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| <h1> | |
| <a href="http://www.lua.org/"><img src="logo.gif" alt="" border="0"></a> | |
| Lua 5.2 Reference Manual | |
| </h1> | |
| by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes | |
| <p> | |
| <small> | |
| Copyright © 2011–2013 Lua.org, PUC-Rio. | |
| Freely available under the terms of the | |
| <a href="http://www.lua.org/license.html">Lua license</a>. | |
| </small> | |
| <hr> | |
| <p> | |
| <a href="contents.html#contents">contents</A> | |
| · | |
| <a href="contents.html#index">index</A> | |
| <!-- ====================================================================== --> | |
| <p> | |
| <!-- $Id: manual.of,v 1.103 2013/03/14 18:51:56 roberto Exp $ --> | |
| <h1>1 – <a name="1">Introduction</a></h1> | |
| <p> | |
| Lua is an extension programming language designed to support | |
| general procedural programming with data description | |
| facilities. | |
| It also offers good support for object-oriented programming, | |
| functional programming, and data-driven programming. | |
| Lua is intended to be used as a powerful, lightweight, | |
| embeddable scripting language for any program that needs one. | |
| Lua is implemented as a library, written in <em>clean C</em>, | |
| the common subset of Standard C and C++. | |
| <p> | |
| Being an extension language, Lua has no notion of a "main" program: | |
| it only works <em>embedded</em> in a host client, | |
| called the <em>embedding program</em> or simply the <em>host</em>. | |
| The host program can invoke functions to execute a piece of Lua code, | |
| can write and read Lua variables, | |
| and can register C functions to be called by Lua code. | |
| Through the use of C functions, Lua can be augmented to cope with | |
| a wide range of different domains, | |
| thus creating customized programming languages sharing a syntactical framework. | |
| The Lua distribution includes a sample host program called <code>lua</code>, | |
| which uses the Lua library to offer a complete, standalone Lua interpreter, | |
| for interactive or batch use. | |
| <p> | |
| Lua is free software, | |
| and is provided as usual with no guarantees, | |
| as stated in its license. | |
| The implementation described in this manual is available | |
| at Lua's official web site, <code>www.lua.org</code>. | |
| <p> | |
| Like any other reference manual, | |
| this document is dry in places. | |
| For a discussion of the decisions behind the design of Lua, | |
| see the technical papers available at Lua's web site. | |
| For a detailed introduction to programming in Lua, | |
| see Roberto's book, <em>Programming in Lua</em>. | |
| <h1>2 – <a name="2">Basic Concepts</a></h1> | |
| <p> | |
| This section describes the basic concepts of the language. | |
| <h2>2.1 – <a name="2.1">Values and Types</a></h2> | |
| <p> | |
| Lua is a <em>dynamically typed language</em>. | |
| 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. | |
| <p> | |
| All values in Lua are <em>first-class values</em>. | |
| This means that all values can be stored in variables, | |
| passed as arguments to other functions, and returned as results. | |
| <p> | |
| There are eight basic types in Lua: | |
| <em>nil</em>, <em>boolean</em>, <em>number</em>, | |
| <em>string</em>, <em>function</em>, <em>userdata</em>, | |
| <em>thread</em>, and <em>table</em>. | |
| <em>Nil</em> is the type of the value <b>nil</b>, | |
| whose main property is to be different from any other value; | |
| it usually represents the absence of a useful value. | |
| <em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>. | |
| Both <b>nil</b> and <b>false</b> make a condition false; | |
| any other value makes it true. | |
| <em>Number</em> represents real (double-precision floating-point) numbers. | |
| Operations on numbers follow the same rules of | |
| the underlying C implementation, | |
| which, in turn, usually follows the IEEE 754 standard. | |
| (It is easy to build Lua interpreters that use other | |
| internal representations for numbers, | |
| such as single-precision floats or long integers; | |
| see file <code>luaconf.h</code>.) | |
| <em>String</em> represents immutable sequences of bytes. | |
| Lua is 8-bit clean: | |
| strings can contain any 8-bit value, | |
| including embedded zeros ('<code>\0</code>'). | |
| <p> | |
| Lua can call (and manipulate) functions written in Lua and | |
| functions written in C | |
| (see <a href="#3.4.9">§3.4.9</a>). | |
| <p> | |
| The type <em>userdata</em> is provided to allow arbitrary C data to | |
| be stored in Lua variables. | |
| A userdata value is a pointer to a block of raw memory. | |
| There are two kinds of userdata: | |
| full userdata, where the block of memory is managed by Lua, | |
| and light userdata, where the block of memory is managed by the host. | |
| Userdata has no predefined operations in Lua, | |
| except assignment and identity test. | |
| By using <em>metatables</em>, | |
| the programmer can define operations for full userdata values | |
| (see <a href="#2.4">§2.4</a>). | |
| Userdata values cannot be created or modified in Lua, | |
| only through the C API. | |
| This guarantees the integrity of data owned by the host program. | |
| <p> | |
| The type <em>thread</em> represents independent threads of execution | |
| and it is used to implement coroutines (see <a href="#2.6">§2.6</a>). | |
| Do not confuse Lua threads with operating-system threads. | |
| Lua supports coroutines on all systems, | |
| even those that do not support threads. | |
| <p> | |
| The type <em>table</em> implements associative arrays, | |
| that is, arrays that can be indexed not only with numbers, | |
| but with any Lua value except <b>nil</b> and NaN | |
| (<em>Not a Number</em>, a special numeric value used to represent | |
| undefined or unrepresentable results, such as <code>0/0</code>). | |
| Tables can be <em>heterogeneous</em>; | |
| that is, they can contain values of all types (except <b>nil</b>). | |
| Any key with value <b>nil</b> is not considered part of the table. | |
| Conversely, any key that is not part of a table has | |
| an associated value <b>nil</b>. | |
| <p> | |
| Tables are the sole data structuring mechanism in Lua; | |
| they can be used to represent ordinary arrays, sequences, | |
| symbol tables, sets, records, graphs, trees, etc. | |
| To represent records, Lua uses the field name as an index. | |
| The language supports this representation by | |
| providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. | |
| There are several convenient ways to create tables in Lua | |
| (see <a href="#3.4.8">§3.4.8</a>). | |
| <p> | |
| We use the term <em>sequence</em> to denote a table where | |
| the set of all positive numeric keys is equal to <em>{1..n}</em> | |
| for some integer <em>n</em>, | |
| which is called the length of the sequence (see <a href="#3.4.6">§3.4.6</a>). | |
| <p> | |
| 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 <em>methods</em> (see <a href="#3.4.10">§3.4.10</a>). | |
| <p> | |
| The indexing of tables follows | |
| the definition of raw equality in the language. | |
| The expressions <code>a[i]</code> and <code>a[j]</code> | |
| denote the same table element | |
| if and only if <code>i</code> and <code>j</code> are raw equal | |
| (that is, equal without metamethods). | |
| <p> | |
| Tables, functions, threads, and (full) userdata values are <em>objects</em>: | |
| variables do not actually <em>contain</em> these values, | |
| only <em>references</em> to them. | |
| Assignment, parameter passing, and function returns | |
| always manipulate references to such values; | |
| these operations do not imply any kind of copy. | |
| <p> | |
| The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type | |
| of a given value (see <a href="#6.1">§6.1</a>). | |
| <h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2> | |
| <p> | |
| As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>, | |
| any reference to a global name <code>var</code> is syntactically translated | |
| to <code>_ENV.var</code>. | |
| Moreover, every chunk is compiled in the scope of | |
| an external local variable called <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>), | |
| so <code>_ENV</code> itself is never a global name in a chunk. | |
| <p> | |
| Despite the existence of this external <code>_ENV</code> variable and | |
| the translation of global names, | |
| <code>_ENV</code> is a completely regular name. | |
| In particular, | |
| you can define new variables and parameters with that name. | |
| Each reference to a global name uses the <code>_ENV</code> that is | |
| visible at that point in the program, | |
| following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>). | |
| <p> | |
| Any table used as the value of <code>_ENV</code> is called an <em>environment</em>. | |
| <p> | |
| Lua keeps a distinguished environment called the <em>global environment</em>. | |
| This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>). | |
| In Lua, the variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value. | |
| <p> | |
| When Lua compiles a chunk, | |
| it initializes the value of its <code>_ENV</code> upvalue | |
| with the global environment (see <a href="#pdf-load"><code>load</code></a>). | |
| Therefore, by default, | |
| global variables in Lua code refer to entries in the global environment. | |
| Moreover, all standard libraries are loaded in the global environment | |
| and several functions there operate on that environment. | |
| You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>) | |
| to load a chunk with a different environment. | |
| (In C, you have to load the chunk and then change the value | |
| of its first upvalue.) | |
| <p> | |
| If you change the global environment in the registry | |
| (through C code or the debug library), | |
| all chunks loaded after the change will get the new environment. | |
| Previously loaded chunks are not affected, however, | |
| as each has its own reference to the environment in its <code>_ENV</code> variable. | |
| Moreover, the variable <a href="#pdf-_G"><code>_G</code></a> | |
| (which is stored in the original global environment) | |
| is never updated by Lua. | |
| <h2>2.3 – <a name="2.3">Error Handling</a></h2> | |
| <p> | |
| Because Lua is an embedded extension language, | |
| all Lua actions start from C code in the host program | |
| calling a function from the Lua library (see <a href="#lua_pcall"><code>lua_pcall</code></a>). | |
| Whenever an error occurs during | |
| the compilation or execution of a Lua chunk, | |
| control returns to the host, | |
| which can take appropriate measures | |
| (such as printing an error message). | |
| <p> | |
| Lua code can explicitly generate an error by calling the | |
| <a href="#pdf-error"><code>error</code></a> function. | |
| If you need to catch errors in Lua, | |
| you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a> | |
| to call a given function in <em>protected mode</em>. | |
| <p> | |
| Whenever there is an error, | |
| an <em>error object</em> (also called an <em>error message</em>) | |
| is propagated with information about the error. | |
| Lua itself only generates errors where the error object is a string, | |
| but programs may generate errors with | |
| any value for the error object. | |
| <p> | |
| When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>, | |
| you may give a <em>message handler</em> | |
| to be called in case of errors. | |
| This function is called with the original error message | |
| and returns a new error message. | |
| It is called before the error unwinds the stack, | |
| so that it can gather more information about the error, | |
| for instance by inspecting the stack and creating a stack traceback. | |
| This message handler is still protected by the protected call; | |
| so, an error inside the message handler | |
| will call the message handler again. | |
| If this loop goes on, Lua breaks it and returns an appropriate message. | |
| <h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2> | |
| <p> | |
| Every value in Lua can have a <em>metatable</em>. | |
| This <em>metatable</em> is an ordinary Lua table | |
| that defines the behavior of the original value | |
| under certain special operations. | |
| You can change several aspects of the behavior | |
| of operations over a value by setting specific fields in its metatable. | |
| For instance, when a non-numeric value is the operand of an addition, | |
| Lua checks for a function in the field "<code>__add</code>" of the value's metatable. | |
| If it finds one, | |
| Lua calls this function to perform the addition. | |
| <p> | |
| The keys in a metatable are derived from the <em>event</em> names; | |
| the corresponding values are called <em>metamethods</em>. | |
| In the previous example, the event is <code>"add"</code> | |
| and the metamethod is the function that performs the addition. | |
| <p> | |
| You can query the metatable of any value | |
| using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. | |
| <p> | |
| You can replace the metatable of tables | |
| using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function. | |
| You cannot change the metatable of other types from Lua | |
| (except by using the debug library); | |
| you must use the C API for that. | |
| <p> | |
| Tables and full userdata have individual metatables | |
| (although multiple tables and userdata can share their metatables). | |
| Values of all other types share one single metatable per type; | |
| that is, there is one single metatable for all numbers, | |
| one for all strings, etc. | |
| By default, a value has no metatable, | |
| but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>). | |
| <p> | |
| A metatable controls how an object behaves in arithmetic operations, | |
| order comparisons, concatenation, length operation, and indexing. | |
| A metatable also can define a function to be called | |
| when a userdata or a table is garbage collected. | |
| When Lua performs one of these operations over a value, | |
| it checks whether this value has a metatable with the corresponding event. | |
| If so, the value associated with that key (the metamethod) | |
| controls how Lua will perform the operation. | |
| <p> | |
| Metatables control the operations listed next. | |
| Each operation is identified by its corresponding name. | |
| The key for each operation is a string with its name prefixed by | |
| two underscores, '<code>__</code>'; | |
| for instance, the key for operation "add" is the | |
| string "<code>__add</code>". | |
| <p> | |
| The semantics of these operations is better explained by a Lua function | |
| describing how the interpreter executes the operation. | |
| The code shown here in Lua is only illustrative; | |
| the real behavior is hard coded in the interpreter | |
| and it is much more efficient than this simulation. | |
| All functions used in these descriptions | |
| (<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.) | |
| are described in <a href="#6.1">§6.1</a>. | |
| In particular, to retrieve the metamethod of a given object, | |
| we use the expression | |
| <pre> | |
| metatable(obj)[event] | |
| </pre><p> | |
| This should be read as | |
| <pre> | |
| rawget(getmetatable(obj) or {}, event) | |
| </pre><p> | |
| This means that the access to a metamethod does not invoke other metamethods, | |
| and access to objects with no metatables does not fail | |
| (it simply results in <b>nil</b>). | |
| <p> | |
| For the unary <code>-</code> and <code>#</code> operators, | |
| the metamethod is called with a dummy second argument. | |
| This extra argument is only to simplify Lua's internals; | |
| it may be removed in future versions and therefore it is not present | |
| in the following code. | |
| (For most uses this extra argument is irrelevant.) | |
| <ul> | |
| <li><b>"add": </b> | |
| the <code>+</code> operation. | |
| <p> | |
| The function <code>getbinhandler</code> below defines how Lua chooses a handler | |
| for a binary operation. | |
| First, Lua tries the first operand. | |
| If its type does not define a handler for the operation, | |
| then Lua tries the second operand. | |
| <pre> | |
| function getbinhandler (op1, op2, event) | |
| return metatable(op1)[event] or metatable(op2)[event] | |
| end | |
| </pre><p> | |
| By using this function, | |
| the behavior of the <code>op1 + op2</code> is | |
| <pre> | |
| function add_event (op1, op2) | |
| local o1, o2 = tonumber(op1), tonumber(op2) | |
| if o1 and o2 then -- both operands are numeric? | |
| return o1 + o2 -- '+' here is the primitive 'add' | |
| else -- at least one of the operands is not numeric | |
| local h = getbinhandler(op1, op2, "__add") | |
| if h then | |
| -- call the handler with both operands | |
| return (h(op1, op2)) | |
| else -- no handler available: default behavior | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"sub": </b> | |
| the <code>-</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"mul": </b> | |
| the <code>*</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"div": </b> | |
| the <code>/</code> operation. | |
| Behavior similar to the "add" operation. | |
| </li> | |
| <li><b>"mod": </b> | |
| the <code>%</code> operation. | |
| Behavior similar to the "add" operation, | |
| with the operation | |
| <code>o1 - floor(o1/o2)*o2</code> as the primitive operation. | |
| </li> | |
| <li><b>"pow": </b> | |
| the <code>^</code> (exponentiation) operation. | |
| Behavior similar to the "add" operation, | |
| with the function <code>pow</code> (from the C math library) | |
| as the primitive operation. | |
| </li> | |
| <li><b>"unm": </b> | |
| the unary <code>-</code> operation. | |
| <pre> | |
| function unm_event (op) | |
| local o = tonumber(op) | |
| if o then -- operand is numeric? | |
| return -o -- '-' here is the primitive 'unm' | |
| else -- the operand is not numeric. | |
| -- Try to get a handler from the operand | |
| local h = metatable(op).__unm | |
| if h then | |
| -- call the handler with the operand | |
| return (h(op)) | |
| else -- no handler available: default behavior | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"concat": </b> | |
| the <code>..</code> (concatenation) operation. | |
| <pre> | |
| function concat_event (op1, op2) | |
| if (type(op1) == "string" or type(op1) == "number") and | |
| (type(op2) == "string" or type(op2) == "number") then | |
| return op1 .. op2 -- primitive string concatenation | |
| else | |
| local h = getbinhandler(op1, op2, "__concat") | |
| if h then | |
| return (h(op1, op2)) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"len": </b> | |
| the <code>#</code> operation. | |
| <pre> | |
| function len_event (op) | |
| if type(op) == "string" then | |
| return strlen(op) -- primitive string length | |
| else | |
| local h = metatable(op).__len | |
| if h then | |
| return (h(op)) -- call handler with the operand | |
| elseif type(op) == "table" then | |
| return #op -- primitive table length | |
| else -- no handler available: error | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| See <a href="#3.4.6">§3.4.6</a> for a description of the length of a table. | |
| </li> | |
| <li><b>"eq": </b> | |
| the <code>==</code> operation. | |
| The function <code>getequalhandler</code> defines how Lua chooses a metamethod | |
| for equality. | |
| A metamethod is selected only when both values | |
| being compared have the same type | |
| and the same metamethod for the selected operation, | |
| and the values are either tables or full userdata. | |
| <pre> | |
| function getequalhandler (op1, op2) | |
| if type(op1) ~= type(op2) or | |
| (type(op1) ~= "table" and type(op1) ~= "userdata") then | |
| return nil -- different values | |
| end | |
| local mm1 = metatable(op1).__eq | |
| local mm2 = metatable(op2).__eq | |
| if mm1 == mm2 then return mm1 else return nil end | |
| end | |
| </pre><p> | |
| The "eq" event is defined as follows: | |
| <pre> | |
| function eq_event (op1, op2) | |
| if op1 == op2 then -- primitive equal? | |
| return true -- values are equal | |
| end | |
| -- try metamethod | |
| local h = getequalhandler(op1, op2) | |
| if h then | |
| return not not h(op1, op2) | |
| else | |
| return false | |
| end | |
| end | |
| </pre><p> | |
| Note that the result is always a boolean. | |
| </li> | |
| <li><b>"lt": </b> | |
| the <code><</code> operation. | |
| <pre> | |
| function lt_event (op1, op2) | |
| if type(op1) == "number" and type(op2) == "number" then | |
| return op1 < op2 -- numeric comparison | |
| elseif type(op1) == "string" and type(op2) == "string" then | |
| return op1 < op2 -- lexicographic comparison | |
| else | |
| local h = getbinhandler(op1, op2, "__lt") | |
| if h then | |
| return not not h(op1, op2) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| Note that the result is always a boolean. | |
| </li> | |
| <li><b>"le": </b> | |
| the <code><=</code> operation. | |
| <pre> | |
| function le_event (op1, op2) | |
| if type(op1) == "number" and type(op2) == "number" then | |
| return op1 <= op2 -- numeric comparison | |
| elseif type(op1) == "string" and type(op2) == "string" then | |
| return op1 <= op2 -- lexicographic comparison | |
| else | |
| local h = getbinhandler(op1, op2, "__le") | |
| if h then | |
| return not not h(op1, op2) | |
| else | |
| h = getbinhandler(op1, op2, "__lt") | |
| if h then | |
| return not h(op2, op1) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| end | |
| </pre><p> | |
| Note that, in the absence of a "le" metamethod, | |
| Lua tries the "lt", assuming that <code>a <= b</code> is | |
| equivalent to <code>not (b < a)</code>. | |
| <p> | |
| As with the other comparison operators, | |
| the result is always a boolean. | |
| </li> | |
| <li><b>"index": </b> | |
| The indexing access <code>table[key]</code>. | |
| Note that the metamethod is tried only | |
| when <code>key</code> is not present in <code>table</code>. | |
| (When <code>table</code> is not a table, | |
| no key is ever present, | |
| so the metamethod is always tried.) | |
| <pre> | |
| function gettable_event (table, key) | |
| local h | |
| if type(table) == "table" then | |
| local v = rawget(table, key) | |
| -- if key is present, return raw value | |
| if v ~= nil then return v end | |
| h = metatable(table).__index | |
| if h == nil then return nil end | |
| else | |
| h = metatable(table).__index | |
| if h == nil then | |
| error(···) | |
| end | |
| end | |
| if type(h) == "function" then | |
| return (h(table, key)) -- call the handler | |
| else return h[key] -- or repeat operation on it | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"newindex": </b> | |
| The indexing assignment <code>table[key] = value</code>. | |
| Note that the metamethod is tried only | |
| when <code>key</code> is not present in <code>table</code>. | |
| <pre> | |
| function settable_event (table, key, value) | |
| local h | |
| if type(table) == "table" then | |
| local v = rawget(table, key) | |
| -- if key is present, do raw assignment | |
| if v ~= nil then rawset(table, key, value); return end | |
| h = metatable(table).__newindex | |
| if h == nil then rawset(table, key, value); return end | |
| else | |
| h = metatable(table).__newindex | |
| if h == nil then | |
| error(···) | |
| end | |
| end | |
| if type(h) == "function" then | |
| h(table, key,value) -- call the handler | |
| else h[key] = value -- or repeat operation on it | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| <li><b>"call": </b> | |
| called when Lua calls a value. | |
| <pre> | |
| function function_event (func, ...) | |
| if type(func) == "function" then | |
| return func(...) -- primitive call | |
| else | |
| local h = metatable(func).__call | |
| if h then | |
| return h(func, ...) | |
| else | |
| error(···) | |
| end | |
| end | |
| end | |
| </pre><p> | |
| </li> | |
| </ul> | |
| <h2>2.5 – <a name="2.5">Garbage Collection</a></h2> | |
| <p> | |
| Lua performs automatic memory management. | |
| This means that | |
| you have to worry neither about allocating memory for new objects | |
| nor about freeing it when the objects are no longer needed. | |
| Lua manages memory automatically by running | |
| a <em>garbage collector</em> to collect all <em>dead objects</em> | |
| (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. | |
| <p> | |
| Lua implements an incremental mark-and-sweep collector. | |
| It uses two numbers to control its garbage-collection cycles: | |
| the <em>garbage-collector pause</em> and | |
| the <em>garbage-collector step multiplier</em>. | |
| Both use percentage points as units | |
| (e.g., a value of 100 means an internal value of 1). | |
| <p> | |
| 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. | |
| <p> | |
| 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. | |
| Values smaller than 100 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. | |
| <p> | |
| 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. | |
| <p> | |
| You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C | |
| or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. | |
| You can also use these functions to control | |
| the collector directly (e.g., stop and restart it). | |
| <p> | |
| As an experimental feature in Lua 5.2, | |
| you can change the collector's operation mode | |
| from incremental to <em>generational</em>. | |
| A <em>generational collector</em> assumes that most objects die young, | |
| and therefore it traverses only young (recently created) objects. | |
| This behavior can reduce the time used by the collector, | |
| but also increases memory usage (as old dead objects may accumulate). | |
| To mitigate this second problem, | |
| from time to time the generational collector performs a full collection. | |
| Remember that this is an experimental feature; | |
| you are welcome to try it, | |
| but check your gains. | |
| <h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3> | |
| <p> | |
| You can set garbage-collector metamethods for tables | |
| and, using the C API, | |
| for full userdata (see <a href="#2.4">§2.4</a>). | |
| These metamethods are also called <em>finalizers</em>. | |
| 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). | |
| <p> | |
| For an object (table or userdata) to be finalized when collected, | |
| you must <em>mark</em> it for finalization. | |
| You mark an object for finalization when you set its metatable | |
| and the metatable has a field indexed by the string "<code>__gc</code>". | |
| Note that if you set a metatable without a <code>__gc</code> field | |
| and later create that field in the metatable, | |
| the object will not be marked for finalization. | |
| However, after an object is marked, | |
| you can freely change the <code>__gc</code> field of its metatable. | |
| <p> | |
| 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 does the equivalent of the following function | |
| for each object in that list: | |
| <pre> | |
| function gc_event (obj) | |
| local h = metatable(obj).__gc | |
| if type(h) == "function" then | |
| h(obj) | |
| end | |
| end | |
| </pre> | |
| <p> | |
| At the end of each garbage-collection cycle, | |
| the finalizers for objects are called in | |
| the reverse order that they were marked for collection, | |
| 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. | |
| <p> | |
| Because the object being collected must still be used by the finalizer, | |
| it (and other objects accessible only through it) | |
| must be <em>resurrected</em> 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 there is a permanent resurrection. | |
| In any case, | |
| the object memory is freed only when it becomes completely inaccessible; | |
| its finalizer will never be called twice. | |
| <p> | |
| When you close a state (see <a href="#lua_close"><code>lua_close</code></a>), | |
| Lua calls the finalizers of all objects marked for finalization, | |
| following the reverse order that they were marked. | |
| If any finalizer marks new objects for collection during that phase, | |
| these new objects will not be finalized. | |
| <h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3> | |
| <p> | |
| A <em>weak table</em> is a table whose elements are | |
| <em>weak references</em>. | |
| 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. | |
| <p> | |
| 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 | |
| <code>__mode</code> field of its metatable. | |
| If the <code>__mode</code> field is a string containing the character '<code>k</code>', | |
| the keys in the table are weak. | |
| If <code>__mode</code> contains '<code>v</code>', | |
| the values in the table are weak. | |
| <p> | |
| A table with weak keys and strong values | |
| is also called an <em>ephemeron table</em>. | |
| 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. | |
| <p> | |
| 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. | |
| <p> | |
| 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 its associated value is collected). | |
| Although strings are subject to garbage collection, | |
| they do not have an explicit construction, | |
| and therefore are not removed from weak tables. | |
| <p> | |
| 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. | |
| <p> | |
| If a weak table is among the resurrected objects in a collection cycle, | |
| it may not be properly cleared until the next cycle. | |
| <h2>2.6 – <a name="2.6">Coroutines</a></h2> | |
| <p> | |
| Lua supports coroutines, | |
| also called <em>collaborative multithreading</em>. | |
| 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. | |
| <p> | |
| You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>. | |
| Its sole argument is a function | |
| that is the main function of the coroutine. | |
| The <code>create</code> function only creates a new coroutine and | |
| returns a handle to it (an object of type <em>thread</em>); | |
| it does not start the coroutine. | |
| <p> | |
| You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. | |
| When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| passing as its first argument | |
| a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, | |
| the coroutine starts its execution, | |
| at the first line of its main function. | |
| Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on | |
| to the coroutine main function. | |
| After the coroutine starts running, | |
| it runs until it terminates or <em>yields</em>. | |
| <p> | |
| A coroutine can terminate its execution in two ways: | |
| normally, when its main function returns | |
| (explicitly or implicitly, after the last instruction); | |
| and abnormally, if there is an unprotected error. | |
| In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>, | |
| plus any values returned by the coroutine main function. | |
| In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b> | |
| plus an error message. | |
| <p> | |
| A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. | |
| When a coroutine yields, | |
| the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> 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, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>, | |
| plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. | |
| The next time you resume the same coroutine, | |
| it continues its execution from the point where it yielded, | |
