     __________________________________________________________________

             Lunacy (Lua) 5.1 Reference Manual (Release 2026-07-04)

   by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes,
   and Sam Trenholme

   Copyright © 2006-2012 Lua.org, PUC-Rio. Copyright © 2020-2026 Sam
   Trenholme. Freely available under the terms of the Lua license.
     __________________________________________________________________

Contents

     * 0 – Lunacy notes
     * 1 – Introduction
     * 2 – The Language
          + 2.1 – Lexical Conventions
          + 2.2 – Values and Types
               o 2.2.1 – Coercion
          + 2.3 – Variables
          + 2.4 – Statements
               o 2.4.1 – Chunks
               o 2.4.2 – Blocks
               o 2.4.3 – Assignment
               o 2.4.4 – Control Structures
               o 2.4.5 – For Statement
               o 2.4.6 – Function Calls as Statements
               o 2.4.7 – Local Declarations
          + 2.5 – Expressions
               o 2.5.1 – Arithmetic Operators
               o 2.5.2 – Relational Operators
               o 2.5.3 – Logical Operators
               o 2.5.4 – Concatenation
               o 2.5.5 – The Length Operator
               o 2.5.6 – Precedence
               o 2.5.7 – Table Constructors
               o 2.5.8 – Function Calls
               o 2.5.9 – Function Definitions
          + 2.6 – Visibility Rules
          + 2.7 – Error Handling
          + 2.8 – Metatables
          + 2.9 – Environments
          + 2.10 – Garbage Collection
               o 2.10.1 – Garbage-Collection Metamethods
               o 2.10.2 – Weak Tables
          + 2.11 – Coroutines
     * 3 – The Application Program Interface
          + 3.1 – The Stack
          + 3.2 – Stack Size
          + 3.3 – Pseudo-Indices
          + 3.4 – C Closures
          + 3.5 – Registry
          + 3.6 – Error Handling in C
          + 3.7 – Functions and Types
          + 3.8 – The Debug Interface
     * 4 – The Auxiliary Library
          + 4.1 – Functions and Types
     * 5 – Standard Libraries
          + 5.1 – Basic Functions
          + 5.2 – Coroutine Manipulation
          + 5.3 – Modules
          + 5.4 – String Manipulation
               o 5.4.1 – Patterns
          + 5.5 – Table Manipulation
          + 5.6 – Mathematical Functions
               o 5.6.1 – Random number generation
          + 5.7 – Input and Output Facilities
          + 5.8 – Operating System Facilities
          + 5.9 – The Debug Library
          + 5.10 – Bitwise Operations
          + 5.11 – Spawner
          + 5.12 – lfs
     * 6 – Lua Stand-alone
     * 7 – Incompatibilities with the Previous Version
          + 7.1 – Changes in the Language
          + 7.2 – Changes in the Libraries
          + 7.3 – Changes in the API
     * 8 – The Complete Syntax of Lua

     __________________________________________________________________

                                0 - Lunacy notes

   Lunacy is a fork of Lua 5.1.5 designed to be compiled as a tiny
   (116,224 byte) Windows 32-bit binary which is (as of 2026) Windows XP,
   Windows 10, and Windows 11 compatible.

   To make sure we don't have issues come January 19, 2038, os.clock(),
   os.date(), and os.difftime() have all been removed (If you want to play
   with dates, use a 64-bit compile of Lua so we don’t have headaches come
   2038). os.time() has a simplified API: Only os.time() with no arguments
   works correctly. In addition, there is now a call, lunacy.today(),
   which returns seven members: Year, month, day, day of week, hour,
   minute, and second.

   math.random() uses RadioGatun[32] instead of rand() to get higher
   quality random numbers. There is now math.rand16(), which generates
   16-bit random numbers; math.random() works as usual. math.randomseed()
   is here, but it now is designed to accept strings as the seed. However,
   since Lua has built-in coercion, randomseed will also accept a number
   for the seed: Lua converts the number in to a string before having it
   seed RadioGatun's state. Note that a seed can not have the NUL
   character; if it does, the string is truncated at the NUL character.

   Lunacy also includes a built in version of the commonly used
   luafilesystem suite:

for a in lfs.dir(".") do
  local b = lfs.attributes(a)
  print(a,b.mode)
end

   Note that only the calls lfs.attributes, lfs.chdir, lfs.currentdir,
   lfs.dir, lfs.mkdir, lfs.rmdir, and lfs.symlinkattributes are included.
   The only file attributes are size, mode, and nlink; other attributes
   return nonsense values in Windows or have Y2038 issues.

   In addition, some of the bit32 lib has been added, in a manner which
   appears Lua 5.2/5.3 compatible.

   For security reasons, Lunacy uses a variant of SipHash as the string
   hash compression function. The variant used is “HalfSipHash-1-3”, the
   32-bit version of SipHash with fewer rounds. This balances the need to
   both have a secure hash compression function while using one with a
   minimum performance penalty on both 32-bit and 64-bit builds of Lunacy.
   My testing indicates this hash function only slows down real-world
   performance by 2.5% to 3%, regardless of whether we build a 32-bit or
   64-bit binary.

   Since HalfSiphash only has a 64-bit key, it is not fully secure in
   cases where an attacker has significant computing resources to brute
   force the key, and where the attacker is able to see the hash
   compression values for strings. However, in the case of using
   HalfSipHash-1-3 as a hash compression function, an attacker will not be
   able to see the hash compression values; to do so would require viewing
   the memory used by a Lua process — if an attacker has that level of
   access, there are other far more devastating attacks they can perform.

   When linking to Lunacy, a C program can run this code before running
   any Lua code: SipHashSetKey(x, y); Where "x" and "y" are suitably
   random 32-bit numbers (uint32_t). Do not call SipHashSetKey() once any
   Lua code is running; otherwise things will break very badly in Lua.

   Security note An attacker with access to the order items are iterated
   from a table can obtain the SipHash key with 2^64 effort. If this is a
   concern, please do not expose the output of table iterators to
   untrusted parties. One simple way to do this is to use the following
   public domain sPairs() function instead of pairs() (usage is the same,
   e.g. for key,value in sPairs(someTable)):

function sPairs(inTable, sFunc)
  if not sFunc then
    sFunc = function(a, b)
      local ta = type(a)
      local tb = type(b)
      if(ta == tb)
        then return a < b
      end
      return tostring(ta) <
             tostring(tb)
    end
  end
  local keyList = {}
  local index = 1
  for k,_ in pairs(inTable) do
    table.insert(keyList,k)
  end
  table.sort(keyList, sFunc)
  return function()
    key = keyList[index]
    index = index + 1
    return key, inTable[key]
  end
end

   Lunacy also has a port of Steve Donovan’s spawner library so that
   Lunacy has popen2 support to spawn sub-processes with both input and
   output piped to the Lunacy script.

   Example popen2 usage:

w, r = spawner.popen2("wc")
w:write("Hello, world!\n")
w:flush()
w:close()
print(r:read())

   Security note Please do not pass untrusted input to the spawner calls;
   they do not escape shell characters and allow any program to be
   executed.

   When in interactive mode, if the first character is a number or the '('
   character, Lunacy will return the results of the arithmetic expression.
   This way, if one types 1 + 1 while in terminal mode, Lunacy will print
   “2” on the terminal.

   For things like math.sin(3.141592653 / 4), '=' is still needed, e.g. =
   math.sin(3.141592653 / 4), but the first character being [0-9] (a
   number) or '(' covers the lion’s share of desktop calculator usage
   cases.

   Contents

                                1 - Introduction

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

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

   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 (Second
   Edition).

   Contents

                                2 - 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.

   The 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 §8 at the end of this manual.

   Contents

2.1 - Lexical Conventions

   Names (also called identifiers) in Lua can be any string of letters,
   digits, and underscores, not beginning with a digit. This coincides
   with the definition of names in most languages. (The definition of
   letter depends on the current locale: any character considered
   alphabetic by the current locale can be used in an identifier.)
   Identifiers are used to name variables and table fields.

   The following keywords are reserved and cannot be used as names:
     and       break     do        else      elseif
     end       false     for       function  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, names starting
   with an underscore followed by uppercase letters (such as _VERSION) are
   reserved for internal global variables used by Lua.

   The following strings denote other tokens:
     +     -     *     /     %     ^     #
     ==    ~=    <=    >=    <     >     =
     (     )     {     }     [     ]
     ;     :     ,     .     ..    ...

   Literal strings can be delimited by matching single or double quotes,
   and can contain the following C-like escape sequences: '\a' (bell),
   '\b' (backspace), '\f' (form feed), '\n' (newline), '\r' (carriage
   return), '\t' (horizontal tab), '\v' (vertical tab), '\\' (backslash),
   '\"' (quotation mark [double quote]), and '\'' (apostrophe [single
   quote]). Moreover, a backslash followed by a real newline results in a
   newline in the string. A character in a string can also be specified by
   its numerical value using the escape sequence \ddd, where ddd is a
   sequence of up to three decimal digits. (Note that if a numerical
   escape is to be followed by a digit, it must be expressed using exactly
   three digits.) Strings in Lua can contain any 8-bit value, including
   embedded zeros, which can be specified as '\0'.

   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 string
   starts with an opening long bracket of any level and ends at the first
   closing long 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. They can contain anything
   except a closing bracket of the proper level.

   For convenience, when the opening long bracket is immediately followed
   by a newline, the newline is not included in the string. As an example,
   in a system using ASCII (in which 'a' is coded as 97, newline is coded
   as 10, and '1' is coded as 49), the five literal strings below denote
   the same string:
     a = 'alo\n123"'
     a = "alo\n123\""
     a = '\97lo\10\04923"'
     a = [[alo
     123"]]
     a = [==[
     alo
     123"]==]

   A numerical constant can be written with an optional decimal part and
   an optional decimal exponent. Lua also accepts integer hexadecimal
   constants, by prefixing them with 0x. Examples of valid numerical
   constants are
     3   3.0   3.1416   314.16e-2   0.31416E1   0xff   0x56

   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.

   Contents

2.2 - 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. Nil is the type of the value
   nil, whose main property is to be different from any other value; it
   usually represents the absence of a useful value. Boolean is the type
   of the values false and true. Both nil and false make a condition
   false; any other value makes it true. Number represents real
   (double-precision floating-point) numbers. (It is easy to build Lua
   interpreters that use other internal representations for numbers, such
   as single-precision float or long integers; see file luaconf.h.) String
   represents arrays of characters. Lua is 8-bit clean: strings can
   contain any 8-bit character, including embedded zeros ('\0') (see
   §2.1).

   Lua can call (and manipulate) functions written in Lua and functions
   written in C (see §2.5.8).

   The type userdata is provided to allow arbitrary C data to be stored in
   Lua variables. This type corresponds to a block of raw memory and has
   no pre-defined operations in Lua, except assignment and identity test.
   However, by using metatables, the programmer can define operations for
   userdata values (see §2.8). 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 §2.11). Do not confuse Lua threads
   with operating-system threads. Lua supports coroutines on all systems,
   even those that do not support threads.

   The type table implements associative arrays, that is, arrays that can
   be indexed not only with numbers, but with any value (except nil).
   Tables can be heterogeneous; that is, they can contain values of all
   types (except nil). Tables are the sole data structuring mechanism in
   Lua; they can be used to represent ordinary arrays, 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 §2.5.7).

   Like indices, the value of a table field can be of any type (except
   nil). In particular, because functions are first-class values, table
   fields can contain functions. Thus tables can also carry methods (see
   §2.5.9).

   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.

  2.2.1 - Coercion

   Lua provides automatic conversion between string and number values at
   run time. Any arithmetic operation applied to a string tries to convert
   this string to a number, following the usual conversion rules.
   Conversely, whenever a number is used where a string is expected, the
   number is converted to a string, in a reasonable format. For complete
   control over how numbers are converted to strings, use the format
   function from the string library (see string.format).

   Contents

2.3 - 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 §2.1.

   Any variable is assumed to be global unless explicitly declared as a
   local (see §2.4.7). Local variables are lexically scoped: local
   variables can be freely accessed by functions defined inside their
   scope (see §2.6).

   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 global variables and 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 §2.8 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

   All global variables live as fields in ordinary Lua tables, called
   environment tables or simply environments (see §2.9). Each function has
   its own reference to an environment, so that all global variables in
   this function will refer to this environment table. When a function is
   created, it inherits the environment from the function that created it.
   To get the environment table of a Lua function, you call getfenv. To
   replace it, you call setfenv. (You can only manipulate the environment
   of C functions through the debug library; (see §5.9).)

   An access to a global variable x is equivalent to _env.x, which in turn
   is equivalent to
     gettable_event(_env, "x")

   where _env is the environment of the running function. (See §2.8 for a
   complete description of the gettable_event function. This function is
   not defined or callable in Lua. Similarly, the _env variable is not
   defined in Lua. We use them here only for explanatory purposes.)

   Contents

2.4 - 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.

  2.4.1 - Chunks

   The unit of execution of Lua is called a chunk. A chunk is simply a
   sequence of statements, which are executed sequentially. Each statement
   can be optionally followed by a semicolon:
        chunk ::= {stat [`;´]}

   There are no empty statements and thus ';;' is not legal.

   Lua handles a chunk as the body of an anonymous function with a
   variable number of arguments (see §2.5.9). As such, chunks can define
   local variables, receive arguments, and return values.

