assertion failed!" + + + + +

`collectgarbage ([opt [, arg]])`

+ + +

+This function is a generic interface to the garbage collector. +It performs different functions according to its first argument, opt: + +

"collect": +performs a full garbage-collection cycle. +This is the default option. +
"stop": +stops automatic execution of the garbage collector. +The collector will run only when explicitly invoked, +until a call to restart it. +
"restart": +restarts automatic execution of the garbage collector. +
"count": +returns the total memory in use by Lua in Kbytes. +The value has a fractional part, +so that it multiplied by 1024 +gives the exact number of bytes in use by Lua +(except for overflows). +
"step": +performs a garbage-collection step. +The step "size" is controlled by arg. +With a zero value, +the collector will perform one basic (indivisible) step. +For non-zero values, +the collector will perform as if that amount of memory +(in KBytes) had been allocated by Lua. +Returns true if the step finished a collection cycle. +
"setpause": +sets arg as the new value for the pause of +the collector (see §2.5). +Returns the previous value for pause. +
"setstepmul": +sets arg as the new value for the step multiplier of +the collector (see §2.5). +Returns the previous value for step. +
"isrunning": +returns a boolean that tells whether the collector is running +(i.e., not stopped). +

+ + + +

`dofile ([filename])`

+Opens the named file and executes its contents as a Lua chunk. +When called without arguments, +dofile executes the contents of the standard input (stdin). +Returns all values returned by the chunk. +In case of errors, dofile propagates the error +to its caller (that is, dofile does not run in protected mode). + + + + +

`error (message [, level])`

+Terminates the last protected function called +and returns message as the error object. +Function error never returns. + + +

+Usually, error adds some information about the error position +at the beginning of the message, if the message is a string. +The level argument specifies how to get the error position. +With level 1 (the default), the error position is where the +error function was called. +Level 2 points the error to where the function +that called error was called; and so on. +Passing a level 0 avoids the addition of error position information +to the message. + + + + +

`_G`

+A global variable (not a function) that +holds the global environment (see §2.2). +Lua itself does not use this variable; +changing its value does not affect any environment, +nor vice versa. + + + + +

`getmetatable (object)`

+ + +

+If object does not have a metatable, returns nil. +Otherwise, +if the object's metatable has a "__metatable" field, +returns the associated value. +Otherwise, returns the metatable of the given object. + + + + +

`ipairs (t)`

+ + +

+Returns three values (an iterator function, the table t, and 0) +so that the construction + +

+     for i,v in ipairs(t) do body end
+

+will iterate over the key–value pairs +(1,t[1]), (2,t[2]), ..., +up to the first nil value. + + + + +

`load (chunk [, chunkname [, mode [, env]]])`

+ + +

+Loads a chunk. + + +

+If chunk is a string, the chunk is this string. +If chunk is a function, +load calls it repeatedly to get the chunk pieces. +Each call to chunk must return a string that concatenates +with previous results. +A return of an empty string, nil, or no value signals the end of the chunk. + + +

+If there are no syntactic errors, +returns the compiled chunk as a function; +otherwise, returns nil plus the error message. + + +

+If the resulting function has upvalues, +the first upvalue is set to the value of env, +if that parameter is given, +or to the value of the global environment. +Other upvalues are initialized with nil. +(When you load a main chunk, +the resulting function will always have exactly one upvalue, +the _ENV variable (see §2.2). +However, +when you load a binary chunk created from a function (see string.dump), +the resulting function can have an arbitrary number of upvalues.) +All upvalues are fresh, that is, +they are not shared with any other function. + + +

+chunkname is used as the name of the chunk for error messages +and debug information (see §4.9). +When absent, +it defaults to chunk, if chunk is a string, +or to "=(load)" otherwise. + + +

+The string mode controls whether the chunk can be text or binary +(that is, a precompiled chunk). +It may be the string "b" (only binary chunks), +"t" (only text chunks), +or "bt" (both binary and text). +The default is "bt". + + +

+Lua does not check the consistency of binary chunks. +Maliciously crafted binary chunks can crash +the interpreter. + + + + +

`loadfile ([filename [, mode [, env]]])`

+ + +

+Similar to load, +but gets the chunk from file filename +or from the standard input, +if no file name is given. + + + + +

`next (table [, index])`

+ + +

+Allows a program to traverse all fields of a table. +Its first argument is a table and its second argument +is an index in this table. +next returns the next index of the table +and its associated value. +When called with nil as its second argument, +next returns an initial index +and its associated value. +When called with the last index, +or with nil in an empty table, +next returns nil. +If the second argument is absent, then it is interpreted as nil. +In particular, +you can use next(t) to check whether a table is empty. + + +

+The order in which the indices are enumerated is not specified, +even for numeric indices. +(To traverse a table in numerical order, +use a numerical for.) + + +

+The behavior of next is undefined if, +during the traversal, +you assign any value to a non-existent field in the table. +You may however modify existing fields. +In particular, you may clear existing fields. + + + + +

`pairs (t)`

+ + +

+If t has a metamethod __pairs, +calls it with t as argument and returns the first three +results from the call. + + +

+Otherwise, +returns three values: the next function, the table t, and nil, +so that the construction + +

+     for k,v in pairs(t) do body end
+

+will iterate over all key–value pairs of table t. + + +

+See function next for the caveats of modifying +the table during its traversal. + + + + +

`pcall (f [, arg1, ···])`

+ + +

+Calls function f with +the given arguments in protected mode. +This means that any error inside f is not propagated; +instead, pcall catches the error +and returns a status code. +Its first result is the status code (a boolean), +which is true if the call succeeds without errors. +In such case, pcall also returns all results from the call, +after this first result. +In case of any error, pcall returns false plus the error message. + + + + +

`print (···)`

+Receives any number of arguments +and prints their values to stdout, +using the tostring function to convert each argument to a string. +print is not intended for formatted output, +but only as a quick way to show a value, +for instance for debugging. +For complete control over the output, +use string.format and io.write. + + + + +

`rawequal (v1, v2)`

+Checks whether v1 is equal to v2, +without invoking any metamethod. +Returns a boolean. + + + + +

`rawget (table, index)`

+Gets the real value of table[index], +without invoking any metamethod. +table must be a table; +index may be any value. + + + + +

`rawlen (v)`

+Returns the length of the object v, +which must be a table or a string, +without invoking any metamethod. +Returns an integer. + + + + +

`rawset (table, index, value)`

+Sets the real value of table[index] to value, +without invoking any metamethod. +table must be a table, +index any value different from nil and NaN, +and value any Lua value. + + +

+This function returns table. + + + + +

`select (index, ···)`

+ + +

+If index is a number, +returns all arguments after argument number index; +a negative number indexes from the end (-1 is the last argument). +Otherwise, index must be the string "#", +and select returns the total number of extra arguments it received. + + + + +

`setmetatable (table, metatable)`

+ + +

+Sets the metatable for the given table. +(To change the metatable of other types from Lua code, +you must use the debug library (§6.10).) +If metatable is nil, +removes the metatable of the given table. +If the original metatable has a "__metatable" field, +raises an error. + + +

+This function returns table. + + + + +

`tonumber (e [, base])`

+ + +

+When called with no base, +tonumber tries to convert its argument to a number. +If the argument is already a number or +a string convertible to a number, +then tonumber returns this number; +otherwise, it returns nil. + + +

+The conversion of strings can result in integers or floats, +according to the lexical conventions of Lua (see §3.1). +(The string may have leading and trailing spaces and a sign.) + + +

+When called with base, +then e must be a string to be interpreted as +an integer numeral in that base. +The base may be any integer between 2 and 36, inclusive. +In bases above 10, the letter 'A' (in either upper or lower case) +represents 10, 'B' represents 11, and so forth, +with 'Z' representing 35. +If the string e is not a valid numeral in the given base, +the function returns nil. + + + + +

`tostring (v)`

+Receives a value of any type and +converts it to a string in a human-readable format. +(For complete control of how numbers are converted, +use string.format.) + + +

+If the metatable of v has a "__tostring" field, +then tostring calls the corresponding value +with v as argument, +and uses the result of the call as its result. + + + + +

`type (v)`

+Returns the type of its only argument, coded as a string. +The possible results of this function are +"nil" (a string, not the value nil), +"number", +"string", +"boolean", +"table", +"function", +"thread", +and "userdata". + + + + +

`_VERSION`

+ + +

+A global variable (not a function) that +holds a string containing the running Lua version. +The current value of this variable is "Lua 5.3". + + + + +

`xpcall (f, msgh [, arg1, ···])`

+ + +

+This function is similar to pcall, +except that it sets a new message handler msgh. + + + + + + + +

6.2 – Coroutine Manipulation

+ +

+This library comprises the operations to manipulate coroutines, +which come inside the table coroutine. +See §2.6 for a general description of coroutines. + + +

`coroutine.create (f)`

+ + +

+Creates a new coroutine, with body f. +f must be a function. +Returns this new coroutine, +an object with type "thread". + + + + +

`coroutine.isyieldable ()`

+ + +

+Returns true when the running coroutine can yield. + + +

+A running coroutine is yieldable if it is not the main thread and +it is not inside a non-yieldable C function. + + + + +

`coroutine.resume (co [, val1, ···])`

+ + +

+Starts or continues the execution of coroutine co. +The first time you resume a coroutine, +it starts running its body. +The values val1, ... are passed +as the arguments to the body function. +If the coroutine has yielded, +resume restarts it; +the values val1, ... are passed +as the results from the yield. + + +