| with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra | |
| arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. | |
| <p> | |
| Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, | |
| the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> 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 <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. | |
| <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| except the first one (the boolean error code). | |
| Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, | |
| <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors; | |
| any error is propagated to the caller. | |
| <p> | |
| As an example of how coroutines work, | |
| consider the following code: | |
| <pre> | |
| 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")) | |
| </pre><p> | |
| When you run it, it produces the following output: | |
| <pre> | |
| 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 | |
| </pre> | |
| <p> | |
| You can also create and manipulate coroutines through the C API: | |
| see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>, | |
| and <a href="#lua_yield"><code>lua_yield</code></a>. | |
| <h1>3 – <a name="3">The Language</a></h1> | |
| <p> | |
| 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. | |
| <p> | |
| Language constructs will be explained using the usual extended BNF notation, | |
| in which | |
| {<em>a</em>} means 0 or more <em>a</em>'s, and | |
| [<em>a</em>] means an optional <em>a</em>. | |
| Non-terminals are shown like non-terminal, | |
| keywords are shown like <b>kword</b>, | |
| and other terminal symbols are shown like ‘<b>=</b>’. | |
| The complete syntax of Lua can be found in <a href="#9">§9</a> | |
| at the end of this manual. | |
| <h2>3.1 – <a name="3.1">Lexical Conventions</a></h2> | |
| <p> | |
| 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. | |
| <p> | |
| <em>Names</em> | |
| (also called <em>identifiers</em>) | |
| 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. | |
| <p> | |
| The following <em>keywords</em> are reserved | |
| and cannot be used as names: | |
| <pre> | |
| and break do else elseif end | |
| false for function goto if in | |
| local nil not or repeat return | |
| then true until while | |
| </pre> | |
| <p> | |
| Lua is a case-sensitive language: | |
| <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> | |
| are two different, valid names. | |
| As a convention, names starting with an underscore followed by | |
| uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>) | |
| are reserved for variables used by Lua. | |
| <p> | |
| The following strings denote other tokens: | |
| <pre> | |
| + - * / % ^ # | |
| == ~= <= >= < > = | |
| ( ) { } [ ] :: | |
| ; : , . .. ... | |
| </pre> | |
| <p> | |
| <em>Literal strings</em> | |
| can be delimited by matching single or double quotes, | |
| and can contain the following C-like escape sequences: | |
| '<code>\a</code>' (bell), | |
| '<code>\b</code>' (backspace), | |
| '<code>\f</code>' (form feed), | |
| '<code>\n</code>' (newline), | |
| '<code>\r</code>' (carriage return), | |
| '<code>\t</code>' (horizontal tab), | |
| '<code>\v</code>' (vertical tab), | |
| '<code>\\</code>' (backslash), | |
| '<code>\"</code>' (quotation mark [double quote]), | |
| and '<code>\'</code>' (apostrophe [single quote]). | |
| A backslash followed by a real newline | |
| results in a newline in the string. | |
| The escape sequence '<code>\z</code>' 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. | |
| <p> | |
| A byte in a literal string can also be specified by its numerical value. | |
| This can be done with the escape sequence <code>\x<em>XX</em></code>, | |
| where <em>XX</em> is a sequence of exactly two hexadecimal digits, | |
| or with the escape sequence <code>\<em>ddd</em></code>, | |
| where <em>ddd</em> is a sequence of up to three decimal digits. | |
| (Note that if a decimal escape is to be followed by a digit, | |
| it must be expressed using exactly three digits.) | |
| Strings in Lua can contain any 8-bit value, including embedded zeros, | |
| which can be specified as '<code>\0</code>'. | |
| <p> | |
| Literal strings can also be defined using a long format | |
| enclosed by <em>long brackets</em>. | |
| We define an <em>opening long bracket of level <em>n</em></em> as an opening | |
| square bracket followed by <em>n</em> equal signs followed by another | |
| opening square bracket. | |
| So, an opening long bracket of level 0 is written as <code>[[</code>, | |
| an opening long bracket of level 1 is written as <code>[=[</code>, | |
| and so on. | |
| A <em>closing long bracket</em> is defined similarly; | |
| for instance, a closing long bracket of level 4 is written as <code>]====]</code>. | |
| A <em>long literal</em> 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 proper 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. | |
| <p> | |
| 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. | |
| <p> | |
| 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 '<code>a</code>' is coded as 97, | |
| newline is coded as 10, and '<code>1</code>' is coded as 49), | |
| the five literal strings below denote the same string: | |
| <pre> | |
| a = 'alo\n123"' | |
| a = "alo\n123\"" | |
| a = '\97lo\10\04923"' | |
| a = [[alo | |
| 123"]] | |
| a = [==[ | |
| alo | |
| 123"]==] | |
| </pre> | |
| <p> | |
| A <em>numerical constant</em> can be written with an optional fractional part | |
| and an optional decimal exponent, | |
| marked by a letter '<code>e</code>' or '<code>E</code>'. | |
| Lua also accepts hexadecimal constants, | |
| which start with <code>0x</code> or <code>0X</code>. | |
| Hexadecimal constants also accept an optional fractional part | |
| plus an optional binary exponent, | |
| marked by a letter '<code>p</code>' or '<code>P</code>'. | |
| Examples of valid numerical constants are | |
| <pre> | |
| 3 3.0 3.1416 314.16e-2 0.31416E1 | |
| 0xff 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1 | |
| </pre> | |
| <p> | |
| A <em>comment</em> starts with a double hyphen (<code>--</code>) | |
| anywhere outside a string. | |
| If the text immediately after <code>--</code> is not an opening long bracket, | |
| the comment is a <em>short comment</em>, | |
| which runs until the end of the line. | |
| Otherwise, it is a <em>long comment</em>, | |
| which runs until the corresponding closing long bracket. | |
| Long comments are frequently used to disable code temporarily. | |
| <h2>3.2 – <a name="3.2">Variables</a></h2> | |
| <p> | |
| Variables are places that store values. | |
| There are three kinds of variables in Lua: | |
| global variables, local variables, and table fields. | |
| <p> | |
| 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): | |
| <pre> | |
| var ::= Name | |
| </pre><p> | |
| Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>. | |
| <p> | |
| Any variable name is assumed to be global unless explicitly declared | |
| as a local (see <a href="#3.3.7">§3.3.7</a>). | |
| Local variables are <em>lexically scoped</em>: | |
| local variables can be freely accessed by functions | |
| defined inside their scope (see <a href="#3.5">§3.5</a>). | |
| <p> | |
| Before the first assignment to a variable, its value is <b>nil</b>. | |
| <p> | |
| Square brackets are used to index a table: | |
| <pre> | |
| var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | |
| </pre><p> | |
| The meaning of accesses to table fields can be changed via metatables. | |
| An access to an indexed variable <code>t[i]</code> is equivalent to | |
| a call <code>gettable_event(t,i)</code>. | |
| (See <a href="#2.4">§2.4</a> for a complete description of the | |
| <code>gettable_event</code> function. | |
| This function is not defined or callable in Lua. | |
| We use it here only for explanatory purposes.) | |
| <p> | |
| The syntax <code>var.Name</code> is just syntactic sugar for | |
| <code>var["Name"]</code>: | |
| <pre> | |
| var ::= prefixexp ‘<b>.</b>’ Name | |
| </pre> | |
| <p> | |
| An access to a global variable <code>x</code> | |
| is equivalent to <code>_ENV.x</code>. | |
| Due to the way that chunks are compiled, | |
| <code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>). | |
| <h2>3.3 – <a name="3.3">Statements</a></h2> | |
| <p> | |
| 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. | |
| <h3>3.3.1 – <a name="3.3.1">Blocks</a></h3> | |
| <p> | |
| A block is a list of statements, | |
| which are executed sequentially: | |
| <pre> | |
| block ::= {stat} | |
| </pre><p> | |
| Lua has <em>empty statements</em> | |
| that allow you to separate statements with semicolons, | |
| start a block with a semicolon | |
| or write two semicolons in sequence: | |
| <pre> | |
| stat ::= ‘<b>;</b>’ | |
| </pre> | |
| <p> | |
| Function calls and assignments | |
| can start with an open parenthesis. | |
| This possibility leads to an ambiguity in Lua's grammar. | |
| Consider the following fragment: | |
| <pre> | |
| a = b + c | |
| (print or io.write)('done') | |
| </pre><p> | |
| The grammar could see it in two ways: | |
| <pre> | |
| a = b + c(print or io.write)('done') | |
| a = b + c; (print or io.write)('done') | |
| </pre><p> | |
| 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: | |
| <pre> | |
| ;(print or io.write)('done') | |
| </pre> | |
| <p> | |
| A block can be explicitly delimited to produce a single statement: | |
| <pre> | |
| stat ::= <b>do</b> block <b>end</b> | |
| </pre><p> | |
| Explicit blocks are useful | |
| to control the scope of variable declarations. | |
| Explicit blocks are also sometimes used to | |
| add a <b>return</b> statement in the middle | |
| of another block (see <a href="#3.3.4">§3.3.4</a>). | |
| <h3>3.3.2 – <a name="3.3.2">Chunks</a></h3> | |
| <p> | |
| The unit of compilation of Lua is called a <em>chunk</em>. | |
| Syntactically, | |
| a chunk is simply a block: | |
| <pre> | |
| chunk ::= block | |
| </pre> | |
| <p> | |
| Lua handles a chunk as the body of an anonymous function | |
| with a variable number of arguments | |
| (see <a href="#3.4.10">§3.4.10</a>). | |
| 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 <code>_ENV</code> (see <a href="#2.2">§2.2</a>). | |
| The resulting function always has <code>_ENV</code> as its only upvalue, | |
| even if it does not use that variable. | |
| <p> | |
| A chunk can be stored in a file or in a string inside the host program. | |
| To execute a chunk, | |
| Lua first precompiles the chunk into instructions for a virtual machine, | |
| and then it executes the compiled code | |
| with an interpreter for the virtual machine. | |
| <p> | |
| Chunks can also be precompiled into binary form; | |
| see program <code>luac</code> for details. | |
| Programs in source and compiled forms are interchangeable; | |
| Lua automatically detects the file type and acts accordingly. | |
| <h3>3.3.3 – <a name="3.3.3">Assignment</a></h3> | |
| <p> | |
| 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: | |
| <pre> | |
| stat ::= varlist ‘<b>=</b>’ explist | |
| varlist ::= var {‘<b>,</b>’ var} | |
| explist ::= exp {‘<b>,</b>’ exp} | |
| </pre><p> | |
| Expressions are discussed in <a href="#3.4">§3.4</a>. | |
| <p> | |
| Before the assignment, | |
| the list of values is <em>adjusted</em> 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 <b>nil</b>'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 <a href="#3.4">§3.4</a>). | |
| <p> | |
| The assignment statement first evaluates all its expressions | |
| and only then are the assignments performed. | |
| Thus the code | |
| <pre> | |
| i = 3 | |
| i, a[i] = i+1, 20 | |
| </pre><p> | |
| sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> | |
| because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) | |
| before it is assigned 4. | |
| Similarly, the line | |
| <pre> | |
| x, y = y, x | |
| </pre><p> | |
| exchanges the values of <code>x</code> and <code>y</code>, | |
| and | |
| <pre> | |
| x, y, z = y, z, x | |
| </pre><p> | |
| cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. | |
| <p> | |
| The meaning of assignments to global variables | |
| and table fields can be changed via metatables. | |
| An assignment to an indexed variable <code>t[i] = val</code> is equivalent to | |
| <code>settable_event(t,i,val)</code>. | |
| (See <a href="#2.4">§2.4</a> for a complete description of the | |
| <code>settable_event</code> function. | |
| This function is not defined or callable in Lua. | |
| We use it here only for explanatory purposes.) | |
| <p> | |
| An assignment to a global variable <code>x = val</code> | |
| is equivalent to the assignment | |
| <code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>). | |
| <h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p> | |
| The control structures | |
| <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and | |
| familiar syntax: | |
| <pre> | |
| stat ::= <b>while</b> exp <b>do</b> block <b>end</b> | |
| stat ::= <b>repeat</b> block <b>until</b> exp | |
| stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | |
| </pre><p> | |
| Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>). | |
| <p> | |
| The condition expression of a | |
| control structure can return any value. | |
| Both <b>false</b> and <b>nil</b> are considered false. | |
| All values different from <b>nil</b> and <b>false</b> are considered true | |
| (in particular, the number 0 and the empty string are also true). | |
| <p> | |
| In the <b>repeat</b>–<b>until</b> loop, | |
| the inner block does not end at the <b>until</b> keyword, | |
| but only after the condition. | |
| So, the condition can refer to local variables | |
| declared inside the loop block. | |
| <p> | |
| The <b>goto</b> statement transfers the program control to a label. | |
| For syntactical reasons, | |
| labels in Lua are considered statements too: | |
| <pre> | |
| stat ::= <b>goto</b> Name | |
| stat ::= label | |
| label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ | |
| </pre> | |
| <p> | |
| 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. | |
| <p> | |
| Labels and empty statements are called <em>void statements</em>, | |
| as they perform no actions. | |
| <p> | |
| The <b>break</b> statement terminates the execution of a | |
| <b>while</b>, <b>repeat</b>, or <b>for</b> loop, | |
| skipping to the next statement after the loop: | |
| <pre> | |
| stat ::= <b>break</b> | |
| </pre><p> | |
| A <b>break</b> ends the innermost enclosing loop. | |
| <p> | |
| The <b>return</b> statement is used to return values | |
| from a function or a chunk (which is a function in disguise). | |
| Functions can return more than one value, | |
| so the syntax for the <b>return</b> statement is | |
| <pre> | |
| stat ::= <b>return</b> [explist] [‘<b>;</b>’] | |
| </pre> | |
| <p> | |
| The <b>return</b> statement can only be written | |
| as the last statement of a block. | |
| If it is really necessary to <b>return</b> in the middle of a block, | |
| then an explicit inner block can be used, | |
| as in the idiom <code>do return end</code>, | |
| because now <b>return</b> is the last statement in its (inner) block. | |
| <h3>3.3.5 – <a name="3.3.5">For Statement</a></h3> | |
| <p> | |
| The <b>for</b> statement has two forms: | |
| one numeric and one generic. | |
| <p> | |
| The numeric <b>for</b> loop repeats a block of code while a | |
| control variable runs through an arithmetic progression. | |
| It has the following syntax: | |
| <pre> | |
| stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> | |
| </pre><p> | |
| The <em>block</em> is repeated for <em>name</em> starting at the value of | |
| the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the | |
| third <em>exp</em>. | |
| More precisely, a <b>for</b> statement like | |
| <pre> | |
| for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end | |
| </pre><p> | |
| is equivalent to the code: | |
| <pre> | |
| do | |
| local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>) | |
| if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end | |
| while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do | |
| local v = <em>var</em> | |
| <em>block</em> | |
| <em>var</em> = <em>var</em> + <em>step</em> | |
| end | |
| end | |
| </pre><p> | |
| Note the following: | |
| <ul> | |
| <li> | |
| All three control expressions are evaluated only once, | |
| before the loop starts. | |
| They must all result in numbers. | |
| </li> | |
| <li> | |
| <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. | |
| The names shown here are for explanatory purposes only. | |
| </li> | |
| <li> | |
| If the third expression (the step) is absent, | |
| then a step of 1 is used. | |
| </li> | |
| <li> | |
| You can use <b>break</b> to exit a <b>for</b> loop. | |
| </li> | |
| <li> | |
| The loop variable <code>v</code> is local to the loop; | |
| you cannot use its value after the <b>for</b> ends or is broken. | |
| If you need this value, | |
| assign it to another variable before breaking or exiting the loop. | |
| </li> | |
| </ul> | |
| <p> | |
| The generic <b>for</b> statement works over functions, | |
| called <em>iterators</em>. | |
| On each iteration, the iterator function is called to produce a new value, | |
| stopping when this new value is <b>nil</b>. | |
| The generic <b>for</b> loop has the following syntax: | |
| <pre> | |
| stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | |
| namelist ::= Name {‘<b>,</b>’ Name} | |
| </pre><p> | |
| A <b>for</b> statement like | |
| <pre> | |
| for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end | |
| </pre><p> | |
| is equivalent to the code: | |
| <pre> | |
| do | |
| local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> | |
| while true do | |
| local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) | |
| if <em>var_1</em> == nil then break end | |
| <em>var</em> = <em>var_1</em> | |
| <em>block</em> | |
| end | |
| end | |
| </pre><p> | |
| Note the following: | |
| <ul> | |
| <li> | |
| <code><em>explist</em></code> is evaluated only once. | |
| Its results are an <em>iterator</em> function, | |
| a <em>state</em>, | |
| and an initial value for the first <em>iterator variable</em>. | |
| </li> | |
| <li> | |
| <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables. | |
| The names are here for explanatory purposes only. | |
| </li> | |
| <li> | |
| You can use <b>break</b> to exit a <b>for</b> loop. | |
| </li> | |
| <li> | |
| The loop variables <code><em>var_i</em></code> are local to the loop; | |
| you cannot use their values after the <b>for</b> ends. | |
| If you need these values, | |
| then assign them to other variables before breaking or exiting the loop. | |
| </li> | |
| </ul> | |
| <h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p> | |
| To allow possible side-effects, | |
| function calls can be executed as statements: | |
| <pre> | |
| stat ::= functioncall | |
| </pre><p> | |
| In this case, all returned values are thrown away. | |
| Function calls are explained in <a href="#3.4.9">§3.4.9</a>. | |
| <h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p> | |
| Local variables can be declared anywhere inside a block. | |
| The declaration can include an initial assignment: | |
| <pre> | |
| stat ::= <b>local</b> namelist [‘<b>=</b>’ explist] | |
| </pre><p> | |
| If present, an initial assignment has the same semantics | |
| of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>). | |
| Otherwise, all variables are initialized with <b>nil</b>. | |
| <p> | |
| A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>), | |
| and so local variables can be declared in a chunk outside any explicit block. | |
| <p> | |
| The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>. | |
| <h2>3.4 – <a name="3.4">Expressions</a></h2> | |
| <p> | |
| The basic expressions in Lua are the following: | |
| <pre> | |
| exp ::= prefixexp | |
| exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | |
| exp ::= Number | |
| exp ::= String | |
| exp ::= functiondef | |
| exp ::= tableconstructor | |
| exp ::= ‘<b>...</b>’ | |
| exp ::= exp binop exp | |
| exp ::= unop exp | |
| prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ | |
| </pre> | |
| <p> | |
| Numbers and literal strings are explained in <a href="#3.1">§3.1</a>; | |
| variables are explained in <a href="#3.2">§3.2</a>; | |
| function definitions are explained in <a href="#3.4.10">§3.4.10</a>; | |
| function calls are explained in <a href="#3.4.9">§3.4.9</a>; | |
| table constructors are explained in <a href="#3.4.8">§3.4.8</a>. | |
| Vararg expressions, | |
| denoted by three dots ('<code>...</code>'), can only be used when | |
| directly inside a vararg function; | |
| they are explained in <a href="#3.4.10">§3.4.10</a>. | |
| <p> | |
| Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>), | |
| relational operators (see <a href="#3.4.3">§3.4.3</a>), logical operators (see <a href="#3.4.4">§3.4.4</a>), | |
| and the concatenation operator (see <a href="#3.4.5">§3.4.5</a>). | |
| Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>), | |
| the unary <b>not</b> (see <a href="#3.4.4">§3.4.4</a>), | |
| and the unary <em>length operator</em> (see <a href="#3.4.6">§3.4.6</a>). | |
| <p> | |
| Both function calls and vararg expressions can result in multiple values. | |
| If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>), | |
| 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 <b>nil</b> if there are no values. | |
| <p> | |
| Here are some examples: | |
| <pre> | |
| 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 | |
| </pre> | |
| <p> | |
| Any expression enclosed in parentheses always results in only one value. | |
| Thus, | |
| <code>(f(x,y,z))</code> is always a single value, | |
| even if <code>f</code> returns several values. | |
| (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> | |
| or <b>nil</b> if <code>f</code> does not return any values.) | |
| <h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p> | |
| Lua supports the usual arithmetic operators: | |
| the binary <code>+</code> (addition), | |
| <code>-</code> (subtraction), <code>*</code> (multiplication), | |
| <code>/</code> (division), <code>%</code> (modulo), and <code>^</code> (exponentiation); | |
| and unary <code>-</code> (mathematical negation). | |
| If the operands are numbers, or strings that can be converted to | |
| numbers (see <a href="#3.4.2">§3.4.2</a>), | |
| then all operations have the usual meaning. | |
| Exponentiation works for any exponent. | |
| For instance, <code>x^(-0.5)</code> computes the inverse of the square root of <code>x</code>. | |
| Modulo is defined as | |
| <pre> | |
| a % b == a - math.floor(a/b)*b | |
| </pre><p> | |
| That is, it is the remainder of a division that rounds | |
| the quotient towards minus infinity. | |
| <h3>3.4.2 – <a name="3.4.2">Coercion</a></h3> | |
| <p> | |
| Lua provides automatic conversion between | |
| string and number values at run time. | |
| Any arithmetic operation applied to a string tries to convert | |
| this string to a number, following the rules of the Lua lexer. | |
| (The string may have leading and trailing spaces and a sign.) | |
| Conversely, whenever a number is used where a string is expected, | |
| the number is converted to a string, in a reasonable format. | |
| For complete control over how numbers are converted to strings, | |
| use the <code>format</code> function from the string library | |
| (see <a href="#pdf-string.format"><code>string.format</code></a>). | |
| <h3>3.4.3 – <a name="3.4.3">Relational Operators</a></h3><p> | |
| The relational operators in Lua are | |
| <pre> | |
| == ~= < > <= >= | |
| </pre><p> | |
| These operators always result in <b>false</b> or <b>true</b>. | |
| <p> | |
| Equality (<code>==</code>) first compares the type of its operands. | |
| If the types are different, then the result is <b>false</b>. | |
| Otherwise, the values of the operands are compared. | |
| Numbers and strings are compared in the usual way. | |
| 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. | |
| <p> | |
| You can change the way that Lua compares tables and userdata | |
| by using the "eq" metamethod (see <a href="#2.4">§2.4</a>). | |
| <p> | |
| The conversion rules of <a href="#3.4.2">§3.4.2</a> | |
| do not apply to equality comparisons. | |
| Thus, <code>"0"==0</code> evaluates to <b>false</b>, | |
| and <code>t[0]</code> and <code>t["0"]</code> denote different | |
| entries in a table. | |
| <p> | |
| The operator <code>~=</code> is exactly the negation of equality (<code>==</code>). | |
| <p> | |
| The order operators work as follows. | |
| If both arguments are numbers, then they are compared as such. | |
| Otherwise, if both arguments are strings, | |
| then their values are compared according to the current locale. | |
| Otherwise, Lua tries to call the "lt" or the "le" | |
| metamethod (see <a href="#2.4">§2.4</a>). | |
| A comparison <code>a > b</code> is translated to <code>b < a</code> | |
| and <code>a >= b</code> is translated to <code>b <= a</code>. | |
| <h3>3.4.4 – <a name="3.4.4">Logical Operators</a></h3><p> | |
| The logical operators in Lua are | |
| <b>and</b>, <b>or</b>, and <b>not</b>. | |
| Like the control structures (see <a href="#3.3.4">§3.3.4</a>), | |
| all logical operators consider both <b>false</b> and <b>nil</b> as false | |
| and anything else as true. | |
| <p> | |
| The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>. | |
| The conjunction operator <b>and</b> returns its first argument | |
| if this value is <b>false</b> or <b>nil</b>; | |
| otherwise, <b>and</b> returns its second argument. | |
| The disjunction operator <b>or</b> returns its first argument | |
| if this value is different from <b>nil</b> and <b>false</b>; | |
| otherwise, <b>or</b> returns its second argument. | |
| Both <b>and</b> and <b>or</b> use short-cut evaluation; | |
| that is, | |
| the second operand is evaluated only if necessary. | |
| Here are some examples: | |
| <pre> | |
| 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 | |
| </pre><p> | |
| (In this manual, | |
| <code>--></code> indicates the result of the preceding expression.) | |
| <h3>3.4.5 – <a name="3.4.5">Concatenation</a></h3><p> | |
| The string concatenation operator in Lua is | |
| denoted by two dots ('<code>..</code>'). | |
| If both operands are strings or numbers, then they are converted to | |
| strings according to the rules mentioned in <a href="#3.4.2">§3.4.2</a>. | |
| Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>). | |
| <h3>3.4.6 – <a name="3.4.6">The Length Operator</a></h3> | |
| <p> | |
| The length operator is denoted by the unary prefix operator <code>#</code>. | |
| The length of a string is its number of bytes | |
| (that is, the usual meaning of string length when each | |
| character is one byte). | |
| <p> | |
| A program can modify the behavior of the length operator for | |
| any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>). | |
| <p> | |
| Unless a <code>__len</code> metamethod is given, | |
| the length of a table <code>t</code> is only defined if the | |
| table is a <em>sequence</em>, | |
| that is, | |
| the set of its positive numeric keys is equal to <em>{1..n}</em> | |
| for some integer <em>n</em>. | |
| In that case, <em>n</em> is its length. | |
| Note that a table like | |
| <pre> | |
| {10, 20, nil, 40} | |
| </pre><p> | |
| is not a sequence, because it has the key <code>4</code> | |
| but does not have the key <code>3</code>. | |
| (So, there is no <em>n</em> such that the set <em>{1..n}</em> 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. | |
| <h3>3.4.7 – <a name="3.4.7">Precedence</a></h3><p> | |
| Operator precedence in Lua follows the table below, | |
| from lower to higher priority: | |
| <pre> | |
| or | |
| and | |
| < > <= >= ~= == | |
| .. | |
| + - | |
| * / % | |
| not # - (unary) | |
| ^ | |
| </pre><p> | |
| As usual, | |
| you can use parentheses to change the precedences of an expression. | |
| The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>') | |
| operators are right associative. | |
| All other binary operators are left associative. | |
| <h3>3.4.8 – <a name="3.4.8">Table Constructors</a></h3><p> | |
| 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 | |
| <pre> | |
| tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ | |
| fieldlist ::= field {fieldsep field} [fieldsep] | |
| field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp | |
| fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ | |
| </pre> | |
| <p> | |
| Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry | |
| with key <code>exp1</code> and value <code>exp2</code>. | |
| A field of the form <code>name = exp</code> is equivalent to | |
| <code>["name"] = exp</code>. | |
| Finally, fields of the form <code>exp</code> are equivalent to | |
| <code>[i] = exp</code>, where <code>i</code> are consecutive numerical integers, | |
| starting with 1. | |
| Fields in the other formats do not affect this counting. | |
| For example, | |
| <pre> | |
| a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 } | |
| </pre><p> | |
| is equivalent to | |
| <pre> | |
| 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 | |
| </pre> | |
| <p> | |
| If the last field in the list has the form <code>exp</code> | |
| and the expression is a function call or a vararg expression, | |
| then all values returned by this expression enter the list consecutively | |
| (see <a href="#3.4.9">§3.4.9</a>). | |
| <p> | |
| The field list can have an optional trailing separator, | |
| as a convenience for machine-generated code. | |
| <h3>3.4.9 – <a name="3.4.9">Function Calls</a></h3><p> | |
| A function call in Lua has the following syntax: | |
| <pre> | |
| functioncall ::= prefixexp args | |
| </pre><p> | |
| In a function call, | |
| first prefixexp and args are evaluated. | |
| If the value of prefixexp has type <em>function</em>, | |
| 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 <a href="#2.4">§2.4</a>). | |
| <p> | |
| The form | |
| <pre> | |
| functioncall ::= prefixexp ‘<b>:</b>’ Name args | |
| </pre><p> | |
| can be used to call "methods". | |
| A call <code>v:name(<em>args</em>)</code> | |
| is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, | |
| except that <code>v</code> is evaluated only once. | |
| <p> | |
| Arguments have the following syntax: | |
| <pre> | |
| args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | |
| args ::= tableconstructor | |
| args ::= String | |
| </pre><p> | |
| All argument expressions are evaluated before the call. | |
| A call of the form <code>f{<em>fields</em>}</code> is | |
| syntactic sugar for <code>f({<em>fields</em>})</code>; | |
| that is, the argument list is a single new table. | |
| A call of the form <code>f'<em>string</em>'</code> | |
| (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>) | |
| is syntactic sugar for <code>f('<em>string</em>')</code>; | |
| that is, the argument list is a single literal string. | |
| <p> | |
| A call of the form <code>return <em>functioncall</em></code> is called | |
| a <em>tail call</em>. | |
| Lua implements <em>proper tail calls</em> | |
| (or <em>proper tail recursion</em>): | |
| 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 <b>return</b> 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: | |
| <pre> | |
| 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 | |
