+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,
@@ -37,56 +47,68 @@ 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++).
+(that is, in the common subset of ANSI C and C++).
-
Being an extension language, Lua has no notion of a "main" program:
+
+
+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
+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,
+
+
+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,
+
+
+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.
+see Roberto's book, Programming in Lua (Second Edition).
+
+
+
+
This section describes the lexis, the syntax, and the semantics of Lua.
+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,
+
+
+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 in italics,
-keywords are shown in bold,
-and other terminal symbols are shown in typewriter font,
-enclosed in single quotes.
+{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 at the end of this manual.
-
+Names
(also called identifiers)
in Lua can be any string of letters,
digits, and underscores,
@@ -97,58 +119,65 @@ 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
+
+
+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
+ 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:
+
+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)
+uppercase letters (such as _VERSION)
are reserved for internal global variables used by Lua.
-
+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)
-
\' --- apostrophe (single quote)
-
-Moreover, a `\newline´
-(that is, a backslash followed by a real newline)
+'\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 may also be specified by its numerical value
-using the escape sequence `\ddd´,
+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 may contain any 8-bit value, including embedded zeros,
-which can be specified as `\0´.
+which can be specified as '\0'.
-
To put a double (single) quote, a newline, a backslash,
+
+
+To put a double (single) quote, a newline, a backslash,
or an embedded zero
inside a literal string enclosed by double (single) quotes
you must use an escape sequence.
@@ -156,52 +185,59 @@ Any other character may be directly inserted into the literal.
(Some control characters may cause problems for the file system,
but Lua has no problem with them.)
-
Literal strings can also be defined using a long format
+
+
+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 [=[,
+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 ]====].
+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 may run for several lines,
do not interpret any escape sequences,
and ignore long brackets of any other level.
-They may contain anything except a closing bracket of the proper level
-or embedded zeros.
+They may contain anything except a closing bracket of the proper level.
-
For convenience,
+
+
+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 four literals below denote the same string:
+(in which 'a' is coded as 97,
+newline is coded as 10, and '1' is coded as 49),
+the five literals below denote the same string:
+
- (1) 'alo\n123"'
- (2) "alo\n123\""
- (3) '\97lo\10\04923"'
- (4) [[alo
- 123"]]
- (5) [==[
- alo
- 123"]==]
+ a = 'alo\n123"'
+ a = "alo\n123\""
+ a = '\97lo\10\04923"'
+ a = [[alo
+ 123"]]
+ a = [==[
+ alo
+ 123"]==]
-
Numerical constants may be written with an optional decimal part
+
+A numerical constant may 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
+
+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,
@@ -210,19 +246,28 @@ Otherwise, it is a long comment,
which runs until the corresponding closing long bracket.
Long comments are frequently used to disable code temporarily.
-
+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.
+
+
+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:
+
+
+There are eight basic types in Lua:
nil, boolean, number,
string, function, userdata,
thread, and table.
@@ -235,37 +280,45 @@ 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.)
+such as single-precision float or long integers;
+see file luaconf.h.)
String represents arrays of characters.
Lua is 8-bit clean:
-Strings may contain any 8-bit character,
-including embedded zeros (`\0´) (see 2.1).
+strings may contain any 8-bit character,
+including embedded zeros ('\0') (see §2.1).
-
Lua can call (and manipulate) functions written in Lua and
+
+
+Lua can call (and manipulate) functions written in Lua and
functions written in C
-(see 2.5.8).
+(see §2.5.8).
-
The type userdata is provided to allow arbitrary C data to
+
+
+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).
+(see §2.8).
Userdata values cannot be created or modified in Lua,
-only through the C API.
+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).
+
+
+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,
+
+
+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;
@@ -277,28 +330,37 @@ 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).
+(see §2.5.7).
-
Like indices,
+
+
+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 may contain functions.
-Thus tables may also carry methods (see 2.5.9).
+Thus tables may also carry methods (see §2.5.9).
-
Tables, functions, threads, and (full) userdata values are objects:
+
+
+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
+
+
+The library function type returns a string describing the type
of a given value.
-
+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.
@@ -308,57 +370,72 @@ For complete control over how numbers are converted to strings,
use the format function from the string library
(see string.format).
-
2.3 - Variables
-
Variables are places that store values.
+
+
+
+
+
+
Variables are assumed to be global unless explicitly declared local
-(see 2.4.7).
+
+
+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).
+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:
+
+Before the first assignment to a variable, its value is nil.
+
+
+
+Square brackets are used to index a table:
+
var ::= prefixexp `[´ exp `]´
-
-The first expression (prefixexp) should result in a table value;
-the second expression (exp)
-identifies a specific entry in this table.
-The expression denoting the table to be indexed has a restricted syntax;
-see 2.5 for details.
-
-
The syntax var.Name is just syntactic sugar for
-var["Name"] and is used to denote table fields:
-
- var ::= prefixexp `.´ Name
-
-
-
The meaning of accesses to global variables
+
+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
+(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.)
-
All global variables live as fields in ordinary Lua tables,
+
+
+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).
+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.
@@ -368,92 +445,124 @@ 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).)
+(You can only manipulate the environment of C functions
+through the debug library; (see §5.9).)
-
An access to a global variable x
+
+
+An access to a global variable x
is equivalent to _env.x,
which in turn is equivalent to
+
- gettable_event(_env, "x")
-
+ gettable_event(_env, "x")
+
where _env is the environment of the running function.
-(See 2.8 for a complete description of the
+(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.)
-
2.4 - Statements
-
Lua supports an almost conventional set of statements,
+
+
+
+
+Lua supports an almost conventional set of statements,
similar to those in Pascal or C.
This set includes
assignment, control structures, function calls,
-table constructors, and variable declarations.
+and variable declarations.
-
2.4.1 - Chunks
-
The unit of execution of Lua is called a chunk.
+
+
+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.
+
+There are no empty statements and thus ';;' is not legal.
-
Lua handles a chunk as the body of an anonymous function
+
+
+Lua handles a chunk as the body of an anonymous function
with a variable number of arguments
-(see 2.5.9).
+(see §2.5.9).
As such, chunks can define local variables,
receive arguments, and return values.
-
A chunk may be stored in a file or in a string inside the host program.
+
+
+A chunk may be stored in a file or in a string inside the host program.
When a chunk is executed, first it is pre-compiled into instructions for
a virtual machine,
and then the compiled code is executed
by an interpreter for the virtual machine.
-
Chunks may also be pre-compiled into binary form;
+
+
+Chunks may 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.
-
A block is a list of statements;
syntactically, a block is the same as a chunk:
+
block ::= chunk
-
A block may be explicitly delimited to produce a single statement:
+
+A block may 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).
+of another block (see §2.4.4).
-
+Lua allows multiple assignment.
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 ::= varlist1 `=´ explist1
varlist1 ::= var {`,´ var}
explist1 ::= exp {`,´ exp}
-
+Before the assignment,
the list of values is adjusted to the length of
the list of variables.
If there are more values than needed,
@@ -463,217 +572,307 @@ 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 this call enter in the list of values,
before the adjustment
-(except when the call is enclosed in parentheses; see 2.5).
+(except when the call is enclosed in parentheses; see §2.5).
-
The assignment statement first evaluates all its expressions
+
+
+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
-
+ 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.
+before it is assigned 4.
Similarly, the line
+
- x, y = y, x
-
+ x, y = y, x
+
exchanges the values of x and y.
-
The meaning of assignments to global variables
+
+
+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
+(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
+
+
+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)
-
+ 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.)
-
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).
+
+Lua also has a for statement, in two flavors (see §2.4.5).
-
The condition expression of a
+
+
+The condition expression of a
control structure may 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,
+
+
+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
+
+
+The return statement is used to return values
from a function or a chunk (which is just a function).
Functions and chunks may return more than one value,
so the syntax for the return statement is
+
stat ::= return [explist1]
-
The break statement is used to terminate the execution of a
+
+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
+
+
+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´,
+do return end and do break end,
because now return and break are the last statements in
their (inner) blocks.
-
+
+The for statement has two forms:
one numeric and one generic.
-
The numeric for loop repeats a block of code while a
+
+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 var = e1, e2, e3 do block end
-
+ 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 var = _var
- block
- _var = _var + _step
- end
+ 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,
+
+
+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.
+
+
+
+var, limit, and step are invisible variables.
The names are here 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 var is local to the loop;
+
+
+
+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 the value of the loop variable var,
-then assign it to another variable before breaking or exiting the loop.
+If you need this value,
+assign it to another variable before breaking or exiting the loop.
+
+
-
The generic for statement works over functions,
+
+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 explist1 do block end
namelist ::= Name {`,´ Name}
-
+
A for statement like
+
- for var_1, ..., var_n in explist do block end
-
+ 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
+ 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.
+
+
+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.
+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 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.
+
Local variables may be declared anywhere inside a block.