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

   Chunks can also be pre-compiled into binary form; see program luac for
   details. Programs in source and compiled forms are interchangeable; Lua
   automatically detects the file type and acts accordingly.

  2.4.2 - Blocks

   A block is a list of statements; syntactically, a block is the same as
   a chunk:
        block ::= chunk

   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
   or break statement in the middle of another block (see §2.4.4).

  2.4.3 - 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 §2.5.

   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 §2.5).

   The assignment statement first evaluates all its expressions and only
   then are the assignments 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 §2.8 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 variable x = val is equivalent to the
   assignment _env.x = val, which in turn is equivalent to
     settable_event(_env, "x", val)

   where _env is the environment of the running function. (The _env
   variable is not defined in Lua. We use it here only for explanatory
   purposes.)

  2.4.4 - 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 §2.4.5).

   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 return statement is used to return values from a function or a
   chunk (which is just a function). Functions and chunks can return more
   than one value, and so the syntax for the return statement is
        stat ::= return [explist]

   The break statement is used to terminate 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 and break statements can only be written as the last
   statement of a block. If it is really necessary to return or break in
   the middle of a block, then an explicit inner block can be used, as in
   the idioms do return end and do break end, because now return and break
   are the last statements in their (inner) blocks.

  2.4.5 - For Statement

   The for statement has two forms: one numeric and one generic.

   The numeric 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
       while (step > 0 and var <= limit) or (step <= 0 and var >= limit) do
         local v = var
         block
         var = var + step
       end
     end

   Note the following:
     * All three control expressions are evaluated only once, before the
       loop starts. They must all result in numbers.
     * var, limit, and step are invisible variables. The names shown here
       are for explanatory purposes only.
     * If the third expression (the step) is absent, then a step of 1 is
       used.
     * You can use break to exit a for loop.
     * The loop variable v is local to the loop; you cannot use its value
       after the for ends or is broken. If you need this value, assign it
       to another variable before breaking or exiting the loop.

   The generic for statement works over functions, called iterators. On
   each iteration, the iterator function is called to produce a new value,
   stopping when this new value is nil. The generic for loop has the
   following syntax:
        stat ::= for namelist in explist do block end
        namelist ::= Name {`,´ Name}

   A for statement like
     for var_1, ···, var_n in explist do block end

   is equivalent to the code:
     do
       local f, s, var = explist
       while true do
         local var_1, ···, var_n = f(s, var)
         var = var_1
         if var == nil then break end
         block
       end
     end

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

  2.4.6 - 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 §2.5.8.

  2.4.7 - 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 §2.4.3). Otherwise, all variables are initialized with
   nil.

   A chunk is also a block (see §2.4.1), and so local variables can be
   declared in a chunk outside any explicit block. The scope of such local
   variables extends until the end of the chunk.

   The visibility rules for local variables are explained in §2.6.

   Contents

2.5 - Expressions

   The basic expressions in Lua are the following:
        exp ::= prefixexp
        exp ::= nil | false | true
        exp ::= Number
        exp ::= String
        exp ::= function
        exp ::= tableconstructor
        exp ::= `...´
        exp ::= exp binop exp
        exp ::= unop exp
        prefixexp ::= var | functioncall | `(´ exp `)´

   Numbers and literal strings are explained in §2.1; variables are
   explained in §2.3; function definitions are explained in §2.5.9;
   function calls are explained in §2.5.8; table constructors are
   explained in §2.5.7. Vararg expressions, denoted by three dots ('...'),
   can only be used when directly inside a vararg function; they are
   explained in §2.5.9.

   Binary operators comprise arithmetic operators (see §2.5.1), relational
   operators (see §2.5.2), logical operators (see §2.5.3), and the
   concatenation operator (see §2.5.4). Unary operators comprise the unary
   minus (see §2.5.1), the unary not (see §2.5.3), and the unary length
   operator (see §2.5.5).

   Both function calls and vararg expressions can result in multiple
   values. If an expression is used as a statement (only possible for
   function calls (see §2.4.6)), 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 call is enclosed in parentheses). In all
   other contexts, Lua adjusts the result list to one element, discarding
   all values except the first one.

   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.)

  2.5.1 - Arithmetic Operators

   Lua supports the usual arithmetic operators: the binary + (addition), -
   (subtraction), * (multiplication), / (division), % (modulo), and ^
   (exponentiation); and unary - (negation). If the operands are numbers,
   or strings that can be converted to numbers (see §2.2.1), then all
   operations have the usual meaning. Exponentiation works for any
   exponent. For instance, x^(-0.5) computes the inverse of the square
   root of x. Modulo is defined as
     a % b == a - math.floor(a/b)*b

   That is, it is the remainder of a division that rounds the quotient
   towards minus infinity.

  2.5.2 - Relational Operators

   The relational operators in Lua are
     ==    ~=    <     >     <=    >=

   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. Numbers and strings are compared in the usual
   way. Objects (tables, userdata, threads, and functions) 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, thread,
   or function), this new object is different from any previously existing
   object.

   You can change the way that Lua compares tables and userdata by using
   the "eq" metamethod (see §2.8).

   The conversion rules of §2.2.1 do not apply to equality comparisons.
   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 as such. 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 §2.8). A comparison a > b is translated to b < a and a >= b is
   translated to b <= a.

  2.5.3 - Logical Operators

   The logical operators in Lua are and, or, and not. Like the control
   structures (see §2.4.4), 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-cut 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.)

  2.5.4 - 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 mentioned in §2.2.1. Otherwise, the
   "concat" metamethod is called (see §2.8).

  2.5.5 - The Length Operator

   The length operator is denoted by the unary 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 of a table t is defined to be any integer index n such that
   t[n] is not nil and t[n+1] is nil; moreover, if t[1] is nil, n can be
   zero. For a regular array, with non-nil values from 1 to a given n, its
   length is exactly that n, the index of its last value. If the array has
   "holes" (that is, nil values between other non-nil values), then #t can
   be any of the indices that directly precedes a nil value (that is, it
   may consider any such nil value as the end of the array).

  2.5.6 - Precedence

   Operator precedence in Lua follows the table below, from lower to
   higher priority:
     or
     and
     <     >     <=    >=    ~=    ==
     ..
     +     -
     *     /     %
     not   #     - (unary)
     ^

   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.

  2.5.7 - 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 numerical 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

   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 §2.5.8). To avoid this,
   enclose the function call or the vararg expression in parentheses (see
   §2.5).

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

  2.5.8 - 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 §2.8).

   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 ::= String

   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.

   As an exception to the free-format syntax of Lua, you cannot put a line
   break before the '(' in a function call. This restriction avoids some
   ambiguities in the language. If you write
     a = f
     (g).x(a)

   Lua would see that as a single statement, a = f(g).x(a). So, if you
   want two statements, you must add a semi-colon between them. If you
   actually want to call f, you must remove the line break before (g).

   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

  2.5.9 - Function Definitions

   The syntax for function definition is
        function ::= 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 pre-compiles a chunk, all its function bodies are
   pre-compiled 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. Different instances of
   the same function can refer to different external local variables and
   can have different environment tables.

   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 variadic or
   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 §2.4.4). If
   control reaches the end of a function without encountering a return
   statement, then the function returns with no results.

   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

   Contents

2.6 - Visibility Rules

   Lua is a lexically scoped language. The scope of variables begins at
   the first statement after their declaration and lasts until the end 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.

   Contents

2.7 - 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
   (see lua_pcall). Whenever an error occurs during Lua compilation or
   execution, control returns to C, 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 the pcall
   function.

   Contents

2.8 - Metatables

   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" in its metatable. If it
   finds one, Lua calls this function to perform the addition.

   We call the keys in a metatable events and the values metamethods. In
   the previous example, the event is "add" and the metamethod is the
   function that performs the addition.

   You can query the metatable of any value through the getmetatable
   function.

   You can replace the metatable of tables through the setmetatable
   function. You cannot change the metatable of other types from Lua
   (except by using the debug library); you must 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.

   A metatable controls how an object behaves in arithmetic operations,
   order comparisons, concatenation, length operation, and indexing. A
   metatable also can define a function to be called when a userdata is
   garbage collected. For each of these operations Lua associates a
   specific key called an event. When Lua performs one of these operations
   over a value, it checks whether this value has a metatable with the
   corresponding event. If so, the value associated with that key (the
   metamethod) controls how Lua will perform the operation.

   Metatables control the operations listed next. Each operation is
   identified by its corresponding name. The key for each operation is a
   string with its name prefixed by two underscores, '__'; for instance,
   the key for operation "add" is the string "__add". The semantics of
   these operations is better explained by a Lua function describing how
   the interpreter executes the operation.

   The code shown here in Lua is only illustrative; the real behavior is
   hard coded in the interpreter and it is much more efficient than this
   simulation. All functions used in these descriptions (rawget, tonumber,
   etc.) are described in §5.1. In particular, to retrieve the metamethod
   of a given object, we use the expression
     metatable(obj)[event]

   This should be read as
     rawget(getmetatable(obj) or {}, event)

   That is, the access to a metamethod does not invoke other metamethods,
   and the access to objects with no metatables does not fail (it simply
   results in nil).
     * "add": the + operation.
       The function getbinhandler below defines how Lua chooses a handler
       for a binary operation. First, Lua tries the first operand. If its
       type does not define a handler for the operation, then Lua tries
       the second operand.
     function getbinhandler (op1, op2, event)
       return metatable(op1)[event] or metatable(op2)[event]
     end

       By using this function, the behavior of the op1 + op2 is
     function add_event (op1, op2)
       local o1, o2 = tonumber(op1), tonumber(op2)
       if o1 and o2 then  -- both operands are numeric?
         return o1 + o2   -- '+' here is the primitive 'add'
       else  -- at least one of the operands is not numeric
         local h = getbinhandler(op1, op2, "__add")
         if h then
           -- call the handler with both operands
           return (h(op1, op2))
         else  -- no handler available: default behavior
           error(···)
         end
       end
     end

     * "sub": the - operation. Behavior similar to the "add" operation.
     * "mul": the * operation. Behavior similar to the "add" operation.
     * "div": the / operation. Behavior similar to the "add" operation.
     * "mod": the % operation. Behavior similar to the "add" operation,
       with the operation o1 - floor(o1/o2)*o2 as the primitive operation.
     * "pow": the ^ (exponentiation) operation. Behavior similar to the
       "add" operation, with the function pow (from the C math library) as
       the primitive operation.
     * "unm": the unary - operation.
     function unm_event (op)
       local o = tonumber(op)
       if o then  -- operand is numeric?
         return -o  -- '-' here is the primitive 'unm'
       else  -- the operand is not numeric.
         -- Try to get a handler from the operand
         local h = metatable(op).__unm
         if h then
           -- call the handler with the operand
           return (h(op))
         else  -- no handler available: default behavior
           error(···)
         end
       end
     end

     * "concat": the .. (concatenation) operation.
     function concat_event (op1, op2)
       if (type(op1) == "string" or type(op1) == "number") and
          (type(op2) == "string" or type(op2) == "number") then
         return op1 .. op2  -- primitive string concatenation
       else
         local h = getbinhandler(op1, op2, "__concat")
         if h then
           return (h(op1, op2))
         else
           error(···)
         end
       end
     end

     * "len": the # operation.
     function len_event (op)
       if type(op) == "string" then
         return strlen(op)         -- primitive string length
       elseif type(op) == "table" then
         return #op                -- primitive table length
       else
         local h = metatable(op).__len
         if h then
           -- call the handler with the operand
           return (h(op))
         else  -- no handler available: default behavior
           error(···)
         end
       end
     end

       See §2.5.5 for a description of the length of a table.
     * "eq": the == operation. The function getcomphandler defines how Lua
       chooses a metamethod for comparison operators. A metamethod only is
       selected when both objects being compared have the same type and
       the same metamethod for the selected operation.
     function getcomphandler (op1, op2, event)
       if type(op1) ~= type(op2) then return nil end
       local mm1 = metatable(op1)[event]
       local mm2 = metatable(op2)[event]
       if mm1 == mm2 then return mm1 else return nil end
     end

       The "eq" event is defined as follows:
     function eq_event (op1, op2)
       if type(op1) ~= type(op2) then  -- different types?
         return false   -- different objects
       end
       if op1 == op2 then   -- primitive equal?
         return true   -- objects are equal
       end
       -- try metamethod
       local h = getcomphandler(op1, op2, "__eq")
       if h then
         return (h(op1, op2))
       else
         return false
       end
     end

       a ~= b is equivalent to not (a == b).
     * "lt": the < operation.
     function lt_event (op1, op2)
       if type(op1) == "number" and type(op2) == "number" then
         return op1 < op2   -- numeric comparison
       elseif type(op1) == "string" and type(op2) == "string" then
         return op1 < op2   -- lexicographic comparison
       else
         local h = getcomphandler(op1, op2, "__lt")
         if h then
           return (h(op1, op2))
         else
           error(···)
         end
       end
     end

       a > b is equivalent to b < a.
     * "le": the <= operation.
     function le_event (op1, op2)
       if type(op1) == "number" and type(op2) == "number" then
         return op1 <= op2   -- numeric comparison
       elseif type(op1) == "string" and type(op2) == "string" then
         return op1 <= op2   -- lexicographic comparison
       else
         local h = getcomphandler(op1, op2, "__le")
         if h then
           return (h(op1, op2))
         else
           h = getcomphandler(op1, op2, "__lt")
           if h then
             return not h(op2, op1)
           else
             error(···)
           end
         end
       end
     end

       a >= b is equivalent to b <= a. Note that, in the absence of a "le"
       metamethod, Lua tries the "lt", assuming that a <= b is equivalent
       to not (b < a).
     * "index": The indexing access table[key].
     function gettable_event (table, key)
       local h
       if type(table) == "table" then
         local v = rawget(table, key)
         if v ~= nil then return v end
         h = metatable(table).__index
         if h == nil then return nil end
       else
         h = metatable(table).__index
         if h == nil then
           error(···)
         end
       end
       if type(h) == "function" then
         return (h(table, key))     -- call the handler
       else return h[key]           -- or repeat operation on it
       end
     end

     * "newindex": The indexing assignment table[key] = value.
     function settable_event (table, key, value)
       local h
       if type(table) == "table" then
         local v = rawget(table, key)
         if v ~= nil then rawset(table, key, value); return end
         h = metatable(table).__newindex
         if h == nil then rawset(table, key, value); return end
       else
         h = metatable(table).__newindex
         if h == nil then
           error(···)
         end
       end
       if type(h) == "function" then
         h(table, key,value)           -- call the handler
       else h[key] = value             -- or repeat operation on it
       end
     end

     * "call": called when Lua calls a value.
     function function_event (func, ...)
       if type(func) == "function" then
         return func(...)   -- primitive call
       else
         local h = metatable(func).__call
         if h then
           return h(func, ...)
         else
           error(···)
         end
       end
     end

   Contents

2.9 - Environments

   Besides metatables, objects of types thread, function, and userdata
   have another table associated with them, called their environment. Like
   metatables, environments are regular tables and multiple objects can
   share the same environment.