| </pre> | |
| <h3>3.4.10 – <a name="3.4.10">Function Definitions</a></h3> | |
| <p> | |
| The syntax for function definition is | |
| <pre> | |
| functiondef ::= <b>function</b> funcbody | |
| funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> | |
| </pre> | |
| <p> | |
| The following syntactic sugar simplifies function definitions: | |
| <pre> | |
| stat ::= <b>function</b> funcname funcbody | |
| stat ::= <b>local</b> <b>function</b> Name funcbody | |
| funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] | |
| </pre><p> | |
| The statement | |
| <pre> | |
| function f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| f = function () <em>body</em> end | |
| </pre><p> | |
| The statement | |
| <pre> | |
| function t.a.b.c.f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| t.a.b.c.f = function () <em>body</em> end | |
| </pre><p> | |
| The statement | |
| <pre> | |
| local function f () <em>body</em> end | |
| </pre><p> | |
| translates to | |
| <pre> | |
| local f; f = function () <em>body</em> end | |
| </pre><p> | |
| not to | |
| <pre> | |
| local f = function () <em>body</em> end | |
| </pre><p> | |
| (This only makes a difference when the body of the function | |
| contains references to <code>f</code>.) | |
| <p> | |
| A function definition is an executable expression, | |
| whose value has type <em>function</em>. | |
| When Lua precompiles a chunk, | |
| all its function bodies are precompiled too. | |
| Then, whenever Lua executes the function definition, | |
| the function is <em>instantiated</em> (or <em>closed</em>). | |
| This function instance (or <em>closure</em>) | |
| is the final value of the expression. | |
| <p> | |
| Parameters act as local variables that are | |
| initialized with the argument values: | |
| <pre> | |
| parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ | |
| </pre><p> | |
| When a function is called, | |
| the list of arguments is adjusted to | |
| the length of the list of parameters, | |
| unless the function is a <em>vararg function</em>, | |
| which is indicated by three dots ('<code>...</code>') | |
| 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 <em>vararg expression</em>, | |
| 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). | |
| <p> | |
| As an example, consider the following definitions: | |
| <pre> | |
| function f(a, b) end | |
| function g(a, b, ...) end | |
| function r() return 1,2,3 end | |
| </pre><p> | |
| Then, we have the following mapping from arguments to parameters and | |
| to the vararg expression: | |
| <pre> | |
| 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 | |
| </pre> | |
| <p> | |
| Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>). | |
| If control reaches the end of a function | |
| without encountering a <b>return</b> statement, | |
| then the function returns with no results. | |
| <p> | |
| 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. | |
| <p> | |
| The <em>colon</em> syntax | |
| is used for defining <em>methods</em>, | |
| that is, functions that have an implicit extra parameter <code>self</code>. | |
| Thus, the statement | |
| <pre> | |
| function t.a.b.c:f (<em>params</em>) <em>body</em> end | |
| </pre><p> | |
| is syntactic sugar for | |
| <pre> | |
| t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end | |
| </pre> | |
| <h2>3.5 – <a name="3.5">Visibility Rules</a></h2> | |
| <p> | |
| 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: | |
| <pre> | |
| 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) | |
| </pre> | |
| <p> | |
| Notice that, in a declaration like <code>local x = x</code>, | |
| the new <code>x</code> being declared is not in scope yet, | |
| and so the second <code>x</code> refers to the outside variable. | |
| <p> | |
| 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 <em>upvalue</em>, or <em>external local variable</em>, | |
| inside the inner function. | |
| <p> | |
| Notice that each execution of a <b>local</b> statement | |
| defines new local variables. | |
| Consider the following example: | |
| <pre> | |
| a = {} | |
| local x = 20 | |
| for i=1,10 do | |
| local y = 0 | |
| a[i] = function () y=y+1; return x+y end | |
| end | |
| </pre><p> | |
| The loop creates ten closures | |
| (that is, ten instances of the anonymous function). | |
| Each of these closures uses a different <code>y</code> variable, | |
| while all of them share the same <code>x</code>. | |
| <h1>4 – <a name="4">The Application Program Interface</a></h1> | |
| <p> | |
| 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 <a name="pdf-lua.h"><code>lua.h</code></a>. | |
| <p> | |
| 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. | |
| <p> | |
| 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 <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined. | |
| <h2>4.1 – <a name="4.1">The Stack</a></h2> | |
| <p> | |
| Lua uses a <em>virtual stack</em> to pass values to and from C. | |
| Each element in this stack represents a Lua value | |
| (<b>nil</b>, number, string, etc.). | |
| <p> | |
| 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 <a href="#lua_CFunction"><code>lua_CFunction</code></a>). | |
| <p> | |
| 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 <em>index</em>: | |
| 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 <em>n</em> elements, | |
| then index 1 represents the first element | |
| (that is, the element that was pushed onto the stack first) | |
| and | |
| index <em>n</em> represents the last element; | |
| index -1 also represents the last element | |
| (that is, the element at the top) | |
| and index <em>-n</em> represents the first element. | |
| <h2>4.2 – <a name="4.2">Stack Size</a></h2> | |
| <p> | |
| When you interact with the Lua API, | |
| you are responsible for ensuring consistency. | |
| In particular, | |
| <em>you are responsible for controlling stack overflow</em>. | |
| You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a> | |
| to ensure that the stack has extra slots when pushing new elements. | |
| <p> | |
| Whenever Lua calls C, | |
| it ensures that the stack has at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots. | |
| <code>LUA_MINSTACK</code> 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. | |
| <p> | |
| When you call a Lua function | |
| without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>), | |
| Lua ensures that the stack has enough size 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 <a href="#lua_checkstack"><code>lua_checkstack</code></a>. | |
| <h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2> | |
| <p> | |
| Any function in the API that receives stack indices | |
| works only with <em>valid indices</em> or <em>acceptable indices</em>. | |
| <p> | |
| A <em>valid index</em> is an index that refers to a | |
| real position within the stack, that is, | |
| its position lies between 1 and the stack top | |
| (<code>1 ≤ abs(index) ≤ top</code>). | |
| Usually, functions that can modify the value at an index | |
| require valid indices. | |
| <p> | |
| Unless otherwise noted, | |
| any function that accepts valid indices also accepts <em>pseudo-indices</em>, | |
| 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 <a href="#4.4">§4.4</a>). | |
| <p> | |
| 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 <em>acceptable index</em> 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. | |
| <p> | |
| 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. | |
| <p> | |
| 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 <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>, | |
| which behaves like a nil value. | |
| <h2>4.4 – <a name="4.4">C Closures</a></h2> | |
| <p> | |
| When a C function is created, | |
| it is possible to associate some values with it, | |
| thus creating a <em>C closure</em> | |
| (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>); | |
| these values are called <em>upvalues</em> and are | |
| accessible to the function whenever it is called. | |
| <p> | |
| Whenever a C function is called, | |
| its upvalues are located at specific pseudo-indices. | |
| These pseudo-indices are produced by the macro | |
| <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>. | |
| The first value associated with a function is at position | |
| <code>lua_upvalueindex(1)</code>, and so on. | |
| Any access to <code>lua_upvalueindex(<em>n</em>)</code>, | |
| where <em>n</em> is greater than the number of upvalues of the | |
| current function (but not greater than 256), | |
| produces an acceptable but invalid index. | |
| <h2>4.5 – <a name="4.5">Registry</a></h2> | |
| <p> | |
| Lua provides a <em>registry</em>, | |
| 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 | |
| <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>, | |
| which is a valid index. | |
| Any C library can store data into this table, | |
| but it should 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 global names, | |
| string keys starting with an underscore followed by | |
| uppercase letters are reserved for Lua. | |
| <p> | |
| The integer keys in the registry are used by the reference mechanism, | |
| implemented by the auxiliary library, | |
| and by some predefined values. | |
| Therefore, integer keys should not be used for other purposes. | |
| <p> | |
| 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 <code>lua.h</code>. | |
| The following constants are defined: | |
| <ul> | |
| <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has | |
| the main thread of the state. | |
| (The main thread is the one created together with the state.) | |
| </li> | |
| <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has | |
| the global environment. | |
| </li> | |
| </ul> | |
| <h2>4.6 – <a name="4.6">Error Handling in C</a></h2> | |
| <p> | |
| Internally, Lua uses the C <code>longjmp</code> facility to handle errors. | |
| (You can also choose to use exceptions if you compile Lua as C++; | |
| search for <code>LUAI_THROW</code> in the source code.) | |
| When Lua faces any error | |
| (such as a memory allocation error, type errors, syntax errors, | |
| and runtime errors) | |
| it <em>raises</em> an error; | |
| that is, it does a long jump. | |
| A <em>protected environment</em> uses <code>setjmp</code> | |
| to set a recovery point; | |
| any error jumps to the most recent active recovery point. | |
| <p> | |
| If an error happens outside any protected environment, | |
| Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) | |
| and then calls <code>abort</code>, | |
| 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). | |
| <p> | |
| The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>); | |
| in particular, the error message is at the top of the stack. | |
| However, there is no guarantees about stack space. | |
| To push anything on the stack, | |
| the panic function should first check the available space (see <a href="#4.2">§4.2</a>). | |
| <p> | |
| Most functions in the API can throw an error, | |
| for instance due to a memory allocation error. | |
| The documentation for each function indicates whether | |
| it can throw errors. | |
| <p> | |
| Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>. | |
| <h2>4.7 – <a name="4.7">Handling Yields in C</a></h2> | |
| <p> | |
| Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine. | |
| Therefore, if a function <code>foo</code> calls an API function | |
| and this API function yields | |
| (directly or indirectly by calling another function that yields), | |
| Lua cannot return to <code>foo</code> any more, | |
| because the <code>longjmp</code> removes its frame from the C stack. | |
| <p> | |
| To avoid this kind of problem, | |
| Lua raises an error whenever it tries to yield across an API call, | |
| except for three functions: | |
| <a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>. | |
| All those functions receive a <em>continuation function</em> | |
| (as a parameter called <code>k</code>) to continue execution after a yield. | |
| <p> | |
| We need to set some terminology to explain continuations. | |
| We have a C function called from Lua which we will call | |
| the <em>original function</em>. | |
| This original function then calls one of those three functions in the C API, | |
| which we will call the <em>callee function</em>, | |
| that then yields the current thread. | |
| (This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>, | |
| or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a> | |
| and the function called by them yields.) | |
| <p> | |
| 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 <em>continuation function</em>, | |
| 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. | |
| <p> | |
| 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 <a href="#lua_callk"><code>lua_callk</code></a> 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. | |
| <p> | |
| The only difference in the Lua state between the original function | |
| and its continuation is the result of a call to <a href="#lua_getctx"><code>lua_getctx</code></a>. | |
| <h2>4.8 – <a name="4.8">Functions and Types</a></h2> | |
| <p> | |
| Here we list all functions and types from the C API in | |
| alphabetical order. | |
| Each function has an indicator like this: | |
| <span class="apii">[-o, +p, <em>x</em>]</span> | |
| <p> | |
| The first field, <code>o</code>, | |
| is how many elements the function pops from the stack. | |
| The second field, <code>p</code>, | |
| 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 <code>x|y</code> means the function can push (or pop) | |
| <code>x</code> or <code>y</code> elements, | |
| depending on the situation; | |
| an interrogation mark '<code>?</code>' 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, <code>x</code>, | |
| tells whether the function may throw errors: | |
| '<code>-</code>' means the function never throws any error; | |
| '<code>e</code>' means the function may throw errors; | |
| '<code>v</code>' means the function may throw an error on purpose. | |
| <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_absindex (lua_State *L, int idx);</pre> | |
| <p> | |
| Converts the acceptable index <code>idx</code> into an absolute index | |
| (that is, one that does not depend on the stack top). | |
| <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3> | |
| <pre>typedef void * (*lua_Alloc) (void *ud, | |
| void *ptr, | |
| size_t osize, | |
| size_t nsize);</pre> | |
| <p> | |
| The type of the memory-allocation function used by Lua states. | |
| The allocator function must provide a | |
| functionality similar to <code>realloc</code>, | |
| but not exactly the same. | |
| Its arguments are | |
| <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>; | |
| <code>ptr</code>, a pointer to the block being allocated/reallocated/freed; | |
| <code>osize</code>, the original size of the block or some code about what | |
| is being allocated; | |
| <code>nsize</code>, the new size of the block. | |
| <p> | |
| When <code>ptr</code> is not <code>NULL</code>, | |
| <code>osize</code> is the size of the block pointed by <code>ptr</code>, | |
| that is, the size given when it was allocated or reallocated. | |
| <p> | |
| When <code>ptr</code> is <code>NULL</code>, | |
| <code>osize</code> encodes the kind of object that Lua is allocating. | |
| <code>osize</code> is any of | |
| <a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, | |
| <a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when) | |
| Lua is creating a new object of that type. | |
| When <code>osize</code> is some other value, | |
| Lua is allocating memory for something else. | |
| <p> | |
| Lua assumes the following behavior from the allocator function: | |
| <p> | |
| When <code>nsize</code> is zero, | |
| the allocator should behave like <code>free</code> | |
| and return <code>NULL</code>. | |
| <p> | |
| When <code>nsize</code> is not zero, | |
| the allocator should behave like <code>realloc</code>. | |
| The allocator returns <code>NULL</code> | |
| if and only if it cannot fulfill the request. | |
| Lua assumes that the allocator never fails when | |
| <code>osize >= nsize</code>. | |
| <p> | |
| Here is a simple implementation for the allocator function. | |
| It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>. | |
| <pre> | |
| 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); | |
| } | |
| </pre><p> | |
| Note that Standard C ensures | |
| that <code>free(NULL)</code> has no effect and that | |
| <code>realloc(NULL, size)</code> is equivalent to <code>malloc(size)</code>. | |
| This code assumes that <code>realloc</code> does not fail when shrinking a block. | |
| (Although Standard C does not ensure this behavior, | |
| it seems to be a safe assumption.) | |
| <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p> | |
| <span class="apii">[-(2|1), +1, <em>e</em>]</span> | |
| <pre>void lua_arith (lua_State *L, int op);</pre> | |
| <p> | |
| Performs an arithmetic operation over the two values | |
| (or one, in the case of negation) | |
| 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). | |
| <p> | |
| The value of <code>op</code> must be one of the following constants: | |
| <ul> | |
| <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li> | |
| <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li> | |
| <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li> | |
| <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs division (<code>/</code>)</li> | |
| <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li> | |
| <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li> | |
| <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li> | |
| </ul> | |
| <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> | |
| <p> | |
| Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>). | |
| <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> | |
| <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span> | |
| <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> | |
| <p> | |
| Calls a function. | |
| <p> | |
| 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 <a href="#lua_call"><code>lua_call</code></a>; | |
| <code>nargs</code> 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 <code>nresults</code>, | |
| unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. | |
| 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. | |
| <p> | |
| Any error inside the called function is propagated upwards | |
| (with a <code>longjmp</code>). | |
| <p> | |
| The following example shows how the host program can do the | |
| equivalent to this Lua code: | |
| <pre> | |
| a = f("how", t.x, 14) | |
| </pre><p> | |
| Here it is in C: | |
| <pre> | |
| lua_getglobal(L, "f"); /* function to be called */ | |
| lua_pushstring(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' */ | |
| </pre><p> | |
| Note that the code above is "balanced": | |
| at its end, the stack is back to its original configuration. | |
| This is considered good programming practice. | |
| <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p> | |
| <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> | |
| <pre>void lua_callk (lua_State *L, int nargs, int nresults, int ctx, | |
| lua_CFunction k);</pre> | |
| <p> | |
| This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>, | |
| but allows the called function to yield (see <a href="#4.7">§4.7</a>). | |
| <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3> | |
| <pre>typedef int (*lua_CFunction) (lua_State *L);</pre> | |
| <p> | |
| Type for C functions. | |
| <p> | |
| 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, | |
| <code>lua_gettop(L)</code> 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 <code>lua_gettop(L)</code>. | |
| 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. | |
| <p> | |
| As an example, the following function receives a variable number | |
| of numerical arguments and returns their average and sum: | |
| <pre> | |
| static int foo (lua_State *L) { | |
| int n = lua_gettop(L); /* number of arguments */ | |
| lua_Number sum = 0; | |
| int i; | |
| for (i = 1; i <= n; i++) { | |
| if (!lua_isnumber(L, i)) { | |
| lua_pushstring(L, "incorrect argument"); | |
| lua_error(L); | |
| } | |
| sum += lua_tonumber(L, i); | |
| } | |
| lua_pushnumber(L, sum/n); /* first result */ | |
| lua_pushnumber(L, sum); /* second result */ | |
| return 2; /* number of results */ | |
| } | |
| </pre> | |
| <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_checkstack (lua_State *L, int extra);</pre> | |
| <p> | |
| Ensures that there are at least <code>extra</code> free stack slots in the stack. | |
| It returns false if it cannot fulfill the request, | |
| because it would cause the stack to be larger than a fixed maximum size | |
| (typically at least a few thousand elements) or | |
| because it cannot allocate memory for the new stack size. | |
| This function never shrinks the stack; | |
| if the stack is already larger than the new size, | |
| it is left unchanged. | |
| <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void lua_close (lua_State *L);</pre> | |
| <p> | |
| 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, | |
| might need to close states as soon as they are not needed. | |
| <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre> | |
| <p> | |
| Compares two Lua values. | |
| Returns 1 if the value at index <code>index1</code> satisfies <code>op</code> | |
| when compared with the value at index <code>index2</code>, | |
| 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 non valid. | |
| <p> | |
| The value of <code>op</code> must be one of the following constants: | |
| <ul> | |
| <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li> | |
| <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li> | |
| <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li> | |
| </ul> | |
| <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> | |
| <span class="apii">[-n, +1, <em>e</em>]</span> | |
| <pre>void lua_concat (lua_State *L, int n);</pre> | |
| <p> | |
| Concatenates the <code>n</code> values at the top of the stack, | |
| pops them, and leaves the result at the top. | |
| If <code>n</code> is 1, the result is the single value on the stack | |
| (that is, the function does nothing); | |
| if <code>n</code> is 0, the result is the empty string. | |
| Concatenation is performed following the usual semantics of Lua | |
| (see <a href="#3.4.5">§3.4.5</a>). | |
| <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre> | |
| <p> | |
| Moves the element at index <code>fromidx</code> | |
| into the valid index <code>toidx</code> | |
| without shifting any element | |
| (therefore replacing the value at that position). | |
| <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> | |
| <p> | |
| Creates a new empty table and pushes it onto the stack. | |
| Parameter <code>narr</code> is a hint for how many elements the table | |
| will have as a sequence; | |
| parameter <code>nrec</code> 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 <a href="#lua_newtable"><code>lua_newtable</code></a>. | |
| <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_dump (lua_State *L, lua_Writer writer, void *data);</pre> | |
| <p> | |
| 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, | |
| <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>) | |
| with the given <code>data</code> | |
| to write them. | |
| <p> | |
| The value returned is the error code returned by the last | |
| call to the writer; | |
| 0 means no errors. | |
| <p> | |
| This function does not pop the Lua function from the stack. | |
| <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>v</em>]</span> | |
| <pre>int lua_error (lua_State *L);</pre> | |
| <p> | |
| Generates a Lua error. | |
| The error message (which can actually be a Lua value of any type) | |
| must be on the stack top. | |
| This function does a long jump, | |
| and therefore never returns | |
| (see <a href="#luaL_error"><code>luaL_error</code></a>). | |
| <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int lua_gc (lua_State *L, int what, int data);</pre> | |
| <p> | |
| Controls the garbage collector. | |
| <p> | |
| This function performs several tasks, | |
| according to the value of the parameter <code>what</code>: | |
| <ul> | |
| <li><b><code>LUA_GCSTOP</code>: </b> | |
| stops the garbage collector. | |
| </li> | |
| <li><b><code>LUA_GCRESTART</code>: </b> | |
| restarts the garbage collector. | |
| </li> | |
| <li><b><code>LUA_GCCOLLECT</code>: </b> | |
| performs a full garbage-collection cycle. | |
| </li> | |
| <li><b><code>LUA_GCCOUNT</code>: </b> | |
| returns the current amount of memory (in Kbytes) in use by Lua. | |
| </li> | |
| <li><b><code>LUA_GCCOUNTB</code>: </b> | |
| returns the remainder of dividing the current amount of bytes of | |
| memory in use by Lua by 1024. | |
| </li> | |
| <li><b><code>LUA_GCSTEP</code>: </b> | |
| performs an incremental step of garbage collection. | |
| The step "size" is controlled by <code>data</code> | |
| (larger values mean more steps) in a non-specified way. | |
| If you want to control the step size | |
| you must experimentally tune the value of <code>data</code>. | |
| The function returns 1 if the step finished a | |
| garbage-collection cycle. | |
| </li> | |
| <li><b><code>LUA_GCSETPAUSE</code>: </b> | |
| sets <code>data</code> as the new value | |
| for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>). | |
| The function returns the previous value of the pause. | |
| </li> | |
| <li><b><code>LUA_GCSETSTEPMUL</code>: </b> | |
| sets <code>data</code> as the new value for the <em>step multiplier</em> of | |
| the collector (see <a href="#2.5">§2.5</a>). | |
| The function returns the previous value of the step multiplier. | |
| </li> | |
| <li><b><code>LUA_GCISRUNNING</code>: </b> | |
| returns a boolean that tells whether the collector is running | |
| (i.e., not stopped). | |
| </li> | |
| <li><b><code>LUA_GCGEN</code>: </b> | |
| changes the collector to generational mode | |
| (see <a href="#2.5">§2.5</a>). | |
| </li> | |
| <li><b><code>LUA_GCINC</code>: </b> | |
| changes the collector to incremental mode. | |
| This is the default mode. | |
| </li> | |
| </ul> | |
| <p> | |
| For more details about these options, | |
| see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>. | |
| <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> | |
| <p> | |
| Returns the memory-allocation function of a given state. | |
| If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the | |
| opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>. | |
| <hr><h3><a name="lua_getctx"><code>lua_getctx</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_getctx (lua_State *L, int *ctx);</pre> | |
| <p> | |
| This function is called by a continuation function (see <a href="#4.7">§4.7</a>) | |
| to retrieve the status of the thread and a context information. | |
| <p> | |
| When called in the original function, | |
| <a href="#lua_getctx"><code>lua_getctx</code></a> always returns <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> | |
| and does not change the value of its argument <code>ctx</code>. | |
| When called inside a continuation function, | |
| <a href="#lua_getctx"><code>lua_getctx</code></a> returns <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> and sets | |
| the value of <code>ctx</code> to be the context information | |
| (the value passed as the <code>ctx</code> argument | |
| to the callee together with the continuation function). | |
| <p> | |
| When the callee is <a href="#lua_pcallk"><code>lua_pcallk</code></a>, | |
| Lua may also call its continuation function | |
| to handle errors during the call. | |
| That is, upon an error in the function called by <a href="#lua_pcallk"><code>lua_pcallk</code></a>, | |
| Lua may not return to the original function | |
| but instead may call the continuation function. | |
| In that case, a call to <a href="#lua_getctx"><code>lua_getctx</code></a> will return the error code | |
| (the value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>); | |
| the value of <code>ctx</code> will be set to the context information, | |
| as in the case of a yield. | |
| <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_getfield (lua_State *L, int index, const char *k);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[k]</code>, | |
| where <code>t</code> is the value at the given index. | |
| As in Lua, this function may trigger a metamethod | |
| for the "index" event (see <a href="#2.4">§2.4</a>). | |
| <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_getglobal (lua_State *L, const char *name);</pre> | |
| <p> | |
| Pushes onto the stack the value of the global <code>name</code>. | |
| <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), –]</span> | |
| <pre>int lua_getmetatable (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the metatable of the value at the given index. | |
| If the value does not have a metatable, | |
| the function returns 0 and pushes nothing on the stack. | |
| <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> | |
| <span class="apii">[-1, +1, <em>e</em>]</span> | |
| <pre>void lua_gettable (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[k]</code>, | |
| where <code>t</code> is the value at the given index | |
| and <code>k</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the key from the stack | |
| (putting the resulting value in its place). | |
| As in Lua, this function may trigger a metamethod | |
| for the "index" event (see <a href="#2.4">§2.4</a>). | |
| <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_gettop (lua_State *L);</pre> | |
| <p> | |
| Returns the index of the top element in the stack. | |
| Because indices start at 1, | |
| this result is equal to the number of elements in the stack | |
| (and so 0 means an empty stack). | |
| <hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_getuservalue (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes onto the stack the Lua value associated with the userdata | |
| at the given index. | |
| This Lua value must be a table or <b>nil</b>. | |
| <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> | |
| <span class="apii">[-1, +1, –]</span> | |
| <pre>void lua_insert (lua_State *L, int index);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3> | |
| <pre>typedef ptrdiff_t lua_Integer;</pre> | |
| <p> | |
| The type used by the Lua API to represent signed integral values. | |
| <p> | |
| By default it is a <code>ptrdiff_t</code>, | |
| which is usually the largest signed integral type the machine handles | |
| "comfortably". | |
| <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isboolean (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a boolean, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_iscfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a C function, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a function | |
| (either C or Lua), and 0 otherwise. | |
| <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_islightuserdata (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a light userdata, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isnil (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is <b>nil</b>, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isnone (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the given index is not valid, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isnoneornil (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the given index is not valid | |