The declaration may include an initial assignment:
+
stat ::= local namelist [`=´ explist1]
-
+
If present, an initial assignment has the same semantics
-of a multiple assignment (see 2.4.3).
+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.
-
2.5 - Expressions
+
+The visibility rules for local variables are explained in §2.6.
+
+
+
+
+
+
+
+
exp ::= prefixexp
- exp ::= nil | false | true
+ exp ::= nil | false | true
exp ::= Number
exp ::= String
exp ::= function
@@ -681,132 +880,161 @@ The basic expressions in Lua are the following:
exp ::= `...´
exp ::= exp binop exp
exp ::= unop exp
- prefixexp ::= var | functioncall | `(´ 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.
+
+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 inside
-vararg functions;
-they are explained in 2.5.9.
+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), and logical operators (see 2.5.3).
-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).
+
+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 may result in multiple values.
-If the expression is used as a statement (see 2.4.6)
+
+
+Both function calls and vararg expressions may result in multiple values.
+If the expression is used as a statement (see §2.4.6)
(only possible for function calls),
then its return list is adjusted to zero elements,
thus discarding all returned values.
-If the expression is used inside another expression
-or in the middle of a list of expressions,
-then its result list is adjusted to one element,
-thus discarding all values except the first one.
-If the expression is used as the last element of a list of expressions,
-then no adjustment is made,
-unless the call is enclosed in parentheses.
+If the 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:
-
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 values returned by 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 may 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 values returned by f()
- return ... -- returns all received vararg parameters
- return x,y,f() -- returns x, y, and all values returned by f()
- {f()} -- creates a list with all values returned by f()
- {...} -- creates a list with all vararg parameters
- {f(), nil} -- f() is adjusted to 1 result
+ 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 may 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
-
An expression enclosed in parentheses always results in only one value.
+
+An 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.)
-
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),
+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.
-Modulus is defined as
+Modulo is defined as
+
- a % b == a - math.floor(a/b)*b
-
+ a % b == a - math.floor(a/b)*b
+
That is, it is the remainder of a division that rounds
the quotient towards minus infinity.
-
Equality (==) first compares the type of its operands.
+
+
+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.
+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).
-
+You can change the way that Lua compares tables and userdata
+by using the "eq" metamethod (see §2.8).
+
+
+
+The conversion rules of §2.2.1do 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 operator ~= is exactly the negation of equality (==).
-
The order operators work as follows.
+
+
+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).
+metamethod (see §2.8).
-
-Like the control structures (see 2.4.4),
+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 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.
@@ -817,34 +1045,46 @@ 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
-
+ 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.)
+--> indicates the result of the preceding expression.)
-
The string concatenation operator in Lua is
-denoted by two dots (`..´).
+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).
+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 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
+
+
+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 may be zero.
@@ -858,39 +1098,50 @@ directly precedes a nil value
(that is, it may consider any such nil value as the end of
the array).
-
Operator precedence in Lua follows the table below,
from lower to higher priority:
+
- or
- and
- < > <= >= ~= ==
- ..
- + -
- * / %
- not # - (unary)
- ^
-
+ or
+ and
+ < > <= >= ~= ==
+ ..
+ + -
+ * / %
+ not # - (unary)
+ ^
+
As usual,
you can use parentheses to change the precedences of an expression.
-The concatenation (`..´) and exponentiation (`^´)
+The concatenation ('..') and exponentiation ('^')
operators are right associative.
All other binary operators are left associative.
-
Table constructors are expressions that create tables.
Every time a constructor is evaluated, a new table is created.
Constructors can be used to create empty tables,
or to create a table and initialize some of its fields.
The general syntax for constructors is
+
Each field of the form [exp1] = exp2 adds to the new table an entry
+
+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.
@@ -899,90 +1150,113 @@ Finally, fields of the form exp are equivalent to
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 }
-
+ 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
+ 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
+
+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).
+(see §2.5.8).
To avoid this,
enclose the function call (or the vararg expression)
-in parentheses (see 2.5).
+in parentheses (see §2.5).
-
The field list may have an optional trailing separator,
+
+
+The field list may have an optional trailing separator,
as a convenience for machine-generated code.
-
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,
+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,
+Otherwise, the prefixexp "call" metamethod is called,
+having as first parameter the value of prefixexp,
followed by the original call arguments
-(see 2.8).
+(see §2.8).
+
+
+
+The form
-
The form
functioncall ::= prefixexp `:´ Name args
-
+
can be used to call "methods".
-A call v:name(...)
-is syntactic sugar for v.name(v,...),
+A call v:name(args)
+is syntactic sugar for v.name(v,args),
except that v is evaluated only once.
-
All argument expressions are evaluated before the call.
-A call of the form f{...} is syntactic sugar for f({...});
+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'...'
-(or f"..." or f[[...]]) is syntactic sugar for f('...');
+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.
+
+
+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)
-
+ 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 returnfunctioncall is called
+
+
+A call of the form returnfunctioncall is called
a tail call.
Lua implements proper tail calls
(or proper tail recursion):
-In a tail call,
+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.
@@ -993,60 +1267,77 @@ 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
+ 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
function ::= function funcbody
funcbody ::= `(´ [parlist1] `)´ block end
-
The following syntactic sugar simplifies function definitions:
+
+The following syntactic sugar simplifies function definitions:
+
stat ::= function funcname funcbody
stat ::= localfunction Name funcbody
funcname ::= Name {`.´ Name} [`:´ Name]
-
+
The statement
+
- function f () ... end
-
+ function f () body end
+
translates to
+
- f = function () ... end
-
+ f = function () body end
+
The statement
+
- function t.a.b.c.f () ... end
-
+ function t.a.b.c.f () body end
+
translates to
+
- t.a.b.c.f = function () ... end
-
+ t.a.b.c.f = function () body end
+
The statement
+
- local function f () ... end
-
+ local function f () body end
+
translates to
+
- local f; f = function () ... end
-
-not this:
+ local f; f = function () body end
+
+not to
+
- local f = function () ... end
-
+ 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,
+
+
+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.
@@ -1058,17 +1349,20 @@ Different instances of the same function
may refer to different external local variables
and may have different environment tables.
-
Parameters act as local variables that are
+
+
+Parameters act as local variables that are
initialized with the argument values:
+
- parlist1 ::= namelist [`,´ `...´] | `...´
-
+ parlist1 ::= 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.
+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,
@@ -1082,114 +1376,148 @@ If the expression is used as the last element of a list of expressions,
then no adjustment is made
(unless the call is enclosed in parentheses).
-
As an example, consider the following definitions:
+
+
+As an example, consider the following definitions:
+
- function f(a, b) end
- function g(a, b, ...) end
- function r() return 1,2,3 end
-
+ 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:
+
Results are returned using the return statement (see 2.4.4).
+
+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
+
+
+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 (...) ... end
-
+ function t.a.b.c:f (params) body end
+
is syntactic sugar for
+
- t.a.b.c.f = function (self, ...) ... end
+ t.a.b.c.f = function (self, params) body end
+
+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
+ 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) --> 10 (the global one)
+ print(x) --> 11
+ end
+ print(x) --> 10 (the global one)
-
Notice that, in a declaration like local x = x,
+
+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,
+
+
+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
+
+
+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
-
+ 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.
-
2.7 - Error Handling
-
Because Lua is an embedded extension language,
-all Lua actions start from C code in the host program
+
+
+
+
+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
+
+
+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.
-
+Every value in Lua may have a metatable.
This metatable is an ordinary Lua table
that defines the behavior of the original value
under certain special operations.
@@ -1200,29 +1528,38 @@ 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
+
+
+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
+
+
+You can query the metatable of any value
through the getmetatable function.
-
You can replace the metatable of tables
+
+
+You can replace the metatable of tables
through the setmetatable
function.
You cannot change the metatable of other types from Lua
(except using the debug library);
-you must use the C API for that.
+you must use the C API for that.
-
Tables and userdata have individual metatables
-(although multiple tables and userdata can share
-a same table as their metatable);
+
+
+Tables and userdata have individual metatables
+(although multiple tables and userdata can share their metatables);
values of all other types share one single metatable per type.
So, there is one single metatable for all numbers,
and for all strings, etc.
-
A metatable may control how an object behaves in arithmetic operations,
+
+
+A metatable may control how an object behaves in arithmetic operations,
order comparisons, concatenation, length operation, and indexing.
A metatable can also define a function to be called when a userdata
is garbage collected.
@@ -1230,342 +1567,415 @@ 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)
+If so, the value associated with that key (the metamethod)
controls how Lua will perform the operation.
-
Metatables control the operations listed next.
+
+
+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, `__´;
+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 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.
+are described in §5.1.
In particular, to retrieve the metamethod of a given object,
we use the expression
+
- metatable(obj)[event]
-
+ metatable(obj)[event]
+
This should be read as
+
- rawget(getmetatable(obj) or {}, event)
-
+ 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
+
+
+
+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
-
-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("...")