   Threads are created sharing the environment of the creating thread.
   Userdata and C functions are created sharing the environment of the
   creating C function. Non-nested Lua functions (created by loadfile,
   loadstring or load) are created sharing the environment of the creating
   thread. Nested Lua functions are created sharing the environment of the
   creating Lua function.

   Environments associated with userdata have no meaning for Lua. It is
   only a convenience feature for programmers to associate a table to a
   userdata.

   Environments associated with threads are called global environments.
   They are used as the default environment for threads and non-nested Lua
   functions created by the thread and can be directly accessed by C code
   (see §3.3).

   The environment associated with a C function can be directly accessed
   by C code (see §3.3). It is used as the default environment for other
   C functions and userdata created by the function.

   Environments associated with Lua functions are used to resolve all
   accesses to global variables within the function (see §2.3). They are
   used as the default environment for nested Lua functions created by the
   function.

   You can change the environment of a Lua function or the running thread
   by calling setfenv. You can get the environment of a Lua function or
   the running thread by calling getfenv. To manipulate the environment of
   other objects (userdata, C functions, other threads) you must use the
   C API.

   Contents

2.10 - Garbage Collection

   Lua performs automatic memory management. This means that you have to
   worry neither about allocating memory for new objects nor about freeing
   it when the objects are no longer needed. Lua manages memory
   automatically by running a garbage collector from time to time 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: tables, userdata, functions, threads, strings, 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 (so that 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 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. Values
   smaller than 100 make the collector too slow and can result in the
   collector never finishing a cycle. The default, 200, means that the
   collector runs at "twice" the speed of memory allocation.

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

  2.10.1 - Garbage-Collection Metamethods

   Using the C API, you can set garbage-collector metamethods for userdata
   (see §2.8). 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).

   Garbage userdata with a field __gc in their metatables are not
   collected immediately by the garbage collector. Instead, Lua puts them
   in a list. After the collection, Lua does the equivalent of the
   following function for each userdata in that list:
     function gc_event (udata)
       local h = metatable(udata).__gc
       if h then
         h(udata)
       end
     end

   At the end of each garbage-collection cycle, the finalizers for
   userdata are called in reverse order of their creation, among those
   collected in that cycle. That is, the first finalizer to be called is
   the one associated with the userdata created last in the program. The
   userdata itself is freed only in the next garbage-collection cycle.

  2.10.2 - 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 this object.

   A weak table can have weak keys, weak values, or both. A table with
   weak keys allows the collection of its keys, but prevents the
   collection of its values. 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.

   After you use a table as a metatable, you should not change the value
   of its __mode field. Otherwise, the weak behavior of the tables
   controlled by this metatable is undefined.

   Contents

2.11 - 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 with a call to 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 execution.

   When you first call coroutine.resume, passing as its first argument a
   thread returned by coroutine.create, the coroutine starts its
   execution, at the first line of its main function. Extra arguments
   passed to coroutine.resume are passed on to the coroutine main
   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 the
   first case, coroutine.resume returns true, plus any values returned by
   the coroutine main function. In case of errors, coroutine.resume
   returns false plus an error message.

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

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

   As an example, 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

   Contents

                     3 - 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. 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 a proper definition for the macro
   luai_apicheck, in file luaconf.h.

   Contents

3.1 - The Stack

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

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

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

   Contents

3.2 - Stack Size

   When you interact with 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 grow the stack
   size.

   Whenever Lua calls C, it ensures that at least LUA_MINSTACK stack
   positions are available. 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.

   Most query functions accept as indices any value inside the available
   stack space, that is, indices up to the maximum stack size you have set
   through lua_checkstack. Such indices are called acceptable indices.
   More formally, we define an acceptable index as follows:
     (index < 0 && abs(index) <= top) ||
     (index > 0 && index <= stackspace)

   Note that 0 is never an acceptable index.

   Contents

3.3 - Pseudo-Indices

   Unless otherwise noted, any function that accepts valid indices can
   also be called with pseudo-indices, which represent some Lua values
   that are accessible to C code but which are not in the stack.
   Pseudo-indices are used to access the thread environment, the function
   environment, the registry, and the upvalues of a C function (see §3.4).

   The thread environment (where global variables live) is always at
   pseudo-index LUA_GLOBALSINDEX. The environment of the running
   C function is always at pseudo-index LUA_ENVIRONINDEX.

   To access and change the value of global variables, you can use regular
   table operations over an environment table. For instance, to access the
   value of a global variable, do
     lua_getfield(L, LUA_GLOBALSINDEX, varname);

   Contents

3.4 - C Closures

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

   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 value associated with a function is at
   position 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), produces an acceptable
   (but invalid) index.

   Contents

3.5 - Registry

   Lua provides a registry, a pre-defined table that can be used by any
   C code to store whatever Lua value it needs to store. This table is
   always located at pseudo-index LUA_REGISTRYINDEX. Any C library can
   store data into this table, but it should take care to choose keys
   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.

   The integer keys in the registry are used by the reference mechanism,
   implemented by the auxiliary library, and therefore should not be used
   for other purposes.

   Contents

3.6 - Error Handling in C

   Internally, Lua uses the C longjmp facility to handle errors. (You can
   also choose to use exceptions if you use C++; see file luaconf.h.) When
   Lua faces any error (such as memory allocation errors, type errors,
   syntax errors, and runtime errors) it raises an error; that is, it does
   a long jump. A protected environment uses setjmp to set a recover
   point; any error jumps to the most recent active recover point.

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

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

   Contents

3.7 - 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 throw errors: '-' means the function never throws any error; 'm'
   means the function may throw an error only due to not enough memory;
   'e' means the function may throw other kinds of errors; 'v' means the
   function may throw an error on purpose.
     __________________________________________________________________

  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;
   nsize, the new size of the block. ptr is NULL if and only if osize is
   zero. When nsize is zero, the allocator must return NULL; if osize is
   not zero, it should free the block pointed to by ptr. When nsize is not
   zero, the allocator returns NULL if and only if it cannot fill the
   request. When nsize is not zero and osize is zero, the allocator should
   behave like malloc. When nsize and osize are not zero, the allocator
   behaves like realloc. 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);
     }

   This code assumes that free(NULL) has no effect and that realloc(NULL,
   size) is equivalent to malloc(size). ANSI C ensures both behaviors.
     __________________________________________________________________

  lua_atpanic

   [-0, +0, -]
lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);

   Sets a new panic function and returns the old one.

   If an error happens outside any protected environment, Lua calls a
   panic function and then calls exit(EXIT_FAILURE), thus exiting the host
   application. Your panic function can avoid this exit by never returning
   (e.g., doing a long jump).

   The panic function can access the error message at the top of the
   stack.
     __________________________________________________________________

  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. 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_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */
     lua_pushstring(L, "how");                        /* 1st argument */
     lua_getfield(L, LUA_GLOBALSINDEX, "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_setfield(L, LUA_GLOBALSINDEX, "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_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
   numerical arguments and returns their average and sum:
     static int foo (lua_State *L) {
       int n = lua_gettop(L);    /* number of arguments */
       lua_Number sum = 0;
       int i;
       for (i = 1; i <= n; i++) {
         if (!lua_isnumber(L, i)) {
           lua_pushstring(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, m]
int lua_checkstack (lua_State *L, int extra);

   Ensures that there are at least extra free stack slots in the stack. It
   returns false if it cannot grow the stack to that size. This function
   never shrinks the stack; if the stack is already larger than the new
   size, 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, such as a
   daemon or a web server, might need to release states as soon as they
   are not needed, to avoid growing too large.
     __________________________________________________________________

  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 §2.5.4).
     __________________________________________________________________

  lua_cpcall

   [-0, +(0|1), -]
int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);

   Calls the C function func in protected mode. func starts with only one
   element in its stack, a light userdata containing ud. In case of
   errors, lua_cpcall returns the same error codes as lua_pcall, plus the
   error object on the top of the stack; otherwise, it returns zero, and
   does not change the stack. All values returned by func are discarded.
     __________________________________________________________________

  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. The new table
   has space pre-allocated for narr array elements and nrec non-array
   elements. This pre-allocation is useful when you know exactly how many
   elements the table will have. Otherwise you can use the function
   lua_newtable.
     __________________________________________________________________

  lua_dump

   [-0, +0, m]
int lua_dump (lua_State *L, lua_Writer writer, void *data);

   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.

   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_equal

   [-0, +0, e]
int lua_equal (lua_State *L, int index1, int index2);

   Returns 1 if the two values in acceptable indices index1 and index2 are
   equal, following the semantics of the Lua == operator (that is, may
   call metamethods). Otherwise returns 0. Also returns 0 if any of the
   indices is non valid.
     __________________________________________________________________

  lua_error

   [-1, +0, v]
int lua_error (lua_State *L);

   Generates a Lua error. The error message (which can actually be a Lua
   value of any type) must be on the stack top. This function does a long
   jump, and therefore never returns. (see luaL_error).
     __________________________________________________________________

  lua_gc

   [-0, +0, e]
int lua_gc (lua_State *L, int what, int data);

   Controls the garbage collector.

   This function performs several tasks, according to the value of the
   parameter what:
     * LUA_GCSTOP: stops the garbage collector.
     * LUA_GCRESTART: restarts the garbage collector.
     * LUA_GCCOLLECT: performs a full garbage-collection cycle.
     * LUA_GCCOUNT: returns the current amount of memory (in Kbytes) in
       use by Lua.
     * LUA_GCCOUNTB: returns the remainder of dividing the current amount
       of bytes of memory in use by Lua by 1024.
     * LUA_GCSTEP: performs an incremental step of garbage collection. The
       step "size" is controlled by data (larger values mean more steps)
       in a non-specified way. If you want to control the step size you
       must experimentally tune the value of data. The function returns 1
       if the step finished a garbage-collection cycle.
     * LUA_GCSETPAUSE: sets data as the new value for the pause of the
       collector (see §2.10). The function returns the previous value of
       the pause.
     * LUA_GCSETSTEPMUL: sets data as the new value for the step
       multiplier of the collector (see §2.10). The function returns the
       previous value of the step multiplier.
     __________________________________________________________________

  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 passed to lua_newstate.
     __________________________________________________________________

  lua_getfenv

   [-0, +1, -]
void lua_getfenv (lua_State *L, int index);

   Pushes onto the stack the environment table of the value at the given
   index.
     __________________________________________________________________

  lua_getfield

   [-0, +1, e]
void 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
   valid index. As in Lua, this function may trigger a metamethod for the
   "index" event (see §2.8).
     __________________________________________________________________

  lua_getglobal

   [-0, +1, e]
void lua_getglobal (lua_State *L, const char *name);

   Pushes onto the stack the value of the global name. It is defined as a
   macro:
     #define lua_getglobal(L,s)  lua_getfield(L, LUA_GLOBALSINDEX, s)
     __________________________________________________________________

  lua_getmetatable

   [-0, +(0|1), -]
int lua_getmetatable (lua_State *L, int index);

   Pushes onto the stack the metatable of the value at the given
   acceptable index. If the index is not valid, or if the value does not
   have a metatable, the function returns 0 and pushes nothing on the
   stack.
     __________________________________________________________________

  lua_gettable

   [-1, +1, e]
void lua_gettable (lua_State *L, int index);

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

   This function pops the key from the stack (putting the resulting value
   in its place). As in Lua, this function may trigger a metamethod for
   the "index" event (see §2.8).
     __________________________________________________________________

  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
   (and so 0 means an empty stack).
     __________________________________________________________________

  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. Cannot be called with a
   pseudo-index, because a pseudo-index is not an actual stack position.
     __________________________________________________________________

  lua_Integer

typedef ptrdiff_t lua_Integer;

   The type used by the Lua API to represent integral values.

