Original copyright © 2015 Lua.org, PUC-Rio. Freely available under the terms of the Lua license. Modified for Luan.
Luan is a high level programming language based on Lua. A great strength of Lua is its simplicity and Luan takes this even further, being even simpler than Lua. The goal is to provide a simple programming language for the casual programmer with as few concepts as possible so that one can quickly learn the language and then easily understand any code written in Luan.
Luan is implemented in Java and is tightly coupled with Java. So it makes a great scripting language for Java programmers.
Unlike Lua which is meant to be embedded, Luan is meant to be a full scripting language. This done not by adding feature to Luan, but rather by providing a complete set of libraries.
This section describes the basic concepts of the language.
Luan 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 Luan 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 Luan: nil, boolean, number, string, binary, function, userdata, and table. Nil is the type of the value nil, whose main property is to be different from any other value; it usually represents the absence of a useful value. Nil is implemented as the Java value null. Boolean is the type of the values false and true. Boolean is implemented as the Java class Boolean. Number represents both integer numbers and real (floating-point) numbers. Number is implemented as the Java class Number. Any Java subclass of Number is allowed and this is invisible to the Luan user. Operations on numbers follow the same rules of the underlying Java implementation. String is implemented as the Java class String. Binary is implemented as the Java type byte[].
Luan can call (and manipulate) functions written in Luan and functions written in Java (see §3.4.10). Both are represented by the type function.
The type userdata is provided to allow arbitrary Java objects to be stored in Luan variables. A userdata value is a Java object that isn't one of the standard Luan types. Userdata has no predefined operations in Luan, except assignment and identity test. Userdata is useful then Java access is enabled in Luan
The type table implements associative arrays, that is, arrays that can be indexed not only with numbers, but with any Luan value except nil. Tables can be heterogeneous; that is, they can contain values of all types (except nil). Any key with value nil is not considered part of the table. Conversely, any key that is not part of a table has an associated value nil.
Tables are the sole data-structuring mechanism in Luan; they can be used to represent ordinary arrays, sequences, symbol tables, sets, records, graphs, trees, etc. To represent records, Luan 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 Luan (see §3.4.9).
We use the term sequence to denote a table where the set of all positive numeric keys is equal to {1..n} for some non-negative integer n, which is called the length of the sequence (see §3.4.7).
Like indices, the values of table fields can be of any type. In particular, because functions are first-class values, table fields can contain functions. Thus tables can also carry methods (see §3.4.11).
The indexing of tables follows the definition of raw equality in the language. The expressions a[i] and a[j] denote the same table element if and only if i and j are raw equal (that is, equal without metamethods). In particular, floats with integral values are equal to their respective integers (e.g., 1.0 == 1).
Luan values are objects: variables do not actually contain values, only references to them. Assignment, parameter passing, and function returns always manipulate references to values; these operations do not imply any kind of copy.
The library function Luan.type returns a string describing the type of a given value (see §6.1).
As will be discussed in §3.2 and §3.3.3, any reference to a free name (that is, a name not bound to any declaration) var is syntactically translated to _ENV.var. Moreover, every chunk is compiled in the scope of an external local variable named _ENV (see §3.3.2), so _ENV itself is never a free name in a chunk.
Despite the existence of this external _ENV variable and the translation of free names, _ENV is a completely regular name. In particular, you can define new variables and parameters with that name. Each reference to a free name uses the _ENV that is visible at that point in the program, following the usual visibility rules of Luan (see §3.5).
Any table used as the value of _ENV is called an environment.
When Luan loads a chunk, the default value for its _ENV is an empty table.
Luan also provides all chunks with two other local values: require and java. These are functions used to load and access libraries and other modules.
Luan code can explicitly generate an error by calling the error function. If you need to catch errors in Luan, you can use pcall or try to call a given function in protected mode.
Whenever there is an error, an error object (also called an error message) is propagated with information about the error. Luan itself only generates errors whose error object is a string, but programs may generate errors with any value as the error object. It is up to the Luan program or its host to handle such error objects.
Every table in Luan can have a metatable. This metatable is an ordinary Luan table that defines the behavior of the original value under certain special operations. You can change several aspects of the behavior of operations over a value by setting specific fields in its metatable. For instance, when a table is the operand of an addition, Luan checks for a function in the field "__add" of the table's metatable. If it finds one, Luan calls this function to perform the addition.
The keys in a metatable are derived from the event names;
the corresponding values are called
You can query the metatable of any table
using the get_metatable function.
You can replace the metatable of tables
using the set_metatable function.
A metatable controls how a table behaves in
arithmetic operations, bitwise operations,
order comparisons, concatenation, length operation, calls, and indexing.
A detailed list of events controlled by metatables is given next.
Each operation is identified by its corresponding event name.
The key for each event is a string with its name prefixed by
two underscores, '__';
for instance, the key for operation "add" is the
string "__add".
Note that queries for metamethods are always raw;
the access to a metamethod does not invoke other metamethods.
You can emulate how Luan queries a metamethod for an object obj
with the following code:
Here are the events:
Despite the name,
the metamethod for this event can be either a function or a table.
If it is a function,
it is called with table and key as arguments.
If it is a table,
the final result is the result of indexing this table with key.
(This indexing is regular, not raw,
and therefore can trigger another metamethod.)
Like with indexing,
the metamethod for this event can be either a function or a table.
If it is a function,
it is called with table, key, and value as arguments.
If it is a table,
Luan does an indexing assignment to this table with the same key and value.
(This assignment is regular, not raw,
and therefore can trigger another metamethod.)
Whenever there is a "newindex" metamethod,
Luan does not perform the primitive assignment.
(If necessary,
the metamethod itself can call raw_set
to do the assignment.)
Lua performs automatic memory management.
This means that
you do not have to worry about allocating memory for new objects
or freeing it when the objects are no longer needed.
Lua manages memory automatically by running
a garbage collector to collect all dead objects
(that is, objects that are no longer accessible from Lua).
All memory used by Lua is subject to automatic management:
strings, tables, userdata, functions, threads, internal structures, etc.
Lua implements an incremental mark-and-sweep collector.
It uses two numbers to control its garbage-collection cycles:
the garbage-collector pause and
the garbage-collector step multiplier.
Both use percentage points as units
(e.g., a value of 100 means an internal value of 1).
The garbage-collector pause
controls how long the collector waits before starting a new cycle.
Larger values make the collector less aggressive.
Values smaller than 100 mean the collector will not wait to
start a new cycle.
A value of 200 means that the collector waits for the total memory in use
to double before starting a new cycle.
The garbage-collector step multiplier
controls the relative speed of the collector relative to
memory allocation.
Larger values make the collector more aggressive but also increase
the size of each incremental step.
You should not use values smaller than 100,
because they make the collector too slow and
can result in the collector never finishing a cycle.
The default is 200,
which means that the collector runs at "twice"
the speed of memory allocation.
If you set the step multiplier to a very large number
(larger than 10% of the maximum number of
bytes that the program may use),
the collector behaves like a stop-the-world collector.
If you then set the pause to 200,
the collector behaves as in old Lua versions,
doing a complete collection every time Lua doubles its
memory usage.
You can change these numbers by calling
You can set garbage-collector metamethods for tables
and, using the C API,
for full userdata (see §2.4).
These metamethods are also called finalizers.
Finalizers allow you to coordinate Lua's garbage collection
with external resource management
(such as closing files, network or database connections,
or freeing your own memory).
For an object (table or userdata) to be finalized when collected,
you must mark it for finalization.
You mark an object for finalization when you set its metatable
and the metatable has a field indexed by the string "
When a marked object becomes garbage,
it is not collected immediately by the garbage collector.
Instead, Lua puts it in a list.
After the collection,
Lua goes through that list.
For each object in the list,
it checks the object's
At the end of each garbage-collection cycle,
the finalizers for objects are called in
the reverse order that the objects were marked for finalization,
among those collected in that cycle;
that is, the first finalizer to be called is the one associated
with the object marked last in the program.
The execution of each finalizer may occur at any point during
the execution of the regular code.
Because the object being collected must still be used by the finalizer,
that object (and other objects accessible only through it)
must be resurrected by Lua.
Usually, this resurrection is transient,
and the object memory is freed in the next garbage-collection cycle.
However, if the finalizer stores the object in some global place
(e.g., a global variable),
then the resurrection is permanent.
Moreover, if the finalizer marks a finalizing object for finalization again,
its finalizer will be called again in the next cycle where the
object is unreachable.
In any case,
the object memory is freed only in the GC cycle where
the object is unreachable and not marked for finalization.
When you close a state (see
A weak table is a table whose elements are
weak references.
A weak reference is ignored by the garbage collector.
In other words,
if the only references to an object are weak references,
then the garbage collector will collect that object.
A weak table can have weak keys, weak values, or both.
A table with weak 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
A table with weak keys and strong values
is also called an ephemeron table.
In an ephemeron table,
a value is considered reachable only if its key is reachable.
In particular,
if the only reference to a key comes through its value,
the pair is removed.
Any change in the weakness of a table may take effect only
at the next collect cycle.
In particular, if you change the weakness to a stronger mode,
Lua may still collect some items from that table
before the change takes effect.
Only objects that have an explicit construction
are removed from weak tables.
Values, such as numbers and light C functions,
are not subject to garbage collection,
and therefore are not removed from weak tables
(unless their associated values are collected).
Although strings are subject to garbage collection,
they do not have an explicit construction,
and therefore are not removed from weak tables.
Resurrected objects
(that is, objects being finalized
and objects accessible only through objects being finalized)
have a special behavior in weak tables.
They are removed from weak values before running their finalizers,
but are removed from weak keys only in the next collection
after running their finalizers, when such objects are actually freed.
This behavior allows the finalizer to access properties
associated with the object through weak tables.
If a weak table is among the resurrected objects in a collection cycle,
it may not be properly cleared until the next cycle.
Lua supports coroutines,
also called collaborative multithreading.
A coroutine in Lua represents an independent thread of execution.
Unlike threads in multithread systems, however,
a coroutine only suspends its execution by explicitly calling
a yield function.
You create a coroutine by calling
You execute a coroutine by calling
A coroutine can terminate its execution in two ways:
normally, when its main function returns
(explicitly or implicitly, after the last instruction);
and abnormally, if there is an unprotected error.
In case of normal termination,
A coroutine yields by calling
Like
As an example of how coroutines work,
consider the following code:
When you run it, it produces the following output:
You can also create and manipulate coroutines through the C API:
see functions
This section describes the lexis, the syntax, and the semantics of Lua.
In other words,
this section describes
which tokens are valid,
how they can be combined,
and what their combinations mean.
Language constructs will be explained using the usual extended BNF notation,
in which
{a} means 0 or more a's, and
[a] means an optional a.
Non-terminals are shown like non-terminal,
keywords are shown like kword,
and other terminal symbols are shown like ‘=’.
The complete syntax of Lua can be found in §9
at the end of this manual.
Lua is a free-form language.
It ignores spaces (including new lines) and comments
between lexical elements (tokens),
except as delimiters between names and keywords.
Names
(also called identifiers)
in Lua can be any string of letters,
digits, and underscores,
not beginning with a digit.
Identifiers are used to name variables, table fields, and labels.
The following keywords are reserved
and cannot be used as names:
Lua is a case-sensitive language:
The following strings denote other tokens:
Literal strings
can be delimited by matching single or double quotes,
and can contain the following C-like escape sequences:
'
Strings in Lua can contain any 8-bit value, including embedded zeros,
which can be specified as '
The UTF-8 encoding of a Unicode character
can be inserted in a literal string with
the escape sequence
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
Any byte in a literal string not
explicitly affected by the previous rules represents itself.
However, Lua opens files for parsing in text mode,
and the system file functions may have problems with
some control characters.
So, it is safer to represent
non-text data as a quoted literal with
explicit escape sequences for non-text characters.
For convenience,
when the opening long bracket is immediately followed by a newline,
the newline is not included in the string.
As an example, in a system using ASCII
(in which '
A numerical constant (or numeral)
can be written with an optional fractional part
and an optional decimal exponent,
marked by a letter '
Examples of valid float constants are
A comment starts with a double hyphen (
Variables are places that store values.
There are three kinds of variables in Lua:
global variables, local variables, and table fields.
A single name can denote a global variable or a local variable
(or a function's formal parameter,
which is a particular kind of local variable):
Name denotes identifiers, as defined in §3.1.
Any variable name is assumed to be global unless explicitly declared
as a local (see §3.3.7).
Local variables are lexically scoped:
local variables can be freely accessed by functions
defined inside their scope (see §3.5).
Before the first assignment to a variable, its value is nil.
Square brackets are used to index a table:
The meaning of accesses to table fields can be changed via metatables.
An access to an indexed variable
The syntax
An access to a global variable
Lua supports an almost conventional set of statements,
similar to those in Pascal or C.
This set includes
assignments, control structures, function calls,
and variable declarations.
A block is a list of statements,
which are executed sequentially:
Lua has empty statements
that allow you to separate statements with semicolons,
start a block with a semicolon
or write two semicolons in sequence:
Function calls and assignments
can start with an open parenthesis.
This possibility leads to an ambiguity in Lua's grammar.
Consider the following fragment:
The grammar could see it in two ways:
The current parser always sees such constructions
in the first way,
interpreting the open parenthesis
as the start of the arguments to a call.
To avoid this ambiguity,
it is a good practice to always precede with a semicolon
statements that start with a parenthesis:
A block can be explicitly delimited to produce a single statement:
Explicit blocks are useful
to control the scope of variable declarations.
Explicit blocks are also sometimes used to
add a return statement in the middle
of another block (see §3.3.4).
The unit of compilation of Lua is called a chunk.
Syntactically,
a chunk is simply a block:
Lua handles a chunk as the body of an anonymous function
with a variable number of arguments
(see §3.4.11).
As such, chunks can define local variables,
receive arguments, and return values.
Moreover, such anonymous function is compiled as in the
scope of an external local variable called
A chunk can be stored in a file or in a string inside the host program.
To execute a chunk,
Lua first loads it,
precompiling the chunk's code into instructions for a virtual machine,
and then Lua executes the compiled code
with an interpreter for the virtual machine.
Chunks can also be precompiled into binary form;
see program
Lua allows multiple assignments.
Therefore, the syntax for assignment
defines a list of variables on the left side
and a list of expressions on the right side.
The elements in both lists are separated by commas:
Expressions are discussed in §3.4.
Before the assignment,
the list of values is adjusted to the length of
the list of variables.
If there are more values than needed,
the excess values are thrown away.
If there are fewer values than needed,
the list is extended with as many nil's as needed.
If the list of expressions ends with a function call,
then all values returned by that call enter the list of values,
before the adjustment
(except when the call is enclosed in parentheses; see §3.4).
The assignment statement first evaluates all its expressions
and only then the assignments are performed.
Thus the code
sets
exchanges the values of
cyclically permutes the values of
The meaning of assignments to global variables
and table fields can be changed via metatables.
An assignment to an indexed variable
An assignment to a global name
The control structures
if, while, and repeat have the usual meaning and
familiar syntax:
Lua also has a for statement, in two flavors (see §3.3.5).
The condition expression of a
control structure can return any value.
Both false and nil are considered false.
All values different from nil and false are considered true
(in particular, the number 0 and the empty string are also true).
In the repeat–until loop,
the inner block does not end at the until keyword,
but only after the condition.
So, the condition can refer to local variables
declared inside the loop block.
The goto statement transfers the program control to a label.
For syntactical reasons,
labels in Lua are considered statements too:
A label is visible in the entire block where it is defined,
except
inside nested blocks where a label with the same name is defined and
inside nested functions.
A goto may jump to any visible label as long as it does not
enter into the scope of a local variable.
Labels and empty statements are called void statements,
as they perform no actions.
The break statement terminates the execution of a
while, repeat, or for loop,
skipping to the next statement after the loop:
A break ends the innermost enclosing loop.
The return statement is used to return values
from a function or a chunk
(which is an anonymous function).
Functions can return more than one value,
so the syntax for the return statement is
The return statement can only be written
as the last statement of a block.
If it is really necessary to return in the middle of a block,
then an explicit inner block can be used,
as in the idiom
The for statement has two forms:
one numeric and one generic.
The numeric for loop repeats a block of code while a
control variable runs through an arithmetic progression.
It has the following syntax:
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
is equivalent to the code:
Note the following:
The generic for statement works over functions,
called iterators.
On each iteration, the iterator function is called to produce a new value,
stopping when this new value is nil.
The generic for loop has the following syntax:
A for statement like
is equivalent to the code:
Note the following:
To allow possible side-effects,
function calls can be executed as statements:
In this case, all returned values are thrown away.
Function calls are explained in §3.4.10.
Local variables can be declared anywhere inside a block.
The declaration can include an initial assignment:
If present, an initial assignment has the same semantics
of a multiple assignment (see §3.3.3).
Otherwise, all variables are initialized with nil.
A chunk is also a block (see §3.3.2),
and so local variables can be declared in a chunk outside any explicit block.
The visibility rules for local variables are explained in §3.5.
The basic expressions in Lua are the following:
Numerals and literal strings are explained in §3.1;
variables are explained in §3.2;
function definitions are explained in §3.4.11;
function calls are explained in §3.4.10;
table constructors are explained in §3.4.9.
Vararg expressions,
denoted by three dots ('
Binary operators comprise arithmetic operators (see §3.4.1),
bitwise operators (see §3.4.2),
relational operators (see §3.4.4), logical operators (see §3.4.5),
and the concatenation operator (see §3.4.6).
Unary operators comprise the unary minus (see §3.4.1),
the unary bitwise not (see §3.4.2),
the unary logical not (see §3.4.5),
and the unary length operator (see §3.4.7).
Both function calls and vararg expressions can result in multiple values.
If a function call is used as a statement (see §3.3.6),
then its return list is adjusted to zero elements,
thus discarding all returned values.
If an expression is used as the last (or the only) element
of a list of expressions,
then no adjustment is made
(unless the expression is enclosed in parentheses).
In all other contexts,
Lua adjusts the result list to one element,
either discarding all values except the first one
or adding a single nil if there are no values.
Here are some examples:
Any expression enclosed in parentheses always results in only one value.
Thus,
Lua supports the following arithmetic operators:
With the exception of exponentiation and float division,
the arithmetic operators work as follows:
If both operands are integers,
the operation is performed over integers and the result is an integer.
Otherwise, if both operands are numbers
or strings that can be converted to
numbers (see §3.4.3),
then they are converted to floats,
the operation is performed following the usual rules
for floating-point arithmetic
(usually the IEEE 754 standard),
and the result is a float.
Exponentiation and float division (
Floor division (
Modulo is defined as the remainder of a division
that rounds the quotient towards minus infinite (floor division).
In case of overflows in integer arithmetic,
all operations wrap around,
according to the usual rules of two-complement arithmetic.
(In other words,
they return the unique representable integer
that is equal modulo 264 to the mathematical result.)
Lua supports the following bitwise operators:
All bitwise operations convert its operands to integers
(see §3.4.3),
operate on all bits of those integers,
and result in an integer.
Both right and left shifts fill the vacant bits with zeros.
Negative displacements shift to the other direction;
displacements with absolute values equal to or higher than
the number of bits in an integer
result in zero (as all bits are shifted out).
Lua provides some automatic conversions between some
types and representations at run time.
Bitwise operators always convert float operands to integers.
Exponentiation and float division
always convert integer operands to floats.
All other arithmetic operations applied to mixed numbers
(integers and floats) convert the integer operand to a float;
this is called the usual rule.
The C API also converts both integers to floats and
floats to integers, as needed.
Moreover, string concatenation accepts numbers as arguments,
besides strings.
Lua also converts strings to numbers,
whenever a number is expected.
In a conversion from integer to float,
if the integer value has an exact representation as a float,
that is the result.
Otherwise,
the conversion gets the nearest higher or
the nearest lower representable value.
This kind of conversion never fails.
The conversion from float to integer
checks whether the float has an exact representation as an integer
(that is, the float has an integral value and
it is in the range of integer representation).
If it does, that representation is the result.
Otherwise, the conversion fails.
The conversion from strings to numbers goes as follows:
First, the string is converted to an integer or a float,
following its syntax and the rules of the Lua lexer.
(The string may have also leading and trailing spaces and a sign.)
Then, the resulting number is converted to the required type
(float or integer) according to the previous rules.
The conversion from numbers to strings uses a
non-specified human-readable format.
For complete control over how numbers are converted to strings,
use the
Lua supports the following relational operators:
These operators always result in false or true.
Equality (
Tables, userdata, and threads
are compared by reference:
two objects are considered equal only if they are the same object.
Every time you create a new object
(a table, userdata, or thread),
this new object is different from any previously existing object.
Closures with the same reference are always equal.
Closures with any detectable difference
(different behavior, different definition) are always different.
You can change the way that Lua compares tables and userdata
by using the "eq" metamethod (see §2.4).
Equality comparisons do not convert strings to numbers
or vice versa.
Thus,
The operator
The order operators work as follows.
If both arguments are numbers,
then they are compared following
the usual rule for binary operations.
Otherwise, if both arguments are strings,
then their values are compared according to the current locale.
Otherwise, Lua tries to call the "lt" or the "le"
metamethod (see §2.4).
A comparison
The logical operators in Lua are
and, or, and not.
Like the control structures (see §3.3.4),
all logical operators consider both false and nil as false
and anything else as true.
The negation operator not always returns false or true.
The conjunction operator and returns its first argument
if this value is false or nil;
otherwise, and returns its second argument.
The disjunction operator or returns its first argument
if this value is different from nil and false;
otherwise, or returns its second argument.
Both and and or use short-circuit evaluation;
that is,
the second operand is evaluated only if necessary.