| or if the value at this index is <b>nil</b>, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isnumber (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a number | |
| or a string convertible to a number, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isstring (lua_State *L, int index);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_istable (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a table, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isthread (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a thread, | |
| and 0 otherwise. | |
| <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_isuserdata (lua_State *L, int index);</pre> | |
| <p> | |
| Returns 1 if the value at the given index is a userdata | |
| (either full or light), and 0 otherwise. | |
| <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_len (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the "length" of the value at the given index; | |
| it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>). | |
| The result is pushed on the stack. | |
| <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>int lua_load (lua_State *L, | |
| lua_Reader reader, | |
| void *data, | |
| const char *source, | |
| const char *mode);</pre> | |
| <p> | |
| Loads a Lua chunk (without running it). | |
| If there are no errors, | |
| <code>lua_load</code> pushes the compiled chunk as a Lua | |
| function on top of the stack. | |
| Otherwise, it pushes an error message. | |
| <p> | |
| The return values of <code>lua_load</code> are: | |
| <ul> | |
| <li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li> | |
| <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b> | |
| syntax error during precompilation;</li> | |
| <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> | |
| memory allocation error;</li> | |
| <li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> | |
| error while running a <code>__gc</code> metamethod. | |
| (This error has no relation with the chunk being loaded. | |
| It is generated by the garbage collector.) | |
| </li> | |
| </ul> | |
| <p> | |
| The <code>lua_load</code> function uses a user-supplied <code>reader</code> function | |
| to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>). | |
| The <code>data</code> argument is an opaque value passed to the reader function. | |
| <p> | |
| The <code>source</code> argument gives a name to the chunk, | |
| which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>). | |
| <p> | |
| <code>lua_load</code> automatically detects whether the chunk is text or binary | |
| and loads it accordingly (see program <code>luac</code>). | |
| The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>, | |
| with the addition that | |
| a <code>NULL</code> value is equivalent to the string "<code>bt</code>". | |
| <p> | |
| <code>lua_load</code> uses the stack internally, | |
| so the reader function should always leave the stack | |
| unmodified when returning. | |
| <p> | |
| If the resulting function has one upvalue, | |
| this upvalue is set to the value of the global environment | |
| stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>). | |
| When loading main chunks, | |
| this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). | |
| <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> | |
| <p> | |
| Creates a new thread running in a new, independent state. | |
| Returns <code>NULL</code> if cannot create the thread or the state | |
| (due to lack of memory). | |
| The argument <code>f</code> is the allocator function; | |
| Lua does all memory allocation for this state through this function. | |
| The second argument, <code>ud</code>, is an opaque pointer that Lua | |
| passes to the allocator in every call. | |
| <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void lua_newtable (lua_State *L);</pre> | |
| <p> | |
| Creates a new empty table and pushes it onto the stack. | |
| It is equivalent to <code>lua_createtable(L, 0, 0)</code>. | |
| <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>lua_State *lua_newthread (lua_State *L);</pre> | |
| <p> | |
| Creates a new thread, pushes it on the stack, | |
| and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> 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. | |
| <p> | |
| There is no explicit function to close or to destroy a thread. | |
| Threads are subject to garbage collection, | |
| like any Lua object. | |
| <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> | |
| <span class="apii">[-1, +(2|0), <em>e</em>]</span> | |
| <pre>int lua_next (lua_State *L, int index);</pre> | |
| <p> | |
| 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 href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). | |
| <p> | |
| A typical traversal looks like this: | |
| <pre> | |
| /* 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); | |
| } | |
| </pre> | |
| <p> | |
| While traversing a table, | |
| do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, | |
| unless you know that the key is actually a string. | |
| Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change | |
| the value at the given index; | |
| this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. | |
| <p> | |
| See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying | |
| the table during its traversal. | |
| <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> | |
| <pre>typedef double lua_Number;</pre> | |
| <p> | |
| The type of numbers in Lua. | |
| By default, it is double, but that can be changed in <code>luaconf.h</code>. | |
| Through this configuration file you can change | |
| Lua to operate with another type for numbers (e.g., float or long). | |
| <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> | |
| <span class="apii">[-(nargs + 1), +(nresults|1), –]</span> | |
| <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre> | |
| <p> | |
| Calls a function in protected mode. | |
| <p> | |
| Both <code>nargs</code> and <code>nresults</code> have the same meaning as | |
| in <a href="#lua_call"><code>lua_call</code></a>. | |
| If there are no errors during the call, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>. | |
| However, if there is any error, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> catches it, | |
| pushes a single value on the stack (the error message), | |
| and returns an error code. | |
| Like <a href="#lua_call"><code>lua_call</code></a>, | |
| <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function | |
| and its arguments from the stack. | |
| <p> | |
| If <code>msgh</code> is 0, | |
| then the error message returned on the stack | |
| is exactly the original error message. | |
| Otherwise, <code>msgh</code> is the stack index of a | |
| <em>message handler</em>. | |
| (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 <a href="#lua_pcall"><code>lua_pcall</code></a>. | |
| <p> | |
| 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 <a href="#lua_pcall"><code>lua_pcall</code></a>, | |
| since by then the stack has unwound. | |
| <p> | |
| The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following codes | |
| (defined in <code>lua.h</code>): | |
| <ul> | |
| <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b> | |
| success.</li> | |
| <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b> | |
| a runtime error. | |
| </li> | |
| <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> | |
| memory allocation error. | |
| For such errors, Lua does not call the message handler. | |
| </li> | |
| <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b> | |
| error while running the message handler. | |
| </li> | |
| <li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> | |
| error while running a <code>__gc</code> metamethod. | |
| (This error typically has no relation with the function being called. | |
| It is generated by the garbage collector.) | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p> | |
| <span class="apii">[-(nargs + 1), +(nresults|1), –]</span> | |
| <pre>int lua_pcallk (lua_State *L, | |
| int nargs, | |
| int nresults, | |
| int errfunc, | |
| int ctx, | |
| lua_CFunction k);</pre> | |
| <p> | |
| This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>, | |
| but allows the called function to yield (see <a href="#4.7">§4.7</a>). | |
| <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> | |
| <span class="apii">[-n, +0, –]</span> | |
| <pre>void lua_pop (lua_State *L, int n);</pre> | |
| <p> | |
| Pops <code>n</code> elements from the stack. | |
| <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushboolean (lua_State *L, int b);</pre> | |
| <p> | |
| Pushes a boolean value with value <code>b</code> onto the stack. | |
| <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> | |
| <span class="apii">[-n, +1, <em>e</em>]</span> | |
| <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> | |
| <p> | |
| Pushes a new C closure onto the stack. | |
| <p> | |
| When a C function is created, | |
| it is possible to associate some values with it, | |
| thus creating a C closure (see <a href="#4.4">§4.4</a>); | |
| these values are then accessible to the function whenever it is called. | |
| To associate values with a C function, | |
| first these values should be pushed onto the stack | |
| (when there are multiple values, the first value is pushed first). | |
| Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> | |
| is called to create and push the C function onto the stack, | |
| with the argument <code>n</code> telling how many values should be | |
| associated with the function. | |
| <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. | |
| <p> | |
| The maximum value for <code>n</code> is 255. | |
| <p> | |
| When <code>n</code> is zero, | |
| this function creates a <em>light C function</em>, | |
| which is just a pointer to the C function. | |
| In that case, it never throws a memory error. | |
| <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> | |
| <p> | |
| 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 <code>function</code> that, | |
| when called, invokes the corresponding C function. | |
| <p> | |
| Any function to be registered in Lua must | |
| follow the correct protocol to receive its parameters | |
| and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). | |
| <p> | |
| <code>lua_pushcfunction</code> is defined as a macro: | |
| <pre> | |
| #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0) | |
| </pre><p> | |
| Note that <code>f</code> is used twice. | |
| <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> | |
| <p> | |
| Pushes onto the stack a formatted string | |
| and returns a pointer to this string. | |
| It is similar to the ANSI C function <code>sprintf</code>, | |
| but has some important differences: | |
| <ul> | |
| <li> | |
| You do not have to allocate space for the result: | |
| the result is a Lua string and Lua takes care of memory allocation | |
| (and deallocation, through garbage collection). | |
| </li> | |
| <li> | |
| The conversion specifiers are quite restricted. | |
| There are no flags, widths, or precisions. | |
| The conversion specifiers can only be | |
| '<code>%%</code>' (inserts a '<code>%</code>' in the string), | |
| '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions), | |
| '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>), | |
| '<code>%p</code>' (inserts a pointer as a hexadecimal numeral), | |
| '<code>%d</code>' (inserts an <code>int</code>), and | |
| '<code>%c</code>' (inserts an <code>int</code> as a byte). | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushglobaltable (lua_State *L);</pre> | |
| <p> | |
| Pushes the global environment onto the stack. | |
| <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> | |
| <p> | |
| Pushes a number with value <code>n</code> onto the stack. | |
| <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> | |
| <p> | |
| Pushes a light userdata onto the stack. | |
| <p> | |
| Userdata represent C values in Lua. | |
| A <em>light userdata</em> represents a pointer, a <code>void*</code>. | |
| 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. | |
| <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre> | |
| <p> | |
| This macro is equivalent to <a href="#lua_pushlstring"><code>lua_pushlstring</code></a>, | |
| but can be used only when <code>s</code> is a literal string. | |
| It automatically provides the string length. | |
| <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre> | |
| <p> | |
| Pushes the string pointed to by <code>s</code> with size <code>len</code> | |
| onto the stack. | |
| Lua makes (or reuses) an internal copy of the given string, | |
| so the memory at <code>s</code> can be freed or reused immediately after | |
| the function returns. | |
| The string can contain any binary data, | |
| including embedded zeros. | |
| <p> | |
| Returns a pointer to the internal copy of the string. | |
| <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushnil (lua_State *L);</pre> | |
| <p> | |
| Pushes a nil value onto the stack. | |
| <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> | |
| <p> | |
| Pushes a number with value <code>n</code> onto the stack. | |
| <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre> | |
| <p> | |
| Pushes the zero-terminated string pointed to by <code>s</code> | |
| onto the stack. | |
| Lua makes (or reuses) an internal copy of the given string, | |
| so the memory at <code>s</code> can be freed or reused immediately after | |
| the function returns. | |
| <p> | |
| Returns a pointer to the internal copy of the string. | |
| <p> | |
| If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>. | |
| <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>int lua_pushthread (lua_State *L);</pre> | |
| <p> | |
| Pushes the thread represented by <code>L</code> onto the stack. | |
| Returns 1 if this thread is the main thread of its state. | |
| <hr><h3><a name="lua_pushunsigned"><code>lua_pushunsigned</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushunsigned (lua_State *L, lua_Unsigned n);</pre> | |
| <p> | |
| Pushes a number with value <code>n</code> onto the stack. | |
| <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_pushvalue (lua_State *L, int index);</pre> | |
| <p> | |
| Pushes a copy of the element at the given index | |
| onto the stack. | |
| <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *lua_pushvfstring (lua_State *L, | |
| const char *fmt, | |
| va_list argp);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> | |
| instead of a variable number of arguments. | |
| <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> | |
| <p> | |
| Returns 1 if the two values in indices <code>index1</code> and | |
| <code>index2</code> are primitively equal | |
| (that is, without calling metamethods). | |
| Otherwise returns 0. | |
| Also returns 0 if any of the indices are non valid. | |
| <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> | |
| <span class="apii">[-1, +1, –]</span> | |
| <pre>void lua_rawget (lua_State *L, int index);</pre> | |
| <p> | |
| Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access | |
| (i.e., without metamethods). | |
| <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_rawgeti (lua_State *L, int index, int n);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[n]</code>, | |
| where <code>t</code> is the table at the given index. | |
| The access is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void lua_rawgetp (lua_State *L, int index, const void *p);</pre> | |
| <p> | |
| Pushes onto the stack the value <code>t[k]</code>, | |
| where <code>t</code> is the table at the given index and | |
| <code>k</code> is the pointer <code>p</code> represented as a light userdata. | |
| The access is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>size_t lua_rawlen (lua_State *L, int index);</pre> | |
| <p> | |
| 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 ('<code>#</code>') | |
| with no metamethods; | |
| for userdata, this is the size of the block of memory allocated | |
| for the userdata; | |
| for other values, it is 0. | |
| <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p> | |
| <span class="apii">[-2, +0, <em>e</em>]</span> | |
| <pre>void lua_rawset (lua_State *L, int index);</pre> | |
| <p> | |
| Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment | |
| (i.e., without metamethods). | |
| <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_rawseti (lua_State *L, int index, int n);</pre> | |
| <p> | |
| Does the equivalent of <code>t[n] = v</code>, | |
| where <code>t</code> is the table at the given index | |
| and <code>v</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the value from the stack. | |
| The assignment is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre> | |
| <p> | |
| Does the equivalent of <code>t[k] = v</code>, | |
| where <code>t</code> is the table at the given index, | |
| <code>k</code> is the pointer <code>p</code> represented as a light userdata, | |
| and <code>v</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the value from the stack. | |
| The assignment is raw; | |
| that is, it does not invoke metamethods. | |
| <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> | |
| <pre>typedef const char * (*lua_Reader) (lua_State *L, | |
| void *data, | |
| size_t *size);</pre> | |
| <p> | |
| The reader function used by <a href="#lua_load"><code>lua_load</code></a>. | |
| Every time it needs another piece of the chunk, | |
| <a href="#lua_load"><code>lua_load</code></a> calls the reader, | |
| passing along its <code>data</code> parameter. | |
| The reader must return a pointer to a block of memory | |
| with a new piece of the chunk | |
| and set <code>size</code> 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 <code>NULL</code> or set <code>size</code> to zero. | |
| The reader function may return pieces of any size greater than zero. | |
| <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre> | |
| <p> | |
| Sets the C function <code>f</code> as the new value of global <code>name</code>. | |
| It is defined as a macro: | |
| <pre> | |
| #define lua_register(L,n,f) \ | |
| (lua_pushcfunction(L, f), lua_setglobal(L, n)) | |
| </pre> | |
| <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> | |
| <span class="apii">[-1, +0, –]</span> | |
| <pre>void lua_remove (lua_State *L, int index);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> | |
| <span class="apii">[-1, +0, –]</span> | |
| <pre>void lua_replace (lua_State *L, int index);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> | |
| <span class="apii">[-?, +?, –]</span> | |
| <pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre> | |
| <p> | |
| Starts and resumes a coroutine in a given thread. | |
| <p> | |
| To start a coroutine, | |
| you push onto the thread stack the main function plus any arguments; | |
| then you call <a href="#lua_resume"><code>lua_resume</code></a>, | |
| with <code>nargs</code> 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 <a href="#lua_yield"><code>lua_yield</code></a>, | |
| or all values returned by the body function. | |
| <a href="#lua_resume"><code>lua_resume</code></a> returns | |
| <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields, | |
| <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution | |
| without errors, | |
| or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>). | |
| <p> | |
| 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. | |
| <p> | |
| To resume a coroutine, | |
| you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>, | |
| put on its stack only the values to | |
| be passed as results from <code>yield</code>, | |
| and then call <a href="#lua_resume"><code>lua_resume</code></a>. | |
| <p> | |
| The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>. | |
| If there is no such coroutine, | |
| this parameter can be <code>NULL</code>. | |
| <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> | |
| <p> | |
| Changes the allocator function of a given state to <code>f</code> | |
| with user data <code>ud</code>. | |
| <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> | |
| <p> | |
| Does the equivalent to <code>t[k] = v</code>, | |
| where <code>t</code> is the value at the given index | |
| and <code>v</code> is the value at the top of the stack. | |
| <p> | |
| This function pops the value from the stack. | |
| As in Lua, this function may trigger a metamethod | |
| for the "newindex" event (see <a href="#2.4">§2.4</a>). | |
| <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>void lua_setglobal (lua_State *L, const char *name);</pre> | |
| <p> | |
| Pops a value from the stack and | |
| sets it as the new value of global <code>name</code>. | |
| <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> | |
| <span class="apii">[-1, +0, –]</span> | |
| <pre>void lua_setmetatable (lua_State *L, int index);</pre> | |
| <p> | |
| Pops a table from the stack and | |
| sets it as the new metatable for the value at the given index. | |
| <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> | |
| <span class="apii">[-2, +0, <em>e</em>]</span> | |
| <pre>void lua_settable (lua_State *L, int index);</pre> | |
| <p> | |
| Does the equivalent to <code>t[k] = v</code>, | |
| where <code>t</code> is the value at the given index, | |
| <code>v</code> is the value at the top of the stack, | |
| and <code>k</code> is the value just below the top. | |
| <p> | |
| 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 <a href="#2.4">§2.4</a>). | |
| <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> | |
| <span class="apii">[-?, +?, –]</span> | |
| <pre>void lua_settop (lua_State *L, int index);</pre> | |
| <p> | |
| 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 <b>nil</b>. | |
| If <code>index</code> is 0, then all stack elements are removed. | |
| <hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p> | |
| <span class="apii">[-1, +0, –]</span> | |
| <pre>void lua_setuservalue (lua_State *L, int index);</pre> | |
| <p> | |
| Pops a table or <b>nil</b> from the stack and sets it as | |
| the new value associated to the userdata at the given index. | |
| <hr><h3><a name="lua_State"><code>lua_State</code></a></h3> | |
| <pre>typedef struct lua_State lua_State;</pre> | |
| <p> | |
| 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. | |
| <p> | |
| A pointer to this structure must be passed as the first argument to | |
| every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, | |
| which creates a Lua state from scratch. | |
| <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_status (lua_State *L);</pre> | |
| <p> | |
| Returns the status of the thread <code>L</code>. | |
| <p> | |
| The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread, | |
| an error code if the thread finished the execution | |
| of a <a href="#lua_resume"><code>lua_resume</code></a> with an error, | |
| or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. | |
| <p> | |
| You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>. | |
| You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> | |
| (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> | |
| (to resume a coroutine). | |
| <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_toboolean (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the Lua value at the given index to a C boolean | |
| value (0 or 1). | |
| Like all tests in Lua, | |
| <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value | |
| different from <b>false</b> and <b>nil</b>; | |
| otherwise it returns false. | |
| (If you want to accept only actual boolean values, | |
| use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) | |
| <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> | |
| <p> | |
| Converts a value at the given index to a C function. | |
| That value must be a C function; | |
| otherwise, returns <code>NULL</code>. | |
| <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre> | |
| <p> | |
| Converts the Lua value at the given index | |
| to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| The Lua value must be a number or a string convertible to a number | |
| (see <a href="#3.4.2">§3.4.2</a>); | |
| otherwise, <code>lua_tointegerx</code> returns 0. | |
| <p> | |
| If the number is not an integer, | |
| it is truncated in some non-specified way. | |
| <p> | |
| If <code>isnum</code> is not <code>NULL</code>, | |
| its referent is assigned a boolean value that | |
| indicates whether the operation succeeded. | |
| <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> | |
| <p> | |
| Converts the Lua value at the given index to a C string. | |
| If <code>len</code> is not <code>NULL</code>, | |
| it also sets <code>*len</code> with the string length. | |
| The Lua value must be a string or a number; | |
| otherwise, the function returns <code>NULL</code>. | |
| If the value is a number, | |
| then <code>lua_tolstring</code> also | |
| <em>changes the actual value in the stack to a string</em>. | |
| (This change confuses <a href="#lua_next"><code>lua_next</code></a> | |
| when <code>lua_tolstring</code> is applied to keys during a table traversal.) | |
| <p> | |
| <code>lua_tolstring</code> returns a fully aligned pointer | |
| to a string inside the Lua state. | |
| This string always has a zero ('<code>\0</code>') | |
| after its last character (as in C), | |
| but can contain other zeros in its body. | |
| Because Lua has garbage collection, | |
| there is no guarantee that the pointer returned by <code>lua_tolstring</code> | |
| will be valid after the corresponding value is removed from the stack. | |
| <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre> | |
| <p> | |
| Converts the Lua value at the given index | |
| to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>). | |
| The Lua value must be a number or a string convertible to a number | |
| (see <a href="#3.4.2">§3.4.2</a>); | |
| otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0. | |
| <p> | |
| If <code>isnum</code> is not <code>NULL</code>, | |
| its referent is assigned a boolean value that | |
| indicates whether the operation succeeded. | |
| <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>const void *lua_topointer (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the value at the given index to a generic | |
| C pointer (<code>void*</code>). | |
| The value can be a userdata, a table, a thread, or a function; | |
| otherwise, <code>lua_topointer</code> returns <code>NULL</code>. | |
| Different objects will give different pointers. | |
| There is no way to convert the pointer back to its original value. | |
| <p> | |
| Typically this function is used only for debug information. | |
| <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>const char *lua_tostring (lua_State *L, int index);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_State *lua_tothread (lua_State *L, int index);</pre> | |
| <p> | |
| Converts the value at the given index to a Lua thread | |
| (represented as <code>lua_State*</code>). | |
| This value must be a thread; | |
| otherwise, the function returns <code>NULL</code>. | |
| <hr><h3><a name="lua_tounsigned"><code>lua_tounsigned</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Unsigned lua_tounsigned (lua_State *L, int index);</pre> | |
| <p> | |
| Equivalent to <a href="#lua_tounsignedx"><code>lua_tounsignedx</code></a> with <code>isnum</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="lua_tounsignedx"><code>lua_tounsignedx</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Unsigned lua_tounsignedx (lua_State *L, int index, int *isnum);</pre> | |
| <p> | |
| Converts the Lua value at the given index | |
| to the unsigned integral type <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>. | |
| The Lua value must be a number or a string convertible to a number | |
| (see <a href="#3.4.2">§3.4.2</a>); | |
| otherwise, <code>lua_tounsignedx</code> returns 0. | |
| <p> | |
| If the number is not an integer, | |
| it is truncated in some non-specified way. | |
| If the number is outside the range of representable values, | |
| it is normalized to the remainder of its division by | |
| one more than the maximum representable value. | |
| <p> | |
| If <code>isnum</code> is not <code>NULL</code>, | |
| its referent is assigned a boolean value that | |
| indicates whether the operation succeeded. | |
| <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void *lua_touserdata (lua_State *L, int index);</pre> | |
| <p> | |
| 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 <code>NULL</code>. | |
| <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_type (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the type of the value in the given valid index, | |
| or <code>LUA_TNONE</code> for a non-valid (but acceptable) index. | |
| The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants | |
| defined in <code>lua.h</code>: | |
| <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a>, | |
| <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>, | |
| <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>, | |
| <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, | |
| <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, | |
| <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, | |
| <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, | |
| <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>, | |
| and | |
| <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>. | |
| <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>const char *lua_typename (lua_State *L, int tp);</pre> | |
| <p> | |
| Returns the name of the type encoded by the value <code>tp</code>, | |
| which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. | |
| <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3> | |
| <pre>typedef unsigned long lua_Unsigned;</pre> | |
| <p> | |
| The type used by the Lua API to represent unsigned integral values. | |
| It must have at least 32 bits. | |
| <p> | |
| By default it is an <code>unsigned int</code> or an <code>unsigned long</code>, | |
| whichever can hold 32-bit values. | |
| <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_upvalueindex (int i);</pre> | |
| <p> | |
| Returns the pseudo-index that represents the <code>i</code>-th upvalue of | |
| the running function (see <a href="#4.4">§4.4</a>). | |
| <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const lua_Number *lua_version (lua_State *L);</pre> | |
| <p> | |
| Returns the address of the version number stored in the Lua core. | |
| When called with a valid <a href="#lua_State"><code>lua_State</code></a>, | |
| returns the address of the version used to create that state. | |
| When called with <code>NULL</code>, | |
| returns the address of the version running the call. | |
| <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> | |
| <pre>typedef int (*lua_Writer) (lua_State *L, | |
| const void* p, | |
| size_t sz, | |
| void* ud);</pre> | |
| <p> | |
| The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. | |
| Every time it produces another piece of chunk, | |
| <a href="#lua_dump"><code>lua_dump</code></a> calls the writer, | |