+ function getbinhandler (op1, op2, event)
+ return metatable(op1)[event] or metatable(op2)[event]
end
- end
- end
-
+
+By using this function,
+the behavior of the op1 + op2 is
-
"sub":
+
+ 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":
+Behavior similar to the "add" operation.
+
+
+
"mul":
the * operation.
-Behavior similar to the "add" operation.
-
"div":
+Behavior similar to the "add" operation.
+
+
+
"div":
the / operation.
-Behavior similar to the "add" operation.
-
"mod":
+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":
+
"pow":
the ^ (exponentiation) operation.
+
Behavior similar to the "add" operation,
-with the function pow (from the C math library)
+with the function pow (from the C math library)
as the primitive operation.
+
-
"unm":
+
"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":
+
+
+ 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":
+
+
+ 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":
+
+
+ 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("...");
+ 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
- end
- end
-
-a > b is equivalent to b < a.
+
+The "eq" event is defined as follows:
-
"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")
+ 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 not h(op2, op1)
+ return h(op1, op2)
else
- error("...");
+ return false
end
end
- end
- end
-
-a >= b is equivalent to b <= a.
+
+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).
+Lua tries the "lt", assuming that a <= b is
+equivalent to not (b < a).
+
-
"index":
+
"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":
+
+
+ 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
- return h(table, key,value) -- call the handler
- else h[key] = value -- or repeat operation on it
- end
- end
-
-
"call":
+
+
+ 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
+ return 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("...")
+ 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
- end
- end
-
+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.
-
Environments associated with userdata have no meaning for Lua.
-It is only a feature for programmers to associate a table to
+
+
+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
+
+
+Environments associated with threads are called
global environments.
-They are used as the default environment for threads and
+They are used as the default environment for their threads and
non-nested functions created by the thread
(through loadfile, loadstring or load)
-and can be directly accessed by C code (see 3.3).
+and can be directly accessed by C code (see §3.3).
-
Environments associated with C functions can be directly
-accessed by C code (see 3.3).
-They are used as the default environment for other C functions
+
+
+Environments associated with C functions can be directly
+accessed by C code (see §3.3).
+They are used as the default environment for other C functions
created by the function.
-
Environments associated with Lua functions are used to resolve
-all accesses to global variables within the function (see 2.3).
+
+
+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 other Lua functions
created by the function.
-
You can change the environment of a Lua function or the
+
+
+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.
+(userdata, C functions, other threads) you must
+use the C API.
-
+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.
@@ -1576,12 +1986,16 @@ to collect all dead objects
All objects in Lua are subject to automatic management:
tables, userdata, functions, threads, and strings.
-
Lua implements an incremental mark-and-sweep collector.
+
+
+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.
-
The garbage-collector pause
+
+
+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 1 mean the collector will not wait to
@@ -1589,100 +2003,131 @@ start a new cycle.
A value of 2 means that the collector waits for the total memory in use
to double before starting a new cycle.
-
The step multiplier
+
+
+The step multiplier
controls the relative speed of the collector relative to
memory allocation.
-Larger values make the collector more aggressive but also increases
+Larger values make the collector more aggressive but also increase
the size of each incremental step.
Values smaller than 1 make the collector too slow and
may result in the collector never finishing a cycle.
The default, 2, means that the collector runs at "twice"
the speed of memory allocation.
-
You can change these numbers by calling lua_gc in C
+
+
+You can change these numbers by calling lua_gc in C
or collectgarbage in Lua.
-Both get as arguments percentage points
-(so an argument 100 means a real value of 1).
+Both get percentage points as arguments
+(so an argument of 100 means a real value of 1).
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).
+
+
+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
+
+
+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
+ function gc_event (udata)
+ local h = metatable(udata).__gc
+ if h then
+ h(udata)
+ end
+ end
-
At the end of each garbage-collection cycle,
+
+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.
-
2.10.2 - Weak Tables
-
A weak table is a table whose elements are
+
+
+
+
+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 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 value of the
+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´,
+If the __mode field is a string containing the character 'k',
the keys in the table are weak.
-If __mode contains `v´,
+If __mode contains 'v',
the values in the table are weak.
-
After you use a table as a metatable,
+
+
+After you use a table as a metatable,
you should not change the value of its field __mode.
Otherwise, the weak behavior of the tables controlled by this
metatable is undefined.
-
+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.
+
+
+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,
+
+
+When you first call coroutine.resume,
passing as its first argument
the thread returned by coroutine.create,
the coroutine starts its execution,
@@ -1692,8 +2137,10 @@ 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
+
+
+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,
@@ -1701,7 +2148,9 @@ 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.
+
+
+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
@@ -1714,170 +2163,218 @@ it continues its execution from the point where it yielded,
with the call to coroutine.yield returning any extra
arguments passed to coroutine.resume.
-
The coroutine.wrap function creates a coroutine,
-just like coroutine.create,
+
+
+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,
+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;
+coroutine.wrap does not catch errors;
any error is propagated to the caller.
-
As an example,
-consider the next 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
-
-
3 - The Application Program Interface
+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
+
-
This section describes the C API for Lua, that is,
-the set of C functions available to the host program to communicate
+
+
+
+
+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.
+are declared in the header file lua.h.
-
Even when we use the term "function",
+
+
+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 its arguments exactly once
+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,
+
+
+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,
+with a proper definition for the macro luai_apicheck,
in file luaconf.h.
-
3.1 - The Stack
-
Lua uses a virtual stack to pass values to and from C.
+
+
+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,
+
+
+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
+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,
+
+
+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);
+(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
+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)
+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).
+if it lies between 1 and the stack top
+(that is, if 1 ≤ abs(index) ≤ top).
-
+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.
+
+
+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
+
+
+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:
+
+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
+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).
+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,
+
+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
+
+When a C function is created,
it is possible to associate some values with it,
-thus creating a C closure;
+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,
+
+
+Whenever a C function is called,
its upvalues are located at specific pseudo-indices.
These pseudo-indices are produced by the macro
-lua_upvalueindex.
+lua_upvalueindex.
The first value associated with a function is at position
lua_upvalueindex(1), and so on.
Any access to lua_upvalueindex(n),
@@ -1885,28 +2382,40 @@ where n is greater than the number of upvalues of the
current function,
produces an acceptable (but invalid) index.
-
3.5 - Registry
-
Lua provides a registry,
-a pre-defined table that can be used by any C code to
+
+
+
+
+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,
+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.
+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,
+
+
+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.
-
3.6 - Error Handling in C
-
Internally, Lua uses the C longjmp facility to handle errors.
+
+
+
+
+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.)
+see file luaconf.h.)
When Lua faces any error
(such as memory allocation errors, type errors, syntax errors,
and runtime errors)
@@ -1916,7 +2425,9 @@ A protected environment uses setjmp
to set a recover point;
any error jumps to the most recent active recover point.
-
Almost any function in the API may raise an error,
+
+
+Almost any function in the API may raise an error,
for instance due to a memory allocation error.
The following functions run in protected mode
(that is, they create a protected environment to run),
@@ -1924,25 +2435,30 @@ so they never raise an error:
lua_newstate, lua_close, lua_load,
lua_pcall, and lua_cpcall.
-
Inside a C function you can raise an error by calling lua_error.
-
3.7 - Functions and Types
+
+Inside a C function you can raise an error by calling lua_error.
-
Here we list all functions and types from the C API in
+
+
+
+
+
+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.
@@ -1962,53 +2478,67 @@ 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.
+osize >= nsize.
+
+
+
+Here is a simple implementation for the allocator function.
+It is used in the auxiliary library by luaL_newstate.
-
Here is a simple implementation for the allocator function.
-It is used in the auxiliary library by lua_newstate.
-static void *l_alloc (void *ud, void *ptr, size_t osize, size_t nsize) {
- (void)ud; /* not used */
- (void)osize; /* not used */
- if (nsize == 0) {
- free(ptr); /* ANSI requires that free(NULL) has no effect */
- return NULL;
- }
- else
- /* ANSI requires that realloc(NULL, size) == malloc(size) */
- return realloc(ptr, nsize);
-}
-
+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 may 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
-
- void lua_call (lua_State *L, int nargs, int nresults);
-
+
+The panic function can access the error message at the top of the stack.
-
Calls a function.
-
To call a function you must use the following protocol:
-First, the function to be called is pushed onto the stack;
+
+
+
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.
@@ -2018,103 +2548,116 @@ 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.
+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
+
+
+Any error inside the called function is propagated upwards
(with a longjmp).
-
The following example shows how the host program may do the
+
+
+The following example shows how the host program may do the
equivalent to this Lua code:
+
- a = f("how", t.x, 14)
-
-Here it is in C:
+ 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 function with 3 arguments and 1 result */
- lua_setfield(L, LUA_GLOBALSINDEX, "a"); /* set global variable `a' */
-
+ 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,
+
+
+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
+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.