+If the coroutine runs without any errors, +resume returns true plus any values passed to yield +(when the coroutine yields) or any values returned by the body function +(when the coroutine terminates). +If there is any error, +resume returns false plus the error message. + + + + +

`coroutine.running ()`

+ + +

+Returns the running coroutine plus a boolean, +true when the running coroutine is the main one. + + + + +

`coroutine.status (co)`

+ + +

+Returns the status of coroutine co, as a string: +"running", +if the coroutine is running (that is, it called status); +"suspended", if the coroutine is suspended in a call to yield, +or if it has not started running yet; +"normal" if the coroutine is active but not running +(that is, it has resumed another coroutine); +and "dead" if the coroutine has finished its body function, +or if it has stopped with an error. + + + + +

`coroutine.wrap (f)`

+ + +

+Creates a new coroutine, with body f. +f must be a function. +Returns a function that resumes the coroutine each time it is called. +Any arguments passed to the function behave as the +extra arguments to resume. +Returns the same values returned by resume, +except the first boolean. +In case of error, propagates the error. + + + + +

`coroutine.yield (···)`

+ + +

+Suspends the execution of the calling coroutine. +Any arguments to yield are passed as extra results to resume. + + + + + + + +

6.3 – Modules

+ +

+The package library provides basic +facilities for loading modules in Lua. +It exports one function directly in the global environment: +require. +Everything else is exported in a table package. + + +

`require (modname)`

+ + +

+Loads the given module. +The function starts by looking into the package.loaded table +to determine whether modname is already loaded. +If it is, then require returns the value stored +at package.loaded[modname]. +Otherwise, it tries to find a loader for the module. + + +

+To find a loader, +require is guided by the package.searchers sequence. +By changing this sequence, +we can change how require looks for a module. +The following explanation is based on the default configuration +for package.searchers. + + +

+First require queries package.preload[modname]. +If it has a value, +this value (which must be a function) is the loader. +Otherwise require searches for a Lua loader using the +path stored in package.path. +If that also fails, it searches for a C loader using the +path stored in package.cpath. +If that also fails, +it tries an all-in-one loader (see package.searchers). + + +

+Once a loader is found, +require calls the loader with two arguments: +modname and an extra value dependent on how it got the loader. +(If the loader came from a file, +this extra value is the file name.) +If the loader returns any non-nil value, +require assigns the returned value to package.loaded[modname]. +If the loader does not return a non-nil value and +has not assigned any value to package.loaded[modname], +then require assigns true to this entry. +In any case, require returns the +final value of package.loaded[modname]. + + +

+If there is any error loading or running the module, +or if it cannot find any loader for the module, +then require raises an error. + + + + +

`package.config`

+ + +

+A string describing some compile-time configurations for packages. +This string is a sequence of lines: + +

The first line is the directory separator string. +Default is '\' for Windows and '/' for all other systems.
The second line is the character that separates templates in a path. +Default is ';'.
The third line is the string that marks the +substitution points in a template. +Default is '?'.
The fourth line is a string that, in a path in Windows, +is replaced by the executable's directory. +Default is '!'.
The fifth line is a mark to ignore all text after it +when building the luaopen_ function name. +Default is '-'.

+ + + +

`package.cpath`

+ + +

+The path used by require to search for a C loader. + + +

+Lua initializes the C path package.cpath in the same way +it initializes the Lua path package.path, +using the environment variable LUA_CPATH_5_3 +or the environment variable LUA_CPATH +or a default path defined in luaconf.h. + + + + +

`package.loaded`

+ + +

+A table used by require to control which +modules are already loaded. +When you require a module modname and +package.loaded[modname] is not false, +require simply returns the value stored there. + + +

+This variable is only a reference to the real table; +assignments to this variable do not change the +table used by require. + + + + +

`package.loadlib (libname, funcname)`

+ + +

+Dynamically links the host program with the C library libname. + + +

+If funcname is "*", +then it only links with the library, +making the symbols exported by the library +available to other dynamically linked libraries. +Otherwise, +it looks for a function funcname inside the library +and returns this function as a C function. +So, funcname must follow the lua_CFunction prototype +(see lua_CFunction). + + +

+This is a low-level function. +It completely bypasses the package and module system. +Unlike require, +it does not perform any path searching and +does not automatically adds extensions. +libname must be the complete file name of the C library, +including if necessary a path and an extension. +funcname must be the exact name exported by the C library +(which may depend on the C compiler and linker used). + + +

+This function is not supported by Standard C. +As such, it is only available on some platforms +(Windows, Linux, Mac OS X, Solaris, BSD, +plus other Unix systems that support the dlfcn standard). + + + + +

`package.path`

+ + +

+The path used by require to search for a Lua loader. + + +

+At start-up, Lua initializes this variable with +the value of the environment variable LUA_PATH_5_3 or +the environment variable LUA_PATH or +with a default path defined in luaconf.h, +if those environment variables are not defined. +Any ";;" in the value of the environment variable +is replaced by the default path. + + + + +

`package.preload`

+ + +

+A table to store loaders for specific modules +(see require). + + +

+This variable is only a reference to the real table; +assignments to this variable do not change the +table used by require. + + + + +

`package.searchers`

+ + +

+A table used by require to control how to load modules. + + +

+Each entry in this table is a searcher function. +When looking for a module, +require calls each of these searchers in ascending order, +with the module name (the argument given to require) as its +sole parameter. +The function can return another function (the module loader) +plus an extra value that will be passed to that loader, +or a string explaining why it did not find that module +(or nil if it has nothing to say). + + +

+Lua initializes this table with four searcher functions. + + +

+The first searcher simply looks for a loader in the +package.preload table. + + +

+The second searcher looks for a loader as a Lua library, +using the path stored at package.path. +The search is done as described in function package.searchpath. + + +

+The third searcher looks for a loader as a C library, +using the path given by the variable package.cpath. +Again, +the search is done as described in function package.searchpath. +For instance, +if the C path is the string + +

+     "./?.so;./?.dll;/usr/local/?/init.so"
+

+the searcher for module foo +will try to open the files ./foo.so, ./foo.dll, +and /usr/local/foo/init.so, in that order. +Once it finds a C library, +this searcher first uses a dynamic link facility to link the +application with the library. +Then it tries to find a C function inside the library to +be used as the loader. +The name of this C function is the string "luaopen_" +concatenated with a copy of the module name where each dot +is replaced by an underscore. +Moreover, if the module name has a hyphen, +its suffix after (and including) the first hyphen is removed. +For instance, if the module name is a.b.c-v2.1, +the function name will be luaopen_a_b_c. + + +

+The fourth searcher tries an all-in-one loader. +It searches the C path for a library for +the root name of the given module. +For instance, when requiring a.b.c, +it will search for a C library for a. +If found, it looks into it for an open function for +the submodule; +in our example, that would be luaopen_a_b_c. +With this facility, a package can pack several C submodules +into one single library, +with each submodule keeping its original open function. + + +

+All searchers except the first one (preload) return as the extra value +the file name where the module was found, +as returned by package.searchpath. +The first searcher returns no extra value. + + + + +

`package.searchpath (name, path [, sep [, rep]])`

+ + +

+Searches for the given name in the given path. + + +

+A path is a string containing a sequence of +templates separated by semicolons. +For each template, +the function replaces each interrogation mark (if any) +in the template with a copy of name +wherein all occurrences of sep +(a dot, by default) +were replaced by rep +(the system's directory separator, by default), +and then tries to open the resulting file name. + + +

+For instance, if the path is the string + +

+     "./?.lua;./?.lc;/usr/local/?/init.lua"
+

+the search for the name foo.a +will try to open the files +./foo/a.lua, ./foo/a.lc, and +/usr/local/foo/a/init.lua, in that order. + + +

+Returns the resulting name of the first file that it can +open in read mode (after closing the file), +or nil plus an error message if none succeeds. +(This error message lists all file names it tried to open.) + + + + + + + +

6.4 – String Manipulation

+ +

+This library provides generic functions for string manipulation, +such as finding and extracting substrings, and pattern matching. +When indexing a string in Lua, the first character is at position 1 +(not at 0, as in C). +Indices are allowed to be negative and are interpreted as indexing backwards, +from the end of the string. +Thus, the last character is at position -1, and so on. + + +

+The string library provides all its functions inside the table +string. +It also sets a metatable for strings +where the __index field points to the string table. +Therefore, you can use the string functions in object-oriented style. +For instance, string.byte(s,i) +can be written as s:byte(i). + + +

+The string library assumes one-byte character encodings. + + +

`string.byte (s [, i [, j]])`

+Returns the internal numeric codes of the characters s[i], +s[i+1], ..., s[j]. +The default value for i is 1; +the default value for j is i. +These indices are corrected +following the same rules of function string.sub. + + +

+Numeric codes are not necessarily portable across platforms. + + + + +

`string.char (···)`

+Receives zero or more integers. +Returns a string with length equal to the number of arguments, +in which each character has the internal numeric code equal +to its corresponding argument. + + +

+Numeric codes are not necessarily portable across platforms. + + + + +

`string.dump (function [, strip])`

+ + +

+Returns a string containing a binary representation +(a binary chunk) +of the given function, +so that a later load on this string returns +a copy of the function (but with new upvalues). +If strip is a true value, +the binary representation may not include all debug information +about the function, +to save space. + + +

+Functions with upvalues have only their number of upvalues saved. +When (re)loaded, +those upvalues receive fresh instances containing nil. +(You can use the debug library to serialize +and reload the upvalues of a function +in a way adequate to your needs.) + + + + +