| passing along the buffer to be written (<code>p</code>), | |
| its size (<code>sz</code>), | |
| and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. | |
| <p> | |
| The writer returns an error code: | |
| 0 means no errors; | |
| any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from | |
| calling the writer again. | |
| <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> | |
| <span class="apii">[-?, +?, –]</span> | |
| <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> | |
| <p> | |
| Exchange values between different threads of the same state. | |
| <p> | |
| This function pops <code>n</code> values from the stack <code>from</code>, | |
| and pushes them onto the stack <code>to</code>. | |
| <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> | |
| <span class="apii">[-?, +?, –]</span> | |
| <pre>int lua_yield (lua_State *L, int nresults);</pre> | |
| <p> | |
| This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>, | |
| but it has no continuation (see <a href="#4.7">§4.7</a>). | |
| Therefore, when the thread resumes, | |
| it returns to the function that called | |
| the function calling <code>lua_yield</code>. | |
| <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p> | |
| <span class="apii">[-?, +?, –]</span> | |
| <pre>int lua_yieldk (lua_State *L, int nresults, int ctx, lua_CFunction k);</pre> | |
| <p> | |
| Yields a coroutine. | |
| <p> | |
| This function should only be called as the | |
| return expression of a C function, as follows: | |
| <pre> | |
| return lua_yieldk (L, n, i, k); | |
| </pre><p> | |
| When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a> in that way, | |
| the running coroutine suspends its execution, | |
| and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns. | |
| The parameter <code>nresults</code> is the number of values from the stack | |
| that are passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. | |
| <p> | |
| When the coroutine is resumed again, | |
| Lua calls the given continuation function <code>k</code> to continue | |
| the execution of the C function that yielded (see <a href="#4.7">§4.7</a>). | |
| This continuation function receives the same stack | |
| from the previous function, | |
| with the results removed and | |
| replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>. | |
| Moreover, | |
| the continuation function may access the value <code>ctx</code> | |
| by calling <a href="#lua_getctx"><code>lua_getctx</code></a>. | |
| <h2>4.9 – <a name="4.9">The Debug Interface</a></h2> | |
| <p> | |
| Lua has no built-in debugging facilities. | |
| Instead, it offers a special interface | |
| by means of functions and <em>hooks</em>. | |
| This interface allows the construction of different | |
| kinds of debuggers, profilers, and other tools | |
| that need "inside information" from the interpreter. | |
| <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3> | |
| <pre>typedef struct lua_Debug { | |
| int event; | |
| const char *name; /* (n) */ | |
| const char *namewhat; /* (n) */ | |
| const char *what; /* (S) */ | |
| const char *source; /* (S) */ | |
| int currentline; /* (l) */ | |
| int linedefined; /* (S) */ | |
| int lastlinedefined; /* (S) */ | |
| unsigned char nups; /* (u) number of upvalues */ | |
| unsigned char nparams; /* (u) number of parameters */ | |
| char isvararg; /* (u) */ | |
| char istailcall; /* (t) */ | |
| char short_src[LUA_IDSIZE]; /* (S) */ | |
| /* private part */ | |
| <em>other fields</em> | |
| } lua_Debug;</pre> | |
| <p> | |
| A structure used to carry different pieces of | |
| information about a function or an activation record. | |
| <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part | |
| of this structure, for later use. | |
| To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information, | |
| call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. | |
| <p> | |
| The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning: | |
| <ul> | |
| <li><b><code>source</code>: </b> | |
| the source of the chunk that created the function. | |
| If <code>source</code> starts with a '<code>@</code>', | |
| it means that the function was defined in a file where | |
| the file name follows the '<code>@</code>'. | |
| If <code>source</code> starts with a '<code>=</code>', | |
| the remainder of its contents describe the source in a user-dependent manner. | |
| Otherwise, | |
| the function was defined in a string where | |
| <code>source</code> is that string. | |
| </li> | |
| <li><b><code>short_src</code>: </b> | |
| a "printable" version of <code>source</code>, to be used in error messages. | |
| </li> | |
| <li><b><code>linedefined</code>: </b> | |
| the line number where the definition of the function starts. | |
| </li> | |
| <li><b><code>lastlinedefined</code>: </b> | |
| the line number where the definition of the function ends. | |
| </li> | |
| <li><b><code>what</code>: </b> | |
| the string <code>"Lua"</code> if the function is a Lua function, | |
| <code>"C"</code> if it is a C function, | |
| <code>"main"</code> if it is the main part of a chunk. | |
| </li> | |
| <li><b><code>currentline</code>: </b> | |
| the current line where the given function is executing. | |
| When no line information is available, | |
| <code>currentline</code> is set to -1. | |
| </li> | |
| <li><b><code>name</code>: </b> | |
| 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 <code>lua_getinfo</code> function checks how the function was | |
| called to find a suitable name. | |
| If it cannot find a name, | |
| then <code>name</code> is set to <code>NULL</code>. | |
| </li> | |
| <li><b><code>namewhat</code>: </b> | |
| explains the <code>name</code> field. | |
| The value of <code>namewhat</code> can be | |
| <code>"global"</code>, <code>"local"</code>, <code>"method"</code>, | |
| <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), | |
| according to how the function was called. | |
| (Lua uses the empty string when no other option seems to apply.) | |
| </li> | |
| <li><b><code>istailcall</code>: </b> | |
| true if this function invocation was called by a tail call. | |
| In this case, the caller of this level is not in the stack. | |
| </li> | |
| <li><b><code>nups</code>: </b> | |
| the number of upvalues of the function. | |
| </li> | |
| <li><b><code>nparams</code>: </b> | |
| the number of fixed parameters of the function | |
| (always 0 for C functions). | |
| </li> | |
| <li><b><code>isvararg</code>: </b> | |
| true if the function is a vararg function | |
| (always true for C functions). | |
| </li> | |
| </ul> | |
| <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_Hook lua_gethook (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook function. | |
| <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_gethookcount (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook count. | |
| <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_gethookmask (lua_State *L);</pre> | |
| <p> | |
| Returns the current hook mask. | |
| <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> | |
| <span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span> | |
| <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> | |
| <p> | |
| Gets information about a specific function or function invocation. | |
| <p> | |
| To get information about a function invocation, | |
| the parameter <code>ar</code> must be a valid activation record that was | |
| filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or | |
| given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). | |
| <p> | |
| To get information about a function you push it onto the stack | |
| and start the <code>what</code> string with the character '<code>></code>'. | |
| (In that case, | |
| <code>lua_getinfo</code> pops the function from the top of the stack.) | |
| For instance, to know in which line a function <code>f</code> was defined, | |
| you can write the following code: | |
| <pre> | |
| lua_Debug ar; | |
| lua_getglobal(L, "f"); /* get global 'f' */ | |
| lua_getinfo(L, ">S", &ar); | |
| printf("%d\n", ar.linedefined); | |
| </pre> | |
| <p> | |
| Each character in the string <code>what</code> | |
| selects some fields of the structure <code>ar</code> to be filled or | |
| a value to be pushed on the stack: | |
| <ul> | |
| <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>; | |
| </li> | |
| <li><b>'<code>S</code>': </b> | |
| fills in the fields <code>source</code>, <code>short_src</code>, | |
| <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>; | |
| </li> | |
| <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>; | |
| </li> | |
| <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>; | |
| </li> | |
| <li><b>'<code>u</code>': </b> fills in the fields | |
| <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>; | |
| </li> | |
| <li><b>'<code>f</code>': </b> | |
| pushes onto the stack the function that is | |
| running at the given level; | |
| </li> | |
| <li><b>'<code>L</code>': </b> | |
| pushes onto the stack a table whose indices are the | |
| numbers of the lines that are valid on the function. | |
| (A <em>valid line</em> 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.) | |
| </li> | |
| </ul> | |
| <p> | |
| This function returns 0 on error | |
| (for instance, an invalid option in <code>what</code>). | |
| <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), –]</span> | |
| <pre>const char *lua_getlocal (lua_State *L, lua_Debug *ar, int n);</pre> | |
| <p> | |
| Gets information about a local variable of | |
| a given activation record or a given function. | |
| <p> | |
| In the first case, | |
| the parameter <code>ar</code> must be a valid activation record that was | |
| filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or | |
| given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). | |
| The index <code>n</code> selects which local variable to inspect; | |
| see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices | |
| and names. | |
| <p> | |
| <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack | |
| and returns its name. | |
| <p> | |
| In the second case, <code>ar</code> should be <code>NULL</code> 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. | |
| <p> | |
| Returns <code>NULL</code> (and pushes nothing) | |
| when the index is greater than | |
| the number of active local variables. | |
| <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> | |
| <p> | |
| Gets information about the interpreter runtime stack. | |
| <p> | |
| This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with | |
| an identification of the <em>activation record</em> | |
| of the function executing at a given level. | |
| Level 0 is the current running function, | |
| whereas level <em>n+1</em> is the function that has called level <em>n</em> | |
| (except for tail calls, which do not count on the stack). | |
| When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; | |
| when called with a level greater than the stack depth, | |
| it returns 0. | |
| <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), –]</span> | |
| <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> | |
| <p> | |
| 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.) | |
| <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue, | |
| pushes the upvalue's value onto the stack, | |
| and returns its name. | |
| <code>funcindex</code> 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.) | |
| <p> | |
| Returns <code>NULL</code> (and pushes nothing) | |
| when the index is greater than the number of upvalues. | |
| For C functions, this function uses the empty string <code>""</code> | |
| as a name for all upvalues. | |
| <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3> | |
| <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre> | |
| <p> | |
| Type for debugging hook functions. | |
| <p> | |
| Whenever a hook is called, its <code>ar</code> argument has its field | |
| <code>event</code> set to the specific event that triggered the hook. | |
| Lua identifies these events with the following constants: | |
| <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>, | |
| <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>, | |
| and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>. | |
| Moreover, for line events, the field <code>currentline</code> is also set. | |
| To get the value of any other field in <code>ar</code>, | |
| the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. | |
| <p> | |
| For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>, | |
| the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call; | |
| in this case, there will be no corresponding return event. | |
| <p> | |
| 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. | |
| <p> | |
| Hook functions cannot have continuations, | |
| that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>, | |
| <a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>. | |
| <p> | |
| 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 <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero. | |
| <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>int lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre> | |
| <p> | |
| Sets the debugging hook function. | |
| <p> | |
| Argument <code>f</code> is the hook function. | |
| <code>mask</code> specifies on which events the hook will be called: | |
| it is formed by a bitwise or of the constants | |
| <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>, | |
| <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>, | |
| <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>, | |
| and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>. | |
| The <code>count</code> argument is only meaningful when the mask | |
| includes <code>LUA_MASKCOUNT</code>. | |
| For each event, the hook is called as explained below: | |
| <ul> | |
| <li><b>The call hook: </b> is called when the interpreter calls a function. | |
| The hook is called just after Lua enters the new function, | |
| before the function gets its arguments. | |
| </li> | |
| <li><b>The return hook: </b> is called when the interpreter returns from a function. | |
| The hook is called just before Lua leaves the function. | |
| There is no standard way to access the values | |
| to be returned by the function. | |
| </li> | |
| <li><b>The line hook: </b> is called when the interpreter is about to | |
| start the execution of a new line of code, | |
| or when it jumps back in the code (even to the same line). | |
| (This event only happens while Lua is executing a Lua function.) | |
| </li> | |
| <li><b>The count hook: </b> is called after the interpreter executes every | |
| <code>count</code> instructions. | |
| (This event only happens while Lua is executing a Lua function.) | |
| </li> | |
| </ul> | |
| <p> | |
| A hook is disabled by setting <code>mask</code> to zero. | |
| <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> | |
| <span class="apii">[-(0|1), +0, –]</span> | |
| <pre>const char *lua_setlocal (lua_State *L, lua_Debug *ar, int n);</pre> | |
| <p> | |
| Sets the value of a local variable of a given activation record. | |
| Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a> | |
| (see <a href="#lua_getlocal"><code>lua_getlocal</code></a>). | |
| <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack | |
| to the variable and returns its name. | |
| It also pops the value from the stack. | |
| <p> | |
| Returns <code>NULL</code> (and pops nothing) | |
| when the index is greater than | |
| the number of active local variables. | |
| <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> | |
| <span class="apii">[-(0|1), +0, –]</span> | |
| <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> | |
| <p> | |
| 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 <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> | |
| (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>). | |
| <p> | |
| Returns <code>NULL</code> (and pops nothing) | |
| when the index is greater than the number of upvalues. | |
| <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre> | |
| <p> | |
| Returns an unique identifier for the upvalue numbered <code>n</code> | |
| from the closure at index <code>funcindex</code>. | |
| Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> | |
| (see <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>) | |
| (but <code>n</code> cannot be greater than the number of upvalues). | |
| <p> | |
| 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. | |
| <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1, | |
| int funcindex2, int n2);</pre> | |
| <p> | |
| Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code> | |
| refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>. | |
| <h1>5 – <a name="5">The Auxiliary Library</a></h1> | |
| <p> | |
| The <em>auxiliary library</em> 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. | |
| <p> | |
| All functions and types from the auxiliary library | |
| are defined in header file <code>lauxlib.h</code> and | |
| have a prefix <code>luaL_</code>. | |
| <p> | |
| 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. | |
| <p> | |
| 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. | |
| <p> | |
| Several functions in the auxiliary library are used to | |
| check C function arguments. | |
| Because the error message is formatted for arguments | |
| (e.g., "<code>bad argument #1</code>"), | |
| you should not use these functions for other stack values. | |
| <p> | |
| Functions called <code>luaL_check*</code> | |
| always throw an error if the check is not satisfied. | |
| <h2>5.1 – <a name="5.1">Functions and Types</a></h2> | |
| <p> | |
| Here we list all functions and types from the auxiliary library | |
| in alphabetical order. | |
| <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> | |
| <p> | |
| Adds the byte <code>c</code> to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> | |
| <p> | |
| Adds the string pointed to by <code>s</code> with length <code>l</code> to | |
| the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| The string can contain embedded zeros. | |
| <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> | |
| <p> | |
| Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) | |
| a string of length <code>n</code> previously copied to the | |
| buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). | |
| <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> | |
| <p> | |
| Adds the zero-terminated string pointed to by <code>s</code> | |
| to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| The string cannot contain embedded zeros. | |
| <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> | |
| <span class="apii">[-1, +?, <em>e</em>]</span> | |
| <pre>void luaL_addvalue (luaL_Buffer *B);</pre> | |
| <p> | |
| Adds the value at the top of the stack | |
| to the buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| Pops the value. | |
| <p> | |
| 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. | |
| <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_argcheck (lua_State *L, | |
| int cond, | |
| int arg, | |
| const char *extramsg);</pre> | |
| <p> | |
| Checks whether <code>cond</code> is true. | |
| If not, raises an error with a standard message. | |
| <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre> | |
| <p> | |
| Raises an error with a standard message | |
| that includes <code>extramsg</code> as a comment. | |
| <p> | |
| This function never returns, | |
| but it is an idiom to use it in C functions | |
| as <code>return luaL_argerror(<em>args</em>)</code>. | |
| <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3> | |
| <pre>typedef struct luaL_Buffer luaL_Buffer;</pre> | |
| <p> | |
| Type for a <em>string buffer</em>. | |
| <p> | |
| A string buffer allows C code to build Lua strings piecemeal. | |
| Its pattern of use is as follows: | |
| <ul> | |
| <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> | |
| <li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> | |
| <li> | |
| Then add string pieces to the buffer calling any of | |
| the <code>luaL_add*</code> functions. | |
| </li> | |
| <li> | |
| Finish by calling <code>luaL_pushresult(&b)</code>. | |
| This call leaves the final string on the top of the stack. | |
| </li> | |
| </ul> | |
| <p> | |
| If you know beforehand the total size of the resulting string, | |
| you can use the buffer like this: | |
| <ul> | |
| <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> | |
| <li>Then initialize it and preallocate a space of | |
| size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li> | |
| <li>Then copy the string into that space.</li> | |
| <li> | |
| Finish by calling <code>luaL_pushresultsize(&b, sz)</code>, | |
| where <code>sz</code> is the total size of the resulting string | |
| copied into that space. | |
| </li> | |
| </ul> | |
| <p> | |
| 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 <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) | |
| After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its | |
| level when the buffer was initialized, | |
| plus the final string on its top. | |
| <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> | |
| <p> | |
| Initializes a buffer <code>B</code>. | |
| This function does not allocate any space; | |
| the buffer must be declared as a variable | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre> | |
| <p> | |
| Equivalent to the sequence | |
| <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>. | |
| <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>e</em>]</span> | |
| <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> | |
| <p> | |
| Calls a metamethod. | |
| <p> | |
| If the object at index <code>obj</code> has a metatable and this | |
| metatable has a field <code>e</code>, | |
| 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). | |
| <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checkany (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function has an argument | |
| of any type (including <b>nil</b>) at position <code>arg</code>. | |
| <hr><h3><a name="luaL_checkint"><code>luaL_checkint</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_checkint (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a number | |
| and returns this number cast to an <code>int</code>. | |
| <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a number | |
| and returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| <hr><h3><a name="luaL_checklong"><code>luaL_checklong</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>long luaL_checklong (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a number | |
| and returns this number cast to a <code>long</code>. | |
| <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a string | |
| and returns this string; | |
| if <code>l</code> is not <code>NULL</code> fills <code>*l</code> | |
| with the string's length. | |
| <p> | |
| This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, | |
| so all conversions and caveats of that function apply here. | |
| <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a number | |
| and returns this number. | |
| <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_checkoption (lua_State *L, | |
| int arg, | |
| const char *def, | |
| const char *const lst[]);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a string and | |
| searches for this string in the array <code>lst</code> | |
| (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. | |
| <p> | |
| If <code>def</code> is not <code>NULL</code>, | |
| the function uses <code>def</code> as a default value when | |
| there is no argument <code>arg</code> or when this argument is <b>nil</b>. | |
| <p> | |
| 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.) | |
| <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> | |
| <p> | |
| Grows the stack size to <code>top + sz</code> elements, | |
| raising an error if the stack cannot grow to that size. | |
| <code>msg</code> is an additional text to go into the error message | |
| (or <code>NULL</code> for no additional text). | |
| <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a string | |
| and returns this string. | |
| <p> | |
| This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, | |
| so all conversions and caveats of that function apply here. | |
| <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> has type <code>t</code>. | |
| See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. | |
| <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a userdata | |
| of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and | |
| returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>). | |
| <hr><h3><a name="luaL_checkunsigned"><code>luaL_checkunsigned</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Unsigned luaL_checkunsigned (lua_State *L, int arg);</pre> | |
| <p> | |
| Checks whether the function argument <code>arg</code> is a number | |
| and returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>. | |
| <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void luaL_checkversion (lua_State *L);</pre> | |
| <p> | |
| 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. | |
| <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> | |
| <span class="apii">[-0, +?, <em>e</em>]</span> | |
| <pre>int luaL_dofile (lua_State *L, const char *filename);</pre> | |
| <p> | |
| Loads and runs the given file. | |
| It is defined as the following macro: | |
| <pre> | |
| (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) | |
| </pre><p> | |
| It returns false if there are no errors | |
| or true in case of errors. | |
| <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> | |
| <span class="apii">[-0, +?, –]</span> | |
| <pre>int luaL_dostring (lua_State *L, const char *str);</pre> | |
| <p> | |
| Loads and runs the given string. | |
| It is defined as the following macro: | |
| <pre> | |
| (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) | |
| </pre><p> | |
| It returns false if there are no errors | |
| or true in case of errors. | |
| <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> | |
| <p> | |
| Raises an error. | |
| The error message format is given by <code>fmt</code> | |
| plus any extra arguments, | |
| following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. | |
| 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. | |
| <p> | |
| This function never returns, | |
| but it is an idiom to use it in C functions | |
| as <code>return luaL_error(<em>args</em>)</code>. | |
| <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p> | |
| <span class="apii">[-0, +3, <em>e</em>]</span> | |
| <pre>int luaL_execresult (lua_State *L, int stat);</pre> | |
| <p> | |
| This function produces the return values for | |
| process-related functions in the standard library | |
| (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>). | |
| <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p> | |
| <span class="apii">[-0, +(1|3), <em>e</em>]</span> | |
| <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre> | |
| <p> | |
| This function produces the return values for | |
| file-related functions in the standard library | |
| (<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.). | |
| <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> | |
| <span class="apii">[-0, +(0|1), <em>e</em>]</span> | |
| <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> | |
| <p> | |
| Pushes onto the stack the field <code>e</code> from the metatable | |
| of the object at index <code>obj</code>. | |
| If the object does not have a metatable, | |
| or if the metatable does not have this field, | |
| returns false and pushes nothing. | |
| <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>void luaL_getmetatable (lua_State *L, const char *tname);</pre> | |
| <p> | |
| Pushes onto the stack the metatable associated with name <code>tname</code> | |
| in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). | |
| <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre> | |
| <p> | |
| Ensures that the value <code>t[fname]</code>, | |
| where <code>t</code> is the value at index <code>idx</code>, | |
| 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. | |
| <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *luaL_gsub (lua_State *L, | |
| const char *s, | |
| const char *p, | |
| const char *r);</pre> | |
| <p> | |
| Creates a copy of string <code>s</code> by replacing | |
| any occurrence of the string <code>p</code> | |
| with the string <code>r</code>. | |
| Pushes the resulting string on the stack and returns it. | |
| <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>int luaL_len (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the "length" of the value at the given index | |
| as a number; | |
| it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.6">§3.4.6</a>). | |
| Raises an error if the result of the operation is not a number. | |
| (This case only can happen through metamethods.) | |
| <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>int luaL_loadbuffer (lua_State *L, | |
| const char *buff, | |
| size_t sz, | |
| const char *name);</pre> | |
| <p> | |
| Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>int luaL_loadbufferx (lua_State *L, | |
| const char *buff, | |
| size_t sz, | |
| const char *name, | |
| const char *mode);</pre> | |
| <p> | |
| Loads a buffer as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the | |
| buffer pointed to by <code>buff</code> with size <code>sz</code>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. | |
| <code>name</code> is the chunk name, | |
| used for debug information and error messages. | |
| The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. | |
| <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> | |
| <p> | |
| Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>. | |
| <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>int luaL_loadfilex (lua_State *L, const char *filename, | |
| const char *mode);</pre> | |
| <p> | |
| Loads a file as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file | |
| named <code>filename</code>. | |
| If <code>filename</code> is <code>NULL</code>, | |
| then it loads from the standard input. | |
| The first line in the file is ignored if it starts with a <code>#</code>. | |
| <p> | |
| The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, | |
| but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> | |
| if it cannot open/read the file or the file has a wrong mode. | |
| <p> | |
| As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; | |
| it does not run it. | |
| <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, –]</span> | |
| <pre>int luaL_loadstring (lua_State *L, const char *s);</pre> | |
| <p> | |
| Loads a string as a Lua chunk. | |
| This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in | |
| the zero-terminated string <code>s</code>. | |
| <p> | |
| This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. | |
| <p> | |
| Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; | |
| it does not run it. | |
| <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void luaL_newlib (lua_State *L, const luaL_Reg *l);</pre> | |
| <p> | |
| Creates a new table and registers there | |
| the functions in list <code>l</code>. | |
| It is implemented as the following macro: | |