+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,
+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
+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
+
+
+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 to function `average'");
- lua_error(L);
- }
- sum += lua_tonumber(L, i);
+ 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);
}
- lua_pushnumber(L, sum/n); /* first result */
- lua_pushnumber(L, sum); /* second result */
- return 2; /* number of results */
+ sum += lua_tonumber(L, i);
}
-
-
-
-
lua_checkstack
-
- int lua_checkstack (lua_State *L, int extra);
+ lua_pushnumber(L, sum/n); /* first result */
+ lua_pushnumber(L, sum); /* second result */
+ return 2; /* number of results */
+ }
-
Ensures that there are at least extra free stack slots in the stack.
+
+
+
+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.
-
+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,
@@ -2124,29 +2667,31 @@ 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
-
- void lua_concat (lua_State *L, int n);
-
-
Concatenates the n values at the top of the stack,
+
+
+
+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 string on the stack
+If n is 1, the result is the single string on the stack
(that is, the function does nothing);
if n is 0, the result is the empty string.
Concatenation is done following the usual semantics of Lua
-(see 2.5.4).
-
-
-
lua_cpcall
-
- int lua_cpcall (lua_State *L, lua_CFunction func, void *ud);
-
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,
@@ -2155,28 +2700,30 @@ 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
-
- void lua_createtable (lua_State *L, int narr, int nrec);
-
-
Creates a new empty table and pushes it onto the stack.
+
+
+
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
-
- int lua_dump (lua_State *L, lua_Writer writer, void *data);
-
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,
@@ -2186,347 +2733,443 @@ As it produces parts of the chunk,
with the given data
to write them.
-
The value returned is the error code returned by the last
+
+
+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
-
- int lua_equal (lua_State *L, int index1, int index2);
-
+0 means no errors.
-
Returns 1 if the two values in acceptable indices index1 and
+
+This function does not pop the Lua function from the stack.
+
+
+
+
+
+
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
-
- int lua_error (lua_State *L);
-
+Otherwise returns 0.
+Also returns 0 if any of the indices is non valid.
-
+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
-
- int lua_gc (lua_State *L, int what, int data);
-
+This function performs several tasks,
according to the value of the parameter what:
+
-
LUA_GCSTOP--- stops the garbage collector.
-
LUA_GCRESTART--- restarts the garbage collector.
-
LUA_GCCOLLECT--- performs a full garbage-collection cycle.
-
LUA_GCCOUNT--- returns the current
-amount of memory (in Kbytes) in use by Lua.
-
LUA_GCCOUNTB--- returns the remainder of
-dividing the current amount of bytes of memory in use by Lua
-by 1024.
-
LUA_GCSTEP--- performs an incremental step of
-garbage collection.
+
+
LUA_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 tune experimentally the value of data.
+you must experimentally tune the value of data.
The function returns 1 if the step finished a
garbage-collection cycle.
-
LUA_GCSETPAUSE---
+
+
+
LUA_GCSETPAUSE:
sets data/100 as the new value
-for the pause of the collector (see 2.10).
+for the pause of the collector (see §2.10).
The function returns the previous value of the pause.
-
LUA_GCSETSTEPMUL---
-sets arg/100 as the new value for the step multiplier of
-the collector (see 2.10).
+
+
+
LUA_GCSETSTEPMUL:
+sets data/100 as the new value for the step multiplier of
+the collector (see §2.10).
The function returns the previous value of the step multiplier.
+
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 index.
As in Lua, this function may trigger a metamethod
-for the "index" event (see 2.8).
-
-
+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
-
- void lua_gettable (lua_State *L, int index);
-
+the function returns 0 and pushes nothing on the stack.
-
+Pushes onto the stack the value t[k],
where t is the value at the given valid index index
and k is the value at the top of the stack.
-
This function pops the key from 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).
-
-
+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
-
- void lua_insert (lua_State *L, int index);
-
+(and so 0 means an empty stack).
-
Moves the top element into the given valid 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 integral type the machine handles
+
+
+Returns 1 if the 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.
+
+
+
+
+
+
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
+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.
-
-
+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.
+
+
0: no errors;
+
+
LUA_ERRSYNTAX:
+syntax error during pre-compilation;
lua_load automatically detects whether the chunk is text or binary,
+
+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).
-
lua_load uses a user-supplied reader function to read the chunk
-(see lua_Reader).
+
+
+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).
-
+Creates a new, independent state.
Returns NULL if cannot create the state
(due to lack of memory).
The argument f is the allocator function;
@@ -2534,125 +3177,148 @@ 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
-
- void lua_newtable (lua_State *L);
-
-
Creates a new empty table and pushes it onto the stack.
-Equivalent to lua_createtable(L, 0, 0).
-
-
+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.
+
+
+There is no explicit function to close or to destroy a thread.
Threads are subject to garbage collection,
like any Lua object.
-
+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 represents C values in Lua.
+
+
+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,
+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,
+
+
+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.
-
+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:
+
+
+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) {
- /* `key' is 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)));
- lua_pop(L, 1); /* removes `value'; keeps `key' for next iteration */
- }
+ /* 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,
+
+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_tolstringchanges
the value at the given index;
this confuses the next call to lua_next.
-
+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 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
-
- lua_pcall (lua_State *L, int nargs, int nresults, int errfunc);
-
+for other values, it is 0.
-
Calls a function in protected mode.
-
Both nargs and nresults have the same meaning as
+
+
+
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.
@@ -2664,7 +3330,9 @@ Like lua_call,
lua_pcall always removes the function
and its arguments from the stack.
-
If errfunc is 0,
+
+
+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
@@ -2674,173 +3342,214 @@ 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
+
+
+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
+
+
+The lua_pcall function returns 0 in case of success
or one of the following error codes
(defined in lua.h):
+
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);
+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,
+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,
+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.
-
+Pushes a C function onto the stack.
This function receives a pointer to a C function
-and pushes on the stack a Lua value of type function that,
-when called, invokes the corresponding 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
+
+
+Any function to be registered in Lua must
follow the correct protocol to receive its parameters
and return its results (see lua_CFunction).
-
The call lua_pushcfunction(L, f) is equivalent to
-lua_pushcclosure(L, f, 0).
-
+Pushes onto the stack a formatted string
and returns a pointer to this string.
-It is similar to the C function sprintf,
+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
+
+
+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.
+
+
+
+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).
+'%%' (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).
+
+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 metatables,
-it is not collected (as it was never created).
+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.
-
-
+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.
-
+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
@@ -2848,105 +3557,119 @@ the function returns.
The string cannot contain embedded zeros;
it is assumed to end at the first zero.
-
-
lua_pushthread
-
- void lua_pushthread (lua_State *L);
-
-
Pushes the thread represented by L onto the stack.
-
-
-
lua_pushvalue
-
- void lua_pushvalue (lua_State *L, int index);
-
-
Pushes a copy of the element at the given valid index
+
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
-
- void lua_rawget (lua_State *L, int index);
-
+Otherwise returns 0.
+Also returns 0 if any of the indices are non valid.
-
Similar to lua_gettable, but does a raw access
+
+
+
+
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 index.
The access is raw;
that is, it does not invoke metamethods.
-
-
lua_rawset
-
- void lua_rawset (lua_State *L, int index);
-
-
Similar to lua_settable, but does a raw assignment
+
+
+
+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.
@@ -2957,54 +3680,63 @@ The block must exist until the reader function is called again.
To signal the end of the chunk, the reader must return NULL.
The reader function may return pieces of any size greater than zero.
-
+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
-
- void lua_replace (lua_State *L, int index);
-
-
Moves the top element into the given position (and pops it),
+
+
+
+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 on its stack the main function plus any eventual arguments;
+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.
@@ -3023,137 +3755,155 @@ To restart a coroutine, you put on its stack only the values to
be passed as results from yield,
and then call lua_resume.
-
+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.
-
+Does the equivalent to t[k] = v,
where t is the value at the given valid index 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.
+
+
+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).
-
-
+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;
-
+If index is 0, then all stack elements are removed.
-
Opaque structure that keeps the whole state of a Lua interpreter.
+
+
+
+
+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
+
+
+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.
-
+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.
-
-
+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;
@@ -3162,42 +3912,46 @@ 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
-
- 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;
+
+
+
lua_Integer lua_tointeger (lua_State *L, int idx);
+
+
+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.
+(see §2.2.1);
+otherwise, lua_tointeger returns 0.
-
If the number is not an integer,
+
+
+If the number is not an integer,
it is truncated in some non-specified way.
-
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;
@@ -3208,86 +3962,96 @@ then lua_tolstring also
(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),
+This string always has a zero ('\0')
+after its last character (as in C),
but may 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
-
- lua_Number lua_tonumber (lua_State *L, int index);
-
-
Converts the Lua value at the given acceptable index
-to a number (see lua_Number).