   By default it is a ptrdiff_t, which is usually the largest signed
   integral type the machine handles "comfortably".
     __________________________________________________________________

  lua_isboolean

   [-0, +0, -]
int lua_isboolean (lua_State *L, int index);

   Returns 1 if the value at the given acceptable index has type boolean,
   and 0 otherwise.
     __________________________________________________________________

  lua_iscfunction

   [-0, +0, -]
int lua_iscfunction (lua_State *L, int index);

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

  lua_islightuserdata

   [-0, +0, -]
int lua_islightuserdata (lua_State *L, int index);

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

  lua_isnone

   [-0, +0, -]
int lua_isnone (lua_State *L, int index);

   Returns 1 if the given acceptable index is not valid (that is, it
   refers to an element outside the current stack), and 0 otherwise.
     __________________________________________________________________

  lua_isnoneornil

   [-0, +0, -]
int lua_isnoneornil (lua_State *L, int index);

   Returns 1 if the given acceptable index is not valid (that is, it
   refers to an element outside the current stack) 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 acceptable 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 acceptable 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 acceptable 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 acceptable 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 acceptable index is a userdata
   (either full or light), and 0 otherwise.
     __________________________________________________________________

  lua_lessthan

   [-0, +0, e]
int lua_lessthan (lua_State *L, int index1, int index2);

   Returns 1 if the value at acceptable index index1 is smaller than the
   value at acceptable index index2, following the semantics of the Lua <
   operator (that is, may call metamethods). Otherwise returns 0. Also
   returns 0 if any of the indices is non valid.
     __________________________________________________________________

  lua_load

   [-0, +1, -]
int lua_load (lua_State *L,
              lua_Reader reader,
              void *data,
              const char *chunkname);

   Loads a Lua chunk. 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:
     * 0: no errors;
     * LUA_ERRSYNTAX: syntax error during pre-compilation;
     * LUA_ERRMEM: memory allocation error.

   This function only loads a chunk; it does not run it.

   lua_load automatically detects whether the chunk is text or binary, and
   loads it accordingly (see program luac).

   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 §3.8).
     __________________________________________________________________

  lua_newstate

   [-0, +0, -]
lua_State *lua_newstate (lua_Alloc f, void *ud);

   Creates a new, independent state. Returns NULL if cannot create the
   state (due to lack of memory). The argument f is the allocator
   function; Lua does all memory allocation for this state through this
   function. The second argument, ud, is an opaque pointer that Lua simply
   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 state returned by
   this function shares with the original state all global objects (such
   as tables), 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.

   Userdata represent C values in Lua. A full userdata represents a block
   of memory. It is an object (like a table): you must create it, it can
   have its own metatable, and you can detect when it is being collected.
   A full userdata is only equal to itself (under raw equality).

   When Lua collects a full userdata with a gc metamethod, Lua calls the
   metamethod and marks the userdata as finalized. When this userdata is
   collected again then Lua frees its corresponding 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 changes the value at the given index; this confuses the
   next call to lua_next.
     __________________________________________________________________

  lua_Number

typedef double lua_Number;

   The type of numbers in Lua. By default, it is double, but that can be
   changed in luaconf.h.

   Through the configuration file you can change Lua to operate with
   another type for numbers (e.g., float or long).
     __________________________________________________________________

  lua_objlen

   [-0, +0, -]
size_t lua_objlen (lua_State *L, int index);

   Returns the "length" of the value at the given acceptable index: for
   strings, this is the string length; for tables, this is the result of
   the length operator ('#'); for userdata, this is the size of the block
   of memory allocated for the userdata; for other values, it is 0.
     __________________________________________________________________

  lua_pcall

   [-(nargs + 1), +(nresults|1), -]
int lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);

   Calls a function in protected mode.

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

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

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

   The lua_pcall function returns 0 in case of success or one of the
   following error codes (defined in lua.h):
     * LUA_ERRRUN: a runtime error.
     * LUA_ERRMEM: memory allocation error. For such errors, Lua does not
       call the error handler function.
     * LUA_ERRERR: error while running the error handler function.
     __________________________________________________________________

  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 §3.4); these values are then
   accessible to the function whenever it is called. To associate values
   with a C function, first these values should 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 should be associated
   with the function. lua_pushcclosure also pops these values from the
   stack.

   The maximum value for n is 255.
     __________________________________________________________________

  lua_pushcfunction

   [-0, +1, m]
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 registered in Lua must follow the correct protocol
   to receive its parameters and return its results (see lua_CFunction).

   lua_pushcfunction is defined as a macro:
     #define lua_pushcfunction(L,f)  lua_pushcclosure(L,f,0)
     __________________________________________________________________

  lua_pushfstring

   [-0, +1, m]
const char *lua_pushfstring (lua_State *L, const char *fmt, ...);

   Pushes onto the stack a formatted string and returns a pointer to this
   string. It is similar to the C function sprintf, but has some important
   differences:
     * You do not have to allocate space for the result: the result is a
       Lua string and Lua takes care of memory allocation (and
       deallocation, through garbage collection).
     * The conversion specifiers are quite restricted. There are no flags,
       widths, or precisions. The conversion specifiers can only be '%%'
       (inserts a '%' in the string), '%s' (inserts a zero-terminated
       string, with no size restrictions), '%f' (inserts a lua_Number),
       '%p' (inserts a pointer as a hexadecimal numeral), '%d' (inserts an
       int), and '%c' (inserts an int as a character).
     __________________________________________________________________

  lua_pushinteger

   [-0, +1, -]
void lua_pushinteger (lua_State *L, lua_Integer n);

   Pushes a number 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. 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]
void lua_pushliteral (lua_State *L, const char *s);

   This macro is equivalent to lua_pushlstring, but can be used only when
   s is a literal string. In these cases, it automatically provides the
   string length.
     __________________________________________________________________

  lua_pushlstring

   [-0, +1, m]
void 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 embedded zeros.
     __________________________________________________________________

  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 number with value n onto the stack.
     __________________________________________________________________

  lua_pushstring

   [-0, +1, m]
void 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. The
   string cannot contain embedded zeros; it is assumed to end at the first
   zero.
     __________________________________________________________________

  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 valid 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 acceptable indices index1 and index2 are
   primitively equal (that is, without calling metamethods). Otherwise
   returns 0. Also returns 0 if any of the indices are non valid.
     __________________________________________________________________

  lua_rawget

   [-1, +1, -]
void lua_rawget (lua_State *L, int index);

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

  lua_rawgeti

   [-0, +1, -]
void lua_rawgeti (lua_State *L, int index, int n);

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

  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, int n);

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

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

  lua_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. 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 position (and pops it), without
   shifting any element (therefore replacing the value at the given
   position).
     __________________________________________________________________

  lua_resume

   [-?, +?, -]
int lua_resume (lua_State *L, int narg);

   Starts and resumes a coroutine in a given thread.

   To start a coroutine, you first create a new thread (see
   lua_newthread); then you push onto its stack the main function plus any
   arguments; then you call lua_resume, with narg 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, 0 if the coroutine finishes
   its execution without errors, or an error code in case of errors (see
   lua_pcall). In case of errors, the stack is not unwound, so you can use
   the debug API over it. The error message is on the top of the stack. To
   restart a coroutine, you put on its stack only the values to be passed
   as results from yield, and then call lua_resume.
     __________________________________________________________________

  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_setfenv

   [-1, +0, -]
int lua_setfenv (lua_State *L, int index);

   Pops a table from the stack and sets it as the new environment for the
   value at the given index. If the value at the given index is neither a
   function nor a thread nor a userdata, lua_setfenv returns 0. Otherwise
   it returns 1.
     __________________________________________________________________

  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
   valid 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 §2.8).
     __________________________________________________________________

  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. It is defined as a macro:
     #define lua_setglobal(L,s)   lua_setfield(L, LUA_GLOBALSINDEX, s)
     __________________________________________________________________

  lua_setmetatable

   [-1, +0, -]
int 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 acceptable 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
   valid 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 §2.8).
     __________________________________________________________________

  lua_settop

   [-?, +?, -]
void lua_settop (lua_State *L, int index);

   Accepts any acceptable 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_State

typedef struct lua_State lua_State;

   Opaque structure that keeps the whole state of a Lua interpreter. The
   Lua library is fully reentrant: it has no global variables. All
   information about a state is kept in this structure.

   A pointer to this state 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 for a normal thread, an error code if the thread
   finished its execution with an error, or LUA_YIELD if the thread is
   suspended.
     __________________________________________________________________

  lua_toboolean

   [-0, +0, -]
int lua_toboolean (lua_State *L, int index);

   Converts the Lua value at the given acceptable index to a C boolean
   value (0 or 1). Like all tests in Lua, lua_toboolean returns 1 for any
   Lua value different from false and nil; otherwise it returns 0. It also
   returns 0 when called with a non-valid index. (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 acceptable 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);

   Converts the Lua value at the given acceptable index to the signed
   integral type lua_Integer. The Lua value must be a number or a string
   convertible to a number (see §2.2.1); otherwise, lua_tointeger
   returns 0.

   If the number is not an integer, it is truncated in some non-specified
   way.
     __________________________________________________________________

  lua_tolstring

   [-0, +0, m]
const char *lua_tolstring (lua_State *L, int index, size_t *len);

   Converts the Lua value at the given acceptable index to a C string. If
   len is not NULL, it also 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 fully aligned 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 value
   is removed from the stack.
     __________________________________________________________________

  lua_tonumber

   [-0, +0, -]
lua_Number lua_tonumber (lua_State *L, int index);

   Converts the Lua value at the given acceptable 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 §2.2.1); otherwise, lua_tonumber
   returns 0.
     __________________________________________________________________

  lua_topointer

   [-0, +0, -]
const void *lua_topointer (lua_State *L, int index);

   Converts the value at the given acceptable 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 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 acceptable 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 acceptable 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 acceptable index, or
   LUA_TNONE for a non-valid index (that is, an index to an "empty" stack
   position). The types returned by lua_type are coded by the following
   constants defined in lua.h: LUA_TNIL, 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_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 global state.

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

  lua_yield

   [-?, +?, -]
int lua_yield  (lua_State *L, int nresults);

   Yields a coroutine.

   This function should only be called as the return expression of a
   C function, as follows:
     return lua_yield (L, nresults);

   When a C function calls lua_yield in that way, 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 are passed as results to lua_resume.

   Contents

3.8 - 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 nups;                   /* (u) number of upvalues */
  int linedefined;            /* (S) */
  int lastlinedefined;        /* (S) */
  char short_src[LUA_IDSIZE]; /* (S) */
  /* private part */
  other fields
} lua_Debug;

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

   The fields of lua_Debug have the following meaning:
     * source: If the function was defined in a string, then source is
       that string. If the function was defined in a file, then source
       starts with a '@' followed by the file name.
     * short_src: a "printable" version of source, to be used in error
       messages.
     * linedefined: the line number where the definition of the function
       starts.
     * lastlinedefined: the line number where the definition of the
       function ends.
     * what: the string "Lua" if the function is a Lua function, "C" if it
       is a C function, "main" if it is the main part of a chunk, and
       "tail" if it was a function that did a tail call. In the latter
       case, Lua has no other information about the function.
     * currentline: the current line where the given function is
       executing. When no line information is available, currentline is
       set to -1.
     * name: a reasonable name for the given function. Because functions
       in Lua are first-class values, they do not have a fixed name: some
       functions can be the value of multiple global variables, while
       others can be stored only in a table field. The lua_getinfo
       function checks how the function was called to find a suitable
       name. If it cannot find a name, then name is set to NULL.
     * namewhat: explains the name field. The value of namewhat can be
       "global", "local", "method", "field", "upvalue", or "" (the empty
       string), according to how the function was called. (Lua uses the
       empty string when no other option seems to apply.)
     * nups: the number of upvalues of the function.
     __________________________________________________________________

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

   Returns 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 in 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_getfield(L, LUA_GLOBALSINDEX, "f");  /* get global 'f' */
     lua_getinfo(L, ">S", &ar);
     printf("%d\n", ar.linedefined);

   Each character in the string what selects some fields of the structure
   ar to be filled or a value to be pushed on the stack:
     * 'n': fills in the field name and namewhat;
     * 'S': fills in the fields source, short_src, linedefined,
       lastlinedefined, and what;
     * 'l': fills in the field currentline;
     * 'u': fills in the field nups;
     * 'f': pushes onto the stack the function that is running at the
       given level;
     * 'L': pushes onto the stack a table whose indices are the numbers of
       the lines that are valid on the function. (A valid line is a line
       with some associated code, that is, a line where you can put a
       break point. Non-valid lines include empty lines and comments.)

   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, lua_Debug *ar, int n);

   Gets information about a local variable of a given activation record.
   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 (1 is
   the first parameter or active local variable, and so on, until the last
   active local variable). lua_getlocal pushes the variable's value onto
   the stack and returns its name.

   Variable names starting with '(' (open parentheses) represent internal
   variables (loop control variables, temporaries, and C function locals).

   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);

   Get 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. 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 a closure's upvalue. (For Lua functions,
   upvalues are the external local variables that the function uses, and
   that are consequently included in its closure.) lua_getupvalue gets the
   index n of an upvalue, pushes the upvalue's value onto the stack, and
   returns its name. funcindex points to the closure in the stack.
   (Upvalues have no particular order, as they are active through the
   whole function. So, they are numbered in an arbitrary order.)