Here are some examples:
(In this manual,
The string concatenation operator in Lua is
denoted by two dots ('
The length operator is denoted by the unary prefix operator
A program can modify the behavior of the length operator for
any value but strings through the
Unless a
is not a sequence, because it has the key
Operator precedence in Lua follows the table below,
from lower to higher priority:
As usual,
you can use parentheses to change the precedences of an expression.
The concatenation ('
Table constructors are expressions that create tables.
Every time a constructor is evaluated, a new table is created.
A constructor can be used to create an empty table
or to create a table and initialize some of its fields.
The general syntax for constructors is
Each field of the form
is equivalent to
The order of the assignments in a constructor is undefined.
(This order would be relevant only when there are repeated keys.)
If the last field in the list has the form
The field list can have an optional trailing separator,
as a convenience for machine-generated code.
A function call in Lua has the following syntax:
In a function call,
first prefixexp and args are evaluated.
If the value of prefixexp has type function,
then this function is called
with the given arguments.
Otherwise, the prefixexp "call" metamethod is called,
having as first parameter the value of prefixexp,
followed by the original call arguments
(see §2.4).
The form
can be used to call "methods".
A call
Arguments have the following syntax:
All argument expressions are evaluated before the call.
A call of the form
A call of the form
The syntax for function definition is
The following syntactic sugar simplifies function definitions:
The statement
translates to
The statement
translates to
The statement
translates to
not to
(This only makes a difference when the body of the function
contains references to
A function definition is an executable expression,
whose value has type function.
When Lua precompiles a chunk,
all its function bodies are precompiled too.
Then, whenever Lua executes the function definition,
the function is instantiated (or closed).
This function instance (or closure)
is the final value of the expression.
Parameters act as local variables that are
initialized with the argument values:
When a function is called,
the list of arguments is adjusted to
the length of the list of parameters,
unless the function is a vararg function,
which is indicated by three dots ('
As an example, consider the following definitions:
Then, we have the following mapping from arguments to parameters and
to the vararg expression:
Results are returned using the return statement (see §3.3.4).
If control reaches the end of a function
without encountering a return statement,
then the function returns with no results.
There is a system-dependent limit on the number of values
that a function may return.
This limit is guaranteed to be larger than 1000.
The colon syntax
is used for defining methods,
that is, functions that have an implicit extra parameter
is syntactic sugar for
Lua is a lexically scoped language.
The scope of a local variable begins at the first statement after
its declaration and lasts until the last non-void statement
of the innermost block that includes the declaration.
Consider the following example:
Notice that, in a declaration like
Because of the lexical scoping rules,
local variables can be freely accessed by functions
defined inside their scope.
A local variable used by an inner function is called
an upvalue, or external local variable,
inside the inner function.
Notice that each execution of a local statement
defines new local variables.
Consider the following example:
The loop creates ten closures
(that is, ten instances of the anonymous function).
Each of these closures uses a different
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
Even when we use the term "function",
any facility in the API may be provided as a macro instead.
Except where stated otherwise,
all such macros use each of their arguments exactly once
(except for the first argument, which is always a Lua state),
and so do not generate any hidden side-effects.
As in most C libraries,
the Lua API functions do not check their arguments for validity or consistency.
However, you can change this behavior by compiling Lua
with the macro
Lua uses a virtual stack to pass values to and from C.
Each element in this stack represents a Lua value
(nil, number, string, etc.).
Whenever Lua calls C, the called function gets a new stack,
which is independent of previous stacks and of stacks of
C functions that are still active.
This stack initially contains any arguments to the C function
and it is where the C function pushes its results
to be returned to the caller (see
For convenience,
most query operations in the API do not follow a strict stack discipline.
Instead, they can refer to any element in the stack
by using an index:
A positive index represents an absolute stack position
(starting at 1);
a negative index represents an offset relative to the top of the stack.
More specifically, if the stack has n elements,
then index 1 represents the first element
(that is, the element that was pushed onto the stack first)
and
index n represents the last element;
index -1 also represents the last element
(that is, the element at the top)
and index -n represents the first element.
When you interact with the Lua API,
you are responsible for ensuring consistency.
In particular,
you are responsible for controlling stack overflow.
You can use the function
Whenever Lua calls C,
it ensures that the stack has space for
at least
When you call a Lua function
without a fixed number of results (see
Any function in the API that receives stack indices
works only with valid indices or acceptable indices.
A valid index is an index that refers to a
real position within the stack, that is,
its position lies between 1 and the stack top
(
Unless otherwise noted,
any function that accepts valid indices also accepts pseudo-indices,
which represent some Lua values that are accessible to C code
but which are not in the stack.
Pseudo-indices are used to access the registry
and the upvalues of a C function (see §4.4).
Functions that do not need a specific stack position,
but only a value in the stack (e.g., query functions),
can be called with acceptable indices.
An acceptable index can be any valid index,
including the pseudo-indices,
but it also can be any positive index after the stack top
within the space allocated for the stack,
that is, indices up to the stack size.
(Note that 0 is never an acceptable index.)
Except when noted otherwise,
functions in the API work with acceptable indices.
Acceptable indices serve to avoid extra tests
against the stack top when querying the stack.
For instance, a C function can query its third argument
without the need to first check whether there is a third argument,
that is, without the need to check whether 3 is a valid index.
For functions that can be called with acceptable indices,
any non-valid index is treated as if it
contains a value of a virtual type
When a C function is created,
it is possible to associate some values with it,
thus creating a C closure
(see
Whenever a C function is called,
its upvalues are located at specific pseudo-indices.
These pseudo-indices are produced by the macro
Lua provides a registry,
a predefined table that can be used by any C code to
store whatever Lua values it needs to store.
The registry table is always located at pseudo-index
The integer keys in the registry are used
by the reference mechanism (see
When you create a new Lua state,
its registry comes with some predefined values.
These predefined values are indexed with integer keys
defined as constants in
Internally, Lua uses the C
If an error happens outside any protected environment,
Lua calls a panic function (see
The panic function runs as if it were a message handler (see §2.3);
in particular, the error message is at the top of the stack.
However, there is no guarantee about stack space.
To push anything on the stack,
the panic function must first check the available space (see §4.2).
Most functions in the API can raise an error,
for instance due to a memory allocation error.
The documentation for each function indicates whether
it can raise errors.
Inside a C function you can raise an error by calling
Internally, Lua uses the C
To avoid this kind of problem,
Lua raises an error whenever it tries to yield across an API call,
except for three functions:
We need to set some terminology to explain continuations.
We have a C function called from Lua which we will call
the original function.
This original function then calls one of those three functions in the C API,
which we will call the callee function,
that then yields the current thread.
(This can happen when the callee function is
Suppose the running thread yields while executing the callee function.
After the thread resumes,
it eventually will finish running the callee function.
However,
the callee function cannot return to the original function,
because its frame in the C stack was destroyed by the yield.
Instead, Lua calls a continuation function,
which was given as an argument to the callee function.
As the name implies,
the continuation function should continue the task
of the original function.
As an illustration, consider the following function:
Now we want to allow
the Lua code being run by
In the above code,
the new function
Note the external, explicit call to the continuation:
Lua will call the continuation only if needed, that is,
in case of errors or resuming after a yield.
If the called function returns normally without ever yielding,
Besides the Lua state,
the continuation function has two other parameters:
the final status of the call plus the context value (
Lua treats the continuation function as if it were the original function.
The continuation function receives the same Lua stack
from the original function,
in the same state it would be if the callee function had returned.
(For instance,
after a
Here we list all functions and types from the C API in
alphabetical order.
Each function has an indicator like this:
[-o, +p, x]
The first field,
[-0, +0, –]
Converts the acceptable index
The type of the memory-allocation function used by Lua states.
The allocator function must provide a
functionality similar to
When
When
Lua assumes the following behavior from the allocator function:
When
When
Here is a simple implementation for the allocator function.
It is used in the auxiliary library by
Note that Standard C ensures
that
[-(2|1), +1, e]
Performs an arithmetic or bitwise operation over the two values
(or one, in the case of negations)
at the top of the stack,
with the value at the top being the second operand,
pops these values, and pushes the result of the operation.
The function follows the semantics of the corresponding Lua operator
(that is, it may call metamethods).
The value of
[-0, +0, –]
Sets a new panic function and returns the old one (see §4.6).
[-(nargs+1), +nresults, e]
Calls a function.
To call a function you must use the following protocol:
first, the function to be called is pushed onto the stack;
then, the arguments to the function are pushed
in direct order;
that is, the first argument is pushed first.
Finally you call
Any error inside the called function is propagated upwards
(with a
The following example shows how the host program can do the
equivalent to this Lua code:
Here it is in C:
Note that the code above is balanced:
at its end, the stack is back to its original configuration.
This is considered good programming practice.
[-(nargs + 1), +nresults, e]
This function behaves exactly like
Type for C functions.
In order to communicate properly with Lua,
a C function must use the following protocol,
which defines the way parameters and results are passed:
a C function receives its arguments from Lua in its stack
in direct order (the first argument is pushed first).
So, when the function starts,
As an example, the following function receives a variable number
of numerical arguments and returns their average and their sum:
[-0, +0, –]
Ensures that the stack has space for at least
[-0, +0, –]
Destroys all objects in the given Lua state
(calling the corresponding garbage-collection metamethods, if any)
and frees all dynamic memory used by this state.
On several platforms, you may not need to call this function,
because all resources are naturally released when the host program ends.
On the other hand, long-running programs that create multiple states,
such as daemons or web servers,
will probably need to close states as soon as they are not needed.
[-0, +0, e]
Compares two Lua values.
Returns 1 if the value at index
The value of
[-n, +1, e]
Concatenates the
[-0, +0, –]
Copies the element at index
[-0, +1, e]
Creates a new empty table and pushes it onto the stack.
Parameter
[-0, +0, e]
Dumps a function as a binary chunk.
Receives a Lua function on the top of the stack
and produces a binary chunk that,
if loaded again,
results in a function equivalent to the one dumped.
As it produces parts of the chunk,
If
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.
[-1, +0, v]
Generates a Lua error,
using the value at the top of the stack as the error object.
This function does a long jump,
and therefore never returns
(see
[-0, +0, e]
Controls the garbage collector.
This function performs several tasks,
according to the value of the parameter
For more details about these options,
see
[-0, +0, –]
Returns the memory-allocation function of a given state.
If
[-0, +1, e]
Pushes onto the stack the value
Returns the type of the pushed value.
[-0, +0, –]
Returns a pointer to a raw memory area associated with the
given Lua state.
The application can use this area for any purpose;
Lua does not use it for anything.
Each new thread has this area initialized with a copy
of the area of the main thread.
By default, this area has the size of a pointer to void,
but you can recompile Lua with a different size for this area.
(See
[-0, +1, e]
Pushes onto the stack the value of the global
[-0, +1, e]
Pushes onto the stack the value
Returns the type of the pushed value.
[-0, +(0|1), –]
If the value at the given index has a metatable,
the function pushes that metatable onto the stack and returns 1.
Otherwise,
the function returns 0 and pushes nothing on the stack.
[-1, +1, e]
Pushes onto the stack the value
This function pops the key from the stack,
pushing the resulting value in its place.
As in Lua, this function may trigger a metamethod
for the "index" event (see §2.4).
Returns the type of the pushed value.
[-0, +0, –]
Returns the index of the top element in the stack.
Because indices start at 1,
this result is equal to the number of elements in the stack;
in particular, 0 means an empty stack.
[-0, +1, –]
Pushes onto the stack the Lua value associated with the userdata
at the given index.
Returns the type of the pushed value.
[-1, +1, –]
Moves the top element into the given valid index,
shifting up the elements above this index to open space.
This function cannot be called with a pseudo-index,
because a pseudo-index is not an actual stack position.
The type of integers in Lua.
By default this type is
Lua also defines the constants
[-0, +0, –]
Returns 1 if the value at the given index is a boolean,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a C function,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a function
(either C or Lua), and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is an integer
(that is, the value is a number and is represented as an integer),
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a light userdata,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is nil,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the given index is not valid,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the given index is not valid
or if the value at this index is nil,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a number
or a string convertible to a number,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a string
or a number (which is always convertible to a string),
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a table,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a thread,
and 0 otherwise.
[-0, +0, –]
Returns 1 if the value at the given index is a userdata
(either full or light), and 0 otherwise.
[-0, +0, –]
Returns 1 if the given coroutine can yield,
and 0 otherwise.
The type for continuation-function contexts.
It must be a numerical type.
This type is defined as
Type for continuation functions (see §4.7).
[-0, +1, e]
Returns the length of the value at the given index.
It is equivalent to the '
[-0, +1, –]
Loads a Lua chunk without running it.
If there are no errors,
The return values of
The
The
If the resulting function has upvalues,
its first upvalue is set to the value of the global environment
stored at index
[-0, +0, –]
Creates a new thread running in a new, independent state.
Returns
[-0, +1, e]
Creates a new empty table and pushes it onto the stack.
It is equivalent to
[-0, +1, e]
Creates a new thread, pushes it on the stack,
and returns a pointer to a
There is no explicit function to close or to destroy a thread.
Threads are subject to garbage collection,
like any Lua object.
[-0, +1, e]
This function allocates a new block of memory with the given size,
pushes onto the stack a new full userdata with the block address,
and returns this address.
The host program can freely use this memory.
[-1, +(2|0), e]
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
A typical traversal looks like this:
While traversing a table,
do not call
See function
The type of floats in Lua.
By default this type is double,
but that can be changed to a single float.
(See
Converts a Lua float to a Lua integer.
This macro assumes that
This macro may evaluate its arguments more than once.
[-(nargs + 1), +(nresults|1), –]
Calls a function in protected mode.
Both
If
Typically, the message handler is used to add more debug
information to the error message, such as a stack traceback.
Such information cannot be gathered after the return of
The
[-(nargs + 1), +(nresults|1), –]
This function behaves exactly like
[-n, +0, –]
Pops
[-0, +1, –]
Pushes a boolean value with value
[-n, +1, e]
Pushes a new C closure onto the stack.
When a C function is created,
it is possible to associate some values with it,
thus creating a C closure (see §4.4);
these values are then accessible to the function whenever it is called.
To associate values with a C function,
first these values must be pushed onto the stack
(when there are multiple values, the first value is pushed first).
Then
The maximum value for
When
[-0, +1, –]
Pushes a C function onto the stack.
This function receives a pointer to a C function
and pushes onto the stack a Lua value of type
Any function to be registered in Lua must
follow the correct protocol to receive its parameters
and return its results (see
Note that
[-0, +1, e]
Pushes onto the stack a formatted string
and returns a pointer to this string.
It is similar to the ISO C function
[-0, +1, –]
Pushes the global environment onto the stack.
[-0, +1, –]
Pushes an integer with value
[-0, +1, –]
Pushes a light userdata onto the stack.
Userdata represent C values in Lua.
A light userdata represents a pointer, a
[-0, +1, e]
This macro is equivalent to
[-0, +1, e]
Pushes the string pointed to by
Returns a pointer to the internal copy of the string.
[-0, +1, –]
Pushes a nil value onto the stack.
[-0, +1, –]
Pushes a float with value
[-0, +1, e]
Pushes the zero-terminated string pointed to by
Returns a pointer to the internal copy of the string.
If
[-0, +1, –]
Pushes the thread represented by
[-0, +1, –]
Pushes a copy of the element at the given index
onto the stack.
[-0, +1, e]
Equivalent to
[-0, +0, –]
Returns 1 if the two values in indices
[-1, +1, –]
Similar to
[-0, +1, –]
Pushes onto the stack the value
Returns the type of the pushed value.
[-0, +1, –]
Pushes onto the stack the value
Returns the type of the pushed value.
[-0, +0, –]
Returns the raw "length" of the value at the given index:
for strings, this is the string length;
for tables, this is the result of the length operator ('
[-2, +0, e]
Similar to
[-1, +0, e]
Does the equivalent of
This function pops the value from the stack.
The assignment is raw;
that is, it does not invoke metamethods.
[-1, +0, e]
Does the equivalent of
This function pops the value from the stack.
The assignment is raw;
that is, it does not invoke metamethods.
The reader function used by
[-0, +0, e]
Sets the C function
[-1, +0, –]
Removes the element at the given valid index,
shifting down the elements above this index to fill the gap.
This function cannot be called with a pseudo-index,
because a pseudo-index is not an actual stack position.
[-1, +0, –]
Moves the top element into the given valid index
without shifting any element
(therefore replacing the value at the given index),
and then pops the top element.
[-?, +?, –]
Starts and resumes a coroutine in a given thread.
To start a coroutine,
you push onto the thread stack the main function plus any arguments;
then you call
In case of errors,
the stack is not unwound,
so you can use the debug API over it.
The error message is on the top of the stack.
To resume a coroutine,
you remove any results from the last
The parameter
[-0, +0, –]
Rotates the stack elements from
[-0, +0, –]
Changes the allocator function of a given state to
[-1, +0, e]
Does the equivalent to
This function pops the value from the stack.
As in Lua, this function may trigger a metamethod
for the "newindex" event (see §2.4).
[-1, +0, e]
Pops a value from the stack and
sets it as the new value of global
[-1, +0, e]
Does the equivalent to
This function pops the value from the stack.
As in Lua, this function may trigger a metamethod
for the "newindex" event (see §2.4).
[-1, +0, –]
Pops a table from the stack and
sets it as the new metatable for the value at the given index.
[-2, +0, e]
Does the equivalent to
This function pops both the key and the value from the stack.
As in Lua, this function may trigger a metamethod
for the "newindex" event (see §2.4).
[-?, +?, –]
Accepts any index, or 0,
and sets the stack top to this index.
If the new top is larger than the old one,
then the new elements are filled with nil.
If
[-1, +0, –]
Pops a value from the stack and sets it as
the new value associated to the userdata at the given index.
An opaque structure that points to a thread and indirectly
(through the thread) to the whole state of a Lua interpreter.
The Lua library is fully reentrant:
it has no global variables.
All information about a state is accessible through this structure.
A pointer to this structure must be passed as the first argument to
every function in the library, except to
[-0, +0, –]
Returns the status of the thread
The status can be 0 (
You can only call functions in threads with status
[-0, +1, –]
Converts the zero-terminated string
[-0, +0, –]
Converts the Lua value at the given index to a C boolean
value (0 or 1).
Like all tests in Lua,
[-0, +0, –]
Converts a value at the given index to a C function.
That value must be a C function;
otherwise, returns
[-0, +0, –]
Equivalent to
[-0, +0, –]
Converts the Lua value at the given index
to the signed integral type
If
[-0, +0, e]
Converts the Lua value at the given index to a C string.
If
Because Lua has garbage collection,
there is no guarantee that the pointer returned by
[-0, +0, –]
Equivalent to
[-0, +0, –]
Converts the Lua value at the given index
to the C type
If
[-0, +0, –]
Converts the value at the given index to a generic
C pointer (
Typically this function is used only for debug information.
[-0, +0, e]
Equivalent to
[-0, +0, –]
Converts the value at the given index to a Lua thread
(represented as
[-0, +0, –]
If the value at the given index is a full userdata,
returns its block address.
If the value is a light userdata,
returns its pointer.
Otherwise, returns
[-0, +0, –]
Returns the type of the value in the given valid index,
or
[-0, +0, –]
Returns the name of the type encoded by the value
The unsigned version of
[-0, +0, –]
Returns the pseudo-index that represents the
[-0, +0, v]
Returns the address of the version number stored in the Lua core.
When called with a valid
The type of the writer function used by
The writer returns an error code:
0 means no errors;
any other value means an error and stops
[-?, +?, –]
Exchange values between different threads of the same state.
This function pops
[-?, +?, e]
This function is equivalent to
[-?, +?, e]
Yields a coroutine (thread).
When a C function calls
When the coroutine is resumed again,
Lua calls the given continuation function
Usually, this function does not return;
when the coroutine eventually resumes,
it continues executing the continuation function.
However, there is one special case,
which is when this function is called
from inside a line hook (see §4.9).
In that case,
This function can raise an error if it is called from a thread
with a pending C call with no continuation function,
or it is called from a thread that is not running inside a resume
(e.g., the main thread).
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.
A structure used to carry different pieces of
information about a function or an activation record.
The fields of
[-0, +0, –]
Returns the current hook function.
[-0, +0, –]
Returns the current hook count.
[-0, +0, –]
Returns the current hook mask.
[-(0|1), +(0|1|2), e]
Gets information about a specific function or function invocation.
To get information about a function invocation,
the parameter
To get information about a function you push it onto the stack
and start the
Each character in the string
If this option is given together with option '
This function returns 0 on error
(for instance, an invalid option in
[-0, +(0|1), –]
Gets information about a local variable of
a given activation record or a given function.
In the first case,
the parameter
In the second case,
Returns
[-0, +0, –]
Gets information about the interpreter runtime stack.
This function fills parts of a
[-0, +(0|1), –]
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.)
Returns
Type for debugging hook functions.
Whenever a hook is called, its
For call events,
While Lua is running a hook, it disables other calls to hooks.
Therefore, if a hook calls back Lua to execute a function or a chunk,
this execution occurs without any calls to hooks.
Hook functions cannot have continuations,
that is, they cannot call
Hook functions can yield under the following conditions:
Only count and line events can yield
and they cannot yield any value;
to yield a hook function must finish its execution
calling
[-0, +0, –]
Sets the debugging hook function.
Argument
A hook is disabled by setting
[-(0|1), +0, –]
Sets the value of a local variable of a given activation record.
Parameters
Returns
[-(0|1), +0, –]
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
Returns
[-0, +0, –]
Returns a unique identifier for the upvalue numbered
These unique identifiers allow a program to check whether different
closures share upvalues.
Lua closures that share an upvalue
(that is, that access a same external local variable)
will return identical ids for those upvalue indices.
[-0, +0, –]
Make the
The auxiliary library provides several convenient functions
to interface C with Lua.