+
+
+
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
-
- const void *lua_topointer (lua_State *L, int index);
-
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 may be a userdata, a table, a thread, or a function;
otherwise, lua_topointer returns NULL.
-Lua ensures that different objects return different pointers.
-There is no direct way to convert the pointer back to its original value.
-
-
Typically this function is used only for debug information.
-
-
-
lua_tostring
-
- const char *lua_tostring (lua_State *L, int index);
-
+Different objects will give different pointers.
+There is no way to convert the pointer back to its original value.
-
Equivalent to lua_tolstring with len equal to NULL.
-
-
-
lua_tothread
-
- lua_State *lua_tothread (lua_State *L, int index);
-
+
+Typically this function is used only for debug information.
-
Converts the value at the given acceptable index to a Lua thread
+
+
+
+
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
-
- void *lua_touserdata (lua_State *L, int index);
-
-
If the value at the given acceptable index is a full userdata,
+
+
+
+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
-
- int lua_type (lua_State *L, int index);
-
-
Returns the type of the value in the given acceptable 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
@@ -3303,230 +4067,301 @@ defined in lua.h:
and
LUA_TLIGHTUSERDATA.
-
-
lua_typename
-
- const char *lua_typename (lua_State *L, int tp);
-
-
Returns the name of the type encoded by the value tp,
+
+
+
+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;
+
+
+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,
+
+
+This function should only be called as the
+return expression of a C function, as follows:
+
- 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,
+ 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.
-
-
3.8 - The Debug Interface
-
Lua has no built-in debugging facilities.
+
+
+
+
+
+
+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 */
- ...
- } 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:
+
+
+The fields of lua_Debug have the following meaning:
+
-
source ---
+
+
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.
+then source starts with a '@' followed by the file name.
+
-
short_src ---
+
short_src:
a "printable" version of source, to be used in error messages.
+
-
linedefined ---
+
linedefined:
the line number where the definition of the function starts.
+
-
lastlinedefined ---
+
lastlinedefined:
the line number where the definition of the function ends.
+
-
what ---
+
what:
the string "Lua" if the function is a Lua function,
-"C" if it is a C 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 ---
+
currentline:
the current line where the given function is executing.
When no line information is available,
-currentline is set to -1.
+currentline is set to -1.
+
-
name ---
+
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 may be the value of multiple global variables,
+some functions may be the value of multiple global variables,
while others may 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 ---
+
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.)
+
Fills the fields of lua_Debug with useful information.
-
This function returns 0 on error
-(for instance, an invalid option in what).
-Each character in the string what
-selects some fields of the structure ar to be filled,
-as indicated by the letter in parentheses in the definition of lua_Debug:
-`S´ fills in the fields source, linedefined,
-lastlinedefined,
-and what;
-`l´ fills in the field currentline, etc.
-Moreover, `f´ pushes onto the stack the function that is
-running at the given level.
+
To get information about a function that is not active
-(that is, not in the stack),
-you push it onto the stack
-and start the what string with the character `>´.
+
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);
+ 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).
-
Gets information about a local variable of a given activation record.
+
+
+
+
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).
@@ -3536,40 +4371,48 @@ 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)
+
+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
-
- 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
+
+
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,
+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
-
- const char *lua_getupvalue (lua_State *L, int funcindex, int n);
-
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.)
@@ -3581,26 +4424,31 @@ and returns its name.
as they are active through the whole function.
So, they are numbered in an arbitrary order.)
-
Returns NULL (and pushes nothing)
+
+
+Returns NULL (and pushes nothing)
when the index is greater than the number of upvalues.
-For C functions, this function uses the empty string ""
+For C functions, this function uses the empty string ""
as a name for all upvalues.
-
+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.
+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.
@@ -3610,86 +4458,114 @@ 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.
+
+
+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
-
- int lua_sethook (lua_State *L, lua_Hook func, int mask, int count);
-
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.
+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 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 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
+
+
+
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
+
+
+
The count hook: is called after the interpreter executes every
count instructions.
(This event only happens while Lua is executing a Lua function.)
+
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)
+
+
+Returns NULL (and pops nothing)
when the index is greater than
the number of active local variables.
-
-
lua_setupvalue
-
- const char *lua_setupvalue (lua_State *L, int funcindex, int n);
-
-
Sets the value of a closure's upvalue.
-Parameters funcindex and n are as in lua_getupvalue
-(see lua_getupvalue).
+
+
+
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)
+
+
+Returns NULL (and pops nothing)
when the index is greater than the number of upvalues.
-
+
The auxiliary library provides several convenient functions
to interface C with Lua.
While the basic API provides the primitive functions for all
@@ -3697,137 +4573,175 @@ interactions between C and Lua,
the auxiliary library provides higher-level functions for some
common tasks.
-
All functions from the auxiliary library
+
+
+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
+
+
+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.
+
+
+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 raise an error if the check is not satisfied.
Because the error message is formatted for arguments
-(e.g., "bad argument #1"),
+(e.g., "bad argument #1"),
you should not use these functions for other stack values.
-
4.1 - Functions and Types
-
Here we list all functions and types from the auxiliary library
+
+
+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)
+
+
+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.
-
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:
+
- void luaL_argcheck (lua_State *L, int cond, int numarg,
- const char *extramsg);
+ bad argument #<narg> to <func> (<extramsg>)
-
Checks whether cond is true.
-If not, raises an error with message
-"bad argument #<numarg> to <func> (<extramsg>)",
-where func is retrieved from the call stack.
-
+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
+
+
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).
+
+
+
+You finish by calling luaL_pushresult(&b).
This call leaves the final string on the top of the stack.
+
+
-
During its normal operation,
+
+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.
@@ -3842,168 +4756,224 @@ After calling luaL_pushresult the st
level when the buffer was initialized,
plus the final string on its top.
-
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 on the
+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).
-
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).
-If def is not NULL,
-uses def as a default value when
-the function has no argument narg or if this argument is nil.
-
-
Returns the index in the array where the string was found.
+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.
-
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.
-
+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.
-
Grows the stack size to top + sz elements,
+
+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.)
+
+
+
+
+
+
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
-
- const char *luaL_checkstring (lua_State *L, int narg);
-
-
Checks whether the function argument narg is a string
+
+
+
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.
@@ -4011,298 +4981,361 @@ 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 as return luaL_error ...
-in C functions.
-
-
luaL_getmetafield
-
- int luaL_getmetafield (lua_State *L, int obj, const char *e);
-
+
+This function never returns,
+but it is an idiom to use it in C functions
+as return luaL_error(args).
-
Pushes on the stack the field e from the metatable
+
+
+
+
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.
-
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
+
+
+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.
-
-
luaL_loadstring
-
- int luaL_loadstring (lua_State *L, const char *s);
-
+
+
+As lua_load, this function only loads the chunk;
+it does not run it.
-
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 on the stack the final value associated
+
+
+In both cases pushes onto the stack the final value associated
with tname in the registry.
-
-
luaL_newstate
-
- lua_State *luaL_newstate (void);
-
-
Creates a new Lua state, calling lua_newstate with an
-allocation function based on the standard C realloc function
-and setting a panic function (see lua_atpanic) that prints
+
+
+
+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,
+
+
+Returns the new state,
or NULL if there is a memory allocation error.
-
-
luaL_openlibs
-
- void luaL_openlibs (lua_State *L);
-
-
Opens all standard Lua libraries into the given state.
-
-
-
luaL_optint
-
- 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
-
- lua_Integer luaL_optinteger (lua_State *L, int narg, lua_Integer d);
-
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
-
- long luaL_optlong (lua_State *L, int narg, long d);
-
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.
-
+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
-
- void luaL_pushresult (luaL_Buffer *B);
-
-
Finishes the use of buffer B leaving the final string on
+
+
+
+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.
+
+
+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
+
+
+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.
-
+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.
-
+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,
-creates a new table t,
+
+
+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.
@@ -4310,70 +5343,91 @@ 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
+
+
+In any case the function leaves the table
on the top of the stack.
-
Releases reference ref from the table at index t
+
+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
-
- void luaL_where (lua_State *L, int lvl);
-
-
-
-
Pushes on the stack a string identifying the current position
-of the control at level lvl in the call stack.
-Typically this string has the 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.
+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.
+
+
+
+
+
+
+
+
+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);
@@ -4381,79 +5435,127 @@ 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., sort).
-
All libraries are implemented through the official C API
-and are provided as separate C modules.
+
+
+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;
-
package library;
-
string manipulation;
-
table manipulation;
-
mathematical functions (sin, log, etc.);
-
input and output;
-
operating system facilities;
-
debug facilities.
-
+
+
basic 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 must call
-luaL_openlibs,
-which open all standard libraries.
+
+
+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 and the Operating System libraries),
-and luaopen_debug (for the debug library).
-These functions are declared in lualib.h
+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 and the Operating System libraries),
+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.
+you must call them like any other Lua C function,
+e.g., by using lua_call.