| <pre> | |
| (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0)) | |
| </pre> | |
| <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre> | |
| <p> | |
| Creates a new table with a size optimized | |
| to store all entries in the array <code>l</code> | |
| (but does not actually store them). | |
| It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> | |
| (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>). | |
| <p> | |
| It is implemented as a macro. | |
| The array <code>l</code> must be the actual array, | |
| not a pointer to it. | |
| <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> | |
| <p> | |
| If the registry already has the key <code>tname</code>, | |
| returns 0. | |
| Otherwise, | |
| creates a new table to be used as a metatable for userdata, | |
| adds it to the registry with key <code>tname</code>, | |
| and returns 1. | |
| <p> | |
| In both cases pushes onto the stack the final value associated | |
| with <code>tname</code> in the registry. | |
| <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>lua_State *luaL_newstate (void);</pre> | |
| <p> | |
| Creates a new Lua state. | |
| It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an | |
| allocator based on the standard C <code>realloc</code> function | |
| and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints | |
| an error message to the standard error output in case of fatal | |
| errors. | |
| <p> | |
| Returns the new state, | |
| or <code>NULL</code> if there is a memory allocation error. | |
| <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>void luaL_openlibs (lua_State *L);</pre> | |
| <p> | |
| Opens all standard Lua libraries into the given state. | |
| <hr><h3><a name="luaL_optint"><code>luaL_optint</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>int luaL_optint (lua_State *L, int arg, int d);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a number, | |
| returns this number cast to an <code>int</code>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Integer luaL_optinteger (lua_State *L, | |
| int arg, | |
| lua_Integer d);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a number, | |
| returns this number cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optlong"><code>luaL_optlong</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>long luaL_optlong (lua_State *L, int arg, long d);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a number, | |
| returns this number cast to a <code>long</code>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_optlstring (lua_State *L, | |
| int arg, | |
| const char *d, | |
| size_t *l);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a string, | |
| returns this string. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <p> | |
| If <code>l</code> is not <code>NULL</code>, | |
| fills the position <code>*l</code> with the result's length. | |
| <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a number, | |
| returns this number. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>const char *luaL_optstring (lua_State *L, | |
| int arg, | |
| const char *d);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a string, | |
| returns this string. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>d</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_optunsigned"><code>luaL_optunsigned</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>v</em>]</span> | |
| <pre>lua_Unsigned luaL_optunsigned (lua_State *L, | |
| int arg, | |
| lua_Unsigned u);</pre> | |
| <p> | |
| If the function argument <code>arg</code> is a number, | |
| returns this number cast to a <a href="#lua_Unsigned"><code>lua_Unsigned</code></a>. | |
| If this argument is absent or is <b>nil</b>, | |
| returns <code>u</code>. | |
| Otherwise, raises an error. | |
| <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> | |
| <p> | |
| Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a> | |
| with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>. | |
| <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p> | |
| <span class="apii">[-?, +?, <em>e</em>]</span> | |
| <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre> | |
| <p> | |
| Returns an address to a space of size <code>sz</code> | |
| where you can copy a string to be added to buffer <code>B</code> | |
| (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). | |
| After copying the string into this space you must call | |
| <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add | |
| it to the buffer. | |
| <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> | |
| <span class="apii">[-?, +1, <em>e</em>]</span> | |
| <pre>void luaL_pushresult (luaL_Buffer *B);</pre> | |
| <p> | |
| Finishes the use of buffer <code>B</code> leaving the final string on | |
| the top of the stack. | |
| <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p> | |
| <span class="apii">[-?, +1, <em>e</em>]</span> | |
| <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre> | |
| <p> | |
| Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>. | |
| <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> | |
| <span class="apii">[-1, +0, <em>e</em>]</span> | |
| <pre>int luaL_ref (lua_State *L, int t);</pre> | |
| <p> | |
| Creates and returns a <em>reference</em>, | |
| in the table at index <code>t</code>, | |
| for the object at the top of the stack (and pops the object). | |
| <p> | |
| A reference is a unique integer key. | |
| As long as you do not manually add integer keys into table <code>t</code>, | |
| <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. | |
| You can retrieve an object referred by reference <code>r</code> | |
| by calling <code>lua_rawgeti(L, t, r)</code>. | |
| Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. | |
| <p> | |
| If the object at the top of the stack is <b>nil</b>, | |
| <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. | |
| The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different | |
| from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. | |
| <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> | |
| <pre>typedef struct luaL_Reg { | |
| const char *name; | |
| lua_CFunction func; | |
| } luaL_Reg;</pre> | |
| <p> | |
| Type for arrays of functions to be registered by | |
| <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>. | |
| <code>name</code> is the function name and <code>func</code> is a pointer to | |
| the function. | |
| Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with an sentinel entry | |
| in which both <code>name</code> and <code>func</code> are <code>NULL</code>. | |
| <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void luaL_requiref (lua_State *L, const char *modname, | |
| lua_CFunction openf, int glb);</pre> | |
| <p> | |
| Calls function <code>openf</code> with string <code>modname</code> as an argument | |
| and sets the call result in <code>package.loaded[modname]</code>, | |
| as if that function has been called through <a href="#pdf-require"><code>require</code></a>. | |
| <p> | |
| If <code>glb</code> is true, | |
| also stores the result into global <code>modname</code>. | |
| <p> | |
| Leaves a copy of that result on the stack. | |
| <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p> | |
| <span class="apii">[-nup, +0, <em>e</em>]</span> | |
| <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre> | |
| <p> | |
| Registers all functions in the array <code>l</code> | |
| (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack | |
| (below optional upvalues, see next). | |
| <p> | |
| When <code>nup</code> is not zero, | |
| all functions are created sharing <code>nup</code> 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. | |
| <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre> | |
| <p> | |
| Sets the metatable of the object at the top of the stack | |
| as the metatable associated with name <code>tname</code> | |
| in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). | |
| <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p> | |
| <span class="apii">[-0, +0, <em>e</em>]</span> | |
| <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre> | |
| <p> | |
| This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>, | |
| except that, when the test fails, | |
| it returns <code>NULL</code> instead of throwing an error. | |
| <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre> | |
| <p> | |
| 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 <code>len</code> is not <code>NULL</code>, | |
| the function also sets <code>*len</code> with the string length. | |
| <p> | |
| If the value has a metatable with a <code>"__tostring"</code> field, | |
| then <code>luaL_tolstring</code> calls the corresponding metamethod | |
| with the value as argument, | |
| and uses the result of the call as its result. | |
| <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg, | |
| int level);</pre> | |
| <p> | |
| Creates and pushes a traceback of the stack <code>L1</code>. | |
| If <code>msg</code> is not <code>NULL</code> it is appended | |
| at the beginning of the traceback. | |
| The <code>level</code> parameter tells at which level | |
| to start the traceback. | |
| <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>const char *luaL_typename (lua_State *L, int index);</pre> | |
| <p> | |
| Returns the name of the type of the value at the given index. | |
| <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> | |
| <span class="apii">[-0, +0, –]</span> | |
| <pre>void luaL_unref (lua_State *L, int t, int ref);</pre> | |
| <p> | |
| Releases reference <code>ref</code> from the table at index <code>t</code> | |
| (see <a href="#luaL_ref"><code>luaL_ref</code></a>). | |
| The entry is removed from the table, | |
| so that the referred object can be collected. | |
| The reference <code>ref</code> is also freed to be used again. | |
| <p> | |
| If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, | |
| <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. | |
| <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> | |
| <span class="apii">[-0, +1, <em>e</em>]</span> | |
| <pre>void luaL_where (lua_State *L, int lvl);</pre> | |
| <p> | |
| Pushes onto the stack a string identifying the current position | |
| of the control at level <code>lvl</code> in the call stack. | |
| Typically this string has the following format: | |
| <pre> | |
| <em>chunkname</em>:<em>currentline</em>: | |
| </pre><p> | |
| Level 0 is the running function, | |
| level 1 is the function that called the running function, | |
| etc. | |
| <p> | |
| This function is used to build a prefix for error messages. | |
| <h1>6 – <a name="6">Standard Libraries</a></h1> | |
| <p> | |
| 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., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); | |
| 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., <a href="#pdf-table.sort"><code>table.sort</code></a>). | |
| <p> | |
| All libraries are implemented through the official C API | |
| and are provided as separate C modules. | |
| Currently, Lua has the following standard libraries: | |
| <ul> | |
| <li>basic library (<a href="#6.1">§6.1</a>);</li> | |
| <li>coroutine library (<a href="#6.2">§6.2</a>);</li> | |
| <li>package library (<a href="#6.3">§6.3</a>);</li> | |
| <li>string manipulation (<a href="#6.4">§6.4</a>);</li> | |
| <li>table manipulation (<a href="#6.5">§6.5</a>);</li> | |
| <li>mathematical functions (<a href="#6.6">§6.6</a>) (sin, log, etc.);</li> | |
| <li>bitwise operations (<a href="#6.7">§6.7</a>);</li> | |
| <li>input and output (<a href="#6.8">§6.8</a>);</li> | |
| <li>operating system facilities (<a href="#6.9">§6.9</a>);</li> | |
| <li>debug facilities (<a href="#6.10">§6.10</a>).</li> | |
| </ul><p> | |
| 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. | |
| <p> | |
| To have access to these libraries, | |
| the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function, | |
| which opens all standard libraries. | |
| Alternatively, | |
| the host program can open them individually by using | |
| <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call | |
| <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library), | |
| <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library), | |
| <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library), | |
| <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), | |
| <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), | |
| <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), | |
| <a name="pdf-luaopen_bit32"><code>luaopen_bit32</code></a> (for the bit library), | |
| <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), | |
| <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the Operating System library), | |
| and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). | |
| These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>. | |
| <h2>6.1 – <a name="6.1">Basic Functions</a></h2> | |
| <p> | |
| 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. | |
| <p> | |
| <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3> | |
| Issues an error when | |
| the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); | |
| otherwise, returns all its arguments. | |
| <code>message</code> is an error message; | |
| when absent, it defaults to "assertion failed!" | |
| <p> | |
| <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3> | |
| <p> | |
| This function is a generic interface to the garbage collector. | |
| It performs different functions according to its first argument, <code>opt</code>: | |
| <ul> | |
| <li><b>"<code>collect</code>": </b> | |
| performs a full garbage-collection cycle. | |
| This is the default option. | |
| </li> | |
| <li><b>"<code>stop</code>": </b> | |
| stops automatic execution of the garbage collector. | |
| The collector will run only when explicitly invoked, | |
| until a call to restart it. | |
| </li> | |
| <li><b>"<code>restart</code>": </b> | |
| restarts automatic execution of the garbage collector. | |
| </li> | |
| <li><b>"<code>count</code>": </b> | |
| returns the total memory in use by Lua (in Kbytes) and | |
| a second value with the total memory in bytes modulo 1024. | |
| The first value has a fractional part, | |
| so the following equality is always true: | |
| <pre> | |
| k, b = collectgarbage("count") | |
| assert(k*1024 == math.floor(k)*1024 + b) | |
| </pre><p> | |
| (The second result is useful when Lua is compiled | |
| with a non floating-point type for numbers.) | |
| </li> | |
| <li><b>"<code>step</code>": </b> | |
| performs a garbage-collection step. | |
| The step "size" is controlled by <code>arg</code> | |
| (larger values mean more steps) in a non-specified way. | |
| If you want to control the step size | |
| you must experimentally tune the value of <code>arg</code>. | |
| Returns <b>true</b> if the step finished a collection cycle. | |
| </li> | |
| <li><b>"<code>setpause</code>": </b> | |
| sets <code>arg</code> as the new value for the <em>pause</em> of | |
| the collector (see <a href="#2.5">§2.5</a>). | |
| Returns the previous value for <em>pause</em>. | |
| </li> | |
| <li><b>"<code>setstepmul</code>": </b> | |
| sets <code>arg</code> as the new value for the <em>step multiplier</em> of | |
| the collector (see <a href="#2.5">§2.5</a>). | |
| Returns the previous value for <em>step</em>. | |
| </li> | |
| <li><b>"<code>isrunning</code>": </b> | |
| returns a boolean that tells whether the collector is running | |
| (i.e., not stopped). | |
| </li> | |
| <li><b>"<code>generational</code>": </b> | |
| changes the collector to generational mode. | |
| This is an experimental feature (see <a href="#2.5">§2.5</a>). | |
| </li> | |
| <li><b>"<code>incremental</code>": </b> | |
| changes the collector to incremental mode. | |
| This is the default mode. | |
| </li> | |
| </ul> | |
| <p> | |
| <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3> | |
| Opens the named file and executes its contents as a Lua chunk. | |
| When called without arguments, | |
| <code>dofile</code> executes the contents of the standard input (<code>stdin</code>). | |
| Returns all values returned by the chunk. | |
| In case of errors, <code>dofile</code> propagates the error | |
| to its caller (that is, <code>dofile</code> does not run in protected mode). | |
| <p> | |
| <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3> | |
| Terminates the last protected function called | |
| and returns <code>message</code> as the error message. | |
| Function <code>error</code> never returns. | |
| <p> | |
| Usually, <code>error</code> adds some information about the error position | |
| at the beginning of the message, if the message is a string. | |
| The <code>level</code> argument specifies how to get the error position. | |
| With level 1 (the default), the error position is where the | |
| <code>error</code> function was called. | |
| Level 2 points the error to where the function | |
| that called <code>error</code> was called; and so on. | |
| Passing a level 0 avoids the addition of error position information | |
| to the message. | |
| <p> | |
| <hr><h3><a name="pdf-_G"><code>_G</code></a></h3> | |
| A global variable (not a function) that | |
| holds the global environment (see <a href="#2.2">§2.2</a>). | |
| Lua itself does not use this variable; | |
| changing its value does not affect any environment, | |
| nor vice-versa. | |
| <p> | |
| <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3> | |
| <p> | |
| If <code>object</code> does not have a metatable, returns <b>nil</b>. | |
| Otherwise, | |
| if the object's metatable has a <code>"__metatable"</code> field, | |
| returns the associated value. | |
| Otherwise, returns the metatable of the given object. | |
| <p> | |
| <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3> | |
| <p> | |
| If <code>t</code> has a metamethod <code>__ipairs</code>, | |
| calls it with <code>t</code> as argument and returns the first three | |
| results from the call. | |
| <p> | |
| Otherwise, | |
| returns three values: an iterator function, the table <code>t</code>, and 0, | |
| so that the construction | |
| <pre> | |
| for i,v in ipairs(t) do <em>body</em> end | |
| </pre><p> | |
| will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ..., | |
| up to the first integer key absent from the table. | |
| <p> | |
| <hr><h3><a name="pdf-load"><code>load (ld [, source [, mode [, env]]])</code></a></h3> | |
| <p> | |
| Loads a chunk. | |
| <p> | |
| If <code>ld</code> is a string, the chunk is this string. | |
| If <code>ld</code> is a function, | |
| <code>load</code> calls it repeatedly to get the chunk pieces. | |
| Each call to <code>ld</code> must return a string that concatenates | |
| with previous results. | |
| A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. | |
| <p> | |
| If there are no syntactic errors, | |
| returns the compiled chunk as a function; | |
| otherwise, returns <b>nil</b> plus the error message. | |
| <p> | |
| If the resulting function has upvalues, | |
| the first upvalue is set to the value of <code>env</code>, | |
| if that parameter is given, | |
| or to the value of the global environment. | |
| (When you load a main chunk, | |
| the resulting function will always have exactly one upvalue, | |
| the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). | |
| When you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>), | |
| the resulting function can have arbitrary upvalues.) | |
| <p> | |
| <code>source</code> is used as the source of the chunk for error messages | |
| and debug information (see <a href="#4.9">§4.9</a>). | |
| When absent, | |
| it defaults to <code>ld</code>, if <code>ld</code> is a string, | |
| or to "<code>=(load)</code>" otherwise. | |
| <p> | |
| The string <code>mode</code> controls whether the chunk can be text or binary | |
| (that is, a precompiled chunk). | |
| It may be the string "<code>b</code>" (only binary chunks), | |
| "<code>t</code>" (only text chunks), | |
| or "<code>bt</code>" (both binary and text). | |
| The default is "<code>bt</code>". | |
| <p> | |
| <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3> | |
| <p> | |
| Similar to <a href="#pdf-load"><code>load</code></a>, | |
| but gets the chunk from file <code>filename</code> | |
| or from the standard input, | |
| if no file name is given. | |
| <p> | |
| <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3> | |
| <p> | |
| 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. | |
| <code>next</code> returns the next index of the table | |
| and its associated value. | |
| When called with <b>nil</b> as its second argument, | |
| <code>next</code> returns an initial index | |
| and its associated value. | |
| When called with the last index, | |
| or with <b>nil</b> in an empty table, | |
| <code>next</code> returns <b>nil</b>. | |
| If the second argument is absent, then it is interpreted as <b>nil</b>. | |
| In particular, | |
| you can use <code>next(t)</code> to check whether a table is empty. | |
| <p> | |
| The order in which the indices are enumerated is not specified, | |
| <em>even for numeric indices</em>. | |
| (To traverse a table in numeric order, | |
| use a numerical <b>for</b>.) | |
| <p> | |
| The behavior of <code>next</code> 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. | |
| <p> | |
| <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> | |
| <p> | |
| If <code>t</code> has a metamethod <code>__pairs</code>, | |
| calls it with <code>t</code> as argument and returns the first three | |
| results from the call. | |
| <p> | |
| Otherwise, | |
| returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>, | |
| so that the construction | |
| <pre> | |
| for k,v in pairs(t) do <em>body</em> end | |
| </pre><p> | |
| will iterate over all key–value pairs of table <code>t</code>. | |
| <p> | |
| See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying | |
| the table during its traversal. | |
| <p> | |
| <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3> | |
| <p> | |
| Calls function <code>f</code> with | |
| the given arguments in <em>protected mode</em>. | |
| This means that any error inside <code>f</code> is not propagated; | |
| instead, <code>pcall</code> 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, <code>pcall</code> also returns all results from the call, | |
| after this first result. | |
| In case of any error, <code>pcall</code> returns <b>false</b> plus the error message. | |
| <p> | |
| <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3> | |
| Receives any number of arguments | |
| and prints their values to <code>stdout</code>, | |
| using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string. | |
| <code>print</code> 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 <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3> | |
| Checks whether <code>v1</code> is equal to <code>v2</code>, | |
| without invoking any metamethod. | |
| Returns a boolean. | |
| <p> | |
| <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3> | |
| Gets the real value of <code>table[index]</code>, | |
| without invoking any metamethod. | |
| <code>table</code> must be a table; | |
| <code>index</code> may be any value. | |
| <p> | |
| <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3> | |
| Returns the length of the object <code>v</code>, | |
| which must be a table or a string, | |
| without invoking any metamethod. | |
| Returns an integer number. | |
| <p> | |
| <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3> | |
| Sets the real value of <code>table[index]</code> to <code>value</code>, | |
| without invoking any metamethod. | |
| <code>table</code> must be a table, | |
| <code>index</code> any value different from <b>nil</b> and NaN, | |
| and <code>value</code> any Lua value. | |
| <p> | |
| This function returns <code>table</code>. | |
| <p> | |
| <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3> | |
| <p> | |
| If <code>index</code> is a number, | |
| returns all arguments after argument number <code>index</code>; | |
| a negative number indexes from the end (-1 is the last argument). | |
| Otherwise, <code>index</code> must be the string <code>"#"</code>, | |
| and <code>select</code> returns the total number of extra arguments it received. | |
| <p> | |
| <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> | |
| <p> | |
| Sets the metatable for the given table. | |
| (You cannot change the metatable of other types from Lua, only from C.) | |
| If <code>metatable</code> is <b>nil</b>, | |
| removes the metatable of the given table. | |
| If the original metatable has a <code>"__metatable"</code> field, | |
| raises an error. | |
| <p> | |
| This function returns <code>table</code>. | |
| <p> | |
| <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3> | |
| <p> | |
| When called with no <code>base</code>, | |
| <code>tonumber</code> tries to convert its argument to a number. | |
| If the argument is already a number or | |
| a string convertible to a number (see <a href="#3.4.2">§3.4.2</a>), | |
| then <code>tonumber</code> returns this number; | |
| otherwise, it returns <b>nil</b>. | |
| <p> | |
| When called with <code>base</code>, | |
| then <code>e</code> should 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 '<code>A</code>' (in either upper or lower case) | |
| represents 10, '<code>B</code>' represents 11, and so forth, | |
| with '<code>Z</code>' representing 35. | |
| If the string <code>e</code> is not a valid numeral in the given base, | |
| the function returns <b>nil</b>. | |
| <p> | |
| <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3> | |
| Receives a value of any type and | |
| converts it to a string in a reasonable format. | |
| (For complete control of how numbers are converted, | |
| use <a href="#pdf-string.format"><code>string.format</code></a>.) | |
| <p> | |
| If the metatable of <code>v</code> has a <code>"__tostring"</code> field, | |
| then <code>tostring</code> calls the corresponding value | |
| with <code>v</code> as argument, | |
| and uses the result of the call as its result. | |
| <p> | |
| <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3> | |
| Returns the type of its only argument, coded as a string. | |
| The possible results of this function are | |
| "<code>nil</code>" (a string, not the value <b>nil</b>), | |
| "<code>number</code>", | |
| "<code>string</code>", | |
| "<code>boolean</code>", | |
| "<code>table</code>", | |
| "<code>function</code>", | |
| "<code>thread</code>", | |
| and "<code>userdata</code>". | |
| <p> | |
| <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3> | |
| A global variable (not a function) that | |
| holds a string containing the current interpreter version. | |
| The current contents of this variable is "<code>Lua 5.2</code>". | |
| <p> | |
| <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3> | |
| <p> | |
| This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, | |
| except that it sets a new message handler <code>msgh</code>. | |
| <h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2> | |
| <p> | |
| The operations related to coroutines comprise a sub-library of | |
| the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. | |
| See <a href="#2.6">§2.6</a> for a general description of coroutines. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3> | |
| <p> | |
| Creates a new coroutine, with body <code>f</code>. | |
| <code>f</code> must be a Lua function. | |
| Returns this new coroutine, | |
| an object with type <code>"thread"</code>. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3> | |
| <p> | |
| Starts or continues the execution of coroutine <code>co</code>. | |
| The first time you resume a coroutine, | |
| it starts running its body. | |
| The values <code>val1</code>, ... are passed | |
| as the arguments to the body function. | |
| If the coroutine has yielded, | |
| <code>resume</code> restarts it; | |
| the values <code>val1</code>, ... are passed | |
| as the results from the yield. | |
| <p> | |
| If the coroutine runs without any errors, | |
| <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code> | |
| (if the coroutine yields) or any values returned by the body function | |
| (if the coroutine terminates). | |
| If there is any error, | |
| <code>resume</code> returns <b>false</b> plus the error message. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3> | |
| <p> | |
| Returns the running coroutine plus a boolean, | |
| true when the running coroutine is the main one. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3> | |
| <p> | |
| Returns the status of coroutine <code>co</code>, as a string: | |
| <code>"running"</code>, | |
| if the coroutine is running (that is, it called <code>status</code>); | |
| <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>, | |
| or if it has not started running yet; | |
| <code>"normal"</code> if the coroutine is active but not running | |
| (that is, it has resumed another coroutine); | |
| and <code>"dead"</code> if the coroutine has finished its body function, | |
| or if it has stopped with an error. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3> | |
| <p> | |
| Creates a new coroutine, with body <code>f</code>. | |
| <code>f</code> 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 <code>resume</code>. | |
| Returns the same values returned by <code>resume</code>, | |
| except the first boolean. | |
| In case of error, propagates the error. | |
| <p> | |
| <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3> | |
| <p> | |
| Suspends the execution of the calling coroutine. | |
| Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. | |
| <h2>6.3 – <a name="6.3">Modules</a></h2> | |
| <p> | |
| The package library provides basic | |
| facilities for loading modules in Lua. | |
| It exports one function directly in the global environment: | |
| <a href="#pdf-require"><code>require</code></a>. | |
| Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> | |
| <p> | |
| Loads the given module. | |
| The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table | |
| to determine whether <code>modname</code> is already loaded. | |
| If it is, then <code>require</code> returns the value stored | |
| at <code>package.loaded[modname]</code>. | |
| Otherwise, it tries to find a <em>loader</em> for the module. | |
| <p> | |
| To find a loader, | |
| <code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence. | |
| By changing this sequence, | |
| we can change how <code>require</code> looks for a module. | |
| The following explanation is based on the default configuration | |
| for <a href="#pdf-package.searchers"><code>package.searchers</code></a>. | |
| <p> | |
| First <code>require</code> queries <code>package.preload[modname]</code>. | |
| If it has a value, | |
| this value (which should be a function) is the loader. | |
| Otherwise <code>require</code> searches for a Lua loader using the | |
| path stored in <a href="#pdf-package.path"><code>package.path</code></a>. | |
| If that also fails, it searches for a C loader using the | |
| path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. | |
| If that also fails, | |
| it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>). | |
| <p> | |
| Once a loader is found, | |
| <code>require</code> calls the loader with two arguments: | |