While the basic API provides the primitive functions for all
interactions between C and Lua,
the auxiliary library provides higher-level functions for some
common tasks.
All functions and types from the auxiliary library
are defined in header file
All functions in the auxiliary library are built on
top of the basic API,
and so they provide nothing that cannot be done with that API.
Nevertheless, the use of the auxiliary library ensures
more consistency to your code.
Several functions in the auxiliary library use internally some
extra stack slots.
When a function in the auxiliary library uses less than five slots,
it does not check the stack size;
it simply assumes that there are enough slots.
Several functions in the auxiliary library are used to
check C function arguments.
Because the error message is formatted for arguments
(e.g., "
Functions called
Here we list all functions and types from the auxiliary library
in alphabetical order.
[-?, +?, e]
Adds the byte
[-?, +?, e]
Adds the string pointed to by
[-?, +?, e]
Adds to the buffer
[-?, +?, e]
Adds the zero-terminated string pointed to by
[-1, +?, e]
Adds the value at the top of the stack
to the buffer
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.
[-0, +0, v]
Checks whether
[-0, +0, v]
Raises an error reporting a problem with argument
This function never returns.
Type for a string buffer.
A string buffer allows C code to build Lua strings piecemeal.
Its pattern of use is as follows:
If you know beforehand the total size of the resulting string,
you can use the buffer like this:
During its normal operation,
a string buffer uses a variable number of stack slots.
So, while using a buffer, you cannot assume that you know where
the top of the stack is.
You can use the stack between successive calls to buffer operations
as long as that use is balanced;
that is,
when you call a buffer operation,
the stack is at the same level
it was immediately after the previous buffer operation.
(The only exception to this rule is
[-0, +0, –]
Initializes a buffer
[-?, +?, e]
Equivalent to the sequence
[-0, +(0|1), e]
Calls a metamethod.
If the object at index
[-0, +0, v]
Checks whether the function has an argument
of any type (including nil) at position
[-0, +0, v]
Checks whether the function argument
[-0, +0, v]
Checks whether the function argument
This function uses
[-0, +0, v]
Checks whether the function argument
[-0, +0, v]
Checks whether the function argument
If
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.)
[-0, +0, v]
Grows the stack size to
[-0, +0, v]
Checks whether the function argument
This function uses
[-0, +0, v]
Checks whether the function argument
[-0, +0, v]
Checks whether the function argument
[-0, +0, –]
Checks whether the core running the call,
the core that created the Lua state,
and the code making the call are all using the same version of Lua.
Also checks whether the core running the call
and the core that created the Lua state
are using the same address space.
[-0, +?, e]
Loads and runs the given file.
It is defined as the following macro:
It returns false if there are no errors
or true in case of errors.
[-0, +?, –]
Loads and runs the given string.
It is defined as the following macro:
It returns false if there are no errors
or true in case of errors.
[-0, +0, v]
Raises an error.
The error message format is given by
This function never returns,
but it is an idiom to use it in C functions
as
[-0, +3, e]
This function produces the return values for
process-related functions in the standard library
(
[-0, +(1|3), e]
This function produces the return values for
file-related functions in the standard library
(
[-0, +(0|1), e]
Pushes onto the stack the field
[-0, +1, –]
Pushes onto the stack the metatable associated with name
[-0, +1, e]
Ensures that the value
[-0, +1, e]
Creates a copy of string
[-0, +0, e]
Returns the "length" of the value at the given index
as a number;
it is equivalent to the '
[-0, +1, –]
Equivalent to
[-0, +1, –]
Loads a buffer as a Lua chunk.
This function uses
This function returns the same results as
[-0, +1, e]
Equivalent to
[-0, +1, e]
Loads a file as a Lua chunk.
This function uses
The string
This function returns the same results as
As
[-0, +1, –]
Loads a string as a Lua chunk.
This function uses
This function returns the same results as
Also as
[-0, +1, e]
Creates a new table and registers there
the functions in list
It is implemented as the following macro:
The array
[-0, +1, e]
Creates a new table with a size optimized
to store all entries in the array
It is implemented as a macro.
The array
[-0, +1, e]
If the registry already has the key
In both cases pushes onto the stack the final value associated
with
[-0, +0, –]
Creates a new Lua state.
It calls
Returns the new state,
or
[-0, +0, e]
Opens all standard Lua libraries into the given state.
[-0, +0, v]
If the function argument
[-0, +0, v]
If the function argument
If
[-0, +0, v]
If the function argument
[-0, +0, v]
If the function argument
[-?, +?, e]
Equivalent to
[-?, +?, e]
Returns an address to a space of size
[-?, +1, e]
Finishes the use of buffer
[-?, +1, e]
Equivalent to the sequence
[-1, +0, e]
Creates and returns a reference,
in the table at index
A reference is a unique integer key.
As long as you do not manually add integer keys into table
If the object at the top of the stack is nil,
Type for arrays of functions to be registered by
[-0, +1, e]
If
If
Leaves a copy of the module on the stack.
[-nup, +0, e]
Registers all functions in the array
When
[-0, +0, –]
Sets the metatable of the object at the top of the stack
as the metatable associated with name
The standard representation for file handles,
which is used by the standard I/O library.
A file handle is implemented as a full userdata,
with a metatable called
This userdata must start with the structure
[-0, +0, e]
This function works like
[-0, +1, e]
Converts any Lua value at the given index to a C string
in a reasonable format.
The resulting string is pushed onto the stack and also
returned by the function.
If
If the value has a metatable with a
[-0, +1, e]
Creates and pushes a traceback of the stack
[-0, +0, –]
Returns the name of the type of the value at the given index.
[-0, +0, –]
Releases reference
If
[-0, +1, e]
Pushes onto the stack a string identifying the current position
of the control at level
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.,
All libraries are implemented through the official C API
and are provided as separate C modules.
Currently, Lua has the following standard libraries:
Except for the basic and the package libraries,
each library provides all its functions as fields of a global table
or as methods of its objects.
To have access to these libraries,
the C host program should call the
The basic library provides core functions to Lua.
If you do not include this library in your application,
you should check carefully whether you need to provide
implementations for some of its facilities.
Calls
This function is a generic interface to the garbage collector.
It performs different functions according to its first argument,
Usually,
If
Returns three values (an iterator function, the table
will iterate over the key–value pairs
(
Loads a chunk.
If
If there are no syntactic errors,
returns the compiled chunk as a function;
otherwise, returns nil plus the error message.
If the resulting function has upvalues,
the first upvalue is set to the value of
The string
Lua does not check the consistency of binary chunks.
Maliciously crafted binary chunks can crash
the interpreter.
Similar to
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.
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.)
The behavior of
If
Otherwise,
returns three values: the
will iterate over all key–value pairs of table
See function
Calls function
This function returns
If
Sets the metatable for the given table.
(You cannot change the metatable of other types from Lua, only from C.)
If
This function returns
When called with no
The conversion of strings can result in integers or floats,
according to the lexical conventions of Lua (see §3.1).
(The string may have leading and trailing spaces and a sign.)
When called with
If the metatable of
This function is similar to
The operations related to coroutines comprise a sub-library of
the basic library and come inside the table
Creates a new coroutine, with body
Returns true when the running coroutine can yield.
A running coroutine is yieldable if it is not the main thread and
it is not inside a non-yieldable C function.
Starts or continues the execution of coroutine
If the coroutine runs without any errors,
Returns the running coroutine plus a boolean,
true when the running coroutine is the main one.
Returns the status of coroutine
Creates a new coroutine, with body
Suspends the execution of the calling coroutine.
Any arguments to
The package library provides basic
facilities for loading modules in Lua.
It exports one function directly in the global environment:
Loads the given module.
The function starts by looking into the
To find a loader,
First
Once a loader is found,
If there is any error loading or running the module,
or if it cannot find any loader for the module,
then
A string describing some compile-time configurations for packages.
This string is a sequence of lines:
The path used by
Lua initializes the C path
A table used by
This variable is only a reference to the real table;
assignments to this variable do not change the
table used by
Dynamically links the host program with the C library
If
This is a low-level function.
It completely bypasses the package and module system.
Unlike
This function is not supported by Standard C.
As such, it is only available on some platforms
(Windows, Linux, Mac OS X, Solaris, BSD,
plus other Unix systems that support the
The path used by
At start-up, Lua initializes this variable with
the value of the environment variable
A table to store loaders for specific modules
(see
This variable is only a reference to the real table;
assignments to this variable do not change the
table used by
A table used by
Each entry in this table is a searcher function.
When looking for a module,
Lua initializes this table with four searcher functions.
The first searcher simply looks for a loader in the
The second searcher looks for a loader as a Lua library,
using the path stored at
The third searcher looks for a loader as a C library,
using the path given by the variable
the searcher for module
The fourth searcher tries an all-in-one loader.
It searches the C path for a library for
the root name of the given module.
For instance, when requiring
All searchers except the first one (preload) return as the extra value
the file name where the module was found,
as returned by
Searches for the given
A path is a string containing a sequence of
templates separated by semicolons.
For each template,
the function replaces each interrogation mark (if any)
in the template with a copy of
For instance, if the path is the string
the search for the name
Returns the resulting name of the first file that it can
open in read mode (after closing the file),
or nil plus an error message if none succeeds.
(This error message lists all file names it tried to open.)
This library provides generic functions for string manipulation,
such as finding and extracting substrings, and pattern matching.
When indexing a string in Lua, the first character is at position 1
(not at 0, as in C).
Indices are allowed to be negative and are interpreted as indexing backwards,
from the end of the string.
Thus, the last character is at position -1, and so on.
The string library provides all its functions inside the table
The string library assumes one-byte character encodings.
Numerical codes are not necessarily portable across platforms.
Numerical codes are not necessarily portable across platforms.
Returns a string containing a binary representation
(a binary chunk)
of the given function,
so that a later
Functions with upvalues have only their number of upvalues saved.
When (re)loaded,
those upvalues receive fresh instances containing nil.
(You can use the debug library to serialize
and reload the upvalues of a function
in a way adequate to your needs.)
Looks for the first match of
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 ISO C function
may produce the string:
Options
As an example, the following loop
will iterate over all the words from string
The next example collects all pairs
For this function, a caret '
If
If
If
In any case,
if the pattern specifies no captures,
then it behaves as if the whole pattern was inside a capture.
If the value returned by the table query or by the function call
is a string or a number,
then it is used as the replacement string;
otherwise, if it is false or nil,
then there is no replacement
(that is, the original match is kept in the string).
Here are some examples:
Returns a binary string containing the values
Returns the size of a string resulting from
If, after the translation of negative indices,
Returns the values packed in string
Patterns in Lua are described by regular strings,
which are interpreted as patterns by the pattern-matching functions
A character class is used to represent a set of characters.
The following combinations are allowed in describing a character class:
The interaction between ranges and classes is not defined.
Therefore, patterns like
For all classes represented by single letters (
The definitions of letter, space, and other character groups
depend on the current locale.
In particular, the class
A pattern item can be
A pattern is a sequence of pattern items.
A caret '
A pattern can contain sub-patterns enclosed in parentheses;
they describe captures.
When a match succeeds, the substrings of the subject string
that match captures are stored (captured) for future use.
Captures are numbered according to their left parentheses.
For instance, in the pattern
As a special case, the empty capture
The first argument to
A format string is a sequence of conversion options.
The conversion options are as follows:
(A "
For options "
Any format string starts as if prefixed by "
Alignment works as follows:
For each option,
the format gets extra padding until the data starts
at an offset that is a multiple of the minimum between the
option size and the maximum alignment;
this minimum must be a power of 2.
Options "
All padding is filled with zeros by
This library provides basic support for UTF-8 encoding.
It provides all its functions inside the table
Unless stated otherwise,
all functions that expect a byte position as a parameter
assume that the given position is either the start of a byte sequence
or one plus the length of the subject string.
As in the string library,
negative indices count from the end of the string.
Returns values so that the construction
will iterate over all characters in string
As a special case,
when
This function assumes that
This library provides generic functions for table manipulation.
It provides all its functions inside the table
Remember that, whenever an operation needs the length of a table,
the table must be a proper sequence
or have a
Given a list where all elements are strings or numbers,
returns the string
Inserts element
Moves elements from table
Returns a new table with all parameters stored into keys 1, 2, etc.
and with a field "
Removes from
The default value for
Sorts list elements in a given order, in-place,
from
The sort algorithm is not stable;
that is, elements considered equal by the given order
may have their relative positions changed by the sort.
Returns the elements from the given list.
This function is equivalent to
By default,
This library provides basic mathematical functions.
It provides all its functions and constants inside the table
Returns the absolute value of
Returns the arc cosine of
Returns the arc sine of
Returns the arc tangent of
The default value for
Returns the smallest integral value larger than or equal to
Returns the cosine of
Converts the angle
Returns the value ex
(where
Returns the largest integral value smaller than or equal to
Returns the remainder of the division of
The float value
Returns the logarithm of
Returns the argument with the maximum value,
according to the Lua operator
Returns the argument with the minimum value,
according to the Lua operator
Returns the integral part of
The value of π.
Converts the angle
When called without arguments,
returns a pseudo-random float with uniform distribution
in the range [0,1).
When called with two integers
This function is an interface to the underling
pseudo-random generator function provided by C.
No guarantees can be given for its statistical properties.
Sets
Returns the sine of
Returns the square root of
Returns the tangent of
If the value
Returns "
Returns a boolean,
true if integer
The I/O library provides two different styles for file manipulation.
The first one uses implicit file handles;
that is, there are operations to set a default input file and a
default output file,
and all input/output operations are over these default files.
The second style uses explicit file handles.
When using implicit file handles,
all operations are supplied by table
The table
Unless otherwise stated,
all I/O functions return nil on failure
(plus an error message as a second result and
a system-dependent error code as a third result)
and some value different from nil on success.
On non-POSIX systems,
the computation of the error message and error code
in case of errors
may be not thread safe,
because they rely on the global C variable
Equivalent to
Equivalent to
When called with a file name, it opens the named file (in text mode),
and sets its handle as the default input file.
When called with a file handle,
it simply sets this file handle as the default input file.
When called without parameters,
it returns the current default input file.
In case of errors this function raises the error,
instead of returning an error code.
Opens the given file name in read mode
and returns an iterator function that
works like
The call
In case of errors this function raises the error,
instead of returning an error code.
This function opens a file,
in the mode specified in the string
The
The
Similar to
This function is system dependent and is not available
on all platforms.
Starts program
Equivalent to
Returns a handle for a temporary file.
This file is opened in update mode
and it is automatically removed when the program ends.
Checks whether
Equivalent to
Closes
When closing a file handle created with
Saves any written data to
Returns an iterator function that,
each time it is called,
reads the file according to the given formats.
When no format is given,
uses "
will iterate over all characters of the file,
starting at the current position.
Unlike
In case of errors this function raises the error,
instead of returning an error code.
Reads the file
The available formats are
The formats "
Sets and gets the file position,
measured from the beginning of the file,
to the position given by
In case of success,
The default value for
Sets the buffering mode for an output file.
There are three available modes:
For the last two cases,
Writes the value of each of its arguments to
In case of success, this function returns
This library is implemented through table
Returns an approximation of the amount in seconds of CPU time
used by the program.
Returns a string or a table containing date and time,
formatted according to the given string
If the
If
If
When called without arguments,
On non-POSIX systems,
this function may be not thread safe
because of its reliance on C function
Returns the difference, in seconds,
from time
This function is equivalent to the ISO C function
When called without a
Calls the ISO C function
If the optional second argument
Returns the value of the process environment variable
Deletes the file (or empty directory, on POSIX systems)
with the given name.
If this function fails, it returns nil,
plus a string describing the error and the error code.
Renames file or directory named
Sets the current locale of the program.
If
When called with nil as the first argument,
this function only returns the name of the current locale
for the given category.
This function may be not thread safe
because of its reliance on C function
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
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
Returns a string with a file name that can
be used for a temporary file.
The file must be explicitly opened before its use
and explicitly removed when no longer needed.
On POSIX systems,
this function also creates a file with that name,
to avoid security risks.
(Someone else might create the file with wrong permissions
in the time between getting the name and creating the file.)
You still have to open the file to use it
and to remove it (even if you do not use it).
When possible,
you may prefer to use
This library provides
the functionality of the debug interface (§4.9) to Lua programs.
You should exert care when using this library.
Several of its functions
violate basic assumptions about Lua code
(e.g., that variables local to a function
cannot be accessed from outside;
that userdata metatables cannot be changed by Lua code;
that Lua programs do not crash)
and therefore can compromise otherwise secure code.
Moreover, some functions in this library may be slow.
All functions in this library are provided
inside the
Enters an interactive mode with the user,
running each string that the user enters.
Using simple commands and other debug facilities,
the user can inspect global and local variables,
change their values, evaluate expressions, and so on.
A line containing only the word
Note that commands for
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
Returns a table with information about a function.
You can give the function directly
or you can give a number as the value of
The returned table can contain all the fields returned by
For instance, the expression
This function returns the name and the value of the local variable
with index
The first parameter or local variable has index 1, and so on,
following the order that they are declared in the code,
counting only the variables that are active
in the current scope of the function.
Negative indices refer to vararg parameters;
-1 is the first vararg parameter.
The function returns nil if there is no variable with the given index,
and raises an error when called with a level out of range.
(You can call
Variable names starting with '
The parameter
Returns the metatable of the given
Returns the registry table (see §4.5).
This function returns the name and the value of the upvalue
with index
Variable names starting with '
Returns the Lua value associated to
Sets the given function as a hook.
The string
Moreover,
with a
When called without arguments,
When the hook is called, its first parameter is a string
describing the event that has triggered its call:
This function assigns the value
See
Sets the metatable for the given
This function assigns the value
Sets the given
Returns
If
Returns a unique identifier (as a light userdata)
for the upvalue numbered
These unique identifiers allow a program to check whether different
closures share upvalues.
Lua closures that share an upvalue
(that is, that access a same external local variable)
will return identical ids for those upvalue indices.
Make the
Although Lua has been designed as an extension language,
to be embedded in a host C program,
it is also frequently used as a standalone language.
An interpreter for Lua as a standalone language,
called simply
The options are:
After handling its options,
When called without option
When called with option
All options are handled in order, except
will first set
Before running any code,
the table is like this:
If there is no script in the call,
the interpreter name goes to index 0,
followed by the other arguments.
For instance, the call
will print "
In interactive mode,
Lua repeatedly prompts and waits for a line.
After reading a line,
Lua first try to interpret the line as an expression.
If it succeeds, it prints its value.
Otherwise, it interprets the line as a statement.
If you write an incomplete statement,
the interpreter waits for its completion
by issuing a different prompt.
In case of unprotected errors in the script,
the interpreter reports the error to the standard error stream.
If the error object is not a string but
has a metamethod
When finishing normally,
the interpreter closes its main Lua state
(see
To allow the use of Lua as a
script interpreter in Unix systems,
the standalone interpreter skips
the first line of a chunk if it starts with
(Of course,
the location of the Lua interpreter may be different in your machine.
If
is a more portable solution.)
Here we list the incompatibilities that you may find when moving a program
from Lua 5.2 to Lua 5.3.
You can avoid some incompatibilities by compiling Lua with
appropriate options (see file
Lua versions can always change the C API in ways that
do not imply source-code changes in a program,
such as the numeric values for constants
or the implementation of functions as macros.
Therefore,
you should not assume that binaries are compatible between
different Lua versions.
Always recompile clients of the Lua API when
using a new version.
Similarly, Lua versions can always change the internal representation
of precompiled chunks;
precompiled chunks are not compatible between different Lua versions.
The standard paths in the official distribution may
change between versions.
You can fix these differences by forcing a number to be a float
(in Lua 5.2 all numbers were float),
in particular writing constants with an ending
(Formally this is not an incompatibility,
because Lua does not specify how numbers are formatted as strings,
but some programs assumed a specific format.)
Here is the complete syntax of Lua in extended BNF.
As usual in extended BNF,
{A} means 0 or more As,
and [A] means an optional A.
(For operator precedences, see §3.4.8;
for a description of the terminals
Name, Numeral,
and LiteralString, see §3.1.)
raw_get(get_metatable(obj) or {}, "__" .. event_name)
2.5 – Garbage Collection
lua_gc in C
or collectgarbage in Lua.
You can also use these functions to control
the collector directly (e.g., stop and restart it).
2.5.1 – Garbage-Collection Metamethods
__gc".
Note that if you set a metatable without a __gc field
and later create that field in the metatable,
the object will not be marked for finalization.
However, after an object has been marked,
you can freely change the __gc field of its metatable.
__gc metamethod:
If it is a function,
Lua calls it with the object as its single argument;
if the metamethod is not a function,
Lua simply ignores it.
lua_close),
Lua calls the finalizers of all objects marked for finalization,
following the reverse order that they were marked.
If any finalizer marks objects for collection during that phase,
these marks have no effect.
2.5.2 – Weak Tables
__mode field of its metatable.
If the __mode field is a string containing the character 'k',
the keys in the table are weak.
If __mode contains 'v',
the values in the table are weak.
2.6 – Coroutines
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.
coroutine.resume.
When you first call coroutine.resume,
passing as its first argument
a thread returned by coroutine.create,
the coroutine starts its execution,
at the first line of its main function.
Extra arguments passed to coroutine.resume are passed
as arguments to the coroutine's main function.
After the coroutine starts running,
it runs until it terminates or yields.
coroutine.resume returns true,
plus any values returned by the coroutine main function.
In case of errors, coroutine.resume returns false
plus an error message.
coroutine.yield.
When a coroutine yields,
the corresponding coroutine.resume returns immediately,
even if the yield happens inside nested function calls
(that is, not in the main function,
but in a function directly or indirectly called by the main function).
In the case of a yield, coroutine.resume also returns true,
plus any values passed to coroutine.yield.
