From 859f29e5492861ba4c020002efdf98d49b17fefc Mon Sep 17 00:00:00 2001 From: bloodstalker Date: Wed, 21 Feb 2018 09:20:59 +0330 Subject: removed lua docs [ci skip] --- bruiser/lua-5.3.4/doc/manual.html | 10985 ------------------------------------ 1 file changed, 10985 deletions(-) delete mode 100644 bruiser/lua-5.3.4/doc/manual.html (limited to 'bruiser/lua-5.3.4/doc/manual.html') diff --git a/bruiser/lua-5.3.4/doc/manual.html b/bruiser/lua-5.3.4/doc/manual.html deleted file mode 100644 index 3126b5d..0000000 --- a/bruiser/lua-5.3.4/doc/manual.html +++ /dev/null @@ -1,10985 +0,0 @@ - - - -Lua 5.3 Reference Manual - - - - - - - -

-Lua -Lua 5.3 Reference Manual -

- -

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

- -Copyright © 2015–2017 Lua.org, PUC-Rio. -Freely available under the terms of the -Lua license. - - -

-contents -· -index -· -other versions -
- - -

- - - - - - -

1 – Introduction

- -

-Lua is a powerful, efficient, lightweight, embeddable scripting language. -It supports procedural programming, -object-oriented programming, functional programming, -data-driven programming, and data description. - - -

-Lua combines simple procedural syntax with powerful data description -constructs based on associative arrays and extensible semantics. -Lua is dynamically typed, -runs by interpreting bytecode with a register-based -virtual machine, -and has automatic memory management with -incremental garbage collection, -making it ideal for configuration, scripting, -and rapid prototyping. - - -

-Lua is implemented as a library, written in clean C, -the common subset of Standard C and C++. -The Lua distribution includes a host program called lua, -which uses the Lua library to offer a complete, -standalone Lua interpreter, -for interactive or batch use. -Lua is intended to be used both as a powerful, lightweight, -embeddable scripting language for any program that needs one, -and as a powerful but lightweight and efficient stand-alone language. - - -

-As an extension language, Lua has no notion of a "main" program: -it works embedded in a host client, -called the embedding program or simply the host. -(Frequently, this host is the stand-alone lua program.) -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. - - -

-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, lists, -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). - - -

-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 object -and returns a new error object. -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. -(The message handler is called only for regular runtime errors. -It is not called for memory-allocation errors -nor for errors while running finalizers.) - - - - - -

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 key for each event in a metatable is a string -with the event name prefixed by two underscores; -the corresponding values are called metamethods. -In the previous example, the key is "__add" -and the metamethod is the function that performs the addition. - - -

-You can query the metatable of any value -using the getmetatable function. -Lua queries metamethods in metatables using a raw access (see rawget). -So, to retrieve the metamethod for event ev in object o, -Lua does the equivalent to the following code: - -

-     rawget(getmetatable(o) or {}, "__ev")
-
- -

-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). - - -

-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.) - - -

-A detailed list of events controlled by metatables is given next. -Each operation is identified by its corresponding key. - - - -

- -

-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). - - -

-Because metatables are regular tables, -they can contain arbitrary fields, -not only the event names defined above. -Some functions in the standard library -(e.g., tostring) -use other fields in metatables for their own purposes. - - - - - -

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 object. - - -

-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: - -

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

-A short literal string -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 line break -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. -A short literal string cannot contain unescaped line breaks -nor escapes not forming a valid escape sequence. - - -

-We can specify any byte in a short literal string by its numeric value -(including embedded zeros). -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. - - -

-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"]==]
-
- -

-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 the non-text characters. - - -

-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 radix point or an exponent -denotes a float; -otherwise, -if its value fits in an integer, -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: - -

- -

-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: - -

- - - - -

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: - -

- -

-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: - -

- -

-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). - - -

-All conversions from strings to numbers -accept both a dot and the current locale mark -as the radix character. -(The Lua lexer, however, accepts only a dot.) - - -

-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: - -

-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). - - -

-The length operator applied on a table -returns a border in that table. -A border in a table t is any natural number -that satisfies the following condition: - -

-     (border == 0 or t[border] ~= nil) and t[border + 1] == nil
-

-In words, -a border is any (natural) index in a table -where a non-nil value is followed by a nil value -(or zero, when index 1 is nil). - - -

-A table with exactly one border is called a sequence. -For instance, the table {10, 20, 30, 40, 50} is a sequence, -as it has only one border (5). -The table {10, 20, 30, nil, 50} has two borders (3 and 5), -and therefore it is not a sequence. -The table {nil, 20, 30, nil, nil, 60, nil} -has three borders (0, 3, and 6), -so it is not a sequence, too. -The table {} is a sequence with border 0. -Note that non-natural keys do not interfere -with whether a table is a sequence. - - -

-When t is a sequence, -#t returns its only border, -which corresponds to the intuitive notion of the length of the sequence. -When t is not a sequence, -#t can return any of its borders. -(The exact one depends on details of -the internal representation of the table, -which in turn can depend on how the table was populated and -the memory addresses of its non-numeric keys.) - - -