| <code>modname</code> 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, | |
| <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. | |
| If the loader does not return a non-nil value and | |
| has not assigned any value to <code>package.loaded[modname]</code>, | |
| then <code>require</code> assigns <b>true</b> to this entry. | |
| In any case, <code>require</code> returns the | |
| final value of <code>package.loaded[modname]</code>. | |
| <p> | |
| If there is any error loading or running the module, | |
| or if it cannot find any loader for the module, | |
| then <code>require</code> raises an error. | |
| <p> | |
| <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3> | |
| <p> | |
| A string describing some compile-time configurations for packages. | |
| This string is a sequence of lines: | |
| <ul> | |
| <li>The first line is the directory separator string. | |
| Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li> | |
| <li>The second line is the character that separates templates in a path. | |
| Default is '<code>;</code>'.</li> | |
| <li>The third line is the string that marks the | |
| substitution points in a template. | |
| Default is '<code>?</code>'.</li> | |
| <li>The fourth line is a string that, in a path in Windows, | |
| is replaced by the executable's directory. | |
| Default is '<code>!</code>'.</li> | |
| <li>The fifth line is a mark to ignore all text before it | |
| when building the <code>luaopen_</code> function name. | |
| Default is '<code>-</code>'.</li> | |
| </ul> | |
| <p> | |
| <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3> | |
| <p> | |
| The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader. | |
| <p> | |
| Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way | |
| it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, | |
| using the environment variable <a name="pdf-LUA_CPATH_5_2"><code>LUA_CPATH_5_2</code></a> | |
| or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a> | |
| or a default path defined in <code>luaconf.h</code>. | |
| <p> | |
| <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> | |
| <p> | |
| A table used by <a href="#pdf-require"><code>require</code></a> to control which | |
| modules are already loaded. | |
| When you require a module <code>modname</code> and | |
| <code>package.loaded[modname]</code> is not false, | |
| <a href="#pdf-require"><code>require</code></a> simply returns the value stored there. | |
| <p> | |
| This variable is only a reference to the real table; | |
| assignments to this variable do not change the | |
| table used by <a href="#pdf-require"><code>require</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3> | |
| <p> | |
| Dynamically links the host program with the C library <code>libname</code>. | |
| <p> | |
| If <code>funcname</code> is "<code>*</code>", | |
| 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 <code>funcname</code> inside the library | |
| and returns this function as a C function. | |
| So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype | |
| (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). | |
| <p> | |
| This is a low-level function. | |
| It completely bypasses the package and module system. | |
| Unlike <a href="#pdf-require"><code>require</code></a>, | |
| it does not perform any path searching and | |
| does not automatically adds extensions. | |
| <code>libname</code> must be the complete file name of the C library, | |
| including if necessary a path and an extension. | |
| <code>funcname</code> must be the exact name exported by the C library | |
| (which may depend on the C compiler and linker used). | |
| <p> | |
| 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 <code>dlfcn</code> standard). | |
| <p> | |
| <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3> | |
| <p> | |
| The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader. | |
| <p> | |
| At start-up, Lua initializes this variable with | |
| the value of the environment variable <a name="pdf-LUA_PATH_5_2"><code>LUA_PATH_5_2</code></a> or | |
| the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or | |
| with a default path defined in <code>luaconf.h</code>, | |
| if those environment variables are not defined. | |
| Any "<code>;;</code>" in the value of the environment variable | |
| is replaced by the default path. | |
| <p> | |
| <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> | |
| <p> | |
| A table to store loaders for specific modules | |
| (see <a href="#pdf-require"><code>require</code></a>). | |
| <p> | |
| This variable is only a reference to the real table; | |
| assignments to this variable do not change the | |
| table used by <a href="#pdf-require"><code>require</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3> | |
| <p> | |
| A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. | |
| <p> | |
| Each entry in this table is a <em>searcher function</em>. | |
| When looking for a module, | |
| <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, | |
| with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its | |
| sole parameter. | |
| The function can return another function (the module <em>loader</em>) | |
| plus an extra value that will be passed to that loader, | |
| or a string explaining why it did not find that module | |
| (or <b>nil</b> if it has nothing to say). | |
| <p> | |
| Lua initializes this table with four searcher functions. | |
| <p> | |
| The first searcher simply looks for a loader in the | |
| <a href="#pdf-package.preload"><code>package.preload</code></a> table. | |
| <p> | |
| The second searcher looks for a loader as a Lua library, | |
| using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. | |
| The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. | |
| <p> | |
| The third searcher looks for a loader as a C library, | |
| using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. | |
| Again, | |
| the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. | |
| For instance, | |
| if the C path is the string | |
| <pre> | |
| "./?.so;./?.dll;/usr/local/?/init.so" | |
| </pre><p> | |
| the searcher for module <code>foo</code> | |
| will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, | |
| and <code>/usr/local/foo/init.so</code>, 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 "<code>luaopen_</code>" | |
| concatenated with a copy of the module name where each dot | |
| is replaced by an underscore. | |
| Moreover, if the module name has a hyphen, | |
| its prefix up to (and including) the first hyphen is removed. | |
| For instance, if the module name is <code>a.v1-b.c</code>, | |
| the function name will be <code>luaopen_b_c</code>. | |
| <p> | |
| The fourth searcher tries an <em>all-in-one loader</em>. | |
| It searches the C path for a library for | |
| the root name of the given module. | |
| For instance, when requiring <code>a.b.c</code>, | |
| it will search for a C library for <code>a</code>. | |
| If found, it looks into it for an open function for | |
| the submodule; | |
| in our example, that would be <code>luaopen_a_b_c</code>. | |
| With this facility, a package can pack several C submodules | |
| into one single library, | |
| with each submodule keeping its original open function. | |
| <p> | |
| All searchers except the first one (preload) return as the extra value | |
| the file name where the module was found, | |
| as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. | |
| The first searcher returns no extra value. | |
| <p> | |
| <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3> | |
| <p> | |
| Searches for the given <code>name</code> in the given <code>path</code>. | |
| <p> | |
| A path is a string containing a sequence of | |
| <em>templates</em> separated by semicolons. | |
| For each template, | |
| the function replaces each interrogation mark (if any) | |
| in the template with a copy of <code>name</code> | |
| wherein all occurrences of <code>sep</code> | |
| (a dot, by default) | |
| were replaced by <code>rep</code> | |
| (the system's directory separator, by default), | |
| and then tries to open the resulting file name. | |
| <p> | |
| For instance, if the path is the string | |
| <pre> | |
| "./?.lua;./?.lc;/usr/local/?/init.lua" | |
| </pre><p> | |
| the search for the name <code>foo.a</code> | |
| will try to open the files | |
| <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and | |
| <code>/usr/local/foo/a/init.lua</code>, in that order. | |
| <p> | |
| Returns the resulting name of the first file that it can | |
| open in read mode (after closing the file), | |
| or <b>nil</b> plus an error message if none succeeds. | |
| (This error message lists all file names it tried to open.) | |
| <h2>6.4 – <a name="6.4">String Manipulation</a></h2> | |
| <p> | |
| 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. | |
| <p> | |
| The string library provides all its functions inside the table | |
| <a name="pdf-string"><code>string</code></a>. | |
| It also sets a metatable for strings | |
| where the <code>__index</code> field points to the <code>string</code> table. | |
| Therefore, you can use the string functions in object-oriented style. | |
| For instance, <code>string.byte(s,i)</code> | |
| can be written as <code>s:byte(i)</code>. | |
| <p> | |
| The string library assumes one-byte character encodings. | |
| <p> | |
| <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> | |
| Returns the internal numerical codes of the characters <code>s[i]</code>, | |
| <code>s[i+1]</code>, ..., <code>s[j]</code>. | |
| The default value for <code>i</code> is 1; | |
| the default value for <code>j</code> is <code>i</code>. | |
| These indices are corrected | |
| following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>. | |
| <p> | |
| Numerical codes are not necessarily portable across platforms. | |
| <p> | |
| <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3> | |
| 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. | |
| <p> | |
| Numerical codes are not necessarily portable across platforms. | |
| <p> | |
| <hr><h3><a name="pdf-string.dump"><code>string.dump (function)</code></a></h3> | |
| <p> | |
| Returns a string containing a binary representation of the given function, | |
| so that a later <a href="#pdf-load"><code>load</code></a> on this string returns | |
| a copy of the function (but with new upvalues). | |
| <p> | |
| <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> | |
| <p> | |
| Looks for the first match of | |
| <code>pattern</code> in the string <code>s</code>. | |
| If it finds a match, then <code>find</code> returns the indices of <code>s</code> | |
| where this occurrence starts and ends; | |
| otherwise, it returns <b>nil</b>. | |
| A third, optional numerical argument <code>init</code> specifies | |
| where to start the search; | |
| its default value is 1 and can be negative. | |
| A value of <b>true</b> as a fourth, optional argument <code>plain</code> | |
| turns off the pattern matching facilities, | |
| so the function does a plain "find substring" operation, | |
| with no characters in <code>pattern</code> being considered magic. | |
| Note that if <code>plain</code> is given, then <code>init</code> must be given as well. | |
| <p> | |
| If the pattern has captures, | |
| then in a successful match | |
| the captured values are also returned, | |
| after the two indices. | |
| <p> | |
| <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> | |
| <p> | |
| 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 ANSI C function <code>sprintf</code>. | |
| The only differences are that the options/modifiers | |
| <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>, | |
| and <code>p</code> are not supported | |
| and that there is an extra option, <code>q</code>. | |
| The <code>q</code> 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 | |
| <pre> | |
| string.format('%q', 'a string with "quotes" and \n new line') | |
| </pre><p> | |
| may produce the string: | |
| <pre> | |
| "a string with \"quotes\" and \ | |
| new line" | |
| </pre> | |
| <p> | |
| Options | |
| <code>A</code> and <code>a</code> (when available), | |
| <code>E</code>, <code>e</code>, <code>f</code>, | |
| <code>G</code>, and <code>g</code> all expect a number as argument. | |
| Options <code>c</code>, <code>d</code>, | |
| <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> | |
| also expect a number, | |
| but the range of that number may be limited by | |
| the underlying C implementation. | |
| For options <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code>, | |
| the number cannot be negative. | |
| Option <code>q</code> expects a string; | |
| option <code>s</code> expects a string without embedded zeros. | |
| If the argument to option <code>s</code> is not a string, | |
| it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3> | |
| Returns an iterator function that, | |
| each time it is called, | |
| returns the next captures from <code>pattern</code> over the string <code>s</code>. | |
| If <code>pattern</code> specifies no captures, | |
| then the whole match is produced in each call. | |
| <p> | |
| As an example, the following loop | |
| will iterate over all the words from string <code>s</code>, | |
| printing one per line: | |
| <pre> | |
| s = "hello world from Lua" | |
| for w in string.gmatch(s, "%a+") do | |
| print(w) | |
| end | |
| </pre><p> | |
| The next example collects all pairs <code>key=value</code> from the | |
| given string into a table: | |
| <pre> | |
| t = {} | |
| s = "from=world, to=Lua" | |
| for k, v in string.gmatch(s, "(%w+)=(%w+)") do | |
| t[k] = v | |
| end | |
| </pre> | |
| <p> | |
| For this function, a caret '<code>^</code>' at the start of a pattern does not | |
| work as an anchor, as this would prevent the iteration. | |
| <p> | |
| <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> | |
| Returns a copy of <code>s</code> | |
| in which all (or the first <code>n</code>, if given) | |
| occurrences of the <code>pattern</code> have been | |
| replaced by a replacement string specified by <code>repl</code>, | |
| which can be a string, a table, or a function. | |
| <code>gsub</code> also returns, as its second value, | |
| the total number of matches that occurred. | |
| The name <code>gsub</code> comes from <em>Global SUBstitution</em>. | |
| <p> | |
| If <code>repl</code> is a string, then its value is used for replacement. | |
| The character <code>%</code> works as an escape character: | |
| any sequence in <code>repl</code> of the form <code>%<em>d</em></code>, | |
| with <em>d</em> between 1 and 9, | |
| stands for the value of the <em>d</em>-th captured substring. | |
| The sequence <code>%0</code> stands for the whole match. | |
| The sequence <code>%%</code> stands for a single <code>%</code>. | |
| <p> | |
| If <code>repl</code> is a table, then the table is queried for every match, | |
| using the first capture as the key. | |
| <p> | |
| If <code>repl</code> is a function, then this function is called every time a | |
| match occurs, with all captured substrings passed as arguments, | |
| in order. | |
| <p> | |
| In any case, | |
| if the pattern specifies no captures, | |
| then it behaves as if the whole pattern was inside a capture. | |
| <p> | |
| 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 <b>false</b> or <b>nil</b>, | |
| then there is no replacement | |
| (that is, the original match is kept in the string). | |
| <p> | |
| Here are some examples: | |
| <pre> | |
| 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="5.2"} | |
| x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) | |
| --> x="lua-5.2.tar.gz" | |
| </pre> | |
| <p> | |
| <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3> | |
| Receives a string and returns its length. | |
| The empty string <code>""</code> has length 0. | |
| Embedded zeros are counted, | |
| so <code>"a\000bc\000"</code> has length 5. | |
| <p> | |
| <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3> | |
| 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. | |
| <p> | |
| <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3> | |
| Looks for the first <em>match</em> of | |
| <code>pattern</code> in the string <code>s</code>. | |
| If it finds one, then <code>match</code> returns | |
| the captures from the pattern; | |
| otherwise it returns <b>nil</b>. | |
| If <code>pattern</code> specifies no captures, | |
| then the whole match is returned. | |
| A third, optional numerical argument <code>init</code> specifies | |
| where to start the search; | |
| its default value is 1 and can be negative. | |
| <p> | |
| <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3> | |
| Returns a string that is the concatenation of <code>n</code> copies of | |
| the string <code>s</code> separated by the string <code>sep</code>. | |
| The default value for <code>sep</code> is the empty string | |
| (that is, no separator). | |
| <p> | |
| <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> | |
| Returns a string that is the string <code>s</code> reversed. | |
| <p> | |
| <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> | |
| Returns the substring of <code>s</code> that | |
| starts at <code>i</code> and continues until <code>j</code>; | |
| <code>i</code> and <code>j</code> can be negative. | |
| If <code>j</code> is absent, then it is assumed to be equal to -1 | |
| (which is the same as the string length). | |
| In particular, | |
| the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> | |
| with length <code>j</code>, | |
| and <code>string.sub(s, -i)</code> returns a suffix of <code>s</code> | |
| with length <code>i</code>. | |
| <p> | |
| If, after the translation of negative indices, | |
| <code>i</code> is less than 1, | |
| it is corrected to 1. | |
| If <code>j</code> is greater than the string length, | |
| it is corrected to that length. | |
| If, after these corrections, | |
| <code>i</code> is greater than <code>j</code>, | |
| the function returns the empty string. | |
| <p> | |
| <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3> | |
| 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. | |
| <h3>6.4.1 – <a name="6.4.1">Patterns</a></h3> | |
| <h4>Character Class:</h4><p> | |
| A <em>character class</em> is used to represent a set of characters. | |
| The following combinations are allowed in describing a character class: | |
| <ul> | |
| <li><b><em>x</em>: </b> | |
| (where <em>x</em> is not one of the <em>magic characters</em> | |
| <code>^$()%.[]*+-?</code>) | |
| represents the character <em>x</em> itself. | |
| </li> | |
| <li><b><code>.</code>: </b> (a dot) represents all characters.</li> | |
| <li><b><code>%a</code>: </b> represents all letters.</li> | |
| <li><b><code>%c</code>: </b> represents all control characters.</li> | |
| <li><b><code>%d</code>: </b> represents all digits.</li> | |
| <li><b><code>%g</code>: </b> represents all printable characters except space.</li> | |
| <li><b><code>%l</code>: </b> represents all lowercase letters.</li> | |
| <li><b><code>%p</code>: </b> represents all punctuation characters.</li> | |
| <li><b><code>%s</code>: </b> represents all space characters.</li> | |
| <li><b><code>%u</code>: </b> represents all uppercase letters.</li> | |
| <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li> | |
| <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li> | |
| <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character) | |
| represents the character <em>x</em>. | |
| This is the standard way to escape the magic characters. | |
| Any punctuation character (even the non magic) | |
| can be preceded by a '<code>%</code>' | |
| when used to represent itself in a pattern. | |
| </li> | |
| <li><b><code>[<em>set</em>]</code>: </b> | |
| represents the class which is the union of all | |
| characters in <em>set</em>. | |
| A range of characters can be specified by | |
| separating the end characters of the range, | |
| in ascending order, with a '<code>-</code>', | |
| All classes <code>%</code><em>x</em> described above can also be used as | |
| components in <em>set</em>. | |
| All other characters in <em>set</em> represent themselves. | |
| For example, <code>[%w_]</code> (or <code>[_%w]</code>) | |
| represents all alphanumeric characters plus the underscore, | |
| <code>[0-7]</code> represents the octal digits, | |
| and <code>[0-7%l%-]</code> represents the octal digits plus | |
| the lowercase letters plus the '<code>-</code>' character. | |
| <p> | |
| The interaction between ranges and classes is not defined. | |
| Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> | |
| have no meaning. | |
| </li> | |
| <li><b><code>[^<em>set</em>]</code>: </b> | |
| represents the complement of <em>set</em>, | |
| where <em>set</em> is interpreted as above. | |
| </li> | |
| </ul><p> | |
| For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), | |
| the corresponding uppercase letter represents the complement of the class. | |
| For instance, <code>%S</code> represents all non-space characters. | |
| <p> | |
| The definitions of letter, space, and other character groups | |
| depend on the current locale. | |
| In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. | |
| <h4>Pattern Item:</h4><p> | |
| A <em>pattern item</em> can be | |
| <ul> | |
| <li> | |
| a single character class, | |
| which matches any single character in the class; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>*</code>', | |
| which matches 0 or more repetitions of characters in the class. | |
| These repetition items will always match the longest possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>+</code>', | |
| which matches 1 or more repetitions of characters in the class. | |
| These repetition items will always match the longest possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>-</code>', | |
| which also matches 0 or more repetitions of characters in the class. | |
| Unlike '<code>*</code>', | |
| these repetition items will always match the shortest possible sequence; | |
| </li> | |
| <li> | |
| a single character class followed by '<code>?</code>', | |
| which matches 0 or 1 occurrence of a character in the class; | |
| </li> | |
| <li> | |
| <code>%<em>n</em></code>, for <em>n</em> between 1 and 9; | |
| such item matches a substring equal to the <em>n</em>-th captured string | |
| (see below); | |
| </li> | |
| <li> | |
| <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters; | |
| such item matches strings that start with <em>x</em>, end with <em>y</em>, | |
| and where the <em>x</em> and <em>y</em> are <em>balanced</em>. | |
| This means that, if one reads the string from left to right, | |
| counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>, | |
| the ending <em>y</em> is the first <em>y</em> where the count reaches 0. | |
| For instance, the item <code>%b()</code> matches expressions with | |
| balanced parentheses. | |
| </li> | |
| <li> | |
| <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>; | |
| such item matches an empty string at any position such that | |
| the next character belongs to <em>set</em> | |
| and the previous character does not belong to <em>set</em>. | |
| The set <em>set</em> is interpreted as previously described. | |
| The beginning and the end of the subject are handled as if | |
| they were the character '<code>\0</code>'. | |
| </li> | |
| </ul> | |
| <h4>Pattern:</h4><p> | |
| A <em>pattern</em> is a sequence of pattern items. | |
| A caret '<code>^</code>' at the beginning of a pattern anchors the match at the | |
| beginning of the subject string. | |
| A '<code>$</code>' at the end of a pattern anchors the match at the | |
| end of the subject string. | |
| At other positions, | |
| '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. | |
| <h4>Captures:</h4><p> | |
| A pattern can contain sub-patterns enclosed in parentheses; | |
| they describe <em>captures</em>. | |
| When a match succeeds, the substrings of the subject string | |
| that match captures are stored (<em>captured</em>) for future use. | |
| Captures are numbered according to their left parentheses. | |
| For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, | |
| the part of the string matching <code>"a*(.)%w(%s*)"</code> is | |
| stored as the first capture (and therefore has number 1); | |
| the character matching "<code>.</code>" is captured with number 2, | |
| and the part matching "<code>%s*</code>" has number 3. | |
| <p> | |
| As a special case, the empty capture <code>()</code> captures | |
| the current string position (a number). | |
| For instance, if we apply the pattern <code>"()aa()"</code> on the | |
| string <code>"flaaap"</code>, there will be two captures: 3 and 5. | |
| <h2>6.5 – <a name="6.5">Table Manipulation</a></h2> | |
| <p> | |
| This library provides generic functions for table manipulation. | |
| It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>. | |
| <p> | |
| Remember that, whenever an operation needs the length of a table, | |
| the table should be a proper sequence | |
| or have a <code>__len</code> metamethod (see <a href="#3.4.6">§3.4.6</a>). | |
| All functions ignore non-numeric keys | |
| in tables given as arguments. | |
| <p> | |
| For performance reasons, | |
| all table accesses (get/set) performed by these functions are raw. | |
| <p> | |
| <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3> | |
| <p> | |
| Given a list where all elements are strings or numbers, | |
| returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>. | |
| The default value for <code>sep</code> is the empty string, | |
| the default for <code>i</code> is 1, | |
| and the default for <code>j</code> is <code>#list</code>. | |
| If <code>i</code> is greater than <code>j</code>, returns the empty string. | |
| <p> | |
| <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3> | |
| <p> | |
| Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>, | |
| shifting up the elements | |
| <code>list[pos], list[pos+1], ···, list[#list]</code>. | |
| The default value for <code>pos</code> is <code>#list+1</code>, | |
| so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end | |
| of list <code>t</code>. | |
| <p> | |
| <hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3> | |
| <p> | |
| Returns a new table with all parameters stored into keys 1, 2, etc. | |
| and with a field "<code>n</code>" with the total number of parameters. | |
| Note that the resulting table may not be a sequence. | |
| <p> | |
| <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3> | |
| <p> | |
| Removes from <code>list</code> the element at position <code>pos</code>, | |
| returning the value of the removed element. | |
| When <code>pos</code> is an integer between 1 and <code>#list</code>, | |
| it shifts down the elements | |
| <code>list[pos+1], list[pos+2], ···, list[#list]</code> | |
| and erases element <code>list[#list]</code>; | |
| The index <code>pos</code> can also be 0 when <code>#list</code> is 0, | |
| or <code>#list + 1</code>; | |
| in those cases, the function erases the element <code>list[pos]</code>. | |
| <p> | |
| The default value for <code>pos</code> is <code>#list</code>, | |
| so that a call <code>table.remove(t)</code> removes the last element | |
| of list <code>t</code>. | |
| <p> | |
| <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3> | |
| <p> | |
| Sorts list elements in a given order, <em>in-place</em>, | |
| from <code>list[1]</code> to <code>list[#list]</code>. | |
| If <code>comp</code> 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 <code>not comp(list[i+1],list[i])</code> will be true after the sort). | |
| If <code>comp</code> is not given, | |
| then the standard Lua operator <code><</code> is used instead. | |
| <p> | |
| The sort algorithm is not stable; | |
| that is, elements considered equal by the given order | |
| may have their relative positions changed by the sort. | |
| <p> | |
| <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3> | |
| <p> | |
| Returns the elements from the given table. | |
| This function is equivalent to | |
| <pre> | |
| return list[i], list[i+1], ···, list[j] | |
| </pre><p> | |
| By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>. | |
| <h2>6.6 – <a name="6.6">Mathematical Functions</a></h2> | |
| <p> | |
| This library is an interface to the standard C math library. | |
| It provides all its functions inside the table <a name="pdf-math"><code>math</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> | |
| <p> | |
| Returns the absolute value of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3> | |
| <p> | |
| Returns the arc cosine of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3> | |
| <p> | |
| Returns the arc sine of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.atan"><code>math.atan (x)</code></a></h3> | |
| <p> | |
| Returns the arc tangent of <code>x</code> (in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.atan2"><code>math.atan2 (y, x)</code></a></h3> | |
| <p> | |
| Returns the arc tangent of <code>y/x</code> (in radians), | |
| but uses the signs of both parameters to find the | |
| quadrant of the result. | |
| (It also handles correctly the case of <code>x</code> being zero.) | |
| <p> | |
| <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> | |
| <p> | |
| Returns the smallest integer larger than or equal to <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3> | |
| <p> | |
| Returns the cosine of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.cosh"><code>math.cosh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic cosine of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3> | |
| <p> | |
| Returns the angle <code>x</code> (given in radians) in degrees. | |
| <p> | |
| <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> | |
| <p> | |
| Returns the value <em>e<sup>x</sup></em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> | |
| <p> | |
| Returns the largest integer smaller than or equal to <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> | |
| <p> | |
| Returns the remainder of the division of <code>x</code> by <code>y</code> | |
| that rounds the quotient towards zero. | |
| <p> | |
| <hr><h3><a name="pdf-math.frexp"><code>math.frexp (x)</code></a></h3> | |
| <p> | |
| Returns <code>m</code> and <code>e</code> such that <em>x = m2<sup>e</sup></em>, | |
| <code>e</code> is an integer and the absolute value of <code>m</code> is | |
| in the range <em>[0.5, 1)</em> | |
| (or zero when <code>x</code> is zero). | |
| <p> | |
| <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> | |
| <p> | |
| The value <code>HUGE_VAL</code>, | |
| a value larger than or equal to any other numerical value. | |
| <p> | |
| <hr><h3><a name="pdf-math.ldexp"><code>math.ldexp (m, e)</code></a></h3> | |
| <p> | |
| Returns <em>m2<sup>e</sup></em> (<code>e</code> should be an integer). | |
| <p> | |
| <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3> | |
| <p> | |
| Returns the logarithm of <code>x</code> in the given base. | |
| The default for <code>base</code> is <em>e</em> | |
| (so that the function returns the natural logarithm of <code>x</code>). | |
| <p> | |
| <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> | |
| <p> | |
| Returns the maximum value among its arguments. | |
| <p> | |
| <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> | |
| <p> | |
| Returns the minimum value among its arguments. | |