The next time you resume the same coroutine,
it continues its execution from the point where it yielded,
with the call to coroutine.yield returning any extra
arguments passed to coroutine.resume.
coroutine.create,
the coroutine.wrap function also creates a coroutine,
but instead of returning the coroutine itself,
it returns a function that, when called, resumes the coroutine.
Any arguments passed to this function
go as extra arguments to coroutine.resume.
coroutine.wrap returns all the values returned by coroutine.resume,
except the first one (the boolean error code).
Unlike coroutine.resume,
coroutine.wrap does not catch errors;
any error is propagated to the caller.
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"))
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
lua_newthread, lua_resume,
and lua_yield.
3 – The Language
3.1 – Lexical Conventions
and break do else elseif end
false for function goto if in
local nil not or repeat return
then true until while
and is a reserved word, but And and AND
are two different, valid names.
As a convention,
programs should avoid creating
names that start with an underscore followed by
one or more uppercase letters (such as _VERSION).
+ - * / % ^ #
& ~ | << >> //
== ~= <= >= < > =
( ) { } [ ] ::
; : , . .. ...
\a' (bell),
'\b' (backspace),
'\f' (form feed),
'\n' (newline),
'\r' (carriage return),
'\t' (horizontal tab),
'\v' (vertical tab),
'\\' (backslash),
'\"' (quotation mark [double quote]),
and '\'' (apostrophe [single quote]).
A backslash followed by a real newline
results in a newline in the string.
The escape sequence '\z' skips the following span
of white-space characters,
including line breaks;
it is particularly useful to break and indent a long literal string
into multiple lines without adding the newlines and spaces
into the string contents.
\0'.
More generally,
we can specify any byte in a literal string by its numerical value.
This can be done
with the escape sequence \xXX,
where XX is a sequence of exactly two hexadecimal digits,
or with the escape sequence \ddd,
where ddd is a sequence of up to three decimal digits.
(Note that if a decimal escape sequence is to be followed by a digit,
it must be expressed using exactly three digits.)
\u{XXX}
(note the mandatory enclosing brackets),
where XXX is a sequence of one or more hexadecimal digits
representing the character code point.
[[,
an opening long bracket of level 1 is written as [=[,
and so on.
A closing long bracket is defined similarly;
for instance,
a closing long bracket of level 4 is written as ]====].
A long literal starts with an opening long bracket of any level and
ends at the first closing long bracket of the same level.
It can contain any text except a closing bracket of the same level.
Literals in this bracketed form can run for several lines,
do not interpret any escape sequences,
and ignore long brackets of any other level.
Any kind of end-of-line sequence
(carriage return, newline, carriage return followed by newline,
or newline followed by carriage return)
is converted to a simple newline.
a' is coded as 97,
newline is coded as 10, and '1' is coded as 49),
the five literal strings below denote the same string:
a = 'alo\n123"'
a = "alo\n123\""
a = '\97lo\10\04923"'
a = [[alo
123"]]
a = [==[
alo
123"]==]
e' or 'E'.
Lua also accepts hexadecimal constants,
which start with 0x or 0X.
Hexadecimal constants also accept an optional fractional part
plus an optional binary exponent,
marked by a letter 'p' or 'P'.
A numeric constant with a fractional dot or an exponent
denotes a float;
otherwise it denotes an integer.
Examples of valid integer constants are
3 345 0xff 0xBEBADA
3.0 3.1416 314.16e-2 0.31416E1 34e1
0x0.1E 0xA23p-4 0X1.921FB54442D18P+1
--)
anywhere outside a string.
If the text immediately after -- is not an opening long bracket,
the comment is a short comment,
which runs until the end of the line.
Otherwise, it is a long comment,
which runs until the corresponding closing long bracket.
Long comments are frequently used to disable code temporarily.
3.2 – Variables
var ::= Name
var ::= prefixexp ‘[’ exp ‘]’
t[i] is equivalent to
a call gettable_event(t,i).
(See §2.4 for a complete description of the
gettable_event function.
This function is not defined or callable in Lua.
We use it here only for explanatory purposes.)
var.Name is just syntactic sugar for
var["Name"]:
var ::= prefixexp ‘.’ Name
x
is equivalent to _ENV.x.
Due to the way that chunks are compiled,
_ENV is never a global name (see §2.2).
3.3 – Statements
3.3.1 – Blocks
block ::= {stat}
stat ::= ‘;’
a = b + c
(print or io.write)('done')
a = b + c(print or io.write)('done')
a = b + c; (print or io.write)('done')
;(print or io.write)('done')
stat ::= do block end
3.3.2 – Chunks
chunk ::= block
_ENV (see §2.2).
The resulting function always has _ENV as its only upvalue,
even if it does not use that variable.
luac and function string.dump for details.
Programs in source and compiled forms are interchangeable;
Lua automatically detects the file type and acts accordingly (see load).
3.3.3 – Assignment
stat ::= varlist ‘=’ explist
varlist ::= var {‘,’ var}
explist ::= exp {‘,’ exp}
i = 3
i, a[i] = i+1, 20
a[3] to 20, without affecting a[4]
because the i in a[i] is evaluated (to 3)
before it is assigned 4.
Similarly, the line
x, y = y, x
x and y,
and
x, y, z = y, z, x
x, y, and z.
t[i] = val is equivalent to
settable_event(t,i,val).
(See §2.4 for a complete description of the
settable_event function.
This function is not defined or callable in Lua.
We use it here only for explanatory purposes.)
x = val
is equivalent to the assignment
_ENV.x = val (see §2.2).
3.3.4 – Control Structures
stat ::= while exp do block end
stat ::= repeat block until exp
stat ::= if exp then block {elseif exp then block} [else block] end
stat ::= goto Name
stat ::= label
label ::= ‘::’ Name ‘::’
stat ::= break
stat ::= return [explist] [‘;’]
do return end,
because now return is the last statement in its (inner) block.
3.3.5 – For Statement
stat ::= for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end
for v = e1, e2, e3 do block end
do
local var, limit, step = tonumber(e1), tonumber(e2), tonumber(e3)
if not (var and limit and step) then error() end
var = var - step
while true do
var = var + step
if (step >= 0 and var > limit) or (step < 0 and var < limit) then
break
end
local v = var
block
end
end
var, limit, and step are invisible variables.
The names shown here are for explanatory purposes only.
v is local to the loop body.
If you need its value after the loop,
assign it to another variable before exiting the loop.
stat ::= for namelist in explist do block end
namelist ::= Name {‘,’ Name}
for var_1, ···, var_n in explist do block end
do
local f, s, var = explist
while true do
local var_1, ···, var_n = f(s, var)
if var_1 == nil then break end
var = var_1
block
end
end
explist is evaluated only once.
Its results are an iterator function,
a state,
and an initial value for the first iterator variable.
f, s, and var are invisible variables.
The names are here for explanatory purposes only.
var_i are local to the loop;
you cannot use their values after the for ends.
If you need these values,
then assign them to other variables before breaking or exiting the loop.
3.3.6 – Function Calls as Statements
stat ::= functioncall
3.3.7 – Local Declarations
stat ::= local namelist [‘=’ explist]
3.4 – Expressions
exp ::= prefixexp
exp ::= nil | false | true
exp ::= Numeral
exp ::= LiteralString
exp ::= functiondef
exp ::= tableconstructor
exp ::= ‘...’
exp ::= exp binop exp
exp ::= unop exp
prefixexp ::= var | functioncall | ‘(’ exp ‘)’
...'), can only be used when
directly inside a vararg function;
they are explained in §3.4.11.
f() -- adjusted to 0 results
g(f(), x) -- f() is adjusted to 1 result
g(x, f()) -- g gets x plus all results from f()
a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
a,b = ... -- a gets the first vararg parameter, b gets
-- the second (both a and b can get nil if there
-- is no corresponding vararg parameter)
a,b,c = x, f() -- f() is adjusted to 2 results
a,b,c = f() -- f() is adjusted to 3 results
return f() -- returns all results from f()
return ... -- returns all received vararg parameters
return x,y,f() -- returns x, y, and all results from f()
{f()} -- creates a list with all results from f()
{...} -- creates a list with all vararg parameters
{f(), nil} -- f() is adjusted to 1 result
(f(x,y,z)) is always a single value,
even if f returns several values.
(The value of (f(x,y,z)) is the first value returned by f
or nil if f does not return any values.)
3.4.1 – Arithmetic Operators
+: addition-: subtraction*: multiplication/: float division//: floor division%: modulo^: exponentiation-: unary minus/)
always convert their operands to floats
and the result is always a float.
Exponentiation uses the ISO C function pow,
so that it works for non-integer exponents too.
//) is a division
that rounds the quotient towards minus infinite,
that is, the floor of the division of its operands.
3.4.2 – Bitwise Operators
&: bitwise and|: bitwise or~: bitwise exclusive or>>: right shift<<: left shift~: unary bitwise not3.4.3 – Coercions and Conversions
format function from the string library
(see string.format).
3.4.4 – Relational Operators
==: equality~=: inequality<: less than>: greater than<=: less or equal>=: greater or equal==) first compares the type of its operands.
If the types are different, then the result is false.
Otherwise, the values of the operands are compared.
Strings are compared in the obvious way.
Numbers follow the usual rule for binary operations:
if both operands are integers,
they are compared as integers;
otherwise, they are converted to floats
and compared as such.
"0"==0 evaluates to false,
and t[0] and t["0"] denote different
entries in a table.
~= is exactly the negation of equality (==).
a > b is translated to b < a
and a >= b is translated to b <= a.
3.4.5 – Logical Operators
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
--> indicates the result of the preceding expression.)
3.4.6 – Concatenation
..').
If both operands are strings or numbers, then they are converted to
strings according to the rules described in §3.4.3.
Otherwise, the __concat metamethod is called (see §2.4).
3.4.7 – The Length Operator
#.
The length of a string is its number of bytes
(that is, the usual meaning of string length when each
character is one byte).
__len metamethod (see §2.4).
__len metamethod is given,
the length of a table t is only defined if the
table is a sequence,
that is,
the set of its positive numeric keys is equal to {1..n}
for some non-negative integer n.
In that case, n is its length.
Note that a table like
{10, 20, nil, 40}
4
but does not have the key 3.
(So, there is no n such that the set {1..n} is equal
to the set of positive numeric keys of that table.)
Note, however, that non-numeric keys do not interfere
with whether a table is a sequence.
3.4.8 – Precedence
or
and
< > <= >= ~= ==
|
~
&
<< >>
..
+ -
* / // %
unary operators (not # - ~)
^
..') and exponentiation ('^')
operators are right associative.
All other binary operators are left associative.
3.4.9 – Table Constructors
tableconstructor ::= ‘{’ [fieldlist] ‘}’
fieldlist ::= field {fieldsep field} [fieldsep]
field ::= ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp
fieldsep ::= ‘,’ | ‘;’
[exp1] = exp2 adds to the new table an entry
with key exp1 and value exp2.
A field of the form name = exp is equivalent to
["name"] = exp.
Finally, fields of the form exp are equivalent to
[i] = exp, where i are consecutive integers
starting with 1.
Fields in the other formats do not affect this counting.
For example,
a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 }
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
exp
and the expression is a function call or a vararg expression,
then all values returned by this expression enter the list consecutively
(see §3.4.10).
3.4.10 – Function Calls
functioncall ::= prefixexp args
functioncall ::= prefixexp ‘:’ Name args
v:name(args)
is syntactic sugar for v.name(v,args),
except that v is evaluated only once.
args ::= ‘(’ [explist] ‘)’
args ::= tableconstructor
args ::= LiteralString
f{fields} is
syntactic sugar for f({fields});
that is, the argument list is a single new table.
A call of the form f'string'
(or f"string" or f[[string]])
is syntactic sugar for f('string');
that is, the argument list is a single literal string.
return functioncall is called
a tail call.
Lua implements proper tail calls
(or proper tail recursion):
in a tail call,
the called function reuses the stack entry of the calling function.
Therefore, there is no limit on the number of nested tail calls that
a program can execute.
However, a tail call erases any debug information about the
calling function.
Note that a tail call only happens with a particular syntax,
where the return has one single function call as argument;
this syntax makes the calling function return exactly
the returns of the called function.
So, none of the following examples are tail calls:
return (f(x)) -- results adjusted to 1
return 2 * f(x)
return x, f(x) -- additional results
f(x); return -- results discarded
return x or f(x) -- results adjusted to 1
3.4.11 – Function Definitions
functiondef ::= function funcbody
funcbody ::= ‘(’ [parlist] ‘)’ block end
stat ::= function funcname funcbody
stat ::= local function Name funcbody
funcname ::= Name {‘.’ Name} [‘:’ Name]
function f () body end
f = function () body end
function t.a.b.c.f () body end
t.a.b.c.f = function () body end
local function f () body end
local f; f = function () body end
local f = function () body end
f.)
parlist ::= namelist [‘,’ ‘...’] | ‘...’
...')
at the end of its parameter list.
A vararg function does not adjust its argument list;
instead, it collects all extra arguments and supplies them
to the function through a vararg expression,
which is also written as three dots.
The value of this expression is a list of all actual extra arguments,
similar to a function with multiple results.
If a vararg expression is used inside another expression
or in the middle of a list of expressions,
then its return list is adjusted to one element.
If the expression is used as the last element of a list of expressions,
then no adjustment is made
(unless that last expression is enclosed in parentheses).
function f(a, b) end
function g(a, b, ...) end
function r() return 1,2,3 end
CALL PARAMETERS
f(3) a=3, b=nil
f(3, 4) a=3, b=4
f(3, 4, 5) a=3, b=4
f(r(), 10) a=1, b=10
f(r()) a=1, b=2
g(3) a=3, b=nil, ... --> (nothing)
g(3, 4) a=3, b=4, ... --> (nothing)
g(3, 4, 5, 8) a=3, b=4, ... --> 5 8
g(5, r()) a=5, b=1, ... --> 2 3
self.
Thus, the statement
function t.a.b.c:f (params) body end
t.a.b.c.f = function (self, params) body end
3.5 – Visibility Rules
x = 10 -- global variable
do -- new block
local x = x -- new 'x', with value 10
print(x) --> 10
x = x+1
do -- another block
local x = x+1 -- another 'x'
print(x) --> 12
end
print(x) --> 11
end
print(x) --> 10 (the global one)
local x = x,
the new x being declared is not in scope yet,
and so the second x refers to the outside variable.
a = {}
local x = 20
for i=1,10 do
local y = 0
a[i] = function () y=y+1; return x+y end
end
y variable,
while all of them share the same x.
4 – The Application Program Interface
lua.h.
LUA_USE_APICHECK defined.
4.1 – The Stack
lua_CFunction).
4.2 – Stack Size
lua_checkstack
to ensure that the stack has enough space for pushing new elements.
LUA_MINSTACK extra slots.
LUA_MINSTACK is defined as 20,
so that usually you do not have to worry about stack space
unless your code has loops pushing elements onto the stack.
lua_call),
Lua ensures that the stack has enough space for all results,
but it does not ensure any extra space.
So, before pushing anything in the stack after such a call
you should use lua_checkstack.
4.3 – Valid and Acceptable Indices
1 ≤ abs(index) ≤ top).
Usually, functions that can modify the value at an index
require valid indices.
LUA_TNONE,
which behaves like a nil value.
4.4 – C Closures
lua_pushcclosure);
these values are called upvalues and are
accessible to the function whenever it is called.
lua_upvalueindex.
The first value associated with a function is at position
lua_upvalueindex(1), and so on.
Any access to lua_upvalueindex(n),
where n is greater than the number of upvalues of the
current function (but not greater than 256),
produces an acceptable but invalid index.
4.5 – Registry
LUA_REGISTRYINDEX,
which is a valid index.
Any C library can store data into this table,
but it must take care to choose keys
that are different from those used
by other libraries, to avoid collisions.
Typically, you should use as key a string containing your library name,
or a light userdata with the address of a C object in your code,
or any Lua object created by your code.
As with variable names,
string keys starting with an underscore followed by
uppercase letters are reserved for Lua.
luaL_ref)
and by some predefined values.
Therefore, integer keys must not be used for other purposes.
lua.h.
The following constants are defined:
LUA_RIDX_MAINTHREAD: At this index the registry has
the main thread of the state.
(The main thread is the one created together with the state.)
LUA_RIDX_GLOBALS: At this index the registry has
the global environment.
4.6 – Error Handling in C
longjmp facility to handle errors.
(Lua will use exceptions if you compile it as C++;
search for LUAI_THROW in the source code for details.)
When Lua faces any error
(such as a memory allocation error, type errors, syntax errors,
and runtime errors)
it raises an error;
that is, it does a long jump.
A protected environment uses setjmp
to set a recovery point;
any error jumps to the most recent active recovery point.
lua_atpanic)
and then calls abort,
thus exiting the host application.
Your panic function can avoid this exit by
never returning
(e.g., doing a long jump to your own recovery point outside Lua).
lua_error.
4.7 – Handling Yields in C
longjmp facility to yield a coroutine.
Therefore, if a C function foo calls an API function
and this API function yields
(directly or indirectly by calling another function that yields),
Lua cannot return to foo any more,
because the longjmp removes its frame from the C stack.
lua_yieldk, lua_callk, and lua_pcallk.
All those functions receive a continuation function
(as a parameter named k) to continue execution after a yield.
lua_yieldk,
or when the callee function is either lua_callk or lua_pcallk
and the function called by them yields.)
int original_function (lua_State *L) {
... /* code 1 */
status = lua_pcall(L, n, m, h); /* calls Lua */
... /* code 2 */
}
lua_pcall to yield.
First, we can rewrite our function like here:
int k (lua_State *L, int status, lua_KContext ctx) {
... /* code 2 */
}
int original_function (lua_State *L) {
... /* code 1 */
return k(L, lua_pcall(L, n, m, h), ctx);
}
k is a
continuation function (with type lua_KFunction),
which should do all the work that the original function
was doing after calling lua_pcall.
Now, we must inform Lua that it must call k if the Lua code
being executed by lua_pcall gets interrupted in some way
(errors or yielding),
so we rewrite the code as here,
replacing lua_pcall by lua_pcallk:
int original_function (lua_State *L) {
... /* code 1 */
return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1);
}
lua_pcallk (and lua_callk) will also return normally.
(Of course, instead of calling the continuation in that case,
you can do the equivalent work directly inside the original function.)
ctx) that
was passed originally to lua_pcallk.
(Lua does not use this context value;
it only passes this value from the original function to the
continuation function.)
For lua_pcallk,
the status is the same value that would be returned by lua_pcallk,
except that it is LUA_YIELD when being executed after a yield
(instead of LUA_OK).
For lua_yieldk and lua_callk,
the status is always LUA_YIELD when Lua calls the continuation.
(For these two functions,
Lua will not call the continuation in case of errors,
because they do not handle errors.)
Similarly, when using lua_callk,
you should call the continuation function
with LUA_OK as the status.
(For lua_yieldk, there is not much point in calling
directly the continuation function,
because lua_yieldk usually does not return.)
lua_callk the function and its arguments are
removed from the stack and replaced by the results from the call.)
It also has the same upvalues.
Whatever it returns is handled by Lua as if it were the return
of the original function.
4.8 – Functions and Types
o,
is how many elements the function pops from the stack.
The second field, p,
is how many elements the function pushes onto the stack.
(Any function always pushes its results after popping its arguments.)
A field in the form x|y means the function can push (or pop)
x or y elements,
depending on the situation;
an interrogation mark '?' means that
we cannot know how many elements the function pops/pushes
by looking only at its arguments
(e.g., they may depend on what is on the stack).
The third field, x,
tells whether the function may raise errors:
'-' means the function never raises any error;
'e' means the function may raise errors;
'v' means the function may raise an error on purpose.
lua_absindexint lua_absindex (lua_State *L, int idx);
idx into an absolute index
(that is, one that does not depend on the stack top).
lua_Alloctypedef void * (*lua_Alloc) (void *ud,
void *ptr,
size_t osize,
size_t nsize);
realloc,
but not exactly the same.
Its arguments are
ud, an opaque pointer passed to lua_newstate;
ptr, a pointer to the block being allocated/reallocated/freed;
osize, the original size of the block or some code about what
is being allocated;
and nsize, the new size of the block.
ptr is not NULL,
osize is the size of the block pointed by ptr,
that is, the size given when it was allocated or reallocated.
ptr is NULL,
osize encodes the kind of object that Lua is allocating.
osize is any of
LUA_TSTRING, LUA_TTABLE, LUA_TFUNCTION,
LUA_TUSERDATA, or LUA_TTHREAD when (and only when)
Lua is creating a new object of that type.
When osize is some other value,
Lua is allocating memory for something else.
nsize is zero,
the allocator must behave like free
and return NULL.
nsize is not zero,
the allocator must behave like realloc.
The allocator returns NULL
if and only if it cannot fulfill the request.
Lua assumes that the allocator never fails when
osize >= nsize.
luaL_newstate.
static void *l_alloc (void *ud, void *ptr, size_t osize,
size_t nsize) {
(void)ud; (void)osize; /* not used */
if (nsize == 0) {
free(ptr);
return NULL;
}
else
return realloc(ptr, nsize);
}
free(NULL) has no effect and that
realloc(NULL,size) is equivalent to malloc(size).
This code assumes that realloc does not fail when shrinking a block.