   Returns NULL (and pushes nothing) when the index is greater than the
   number of upvalues. For C functions, this function uses the empty
   string "" as a name for all upvalues.
     __________________________________________________________________

  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_HOOKTAILRET, 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 return events,
   event can be LUA_HOOKRET, the normal value, or LUA_HOOKTAILRET. In the
   latter case, Lua is simulating a return from a function that did a tail
   call; in this case, it is useless to call lua_getinfo.

   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.
     __________________________________________________________________

  lua_sethook

   [-0, +0, -]
int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);

   Sets the debugging hook function.

   Argument f is the hook function. mask specifies on which events the
   hook will be called: it is formed by a bitwise or of the constants
   LUA_MASKCALL, LUA_MASKRET, LUA_MASKLINE, and LUA_MASKCOUNT. The count
   argument is only meaningful when the mask includes LUA_MASKCOUNT. For
   each event, the hook is called as explained below:
     * The call hook: is called when the interpreter calls a function. The
       hook is called just after Lua enters the new function, before the
       function gets its arguments.
     * The return hook: is called when the interpreter returns from a
       function. The hook is called just before Lua leaves the function.
       You have no access to the values to be returned by the function.
     * The line hook: is called when the interpreter is about to start the
       execution of a new line of code, or when it jumps back in the code
       (even to the same line). (This event only happens while Lua is
       executing a Lua function.)
     * The count hook: is called after the interpreter executes every
       count instructions. (This event only happens while Lua is executing
       a Lua function.)

   A hook is disabled by setting mask to zero.
     __________________________________________________________________

  lua_setlocal

   [-(0|1), +0, -]
const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);

   Sets the value of a local variable of a given activation record.
   Parameters ar and n are as in lua_getlocal (see lua_getlocal).
   lua_setlocal 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.
     __________________________________________________________________

  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. Parameters funcindex and n are as in the
   lua_getupvalue (see lua_getupvalue).

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

   Contents

                           4 - 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 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 this API.

   Several functions in the auxiliary library are used to check C function
   arguments. Their names are always luaL_check* or luaL_opt*. All of
   these functions throw an error if the check is not satisfied. Because
   the error message is formatted for arguments (e.g., "bad argument #1"),
   you should not use these functions for other stack values.

   Contents

4.1 - Functions and Types

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

  luaL_addchar

   [-0, +0, m]
void luaL_addchar (luaL_Buffer *B, char c);

   Adds the character c to the buffer B (see luaL_Buffer).
     __________________________________________________________________

  luaL_addlstring

   [-0, +0, 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 may contain embedded zeros.
     __________________________________________________________________

  luaL_addsize

   [-0, +0, m]
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

   [-0, +0, 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). The string may not contain embedded zeros.
     __________________________________________________________________

  luaL_addvalue

   [-1, +0, 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 narg,
                    const char *extramsg);

   Checks whether cond is true. If not, raises an error with the following
   message, where func is retrieved from the call stack:
     bad argument #<narg> to <func> (<extramsg>)
     __________________________________________________________________

  luaL_argerror

   [-0, +0, v]
int luaL_argerror (lua_State *L, int narg, const char *extramsg);

   Raises an error with the following message, where func is retrieved
   from the call stack:
     bad argument #<narg> to <func> (<extramsg>)

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

  luaL_Buffer

typedef struct luaL_Buffer luaL_Buffer;

   Type for a string buffer.

   A string buffer allows C code to build Lua strings piecemeal. Its
   pattern of use is as follows:
     * First you declare a variable b of type luaL_Buffer.
     * Then you initialize it with a call luaL_buffinit(L, &b).
     * Then you add string pieces to the buffer calling any of the
       luaL_add* functions.
     * You finish by calling luaL_pushresult(&b). This call leaves the
       final string on the top of the stack.

   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_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 and passes the object as its
   only argument. In this case this function returns 1 and pushes onto the
   stack the value returned by the call. If there is no metatable or no
   metamethod, this function returns 0 (without pushing any value on the
   stack).
     __________________________________________________________________

  luaL_checkany

   [-0, +0, v]
void luaL_checkany (lua_State *L, int narg);

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

  luaL_checkint

   [-0, +0, v]
int luaL_checkint (lua_State *L, int narg);

   Checks whether the function argument narg is a number and returns this
   number cast to an int.
     __________________________________________________________________

  luaL_checkinteger

   [-0, +0, v]
lua_Integer luaL_checkinteger (lua_State *L, int narg);

   Checks whether the function argument narg is a number and returns this
   number cast to a lua_Integer.
     __________________________________________________________________

  luaL_checklong

   [-0, +0, v]
long luaL_checklong (lua_State *L, int narg);

   Checks whether the function argument narg is a number and returns this
   number cast to a long.
     __________________________________________________________________

  luaL_checklstring

   [-0, +0, v]
const char *luaL_checklstring (lua_State *L, int narg, size_t *l);

   Checks whether the function argument narg 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 narg);

   Checks whether the function argument narg is a number and returns this
   number.
     __________________________________________________________________

  luaL_checkoption

   [-0, +0, v]
int luaL_checkoption (lua_State *L,
                      int narg,
                      const char *def,
                      const char *const lst[]);

   Checks whether the function argument narg 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 narg or if 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.
     __________________________________________________________________

  luaL_checkstring

   [-0, +0, v]
const char *luaL_checkstring (lua_State *L, int narg);

   Checks whether the function argument narg 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 narg, int t);

   Checks whether the function argument narg 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 narg, const char *tname);

   Checks whether the function argument narg is a userdata of the type
   tname (see luaL_newmetatable).
     __________________________________________________________________

  luaL_dofile

   [-0, +?, m]
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 0 if there are no errors or 1 in case of errors.
     __________________________________________________________________

  luaL_dostring

   [-0, +?, m]
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 0 if there are no errors or 1 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_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. If the object does not have a metatable, or if the metatable
   does not have this field, returns 0 and pushes nothing.
     __________________________________________________________________

  luaL_getmetatable

   [-0, +1, -]
void luaL_getmetatable (lua_State *L, const char *tname);

   Pushes onto the stack the metatable associated with name tname in the
   registry (see luaL_newmetatable).
     __________________________________________________________________

  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_loadbuffer

   [-0, +1, m]
int luaL_loadbuffer (lua_State *L,
                     const char *buff,
                     size_t sz,
                     const char *name);

   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.
     __________________________________________________________________

  luaL_loadfile

   [-0, +1, m]
int luaL_loadfile (lua_State *L, const char *filename);

   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 #.

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

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

  luaL_loadstring

   [-0, +1, m]
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_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 it to
   the registry with key tname, and returns 1.

   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
   lua_atpanic) 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, m]
void luaL_openlibs (lua_State *L);

   Opens all standard Lua libraries into the given state.
     __________________________________________________________________

  luaL_optint

   [-0, +0, v]
int luaL_optint (lua_State *L, int narg, int d);

   If the function argument narg is a number, returns this number cast to
   an int. If this argument is absent or is nil, returns d. Otherwise,
   raises an error.
     __________________________________________________________________

  luaL_optinteger

   [-0, +0, v]
lua_Integer luaL_optinteger (lua_State *L,
                             int narg,
                             lua_Integer d);

   If the function argument narg is a number, returns this number cast to
   a lua_Integer. If this argument is absent or is nil, returns d.
   Otherwise, raises an error.
     __________________________________________________________________

  luaL_optlong

   [-0, +0, v]
long luaL_optlong (lua_State *L, int narg, long d);

   If the function argument narg is a number, returns this number cast to
   a long. 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 narg,
                             const char *d,
                             size_t *l);

   If the function argument narg 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 results's length.
     __________________________________________________________________

  luaL_optnumber

   [-0, +0, v]
lua_Number luaL_optnumber (lua_State *L, int narg, lua_Number d);

   If the function argument narg 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 narg,
                            const char *d);

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

  luaL_prepbuffer

   [-0, +0, -]
char *luaL_prepbuffer (luaL_Buffer *B);

   Returns an address to a space of size LUAL_BUFFERSIZE 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_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_register. name is
   the function name and func is a pointer to the function. Any array of
   luaL_Reg must end with an sentinel entry in which both name and func
   are NULL.
     __________________________________________________________________

  luaL_register

   [-(0|1), +1, m]
void luaL_register (lua_State *L,
                    const char *libname,
                    const luaL_Reg *l);

   Opens a library.

   When called with libname equal to NULL, it simply registers all
   functions in the list l (see luaL_Reg) into the table on the top of the
   stack.

   When called with a non-null libname, luaL_register creates a new table
   t, sets it as the value of the global variable libname, sets it as the
   value of package.loaded[libname], and registers on it all functions in
   the list l. If there is a table in package.loaded[libname] or in
   variable libname, reuses this table instead of creating a new one.

   In any case the function leaves the table on the top of the stack.
     __________________________________________________________________

  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_typerror

   [-0, +0, v]
int luaL_typerror (lua_State *L, int narg, const char *tname);

   Generates an error with a message like the following:
     location: bad argument narg to 'func' (tname expected, got rt)

   where location is produced by luaL_where, func is the name of the
   current function, and rt is the type name of the actual argument.
     __________________________________________________________________

  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.

   Contents

                             5 - Standard Libraries

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

   All libraries are implemented through the official C API and are
   provided as separate C modules. Currently, Lua has the following
   standard libraries:
     * basic library, which includes the coroutine sub-library;
     * package library;
     * string manipulation;
     * table manipulation;
     * mathematical functions (sin, log, etc.);
     * input and output;
     * operating system facilities;
     * debug facilities.

   Except for the basic and 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, it can open them individually by calling luaopen_base
   (for the basic library), luaopen_package (for the package library),
   luaopen_string (for the string 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 and should not be called directly: you must call them like any
   other Lua C function, e.g., by using lua_call.

   Contents

5.1 - Basic Functions

   The basic library provides some 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])

   Issues an error when the value of its argument v is false (i.e., nil or
   false); otherwise, returns all its arguments. message is an error
   message; when absent, it defaults to "assertion failed!"
     __________________________________________________________________

  collectgarbage ([opt [, arg]])

   This function is a generic interface to the garbage collector. It
   performs different functions according to its first argument, opt:
     * "collect": performs a full garbage-collection cycle. This is the
       default option.
     * "stop": stops the garbage collector.
     * "restart": restarts the garbage collector.
     * "count": returns the total memory in use by Lua (in Kbytes).
     * "step": performs a garbage-collection step. The step "size" is
       controlled by arg (larger values mean more steps) in a
       non-specified way. If you want to control the step size you must
       experimentally tune the value of arg. Returns true if the step
       finished a collection cycle.
     * "setpause": sets arg as the new value for the pause of the
       collector (see §2.10). Returns the previous value for pause.
     * "setstepmul": sets arg as the new value for the step multiplier of
       the collector (see §2.10). Returns the previous value for step.
     __________________________________________________________________

  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 message. Function error never returns.

   Usually, error adds some information about the error position at the
   beginning of the message. 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
   (that is, _G._G = _G). Lua itself does not use this variable; changing
   its value does not affect any environment, nor vice-versa. (Use setfenv
   to change environments.)
     __________________________________________________________________

  getfenv ([f])

   Returns the current environment in use by the function. f can be a Lua
   function or a number that specifies the function at that stack level:
   Level 1 is the function calling getfenv. If the given function is not a
   Lua function, or if f is 0, getfenv returns the global environment. The
   default for f is 1.
     __________________________________________________________________

  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 pairs (1,t[1]), (2,t[2]), ···, up to the first
   integer key absent from the table.
     __________________________________________________________________

  load (func [, chunkname])

   Loads a chunk using function func to get its pieces. Each call to func
   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 errors, returns the compiled chunk as a function;
   otherwise, returns nil plus the error message. The environment of the
   returned function is the global environment.

   chunkname is used as the chunk name for error messages and debug
   information. When absent, it defaults to "=(load)".
     __________________________________________________________________

  loadfile ([filename])

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

  loadstring (string [, chunkname])

   Similar to load, but gets the chunk from the given string.

   To load and run a given string, use the idiom
     assert(loadstring(s))()

   When absent, chunkname defaults to the given string.
     __________________________________________________________________

  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 numeric order, use a
   numerical for or the ipairs function.)

   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)

   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 them to strings. print is not
   intended for formatted output, but only as a quick way to show a value,
   typically for debugging. For formatted output, use string.format.
     __________________________________________________________________

  rawequal (v1, v2)

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

  rawget (table, index)

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

  rawset (table, index, value)

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

   This function returns table.
     __________________________________________________________________

  select (index, ···)

   If index is a number, returns all arguments after argument number
   index. Otherwise, index must be the string "#", and select returns the
   total number of extra arguments it received.
     __________________________________________________________________

  setfenv (f, table)

   Sets the environment to be used by the given function. f can be a Lua
   function or a number that specifies the function at that stack level:
   Level 1 is the function calling setfenv. setfenv returns the given
   function.

   As a special case, when f is 0 setfenv changes the environment of the
   running thread. In this case, setfenv returns no values.
     __________________________________________________________________

  setmetatable (table, metatable)

   Sets the metatable for the given table. (You cannot change the
   metatable of other types from Lua, only from C.) 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])

   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.

   An optional argument specifies the base to interpret the numeral. 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. In base 10 (the
   default), the number can have a decimal part, as well as an optional
   exponent part (see §2.1). In other bases, only unsigned integers are
   accepted.
     __________________________________________________________________

  tostring (e)

   Receives an argument of any type and converts it to a string in a
   reasonable format. For complete control of how numbers are converted,
   use string.format.