-
5.1 - Basic Functions
-
The basic library provides some core functions to Lua.
+
+
+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.
-
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.
+
+
+
+This function is a generic interface to the garbage collector.
It performs different functions according to its first argument, opt:
+
-
"stop" --- stops the garbage collector.
-
"restart" --- restarts the garbage collector.
-
"collect" --- performs a full garbage-collection cycle.
-
"count" --- returns the total memory in use by Lua (in Kbytes).
-
"step" --- performs a garbage-collection step.
+
+
"stop":
+stops the garbage collector.
+
+
+
"restart":
+restarts the garbage collector.
+
+
+
"collect":
+performs a full garbage-collection cycle.
+
+
+
"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 tune experimentally the value of arg.
+you must experimentally tune the value of arg.
Returns true if the step finished a collection cycle.
-
"steppause" ---
+
+
+
"setpause":
sets arg/100 as the new value for the pause of
-the collector (see 2.10).
-
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).
@@ -4461,22 +5563,32 @@ 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).
-
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
+
+
+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
+With level 1 (the default), the error position is where the
error function was called.
-Level 2 points the error to where the function
+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
+Passing a level 0 avoids the addition of error position information
to the message.
-
A global variable (not a function) that
holds the global environment (that is, _G._G = _G).
Lua itself does not use this variable;
@@ -4484,71 +5596,116 @@ changing its value does not affect any environment,
nor vice-versa.
(Use setfenv to change environments.)
-
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.
+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.
+
+
+
+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,
+
+
+
+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 nil (or no value) signals the end of the chunk.
-
If there are no errors,
+
+
+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
+
+
+chunkname is used as the chunk name for error messages
and debug information.
-
+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
@@ -4563,37 +5720,53 @@ 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.
-
Lua has no declaration of fields.
-There is no difference between a
-field not present in a table or a field with value nil.
-Therefore, next only considers fields with non-nil values.
+
+
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,
+
+
+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,
+
+
+
+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),
@@ -4602,7 +5775,11 @@ 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.
-
Receives any number of arguments,
and prints their values to stdout,
using the tostring function to convert them to strings.
@@ -4611,114 +5788,185 @@ but only as a quick way to show a value,
typically for debugging.
For formatted output, use string.format.
-
Gets the real value of table[index],
without invoking any metamethod.
-table must be a table and
-index any value different from nil.
+table must be a table;
+index may be any 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.
-
+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.
+
+
+
+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.
+Level 1 is the function calling setfenv.
setfenv returns the given function.
-
As a special case, when f is 0 setfenv changes
+
+
+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.)
+
+
+
+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.
-
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.
+
+
+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 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 may have a decimal part,
-as well as an optional exponent part (see 2.1).
+as well as an optional exponent part (see §2.1).
In other bases, only unsigned integers are accepted.
-
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,
+
+
+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.
-
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".
+"nil" (a string, not the value nil),
+"number",
+"string",
+"boolean",
+"table",
+"function",
+"thread",
+and "userdata".
-
Returns the elements from the given table.
This function is equivalent to
+
- return list[i], list[i+1], ..., list[j]
-
+ 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).
+By default, i is 1 and j is the length of the list,
+as defined by the length operator (see §2.5.5).
-
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".
+The current contents of this variable is "Lua 5.1".
-
+This function is similar to pcall,
except that you can set a new error handler.
-
xpcall calls function f in protected mode,
+
+
+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,
@@ -4731,46 +5979,77 @@ after this first result.
In case of any error,
xpcall returns false plus the result from err.
-
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.
-
+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.
+
+
+
+Starts or continues the execution of coroutine co.
The first time you resume a coroutine,
it starts running its body.
-The values val1, ..., valn are passed
+The values val1, ··· are passed
as the arguments to the body function.
If the coroutine has yielded,
resume restarts it;
-the values val1, ..., valn are passed
+the values val1, ··· are passed
as the results from the yield.
-
If the coroutine runs without any errors,
+
+
+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.
-
+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,
@@ -4780,9 +6059,15 @@ or if it has not started running yet;
and "dead" if the coroutine has finished its body function,
or if it has stopped with an error.
-
+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
@@ -4791,24 +6076,41 @@ Returns the same values returned by resume,
except the first boolean.
In case of error, propagates the error.
-
coroutine.yield ([val1, ..., valn])
-
Suspends the execution of the calling coroutine.
-The coroutine cannot be running a C function,
+
+
+
+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.
-
+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.
+Everything else is exported in a table package.
-
+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,
@@ -4824,7 +6126,9 @@ 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
+
+
+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.
@@ -4832,36 +6136,48 @@ 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 may receive optional options after
+
+
+This function may 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 table package.loaded
+
+
+
+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,
+
+
+To find a loader,
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.
+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 below).
-
When loading a C library,
+
+
+When loading a C library,
require first uses a dynamic link facility to link the
application with the library.
-Then it tries to find a C function inside this library to
+Then it tries to find a C function inside this library to
be used as the loader.
-The name of this C function is the string "luaopen_"
+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,
@@ -4869,234 +6185,344 @@ 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.
-
If require finds neither a Lua library nor a
-C library for a module,
+
+
+If require finds neither a Lua library nor a
+C library for a module,
it calls the all-in-one loader.
-This loader searches the C path for a library for
+This loader 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.
+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
+With this facility, a package can pack several C submodules
into one single library,
with each submodule keeping its original open function.
-
Once a loader is found,
+
+
+Once a loader is found,
require calls the loader with a single argument, modname.
If the loader returns any value,
-require assigns it to package.loaded[modname].
+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,
+
+
+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
+
+
+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
+using the environment variable LUA_CPATH
(plus another default path defined in luaconf.h).
-
+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.loadlib (libname, funcname)
-
Dynamically links the host program with the C library libname.
+
+
+
+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.
+and returns this function as a C function.
(So, funcname must follow the protocol (see lua_CFunction)).
-
This is a low-level function.
+
+
+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,
+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).
+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.
+
+
+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
+
+
+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
+Any ";;" in the value of the environment variable
is replaced by the default path.
-
A path is a sequence of templates separated by semicolons.
+
+
+A path is a sequence of templates separated by semicolons.
For each template, require will change each interrogation
mark in the template by filename,
which is modname with each dot replaced by a
-"directory separator" (such as "/" in Unix);
+"directory separator" (such as "/" in Unix);
then it will try to load the resulting file name.
So, for instance, if the Lua path is
+
- "./?.lua;./?.lc;/usr/local/?/init.lua"
-
+ "./?.lua;./?.lc;/usr/local/?/init.lua"
+
the search for a Lua loader for module foo
will try to load the files
./foo.lua, ./foo.lc, and
/usr/local/foo/init.lua, in that order.
-
package.preload
-
A table to store loaders for specific modules
+
+
+
+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.
-
5.4 - String Manipulation
-
This library provides generic functions for 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).
+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.
+Thus, the last character is at position -1, and so on.
-
The string library provides all its functions inside the table
-string.
+
+
+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 metatable itself.
+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).
-
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.
+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 (i1, i2, ...)
-Receives 0 or more integers.
+
+Note that numerical codes are not necessarily portable across platforms.
+
+
+
+
+
+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)
+
+Note that numerical codes are not necessarily portable across platforms.
-
Returns a string containing a binary representation of the given 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.
-
Looks for the first match of
pattern in the string s.
-If it finds a match, then find returns the indices of 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 may be negative.
+its default value is 1 and may 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,
+
+
+If the pattern has captures,
then in a successful match
the captured values are also returned,
after the two indices.
-
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.
+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,
+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')
-
+ string.format('%q', 'a string with "quotes" and \n new line')
+
will produce the string:
+
-"a string with \"quotes\" and \
- new line"
+ "a string with \"quotes\" and \
+ new line"
-
The options c, d, E, e, f,
+
+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.
-
string.gmatch (s, pattern)
+
+This function does not accept string values
+containing embedded zeros,
+except as arguments to the q option.
+
+
+
+
+
Returns an iterator function that,
each time it is called,
returns the next captures from pattern over string s.
-
-
If pattern specifies no captures,
+If pattern specifies no captures,
then the whole match is produced in each call.
-
As an example, the following loop
+
+
+As an example, the following loop
+
- s = "hello world from Lua"
- for w in string.gmatch(s, "%a+") do
- print(w)
- end
-
+ 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
+ t = {}
+ s = "from=world, to=Lua"
+ for k, v in string.gmatch(s, "(%w+)=(%w+)") do
+ t[k] = v
+ end
-
string.gsub (s, pattern, repl [, n])
+
+For this function, a '^' at the start of a pattern does not
+work as an anchor, as this would prevent the iteration.
+
+
+
+
+
Returns a copy of s
in which all occurrences of the pattern have been
replaced by a replacement string specified by repl,
@@ -5104,74 +6530,98 @@ which may be a string, a table, or a function.
gsub also returns, as its second value,
the total number of substitutions made.