`string.find (s, pattern [, init [, plain]])`

+ + +

+Looks for the first match of +pattern (see §6.4.1) in the string s. +If it finds a match, then find returns the indices of s +where this occurrence starts and ends; +otherwise, it returns nil. +A third, optional numeric argument init specifies +where to start the search; +its default value is 1 and can be negative. +A value of true as a fourth, optional argument plain +turns off the pattern matching facilities, +so the function does a plain "find substring" operation, +with no characters in pattern being considered magic. +Note that if plain is given, then init must be given as well. + + +

+If the pattern has captures, +then in a successful match +the captured values are also returned, +after the two indices. + + + + +

`string.format (formatstring, ···)`

+ + +

+Returns a formatted version of its variable number of arguments +following the description given in its first argument (which must be a string). +The format string follows the same rules as the ISO C function sprintf. +The only differences are that the options/modifiers +*, h, L, l, n, +and p are not supported +and that there is an extra option, q. +The q option formats a string between double quotes, +using escape sequences when necessary to ensure that +it can safely be read back by the Lua interpreter. +For instance, the call + +

+     string.format('%q', 'a string with "quotes" and \n new line')
+

+may produce the string: + +

+     "a string with \"quotes\" and \
+      new line"
+

+ +

+Options +A, a, E, e, f, +G, and g all expect a number as argument. +Options c, d, +i, o, u, X, and x +expect an integer. +Option q expects a string. +Option s expects a string; +if its argument is not a string, +it is converted to one following the same rules of tostring. +If the option has any modifier (flags, width, length), +the string argument should not contain embedded zeros. + + +

+When Lua is compiled with a non-C99 compiler, +options A and a (hexadecimal floats) +do not support any modifier (flags, width, length). + + + + +

`string.gmatch (s, pattern)`

+Returns an iterator function that, +each time it is called, +returns the next captures from pattern (see §6.4.1) +over the string s. +If pattern specifies no captures, +then the whole match is produced in each call. + + +

+As an example, the following loop +will iterate over all the words from string s, +printing one per line: + +

+     s = "hello world from Lua"
+     for w in string.gmatch(s, "%a+") do
+       print(w)
+     end
+

+The next example collects all pairs key=value from the +given string into a table: + +

+     t = {}
+     s = "from=world, to=Lua"
+     for k, v in string.gmatch(s, "(%w+)=(%w+)") do
+       t[k] = v
+     end
+

+ +

+For this function, a caret '^' at the start of a pattern does not +work as an anchor, as this would prevent the iteration. + + + + +

`string.gsub (s, pattern, repl [, n])`

+Returns a copy of s +in which all (or the first n, if given) +occurrences of the pattern (see §6.4.1) have been +replaced by a replacement string specified by repl, +which can be a string, a table, or a function. +gsub also returns, as its second value, +the total number of matches that occurred. +The name gsub comes from Global SUBstitution. + + +

+If repl is a string, then its value is used for replacement. +The character % works as an escape character: +any sequence in repl of the form %d, +with d between 1 and 9, +stands for the value of the d-th captured substring. +The sequence %0 stands for the whole match. +The sequence %% stands for a single %. + + +

+If repl is a table, then the table is queried for every match, +using the first capture as the key. + + +

+If repl is a function, then this function is called every time a +match occurs, with all captured substrings passed as arguments, +in order. + + +

+In any case, +if the pattern specifies no captures, +then it behaves as if the whole pattern was inside a capture. + + +

+If the value returned by the table query or by the function call +is a string or a number, +then it is used as the replacement string; +otherwise, if it is false or nil, +then there is no replacement +(that is, the original match is kept in the string). + + +

+Here are some examples: + +

+     x = string.gsub("hello world", "(%w+)", "%1 %1")
+     --> x="hello hello world world"
+     
+     x = string.gsub("hello world", "%w+", "%0 %0", 1)
+     --> x="hello hello world"
+     
+     x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
+     --> x="world hello Lua from"
+     
+     x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
+     --> x="home = /home/roberto, user = roberto"
+     
+     x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
+           return load(s)()
+         end)
+     --> x="4+5 = 9"
+     
+     local t = {name="lua", version="5.3"}
+     x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
+     --> x="lua-5.3.tar.gz"
+

+ + + +

`string.len (s)`

+Receives a string and returns its length. +The empty string "" has length 0. +Embedded zeros are counted, +so "a\000bc\000" has length 5. + + + + +

`string.lower (s)`

+Receives a string and returns a copy of this string with all +uppercase letters changed to lowercase. +All other characters are left unchanged. +The definition of what an uppercase letter is depends on the current locale. + + + + +

`string.match (s, pattern [, init])`

+Looks for the first match of +pattern (see §6.4.1) in the string s. +If it finds one, then match returns +the captures from the pattern; +otherwise it returns nil. +If pattern specifies no captures, +then the whole match is returned. +A third, optional numeric argument init specifies +where to start the search; +its default value is 1 and can be negative. + + + + +

`string.pack (fmt, v1, v2, ···)`

+ + +

+Returns a binary string containing the values v1, v2, etc. +packed (that is, serialized in binary form) +according to the format string fmt (see §6.4.2). + + + + +

`string.packsize (fmt)`

+ + +

+Returns the size of a string resulting from string.pack +with the given format. +The format string cannot have the variable-length options +'s' or 'z' (see §6.4.2). + + + + +

`string.rep (s, n [, sep])`

+Returns a string that is the concatenation of n copies of +the string s separated by the string sep. +The default value for sep is the empty string +(that is, no separator). +Returns the empty string if n is not positive. + + +

+(Note that it is very easy to exhaust the memory of your machine +with a single call to this function.) + + + + +

`string.reverse (s)`

+Returns a string that is the string s reversed. + + + + +

`string.sub (s, i [, j])`

+Returns the substring of s that +starts at i and continues until j; +i and j can be negative. +If j is absent, then it is assumed to be equal to -1 +(which is the same as the string length). +In particular, +the call string.sub(s,1,j) returns a prefix of s +with length j, +and string.sub(s, -i) returns a suffix of s +with length i. + + +

+If, after the translation of negative indices, +i is less than 1, +it is corrected to 1. +If j is greater than the string length, +it is corrected to that length. +If, after these corrections, +i is greater than j, +the function returns the empty string. + + + + +

`string.unpack (fmt, s [, pos])`

+ + +

+Returns the values packed in string s (see string.pack) +according to the format string fmt (see §6.4.2). +An optional pos marks where +to start reading in s (default is 1). +After the read values, +this function also returns the index of the first unread byte in s. + + + + +

`string.upper (s)`

+Receives a string and returns a copy of this string with all +lowercase letters changed to uppercase. +All other characters are left unchanged. +The definition of what a lowercase letter is depends on the current locale. + + + + + +

6.4.1 – Patterns

+ +

+Patterns in Lua are described by regular strings, +which are interpreted as patterns by the pattern-matching functions +string.find, +string.gmatch, +string.gsub, +and string.match. +This section describes the syntax and the meaning +(that is, what they match) of these strings. + + + +

Character Class:

+A character class is used to represent a set of characters. +The following combinations are allowed in describing a character class: + +

x: +(where x is not one of the magic characters +^$()%.[]*+-?) +represents the character x itself. +
.: (a dot) represents all characters.
%a: represents all letters.
%c: represents all control characters.
%d: represents all digits.
%g: represents all printable characters except space.
%l: represents all lowercase letters.
%p: represents all punctuation characters.
%s: represents all space characters.
%u: represents all uppercase letters.
%w: represents all alphanumeric characters.
%x: represents all hexadecimal digits.
%x: (where x is any non-alphanumeric character) +represents the character x. +This is the standard way to escape the magic characters. +Any non-alphanumeric character +(including all punctuation characters, even the non-magical) +can be preceded by a '%' +when used to represent itself in a pattern. +
[set]: +represents the class which is the union of all +characters in set. +A range of characters can be specified by +separating the end characters of the range, +in ascending order, with a '-'. +All classes %x described above can also be used as +components in set. +All other characters in set represent themselves. +For example, [%w_] (or [_%w]) +represents all alphanumeric characters plus the underscore, +[0-7] represents the octal digits, +and [0-7%l%-] represents the octal digits plus +the lowercase letters plus the '-' character. + + +
+The interaction between ranges and classes is not defined. +Therefore, patterns like [%a-z] or [a-%%] +have no meaning. +
[^set]: +represents the complement of set, +where set is interpreted as above. +

+For all classes represented by single letters (%a, %c, etc.), +the corresponding uppercase letter represents the complement of the class. +For instance, %S represents all non-space characters. + + +

+The definitions of letter, space, and other character groups +depend on the current locale. +In particular, the class [a-z] may not be equivalent to %l. + + + + + +

Pattern Item:

+A pattern item can be + +

+a single character class, +which matches any single character in the class; +
+a single character class followed by '*', +which matches zero or more repetitions of characters in the class. +These repetition items will always match the longest possible sequence; +
+a single character class followed by '+', +which matches one or more repetitions of characters in the class. +These repetition items will always match the longest possible sequence; +
+a single character class followed by '-', +which also matches zero or more repetitions of characters in the class. +Unlike '*', +these repetition items will always match the shortest possible sequence; +
+a single character class followed by '?', +which matches zero or one occurrence of a character in the class. +It always matches one occurrence if possible; +
+%n, for n between 1 and 9; +such item matches a substring equal to the n-th captured string +(see below); +
+%bxy, where x and y are two distinct characters; +such item matches strings that start with x, end with y, +and where the x and y are balanced. +This means that, if one reads the string from left to right, +counting +1 for an x and -1 for a y, +the ending y is the first y where the count reaches 0. +For instance, the item %b() matches expressions with +balanced parentheses. +
+%f[set], a frontier pattern; +such item matches an empty string at any position such that +the next character belongs to set +and the previous character does not belong to set. +The set set is interpreted as previously described. +The beginning and the end of the subject are handled as if +they were the character '\0'. +