-The computation of the length of a table -has a guaranteed worst time of O(log n), -where n is the largest natural key in the table. - - -

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

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. - - -

-The Lua library is fully reentrant: -it has no global variables. -It keeps all information it needs in a dynamic structure, -called the Lua state. - - -

-Each Lua state has one or more threads, -which correspond to independent, cooperative lines of execution. -The type lua_State (despite its name) refers to a thread. -(Indirectly, through the thread, it also refers to the -Lua state associated to the thread.) - - -

-A pointer to a thread must be passed as the first argument to -every function in the library, except to lua_newstate, -which creates a Lua state from scratch and returns a pointer -to the main thread in the new state. - - - -

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.). -Functions in the API can access this stack through the -Lua state parameter that they receive. - - -

-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 can store temporary -Lua values and must push 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: - -

- - - - -

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 or a type error) -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. - - -

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

-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. - - -

-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, -as its name implies, -is a mechanism of last resort. -Programs should avoid it. -As a general rule, -when a C function is called by Lua with a Lua state, -it can do whatever it wants on that Lua state, -as it should be already protected. -However, -when C code operates on other Lua states -(e.g., a Lua parameter to the function, -a Lua state stored in the registry, or -the result of lua_newthread), -it should use them only in API calls that cannot raise errors. - - -

-The panic function runs as if it were a message handler (see §2.3); -in particular, the error object 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). - - - - - -

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 out-of-memory errors -and errors running a __gc metamethod; -'e' means the function may raise any errors -(it can run arbitrary Lua code, -either directly or through metamethods); -'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_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_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, m] -

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: - -

- -

-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 full 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: - -

- -

-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 (see lua_Alloc). -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 object), -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 object returned on the stack -is exactly the original error object. -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 object -and its return value will be the object -returned on the stack by lua_pcall. - - -

-Typically, the message handler is used to add more debug -information to the error object, 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_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, e] -

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: - -

- -

-Unlike other push functions, -this function checks for the stack space it needs, -including the slot for its result. - - - - - -

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 the __eq metamethod). -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 the __index metamethod. - - -

-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 the __index metamethod. - - -

-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 the __newindex metamethod. - - - - - -

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 __newindex metamethod. - - - - - -

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 object 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 full 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, –] -

const lua_Number *lua_version (lua_State *L);
- -

-Returns the address of the version number -(a C static variable) -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 or a count hook (see §4.9). -In that case, lua_yieldk should be called with no continuation -(probably in the form of lua_yield) and no results, -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: - -

- - - - -

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: - -

- -

-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: - -

- -

-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: - -

- -

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

- -

-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, v] -

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, m] -

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

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

luaL_loadfilex

-[-0, +1, m] -

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 -for file-related errors -(e.g., it cannot open or read the file). - - -

-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_opt

-[-0, +0, e] -

T luaL_opt (L, func, arg, dflt);
- -

-This macro is defined as follows: - -

-     (lua_isnoneornil(L,(arg)) ? (dflt) : func(L,(arg)))
-

-In words, if the argument arg is nil or absent, -the macro results in the default dflt. -Otherwise, it results in the result of calling func -with the state L and the argument index arg as -parameters. -Note that it evaluates the expression dflt only if needed. - - - - - -

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. - - -

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

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: - -

-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: - -

- - - -

-

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 the __eq metamethod. -Returns a boolean. - - - - -

-

rawget (table, index)

-Gets the real value of table[index], -without invoking the __index 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 the __len metamethod. -Returns an integer. - - - - -

-

rawset (table, index, value)

-Sets the real value of table[index] to value, -without invoking the __newindex 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: - -

- - - -

-

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. -When Lua is compiled with a C89 compiler, -options A and a (hexadecimal floats) -do not support any modifier (flags, width, length). - - -

-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. - - - - -

-

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) (for a positive 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: - -

-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 - -

- - - - -

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: - -

-(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, -all caveats about the length operator apply (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, -performing 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. - - -

-Returns the destination table a2. - - - - -

-

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: -elements considered equal by the given order -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 ex -(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 and only 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. -In case of success, -it returns a new file handle. - - -

-The mode string can be any of the following: - -

-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 ()

- - -

-In case of success, -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 - -

-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: - -

-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: - -

-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, 1–7, Sunday is 1), -yday (day of the year, 1–366), -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: - -

- -

-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. -Otherwise, it returns true. - - - - -

-

os.rename (oldname, newname)

- - -

-Renames the file or directory named oldname to newname. -If this function fails, it returns nil, -plus a string describing the error and the error code. -Otherwise, it returns true. - - - - -

-

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 full 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: - -

-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. - - -

-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. - - - - -

-

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: - -

-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. - - -

-If the global variable _PROMPT contains a string, -then its value is used as the prompt. -Similarly, if the global variable _PROMPT2 contains a string, -its value is used as the secondary prompt -(issued during incomplete statements). - - -

-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

- - - - - -

8.2 – Changes in the Libraries

- - - - - -

8.3 – Changes in the API

- - - - - - - -

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 | ‘#’ | ‘~’
-
-
- -

- - - - - - - -

-Last update: -Mon Jan 9 13:30:53 BRST 2017 -

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