(Although Standard C does not ensure this behavior,
it seems to be a safe assumption.)
lua_arithvoid lua_arith (lua_State *L, int op);
op must be one of the following constants:
LUA_OPADD: performs addition (+)LUA_OPSUB: performs subtraction (-)LUA_OPMUL: performs multiplication (*)LUA_OPDIV: performs float division (/)LUA_OPIDIV: performs floor division (//)LUA_OPMOD: performs modulo (%)LUA_OPPOW: performs exponentiation (^)LUA_OPUNM: performs mathematical negation (unary -)LUA_OPBNOT: performs bitwise negation (~)LUA_OPBAND: performs bitwise and (&)LUA_OPBOR: performs bitwise or (|)LUA_OPBXOR: performs bitwise exclusive or (~)LUA_OPSHL: performs left shift (<<)LUA_OPSHR: performs right shift (>>)lua_atpaniclua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);
lua_callvoid lua_call (lua_State *L, int nargs, int nresults);
lua_call;
nargs is the number of arguments that you pushed onto the stack.
All arguments and the function value are popped from the stack
when the function is called.
The function results are pushed onto the stack when the function returns.
The number of results is adjusted to nresults,
unless nresults is LUA_MULTRET.
In this case, all results from the function are pushed.
Lua takes care that the returned values fit into the stack space.
The function results are pushed onto the stack in direct order
(the first result is pushed first),
so that after the call the last result is on the top of the stack.
longjmp).
a = f("how", t.x, 14)
lua_getglobal(L, "f"); /* function to be called */
lua_pushliteral(L, "how"); /* 1st argument */
lua_getglobal(L, "t"); /* table to be indexed */
lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */
lua_remove(L, -2); /* remove 't' from the stack */
lua_pushinteger(L, 14); /* 3rd argument */
lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */
lua_setglobal(L, "a"); /* set global 'a' */
lua_callkvoid lua_callk (lua_State *L,
int nargs,
int nresults,
lua_KContext ctx,
lua_KFunction k);
lua_call,
but allows the called function to yield (see §4.7).
lua_CFunctiontypedef int (*lua_CFunction) (lua_State *L);
lua_gettop(L) returns the number of arguments received by the function.
The first argument (if any) is at index 1
and its last argument is at index lua_gettop(L).
To return values to Lua, a C function just pushes them onto the stack,
in direct order (the first result is pushed first),
and returns the number of results.
Any other value in the stack below the results will be properly
discarded by Lua.
Like a Lua function, a C function called by Lua can also return
many results.
static int foo (lua_State *L) {
int n = lua_gettop(L); /* number of arguments */
lua_Number sum = 0.0;
int i;
for (i = 1; i <= n; i++) {
if (!lua_isnumber(L, i)) {
lua_pushliteral(L, "incorrect argument");
lua_error(L);
}
sum += lua_tonumber(L, i);
}
lua_pushnumber(L, sum/n); /* first result */
lua_pushnumber(L, sum); /* second result */
return 2; /* number of results */
}
lua_checkstackint lua_checkstack (lua_State *L, int n);
n extra slots.
It returns false if it cannot fulfill the request,
either because it would cause the stack
to be larger than a fixed maximum size
(typically at least several thousand elements) or
because it cannot allocate memory for the extra space.
This function never shrinks the stack;
if the stack is already larger than the new size,
it is left unchanged.
lua_closevoid lua_close (lua_State *L);
lua_compareint lua_compare (lua_State *L, int index1, int index2, int op);
index1 satisfies op
when compared with the value at index index2,
following the semantics of the corresponding Lua operator
(that is, it may call metamethods).
Otherwise returns 0.
Also returns 0 if any of the indices is not valid.
op must be one of the following constants:
LUA_OPEQ: compares for equality (==)LUA_OPLT: compares for less than (<)LUA_OPLE: compares for less or equal (<=)lua_concatvoid lua_concat (lua_State *L, int n);
n values at the top of the stack,
pops them, and leaves the result at the top.
If n is 1, the result is the single value on the stack
(that is, the function does nothing);
if n is 0, the result is the empty string.
Concatenation is performed following the usual semantics of Lua
(see §3.4.6).
lua_copyvoid lua_copy (lua_State *L, int fromidx, int toidx);
fromidx
into the valid index toidx,
replacing the value at that position.
Values at other positions are not affected.
lua_createtablevoid lua_createtable (lua_State *L, int narr, int nrec);
narr is a hint for how many elements the table
will have as a sequence;
parameter nrec is a hint for how many other elements
the table will have.
Lua may use these hints to preallocate memory for the new table.
This pre-allocation is useful for performance when you know in advance
how many elements the table will have.
Otherwise you can use the function lua_newtable.
lua_dumpint lua_dump (lua_State *L,
lua_Writer writer,
void *data,
int strip);
lua_dump calls function writer (see lua_Writer)
with the given data
to write them.
strip is true,
the binary representation is created without debug information
about the function.
lua_errorint lua_error (lua_State *L);
luaL_error).
lua_gcint lua_gc (lua_State *L, int what, int data);
what:
LUA_GCSTOP:
stops the garbage collector.
LUA_GCRESTART:
restarts the garbage collector.
LUA_GCCOLLECT:
performs a full garbage-collection cycle.
LUA_GCCOUNT:
returns the current amount of memory (in Kbytes) in use by Lua.
LUA_GCCOUNTB:
returns the remainder of dividing the current amount of bytes of
memory in use by Lua by 1024.
LUA_GCSTEP:
performs an incremental step of garbage collection.
LUA_GCSETPAUSE:
sets data as the new value
for the pause of the collector (see §2.5)
and returns the previous value of the pause.
LUA_GCSETSTEPMUL:
sets data as the new value for the step multiplier of
the collector (see §2.5)
and returns the previous value of the step multiplier.
LUA_GCISRUNNING:
returns a boolean that tells whether the collector is running
(i.e., not stopped).
collectgarbage.
lua_getallocflua_Alloc lua_getallocf (lua_State *L, void **ud);
ud is not NULL, Lua stores in *ud the
opaque pointer given when the memory-allocator function was set.
lua_getfieldint lua_getfield (lua_State *L, int index, const char *k);
t[k],
where t is the value at the given index.
As in Lua, this function may trigger a metamethod
for the "index" event (see §2.4).
lua_getextraspacevoid *lua_getextraspace (lua_State *L);
LUA_EXTRASPACE in luaconf.h.)
lua_getglobalint lua_getglobal (lua_State *L, const char *name);
name.
Returns the type of that value.
lua_getiint lua_geti (lua_State *L, int index, lua_Integer i);
t[i],
where t is the value at the given index.
As in Lua, this function may trigger a metamethod
for the "index" event (see §2.4).
lua_getmetatableint lua_getmetatable (lua_State *L, int index);
lua_gettableint lua_gettable (lua_State *L, int index);
t[k],
where t is the value at the given index
and k is the value at the top of the stack.
lua_gettopint lua_gettop (lua_State *L);
lua_getuservalueint lua_getuservalue (lua_State *L, int index);
lua_insertvoid lua_insert (lua_State *L, int index);
lua_Integertypedef ... lua_Integer;
long long,
(usually a 64-bit two-complement integer),
but that can be changed to long or int
(usually a 32-bit two-complement integer).
(See LUA_INT in luaconf.h.)
LUA_MININTEGER and LUA_MAXINTEGER,
with the minimum and the maximum values that fit in this type.
lua_isbooleanint lua_isboolean (lua_State *L, int index);
lua_iscfunctionint lua_iscfunction (lua_State *L, int index);
lua_isfunctionint lua_isfunction (lua_State *L, int index);
lua_isintegerint lua_isinteger (lua_State *L, int index);
lua_islightuserdataint lua_islightuserdata (lua_State *L, int index);
lua_isnilint lua_isnil (lua_State *L, int index);
lua_isnoneint lua_isnone (lua_State *L, int index);
lua_isnoneornilint lua_isnoneornil (lua_State *L, int index);
lua_isnumberint lua_isnumber (lua_State *L, int index);
lua_isstringint lua_isstring (lua_State *L, int index);
lua_istableint lua_istable (lua_State *L, int index);
lua_isthreadint lua_isthread (lua_State *L, int index);
lua_isuserdataint lua_isuserdata (lua_State *L, int index);
lua_isyieldableint lua_isyieldable (lua_State *L);
lua_KContexttypedef ... lua_KContext;
intptr_t
when intptr_t is available,
so that it can store pointers too.
Otherwise, it is defined as ptrdiff_t.
lua_KFunctiontypedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);
lua_lenvoid lua_len (lua_State *L, int index);
#' operator in Lua (see §3.4.7) and
may trigger a metamethod for the "length" event (see §2.4).
The result is pushed on the stack.
lua_loadint lua_load (lua_State *L,
lua_Reader reader,
void *data,
const char *chunkname,
const char *mode);
lua_load pushes the compiled chunk as a Lua
function on top of the stack.
Otherwise, it pushes an error message.
lua_load are:
LUA_OK: no errors;LUA_ERRSYNTAX:
syntax error during precompilation;LUA_ERRMEM:
memory allocation error;LUA_ERRGCMM:
error while running a __gc metamethod.
(This error has no relation with the chunk being loaded.
It is generated by the garbage collector.)
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.
chunkname argument gives a name to the chunk,
which is used for error messages and in debug information (see §4.9).
lua_load automatically detects whether the chunk is text or binary
and loads it accordingly (see program luac).
The string mode works as in function load,
with the addition that
a NULL value is equivalent to the string "bt".
lua_load uses the stack internally,
so the reader function must always leave the stack
unmodified when returning.
LUA_RIDX_GLOBALS in the registry (see §4.5).
When loading main chunks,
this upvalue will be the _ENV variable (see §2.2).
Other upvalues are initialized with nil.
lua_newstatelua_State *lua_newstate (lua_Alloc f, void *ud);
NULL if it cannot create the thread or the state
(due to lack of memory).
The argument f is the allocator function;
Lua does all memory allocation for this state through this function.
The second argument, ud, is an opaque pointer that Lua
passes to the allocator in every call.
lua_newtablevoid lua_newtable (lua_State *L);
lua_createtable(L, 0, 0).
lua_newthreadlua_State *lua_newthread (lua_State *L);
lua_State that represents this new thread.
The new thread returned by this function shares with the original thread
its global environment,
but has an independent execution stack.
lua_newuserdatavoid *lua_newuserdata (lua_State *L, size_t size);
lua_nextint lua_next (lua_State *L, int index);
lua_next returns 0 (and pushes nothing).
/* 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);
}
lua_tolstring directly on a key,
unless you know that the key is actually a string.
Recall that lua_tolstring may change
the value at the given index;
this confuses the next call to lua_next.
next for the caveats of modifying
the table during its traversal.
lua_Numbertypedef double lua_Number;
LUA_REAL in luaconf.h.)
lua_numbertointegerint lua_numbertointeger (lua_Number n, lua_Integer *p);
n has an integral value.
If that value is within the range of Lua integers,
it is converted to an integer and assigned to *p.
The macro results in a boolean indicating whether the
conversion was successful.
(Note that this range test can be tricky to do
correctly without this macro,
due to roundings.)
lua_pcallint lua_pcall (lua_State *L, int nargs, int nresults, int msgh);
nargs and nresults have the same meaning as
in lua_call.
If there are no errors during the call,
lua_pcall behaves exactly like lua_call.
However, if there is any error,
lua_pcall catches it,
pushes a single value on the stack (the error message),
and returns an error code.
Like lua_call,
lua_pcall always removes the function
and its arguments from the stack.
msgh is 0,
then the error message returned on the stack
is exactly the original error message.
Otherwise, msgh is the stack index of a
message handler.
(In the current implementation, this index cannot be a pseudo-index.)
In case of runtime errors,
this function will be called with the error message
and its return value will be the message
returned on the stack by lua_pcall.
lua_pcall,
since by then the stack has unwound.
lua_pcall function returns one of the following constants
(defined in lua.h):
LUA_OK (0):
success.LUA_ERRRUN:
a runtime error.
LUA_ERRMEM:
memory allocation error.
For such errors, Lua does not call the message handler.
LUA_ERRERR:
error while running the message handler.
LUA_ERRGCMM:
error while running a __gc metamethod.
(This error typically has no relation with the function being called.)
lua_pcallkint lua_pcallk (lua_State *L,
int nargs,
int nresults,
int msgh,
lua_KContext ctx,
lua_KFunction k);
lua_pcall,
but allows the called function to yield (see §4.7).
lua_popvoid lua_pop (lua_State *L, int n);
n elements from the stack.
lua_pushbooleanvoid lua_pushboolean (lua_State *L, int b);
b onto the stack.
lua_pushcclosurevoid lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);
lua_pushcclosure
is called to create and push the C function onto the stack,
with the argument n telling how many values will be
associated with the function.
lua_pushcclosure also pops these values from the stack.
n is 255.
n is zero,
this function creates a light C function,
which is just a pointer to the C function.
In that case, it never raises a memory error.
lua_pushcfunctionvoid lua_pushcfunction (lua_State *L, lua_CFunction f);
function that,
when called, invokes the corresponding C function.
lua_CFunction).
lua_pushcfunction is defined as a macro:
#define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
f is used twice.
lua_pushfstringconst char *lua_pushfstring (lua_State *L, const char *fmt, ...);
sprintf,
but has some important differences:
%%' (inserts the character '%'),
'%s' (inserts a zero-terminated string, with no size restrictions),
'%f' (inserts a lua_Number),
'%L' (inserts a lua_Integer),
'%p' (inserts a pointer as a hexadecimal numeral),
'%d' (inserts an int),
'%c' (inserts an int as a one-byte character), and
'%U' (inserts a long int as a UTF-8 byte sequence).
lua_pushglobaltablevoid lua_pushglobaltable (lua_State *L);
lua_pushintegervoid lua_pushinteger (lua_State *L, lua_Integer n);
n onto the stack.
lua_pushlightuserdatavoid lua_pushlightuserdata (lua_State *L, void *p);
void*.
It is a value (like a number):
you do not create it, it has no individual metatable,
and it is not collected (as it was never created).
A light userdata is equal to "any"
light userdata with the same C address.
lua_pushliteralconst char *lua_pushliteral (lua_State *L, const char *s);
lua_pushlstring,
but can be used only when s is a literal string.
It automatically provides the string length.
lua_pushlstringconst char *lua_pushlstring (lua_State *L, const char *s, size_t len);
s with size len
onto the stack.
Lua makes (or reuses) an internal copy of the given string,
so the memory at s can be freed or reused immediately after
the function returns.
The string can contain any binary data,
including embedded zeros.
lua_pushnilvoid lua_pushnil (lua_State *L);
lua_pushnumbervoid lua_pushnumber (lua_State *L, lua_Number n);
n onto the stack.
lua_pushstringconst char *lua_pushstring (lua_State *L, const char *s);
s
onto the stack.
Lua makes (or reuses) an internal copy of the given string,
so the memory at s can be freed or reused immediately after
the function returns.
s is NULL, pushes nil and returns NULL.
lua_pushthreadint lua_pushthread (lua_State *L);
L onto the stack.
Returns 1 if this thread is the main thread of its state.
lua_pushvaluevoid lua_pushvalue (lua_State *L, int index);
lua_pushvfstringconst char *lua_pushvfstring (lua_State *L,
const char *fmt,
va_list argp);
lua_pushfstring, except that it receives a va_list
instead of a variable number of arguments.
lua_rawequalint lua_rawequal (lua_State *L, int index1, int index2);
index1 and
index2 are primitively equal
(that is, without calling metamethods).
Otherwise returns 0.
Also returns 0 if any of the indices are not valid.
lua_rawgetint lua_rawget (lua_State *L, int index);
lua_gettable, but does a raw access
(i.e., without metamethods).
lua_rawgetiint lua_rawgeti (lua_State *L, int index, lua_Integer n);
t[n],
where t is the table at the given index.
The access is raw;
that is, it does not invoke metamethods.
lua_rawgetpint lua_rawgetp (lua_State *L, int index, const void *p);
t[k],
where t is the table at the given index and
k is the pointer p represented as a light userdata.
The access is raw;
that is, it does not invoke metamethods.
lua_rawlensize_t lua_rawlen (lua_State *L, int index);
#')
with no metamethods;
for userdata, this is the size of the block of memory allocated
for the userdata;
for other values, it is 0.
lua_rawsetvoid lua_rawset (lua_State *L, int index);
lua_settable, but does a raw assignment
(i.e., without metamethods).
lua_rawsetivoid lua_rawseti (lua_State *L, int index, lua_Integer i);
t[i] = v,
where t is the table at the given index
and v is the value at the top of the stack.
lua_rawsetpvoid lua_rawsetp (lua_State *L, int index, const void *p);
t[k] = v,
where t is the table at the given index,
k is the pointer p represented as a light userdata,
and v is the value at the top of the stack.
lua_Readertypedef const char * (*lua_Reader) (lua_State *L,
void *data,
size_t *size);
lua_load.
Every time it needs another piece of the chunk,
lua_load calls the reader,
passing along its data parameter.
The reader must return a pointer to a block of memory
with a new piece of the chunk
and set size to the block size.
The block must exist until the reader function is called again.
To signal the end of the chunk,
the reader must return NULL or set size to zero.
The reader function may return pieces of any size greater than zero.
lua_registervoid lua_register (lua_State *L, const char *name, lua_CFunction f);
f as the new value of global name.
It is defined as a macro:
#define lua_register(L,n,f) \
(lua_pushcfunction(L, f), lua_setglobal(L, n))
lua_removevoid lua_remove (lua_State *L, int index);
lua_replacevoid lua_replace (lua_State *L, int index);
lua_resumeint lua_resume (lua_State *L, lua_State *from, int nargs);
lua_resume,
with nargs being the number of arguments.
This call returns when the coroutine suspends or finishes its execution.
When it returns, the stack contains all values passed to lua_yield,
or all values returned by the body function.
lua_resume returns
LUA_YIELD if the coroutine yields,
LUA_OK if the coroutine finishes its execution
without errors,
or an error code in case of errors (see lua_pcall).
lua_yield,
put on its stack only the values to
be passed as results from yield,
and then call lua_resume.
from represents the coroutine that is resuming L.
If there is no such coroutine,
this parameter can be NULL.
lua_rotatevoid lua_rotate (lua_State *L, int idx, int n);
idx to the top n positions
in the direction of the top, for a positive n,
or -n positions in the direction of the bottom,
for a negative n.
The absolute value of n must not be greater than the size
of the slice being rotated.
lua_setallocfvoid lua_setallocf (lua_State *L, lua_Alloc f, void *ud);
f
with user data ud.
lua_setfieldvoid lua_setfield (lua_State *L, int index, const char *k);
t[k] = v,
where t is the value at the given index
and v is the value at the top of the stack.
lua_setglobalvoid lua_setglobal (lua_State *L, const char *name);
name.
lua_setivoid lua_seti (lua_State *L, int index, lua_Integer n);
t[n] = v,
where t is the value at the given index
and v is the value at the top of the stack.
lua_setmetatablevoid lua_setmetatable (lua_State *L, int index);
lua_settablevoid lua_settable (lua_State *L, int index);
t[k] = v,
where t is the value at the given index,
v is the value at the top of the stack,
and k is the value just below the top.
lua_settopvoid lua_settop (lua_State *L, int index);
index is 0, then all stack elements are removed.
lua_setuservaluevoid lua_setuservalue (lua_State *L, int index);
lua_Statetypedef struct lua_State lua_State;
lua_newstate,
which creates a Lua state from scratch.
lua_statusint lua_status (lua_State *L);
L.
LUA_OK) for a normal thread,
an error code if the thread finished the execution
of a lua_resume with an error,
or LUA_YIELD if the thread is suspended.
LUA_OK.
You can resume threads with status LUA_OK
(to start a new coroutine) or LUA_YIELD
(to resume a coroutine).
lua_stringtonumbersize_t lua_stringtonumber (lua_State *L, const char *s);
s to a number,
pushes that number into the stack,
and returns the total size of the string,
that is, its length plus one.
The conversion can result in an integer or a float,
according to the lexical conventions of Lua (see §3.1).
The string may have leading and trailing spaces and a sign.
If the string is not a valid numeral,
returns 0 and pushes nothing.
(Note that the result can be used as a boolean,
true if the conversion succeeds.)
lua_tobooleanint lua_toboolean (lua_State *L, int index);
lua_toboolean returns true for any Lua value
different from false and nil;
otherwise it returns false.
(If you want to accept only actual boolean values,
use lua_isboolean to test the value's type.)
lua_tocfunctionlua_CFunction lua_tocfunction (lua_State *L, int index);
NULL.
lua_tointegerlua_Integer lua_tointeger (lua_State *L, int index);
lua_tointegerx with isnum equal to NULL.
lua_tointegerxlua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);
lua_Integer.
The Lua value must be an integer,
or a number or string convertible to an integer (see §3.4.3);
otherwise, lua_tointegerx returns 0.
isnum is not NULL,
its referent is assigned a boolean value that
indicates whether the operation succeeded.
lua_tolstringconst char *lua_tolstring (lua_State *L, int index, size_t *len);
len is not NULL,
it also sets *len with the string length.
The Lua value must be a string or a number;
otherwise, the function returns NULL.
If the value is a number,
then lua_tolstring also
changes the actual value in the stack to a string.
(This change confuses lua_next
when lua_tolstring is applied to keys during a table traversal.)
lua_tolstring returns a fully aligned pointer
to a string inside the Lua state.
This string always has a zero ('\0')
after its last character (as in C),
but can contain other zeros in its body.
lua_tolstring
will be valid after the corresponding Lua value is removed from the stack.
lua_tonumberlua_Number lua_tonumber (lua_State *L, int index);
lua_tonumberx with isnum equal to NULL.
lua_tonumberxlua_Number lua_tonumberx (lua_State *L, int index, int *isnum);
lua_Number (see lua_Number).
The Lua value must be a number or a string convertible to a number
(see §3.4.3);
otherwise, lua_tonumberx returns 0.
isnum is not NULL,
its referent is assigned a boolean value that
indicates whether the operation succeeded.
lua_topointerconst void *lua_topointer (lua_State *L, int index);
void*).
The value can be a userdata, a table, a thread, or a function;
otherwise, lua_topointer returns NULL.