+ + + + +

Pattern:

+A pattern is a sequence of pattern items. +A caret '^' at the beginning of a pattern anchors the match at the +beginning of the subject string. +A '$' at the end of a pattern anchors the match at the +end of the subject string. +At other positions, +'^' and '$' have no special meaning and represent themselves. + + + + + +

Captures:

+A pattern can contain sub-patterns enclosed in parentheses; +they describe captures. +When a match succeeds, the substrings of the subject string +that match captures are stored (captured) for future use. +Captures are numbered according to their left parentheses. +For instance, in the pattern "(a*(.)%w(%s*))", +the part of the string matching "a*(.)%w(%s*)" is +stored as the first capture (and therefore has number 1); +the character matching "." is captured with number 2, +and the part matching "%s*" has number 3. + + +

+As a special case, the empty capture () captures +the current string position (a number). +For instance, if we apply the pattern "()aa()" on the +string "flaaap", there will be two captures: 3 and 5. + + + + + + + +

6.4.2 – Format Strings for Pack and Unpack

+ +

+The first argument to string.pack, +string.packsize, and string.unpack +is a format string, +which describes the layout of the structure being created or read. + + +

+A format string is a sequence of conversion options. +The conversion options are as follows: + +

<: sets little endian
>: sets big endian
=: sets native endian
![n]: sets maximum alignment to n +(default is native alignment)
b: a signed byte (char)
B: an unsigned byte (char)
h: a signed short (native size)
H: an unsigned short (native size)
l: a signed long (native size)
L: an unsigned long (native size)
j: a lua_Integer
J: a lua_Unsigned
T: a size_t (native size)
i[n]: a signed int with n bytes +(default is native size)
I[n]: an unsigned int with n bytes +(default is native size)
f: a float (native size)
d: a double (native size)
n: a lua_Number
cn: a fixed-sized string with n bytes
z: a zero-terminated string
s[n]: a string preceded by its length +coded as an unsigned integer with n bytes +(default is a size_t)
x: one byte of padding
Xop: an empty item that aligns +according to option op +(which is otherwise ignored)
' ': (empty space) ignored

+(A "[n]" means an optional integral numeral.) +Except for padding, spaces, and configurations +(options "xX <=>!"), +each option corresponds to an argument (in string.pack) +or a result (in string.unpack). + + +

+For options "!n", "sn", "in", and "In", +n can be any integer between 1 and 16. +All integral options check overflows; +string.pack checks whether the given value fits in the given size; +string.unpack checks whether the read value fits in a Lua integer. + + +

+Any format string starts as if prefixed by "!1=", +that is, +with maximum alignment of 1 (no alignment) +and native endianness. + + +

+Alignment works as follows: +For each option, +the format gets extra padding until the data starts +at an offset that is a multiple of the minimum between the +option size and the maximum alignment; +this minimum must be a power of 2. +Options "c" and "z" are not aligned; +option "s" follows the alignment of its starting integer. + + +

+All padding is filled with zeros by string.pack +(and ignored by string.unpack). + + + + + + + +

6.5 – UTF-8 Support

+ +

+This library provides basic support for UTF-8 encoding. +It provides all its functions inside the table utf8. +This library does not provide any support for Unicode other +than the handling of the encoding. +Any operation that needs the meaning of a character, +such as character classification, is outside its scope. + + +

+Unless stated otherwise, +all functions that expect a byte position as a parameter +assume that the given position is either the start of a byte sequence +or one plus the length of the subject string. +As in the string library, +negative indices count from the end of the string. + + +

`utf8.char (···)`

+Receives zero or more integers, +converts each one to its corresponding UTF-8 byte sequence +and returns a string with the concatenation of all these sequences. + + + + +

`utf8.charpattern`

+The pattern (a string, not a function) "[\0-\x7F\xC2-\xF4][\x80-\xBF]*" +(see §6.4.1), +which matches exactly one UTF-8 byte sequence, +assuming that the subject is a valid UTF-8 string. + + + + +

`utf8.codes (s)`

+ + +

+Returns values so that the construction + +

+     for p, c in utf8.codes(s) do body end
+

+will iterate over all characters in string s, +with p being the position (in bytes) and c the code point +of each character. +It raises an error if it meets any invalid byte sequence. + + + + +

`utf8.codepoint (s [, i [, j]])`

+Returns the codepoints (as integers) from all characters in s +that start between byte position i and j (both included). +The default for i is 1 and for j is i. +It raises an error if it meets any invalid byte sequence. + + + + +

`utf8.len (s [, i [, j]])`

+Returns the number of UTF-8 characters in string s +that start between positions i and j (both inclusive). +The default for i is 1 and for j is -1. +If it finds any invalid byte sequence, +returns a false value plus the position of the first invalid byte. + + + + +

`utf8.offset (s, n [, i])`

+Returns the position (in bytes) where the encoding of the +n-th character of s +(counting from position i) starts. +A negative n gets characters before position i. +The default for i is 1 when n is non-negative +and #s + 1 otherwise, +so that utf8.offset(s, -n) gets the offset of the +n-th character from the end of the string. +If the specified character is neither in the subject +nor right after its end, +the function returns nil. + + +

+As a special case, +when n is 0 the function returns the start of the encoding +of the character that contains the i-th byte of s. + + +

+This function assumes that s is a valid UTF-8 string. + + + + + + + +

6.6 – Table Manipulation

+ +

+This library provides generic functions for table manipulation. +It provides all its functions inside the table table. + + +

+Remember that, whenever an operation needs the length of a table, +the table must be a proper sequence +or have a __len metamethod (see §3.4.7). +All functions ignore non-numeric keys +in the tables given as arguments. + + +

`table.concat (list [, sep [, i [, j]]])`

+ + +

+Given a list where all elements are strings or numbers, +returns the string list[i]..sep..list[i+1] ··· sep..list[j]. +The default value for sep is the empty string, +the default for i is 1, +and the default for j is #list. +If i is greater than j, returns the empty string. + + + + +

`table.insert (list, [pos,] value)`

+ + +

+Inserts element value at position pos in list, +shifting up the elements +list[pos], list[pos+1], ···, list[#list]. +The default value for pos is #list+1, +so that a call table.insert(t,x) inserts x at the end +of list t. + + + + +

`table.move (a1, f, e, t [,a2])`

+ + +

+Moves elements from table a1 to table a2. +This function performs the equivalent to the following +multiple assignment: +a2[t],··· = a1[f],···,a1[e]. +The default for a2 is a1. +The destination range can overlap with the source range. +The number of elements to be moved must fit in a Lua integer. + + + + +

`table.pack (···)`

+ + +

+Returns a new table with all parameters stored into keys 1, 2, etc. +and with a field "n" with the total number of parameters. +Note that the resulting table may not be a sequence. + + + + +

`table.remove (list [, pos])`

+ + +

+Removes from list the element at position pos, +returning the value of the removed element. +When pos is an integer between 1 and #list, +it shifts down the elements +list[pos+1], list[pos+2], ···, list[#list] +and erases element list[#list]; +The index pos can also be 0 when #list is 0, +or #list + 1; +in those cases, the function erases the element list[pos]. + + +

+The default value for pos is #list, +so that a call table.remove(l) removes the last element +of list l. + + + + +

`table.sort (list [, comp])`

+ + +

+Sorts list elements in a given order, in-place, +from list[1] to list[#list]. +If comp is given, +then it must be a function that receives two list elements +and returns true when the first element must come +before the second in the final order +(so that, after the sort, +i < j implies not comp(list[j],list[i])). +If comp is not given, +then the standard Lua operator < is used instead. + + +

+Note that the comp function must define +a strict partial order over the elements in the list; +that is, it must be asymmetric and transitive. +Otherwise, no valid sort may be possible. + + +

+The sort algorithm is not stable; +that is, elements not comparable by the given order +(e.g., equal elements) +may have their relative positions changed by the sort. + + + + +

`table.unpack (list [, i [, j]])`

+ + +

+Returns the elements from the given list. +This function is equivalent to + +

+     return list[i], list[i+1], ···, list[j]
+

+By default, i is 1 and j is #list. + + + + + + + +

6.7 – Mathematical Functions

+ +

+This library provides basic mathematical functions. +It provides all its functions and constants inside the table math. +Functions with the annotation "integer/float" give +integer results for integer arguments +and float results for float (or mixed) arguments. +Rounding functions +(math.ceil, math.floor, and math.modf) +return an integer when the result fits in the range of an integer, +or a float otherwise. + + +

`math.abs (x)`

+ + +

+Returns the absolute value of x. (integer/float) + + + + +

`math.acos (x)`

+ + +

+Returns the arc cosine of x (in radians). + + + + +

`math.asin (x)`

+ + +

+Returns the arc sine of x (in radians). + + + + +

`math.atan (y [, x])`

+ + +

+ +Returns the arc tangent of y/x (in radians), +but uses the signs of both parameters to find the +quadrant of the result. +(It also handles correctly the case of x being zero.) + + +

+The default value for x is 1, +so that the call math.atan(y) +returns the arc tangent of y. + + + + +