   If the metatable of e has a "__tostring" field, then tostring calls the
   corresponding value with e 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".
     __________________________________________________________________

  unpack (list [, i [, j]])

   Returns the elements from the given table. This function is equivalent
   to
     return list[i], list[i+1], ···, list[j]

   except that the above code can be written only for a fixed number of
   elements. By default, i is 1 and j is the length of the list, as
   defined by the length operator (see §2.5.5).
     __________________________________________________________________

  _VERSION

   A global variable (not a function) that holds a string containing the
   current interpreter version. The current contents of this variable is
   "Lua 5.1".
     __________________________________________________________________

  xpcall (f, err)

   This function is similar to pcall, except that you can set a new error
   handler.

   xpcall calls function f in protected mode, using err as the error
   handler. Any error inside f is not propagated; instead, xpcall catches
   the error, calls the err function with the original error object, and
   returns a status code. Its first result is the status code (a boolean),
   which is true if the call succeeds without errors. In this case, xpcall
   also returns all results from the call, after this first result. In
   case of any error, xpcall returns false plus the result from err.

   Contents

5.2 - Coroutine Manipulation

   The operations related to coroutines comprise a sub-library of the
   basic library and come inside the table coroutine. See §2.11 for a
   general description of coroutines.
     __________________________________________________________________

  coroutine.create (f)

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

  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 (if the coroutine yields) or any values returned
   by the body function (if the coroutine terminates). If there is any
   error, resume returns false plus the error message.
     __________________________________________________________________

  coroutine.running ()

   Returns the running coroutine, or nil when called by the main thread.
     __________________________________________________________________

  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 Lua 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. The coroutine cannot
   be running a C function, a metamethod, or an iterator. Any arguments to
   yield are passed as extra results to resume.

   Contents

5.3 - Modules

   The package library provides basic facilities for loading and building
   modules in Lua. It exports two of its functions directly in the global
   environment: require and module. Everything else is exported in a table
   package.
     __________________________________________________________________

  module (name [, ···])

   Creates a module. If there is a table in package.loaded[name], this
   table is the module. Otherwise, if there is a global table t with the
   given name, this table is the module. Otherwise creates a new table t
   and sets it as the value of the global name and the value of
   package.loaded[name]. This function also initializes t._NAME with the
   given name, t._M with the module (t itself), and t._PACKAGE with the
   package name (the full module name minus last component; see below).
   Finally, module sets t as the new environment of the current function
   and the new value of package.loaded[name], so that require returns t.

   If name is a compound name (that is, one with components separated by
   dots), module creates (or reuses, if they already exist) tables for
   each component. For instance, if name is a.b.c, then module stores the
   module table in field c of field b of global a.

   This function can receive optional options after the module name, where
   each option is a function to be applied over the module.
     __________________________________________________________________

  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.loaders array. By
   changing this array, we can change how require looks for a module. The
   following explanation is based on the default configuration for
   package.loaders.

   First require queries package.preload[modname]. If it has a value, this
   value (which should 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.loaders).

   Once a loader is found, require calls the loader with a single
   argument, modname. If the loader returns any value, require assigns the
   returned value to package.loaded[modname]. If the loader returns no
   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 signals an error.
     __________________________________________________________________

  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 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.
     __________________________________________________________________

  package.loaders

   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) 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 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. A path is a sequence of templates separated by
   semicolons. For each template, the searcher will change each
   interrogation mark in the template by filename, which is the module
   name with each dot replaced by a "directory separator" (such as "/" in
   Unix); then it will try to open the resulting file name. So, for
   instance, if the Lua path is the string
     "./?.lua;./?.lc;/usr/local/?/init.lua"

   the search for a Lua file for module foo will try to open the files
   ./foo.lua, ./foo.lc, and /usr/local/foo/init.lua, in that order.

   The third searcher looks for a loader as a C library, using the path
   given by the variable package.cpath. 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 prefix up to (and including) the first hyphen is removed.
   For instance, if the module name is a.v1-b.c, the function name will be
   luaopen_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.
     __________________________________________________________________

  package.loadlib (libname, funcname)

   Dynamically links the host program with the C library libname. Inside
   this library, looks for a function funcname and returns this function
   as a C function. (So, funcname must follow the protocol (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
   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 ANSI 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 or with a default path defined in
   luaconf.h, if the environment variable is 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).
     __________________________________________________________________

  package.seeall (module)

   Sets a metatable for module with its __index field referring to the
   global environment, so that this module inherits values from the global
   environment. To be used as an option to function module.

   Contents

5.4 - 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 numerical 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.

   Note that numerical 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
   numerical code equal to its corresponding argument.

   Note that numerical codes are not necessarily portable across
   platforms.
     __________________________________________________________________

  string.dump (function)

   Returns a string containing a binary representation of the given
   function, so that a later loadstring on this string returns a copy of
   the function. function must be a Lua function without upvalues.
     __________________________________________________________________

  string.find (s, pattern [, init [, plain]])

   Looks for the first match of pattern 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 numerical
   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 printf family
   of standard C functions. The only differences are that the
   options/modifiers *, l, L, n, p, and h are not supported and that there
   is an extra option, q. The q option formats a string in a form suitable
   to be safely read back by the Lua interpreter: the string is written
   between double quotes, and all double quotes, newlines, embedded zeros,
   and backslashes in the string are correctly escaped when written. For
   instance, the call
     string.format('%q', 'a string with "quotes" and \n new line')

   will produce the string:
     "a string with \"quotes\" and \
      new line"

   The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number
   as argument, whereas q and s expect a string.

   This function does not accept string values containing embedded zeros,
   except as arguments to the q option.
     __________________________________________________________________

  string.gmatch (s, pattern)

   Returns an iterator function that, each time it is called, returns the
   next captures from pattern over string s. If pattern specifies no
   captures, then the whole match is produced in each call.

   As an example, the following loop
     s = "hello world from Lua"
     for w in string.gmatch(s, "%a+") do
       print(w)
     end

   will iterate over all the words from string s, printing one per line.
   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 '^' 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 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.

   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 %n, with n between 1 and 9, stands for the value of the n-th
   captured substring (see below). 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 the pattern specifies no captures,
   then the whole match is used 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; if
   the pattern specifies no captures, then the whole match is passed as a
   sole argument.

   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 loadstring(s)()
         end)
     --> x="4+5 = 9"

     local t = {name="lua", version="5.1"}
     x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
     --> x="lua-5.1.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 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 numerical argument init specifies where to
   start the search; its default value is 1 and can be negative.
     __________________________________________________________________

  string.rep (s, n)

   Returns a string that is the concatenation of n copies of the string s.
     __________________________________________________________________

  string.reverse (s)

   Returns a string that is the string s reversed.
     __________________________________________________________________

  string.sub (s, i [, j])

   Returns the substring of s that starts at i and continues until j; i
   and j can be negative. If j is absent, then it is assumed to be equal
   to -1 (which is the same as the string length). In particular, the call
   string.sub(s,1,j) returns a prefix of s with length j, and
   string.sub(s, -i) returns a suffix of s with length i.
     __________________________________________________________________

  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.

  5.4.1 - Patterns

    Character Class:

   A character class is used to represent a set of characters. The
   following combinations are allowed in describing a character class:
     * x: (where x is not one of the magic characters ^$()%.[]*+-?)
       represents the character x itself.
     * .: (a dot) represents all characters.
     * %a: represents all letters.
     * %c: represents all control characters.
     * %d: represents all digits.
     * %l: represents all lowercase letters.
     * %p: represents all punctuation characters.
     * %s: represents all space characters.
     * %u: represents all uppercase letters.
     * %w: represents all alphanumeric characters.
     * %x: represents all hexadecimal digits.
     * %z: represents the character with representation 0.
     * %x: (where x is any non-alphanumeric character) represents the
       character x. This is the standard way to escape the magic
       characters. Any punctuation character (even the non magic) can be
       preceded by a '%' when used to represent itself in a pattern.
     * [set]: represents the class which is the union of all characters in
       set. A range of characters can be specified by separating the end
       characters of the range with a '-'. All classes %x described above
       can also be used as components in set. All other characters in set
       represent themselves. For example, [%w_] (or [_%w]) represents all
       alphanumeric characters plus the underscore, [0-7] represents the
       octal digits, and [0-7%l%-] represents the octal digits plus the
       lowercase letters plus the '-' character.
       The interaction between ranges and classes is not defined.
       Therefore, patterns like [%a-z] or [a-%%] have no meaning.
     * [^set]: represents the complement of set, where set is interpreted
       as above.

   For all classes represented by single letters (%a, %c, etc.), the
   corresponding uppercase letter represents the complement of the class.
   For instance, %S represents all non-space characters.

   The definitions of letter, space, and other character groups depend on
   the current locale. In particular, the class [a-z] may not be
   equivalent to %l.

    Pattern Item:

   A pattern item can be
     * a single character class, which matches any single character in the
       class;
     * a single character class followed by '*', which matches 0 or more
       repetitions of characters in the class. These repetition items will
       always match the longest possible sequence;
     * a single character class followed by '+', which matches 1 or more
       repetitions of characters in the class. These repetition items will
       always match the longest possible sequence;
     * a single character class followed by '-', which also matches 0 or
       more repetitions of characters in the class. Unlike '*', these
       repetition items will always match the shortest possible sequence;
     * a single character class followed by '?', which matches 0 or 1
       occurrence of a character in the class;
     * %n, for n between 1 and 9; such item matches a substring equal to
       the n-th captured string (see below);
     * %bxy, where x and y are two distinct characters; such item matches
       strings that start with x, end with y, and where the x and y are
       balanced. This means that, if one reads the string from left to
       right, counting +1 for an x and -1 for a y, the ending y is the
       first y where the count reaches 0. For instance, the item %b()
       matches expressions with balanced parentheses.

    Pattern:

   A pattern is a sequence of pattern items. A '^' 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.

   A pattern cannot contain embedded zeros. Use %z instead.

   Contents

5.5 - Table Manipulation

   This library provides generic functions for table manipulation. It
   provides all its functions inside the table table.

   Most functions in the table library assume that the table represents an
   array or a list. For these functions, when we talk about the "length"
   of a table we mean the result of the length operator.
     __________________________________________________________________

  table.concat (table [, sep [, i [, j]]])

   Given an array where all elements are strings or numbers, returns
   table[i]..sep..table[i+1] ··· sep..table[j]. The default value for sep
   is the empty string, the default for i is 1, and the default for j is
   the length of the table. If i is greater than j, returns the empty
   string.
     __________________________________________________________________

  table.insert (table, [pos,] value)

   Inserts element value at position pos in table, shifting up other
   elements to open space, if necessary. The default value for pos is n+1,
   where n is the length of the table (see §2.5.5), so that a call
   table.insert(t,x) inserts x at the end of table t.
     __________________________________________________________________

  table.maxn (table)

   Returns the largest positive numerical index of the given table, or
   zero if the table has no positive numerical indices. (To do its job
   this function does a linear traversal of the whole table.)
     __________________________________________________________________

  table.remove (table [, pos])

   Removes from table the element at position pos, shifting down other
   elements to close the space, if necessary. Returns the value of the
   removed element. The default value for pos is n, where n is the length
   of the table, so that a call table.remove(t) removes the last element
   of table t.
     __________________________________________________________________

  table.sort (table [, comp])

   Sorts table elements in a given order, in-place, from table[1] to
   table[n], where n is the length of the table. If comp is given, then it
   must be a function that receives two table elements, and returns true
   when the first is less than the second (so that not comp(a[i+1],a[i])
   will be true after the sort). If comp is not given, then the standard
   Lua operator < is used instead.

   The sort algorithm is not stable; that is, elements considered equal by
   the given order may have their relative positions changed by the sort.

   Contents

5.6 - Mathematical Functions

   This library is an interface to the standard C math library. It
   provides all its functions inside the table math.
     __________________________________________________________________

  math.abs (x)

   Returns the absolute value of x.
     __________________________________________________________________

  math.acos (x)

   Returns the arc cosine of x (in radians).
     __________________________________________________________________

  math.asin (x)

   Returns the arc sine of x (in radians).
     __________________________________________________________________

  math.atan (x)

   Returns the arc tangent of x (in radians).
     __________________________________________________________________

  math.atan2 (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.)
     __________________________________________________________________

  math.ceil (x)

   Returns the smallest integer larger than or equal to x.
     __________________________________________________________________

  math.cos (x)

   Returns the cosine of x (assumed to be in radians).
     __________________________________________________________________

  math.cosh (x)

   Returns the hyperbolic cosine of x.
     __________________________________________________________________

  math.deg (x)

   Returns the angle x (given in radians) in degrees.
     __________________________________________________________________

  math.exp (x)

   Returns the value e^x.
     __________________________________________________________________

  math.floor (x)

   Returns the largest integer 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.
     __________________________________________________________________

  math.frexp (x)

   Returns m and e such that x = m2^e, e is an integer and the absolute
   value of m is in the range [0.5, 1) (or zero when x is zero).
     __________________________________________________________________

  math.huge

   The value HUGE_VAL, a value larger than or equal to any other numerical
   value.
     __________________________________________________________________

  math.ldexp (m, e)

   Returns m2^e (e should be an integer).
     __________________________________________________________________

  math.log (x)

   Returns the natural logarithm of x.
     __________________________________________________________________

  math.log10 (x)

   Returns the base-10 logarithm of x.
     __________________________________________________________________

  math.max (x, ···)

   Returns the maximum value among its arguments.
     __________________________________________________________________

  math.min (x, ···)

   Returns the minimum value among its arguments.
     __________________________________________________________________

  math.modf (x)

   Returns two numbers, the integral part of x and the fractional part of
   x.
     __________________________________________________________________

  math.pi

   The value of pi.
     __________________________________________________________________

  math.pow (x, y)

   Returns x^y. (You can also use the expression x^y to compute this
   value.)
     __________________________________________________________________

  math.rad (x)

   Returns the angle x (given in degrees) in radians.
     __________________________________________________________________

  math.sin (x)

   Returns the sine of x (assumed to be in radians).
     __________________________________________________________________

  math.sinh (x)

   Returns the hyperbolic sine of x.
     __________________________________________________________________

  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.tanh (x)

   Returns the hyperbolic tangent of x.