Different objects will give different pointers.
There is no way to convert the pointer back to its original value.
lua_tostringconst char *lua_tostring (lua_State *L, int index);
lua_tolstring with len equal to NULL.
lua_tothreadlua_State *lua_tothread (lua_State *L, int index);
lua_State*).
This value must be a thread;
otherwise, the function returns NULL.
lua_touserdatavoid *lua_touserdata (lua_State *L, int index);
NULL.
lua_typeint lua_type (lua_State *L, int index);
LUA_TNONE for a non-valid (but acceptable) index.
The types returned by lua_type are coded by the following constants
defined in lua.h:
LUA_TNIL,
LUA_TNUMBER,
LUA_TBOOLEAN,
LUA_TSTRING,
LUA_TTABLE,
LUA_TFUNCTION,
LUA_TUSERDATA,
LUA_TTHREAD,
and
LUA_TLIGHTUSERDATA.
lua_typenameconst char *lua_typename (lua_State *L, int tp);
tp,
which must be one the values returned by lua_type.
lua_Unsignedtypedef ... lua_Unsigned;
lua_Integer.
lua_upvalueindexint lua_upvalueindex (int i);
i-th upvalue of
the running function (see §4.4).
lua_versionconst lua_Number *lua_version (lua_State *L);
lua_State,
returns the address of the version used to create that state.
When called with NULL,
returns the address of the version running the call.
lua_Writertypedef int (*lua_Writer) (lua_State *L,
const void* p,
size_t sz,
void* ud);
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.
lua_dump from
calling the writer again.
lua_xmovevoid lua_xmove (lua_State *from, lua_State *to, int n);
n values from the stack from,
and pushes them onto the stack to.
lua_yieldint lua_yield (lua_State *L, int nresults);
lua_yieldk,
but it has no continuation (see §4.7).
Therefore, when the thread resumes,
it continues the function that called
the function calling lua_yield.
lua_yieldkint lua_yieldk (lua_State *L,
int nresults,
lua_KContext ctx,
lua_KFunction k);
lua_yieldk,
the running coroutine suspends its execution,
and the call to lua_resume that started this coroutine returns.
The parameter nresults is the number of values from the stack
that will be passed as results to lua_resume.
k to continue
the execution of the C function that yielded (see §4.7).
This continuation function receives the same stack
from the previous function,
with the n results removed and
replaced by the arguments passed to lua_resume.
Moreover,
the continuation function receives the value ctx
that was passed to lua_yieldk.
lua_yieldk should be called with no continuation
(probably in the form of lua_yield),
and the hook should return immediately after the call.
Lua will yield and,
when the coroutine resumes again,
it will continue the normal execution
of the (Lua) function that triggered the hook.
4.9 – The Debug Interface
lua_Debugtypedef struct lua_Debug {
int event;
const char *name; /* (n) */
const char *namewhat; /* (n) */
const char *what; /* (S) */
const char *source; /* (S) */
int currentline; /* (l) */
int linedefined; /* (S) */
int lastlinedefined; /* (S) */
unsigned char nups; /* (u) number of upvalues */
unsigned char nparams; /* (u) number of parameters */
char isvararg; /* (u) */
char istailcall; /* (t) */
char short_src[LUA_IDSIZE]; /* (S) */
/* private part */
other fields
} lua_Debug;
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.
lua_Debug have the following meaning:
source:
the name of the chunk that created the function.
If source starts with a '@',
it means that the function was defined in a file where
the file name follows the '@'.
If source starts with a '=',
the remainder of its contents describe the source in a user-dependent manner.
Otherwise,
the function was defined in a string where
source is that string.
short_src:
a "printable" version of source, to be used in error messages.
linedefined:
the line number where the definition of the function starts.
lastlinedefined:
the line number where the definition of the function ends.
what:
the string "Lua" if the function is a Lua function,
"C" if it is a C function,
"main" if it is the main part of a chunk.
currentline:
the current line where the given function is executing.
When no line information is available,
currentline is set to -1.
name:
a reasonable name for the given function.
Because functions in Lua are first-class values,
they do not have a fixed name:
some functions can be the value of multiple global variables,
while others can be stored only in a table field.
The lua_getinfo function checks how the function was
called to find a suitable name.
If it cannot find a name,
then name is set to NULL.
namewhat:
explains the name field.
The value of namewhat can be
"global", "local", "method",
"field", "upvalue", or "" (the empty string),
according to how the function was called.
(Lua uses the empty string when no other option seems to apply.)
istailcall:
true if this function invocation was called by a tail call.
In this case, the caller of this level is not in the stack.
nups:
the number of upvalues of the function.
nparams:
the number of fixed parameters of the function
(always 0 for C functions).
isvararg:
true if the function is a vararg function
(always true for C functions).
lua_gethooklua_Hook lua_gethook (lua_State *L);
lua_gethookcountint lua_gethookcount (lua_State *L);
lua_gethookmaskint lua_gethookmask (lua_State *L);
lua_getinfoint lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);
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).
what string with the character '>'.
(In that case,
lua_getinfo pops the function from the top of the stack.)
For instance, to know in which line a function f was defined,
you can write the following code:
lua_Debug ar;
lua_getglobal(L, "f"); /* get global 'f' */
lua_getinfo(L, ">S", &ar);
printf("%d\n", ar.linedefined);
what
selects some fields of the structure ar to be filled or
a value to be pushed on the stack:
n': fills in the field name and namewhat;
S':
fills in the fields source, short_src,
linedefined, lastlinedefined, and what;
l': fills in the field currentline;
t': fills in the field istailcall;
u': fills in the fields
nups, nparams, and isvararg;
f':
pushes onto the stack the function that is
running at the given level;
L':
pushes onto the stack a table whose indices are the
numbers of the lines that are valid on the function.
(A valid line is a line with some associated code,
that is, a line where you can put a break point.
Non-valid lines include empty lines and comments.)
f',
its table is pushed after the function.
what).
lua_getlocalconst char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);
ar must be a valid activation record that was
filled by a previous call to lua_getstack or
given as argument to a hook (see lua_Hook).
The index n selects which local variable to inspect;
see debug.getlocal for details about variable indices
and names.
lua_getlocal pushes the variable's value onto the stack
and returns its name.
ar must be NULL and the function
to be inspected must be at the top of the stack.
In this case, only parameters of Lua functions are visible
(as there is no information about what variables are active)
and no values are pushed onto the stack.
NULL (and pushes nothing)
when the index is greater than
the number of active local variables.
lua_getstackint lua_getstack (lua_State *L, int level, lua_Debug *ar);
lua_Debug structure with
an identification of the activation record
of the function executing at a given level.
Level 0 is the current running function,
whereas level n+1 is the function that has called level n
(except for tail calls, which do not count on the stack).
When there are no errors, lua_getstack returns 1;
when called with a level greater than the stack depth,
it returns 0.
lua_getupvalueconst char *lua_getupvalue (lua_State *L, int funcindex, int n);
lua_getupvalue gets the index n of an upvalue,
pushes the upvalue's value onto the stack,
and returns its name.
funcindex points to the closure in the stack.
(Upvalues have no particular order,
as they are active through the whole function.
So, they are numbered in an arbitrary order.)
NULL (and pushes nothing)
when the index is greater than the number of upvalues.
For C functions, this function uses the empty string ""
as a name for all upvalues.
lua_Hooktypedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);
ar argument has its field
event set to the specific event that triggered the hook.
Lua identifies these events with the following constants:
LUA_HOOKCALL, LUA_HOOKRET,
LUA_HOOKTAILCALL, LUA_HOOKLINE,
and LUA_HOOKCOUNT.
Moreover, for line events, the field currentline is also set.
To get the value of any other field in ar,
the hook must call lua_getinfo.
event can be LUA_HOOKCALL,
the normal value, or LUA_HOOKTAILCALL, for a tail call;
in this case, there will be no corresponding return event.
lua_yieldk,
lua_pcallk, or lua_callk with a non-null k.
lua_yield with nresults equal to zero.
lua_sethookvoid lua_sethook (lua_State *L, lua_Hook f, int mask, int count);
f is the hook function.
mask specifies on which events the hook will be called:
it is formed by a bitwise or of the constants
LUA_MASKCALL,
LUA_MASKRET,
LUA_MASKLINE,
and LUA_MASKCOUNT.
The count argument is only meaningful when the mask
includes LUA_MASKCOUNT.
For each event, the hook is called as explained below:
count instructions.
(This event only happens while Lua is executing a Lua function.)
mask to zero.
lua_setlocalconst char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);
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.
NULL (and pops nothing)
when the index is greater than
the number of active local variables.
lua_setupvalueconst char *lua_setupvalue (lua_State *L, int funcindex, int n);
funcindex and n are as in the lua_getupvalue
(see lua_getupvalue).
NULL (and pops nothing)
when the index is greater than the number of upvalues.
lua_upvalueidvoid *lua_upvalueid (lua_State *L, int funcindex, int n);
n
from the closure at index funcindex.
Parameters funcindex and n are as in the lua_getupvalue
(see lua_getupvalue)
(but n cannot be greater than the number of upvalues).
lua_upvaluejoinvoid lua_upvaluejoin (lua_State *L, int funcindex1, int n1,
int funcindex2, int n2);
n1-th upvalue of the Lua closure at index funcindex1
refer to the n2-th upvalue of the Lua closure at index funcindex2.
5 – The Auxiliary Library
lauxlib.h and
have a prefix luaL_.
bad argument #1"),
you should not use these functions for other stack values.
luaL_check*
always raise an error if the check is not satisfied.
5.1 – Functions and Types
luaL_addcharvoid luaL_addchar (luaL_Buffer *B, char c);
c to the buffer B
(see luaL_Buffer).
luaL_addlstringvoid luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);
s with length l to
the buffer B
(see luaL_Buffer).
The string can contain embedded zeros.
luaL_addsizevoid luaL_addsize (luaL_Buffer *B, size_t n);
B (see luaL_Buffer)
a string of length n previously copied to the
buffer area (see luaL_prepbuffer).
luaL_addstringvoid luaL_addstring (luaL_Buffer *B, const char *s);
s
to the buffer B
(see luaL_Buffer).
luaL_addvaluevoid luaL_addvalue (luaL_Buffer *B);
B
(see luaL_Buffer).
Pops the value.
luaL_argcheckvoid luaL_argcheck (lua_State *L,
int cond,
int arg,
const char *extramsg);
cond is true.
If it is not, raises an error with a standard message (see luaL_argerror).
luaL_argerrorint luaL_argerror (lua_State *L, int arg, const char *extramsg);
arg
of the C function that called it,
using a standard message
that includes extramsg as a comment:
bad argument #arg to 'funcname' (extramsg)
luaL_Buffertypedef struct luaL_Buffer luaL_Buffer;
b of type luaL_Buffer.luaL_buffinit(L, &b).luaL_add* functions.
luaL_pushresult(&b).
This call leaves the final string on the top of the stack.
b of type luaL_Buffer.sz with a call luaL_buffinitsize(L, &b, sz).luaL_pushresultsize(&b, sz),
where sz is the total size of the resulting string
copied into that space.
luaL_addvalue.)
After calling luaL_pushresult the stack is back to its
level when the buffer was initialized,
plus the final string on its top.
luaL_buffinitvoid luaL_buffinit (lua_State *L, luaL_Buffer *B);
B.
This function does not allocate any space;
the buffer must be declared as a variable
(see luaL_Buffer).
luaL_buffinitsizechar *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);
luaL_buffinit, luaL_prepbuffsize.
luaL_callmetaint luaL_callmeta (lua_State *L, int obj, const char *e);
obj has a metatable and this
metatable has a field e,
this function calls this field passing the object as its only argument.
In this case this function returns true and pushes onto the
stack the value returned by the call.
If there is no metatable or no metamethod,
this function returns false (without pushing any value on the stack).
luaL_checkanyvoid luaL_checkany (lua_State *L, int arg);
arg.
luaL_checkintegerlua_Integer luaL_checkinteger (lua_State *L, int arg);
arg is an integer
(or can be converted to an integer)
and returns this integer cast to a lua_Integer.
luaL_checklstringconst char *luaL_checklstring (lua_State *L, int arg, size_t *l);
arg is a string
and returns this string;
if l is not NULL fills *l
with the string's length.
lua_tolstring to get its result,
so all conversions and caveats of that function apply here.
luaL_checknumberlua_Number luaL_checknumber (lua_State *L, int arg);
arg is a number
and returns this number.
luaL_checkoptionint luaL_checkoption (lua_State *L,
int arg,
const char *def,
const char *const lst[]);
arg is a string and
searches for this string in the array lst
(which must be NULL-terminated).
Returns the index in the array where the string was found.
Raises an error if the argument is not a string or
if the string cannot be found.
def is not NULL,
the function uses def as a default value when
there is no argument arg or when this argument is nil.
luaL_checkstackvoid luaL_checkstack (lua_State *L, int sz, const char *msg);
top + sz elements,
raising an error if the stack cannot grow to that size.
msg is an additional text to go into the error message
(or NULL for no additional text).
luaL_checkstringconst char *luaL_checkstring (lua_State *L, int arg);
arg is a string
and returns this string.
lua_tolstring to get its result,
so all conversions and caveats of that function apply here.
luaL_checktypevoid luaL_checktype (lua_State *L, int arg, int t);
arg has type t.
See lua_type for the encoding of types for t.
luaL_checkudatavoid *luaL_checkudata (lua_State *L, int arg, const char *tname);
arg is a userdata
of the type tname (see luaL_newmetatable) and
returns the userdata address (see lua_touserdata).
luaL_checkversionvoid luaL_checkversion (lua_State *L);
luaL_dofileint luaL_dofile (lua_State *L, const char *filename);
(luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0))
luaL_dostringint luaL_dostring (lua_State *L, const char *str);
(luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0))
luaL_errorint luaL_error (lua_State *L, const char *fmt, ...);
fmt
plus any extra arguments,
following the same rules of lua_pushfstring.
It also adds at the beginning of the message the file name and
the line number where the error occurred,
if this information is available.
return luaL_error(args).
luaL_execresultint luaL_execresult (lua_State *L, int stat);
os.execute and io.close).
luaL_fileresultint luaL_fileresult (lua_State *L, int stat, const char *fname);
io.open, os.rename, file:seek, etc.).
luaL_getmetafieldint luaL_getmetafield (lua_State *L, int obj, const char *e);
e from the metatable
of the object at index obj and returns the type of pushed value.
If the object does not have a metatable,
or if the metatable does not have this field,
pushes nothing and returns LUA_TNIL.
luaL_getmetatableint luaL_getmetatable (lua_State *L, const char *tname);
tname
in the registry (see luaL_newmetatable).
If there is no metatable associated with tname,
returns false and pushes nil.
luaL_getsubtableint luaL_getsubtable (lua_State *L, int idx, const char *fname);
t[fname],
where t is the value at index idx,
is a table,
and pushes that table onto the stack.
Returns true if it finds a previous table there
and false if it creates a new table.
luaL_gsubconst char *luaL_gsub (lua_State *L,
const char *s,
const char *p,
const char *r);
s by replacing
any occurrence of the string p
with the string r.
Pushes the resulting string on the stack and returns it.
luaL_lenlua_Integer luaL_len (lua_State *L, int index);
#' operator in Lua (see §3.4.7).
Raises an error if the result of the operation is not an integer.
(This case only can happen through metamethods.)
luaL_loadbufferint luaL_loadbuffer (lua_State *L,
const char *buff,
size_t sz,
const char *name);
luaL_loadbufferx with mode equal to NULL.
luaL_loadbufferxint luaL_loadbufferx (lua_State *L,
const char *buff,
size_t sz,
const char *name,
const char *mode);
lua_load to load the chunk in the
buffer pointed to by buff with size sz.
lua_load.
name is the chunk name,
used for debug information and error messages.
The string mode works as in function lua_load.
luaL_loadfileint luaL_loadfile (lua_State *L, const char *filename);
luaL_loadfilex with mode equal to NULL.
luaL_loadfilexint luaL_loadfilex (lua_State *L, const char *filename,
const char *mode);
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 #.
mode works as in function lua_load.
lua_load,
but it has an extra error code LUA_ERRFILE
if it cannot open/read the file or the file has a wrong mode.
lua_load, this function only loads the chunk;
it does not run it.
luaL_loadstringint luaL_loadstring (lua_State *L, const char *s);
lua_load to load the chunk in
the zero-terminated string s.
lua_load.
lua_load, this function only loads the chunk;
it does not run it.
luaL_newlibvoid luaL_newlib (lua_State *L, const luaL_Reg l[]);
l.
(luaL_newlibtable(L,l), luaL_setfuncs(L,l,0))
l must be the actual array,
not a pointer to it.
luaL_newlibtablevoid luaL_newlibtable (lua_State *L, const luaL_Reg l[]);
l
(but does not actually store them).
It is intended to be used in conjunction with luaL_setfuncs
(see luaL_newlib).
l must be the actual array,
not a pointer to it.
luaL_newmetatableint luaL_newmetatable (lua_State *L, const char *tname);
tname,
returns 0.
Otherwise,
creates a new table to be used as a metatable for userdata,
adds to this new table the pair __name = tname,
adds to the registry the pair [tname] = new table,
and returns 1.
(The entry __name is used by some error-reporting functions.)
tname in the registry.
luaL_newstatelua_State *luaL_newstate (void);
lua_newstate with an
allocator based on the standard C realloc function
and then sets a panic function (see §4.6) that prints
an error message to the standard error output in case of fatal
errors.
NULL if there is a memory allocation error.
luaL_openlibsvoid luaL_openlibs (lua_State *L);
luaL_optintegerlua_Integer luaL_optinteger (lua_State *L,
int arg,
lua_Integer d);
arg is an integer
(or convertible to an integer),
returns this integer.
If this argument is absent or is nil,
returns d.
Otherwise, raises an error.
luaL_optlstringconst char *luaL_optlstring (lua_State *L,
int arg,
const char *d,
size_t *l);
arg is a string,
returns this string.
If this argument is absent or is nil,
returns d.
Otherwise, raises an error.
l is not NULL,
fills the position *l with the result's length.
luaL_optnumberlua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);
arg is a number,
returns this number.
If this argument is absent or is nil,
returns d.
Otherwise, raises an error.
luaL_optstringconst char *luaL_optstring (lua_State *L,
int arg,
const char *d);
arg is a string,
returns this string.
If this argument is absent or is nil,
returns d.
Otherwise, raises an error.
luaL_prepbufferchar *luaL_prepbuffer (luaL_Buffer *B);
luaL_prepbuffsize
with the predefined size LUAL_BUFFERSIZE.
luaL_prepbuffsizechar *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);
sz
where you can copy a string to be added to buffer B
(see luaL_Buffer).
After copying the string into this space you must call
luaL_addsize with the size of the string to actually add
it to the buffer.
luaL_pushresultvoid luaL_pushresult (luaL_Buffer *B);
B leaving the final string on
the top of the stack.
luaL_pushresultsizevoid luaL_pushresultsize (luaL_Buffer *B, size_t sz);
luaL_addsize, luaL_pushresult.
luaL_refint luaL_ref (lua_State *L, int t);
t,
for the object at the top of the stack (and pops the object).
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.
luaL_ref returns the constant LUA_REFNIL.
The constant LUA_NOREF is guaranteed to be different
from any reference returned by luaL_ref.
luaL_Regtypedef struct luaL_Reg {
const char *name;
lua_CFunction func;
} luaL_Reg;
luaL_setfuncs.
name is the function name and func is a pointer to
the function.
Any array of luaL_Reg must end with a sentinel entry
in which both name and func are NULL.
luaL_requirefvoid luaL_requiref (lua_State *L, const char *modname,
lua_CFunction openf, int glb);
modname is not already present in package.loaded,
calls function openf with string modname as an argument
and sets the call result in package.loaded[modname],
as if that function has been called through require.
glb is true,
also stores the module into global modname.
luaL_setfuncsvoid luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);
l
(see luaL_Reg) into the table on the top of the stack
(below optional upvalues, see next).
nup is not zero,
all functions are created sharing nup upvalues,
which must be previously pushed on the stack
on top of the library table.
These values are popped from the stack after the registration.
luaL_setmetatablevoid luaL_setmetatable (lua_State *L, const char *tname);
tname
in the registry (see luaL_newmetatable).
luaL_Streamtypedef struct luaL_Stream {
FILE *f;
lua_CFunction closef;
} luaL_Stream;
LUA_FILEHANDLE
(where LUA_FILEHANDLE is a macro with the actual metatable's name).
The metatable is created by the I/O library
(see luaL_newmetatable).
luaL_Stream;
it can contain other data after this initial structure.
Field f points to the corresponding C stream
(or it can be NULL to indicate an incompletely created handle).
Field closef points to a Lua function
that will be called to close the stream
when the handle is closed or collected;
this function receives the file handle as its sole argument and
must return either true (in case of success)
or nil plus an error message (in case of error).
Once Lua calls this field,
the field value is changed to NULL
to signal that the handle is closed.
luaL_testudatavoid *luaL_testudata (lua_State *L, int arg, const char *tname);
luaL_checkudata,
except that, when the test fails,
it returns NULL instead of raising an error.
luaL_tolstringconst char *luaL_tolstring (lua_State *L, int idx, size_t *len);
len is not NULL,
the function also sets *len with the string length.
"__tostring" field,
then luaL_tolstring calls the corresponding metamethod
with the value as argument,
and uses the result of the call as its result.
luaL_tracebackvoid luaL_traceback (lua_State *L, lua_State *L1, const char *msg,
int level);
L1.
If msg is not NULL it is appended
at the beginning of the traceback.