`math.ceil (x)`

+ + +

+Returns the smallest integral value larger than or equal to x. + + + + +

`math.cos (x)`

+ + +

+Returns the cosine of x (assumed to be in radians). + + + + +

`math.deg (x)`

+ + +

+Converts the angle x from radians to degrees. + + + + +

`math.exp (x)`

+ + +

+Returns the value e^x +(where e is the base of natural logarithms). + + + + +

`math.floor (x)`

+ + +

+Returns the largest integral value smaller than or equal to x. + + + + +

`math.fmod (x, y)`

+ + +

+Returns the remainder of the division of x by y +that rounds the quotient towards zero. (integer/float) + + + + +

`math.huge`

+ + +

+The float value HUGE_VAL, +a value larger than any other numeric value. + + + + +

`math.log (x [, base])`

+ + +

+Returns the logarithm of x in the given base. +The default for base is e +(so that the function returns the natural logarithm of x). + + + + +

`math.max (x, ···)`

+ + +

+Returns the argument with the maximum value, +according to the Lua operator <. (integer/float) + + + + +

`math.maxinteger`

+An integer with the maximum value for an integer. + + + + +

`math.min (x, ···)`

+ + +

+Returns the argument with the minimum value, +according to the Lua operator <. (integer/float) + + + + +

`math.mininteger`

+An integer with the minimum value for an integer. + + + + +

`math.modf (x)`

+ + +

+Returns the integral part of x and the fractional part of x. +Its second result is always a float. + + + + +

`math.pi`

+ + +

+The value of π. + + + + +

`math.rad (x)`

+ + +

+Converts the angle x from degrees to radians. + + + + +

`math.random ([m [, n]])`

+ + +

+When called without arguments, +returns a pseudo-random float with uniform distribution +in the range [0,1). +When called with two integers m and n, +math.random returns a pseudo-random integer +with uniform distribution in the range [m, n]. +(The value n-m cannot be negative and must fit in a Lua integer.) +The call math.random(n) is equivalent to math.random(1,n). + + +

+This function is an interface to the underling +pseudo-random generator function provided by C. + + + + +

`math.randomseed (x)`

+ + +

+Sets x as the "seed" +for the pseudo-random generator: +equal seeds produce equal sequences of numbers. + + + + +

`math.sin (x)`

+ + +

+Returns the sine of x (assumed to be in radians). + + + + +

`math.sqrt (x)`

+ + +

+Returns the square root of x. +(You can also use the expression x^0.5 to compute this value.) + + + + +

`math.tan (x)`

+ + +

+Returns the tangent of x (assumed to be in radians). + + + + +

`math.tointeger (x)`

+ + +

+If the value x is convertible to an integer, +returns that integer. +Otherwise, returns nil. + + + + +

`math.type (x)`

+ + +

+Returns "integer" if x is an integer, +"float" if it is a float, +or nil if x is not a number. + + + + +

`math.ult (m, n)`

+ + +

+Returns a boolean, +true if integer m is below integer n when +they are compared as unsigned integers. + + + + + + + +

6.8 – Input and Output Facilities

+ +

+The I/O library provides two different styles for file manipulation. +The first one uses implicit file handles; +that is, there are operations to set a default input file and a +default output file, +and all input/output operations are over these default files. +The second style uses explicit file handles. + + +

+When using implicit file handles, +all operations are supplied by table io. +When using explicit file handles, +the operation io.open returns a file handle +and then all operations are supplied as methods of the file handle. + + +

+The table io also provides +three predefined file handles with their usual meanings from C: +io.stdin, io.stdout, and io.stderr. +The I/O library never closes these files. + + +

+Unless otherwise stated, +all I/O functions return nil on failure +(plus an error message as a second result and +a system-dependent error code as a third result) +and some value different from nil on success. +On non-POSIX systems, +the computation of the error message and error code +in case of errors +may be not thread safe, +because they rely on the global C variable errno. + + +

`io.close ([file])`

+ + +

+Equivalent to file:close(). +Without a file, closes the default output file. + + + + +

`io.flush ()`

+ + +

+Equivalent to io.output():flush(). + + + + +

`io.input ([file])`

+ + +

+When called with a file name, it opens the named file (in text mode), +and sets its handle as the default input file. +When called with a file handle, +it simply sets this file handle as the default input file. +When called without parameters, +it returns the current default input file. + + +

+In case of errors this function raises the error, +instead of returning an error code. + + + + +

`io.lines ([filename, ···])`

+ + +

+Opens the given file name in read mode +and returns an iterator function that +works like file:lines(···) over the opened file. +When the iterator function detects the end of file, +it returns no values (to finish the loop) and automatically closes the file. + + +

+The call io.lines() (with no file name) is equivalent +to io.input():lines("*l"); +that is, it iterates over the lines of the default input file. +In this case it does not close the file when the loop ends. + + +

+In case of errors this function raises the error, +instead of returning an error code. + + + + +

`io.open (filename [, mode])`

+ + +

+This function opens a file, +in the mode specified in the string mode. +It returns a new file handle, +or, in case of errors, nil plus an error message. + + +

+The mode string can be any of the following: + +

"r": read mode (the default);
"w": write mode;
"a": append mode;
"r+": update mode, all previous data is preserved;
"w+": update mode, all previous data is erased;
"a+": append update mode, previous data is preserved, + writing is only allowed at the end of file.

+The mode string can also have a 'b' at the end, +which is needed in some systems to open the file in binary mode. + + + + +

`io.output ([file])`

+ + +

+Similar to io.input, but operates over the default output file. + + + + +

`io.popen (prog [, mode])`

+ + +

+This function is system dependent and is not available +on all platforms. + + +

+Starts program prog in a separated process and returns +a file handle that you can use to read data from this program +(if mode is "r", the default) +or to write data to this program +(if mode is "w"). + + + + +

`io.read (···)`

+ + +

+Equivalent to io.input():read(···). + + + + +

`io.tmpfile ()`

+ + +

+Returns a handle for a temporary file. +This file is opened in update mode +and it is automatically removed when the program ends. + + + + +

`io.type (obj)`

+ + +

+Checks whether obj is a valid file handle. +Returns the string "file" if obj is an open file handle, +"closed file" if obj is a closed file handle, +or nil if obj is not a file handle. + + + + +

`io.write (···)`

+ + +

+Equivalent to io.output():write(···). + + + + +

`file:close ()`

+ + +

+Closes file. +Note that files are automatically closed when +their handles are garbage collected, +but that takes an unpredictable amount of time to happen. + + +

+When closing a file handle created with io.popen, +file:close returns the same values +returned by os.execute. + + + + +

`file:flush ()`

+ + +

+Saves any written data to file. + + + + +

`file:lines (···)`

+ + +

+Returns an iterator function that, +each time it is called, +reads the file according to the given formats. +When no format is given, +uses "l" as a default. +As an example, the construction + +

+     for c in file:lines(1) do body end
+

+will iterate over all characters of the file, +starting at the current position. +Unlike io.lines, this function does not close the file +when the loop ends. + + +

+In case of errors this function raises the error, +instead of returning an error code. + + + + +

`file:read (···)`

+ + +

+Reads the file file, +according to the given formats, which specify what to read. +For each format, +the function returns a string or a number with the characters read, +or nil if it cannot read data with the specified format. +(In this latter case, +the function does not read subsequent formats.) +When called without formats, +it uses a default format that reads the next line +(see below). + + +

+The available formats are + +

"n": +reads a numeral and returns it as a float or an integer, +following the lexical conventions of Lua. +(The numeral may have leading spaces and a sign.) +This format always reads the longest input sequence that +is a valid prefix for a numeral; +if that prefix does not form a valid numeral +(e.g., an empty string, "0x", or "3.4e-"), +it is discarded and the function returns nil. +
"a": +reads the whole file, starting at the current position. +On end of file, it returns the empty string. +
"l": +reads the next line skipping the end of line, +returning nil on end of file. +This is the default format. +
"L": +reads the next line keeping the end-of-line character (if present), +returning nil on end of file. +
number: +reads a string with up to this number of bytes, +returning nil on end of file. +If number is zero, +it reads nothing and returns an empty string, +or nil on end of file. +

+The formats "l" and "L" should be used only for text files. + + + + +

`file:seek ([whence [, offset]])`

+ + +

+Sets and gets the file position, +measured from the beginning of the file, +to the position given by offset plus a base +specified by the string whence, as follows: + +

"set": base is position 0 (beginning of the file);
"cur": base is current position;
"end": base is end of file;

+In case of success, seek returns the final file position, +measured in bytes from the beginning of the file. +If seek fails, it returns nil, +plus a string describing the error. + + +

+The default value for whence is "cur", +and for offset is 0. +Therefore, the call file:seek() returns the current +file position, without changing it; +the call file:seek("set") sets the position to the +beginning of the file (and returns 0); +and the call file:seek("end") sets the position to the +end of the file, and returns its size. + + + + +

`file:setvbuf (mode [, size])`

+ + +

+Sets the buffering mode for an output file. +There are three available modes: + +

"no": +no buffering; the result of any output operation appears immediately. +
"full": +full buffering; output operation is performed only +when the buffer is full or when +you explicitly flush the file (see io.flush). +
"line": +line buffering; output is buffered until a newline is output +or there is any input from some special files +(such as a terminal device). +

+For the last two cases, size +specifies the size of the buffer, in bytes. +The default is an appropriate size. + + + + +

`file:write (···)`

+ + +

+Writes the value of each of its arguments to file. +The arguments must be strings or numbers. + + +

+In case of success, this function returns file. +Otherwise it returns nil plus a string describing the error. + + + + + + + +

6.9 – Operating System Facilities

+ +

+This library is implemented through table os. + + +

`os.clock ()`

+ + +

+Returns an approximation of the amount in seconds of CPU time +used by the program. + + + + +