  5.6.1 - Random number generation

   Lunacy uses the RadioGatun[32] algorithm to generate high quality
   pseudo-random numbers. Example code:
math.randomseed(os.time())
print("The 20-sided dice roll is ",math.random(1,20))
     __________________________________________________________________

  math.random ([m [, n]])

   When called without arguments, returns a uniform pseudo-random real
   number in the range [0,1). When called with an integer number m,
   math.random returns a uniform pseudo-random integer in the range [1,
   m]. When called with two integer numbers m and n, math.random returns a
   uniform pseudo-random integer in the range [m, n].

   math.random may also be invoked as rg32.random. The rg32 names are
   aliases to allow stock Lua to load rg32 as a third party library and
   generate the same random numbers as Lunacy. Indeed, the rg32 functions
   use the same random state as the math.random() functions.
     __________________________________________________________________

  math.rand16 ()

   math.rand16() can be used to generate pseudo-random numbers between 0
   and 65535. This function is here so that the random number library can,
   if needed, make the same numbers as the official RadioGatún[32] test
   vectors.

   math.rand16() may be called as rg32.rand16().
     __________________________________________________________________

  rg32.rand32 ()

   rg32.rand32() can be used to generate 32-bit unsigned pseudo-random
   integers. Like math.rand16(), this function is here so that the random
   number library can, if needed, make the same numbers as the official
   RadioGatún[32] test vectors.
     __________________________________________________________________

  rg32.runmill (work)

   This particular routine does not have a “math” alias because this
   should only be used if someone understands the risks and benefits of
   using this routine for security purposes. For example, if one is
   hashing passwords, there are a number of standard password hashing
   routines such as Argon2 which should be considered.

   The function rg32.runmill() is used for “proof of work” protocols, such
   as password hashing. rg32.runmill() takes a single numeric argument:
   The number of work “units” we perform. Each work unit is the amount of
   work needed to generate 64 bits of pseudo-random numbers (64 bits is
   the same as four calls to rg32.rand16() or two calls to rg32.random()).
   For example, to call rg32.runmill(100) has the random number generator
   perform the work needed to make 6400 pseudo-random bits (400
   rg32.rand16() calls or 200 rg32.random() calls).
     __________________________________________________________________

  math.randomseed (x)

   Sets x as the "seed" for the pseudo-random generator: equal seeds
   produce equal sequences of numbers.

   If math.random is called without math.randomseed being called first,
   the default seed “1234” (without the quotes) will be used.

   Note that the value x is a string, not a number. The string is a text,
   not binary, string: The seed can not have ASCII NULLs in it; any other
   character (including UTF-8 hi-bit characters) is allowed.

   If a number is given to randomseed, Lua converts the number in to a
   string before seeding the random state.

   math.randomseed() has the alias rg32.randomseed().

   Contents

5.7 - Input and Output Facilities

   The I/O library provides two different styles for file manipulation.
   The first one uses implicit file descriptors; 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 descriptors.

   When using implicit file descriptors, all operations are supplied by
   table io. When using explicit file descriptors, the operation io.open
   returns a file descriptor and then all operations are supplied as
   methods of the file descriptor.

   The table io also provides three predefined file descriptors 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.
     __________________________________________________________________

  io.close ([file])

   Equivalent to file:close(). Without a file, closes the default output
   file.
     __________________________________________________________________

  io.flush ()

   Equivalent to file:flush over the default output file.
     __________________________________________________________________

  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, each time it is called, returns a new line from the file.
   Therefore, the construction
     for line in io.lines(filename) do body end

   will iterate over all lines of the file. When the iterator function
   detects the end of file, it returns nil (to finish the loop) and
   automatically closes the file.

   The call io.lines() (with no file name) is equivalent to
   io.input():lines(); 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.
     __________________________________________________________________

  io.open (filename [, mode])

   This function opens a file, in the mode specified in the string mode.
   It returns a new file handle, or, in case of errors, nil plus an error
   message.

   The mode string can be any of the following:
     * "r": read mode (the default);
     * "w": write mode;
     * "a": append mode;
     * "r+": update mode, all previous data is preserved;
     * "w+": update mode, all previous data is erased;
     * "a+": append update mode, previous data is preserved, writing is
       only allowed at the end of file.

   The mode string can also have a 'b' at the end, which is needed in some
   systems to open the file in binary mode. This string is exactly what is
   used in the standard C function fopen.
     __________________________________________________________________

  io.output ([file])

   Similar to io.input, but operates over the default output file.
     __________________________________________________________________

  io.popen (prog [, mode])

   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").

   This function is system dependent and is not available on all
   platforms.
     __________________________________________________________________

  io.read (···)

   Equivalent to io.input():read.
     __________________________________________________________________

  io.tmpfile ()

   Returns a handle for a temporary file. This file is opened in update
   mode and it is automatically removed when the program ends.
     __________________________________________________________________

  io.type (obj)

   Checks whether obj is a valid file handle. Returns the string "file" if
   obj is an open file handle, "closed file" if obj is a closed file
   handle, or nil if obj is not a file handle.
     __________________________________________________________________

  io.write (···)

   Equivalent to io.output():write.
     __________________________________________________________________

  file:close ()

   Closes file. Note that files are automatically closed when their
   handles are garbage collected, but that takes an unpredictable amount
   of time to happen.
     __________________________________________________________________

  file:flush ()

   Saves any written data to file.
     __________________________________________________________________

  file:lines ()

   Returns an iterator function that, each time it is called, returns a
   new line from the file. Therefore, the construction
     for line in file:lines() do body end

   will iterate over all lines of the file. (Unlike io.lines, this
   function does not close the file when the loop ends.)
     __________________________________________________________________

  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. When called without formats, it uses a default format
   that reads the entire next line (see below).

   The available formats are
     * "*n": reads a number; this is the only format that returns a number
       instead of a string.
     * "*a": reads the whole file, starting at the current position. On
       end of file, it returns the empty string.
     * "*l": reads the next line (skipping the end of line), returning nil
       on end of file. This is the default format.
     * number: reads a string with up to this number of characters,
       returning nil on end of file. If number is zero, it reads nothing
       and returns an empty string, or nil on end of file.
     __________________________________________________________________

  file:seek ([whence] [, offset])

   Sets and gets the file position, measured from the beginning of the
   file, to the position given by offset plus a base specified by the
   string whence, as follows:
     * "set": base is position 0 (beginning of the file);
     * "cur": base is current position;
     * "end": base is end of file;

   In case of success, function seek returns the final file position,
   measured in bytes from the beginning of the file. If this function
   fails, it returns nil, plus a string describing the error.

   The default value for whence is "cur", and for offset is 0. Therefore,
   the call file:seek() returns the current file position, without
   changing it; the call file:seek("set") sets the position to the
   beginning of the file (and returns 0); and the call file:seek("end")
   sets the position to the end of the file, and returns its size.
     __________________________________________________________________

  file:setvbuf (mode [, size])

   Sets the buffering mode for an output file. There are three available
   modes:
     * "no": no buffering; the result of any output operation appears
       immediately.
     * "full": full buffering; output operation is performed only when the
       buffer is full (or when you explicitly flush the file (see
       io.flush)).
     * "line": line buffering; output is buffered until a newline is
       output or there is any input from some special files (such as a
       terminal device).

   For the last two cases, size specifies the size of the buffer, in
   bytes. The default is an appropriate size.
     __________________________________________________________________

  file:write (···)

   Writes the value of each of its arguments to the file. The arguments
   must be strings or numbers. To write other values, use tostring or
   string.format before write.

   Contents

5.8 - Operating System Facilities

   This library is implemented through table os.
     __________________________________________________________________

  os.clock ()

   os.clock is disabled in this fork of Lua so that code will not have
   issues come January 19, 2038.
     __________________________________________________________________

  os.date ([format [, time]])

   os.date is disabled in this fork of Lua so that code will not have
   issues come January 19, 2038.
     __________________________________________________________________

  os.difftime (t2, t1)

   os.difftime is disabled in this fork of Lua so that code will not have
   issues come January 19, 2038.
     __________________________________________________________________

  os.execute ([command])

   This function is equivalent to the C function system. It passes command
   to be executed by an operating system shell. It returns a status code,
   which is system-dependent. If command is absent, then it returns
   nonzero if a shell is available and zero otherwise.
     __________________________________________________________________

  os.exit ([code])

   Calls the C function exit, with an optional code, to terminate the host
   program. The default value for code is the success code.
     __________________________________________________________________

  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 directory with the given name. Directories must be
   empty to be removed. If this function fails, it returns nil, plus a
   string describing the error.
     __________________________________________________________________

  os.rename (oldname, newname)

   Renames file or directory named oldname to newname. If this function
   fails, it returns nil, plus a string describing the error.
     __________________________________________________________________

  os.setlocale (locale [, category])

   Sets the current locale of the program. locale is a 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.
     __________________________________________________________________

  os.time()

   os.time returns a standard UNIX timestamp: The number of seconds since
   January 1, 1970. The timestamp is year 2038 compliant both in Windows
   systems (even 32-bit Windows systems) via Windows’s “FileTime” API, and
   on 64-bit UNIX and compatible systems.

   os.time is designed to generate a correct timestamp on 32-bit UNIX
   compatible systems until around 2100.

   While the Lua version of this call can accept a table as an argument,
   the Lunacy version of this call accepts no arguments, and always
   returns a simple integer timestamp based on the current system time.

  lunacy.today ()

   lunacy.today returns the current local time as seven numeric items:
    1. Year (four digit format)
    2. Month (1-12)
    3. Day
    4. Day of week (0-6; 0 is Sunday, 6 saturday)
    5. Hour (24 hour military time)
    6. Minute
    7. Second

   Example usage:

   year, month, day, wday, hour, minute, second = lunacy.today()

   lunacy.today is Y2038 compliant if compiled on a 64-bit POSIX system or
   as a Windows 32-bit binary. lunacy.today will return nil on POSIX
   systems with a 32-bit time_t; one might be able to resolve this and run
   the code after Y2038 by going to https://github.com/evalEmpire/y2038
   and patching the source code as needed.
     __________________________________________________________________

  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 some systems (POSIX), 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.

   Contents

5.9 - The Debug Library

   This library provides the functionality of the debug interface to Lua
   programs. You should exert care when using this library. The functions
   provided here should be used exclusively for debugging and similar
   tasks, such as profiling. Please resist the temptation to use them as a
   usual programming tool: they can be very slow. Moreover, several of
   these functions violate some assumptions about Lua code (e.g., that
   variables local to a function cannot be accessed from outside or that
   userdata metatables cannot be changed by Lua code) and therefore can
   compromise otherwise secure code.

   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.getfenv (o)

   Returns the environment of object o.
     __________________________________________________________________

  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,] function [, 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 function,
   which means the function running at level function of the call stack of
   the given thread: level 0 is the current function (getinfo itself);
   level 1 is the function that called getinfo; and so on. If function 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 table
   with 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,] level, local)

   This function returns the name and the value of the local variable with
   index local of the function at level level of the stack. (The first
   parameter or local variable has index 1, and so on, until the last
   active local variable.) 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 debug.getinfo to check whether the
   level is valid.)

   Variable names starting with '(' (open parentheses) represent internal
   variables (loop control variables, temporaries, and C function locals).
     __________________________________________________________________

  debug.getmetatable (object)

   Returns the metatable of the given object or nil if it does not have a
   metatable.
     __________________________________________________________________

  debug.getregistry ()

   Returns the registry table (see §3.5).
     __________________________________________________________________

  debug.getupvalue (func, up)

   This function returns the name and the value of the upvalue with index
   up of the function func. The function returns nil if there is no
   upvalue with the given index.
     __________________________________________________________________

  debug.setfenv (object, table)

   Sets the environment of the given object to the given table. Returns
   object.
     __________________________________________________________________

  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 the
   following characters, with the given meaning:
     * "c": the hook is called every time Lua calls a function;
     * "r": the hook is called every time Lua returns from a function;
     * "l": the hook is called every time Lua enters a new line of code.

   With a count different from zero, the hook is called 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", "return" (or "tail return",
   when simulating a return from a tail call), "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), unless the event is "tail
   return". In this case, Lua is only simulating the return, and a call to
   getinfo will return invalid data.
     __________________________________________________________________

  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.
     __________________________________________________________________

  debug.setmetatable (object, table)

   Sets the metatable for the given object to the given table (which can
   be nil).
     __________________________________________________________________

  debug.setupvalue (func, up, value)

   This function assigns the value value to the upvalue with index up of
   the function func. The function returns nil if there is no upvalue with
   the given index. Otherwise, it returns the name of the upvalue.
     __________________________________________________________________

  debug.traceback ([thread,] [message [, level]])

   Returns a string with a traceback of the call stack. An 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).