-
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,
+
+
+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 %.
+The sequence %% stands for a single %.
-
If repl is a table, then the table is queried for every match,
+
+
+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
+
+
+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
+
+
+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).
-
The optional last parameter n limits
+
+
+The optional last parameter n limits
the maximum number of substitutions to occur.
For instance, when n is 1 only the first occurrence of
pattern is replaced.
-
Here are some examples:
+
+
+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"
+ 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", "%$(%w+)", t)
+ --> x="lua-5.1.tar.gz"
Receives a string and returns a copy of this string with all
uppercase letters changed to lowercase.
All other characters are left unchanged.
The definition of what an uppercase letter is depends on the current locale.
-
Looks for the first match of
pattern in the string s.
If it finds one, then match returns
@@ -5181,20 +6631,32 @@ If pattern specifies no captures,
then the whole match is returned.
A third, optional numerical argument init specifies
where to start the search;
-its default value is 1 and may be negative.
+its default value is 1 and may be negative.
-
Returns the substring of s that
starts at i and continues until j;
i and j may be negative.
-If j is absent, then it is assumed to be equal to -1
+If j is absent, then it is assumed to be equal to -1
(which is the same as the string length).
In particular,
the call string.sub(s,1,j) returns a prefix of s
@@ -5202,44 +6664,68 @@ with length j,
and string.sub(s, -i) returns a suffix of s
with length i.
-
Receives a string and returns a copy of this string with all
lowercase letters changed to uppercase.
All other characters are left unchanged.
The definition of what a lowercase letter is depends on the current locale.
-
A character class is used to represent a set of characters.
The following combinations are allowed in describing a character class:
+
-
x (where x is not one of the magic characters
+
+
x:
+(where x is not one of the magic characters^$()%.[]*+-?)
---- 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 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 `%´
+can be preceded by a '%'
when used to represent itself in a pattern.
+
-
[set] ---
+
[set]:
represents the class which is the union of all
characters in set.
A range of characters may be specified by
-separating the end characters of the range with a `-´.
+separating the end characters of the range with a '-'.
All classes %x described above may also be used as
components in set.
All other characters in set represent themselves.
@@ -5247,71 +6733,105 @@ 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 lowercase letters plus the '-' character.
-
The interaction between ranges and classes is not defined.
+
+
+The interaction between ranges and classes is not defined.
Therefore, patterns like [%a-z] or [a-%%]
have no meaning.
+
-
[^set] ---
+
[^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
+
+
+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 may be
+
-
+
+
a single character class,
which matches any single character in the class;
-
-a single character class followed by `*´,
+
+
+
+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 `+´,
+
+
+
+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 `-´,
+
+
+
+a single character class followed by '-',
which also matches 0 or more repetitions of characters in the class.
-Unlike `*´,
+Unlike '*',
these repetition items will always match the shortest possible sequence;
-
-a single character class followed by `?´,
+
+
+
+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;
+
+
+
+%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,
+
+
+
+%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
+A '^' at the beginning of a pattern anchors the match at the
beginning of the subject string.
-A `$´ at the end of a pattern anchors the match at the
+A '$' at the end of a pattern anchors the match at the
end of the subject string.
At other positions,
-`^´ and `$´ have no special meaning and represent themselves.
+'^' and '$' have no special meaning and represent themselves.
-
+
+
+
+
+
Captures:
A pattern may contain sub-patterns enclosed in parentheses;
they describe captures.
When a match succeeds, the substrings of the subject string
@@ -5319,52 +6839,89 @@ 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.
+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
+
+
+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.
+string "flaaap", there will be two captures: 3 and 5.
-
A pattern cannot contain embedded zeros. Use %z instead.
-
This library provides generic functions for table manipulation.
-It provides all its functions inside the table table.
+It provides all its functions inside the table table.
-
Most functions in the table library assume that the 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.
-
+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,
+
+
+
+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),
+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,
+
+
+
+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,
+
+
+
+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,
@@ -5372,7 +6929,11 @@ where n is the length of the table,
so that a call table.remove(t) removes the last element
of table t.
-
Sorts table elements in a given order, in-place,
from table[1] to table[n],
where n is the length of the table.
@@ -5382,220 +6943,612 @@ 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.
+then the standard Lua operator < is used instead.
-
The sort algorithm is not stable;
+
+
+The sort algorithm is not stable;
that is, elements considered equal by the given order
may have their relative positions changed by the sort.
-
5.6 - Mathematical Functions
-
This library is an interface to the standard C math library.
-It provides all its functions inside the table math.
-The library provides the following functions:
-
-
-
-
-
-
-
-
-
-plus a variable math.pi and
-a variable math.huge,
-with the value HUGE_VAL.
-Most of these functions
-are only interfaces to the corresponding functions in the C library.
-All trigonometric functions work in radians.
-The functions math.deg and math.rad convert
-between radians and degrees.
-
The function math.max returns the maximum
-value of its numeric arguments.
-Similarly, math.min computes the minimum.
-Both can be used with 1, 2, or more arguments.
-
The function math.modf corresponds to the modf C function.
-It returns two values:
-The integral part and the fractional part of its argument.
-The function math.frexp also returns 2 values:
-The normalized fraction and the exponent of its argument.
-
The functions math.random and math.randomseed
-are interfaces to the simple random generator functions
-rand and srand that are provided by ANSI C.
-(No guarantees can be given for their statistical properties.)
+
+
+
+Returns the arc tangent of x/y (in radians),
+but uses the signs of both parameters to find the
+quadrant of the result.
+(It also handles correctly the case of y being zero.)
+
+
+
+
+
+This function is an interface to the simple
+pseudo-random generator function rand provided by ANSI C.
+(No guarantees can be given for its statistical properties.)
+
+
+
When called without arguments,
-math.random returns a pseudo-random real number
+returns a pseudo-random real number
in the range [0,1).
-When called with a number n,
+When called with a number m,
math.random returns
-a pseudo-random integer in the range [1,n].
-When called with two arguments,
-l and u,
+a pseudo-random integer in the range [1, m].
+When called with two numbers m and n,
math.random returns a pseudo-random
-integer in the range [l,u].
-The math.randomseed function sets a "seed"
+integer in the range [m, n].
+
+
+
+
+
+Sets x as the "seed"
for the pseudo-random generator:
-Equal seeds produce equal sequences of numbers.
+equal seeds produce equal sequences of numbers.
-
5.7 - Input and Output Facilities
-
The I/O library provides two different styles for file manipulation.
+
+
+
+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 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.
-
Unless otherwise stated,
+
+The table io also provides
+three predefined file descriptors with their usual meanings from C:
+io.stdin, io.stdout, and io.stderr.
+
+
+
+Unless otherwise stated,
all I/O functions return nil on failure
-(plus an error message as a second result)
+(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.
-
+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,
+
+
+In case of errors this function raises the error,
instead of returning an error code.
-
+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 ... end
-
+ 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() (without a file name) is equivalent
+
+
+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.
-
+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:
+
+
+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 may also have a `b´ at the end,
+
"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 may 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.
+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
+
+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
+
+
+This function is system dependent and is not available
on all platforms.
-
+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.
-
+Closes file.
Note that files are automatically closed when
their handles are garbage collected,
but that takes an unpredictable amount of time to happen.
-
+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,
@@ -5604,39 +7557,63 @@ When called without formats,
it uses a default format that reads the entire next line
(see below).
-
The available formats are
+
+
+The available formats are
+
-
"*n" reads a number;
+
+
"*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.
+
+
+
"*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),
+
+
+
"*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,
+
+
+
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.
+
+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;
-
+
"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",
+
+
+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;
@@ -5645,114 +7622,202 @@ 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.
-
+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.
-
5.8 - Operating System Facilities
-
This library is implemented through table os.
-
os.clock ()
-
Returns an approximation of the amount in seconds of CPU time
+
+
+
+
+Returns a string or a table containing date and time,
formatted according to the given string format.
-
If the time argument is present,
+
+
+If the time argument is present,
this is the time to be formatted
(see the os.time function for a description of this value).
Otherwise, date formats the current time.
-
If format starts with `!´,
+
+
+If format starts with '!',
then the date is formatted in Coordinated Universal Time.
After this optional character,
-if format is *t,
+if format is the string "*t",
then date returns a table with the following fields:
year (four digits), month (1--12), day (1--31),
hour (0--23), min (0--59), sec (0--61),
-wday (weekday, Sunday is 1),
+wday (weekday, Sunday is 1),
yday (day of the year),
and isdst (daylight saving flag, a boolean).
-
If format is not *t,
-then date returns the date as a string,
-formatted according to the same rules as the C function strftime.
-
When called without arguments,
+
+If format is not "*t",
+then date returns the date as a string,
+formatted according to the same rules as the C function strftime.
+
+
+
+When called without arguments,
date returns a reasonable date and time representation that depends on
the host system and on the current locale
(that is, os.date() is equivalent to os.date("%c")).