The level parameter tells at which level
to start the traceback.
luaL_typenameconst char *luaL_typename (lua_State *L, int index);
luaL_unrefvoid luaL_unref (lua_State *L, int t, int ref);
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.
ref is LUA_NOREF or LUA_REFNIL,
luaL_unref does nothing.
luaL_wherevoid luaL_where (lua_State *L, int lvl);
lvl in the call stack.
Typically this string has the following format:
chunkname:currentline:
6 – Standard Libraries
type and getmetatable);
others provide access to "outside" services (e.g., I/O);
and others could be implemented in Lua itself,
but are quite useful or have critical performance requirements that
deserve an implementation in C (e.g., table.sort).
luaL_openlibs function,
which opens all standard libraries.
Alternatively,
the host program can open them individually by using
luaL_requiref to call
luaopen_base (for the basic library),
luaopen_package (for the package library),
luaopen_coroutine (for the coroutine library),
luaopen_string (for the string library),
luaopen_utf8 (for the UTF8 library),
luaopen_table (for the table library),
luaopen_math (for the mathematical library),
luaopen_io (for the I/O library),
luaopen_os (for the operating system library),
and luaopen_debug (for the debug library).
These functions are declared in lualib.h.
6.1 – Basic Functions
assert (v [, message])error if
the value of its argument v is false (i.e., nil or false);
otherwise, returns all its arguments.
In case of error,
message is the error object;
when absent, it defaults to "assertion failed!"
collectgarbage ([opt [, arg]])opt:
collect":
performs a full garbage-collection cycle.
This is the default option.
stop":
stops automatic execution of the garbage collector.
The collector will run only when explicitly invoked,
until a call to restart it.
restart":
restarts automatic execution of the garbage collector.
count":
returns the total memory in use by Lua in Kbytes.
The value has a fractional part,
so that it multiplied by 1024
gives the exact number of bytes in use by Lua
(except for overflows).
step":
performs a garbage-collection step.
The step "size" is controlled by arg.
With a zero value,
the collector will perform one basic (indivisible) step.
For non-zero values,
the collector will perform as if that amount of memory
(in KBytes) had been allocated by Lua.
Returns true if the step finished a collection cycle.
setpause":
sets arg as the new value for the pause of
the collector (see §2.5).
Returns the previous value for pause.
setstepmul":
sets arg as the new value for the step multiplier of
the collector (see §2.5).
Returns the previous value for step.
isrunning":
returns a boolean that tells whether the collector is running
(i.e., not stopped).
Opens the named file and executes its contents as a Lua chunk.
When called without arguments,
dofile ([filename])dofile executes the contents of the standard input (stdin).
Returns all values returned by the chunk.
In case of errors, dofile propagates the error
to its caller (that is, dofile does not run in protected mode).
Terminates the last protected function called
and returns error (message [, level])message as the error object.
Function error never returns.
error adds some information about the error position
at the beginning of the message, if the message is a string.
The level argument specifies how to get the error position.
With level 1 (the default), the error position is where the
error function was called.
Level 2 points the error to where the function
that called error was called; and so on.
Passing a level 0 avoids the addition of error position information
to the message.
A global variable (not a function) that
holds the global environment (see §2.2).
Lua itself does not use this variable;
changing its value does not affect any environment,
nor vice versa.
_Ggetmetatable (object)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)t, and 0)
so that the construction
for i,v in ipairs(t) do body end
1,t[1]), (2,t[2]), ...,
up to the first nil value.
load (chunk [, chunkname [, mode [, env]]])chunk is a string, the chunk is this string.
If chunk is a function,
load calls it repeatedly to get the chunk pieces.
Each call to chunk must return a string that concatenates
with previous results.
A return of an empty string, nil, or no value signals the end of the chunk.
env,
if that parameter is given,
or to the value of the global environment.
Other upvalues are initialized with nil.
(When you load a main chunk,
the resulting function will always have exactly one upvalue,
the _ENV variable (see §2.2).
However,
when you load a binary chunk created from a function (see string.dump),
the resulting function can have an arbitrary number of upvalues.)
All upvalues are fresh, that is,
they are not shared with any other function.
chunkname is used as the name of the chunk for error messages
and debug information (see §4.9).
When absent,
it defaults to chunk, if chunk is a string,
or to "=(load)" otherwise.
mode controls whether the chunk can be text or binary
(that is, a precompiled chunk).
It may be the string "b" (only binary chunks),
"t" (only text chunks),
or "bt" (both binary and text).
The default is "bt".
loadfile ([filename [, mode [, env]]])load,
but gets the chunk from file filename
or from the standard input,
if no file name is given.
next (table [, index])next returns the next index of the table
and its associated value.
When called with nil as its second argument,
next returns an initial index
and its associated value.
When called with the last index,
or with nil in an empty table,
next returns nil.
If the second argument is absent, then it is interpreted as nil.
In particular,
you can use next(t) to check whether a table is empty.
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)t has a metamethod __pairs,
calls it with t as argument and returns the first three
results from the call.
next function, the table t, and nil,
so that the construction
for k,v in pairs(t) do body end
t.
next for the caveats of modifying
the table during its traversal.
pcall (f [, arg1, ···])f with
the given arguments in protected mode.
This means that any error inside f is not propagated;
instead, pcall catches the error
and returns a status code.
Its first result is the status code (a boolean),
which is true if the call succeeds without errors.
In such case, pcall also returns all results from the call,
after this first result.
In case of any error, pcall returns false plus the error message.
Receives any number of arguments
and prints their values to print (···)stdout,
using the tostring function to convert each argument to a string.
print is not intended for formatted output,
but only as a quick way to show a value,
for instance for debugging.
For complete control over the output,
use string.format and io.write.
Checks whether rawequal (v1, v2)v1 is equal to v2,
without invoking any metamethod.
Returns a boolean.
Gets the real value of rawget (table, index)table[index],
without invoking any metamethod.
table must be a table;
index may be any value.
Returns the length of the object rawlen (v)v,
which must be a table or a string,
without invoking any metamethod.
Returns an integer.
Sets the real value of rawset (table, index, value)table[index] to value,
without invoking any metamethod.
table must be a table,
index any value different from nil and NaN,
and value any Lua value.
table.
select (index, ···)index is a number,
returns all arguments after argument number index;
a negative number indexes from the end (-1 is the last argument).
Otherwise, index must be the string "#",
and select returns the total number of extra arguments it received.
setmetatable (table, metatable)metatable is nil,
removes the metatable of the given table.
If the original metatable has a "__metatable" field,
raises an error.
table.
tonumber (e [, base])base,
tonumber tries to convert its argument to a number.
If the argument is already a number or
a string convertible to a number,
then tonumber returns this number;
otherwise, it returns nil.
base,
then e must be a string to be interpreted as
an integer numeral in that base.
The base may be any integer between 2 and 36, inclusive.
In bases above 10, the letter 'A' (in either upper or lower case)
represents 10, 'B' represents 11, and so forth,
with 'Z' representing 35.
If the string e is not a valid numeral in the given base,
the function returns nil.
Receives a value of any type and
converts it to a string in a human-readable format.
Floats always produce strings with some
floating-point indication (either a decimal dot or an exponent).
(For complete control of how numbers are converted,
use tostring (v)string.format.)
v has a "__tostring" field,
then tostring calls the corresponding value
with v as argument,
and uses the result of the call as its result.
Returns the type of its only argument, coded as a string.
The possible results of this function are
"type (v)nil" (a string, not the value nil),
"number",
"string",
"boolean",
"table",
"function",
"thread",
and "userdata".
A global variable (not a function) that
holds a string containing the current interpreter version.
The current value of this variable is "_VERSIONLua 5.3".
xpcall (f, msgh [, arg1, ···])pcall,
except that it sets a new message handler msgh.
6.2 – Coroutine Manipulation
coroutine.
See §2.6 for a general description of coroutines.
coroutine.create (f)f.
f must be a Lua function.
Returns this new coroutine,
an object with type "thread".
coroutine.isyieldable ()coroutine.resume (co [, val1, ···])co.
The first time you resume a coroutine,
it starts running its body.
The values val1, ... are passed
as the arguments to the body function.
If the coroutine has yielded,
resume restarts it;
the values val1, ... are passed
as the results from the yield.
resume returns true plus any values passed to yield
(when the coroutine yields) or any values returned by the body function
(when the coroutine terminates).
If there is any error,
resume returns false plus the error message.
coroutine.running ()coroutine.status (co)co, as a string:
"running",
if the coroutine is running (that is, it called status);
"suspended", if the coroutine is suspended in a call to yield,
or if it has not started running yet;
"normal" if the coroutine is active but not running
(that is, it has resumed another coroutine);
and "dead" if the coroutine has finished its body function,
or if it has stopped with an error.
coroutine.wrap (f)f.
f must be a Lua function.
Returns a function that resumes the coroutine each time it is called.
Any arguments passed to the function behave as the
extra arguments to resume.
Returns the same values returned by resume,
except the first boolean.
In case of error, propagates the error.
coroutine.yield (···)yield are passed as extra results to resume.
6.3 – Modules
require.
Everything else is exported in a table package.
require (modname)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.
require is guided by the package.searchers sequence.
By changing this sequence,
we can change how require looks for a module.
The following explanation is based on the default configuration
for package.searchers.
require queries package.preload[modname].
If it has a value,
this value (which must be a function) is the loader.
Otherwise require searches for a Lua loader using the
path stored in package.path.
If that also fails, it searches for a C loader using the
path stored in package.cpath.
If that also fails,
it tries an all-in-one loader (see package.searchers).
require calls the loader with two arguments:
modname and an extra value dependent on how it got the loader.
(If the loader came from a file,
this extra value is the file name.)
If the loader returns any non-nil value,
require assigns the returned value to package.loaded[modname].
If the loader does not return a non-nil value and
has not assigned any value to package.loaded[modname],
then require assigns true to this entry.
In any case, require returns the
final value of package.loaded[modname].
require raises an error.
package.config
\' for Windows and '/' for all other systems.;'.?'.!'.luaopen_ function name.
Default is '-'.package.cpathrequire to search for a C loader.
package.cpath in the same way
it initializes the Lua path package.path,
using the environment variable LUA_CPATH_5_3
or the environment variable LUA_CPATH
or a default path defined in luaconf.h.
package.loadedrequire 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.
require.
package.loadlib (libname, funcname)libname.
funcname is "*",
then it only links with the library,
making the symbols exported by the library
available to other dynamically linked libraries.
Otherwise,
it looks for a function funcname inside the library
and returns this function as a C function.
So, funcname must follow the lua_CFunction prototype
(see lua_CFunction).
require,
it does not perform any path searching and
does not automatically adds extensions.
libname must be the complete file name of the C library,
including if necessary a path and an extension.
funcname must be the exact name exported by the C library
(which may depend on the C compiler and linker used).
dlfcn standard).
package.pathrequire to search for a Lua loader.
LUA_PATH_5_3 or
the environment variable LUA_PATH or
with a default path defined in luaconf.h,
if those environment variables are not defined.
Any ";;" in the value of the environment variable
is replaced by the default path.
package.preloadrequire).
require.
package.searchersrequire to control how to load modules.
require calls each of these searchers in ascending order,
with the module name (the argument given to require) as its
sole parameter.
The function can return another function (the module loader)
plus an extra value that will be passed to that loader,
or a string explaining why it did not find that module
(or nil if it has nothing to say).
package.preload table.
package.path.
The search is done as described in function package.searchpath.
package.cpath.
Again,
the search is done as described in function package.searchpath.
For instance,
if the C path is the string
"./?.so;./?.dll;/usr/local/?/init.so"
foo
will try to open the files ./foo.so, ./foo.dll,
and /usr/local/foo/init.so, in that order.
Once it finds a C library,
this searcher first uses a dynamic link facility to link the
application with the library.
Then it tries to find a C function inside the library to
be used as the loader.
The name of this C function is the string "luaopen_"
concatenated with a copy of the module name where each dot
is replaced by an underscore.
Moreover, if the module name has a hyphen,
its suffix after (and including) the first hyphen is removed.
For instance, if the module name is a.b.c-v2.1,
the function name will be luaopen_a_b_c.
a.b.c,
it will search for a C library for a.
If found, it looks into it for an open function for
the submodule;
in our example, that would be luaopen_a_b_c.
With this facility, a package can pack several C submodules
into one single library,
with each submodule keeping its original open function.
package.searchpath.
The first searcher returns no extra value.
package.searchpath (name, path [, sep [, rep]])name in the given path.
name
wherein all occurrences of sep
(a dot, by default)
were replaced by rep
(the system's directory separator, by default),
and then tries to open the resulting file name.
"./?.lua;./?.lc;/usr/local/?/init.lua"
foo.a
will try to open the files
./foo/a.lua, ./foo/a.lc, and
/usr/local/foo/a/init.lua, in that order.
6.4 – String Manipulation
string.
It also sets a metatable for strings
where the __index field points to the string table.
Therefore, you can use the string functions in object-oriented style.
For instance, string.byte(s,i)
can be written as s:byte(i).
Returns the internal numerical codes of the characters string.byte (s [, i [, j]])s[i],
s[i+1], ..., s[j].
The default value for i is 1;
the default value for j is i.
These indices are corrected
following the same rules of function string.sub.
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.
string.char (···)string.dump (function [, strip])load on this string returns
a copy of the function (but with new upvalues).
If strip is a true value,
the binary representation is created without debug information
about the function
(local variable names, lines, etc.).
string.find (s, pattern [, init [, plain]])pattern (see §6.4.1) in the string s.
If it finds a match, then find returns the indices of s
where this occurrence starts and ends;
otherwise, it returns nil.
A third, optional numerical argument init specifies
where to start the search;
its default value is 1 and can be negative.
A value of true as a fourth, optional argument plain
turns off the pattern matching facilities,
so the function does a plain "find substring" operation,
with no characters in pattern being considered magic.
Note that if plain is given, then init must be given as well.
string.format (formatstring, ···)sprintf.
The only differences are that the options/modifiers
*, h, L, l, n,
and p are not supported
and that there is an extra option, q.
The q option formats a string between double quotes,
using escape sequences when necessary to ensure that
it can safely be read back by the Lua interpreter.
For instance, the call
string.format('%q', 'a string with "quotes" and \n new line')
"a string with \"quotes\" and \
new line"
A and a (when available),
E, e, f,
G, and g all expect a number as argument.
Options c, d,
i, o, u, X, and x
expect an integer.
Option q expects a string;
option s expects a string without embedded zeros.
If the argument to option s is not a string,
it is converted to one following the same rules of tostring.
Returns an iterator function that,
each time it is called,
returns the next captures from string.gmatch (s, pattern)pattern (see §6.4.1)
over the string s.
If pattern specifies no captures,
then the whole match is produced in each call.
s,
printing one per line:
s = "hello world from Lua"
for w in string.gmatch(s, "%a+") do
print(w)
end
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
^' at the start of a pattern does not
work as an anchor, as this would prevent the iteration.
Returns a copy of string.gsub (s, pattern, repl [, n])s
in which all (or the first n, if given)
occurrences of the pattern (see §6.4.1) have been
replaced by a replacement string specified by repl,
which can be a string, a table, or a function.
gsub also returns, as its second value,
the total number of matches that occurred.
The name gsub comes from Global SUBstitution.
repl is a string, then its value is used for replacement.
The character % works as an escape character:
any sequence in repl of the form %d,
with d between 1 and 9,
stands for the value of the d-th captured substring.
The sequence %0 stands for the whole match.
The sequence %% stands for a single %.
repl is a table, then the table is queried for every match,
using the first capture as the key.
repl is a function, then this function is called every time a
match occurs, with all captured substrings passed as arguments,
in order.
x = string.gsub("hello world", "(%w+)", "%1 %1")
--> x="hello hello world world"
x = string.gsub("hello world", "%w+", "%0 %0", 1)
--> x="hello hello world"
x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1")
--> x="world hello Lua from"
x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv)
--> x="home = /home/roberto, user = roberto"
x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s)
return load(s)()
end)
--> x="4+5 = 9"
local t = {name="lua", version="5.3"}
x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
--> x="lua-5.3.tar.gz"
Receives a string and returns its length.
The empty string string.len (s)"" has length 0.
Embedded zeros are counted,
so "a\000bc\000" has length 5.
Receives a string and returns a copy of this string with all
uppercase letters changed to lowercase.
All other characters are left unchanged.
The definition of what an uppercase letter is depends on the current locale.
string.lower (s)
Looks for the first match of
string.match (s, pattern [, init])pattern (see §6.4.1) in the string s.
If it finds one, then match returns
the captures from the pattern;
otherwise it returns nil.
If pattern specifies no captures,
then the whole match is returned.
A third, optional numerical argument init specifies
where to start the search;
its default value is 1 and can be negative.
string.pack (fmt, v1, v2, ···)v1, v2, etc.
packed (that is, serialized in binary form)
according to the format string fmt (see §6.4.2).
string.packsize (fmt)string.pack
with the given format.
The format string cannot have the variable-length options
's' or 'z' (see §6.4.2).
Returns a string that is the concatenation of string.rep (s, n [, sep])n copies of
the string s separated by the string sep.
The default value for sep is the empty string
(that is, no separator).
Returns the empty string if n is not positive.
Returns a string that is the string string.reverse (s)s reversed.
Returns the substring of string.sub (s, i [, j])s that
starts at i and continues until j;
i and j can be negative.
If j is absent, then it is assumed to be equal to -1
(which is the same as the string length).
In particular,
the call string.sub(s,1,j) returns a prefix of s
with length j,
and string.sub(s, -i) returns a suffix of s
with length i.
i is less than 1,
it is corrected to 1.
If j is greater than the string length,
it is corrected to that length.
If, after these corrections,
i is greater than j,
the function returns the empty string.
string.unpack (fmt, s [, pos])s (see string.pack)
according to the format string fmt (see §6.4.2).
An optional pos marks where
to start reading in s (default is 1).
After the read values,
this function also returns the index of the first unread byte in s.
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.
string.upper (s)6.4.1 – Patterns
string.find,
string.gmatch,
string.gsub,
and string.match.
This section describes the syntax and the meaning
(that is, what they match) of these strings.
Character Class:
^$()%.[]*+-?)
represents the character x itself.
.: (a dot) represents all characters.%a: represents all letters.%c: represents all control characters.%d: represents all digits.%g: represents all printable characters except space.%l: represents all lowercase letters.%p: represents all punctuation characters.%s: represents all space characters.%u: represents all uppercase letters.%w: represents all alphanumeric characters.%x: represents all hexadecimal digits.%x: (where x is any non-alphanumeric character)
represents the character x.
This is the standard way to escape the magic characters.
Any non-alphanumeric character
(including all punctuations, even the non-magical)
can be preceded by a '%'
when used to represent itself in a pattern.
[set]:
represents the class which is the union of all
characters in set.
A range of characters can be specified by
separating the end characters of the range,
in ascending order, with a '-'.
All classes %x described above can also be used as
components in set.
All other characters in set represent themselves.
For example, [%w_] (or [_%w])
represents all alphanumeric characters plus the underscore,
[0-7] represents the octal digits,
and [0-7%l%-] represents the octal digits plus
the lowercase letters plus the '-' character.
[%a-z] or [a-%%]
have no meaning.
[^set]:
represents the complement of set,
where set is interpreted as above.
%a, %c, etc.),
the corresponding uppercase letter represents the complement of the class.
For instance, %S represents all non-space characters.
[a-z] may not be equivalent to %l.
Pattern Item:
*',
which matches zero or more repetitions of characters in the class.
These repetition items will always match the longest possible sequence;
+',
which matches one or more repetitions of characters in the class.
These repetition items will always match the longest possible sequence;
-',
which also matches zero or more repetitions of characters in the class.
Unlike '*',
these repetition items will always match the shortest possible sequence;
?',
which matches zero or one occurrence of a character in the class.
It always matches one occurrence if possible;
%n, for n between 1 and 9;
such item matches a substring equal to the n-th captured string
(see below);
%bxy, where x and y are two distinct characters;
such item matches strings that start with x, end with y,
and where the x and y are balanced.
This means that, if one reads the string from left to right,
counting +1 for an x and -1 for a y,
the ending y is the first y where the count reaches 0.
For instance, the item %b() matches expressions with
balanced parentheses.
%f[set], a frontier pattern;
such item matches an empty string at any position such that
the next character belongs to set
and the previous character does not belong to set.
The set set is interpreted as previously described.
The beginning and the end of the subject are handled as if
they were the character '\0'.
Pattern:
^' at the beginning of a pattern anchors the match at the
beginning of the subject string.
A '$' at the end of a pattern anchors the match at the
end of the subject string.
At other positions,
'^' and '$' have no special meaning and represent themselves.
Captures:
"(a*(.)%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.
() captures
the current string position (a number).
For instance, if we apply the pattern "()aa()" on the
string "flaaap", there will be two captures: 3 and 5.
6.4.2 – Format Strings for Pack and Unpack
string.pack,
string.packsize, and string.unpack
is a format string,
which describes the layout of the structure being created or read.
<: sets little endian>: sets big endian=: sets native endian![n]: sets maximum alignment to n
(default is native alignment)b: a signed byte (char)B: an unsigned byte (char)h: a signed short (native size)H: an unsigned short (native size)l: a signed long (native size)L: an unsigned long (native size)j: a lua_IntegerJ: a lua_UnsignedT: a size_t (native size)i[n]: a signed int with n bytes
(default is native size)I[n]: an unsigned int with n bytes
(default is native size)f: a float (native size)d: a double (native size)n: a lua_Numbercn: a fixed-sized string with n bytesz: a zero-terminated strings[n]: a string preceded by its length
coded as an unsigned integer with n bytes
(default is a size_t)x: one byte of paddingXop: an empty item that aligns
according to option op
(which is otherwise ignored) ': (empty space) ignored[n]" means an optional integral numeral.)
Except for padding, spaces, and configurations
(options "xX <=>!"),
each option corresponds to an argument (in string.pack)
or a result (in string.unpack).