`os.date ([format [, time]])`

+ + +

+Returns a string or a table containing date and time, +formatted according to the given string format. + + +

+If the time argument is present, +this is the time to be formatted +(see the os.time function for a description of this value). +Otherwise, date formats the current time. + + +

+If format starts with '!', +then the date is formatted in Coordinated Universal Time. +After this optional character, +if format is the string "*t", +then date returns a table with the following fields: +year, month (1–12), day (1–31), +hour (0–23), min (0–59), sec (0–61), +wday (weekday, Sunday is 1), +yday (day of the year), +and isdst (daylight saving flag, a boolean). +This last field may be absent +if the information is not available. + + +

+If format is not "*t", +then date returns the date as a string, +formatted according to the same rules as the ISO C function strftime. + + +

+When called without arguments, +date returns a reasonable date and time representation that depends on +the host system and on the current locale. +(More specifically, os.date() is equivalent to os.date("%c").) + + +

+On non-POSIX systems, +this function may be not thread safe +because of its reliance on C function gmtime and C function localtime. + + + + +

`os.difftime (t2, t1)`

+ + +

+Returns the difference, in seconds, +from time t1 to time t2 +(where the times are values returned by os.time). +In POSIX, Windows, and some other systems, +this value is exactly t2-t1. + + + + +

`os.execute ([command])`

+ + +

+This function is equivalent to the ISO C function system. +It passes command to be executed by an operating system shell. +Its first result is true +if the command terminated successfully, +or nil otherwise. +After this first result +the function returns a string plus a number, +as follows: + +

"exit": +the command terminated normally; +the following number is the exit status of the command. +
"signal": +the command was terminated by a signal; +the following number is the signal that terminated the command. +

+ +

+When called without a command, +os.execute returns a boolean that is true if a shell is available. + + + + +

`os.exit ([code [, close]])`

+ + +

+Calls the ISO C function exit to terminate the host program. +If code is true, +the returned status is EXIT_SUCCESS; +if code is false, +the returned status is EXIT_FAILURE; +if code is a number, +the returned status is this number. +The default value for code is true. + + +

+If the optional second argument close is true, +closes the Lua state before exiting. + + + + +

`os.getenv (varname)`

+ + +

+Returns the value of the process environment variable varname, +or nil if the variable is not defined. + + + + +

`os.remove (filename)`

+ + +

+Deletes the file (or empty directory, on POSIX systems) +with the given name. +If this function fails, it returns nil, +plus a string describing the error and the error code. + + + + +

`os.rename (oldname, newname)`

+ + +

+Renames file or directory named oldname to newname. +If this function fails, it returns nil, +plus a string describing the error and the error code. + + + + +

`os.setlocale (locale [, category])`

+ + +

+Sets the current locale of the program. +locale is a system-dependent string specifying a locale; +category is an optional string describing which category to change: +"all", "collate", "ctype", +"monetary", "numeric", or "time"; +the default category is "all". +The function returns the name of the new locale, +or nil if the request cannot be honored. + + +

+If locale is the empty string, +the current locale is set to an implementation-defined native locale. +If locale is the string "C", +the current locale is set to the standard C locale. + + +

+When called with nil as the first argument, +this function only returns the name of the current locale +for the given category. + + +

+This function may be not thread safe +because of its reliance on C function setlocale. + + + + +

`os.time ([table])`

+ + +

+Returns the current time when called without arguments, +or a time representing the local date and time specified by the given table. +This table must have fields year, month, and day, +and may have fields +hour (default is 12), +min (default is 0), +sec (default is 0), +and isdst (default is nil). +Other fields are ignored. +For a description of these fields, see the os.date function. + + +

+The values in these fields do not need to be inside their valid ranges. +For instance, if sec is -10, +it means -10 seconds from the time specified by the other fields; +if hour is 1000, +it means +1000 hours from the time specified by the other fields. + + +

+The returned value is a number, whose meaning depends on your system. +In POSIX, Windows, and some other systems, +this number counts the number +of seconds since some given start time (the "epoch"). +In other systems, the meaning is not specified, +and the number returned by time can be used only as an argument to +os.date and os.difftime. + + + + +

`os.tmpname ()`

+ + +

+Returns a string with a file name that can +be used for a temporary file. +The file must be explicitly opened before its use +and explicitly removed when no longer needed. + + +

+On POSIX systems, +this function also creates a file with that name, +to avoid security risks. +(Someone else might create the file with wrong permissions +in the time between getting the name and creating the file.) +You still have to open the file to use it +and to remove it (even if you do not use it). + + +

+When possible, +you may prefer to use io.tmpfile, +which automatically removes the file when the program ends. + + + + + + + +

6.10 – The Debug Library

+ +

+This library provides +the functionality of the debug interface (§4.9) to Lua programs. +You should exert care when using this library. +Several of its functions +violate basic assumptions about Lua code +(e.g., that variables local to a function +cannot be accessed from outside; +that userdata metatables cannot be changed by Lua code; +that Lua programs do not crash) +and therefore can compromise otherwise secure code. +Moreover, some functions in this library may be slow. + + +

+All functions in this library are provided +inside the debug table. +All functions that operate over a thread +have an optional first argument which is the +thread to operate over. +The default is always the current thread. + + +

`debug.debug ()`

+ + +

+Enters an interactive mode with the user, +running each string that the user enters. +Using simple commands and other debug facilities, +the user can inspect global and local variables, +change their values, evaluate expressions, and so on. +A line containing only the word cont finishes this function, +so that the caller continues its execution. + + +

+Note that commands for debug.debug are not lexically nested +within any function and so have no direct access to local variables. + + + + +

`debug.gethook ([thread])`

+ + +

+Returns the current hook settings of the thread, as three values: +the current hook function, the current hook mask, +and the current hook count +(as set by the debug.sethook function). + + + + +

`debug.getinfo ([thread,] f [, what])`

+ + +

+Returns a table with information about a function. +You can give the function directly +or you can give a number as the value of f, +which means the function running at level f of the call stack +of the given thread: +level 0 is the current function (getinfo itself); +level 1 is the function that called getinfo +(except for tail calls, which do not count on the stack); +and so on. +If f is a number larger than the number of active functions, +then getinfo returns nil. + + +

+The returned table can contain all the fields returned by lua_getinfo, +with the string what describing which fields to fill in. +The default for what is to get all information available, +except the table of valid lines. +If present, +the option 'f' +adds a field named func with the function itself. +If present, +the option 'L' +adds a field named activelines with the table of +valid lines. + + +

+For instance, the expression debug.getinfo(1,"n").name returns +a name for the current function, +if a reasonable name can be found, +and the expression debug.getinfo(print) +returns a table with all available information +about the print function. + + + + +

`debug.getlocal ([thread,] f, local)`

+ + +

+This function returns the name and the value of the local variable +with index local of the function at level f of the stack. +This function accesses not only explicit local variables, +but also parameters, temporaries, etc. + + +

+The first parameter or local variable has index 1, and so on, +following the order that they are declared in the code, +counting only the variables that are active +in the current scope of the function. +Negative indices refer to vararg parameters; +-1 is the first vararg parameter. +The function returns nil if there is no variable with the given index, +and raises an error when called with a level out of range. +(You can call debug.getinfo to check whether the level is valid.) + + +

+Variable names starting with '(' (open parenthesis) +represent variables with no known names +(internal variables such as loop control variables, +and variables from chunks saved without debug information). + + +

+The parameter f may also be a function. +In that case, getlocal returns only the name of function parameters. + + + + +

`debug.getmetatable (value)`

+ + +

+Returns the metatable of the given value +or nil if it does not have a metatable. + + + + +

`debug.getregistry ()`

+ + +

+Returns the registry table (see §4.5). + + + + +

`debug.getupvalue (f, up)`

+ + +

+This function returns the name and the value of the upvalue +with index up of the function f. +The function returns nil if there is no upvalue with the given index. + + +

+Variable names starting with '(' (open parenthesis) +represent variables with no known names +(variables from chunks saved without debug information). + + + + +

`debug.getuservalue (u)`

+ + +

+Returns the Lua value associated to u. +If u is not a userdata, +returns nil. + + + + +

`debug.sethook ([thread,] hook, mask [, count])`

+ + +

+Sets the given function as a hook. +The string mask and the number count describe +when the hook will be called. +The string mask may have any combination of the following characters, +with the given meaning: + +

'c': the hook is called every time Lua calls a function;
'r': the hook is called every time Lua returns from a function;
'l': the hook is called every time Lua enters a new line of code.