-
os.difftime (t2, t1)
-
Returns the number of seconds from time t1 to time t2.
+
+
+
+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.
-
+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.
+
+
+
+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",
@@ -5761,38 +7826,72 @@ the default category is "all".
The function returns the name of the new locale,
or nil if the request cannot be honored.
-
os.time ([table])
-
Returns the current time when called without arguments,
+
+If locale is the empty string,
+the current locate is set to an implementation-defined native locale.
+If locate is the string "C",
+the current locate 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.
+
+
+
+
+
+Returns the current time when called without arguments,
or a time representing the date and time specified by the given table.
This table must have fields year, month, and day,
and may have fields hour, min, sec, and isdst
(for a description of these fields, see the os.date function).
-
The returned value is a number, whose meaning depends on your system.
+
+
+The returned value is a number, whose meaning depends on your system.
In POSIX, Windows, and some other systems, this number counts the number
of seconds since some given start time (the "epoch").
In other systems, the meaning is not specified,
and the number returned by time can be used only as an argument to
date and difftime.
-
+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.
-
+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.
+they can be very slow.
Moreover, several of its functions
violate some assumptions about Lua code
(e.g., that variables local to a function
@@ -5800,12 +7899,22 @@ 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.
-
debug.debug ()
+
+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.
-
+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,
@@ -5813,113 +7922,192 @@ 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
+
+
+Note that commands for debug.debug are not lexically nested
within any function, and so have no direct access to local variables.
-
+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 (function [, what])
-
Returns a table with information about a function.
+
+
+
+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:
-Level 0 is the current function (getinfo itself);
-level 1 is the function that called getinfo;
+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 contains 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.
-If present,
-the option `f´
-adds a field named func with the function itself.
-
For instance, the expression debug.getinfo(1,"n").name returns
+
+The returned table may contain all the fields returned by lua_getinfo,
+with the string what describing which fields to fill in.
+The default for what is to get all information available,
+except the table of valid lines.
+If present,
+the option 'f'
+adds a field named func with the function itself.
+If present,
+the option 'L'
+adds a field named activelines with the table of
+valid lines.
+
+
+
+For instance, the expression debug.getinfo(1,"n").name returns
a name of the current function, if a reasonable name can be found,
-and debug.getinfo(print) returns a table with all available information
+and the expression debug.getinfo(print)
+returns a table with all available information
about the print function.
-
debug.getlocal (level, local)
-
This function returns the name and the value of the local variable
+
+
+
+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,
+(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)
+
+
+Variable names starting with '(' (open parentheses)
represent internal variables
-(loop control variables, temporaries, and C function locals).
+(loop control variables, temporaries, and C function locals).
-
+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.
-
+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.
-
+
"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,
+
+
+When called without arguments,
debug.sethook turns off the hook.
-
When the hook is called, its first parameter is a string
+
+
+When the hook is called, its first parameter is a string
describing the event that has triggered its call:
"call", "return" (or "tail return"),
"line", and "count".
For line events,
the hook also gets the new line number as its second parameter.
Inside a hook,
-you can call getinfo with level 2 to get more information about
+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),
+(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 (level, local, value)
-
This function assigns the value value to the local variable
+
+
+
+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,
@@ -5927,32 +8115,57 @@ 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
+
+
+
+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 ([message])
-
Returns a string with a traceback of the call stack.
-An optional message string is appended
-at the beginning of the traceback.
-This function is typically used with xpcall to produce
-better error messages.
+
Although Lua has been designed as an extension language,
-to be embedded in a host C program,
+
+
+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).
+
+
+
+
+
+
+
+
+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,
@@ -5960,18 +8173,20 @@ 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]]
-
+ lua [options] [script [args]]
+
The options are:
+
-
-estat executes string stat;
-
-lmod "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.
-
+
-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,
@@ -5979,22 +8194,29 @@ When called without arguments,
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,
+
+
+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.
+
+
+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´),
+ $ 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,
+
+
+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,
@@ -6004,244 +8226,296 @@ 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
-
+ $ lua -la b.lua t1 t2
+
the interpreter first runs the file a.lua,
then creates a table
-
-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 `...´.
-
+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,
+
+
+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,
+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.
For instance,
+
- $ lua -e"_PROMPT='myprompt> '" -i
-
+ $ lua -e"_PROMPT='myprompt> '" -i
+
(the outer pair of quotes is for the shell,
the inner pair is for Lua),
or in any Lua programs by assigning to _PROMPT.
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
+
+
+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,
+by using chmod +x and the #! form,
as in
+
-#!/usr/local/bin/lua
-
+ #!/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
-
+ #!/usr/bin/env lua
+
is a more portable solution.)
-
-
-
Incompatibilities with the Previous Version
-
Here we list the incompatibilities that may be found when moving a program
-from Lua 5.0 to Lua 5.1.
+
+Here we list the incompatibilities that you may found 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.
-
The vararg system changed from the pseudo-argument arg with a
table with the extra arguments to the vararg expression.
-(Option LUA_COMPAT_VARARG in luaconf.h.)
+(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 ([[...]]) does not allow nesting.
-You can use the new syntax ([=[...]=]) in these cases.
-(Option LUA_COMPAT_LSTR in luaconf.h.)
+
+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.)
+
Function string.gfind was renamed string.gmatch.
-(Option LUA_COMPAT_GFIND)
+(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.
-(Option LUA_COMPAT_GETN)
+(See compile-time option LUA_COMPAT_GETN in luaconf.h.)
+
-
+
Function loadlib was renamed package.loadlib.
-(Option LUA_COMPAT_LOADLIB)
+(See compile-time option LUA_COMPAT_LOADLIB in luaconf.h.)
+
-
+
Function math.mod was renamed math.fmod.
-(Option LUA_COMPAT_MOD)
+(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.
+
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.
+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.)
+
+Here is the complete syntax of Lua in extended BNF.
+(It does not describe operator precedences.)
-
Here is the complete syntax of Lua in extended BNF.
-It does not describe operator priorities or some syntactical restrictions,
-such as return and break statements
-can only appear as the last statement of a block.
-
-
+
- chunk ::= {stat [`;´]} [laststat[`;´]]
+ chunk ::= {stat [`;´]} [laststat [`;´]]
block ::= chunk
- stat ::= varlist1 `=´ explist1 |
- 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 explist1 do block end |
- function funcname funcbody |
- localfunction Name funcbody |
+ stat ::= varlist1 `=´ explist1 |
+ 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 explist1 do block end |
+ function funcname funcbody |
+ localfunction Name funcbody |
local namelist [`=´ explist1]
- laststat ::= return [explist1] | break
+ laststat ::= return [explist1] | break
funcname ::= Name {`.´ Name} [`:´ Name]
varlist1 ::= var {`,´ var}
- var ::= Name | prefixexp `[´ exp `]´ | prefixexp `.´ Name
+ var ::= Name | prefixexp `[´ exp `]´ | prefixexp `.´ Name
namelist ::= Name {`,´ Name}
explist1 ::= {exp `,´} exp
- exp ::= nil | false | true | Number | String | `...´ |
- function | prefixexp | tableconstructor | exp binop exp | unop exp
+ exp ::= nil | false | true | Number | String | `...´ | function |
+ prefixexp | tableconstructor | exp binop exp | unop exp
- prefixexp ::= var | functioncall | `(´ exp `)´
+ prefixexp ::= var | functioncall | `(´ exp `)´
- functioncall ::= prefixexp args | prefixexp `:´ Name args
+ functioncall ::= prefixexp args | prefixexp `:´ Name args
- args ::= `(´ [explist1] `)´ | tableconstructor | String
+ args ::= `(´ [explist1] `)´ | tableconstructor | String
function ::= function funcbody
funcbody ::= `(´ [parlist1] `)´ block end
- parlist1 ::= namelist [`,´ `...´] | `...´
+ parlist1 ::= namelist [`,´ `...´] | `...´
tableconstructor ::= `{´ [fieldlist] `}´
fieldlist ::= field {fieldsep field} [fieldsep]
- field ::= `[´ exp `]´ `=´ exp | Name `=´ exp | exp
+ field ::= `[´ exp `]´ `=´ exp | Name `=´ exp | exp
- fieldsep ::= `,´ | `;´
+ fieldsep ::= `,´ | `;´
- binop ::= `+´ | `-´ | `*´ | `/´ | `^´ | `%´ | `..´ |
- `<´ | `<=´ | `>´ | `>=´ | `==´ | `~=´ |
- and | or
+ binop ::= `+´ | `-´ | `*´ | `/´ | `^´ | `%´ | `..´ |
+ `<´ | `<=´ | `>´ | `>=´ | `==´ | `~=´ |
+ and | or
- unop ::= `-´ | not | `#´
+ unop ::= `-´ | not | `#´
++ +Lua 5.1 Reference Manual +
+