   Contents

5.10 – Bitwise Operations

   This library provides bitwise operations. It provides all its functions
   inside the table bit32. These operations come from
   https://github.com/LuaDist/bitlib/

   Some examples:

   = bit32.arshift(-1,1) -- returns 4294967295

   = bit32.bnot(0) -- returns 4294967295

   = bit32.lshift(1,31) -- returns 2147483648

   = bit32.lshift(1,32) -- returns 0

   = bit32.rrotate(1,2) -- returns 1073741824
     __________________________________________________________________

  bit32.arshift (x, disp)

   Returns the number x shifted disp bits to the right.

   If the number would be a negative 32-bit integer, we put binary '1' in
   the high-order bits. Otherwise, we put in binary '0'. For example
   0xfffffff0 shifted four bits to the right is 0xffffffff. 0x7fffffff
   shifted four bits to the right is 0x07ffffff.
     __________________________________________________________________

  bit32.band (···)

   Returns the bitwise and of its operands.
     __________________________________________________________________

  bit32.bnot (x)

   Returns the bitwise negation of x.
     __________________________________________________________________

  bit32.bor (···)

   Returns the bitwise or of its operands.
     __________________________________________________________________

  bit32.bxor (···)

   Returns the bitwise exclusive or of its operands.
     __________________________________________________________________

  bit32.lshift (x, disp)

   Returns the number x shifted disp bits to the left.
     __________________________________________________________________

  bit32.rshift (x, disp)

   Returns the number x shifted disp bits to the right.

   This shift operation is what is called logical shift.

   We always put in binary '0' with the high order bits. For example
   0xfffffff0 shifted four bits to the right is 0x0fffffff. 0x7fffffff
   shifted four bits to the right is 0x07ffffff.
     __________________________________________________________________

  bit32.rrotate (x, disp)

   Returns the number x rotated disp bits to the right. This is a 32-bit
   rotate.

   Contents

5.11 – Spawner

   Please note: Spawner may not be present, depending on how Lunacy was
   compiled

   This library provides the ability to have Lunacy open up two-way pipes
   with sub processes. In other words, it allows Lunacy to spawn a child
   process, and to be able to send data to the sub-process’s standard
   input while reading the sub-process’s standard output.

   This is a reasonably simple sub-process generator, and its read() call
   will hang if the sub-process does not have any output for Lunacy to
   read. There are other corner cases where the code may cause things to
   hang, but the code works quite nicely as long as the sub-process is
   reasonably cooperative.

   The code has both a native Windows and a POSIX-compatible library with
   the same API.

   Example usage: Here, wc is a standard *NIX command which reads data
   from the standard input, and outputs the number of words and lines in
   the input data after the input pipe is closed.
w, r = spawner.popen2("wc")
w:write("Hello, world!\n")
w:flush()
w:close()
print(r:read())
     __________________________________________________________________

  spawner.popen2 (command)

   spawner.popen2() takes a single argument: The name of the sub-process
   command we wish to execute. It returns two values:
     * A handle which we can write to (the first return value)
     * A handle which we can read from (the second return value).

   With the write handle, we can flush the write buffer by using the flush
   method. We can also close the sub-process’s standard input by using the
   close method on the write handle. It is possible to abruptly terminate
   the sub-process by using the kill method, but this sends a hard kill
   signal and does not allow the sub-process to gracefully terminate.

   As long as the write handle is open, we can use the write method (which
   takes a string with the data to write to the sub-process as its only
   argument).
     __________________________________________________________________

  spawner.popen (command)

   spawner.popen() takes a single argument: The name of the sub-process
   command we wish to execute. It returns one value, a handle which we can
   read from.

   Running spawner.popen() is equivalent to running spawner.popen2() then
   immediately closing the write handle. It is similar to
   io.popen(command, "r"), where command is the argument given to
   spawner.popen(), but may be useful if io.popen() is having issues.

   Contents

5.12 – lfs

   Please note: Lfs may not be present, depending on how Lunacy was
   compiled

   Lunacy includes a partial port of the luafilesystem library. This
   allows for basic directory traversal in Lunacy scripts.

   Example usage:
for a in lfs.dir(".") do
  local b = lfs.attributes(a)
  print(a,b.mode)
end

   Note that only the calls lfs.attributes, lfs.chdir, lfs.currentdir,
   lfs.dir, lfs.mkdir, lfs.rmdir, and lfs.symlinkattributes are included.
   The only file attributes are size, mode, and nlink; other attributes
   return nonsense values in Windows or have Y2038 issues.

   luafilesystem has a home page at
   https://keplerproject.github.io/luafilesystem/.
     __________________________________________________________________

  lfs.attributes (filename)

   lfs.attributes(filename) returns information about a given directory
   entry. In particular, in Lunacy it returns a table with only three
   entries:
     * size, the size of the file in bytes
     * mode, what kind of file it is (string value). Possible values are
       “file”, “directory”, “link”, “socket”, “named pipe”, “char device”,
       “block device”, and “other”.
     * nlink, the number of hard links to a given file. This will usually
       be 1; if this is not one, it indicates that there this file has a
       hard link, i.e. the file has multiple pointers to it on the file
       system.

   Should the filename point to a non-existent entry, lfs.attributes will
   return nil, and the subsequent return values should indicate the error
   conditions.
     __________________________________________________________________

  lfs.chdir (dir)

   Change the current working directory for the Lunacy process to the
   directory pointed to by “dir”. This is akin to running the “cd”
   command. The exact format of “dir” is OS-dependent.

   This function will return true if successful, nil (and why in
   subsequent return values) if not.

   Example usage:
status, error = lfs.chdir("..")
if not status then
  print(error)
end
     __________________________________________________________________

  lfs.currentdir ()

   This function returns a string indicating the current working
   directory. The format of the string is OS-dependent.

   Example usage:
print(lfs.currentdir())
     __________________________________________________________________

  lfs.dir (location)

   lfs.dir is an iterator function which, when put in a for loop, returns
   a series of strings, each string being a name of a file or directory in
   the folder pointed to by location.

   For example, to list all of the files in the current directory:
for a in lfs.dir(".") do
  print(a)
end
     __________________________________________________________________

  lfs.mkdir (path)

   Make a new empty directory at the location specified in path. Returns
   true on success, nil (with reason in subsequent return value) on error.

   Example usage:
status, error = lfs.mkdir("foo")
if not status then
  print(error)
end
     __________________________________________________________________

  lfs.rmdir (path)

   Remove the directory at the location specified in path. This will
   return an error if the directory is not empty. Returns true on success,
   nil (with reason in subsequent return value) on error.

   Example usage:
status, error = lfs.rmdir("foo")
if not status then
  print(error)
end
     __________________________________________________________________

  lfs.symlinkattributes (filename)

   lfs.symlinkattributes(filename) works the same as
   lfs.attributes(filename), except that, if the file is a symbolic link,
   we return information about the symbolic link instead of information
   about the file or folder the symbolic link points to.

   Contents

                              6 - Lua Stand-alone

   Although Lua has been designed as an extension language, to be embedded
   in a host C program, it is also frequently used as a stand-alone
   language. An interpreter for Lua as a stand-alone language, called
   simply lua, is provided with the standard distribution. The stand-alone
   interpreter includes all standard libraries, including the debug
   library. Its usage is:
     lua [options] [script [args]]

   The options are:
     * -e stat: executes string stat;
     * -l mod: "requires" mod;
     * -i: enters interactive mode after running script;
     * -v: prints version information;
     * --: stops handling options;
     * -: executes stdin as a file and stops handling options.

   After handling its options, lua runs the given script, passing to it
   the given args as string arguments. When called without arguments, lua
   behaves as lua -v -i when the standard input (stdin) is a terminal, and
   as lua - otherwise.

   Before running any argument, the interpreter checks for an environment
   variable LUA_INIT. If its format is @filename, then lua executes the
   file. Otherwise, lua executes the string itself.

   All options are handled in order, except -i. 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 (which is '1'), and
   finally run the file script.lua with no arguments. (Here $ is the shell
   prompt. Your prompt may be different.)

   Before starting to run the script, lua collects all arguments in the
   command line in a global table called arg. The script name is stored at
   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 the options) go to negative indices. For instance, in the
   call
     $ lua -la b.lua t1 t2

   the interpreter first runs the file a.lua, then creates a table
     arg = { [-2] = "lua", [-1] = "-la",
             [0] = "b.lua",
             [1] = "t1", [2] = "t2" }

   and finally runs the file b.lua. The script is called with arg[1],
   arg[2], ··· as arguments; it can also access these arguments with the
   vararg expression '...'.

   In interactive mode, 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). Therefore, both prompts can be changed directly
   on the command line or in any Lua programs by assigning to _PROMPT. See
   the next example:
     $ lua -e"_PROMPT='myprompt> '" -i

   (The outer pair of quotes is for the shell, the inner pair is for Lua.)
   Note the use of -i to enter interactive mode; otherwise, the program
   would just end silently right after the assignment to _PROMPT.

   To allow the use of Lua as a script interpreter in Unix systems, the
   stand-alone 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.)

   Lunacy stand alone can also be used as a desktop calculator. Simply
   type in “lunacy” without any arguments, and type in numeric expressions
   at the Lunacy terminal prompt.

   When in interactive mode, if the first character is a number or the '('
   character, Lunacy will return the results of the arithmetic expression.
   This way, if one types 1 + 1 while in terminal mode, Lunacy will print
   “2” on the terminal.

   For calculations which do not start with a number, like
   math.sin(math.pi / 4), “=” needs to be the first character, e.g. =
   math.sin(math.pi / 4)

   Contents

                7 - Incompatibilities with the Previous Version

   Here we list the incompatibilities that you may find when moving a
   program from Lua 5.0 to Lua 5.1. You can avoid most of the
   incompatibilities compiling Lua with appropriate options (see file
   luaconf.h). However, all these compatibility options will be removed in
   the next version of Lua.

   Contents

7.1 - Changes in the Language

     * The vararg system changed from the pseudo-argument arg with a table
       with the extra arguments to the vararg expression. (See
       compile-time option LUA_COMPAT_VARARG in luaconf.h.)
     * There was a subtle change in the scope of the implicit variables of
       the for statement and for the repeat statement.
     * The long string/long comment syntax ([[string]]) does not allow
       nesting. You can use the new syntax ([=[string]=]) in these cases.
       (See compile-time option LUA_COMPAT_LSTR in luaconf.h.)

   Contents

7.2 - Changes in the Libraries

     * Function string.gfind was renamed string.gmatch. (See compile-time
       option LUA_COMPAT_GFIND in luaconf.h.)
     * When string.gsub is called with a function as its third argument,
       whenever this function returns nil or false the replacement string
       is the whole match, instead of the empty string.
     * Function table.setn was deprecated. Function table.getn corresponds
       to the new length operator (#); use the operator instead of the
       function. (See compile-time option LUA_COMPAT_GETN in luaconf.h.)
     * Function loadlib was renamed package.loadlib. (See compile-time
       option LUA_COMPAT_LOADLIB in luaconf.h.)
     * Function math.mod was renamed math.fmod. (See compile-time option
       LUA_COMPAT_MOD in luaconf.h.)
     * Functions table.foreach and table.foreachi are deprecated. You can
       use a for loop with pairs or ipairs instead.
     * There were substantial changes in function require due to the new
       module system. However, the new behavior is mostly compatible with
       the old, but require gets the path from package.path instead of
       from LUA_PATH.
     * Function collectgarbage has different arguments. Function gcinfo is
       deprecated; use collectgarbage("count") instead.

   Contents

7.3 - Changes in the API

     * The luaopen_* functions (to open libraries) cannot be called
       directly, like a regular C function. They must be called through
       Lua, like a Lua function.
     * Function lua_open was replaced by lua_newstate to allow the user to
       set a memory-allocation function. You can use luaL_newstate from
       the standard library to create a state with a standard allocation
       function (based on realloc).
     * Functions luaL_getn and luaL_setn (from the auxiliary library) are
       deprecated. Use lua_objlen instead of luaL_getn and nothing instead
       of luaL_setn.
     * Function luaL_openlib was replaced by luaL_register.
     * Function luaL_checkudata now throws an error when the given value
       is not a userdata of the expected type. (In Lua 5.0 it returned
       NULL.)

                         8 - The Complete Syntax of Lua

   Here is the complete syntax of Lua in extended BNF. (It does not
   describe operator precedences.)

        chunk ::= {stat [`;´]} [laststat [`;´]]

        block ::= chunk

        stat ::=  varlist `=´ explist |
                 functioncall |
                 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]

        laststat ::= return [explist] | break

        funcname ::= Name {`.´ Name} [`:´ Name]

        varlist ::= var {`,´ var}

        var ::=  Name | prefixexp `[´ exp `]´ | prefixexp `.´ Name

        namelist ::= Name {`,´ Name}

        explist ::= {exp `,´} exp

        exp ::=  nil | false | true | Number | String | `...´ | function |
                 prefixexp | tableconstructor | exp binop exp | unop exp

        prefixexp ::= var | functioncall | `(´ exp `)´

        functioncall ::=  prefixexp args | prefixexp `:´ Name args

        args ::=  `(´ [explist] `)´ | tableconstructor | String

        function ::= 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: Sun Jul 5 2026