!n", "sn", "in", and "In",
n can be any integer between 1 and 16.
All integral options check overflows;
string.pack checks whether the given value fits in the given size;
string.unpack checks whether the read value fits in a Lua integer.
!1=",
that is,
with maximum alignment of 1 (no alignment)
and native endianness.
c" and "z" are not aligned;
option "s" follows the alignment of its starting integer.
string.pack
(and ignored by string.unpack).
6.5 – UTF-8 Support
utf8.
This library does not provide any support for Unicode other
than the handling of the encoding.
Any operation that needs the meaning of a character,
such as character classification, is outside its scope.
Receives zero or more integers,
converts each one to its corresponding UTF-8 byte sequence
and returns a string with the concatenation of all these sequences.
utf8.char (···)
The pattern (a string, not a function) "utf8.charpattern[\0-\x7F\xC2-\xF4][\x80-\xBF]*"
(see §6.4.1),
which matches exactly one UTF-8 byte sequence,
assuming that the subject is a valid UTF-8 string.
utf8.codes (s)
for p, c in utf8.codes(s) do body end
s,
with p being the position (in bytes) and c the code point
of each character.
It raises an error if it meets any invalid byte sequence.
Returns the codepoints (as integers) from all characters in utf8.codepoint (s [, i [, j]])s
that start between byte position i and j (both included).
The default for i is 1 and for j is i.
It raises an error if it meets any invalid byte sequence.
Returns the number of UTF-8 characters in string utf8.len (s [, i [, j]])s
that start between positions i and j (both inclusive).
The default for i is 1 and for j is -1.
If it finds any invalid byte sequence,
returns a false value plus the position of the first invalid byte.
Returns the position (in bytes) where the encoding of the
utf8.offset (s, n [, i])n-th character of s
(counting from position i) starts.
A negative n gets characters before position i.
The default for i is 1 when n is non-negative
and #s + 1 otherwise,
so that utf8.offset(s, -n) gets the offset of the
n-th character from the end of the string.
If the specified character is neither in the subject
nor right after its end,
the function returns nil.
n is 0 the function returns the start of the encoding
of the character that contains the i-th byte of s.
s is a valid UTF-8 string.
6.6 – Table Manipulation
table.
__len metamethod (see §3.4.7).
All functions ignore non-numeric keys
in the tables given as arguments.
table.concat (list [, sep [, i [, j]]])list[i]..sep..list[i+1] ··· sep..list[j].
The default value for sep is the empty string,
the default for i is 1,
and the default for j is #list.
If i is greater than j, returns the empty string.
table.insert (list, [pos,] value)value at position pos in list,
shifting up the elements
list[pos], list[pos+1], ···, list[#list].
The default value for pos is #list+1,
so that a call table.insert(t,x) inserts x at the end
of list t.
table.move (a1, f, e, t [,a2])a1 to table a2.
This function performs the equivalent to the following
multiple assignment:
a2[t],··· = a1[f],···,a1[e].
The default for a2 is a1.
The destination range can overlap with the source range.
Index f must be positive.
table.pack (···)n" with the total number of parameters.
Note that the resulting table may not be a sequence.
table.remove (list [, pos])list the element at position pos,
returning the value of the removed element.
When pos is an integer between 1 and #list,
it shifts down the elements
list[pos+1], list[pos+2], ···, list[#list]
and erases element list[#list];
The index pos can also be 0 when #list is 0,
or #list + 1;
in those cases, the function erases the element list[pos].
pos is #list,
so that a call table.remove(l) removes the last element
of list l.
table.sort (list [, comp])list[1] to list[#list].
If comp is given,
then it must be a function that receives two list elements
and returns true when the first element must come
before the second in the final order
(so that not comp(list[i+1],list[i]) will be true after the sort).
If comp is not given,
then the standard Lua operator < is used instead.
table.unpack (list [, i [, j]])
return list[i], list[i+1], ···, list[j]
i is 1 and j is #list.
6.7 – Mathematical Functions
math.
Functions with the annotation "integer/float" give
integer results for integer arguments
and float results for float (or mixed) arguments.
Rounding functions
(math.ceil, math.floor, and math.modf)
return an integer when the result fits in the range of an integer,
or a float otherwise.
math.abs (x)x. (integer/float)
math.acos (x)x (in radians).
math.asin (x)x (in radians).
math.atan (y [, x])y/x (in radians),
but uses the signs of both parameters to find the
quadrant of the result.
(It also handles correctly the case of x being zero.)
x is 1,
so that the call math.atan(y)
returns the arc tangent of y.
math.ceil (x)x.
math.cos (x)x (assumed to be in radians).
math.deg (x)x from radians to degrees.
math.exp (x)e is the base of natural logarithms).
math.floor (x)x.
math.fmod (x, y)x by y
that rounds the quotient towards zero. (integer/float)
math.hugeHUGE_VAL,
a value larger than any other numerical value.
math.log (x [, base])x in the given base.
The default for base is e
(so that the function returns the natural logarithm of x).
math.max (x, ···)<. (integer/float)
An integer with the maximum value for an integer.
math.maxintegermath.min (x, ···)<. (integer/float)
An integer with the minimum value for an integer.
math.minintegermath.modf (x)x and the fractional part of x.
Its second result is always a float.
math.pimath.rad (x)x from degrees to radians.
math.random ([m [, n]])m and n,
math.random returns a pseudo-random integer
with uniform distribution in the range [m, n].
(The value m-n cannot be negative and must fit in a Lua integer.)
The call math.random(n) is equivalent to math.random(1,n).
math.randomseed (x)x as the "seed"
for the pseudo-random generator:
equal seeds produce equal sequences of numbers.
math.sin (x)x (assumed to be in radians).
math.sqrt (x)x.
(You can also use the expression x^0.5 to compute this value.)
math.tan (x)x (assumed to be in radians).
math.tointeger (x)x is convertible to an integer,
returns that integer.
Otherwise, returns nil.
math.type (x)integer" if x is an integer,
"float" if it is a float,
or nil if x is not a number.
math.ult (m, n)m is below integer n when
they are compared as unsigned integers.
6.8 – Input and Output Facilities
io.
When using explicit file handles,
the operation io.open returns a file handle
and then all operations are supplied as methods of the file handle.
io also provides
three predefined file handles with their usual meanings from C:
io.stdin, io.stdout, and io.stderr.
The I/O library never closes these files.
errno.
io.close ([file])file:close().
Without a file, closes the default output file.
io.flush ()io.output():flush().
io.input ([file])io.lines ([filename ···])file:lines(···) over the opened file.
When the iterator function detects the end of file,
it returns no values (to finish the loop) and automatically closes the file.
io.lines() (with no file name) is equivalent
to io.input():lines("*l");
that is, it iterates over the lines of the default input file.
In this case it does not close the file when the loop ends.
io.open (filename [, mode])mode.
It returns a new file handle,
or, in case of errors, nil plus an error message.
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.mode string can also have a 'b' at the end,
which is needed in some systems to open the file in binary mode.
io.output ([file])io.input, but operates over the default output file.
io.popen (prog [, mode])prog in a separated process and returns
a file handle that you can use to read data from this program
(if mode is "r", the default)
or to write data to this program
(if mode is "w").
io.read (···)io.input():read(···).
io.tmpfile ()io.type (obj)obj is a valid file handle.
Returns the string "file" if obj is an open file handle,
"closed file" if obj is a closed file handle,
or nil if obj is not a file handle.
io.write (···)io.output():write(···).
file:close ()file.
Note that files are automatically closed when
their handles are garbage collected,
but that takes an unpredictable amount of time to happen.
io.popen,
file:close returns the same values
returned by os.execute.
file:flush ()file.
file:lines (···)l" as a default.
As an example, the construction
for c in file:lines(1) do body end
io.lines, this function does not close the file
when the loop ends.
file:read (···)file,
according to the given formats, which specify what to read.
For each format,
the function returns a string or a number with the characters read,
or nil if it cannot read data with the specified format.
(In this latter case,
the function does not read subsequent formats.)
When called without formats,
it uses a default format that reads the next line
(see below).
n":
reads a numeral and returns it as a float or an integer,
following the lexical conventions of Lua.
(The numeral may have leading spaces and a sign.)
This format always reads the longest input sequence that
is a valid prefix for a number;
if that prefix does not form a valid number
(e.g., an empty string, "0x", or "3.4e-"),
it is discarded and the function returns nil.
i":
reads an integral number and returns it as an integer.
a":
reads the whole file, starting at the current position.
On end of file, it returns the empty string.
l":
reads the next line skipping the end of line,
returning nil on end of file.
This is the default format.
L":
reads the next line keeping the end-of-line character (if present),
returning nil on end of file.
number is zero,
it reads nothing and returns an empty string,
or nil on end of file.
l" and "L" should be used only for text files.
file:seek ([whence [, offset]])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;seek returns the final file position,
measured in bytes from the beginning of the file.
If seek fails, it returns nil,
plus a string describing the error.
whence is "cur",
and for offset is 0.
Therefore, the call file:seek() returns the current
file position, without changing it;
the call file:seek("set") sets the position to the
beginning of the file (and returns 0);
and the call file:seek("end") sets the position to the
end of the file, and returns its size.
file:setvbuf (mode [, size])
no":
no buffering; the result of any output operation appears immediately.
full":
full buffering; output operation is performed only
when the buffer is full or when
you explicitly flush the file (see io.flush).
line":
line buffering; output is buffered until a newline is output
or there is any input from some special files
(such as a terminal device).
size
specifies the size of the buffer, in bytes.
The default is an appropriate size.
file:write (···)file.
The arguments must be strings or numbers.
file.
Otherwise it returns nil plus a string describing the error.
6.9 – Operating System Facilities
os.
os.clock ()os.date ([format [, time]])format.
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.
format starts with '!',
then the date is formatted in Coordinated Universal Time.
After this optional character,
if format is the string "*t",
then date returns a table with the following fields:
year (four digits), month (1–12), day (1–31),
hour (0–23), min (0–59), sec (0–61),
wday (weekday, Sunday is 1),
yday (day of the year),
and isdst (daylight saving flag, a boolean).
This last field may be absent
if the information is not available.
format is not "*t",
then date returns the date as a string,
formatted according to the same rules as the ISO C function strftime.
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")).
gmtime and C function localtime.
os.difftime (t2, t1)t1 to time t2
(where the times are values returned by os.time).
In POSIX, Windows, and some other systems,
this value is exactly t2-t1.
os.execute ([command])system.
It passes command to be executed by an operating system shell.
Its first result is true
if the command terminated successfully,
or nil otherwise.
After this first result
the function returns a string plus a number,
as follows:
exit":
the command terminated normally;
the following number is the exit status of the command.
signal":
the command was terminated by a signal;
the following number is the signal that terminated the command.
command,
os.execute returns a boolean that is true if a shell is available.
os.exit ([code [, close]])exit to terminate the host program.
If code is true,
the returned status is EXIT_SUCCESS;
if code is false,
the returned status is EXIT_FAILURE;
if code is a number,
the returned status is this number.
The default value for code is true.
close is true,
closes the Lua state before exiting.
os.getenv (varname)varname,
or nil if the variable is not defined.
os.remove (filename)os.rename (oldname, newname)oldname to newname.
If this function fails, it returns nil,
plus a string describing the error and the error code.
os.setlocale (locale [, category])locale is a system-dependent string specifying a locale;
category is an optional string describing which category to change:
"all", "collate", "ctype",
"monetary", "numeric", or "time";
the default category is "all".
The function returns the name of the new locale,
or nil if the request cannot be honored.
locale is the empty string,
the current locale is set to an implementation-defined native locale.
If locale is the string "C",
the current locale is set to the standard C locale.
setlocale.
os.time ([table])year, month, and day,
and may have fields
hour (default is 12),
min (default is 0),
sec (default is 0),
and isdst (default is nil).
For a description of these fields, see the os.date function.
time can be used only as an argument to
os.date and os.difftime.
os.tmpname ()io.tmpfile,
which automatically removes the file when the program ends.
6.10 – The Debug Library
debug table.
All functions that operate over a thread
have an optional first argument which is the
thread to operate over.
The default is always the current thread.
debug.debug ()cont finishes this function,
so that the caller continues its execution.
debug.debug are not lexically nested
within any function and so have no direct access to local variables.
debug.gethook ([thread])debug.sethook function).
debug.getinfo ([thread,] f [, what])f,
which means the function running at level f of the call stack
of the given thread:
level 0 is the current function (getinfo itself);
level 1 is the function that called getinfo
(except for tail calls, which do not count on the stack);
and so on.
If f is a number larger than the number of active functions,
then getinfo returns nil.
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.
debug.getinfo(1,"n").name returns
a table with a name for the current function,
if a reasonable name can be found,
and the expression debug.getinfo(print)
returns a table with all available information
about the print function.
debug.getlocal ([thread,] f, local)local of the function at level f of the stack.
This function accesses not only explicit local variables,
but also parameters, temporaries, etc.
debug.getinfo to check whether the level is valid.)
(' (open parenthesis)
represent variables with no known names
(internal variables such as loop control variables,
and variables from chunks saved without debug information).
f may also be a function.
In that case, getlocal returns only the name of function parameters.
debug.getmetatable (value)value
or nil if it does not have a metatable.
debug.getregistry ()debug.getupvalue (f, up)up of the function f.
The function returns nil if there is no upvalue with the given index.
(' (open parenthesis)
represent variables with no known names
(variables from chunks saved without debug information).
debug.getuservalue (u)u.
If u is not a userdata,
returns nil.
debug.sethook ([thread,] hook, mask [, count])mask and the number count describe
when the hook will be called.
The string mask may have any combination of the following characters,
with the given meaning:
c': the hook is called every time Lua calls a function;r': the hook is called every time Lua returns from a function;l': the hook is called every time Lua enters a new line of code.count different from zero,
the hook is called also after every count instructions.
debug.sethook turns off the hook.
"call" (or "tail call"),
"return",
"line", and "count".
For line events,
the hook also gets the new line number as its second parameter.
Inside a hook,
you can call getinfo with level 2 to get more information about
the running function
(level 0 is the getinfo function,
and level 1 is the hook function).
debug.setlocal ([thread,] level, local, value)value to the local variable
with index local of the function at level level of the stack.
The function returns nil if there is no local
variable with the given index,
and raises an error when called with a level out of range.
(You can call getinfo to check whether the level is valid.)
Otherwise, it returns the name of the local variable.
debug.getlocal for more information about
variable indices and names.
debug.setmetatable (value, table)value to the given table
(which can be nil).
Returns value.
debug.setupvalue (f, up, value)value to the upvalue
with index up of the function f.
The function returns nil if there is no upvalue
with the given index.
Otherwise, it returns the name of the upvalue.
debug.setuservalue (udata, value)value as
the Lua value associated to the given udata.
udata must be a full userdata.
udata.
debug.traceback ([thread,] [message [, level]])message is present but is neither a string nor nil,
this function returns message without further processing.
Otherwise,
it returns a string with a traceback of the call stack.
The optional message string is appended
at the beginning of the traceback.
An optional level number tells at which level
to start the traceback
(default is 1, the function calling traceback).
debug.upvalueid (f, n)n
from the given function.
debug.upvaluejoin (f1, n1, f2, n2)n1-th upvalue of the Lua closure f1
refer to the n2-th upvalue of the Lua closure f2.
7 – Lua Standalone
lua,
is provided with the standard distribution.
The standalone interpreter includes
all standard libraries, including the debug library.
Its usage is:
lua [options] [script [args]]
-e stat: executes string stat;-l mod: "requires" mod;-i: enters interactive mode after running script;-v: prints version information;-E: ignores environment variables;--: stops handling options;-: executes stdin as a file and stops handling options.lua runs the given script.
When called without arguments,
lua behaves as lua -v -i
when the standard input (stdin) is a terminal,
and as lua - otherwise.
-E,
the interpreter checks for an environment variable LUA_INIT_5_3
(or LUA_INIT if the versioned name is not defined)
before running any argument.
If the variable content has the format @filename,
then lua executes the file.
Otherwise, lua executes the string itself.
-E,
besides ignoring LUA_INIT,
Lua also ignores
the values of LUA_PATH and LUA_CPATH,
setting the values of
package.path and package.cpath
with the default paths defined in luaconf.h.
-i and -E.
For instance, an invocation like
$ lua -e'a=1' -e 'print(a)' script.lua
a to 1, then print the value of a,
and finally run the file script.lua with no arguments.
(Here $ is the shell prompt. Your prompt may be different.)
lua collects all command-line arguments
in a global table called arg.
The script name goes to index 0,
the first argument after the script name goes to index 1,
and so on.
Any arguments before the script name
(that is, the interpreter name plus its options)
go to negative indices.
For instance, in the call
$ lua -la b.lua t1 t2
arg = { [-2] = "lua", [-1] = "-la",
[0] = "b.lua",
[1] = "t1", [2] = "t2" }
$ lua -e "print(arg[1])"
-e".
If there is a script,
the script is called with parameters
arg[1], ···, arg[#arg].
(Like all chunks in Lua,
the script is compiled as a vararg function.)
__tostring,
the interpreter calls this metamethod to produce the final message.
Otherwise, the interpreter converts the error object to a string
and adds a stack traceback to it.
lua_close).
The script can avoid this step by
calling os.exit to terminate.
#.
Therefore, Lua scripts can be made into executable programs
by using chmod +x and the #! form,
as in
#!/usr/local/bin/lua
lua is in your PATH,
then
#!/usr/bin/env lua
8 – Incompatibilities with the Previous Version
luaconf.h).
However,
all these compatibility options will be removed in the future.
8.1 – Changes in the Language
.0
or using x = x + 0.0 to convert a variable.
(This recommendation is only for a quick fix
for an occasional incompatibility;
it is not a general guideline for good programming.
For good programming,
use floats where you need floats
and integers where you need integers.)
.0 suffix
to the result if it looks like an integer.
(For instance, the float 2.0 will be printed as 2.0,
not as 2.)
You should always use an explicit format
when you need a specific format for numbers.
8.2 – Changes in the Libraries
bit32 library has been deprecated.
It is easy to require a compatible external library or,
better yet, to replace its functions with appropriate bitwise operations.
(Keep in mind that bit32 operates on 32-bit integers,
while the bitwise operators in standard Lua operate on 64-bit integers.)
ipairs iterator now respects metamethods and
its __ipairs metamethod has been deprecated.
io.read do not have a starting '*' anymore.
For compatibility, Lua will continue to ignore this character.
atan2, cosh, sinh, tanh, pow,
frexp, and ldexp.
You can replace math.pow(x,y) with x^y;
you can replace math.atan2 with math.atan,
which now accepts one or two parameters;
you can replace math.ldexp(x,exp) with x * 2.0^exp.
For the other operations,
you can either use an external library or
implement them in Lua.
require
changed the way it handles versioned names.
Now, the version should come after the module name
(as is usual in most other tools).
For compatibility, that searcher still tries the old format
if it cannot find an open function according to the new style.
(Lua 5.2 already worked that way,
but it did not document the change.)
8.3 – Changes in the API
lua_getctx,
so lua_getctx has been removed.
Adapt your code accordingly.
lua_dump has an extra parameter, strip.
Use 0 as the value of this parameter to get the old behavior.
lua_pushunsigned, lua_tounsigned, lua_tounsignedx,
luaL_checkunsigned, luaL_optunsigned)
were deprecated.
Use their signed equivalents with a type cast.
luaL_checkint, luaL_optint, luaL_checklong, luaL_optlong)
were deprecated.
Use their equivalent over lua_Integer with a type cast
(or, when possible, use lua_Integer in your code).
9 – The Complete Syntax of Lua
chunk ::= block
block ::= {stat} [retstat]
stat ::= ‘;’ |
varlist ‘=’ explist |
functioncall |
label |
break |
goto Name |
do block end |
while exp do block end |
repeat block until exp |
if exp then block {elseif exp then block} [else block] end |
for Name ‘=’ exp ‘,’ exp [‘,’ exp] do block end |
for namelist in explist do block end |
function funcname funcbody |
local function Name funcbody |
local namelist [‘=’ explist]
retstat ::= return [explist] [‘;’]
label ::= ‘::’ Name ‘::’
funcname ::= Name {‘.’ Name} [‘:’ Name]
varlist ::= var {‘,’ var}
var ::= Name | prefixexp ‘[’ exp ‘]’ | prefixexp ‘.’ Name
namelist ::= Name {‘,’ Name}
explist ::= exp {‘,’ exp}
exp ::= nil | false | true | Numeral | LiteralString | ‘...’ | functiondef |
prefixexp | tableconstructor | exp binop exp | unop exp
prefixexp ::= var | functioncall | ‘(’ exp ‘)’
functioncall ::= prefixexp args | prefixexp ‘:’ Name args
args ::= ‘(’ [explist] ‘)’ | tableconstructor | LiteralString
functiondef ::= function funcbody
funcbody ::= ‘(’ [parlist] ‘)’ block end
parlist ::= namelist [‘,’ ‘...’] | ‘...’
tableconstructor ::= ‘{’ [fieldlist] ‘}’
fieldlist ::= field {fieldsep field} [fieldsep]
field ::= ‘[’ exp ‘]’ ‘=’ exp | Name ‘=’ exp | exp
fieldsep ::= ‘,’ | ‘;’
binop ::= ‘+’ | ‘-’ | ‘*’ | ‘/’ | ‘//’ | ‘^’ | ‘%’ |
‘&’ | ‘~’ | ‘|’ | ‘>>’ | ‘<<’ | ‘..’ |
‘<’ | ‘<=’ | ‘>’ | ‘>=’ | ‘==’ | ‘~=’ |
and | or
unop ::= ‘-’ | not | ‘#’ | ‘~’
Last update:
Fri Jan 16 00:58:20 BRST 2015