+Moreover, +with a count different from zero, +the hook is called also after every count instructions. + + +

+When called without arguments, +debug.sethook turns off the hook. + + +

+When the hook is called, its first parameter is a string +describing the event that has triggered its call: +"call" (or "tail call"), +"return", +"line", and "count". +For line events, +the hook also gets the new line number as its second parameter. +Inside a hook, +you can call getinfo with level 2 to get more information about +the running function +(level 0 is the getinfo function, +and level 1 is the hook function). + + + + +

`debug.setlocal ([thread,] level, local, value)`

+ + +

+This function assigns the value value to the local variable +with index local of the function at level level of the stack. +The function returns nil if there is no local +variable with the given index, +and raises an error when called with a level out of range. +(You can call getinfo to check whether the level is valid.) +Otherwise, it returns the name of the local variable. + + +

+See debug.getlocal for more information about +variable indices and names. + + + + +

`debug.setmetatable (value, table)`

+ + +

+Sets the metatable for the given value to the given table +(which can be nil). +Returns value. + + + + +

`debug.setupvalue (f, up, value)`

+ + +

+This function assigns the value value to the upvalue +with index up of the function f. +The function returns nil if there is no upvalue +with the given index. +Otherwise, it returns the name of the upvalue. + + + + +

`debug.setuservalue (udata, value)`

+ + +

+Sets the given value as +the Lua value associated to the given udata. +udata must be a full userdata. + + +

+Returns udata. + + + + +

`debug.traceback ([thread,] [message [, level]])`

+ + +

+If message is present but is neither a string nor nil, +this function returns message without further processing. +Otherwise, +it returns a string with a traceback of the call stack. +The optional message string is appended +at the beginning of the traceback. +An optional level number tells at which level +to start the traceback +(default is 1, the function calling traceback). + + + + +

`debug.upvalueid (f, n)`

+ + +

+Returns a unique identifier (as a light userdata) +for the upvalue numbered n +from the given function. + + +

`debug.upvaluejoin (f1, n1, f2, n2)`

+ + +

+Make the n1-th upvalue of the Lua closure f1 +refer to the n2-th upvalue of the Lua closure f2. + + + + + + + +

7 – Lua Standalone

+ +

+Although Lua has been designed as an extension language, +to be embedded in a host C program, +it is also frequently used as a standalone language. +An interpreter for Lua as a standalone language, +called simply lua, +is provided with the standard distribution. +The standalone interpreter includes +all standard libraries, including the debug library. +Its usage is: + +

+     lua [options] [script [args]]
+

+The options are: + +

-e stat: executes string stat;
-l mod: "requires" mod;
-i: enters interactive mode after running script;
-v: prints version information;
-E: ignores environment variables;
--: stops handling options;
-: executes stdin as a file and stops handling options.

+After handling its options, lua runs the given script. +When called without arguments, +lua behaves as lua -v -i +when the standard input (stdin) is a terminal, +and as lua - otherwise. + + +

+When called without option -E, +the interpreter checks for an environment variable LUA_INIT_5_3 +(or LUA_INIT if the versioned name is not defined) +before running any argument. +If the variable content has the format @filename, +then lua executes the file. +Otherwise, lua executes the string itself. + + +

+When called with option -E, +besides ignoring LUA_INIT, +Lua also ignores +the values of LUA_PATH and LUA_CPATH, +setting the values of +package.path and package.cpath +with the default paths defined in luaconf.h. + + +

+All options are handled in order, except -i and -E. +For instance, an invocation like + +

+     $ lua -e'a=1' -e 'print(a)' script.lua
+

+will first set a to 1, then print the value of a, +and finally run the file script.lua with no arguments. +(Here $ is the shell prompt. Your prompt may be different.) + + +

+Before running any code, +lua collects all command-line arguments +in a global table called arg. +The script name goes to index 0, +the first argument after the script name goes to index 1, +and so on. +Any arguments before the script name +(that is, the interpreter name plus its options) +go to negative indices. +For instance, in the call + +

+     $ lua -la b.lua t1 t2
+

+the table is like this: + +

+     arg = { [-2] = "lua", [-1] = "-la",
+             [0] = "b.lua",
+             [1] = "t1", [2] = "t2" }
+

+If there is no script in the call, +the interpreter name goes to index 0, +followed by the other arguments. +For instance, the call + +

+     $ lua -e "print(arg[1])"
+

+will print "-e". +If there is a script, +the script is called with parameters +arg[1], ···, arg[#arg]. +(Like all chunks in Lua, +the script is compiled as a vararg function.) + + +

+In interactive mode, +Lua repeatedly prompts and waits for a line. +After reading a line, +Lua first try to interpret the line as an expression. +If it succeeds, it prints its value. +Otherwise, it interprets the line as a statement. +If you write an incomplete statement, +the interpreter waits for its completion +by issuing a different prompt. + + +

+In case of unprotected errors in the script, +the interpreter reports the error to the standard error stream. +If the error object is not a string but +has a metamethod __tostring, +the interpreter calls this metamethod to produce the final message. +Otherwise, the interpreter converts the error object to a string +and adds a stack traceback to it. + + +

+When finishing normally, +the interpreter closes its main Lua state +(see lua_close). +The script can avoid this step by +calling os.exit to terminate. + + +

+To allow the use of Lua as a +script interpreter in Unix systems, +the standalone interpreter skips +the first line of a chunk if it starts with #. +Therefore, Lua scripts can be made into executable programs +by using chmod +x and the #! form, +as in + +

+     #!/usr/local/bin/lua
+

+(Of course, +the location of the Lua interpreter may be different in your machine. +If lua is in your PATH, +then + +

+     #!/usr/bin/env lua
+

+is a more portable solution.) + + + +

8 – Incompatibilities with the Previous Version

+ +

+Here we list the incompatibilities that you may find when moving a program +from Lua 5.2 to Lua 5.3. +You can avoid some incompatibilities by compiling Lua with +appropriate options (see file luaconf.h). +However, +all these compatibility options will be removed in the future. + + +

+Lua versions can always change the C API in ways that +do not imply source-code changes in a program, +such as the numeric values for constants +or the implementation of functions as macros. +Therefore, +you should not assume that binaries are compatible between +different Lua versions. +Always recompile clients of the Lua API when +using a new version. + + +

+Similarly, Lua versions can always change the internal representation +of precompiled chunks; +precompiled chunks are not compatible between different Lua versions. + + +

+The standard paths in the official distribution may +change between versions. + + + +

8.1 – Changes in the Language

+The main difference between Lua 5.2 and Lua 5.3 is the +introduction of an integer subtype for numbers. +Although this change should not affect "normal" computations, +some computations +(mainly those that involve some kind of overflow) +can give different results. + + +
+You can fix these differences by forcing a number to be a float +(in Lua 5.2 all numbers were float), +in particular writing constants with an ending .0 +or using x = x + 0.0 to convert a variable. +(This recommendation is only for a quick fix +for an occasional incompatibility; +it is not a general guideline for good programming. +For good programming, +use floats where you need floats +and integers where you need integers.) +
+The conversion of a float to a string now adds a .0 suffix +to the result if it looks like an integer. +(For instance, the float 2.0 will be printed as 2.0, +not as 2.) +You should always use an explicit format +when you need a specific format for numbers. + + +
+(Formally this is not an incompatibility, +because Lua does not specify how numbers are formatted as strings, +but some programs assumed a specific format.) +
+The generational mode for the garbage collector was removed. +(It was an experimental feature in Lua 5.2.) +

+ + + + +

8.2 – Changes in the Libraries

+The bit32 library has been deprecated. +It is easy to require a compatible external library or, +better yet, to replace its functions with appropriate bitwise operations. +(Keep in mind that bit32 operates on 32-bit integers, +while the bitwise operators in Lua 5.3 operate on Lua integers, +which by default have 64 bits.) +
+The Table library now respects metamethods +for setting and getting elements. +
+The ipairs iterator now respects metamethods and +its __ipairs metamethod has been deprecated. +
+Option names in io.read do not have a starting '*' anymore. +For compatibility, Lua will continue to accept (and ignore) this character. +
+The following functions were deprecated in the mathematical library: +atan2, cosh, sinh, tanh, pow, +frexp, and ldexp. +You can replace math.pow(x,y) with x^y; +you can replace math.atan2 with math.atan, +which now accepts one or two parameters; +you can replace math.ldexp(x,exp) with x * 2.0^exp. +For the other operations, +you can either use an external library or +implement them in Lua. +
+The searcher for C loaders used by require +changed the way it handles versioned names. +Now, the version should come after the module name +(as is usual in most other tools). +For compatibility, that searcher still tries the old format +if it cannot find an open function according to the new style. +(Lua 5.2 already worked that way, +but it did not document the change.) +
+The call collectgarbage("count") now returns only one result. +(You can compute that second result from the fractional part +of the first result.) +

+ + + + +

8.3 – Changes in the API

+ + +

+Continuation functions now receive as parameters what they needed +to get through lua_getctx, +so lua_getctx has been removed. +Adapt your code accordingly. +
+Function lua_dump has an extra parameter, strip. +Use 0 as the value of this parameter to get the old behavior. +
+Functions to inject/project unsigned integers +(lua_pushunsigned, lua_tounsigned, lua_tounsignedx, +luaL_checkunsigned, luaL_optunsigned) +were deprecated. +Use their signed equivalents with a type cast. +
+Macros to project non-default integer types +(luaL_checkint, luaL_optint, luaL_checklong, luaL_optlong) +were deprecated. +Use their equivalent over lua_Integer with a type cast +(or, when possible, use lua_Integer in your code). +

+ + + + +

9 – The Complete Syntax of Lua

+ +

+Here is the complete syntax of Lua in extended BNF. +As usual in extended BNF, +{A} means 0 or more As, +and [A] means an optional A. +(For operator precedences, see §3.4.8; +for a description of the terminals +Name, Numeral, +and LiteralString, see §3.1.) + + + + +

+
+	chunk ::= block
+
+	block ::= {stat} [retstat]
+
+	stat ::=  ‘;’ | 
+		 varlist ‘=’ explist | 
+		 functioncall | 
+		 label | 
+		 break | 
+		 goto Name | 
+		 do block end | 
+		 while exp do block end | 
+		 repeat block until exp | 
+		 if exp then block {elseif exp then block} [else block] end | 
+		 for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end | 
+		 for namelist in explist do block end | 
+		 function funcname funcbody | 
+		 local function Name funcbody | 
+		 local namelist [‘=’ explist] 
+
+	retstat ::= return [explist] [‘;’]
+
+	label ::= ‘::’ Name ‘::’
+
+	funcname ::= Name {‘.’ Name} [‘:’ Name]
+
+	varlist ::= var {‘,’ var}
+
+	var ::=  Name | prefixexp ‘[’ exp ‘]’ | prefixexp ‘.’ Name 
+
+	namelist ::= Name {‘,’ Name}
+
+	explist ::= exp {‘,’ exp}
+
+	exp ::=  nil | false | true | Numeral | LiteralString | ‘...’ | functiondef | 
+		 prefixexp | tableconstructor | exp binop exp | unop exp 
+
+	prefixexp ::= var | functioncall | ‘(’ exp ‘)’
+
+	functioncall ::=  prefixexp args | prefixexp ‘:’ Name args 
+
+	args ::=  ‘(’ [explist] ‘)’ | tableconstructor | LiteralString 
+
+	functiondef ::= function funcbody
+
+	funcbody ::= ‘(’ [parlist] ‘)’ block end
+
+	parlist ::= namelist [‘,’ ‘...’] | ‘...’
+
+	tableconstructor ::= ‘{’ [fieldlist] ‘}’
+
+	fieldlist ::= field {fieldsep field} [fieldsep]
+
+	field ::= ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp
+
+	fieldsep ::= ‘,’ | ‘;’
+
+	binop ::=  ‘+’ | ‘-’ | ‘*’ | ‘/’ | ‘//’ | ‘^’ | ‘%’ | 
+		 ‘&’ | ‘~’ | ‘|’ | ‘>>’ | ‘<<’ | ‘..’ | 
+		 ‘<’ | ‘<=’ | ‘>’ | ‘>=’ | ‘==’ | ‘~=’ | 
+		 and | or
+
+	unop ::= ‘-’ | not | ‘#’ | ‘~’
+
+

+ +

+ + + + + + + + +

+ + + + diff --git a/src/lua/doc/osi-certified-72x60.png b/src/lua/doc/osi-certified-72x60.png new file mode 100644 index 00000000..07df5f6e Binary files /dev/null and b/src/lua/doc/osi-certified-72x60.png differ diff --git a/src/lua/doc/readme.html b/src/lua/doc/readme.html new file mode 100644 index 00000000..152246f9 --- /dev/null +++ b/src/lua/doc/readme.html @@ -0,0 +1,365 @@ + + + +Lua 5.3 readme + + + + + + + +

+ +Welcome to Lua 5.3 +

+ +

+about +· +installation +· +changes +· +license +· +reference manual +

+ +

About Lua

+Lua is a powerful, fast, lightweight, embeddable scripting language +developed by a +team +at +PUC-Rio, +the Pontifical Catholic University of Rio de Janeiro in Brazil. +Lua is +free software +used in many products and projects around the world. + +

+Lua's +official web site +provides complete information +about Lua, +including +an +executive summary +and +updated +documentation, +especially the +reference manual, +which may differ slightly from the +local copy +distributed in this package. + +

Installing Lua

+Lua is distributed in +source +form. +You need to build it before using it. +Building Lua should be straightforward +because +Lua is implemented in pure ANSI C and compiles unmodified in all known +platforms that have an ANSI C compiler. +Lua also compiles unmodified as C++. +The instructions given below for building Lua are for Unix-like platforms. +See also +instructions for other systems +and +customization options. + +

+If you don't have the time or the inclination to compile Lua yourself, +get a binary from +LuaBinaries. +Try also +LuaDist, +a multi-platform distribution of Lua that includes batteries. + +

Building Lua

+In most Unix-like platforms, simply do "make" with a suitable target. +Here are the details. + +

+Open a terminal window and move to +the top-level directory, which is named lua-5.3.x. +The Makefile there controls both the build process and the installation process. +
+
+ Do "make" and see if your platform is listed. + The platforms currently supported are: +
+
+ aix bsd c89 freebsd generic linux macosx mingw posix solaris +
+
+ If your platform is listed, just do "make xxx", where xxx + is your platform name. +
+ If your platform is not listed, try the closest one or posix, generic, + c89, in this order. +
+
+The compilation takes only a few moments +and produces three files in the src directory: +lua (the interpreter), +luac (the compiler), +and liblua.a (the library). +
+
+ To check that Lua has been built correctly, do "make test" + after building Lua. This will run the interpreter and print its version. +

+If you're running Linux and get compilation errors, +make sure you have installed the readline development package +(which is probably named libreadline-dev or readline-devel). +If you get link errors after that, +then try "make linux MYLIBS=-ltermcap". + +

Installing Lua

+ Once you have built Lua, you may want to install it in an official + place in your system. In this case, do "make install". The official + place and the way to install files are defined in the Makefile. You'll + probably need the right permissions to install files. + +

+ To build and install Lua in one step, do "make xxx install", + where xxx is your platform name. + +

+ To install Lua locally, do "make local". + This will create a directory install with subdirectories + bin, include, lib, man, share, + and install Lua as listed below. + + To install Lua locally, but in some other directory, do + "make install INSTALL_TOP=xxx", where xxx is your chosen directory. + The installation starts in the src and doc directories, + so take care if INSTALL_TOP is not an absolute path. + +

+ bin: +: + lua luac +
+ include: +: + lua.h luaconf.h lualib.h lauxlib.h lua.hpp +
+ lib: +: + liblua.a +
+ man/man1: +: + lua.1 luac.1 +

+ +

+ These are the only directories you need for development. + If you only want to run Lua programs, + you only need the files in bin and man. + The files in include and lib are needed for + embedding Lua in C or C++ programs. + +

Customization

+ Three kinds of things can be customized by editing a file: +

Where and how to install Lua — edit Makefile. +
How to build Lua — edit src/Makefile. +
Lua features — edit src/luaconf.h. +

+ +

+ You don't actually need to edit the Makefiles because you may set the + relevant variables in the command line when invoking make. + Nevertheless, it's probably best to edit and save the Makefiles to + record the changes you've made. + +

+ On the other hand, if you need to customize some Lua features, you'll need + to edit src/luaconf.h before building and installing Lua. + The edited file will be the one installed, and + it will be used by any Lua clients that you build, to ensure consistency. + Further customization is available to experts by editing the Lua sources. + +

Building Lua on other systems

+ If you're not using the usual Unix tools, then the instructions for + building Lua depend on the compiler you use. You'll need to create + projects (or whatever your compiler uses) for building the library, + the interpreter, and the compiler, as follows: + +

+library: +: +lapi.c lcode.c lctype.c ldebug.c ldo.c ldump.c lfunc.c lgc.c llex.c +lmem.c lobject.c lopcodes.c lparser.c lstate.c lstring.c ltable.c +ltm.c lundump.c lvm.c lzio.c +lauxlib.c lbaselib.c lbitlib.c lcorolib.c ldblib.c liolib.c +lmathlib.c loslib.c lstrlib.c ltablib.c lutf8lib.c loadlib.c linit.c +
+interpreter: +: + library, lua.c +
+compiler: +: + library, luac.c +

+ +

+ To use Lua as a library in your own programs you'll need to know how to + create and use libraries with your compiler. Moreover, to dynamically load + C libraries for Lua you'll need to know how to create dynamic libraries + and you'll need to make sure that the Lua API functions are accessible to + those dynamic libraries — but don't link the Lua library + into each dynamic library. For Unix, we recommend that the Lua library + be linked statically into the host program and its symbols exported for + dynamic linking; src/Makefile does this for the Lua interpreter. + For Windows, we recommend that the Lua library be a DLL. + In all cases, the compiler luac should be linked statically. + +

+ As mentioned above, you may edit src/luaconf.h to customize + some features before building Lua. + +

Changes since Lua 5.2

+Here are the main changes introduced in Lua 5.3. +The +reference manual +lists the +incompatibilities that had to be introduced. + +

Main changes

integers (64-bit by default) +
official support for 32-bit numbers +
bitwise operators +
basic utf-8 support +
functions for packing and unpacking values + +

+ +Here are the other changes introduced in Lua 5.3: +

Language

userdata can have any Lua value as uservalue +
integer division +
more flexible rules for some metamethods +

+ +

Libraries

ipairs and the table library respect metamethods +
strip option in string.dump +
table library respects metamethods +
new function table.move +
new function string.pack +
new function string.unpack +
new function string.packsize +

+ +

C API

simpler API for continuation functions in C +
lua_gettable and similar functions return type of resulted value +
strip option in lua_dump +
new function: lua_geti +
new function: lua_seti +
new function: lua_isyieldable +
new function: lua_numbertointeger +
new function: lua_rotate +
new function: lua_stringtonumber +

+ +

Lua standalone interpreter

can be used as calculator; no need to prefix with '=' +
arg table available to all code +

+ +

License

+ + + +Lua is free software distributed under the terms of the +MIT license +reproduced below; +it may be used for any purpose, including commercial purposes, +at absolutely no cost without having to ask us. + +The only requirement is that if you do use Lua, +then you should give us credit by including the appropriate copyright notice somewhere in your product or its documentation. + +For details, see +this. + +

+Copyright © 1994–2015 Lua.org, PUC-Rio. + +
+Permission is hereby granted, free of charge, to any person obtaining a copy +of this software and associated documentation files (the "Software"), to deal +in the Software without restriction, including without limitation the rights +to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the Software is +furnished to do so, subject to the following conditions: + +
+The above copyright notice and this permission notice shall be included in +all copies or substantial portions of the Software. + +
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +THE SOFTWARE. +

+ +

+ + + + -- cgit v1.2.3