| <p> | |
| <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> | |
| <p> | |
| Returns two numbers, | |
| the integral part of <code>x</code> and the fractional part of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> | |
| <p> | |
| The value of <em>π</em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.pow"><code>math.pow (x, y)</code></a></h3> | |
| <p> | |
| Returns <em>x<sup>y</sup></em>. | |
| (You can also use the expression <code>x^y</code> to compute this value.) | |
| <p> | |
| <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> | |
| <p> | |
| Returns the angle <code>x</code> (given in degrees) in radians. | |
| <p> | |
| <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> | |
| <p> | |
| This function is an interface to the simple | |
| pseudo-random generator function <code>rand</code> provided by Standard C. | |
| (No guarantees can be given for its statistical properties.) | |
| <p> | |
| When called without arguments, | |
| returns a uniform pseudo-random real number | |
| in the range <em>[0,1)</em>. | |
| When called with an integer number <code>m</code>, | |
| <code>math.random</code> returns | |
| a uniform pseudo-random integer in the range <em>[1, m]</em>. | |
| When called with two integer numbers <code>m</code> and <code>n</code>, | |
| <code>math.random</code> returns a uniform pseudo-random | |
| integer in the range <em>[m, n]</em>. | |
| <p> | |
| <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3> | |
| <p> | |
| Sets <code>x</code> as the "seed" | |
| for the pseudo-random generator: | |
| equal seeds produce equal sequences of numbers. | |
| <p> | |
| <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3> | |
| <p> | |
| Returns the sine of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.sinh"><code>math.sinh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic sine of <code>x</code>. | |
| <p> | |
| <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3> | |
| <p> | |
| Returns the square root of <code>x</code>. | |
| (You can also use the expression <code>x^0.5</code> to compute this value.) | |
| <p> | |
| <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3> | |
| <p> | |
| Returns the tangent of <code>x</code> (assumed to be in radians). | |
| <p> | |
| <hr><h3><a name="pdf-math.tanh"><code>math.tanh (x)</code></a></h3> | |
| <p> | |
| Returns the hyperbolic tangent of <code>x</code>. | |
| <h2>6.7 – <a name="6.7">Bitwise Operations</a></h2> | |
| <p> | |
| This library provides bitwise operations. | |
| It provides all its functions inside the table <a name="pdf-bit32"><code>bit32</code></a>. | |
| <p> | |
| Unless otherwise stated, | |
| all functions accept numeric arguments in the range | |
| <em>(-2<sup>51</sup>,+2<sup>51</sup>)</em>; | |
| each argument is normalized to | |
| the remainder of its division by <em>2<sup>32</sup></em> | |
| and truncated to an integer (in some unspecified way), | |
| so that its final value falls in the range <em>[0,2<sup>32</sup> - 1]</em>. | |
| Similarly, all results are in the range <em>[0,2<sup>32</sup> - 1]</em>. | |
| Note that <code>bit32.bnot(0)</code> is <code>0xFFFFFFFF</code>, | |
| which is different from <code>-1</code>. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.arshift"><code>bit32.arshift (x, disp)</code></a></h3> | |
| <p> | |
| Returns the number <code>x</code> shifted <code>disp</code> bits to the right. | |
| The number <code>disp</code> may be any representable integer. | |
| Negative displacements shift to the left. | |
| <p> | |
| This shift operation is what is called arithmetic shift. | |
| Vacant bits on the left are filled | |
| with copies of the higher bit of <code>x</code>; | |
| vacant bits on the right are filled with zeros. | |
| In particular, | |
| displacements with absolute values higher than 31 | |
| result in zero or <code>0xFFFFFFFF</code> (all original bits are shifted out). | |
| <p> | |
| <hr><h3><a name="pdf-bit32.band"><code>bit32.band (···)</code></a></h3> | |
| <p> | |
| Returns the bitwise <em>and</em> of its operands. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.bnot"><code>bit32.bnot (x)</code></a></h3> | |
| <p> | |
| Returns the bitwise negation of <code>x</code>. | |
| For any integer <code>x</code>, | |
| the following identity holds: | |
| <pre> | |
| assert(bit32.bnot(x) == (-1 - x) % 2^32) | |
| </pre> | |
| <p> | |
| <hr><h3><a name="pdf-bit32.bor"><code>bit32.bor (···)</code></a></h3> | |
| <p> | |
| Returns the bitwise <em>or</em> of its operands. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.btest"><code>bit32.btest (···)</code></a></h3> | |
| <p> | |
| Returns a boolean signaling | |
| whether the bitwise <em>and</em> of its operands is different from zero. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.bxor"><code>bit32.bxor (···)</code></a></h3> | |
| <p> | |
| Returns the bitwise <em>exclusive or</em> of its operands. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.extract"><code>bit32.extract (n, field [, width])</code></a></h3> | |
| <p> | |
| Returns the unsigned number formed by the bits | |
| <code>field</code> to <code>field + width - 1</code> from <code>n</code>. | |
| Bits are numbered from 0 (least significant) to 31 (most significant). | |
| All accessed bits must be in the range <em>[0, 31]</em>. | |
| <p> | |
| The default for <code>width</code> is 1. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.replace"><code>bit32.replace (n, v, field [, width])</code></a></h3> | |
| <p> | |
| Returns a copy of <code>n</code> with | |
| the bits <code>field</code> to <code>field + width - 1</code> | |
| replaced by the value <code>v</code>. | |
| See <a href="#pdf-bit32.extract"><code>bit32.extract</code></a> for details about <code>field</code> and <code>width</code>. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.lrotate"><code>bit32.lrotate (x, disp)</code></a></h3> | |
| <p> | |
| Returns the number <code>x</code> rotated <code>disp</code> bits to the left. | |
| The number <code>disp</code> may be any representable integer. | |
| <p> | |
| For any valid displacement, | |
| the following identity holds: | |
| <pre> | |
| assert(bit32.lrotate(x, disp) == bit32.lrotate(x, disp % 32)) | |
| </pre><p> | |
| In particular, | |
| negative displacements rotate to the right. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.lshift"><code>bit32.lshift (x, disp)</code></a></h3> | |
| <p> | |
| Returns the number <code>x</code> shifted <code>disp</code> bits to the left. | |
| The number <code>disp</code> may be any representable integer. | |
| Negative displacements shift to the right. | |
| In any direction, vacant bits are filled with zeros. | |
| In particular, | |
| displacements with absolute values higher than 31 | |
| result in zero (all bits are shifted out). | |
| <p> | |
| For positive displacements, | |
| the following equality holds: | |
| <pre> | |
| assert(bit32.lshift(b, disp) == (b * 2^disp) % 2^32) | |
| </pre> | |
| <p> | |
| <hr><h3><a name="pdf-bit32.rrotate"><code>bit32.rrotate (x, disp)</code></a></h3> | |
| <p> | |
| Returns the number <code>x</code> rotated <code>disp</code> bits to the right. | |
| The number <code>disp</code> may be any representable integer. | |
| <p> | |
| For any valid displacement, | |
| the following identity holds: | |
| <pre> | |
| assert(bit32.rrotate(x, disp) == bit32.rrotate(x, disp % 32)) | |
| </pre><p> | |
| In particular, | |
| negative displacements rotate to the left. | |
| <p> | |
| <hr><h3><a name="pdf-bit32.rshift"><code>bit32.rshift (x, disp)</code></a></h3> | |
| <p> | |
| Returns the number <code>x</code> shifted <code>disp</code> bits to the right. | |
| The number <code>disp</code> may be any representable integer. | |
| Negative displacements shift to the left. | |
| In any direction, vacant bits are filled with zeros. | |
| In particular, | |
| displacements with absolute values higher than 31 | |
| result in zero (all bits are shifted out). | |
| <p> | |
| For positive displacements, | |
| the following equality holds: | |
| <pre> | |
| assert(bit32.rshift(b, disp) == math.floor(b % 2^32 / 2^disp)) | |
| </pre> | |
| <p> | |
| This shift operation is what is called logical shift. | |
| <h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2> | |
| <p> | |
| The I/O library provides two different styles for file manipulation. | |
| The first one uses implicit file descriptors; | |
| that is, there are operations to set a default input file and a | |
| default output file, | |
| and all input/output operations are over these default files. | |
| The second style uses explicit file descriptors. | |
| <p> | |
| When using implicit file descriptors, | |
| all operations are supplied by table <a name="pdf-io"><code>io</code></a>. | |
| When using explicit file descriptors, | |
| the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file descriptor | |
| and then all operations are supplied as methods of the file descriptor. | |
| <p> | |
| The table <code>io</code> also provides | |
| three predefined file descriptors with their usual meanings from C: | |
| <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. | |
| The I/O library never closes these files. | |
| <p> | |
| Unless otherwise stated, | |
| all I/O functions return <b>nil</b> 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 <b>nil</b> 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 <code>errno</code>. | |
| <p> | |
| <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3> | |
| <p> | |
| Equivalent to <code>file:close()</code>. | |
| Without a <code>file</code>, closes the default output file. | |
| <p> | |
| <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3> | |
| <p> | |
| Equivalent to <code>io.output():flush()</code>. | |
| <p> | |
| <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3> | |
| <p> | |
| 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. | |
| <p> | |
| In case of errors this function raises the error, | |
| instead of returning an error code. | |
| <p> | |
| <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename ···])</code></a></h3> | |
| <p> | |
| Opens the given file name in read mode | |
| and returns an iterator function that | |
| works like <code>file:lines(···)</code> over the opened file. | |
| When the iterator function detects the end of file, | |
| it returns <b>nil</b> (to finish the loop) and automatically closes the file. | |
| <p> | |
| The call <code>io.lines()</code> (with no file name) is equivalent | |
| to <code>io.input():lines()</code>; | |
| 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. | |
| <p> | |
| In case of errors this function raises the error, | |
| instead of returning an error code. | |
| <p> | |
| <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3> | |
| <p> | |
| This function opens a file, | |
| in the mode specified in the string <code>mode</code>. | |
| It returns a new file handle, | |
| or, in case of errors, <b>nil</b> plus an error message. | |
| <p> | |
| The <code>mode</code> string can be any of the following: | |
| <ul> | |
| <li><b>"<code>r</code>": </b> read mode (the default);</li> | |
| <li><b>"<code>w</code>": </b> write mode;</li> | |
| <li><b>"<code>a</code>": </b> append mode;</li> | |
| <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li> | |
| <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li> | |
| <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved, | |
| writing is only allowed at the end of file.</li> | |
| </ul><p> | |
| The <code>mode</code> string can also have a '<code>b</code>' at the end, | |
| which is needed in some systems to open the file in binary mode. | |
| <p> | |
| <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3> | |
| <p> | |
| Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. | |
| <p> | |
| <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3> | |
| <p> | |
| This function is system dependent and is not available | |
| on all platforms. | |
| <p> | |
| Starts program <code>prog</code> in a separated process and returns | |
| a file handle that you can use to read data from this program | |
| (if <code>mode</code> is <code>"r"</code>, the default) | |
| or to write data to this program | |
| (if <code>mode</code> is <code>"w"</code>). | |
| <p> | |
| <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3> | |
| <p> | |
| Equivalent to <code>io.input():read(···)</code>. | |
| <p> | |
| <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3> | |
| <p> | |
| Returns a handle for a temporary file. | |
| This file is opened in update mode | |
| and it is automatically removed when the program ends. | |
| <p> | |
| <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3> | |
| <p> | |
| Checks whether <code>obj</code> is a valid file handle. | |
| Returns the string <code>"file"</code> if <code>obj</code> is an open file handle, | |
| <code>"closed file"</code> if <code>obj</code> is a closed file handle, | |
| or <b>nil</b> if <code>obj</code> is not a file handle. | |
| <p> | |
| <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3> | |
| <p> | |
| Equivalent to <code>io.output():write(···)</code>. | |
| <p> | |
| <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3> | |
| <p> | |
| Closes <code>file</code>. | |
| Note that files are automatically closed when | |
| their handles are garbage collected, | |
| but that takes an unpredictable amount of time to happen. | |
| <p> | |
| When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>, | |
| <a href="#pdf-file:close"><code>file:close</code></a> returns the same values | |
| returned by <a href="#pdf-os.execute"><code>os.execute</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3> | |
| <p> | |
| Saves any written data to <code>file</code>. | |
| <p> | |
| <hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3> | |
| <p> | |
| Returns an iterator function that, | |
| each time it is called, | |
| reads the file according to the given formats. | |
| When no format is given, | |
| uses "*l" as a default. | |
| As an example, the construction | |
| <pre> | |
| for c in file:lines(1) do <em>body</em> end | |
| </pre><p> | |
| will iterate over all characters of the file, | |
| starting at the current position. | |
| Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file | |
| when the loop ends. | |
| <p> | |
| In case of errors this function raises the error, | |
| instead of returning an error code. | |
| <p> | |
| <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3> | |
| <p> | |
| Reads the file <code>file</code>, | |
| 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 <b>nil</b> if it cannot read data with the specified format. | |
| When called without formats, | |
| it uses a default format that reads the next line | |
| (see below). | |
| <p> | |
| The available formats are | |
| <ul> | |
| <li><b>"<code>*n</code>": </b> | |
| reads a number; | |
| this is the only format that returns a number instead of a string. | |
| </li> | |
| <li><b>"<code>*a</code>": </b> | |
| reads the whole file, starting at the current position. | |
| On end of file, it returns the empty string. | |
| </li> | |
| <li><b>"<code>*l</code>": </b> | |
| reads the next line skipping the end of line, | |
| returning <b>nil</b> on end of file. | |
| This is the default format. | |
| </li> | |
| <li><b>"<code>*L</code>": </b> | |
| reads the next line keeping the end of line (if present), | |
| returning <b>nil</b> on end of file. | |
| </li> | |
| <li><b><em>number</em>: </b> | |
| reads a string with up to this number of bytes, | |
| returning <b>nil</b> on end of file. | |
| If number is zero, | |
| it reads nothing and returns an empty string, | |
| or <b>nil</b> on end of file. | |
| </li> | |
| </ul> | |
| <p> | |
| <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3> | |
| <p> | |
| Sets and gets the file position, | |
| measured from the beginning of the file, | |
| to the position given by <code>offset</code> plus a base | |
| specified by the string <code>whence</code>, as follows: | |
| <ul> | |
| <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li> | |
| <li><b>"<code>cur</code>": </b> base is current position;</li> | |
| <li><b>"<code>end</code>": </b> base is end of file;</li> | |
| </ul><p> | |
| In case of success, <code>seek</code> returns the final file position, | |
| measured in bytes from the beginning of the file. | |
| If <code>seek</code> fails, it returns <b>nil</b>, | |
| plus a string describing the error. | |
| <p> | |
| The default value for <code>whence</code> is <code>"cur"</code>, | |
| and for <code>offset</code> is 0. | |
| Therefore, the call <code>file:seek()</code> returns the current | |
| file position, without changing it; | |
| the call <code>file:seek("set")</code> sets the position to the | |
| beginning of the file (and returns 0); | |
| and the call <code>file:seek("end")</code> sets the position to the | |
| end of the file, and returns its size. | |
| <p> | |
| <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3> | |
| <p> | |
| Sets the buffering mode for an output file. | |
| There are three available modes: | |
| <ul> | |
| <li><b>"<code>no</code>": </b> | |
| no buffering; the result of any output operation appears immediately. | |
| </li> | |
| <li><b>"<code>full</code>": </b> | |
| full buffering; output operation is performed only | |
| when the buffer is full or when | |
| you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>). | |
| </li> | |
| <li><b>"<code>line</code>": </b> | |
| line buffering; output is buffered until a newline is output | |
| or there is any input from some special files | |
| (such as a terminal device). | |
| </li> | |
| </ul><p> | |
| For the last two cases, <code>size</code> | |
| specifies the size of the buffer, in bytes. | |
| The default is an appropriate size. | |
| <p> | |
| <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3> | |
| <p> | |
| Writes the value of each of its arguments to <code>file</code>. | |
| The arguments must be strings or numbers. | |
| <p> | |
| In case of success, this function returns <code>file</code>. | |
| Otherwise it returns <b>nil</b> plus a string describing the error. | |
| <h2>6.9 – <a name="6.9">Operating System Facilities</a></h2> | |
| <p> | |
| This library is implemented through table <a name="pdf-os"><code>os</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3> | |
| <p> | |
| Returns an approximation of the amount in seconds of CPU time | |
| used by the program. | |
| <p> | |
| <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3> | |
| <p> | |
| Returns a string or a table containing date and time, | |
| formatted according to the given string <code>format</code>. | |
| <p> | |
| If the <code>time</code> argument is present, | |
| this is the time to be formatted | |
| (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value). | |
| Otherwise, <code>date</code> formats the current time. | |
| <p> | |
| If <code>format</code> starts with '<code>!</code>', | |
| then the date is formatted in Coordinated Universal Time. | |
| After this optional character, | |
| if <code>format</code> is the string "<code>*t</code>", | |
| then <code>date</code> returns a table with the following fields: | |
| <code>year</code> (four digits), <code>month</code> (1–12), <code>day</code> (1–31), | |
| <code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61), | |
| <code>wday</code> (weekday, Sunday is 1), | |
| <code>yday</code> (day of the year), | |
| and <code>isdst</code> (daylight saving flag, a boolean). | |
| This last field may be absent | |
| if the information is not available. | |
| <p> | |
| If <code>format</code> is not "<code>*t</code>", | |
| then <code>date</code> returns the date as a string, | |
| formatted according to the same rules as the ANSI C function <code>strftime</code>. | |
| <p> | |
| When called without arguments, | |
| <code>date</code> returns a reasonable date and time representation that depends on | |
| the host system and on the current locale | |
| (that is, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>). | |
| <p> | |
| On non-Posix systems, | |
| this function may be not thread safe | |
| because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>. | |
| <p> | |
| <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> | |
| <p> | |
| Returns the number of seconds from time <code>t1</code> to time <code>t2</code>. | |
| In POSIX, Windows, and some other systems, | |
| this value is exactly <code>t2</code><em>-</em><code>t1</code>. | |
| <p> | |
| <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3> | |
| <p> | |
| This function is equivalent to the ANSI C function <code>system</code>. | |
| It passes <code>command</code> to be executed by an operating system shell. | |
| Its first result is <b>true</b> | |
| if the command terminated successfully, | |
| or <b>nil</b> otherwise. | |
| After this first result | |
| the function returns a string and a number, | |
| as follows: | |
| <ul> | |
| <li><b>"<code>exit</code>": </b> | |
| the command terminated normally; | |
| the following number is the exit status of the command. | |
| </li> | |
| <li><b>"<code>signal</code>": </b> | |
| the command was terminated by a signal; | |
| the following number is the signal that terminated the command. | |
| </li> | |
| </ul> | |
| <p> | |
| When called without a <code>command</code>, | |
| <code>os.execute</code> returns a boolean that is true if a shell is available. | |
| <p> | |
| <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close])</code></a></h3> | |
| <p> | |
| Calls the ANSI C function <code>exit</code> to terminate the host program. | |
| If <code>code</code> is <b>true</b>, | |
| the returned status is <code>EXIT_SUCCESS</code>; | |
| if <code>code</code> is <b>false</b>, | |
| the returned status is <code>EXIT_FAILURE</code>; | |
| if <code>code</code> is a number, | |
| the returned status is this number. | |
| The default value for <code>code</code> is <b>true</b>. | |
| <p> | |
| If the optional second argument <code>close</code> is true, | |
| closes the Lua state before exiting. | |
| <p> | |
| <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3> | |
| <p> | |
| Returns the value of the process environment variable <code>varname</code>, | |
| or <b>nil</b> if the variable is not defined. | |
| <p> | |
| <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3> | |
| <p> | |
| Deletes the file (or empty directory, on POSIX systems) | |
| with the given name. | |
| If this function fails, it returns <b>nil</b>, | |
| plus a string describing the error and the error code. | |
| <p> | |
| <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3> | |
| <p> | |
| Renames file or directory named <code>oldname</code> to <code>newname</code>. | |
| If this function fails, it returns <b>nil</b>, | |
| plus a string describing the error and the error code. | |
| <p> | |
| <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3> | |
| <p> | |
| Sets the current locale of the program. | |
| <code>locale</code> is a system-dependent string specifying a locale; | |
| <code>category</code> is an optional string describing which category to change: | |
| <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, | |
| <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; | |
| the default category is <code>"all"</code>. | |
| The function returns the name of the new locale, | |
| or <b>nil</b> if the request cannot be honored. | |
| <p> | |
| If <code>locale</code> is the empty string, | |
| the current locale is set to an implementation-defined native locale. | |
| If <code>locale</code> is the string "<code>C</code>", | |
| the current locale is set to the standard C locale. | |
| <p> | |
| When called with <b>nil</b> as the first argument, | |
| this function only returns the name of the current locale | |
| for the given category. | |
| <p> | |
| This function may be not thread safe | |
| because of its reliance on C function <code>setlocale</code>. | |
| <p> | |
| <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3> | |
| <p> | |
| 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 <code>year</code>, <code>month</code>, and <code>day</code>, | |
| and may have fields | |
| <code>hour</code> (default is 12), | |
| <code>min</code> (default is 0), | |
| <code>sec</code> (default is 0), | |
| and <code>isdst</code> (default is <b>nil</b>). | |
| For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function. | |
| <p> | |
| 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 <code>time</code> can be used only as an argument to | |
| <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>. | |
| <p> | |
| <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> | |
| <p> | |
| 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. | |
| <p> | |
| 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). | |
| <p> | |
| When possible, | |
| you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, | |
| which automatically removes the file when the program ends. | |
| <h2>6.10 – <a name="6.10">The Debug Library</a></h2> | |
| <p> | |
| This library provides | |
| the functionality of the debug interface (<a href="#4.9">§4.9</a>) 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. | |
| <p> | |
| All functions in this library are provided | |
| inside the <a name="pdf-debug"><code>debug</code></a> 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. | |
| <p> | |
| <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3> | |
| <p> | |
| 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 <code>cont</code> finishes this function, | |
| so that the caller continues its execution. | |
| <p> | |
| Note that commands for <code>debug.debug</code> are not lexically nested | |
| within any function and so have no direct access to local variables. | |
| <p> | |
| <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3> | |
| <p> | |
| 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 <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). | |
| <p> | |
| <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3> | |
| <p> | |
| Returns a table with information about a function. | |
| You can give the function directly | |
| or you can give a number as the value of <code>f</code>, | |
| which means the function running at level <code>f</code> of the call stack | |
| of the given thread: | |
| level 0 is the current function (<code>getinfo</code> itself); | |
| level 1 is the function that called <code>getinfo</code> | |
| (except for tail calls, which do not count on the stack); | |
| and so on. | |
| If <code>f</code> is a number larger than the number of active functions, | |
| then <code>getinfo</code> returns <b>nil</b>. | |
| <p> | |
| The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, | |
| with the string <code>what</code> describing which fields to fill in. | |
| The default for <code>what</code> is to get all information available, | |
| except the table of valid lines. | |
| If present, | |
| the option '<code>f</code>' | |
| adds a field named <code>func</code> with the function itself. | |
| If present, | |
| the option '<code>L</code>' | |
| adds a field named <code>activelines</code> with the table of | |
| valid lines. | |
| <p> | |
| For instance, the expression <code>debug.getinfo(1,"n").name</code> returns | |
| a table with a name for the current function, | |
| if a reasonable name can be found, | |
| and the expression <code>debug.getinfo(print)</code> | |
| returns a table with all available information | |
| about the <a href="#pdf-print"><code>print</code></a> function. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3> | |
| <p> | |
| This function returns the name and the value of the local variable | |
| with index <code>local</code> of the function at level <code>f</code> of the stack. | |
| This function accesses not only explicit local variables, | |
| but also parameters, temporaries, etc. | |
| <p> | |
| The first parameter or local variable has index 1, and so on, | |
| until the last active variable. | |
| Negative indices refer to vararg parameters; | |
| -1 is the first vararg parameter. | |
| The function returns <b>nil</b> if there is no variable with the given index, | |
| and raises an error when called with a level out of range. | |
| (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.) | |
| <p> | |
| Variable names starting with '<code>(</code>' (open parenthesis) | |
| represent internal variables | |
| (loop control variables, temporaries, varargs, and C function locals). | |
| <p> | |
| The parameter <code>f</code> may also be a function. | |
| In that case, <code>getlocal</code> returns only the name of function parameters. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3> | |
| <p> | |
| Returns the metatable of the given <code>value</code> | |
| or <b>nil</b> if it does not have a metatable. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3> | |
| <p> | |
| Returns the registry table (see <a href="#4.5">§4.5</a>). | |
| <p> | |
| <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3> | |
| <p> | |
| This function returns the name and the value of the upvalue | |
| with index <code>up</code> of the function <code>f</code>. | |
| The function returns <b>nil</b> if there is no upvalue with the given index. | |
| <p> | |
| <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3> | |
| <p> | |
| Returns the Lua value associated to <code>u</code>. | |
| If <code>u</code> is not a userdata, | |
| returns <b>nil</b>. | |
| <p> | |
| <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3> | |
| <p> | |
| Sets the given function as a hook. | |
| The string <code>mask</code> and the number <code>count</code> describe | |
| when the hook will be called. | |
| The string mask may have the following characters, | |
| with the given meaning: | |
| <ul> | |
| <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li> | |
| <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li> | |
| <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li> | |
| </ul><p> | |
| With a <code>count</code> different from zero, | |
| the hook is called after every <code>count</code> instructions. | |
| <p> | |
| When called without arguments, | |
| <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook. | |
| <p> | |
| When the hook is called, its first parameter is a string | |
| describing the event that has triggered its call: | |
| <code>"call"</code> (or <code>"tail call"</code>), | |
| <code>"return"</code>, | |
| <code>"line"</code>, and <code>"count"</code>. | |
| For line events, | |
| the hook also gets the new line number as its second parameter. | |
| Inside a hook, | |
| you can call <code>getinfo</code> with level 2 to get more information about | |
| the running function | |
| (level 0 is the <code>getinfo</code> function, | |
| and level 1 is the hook function). | |
| <p> | |
| <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3> | |
| <p> | |
| This function assigns the value <code>value</code> to the local variable | |
| with index <code>local</code> of the function at level <code>level</code> of the stack. | |
| The function returns <b>nil</b> if there is no local | |
| variable with the given index, | |
| and raises an error when called with a <code>level</code> out of range. | |
| (You can call <code>getinfo</code> to check whether the level is valid.) | |
| Otherwise, it returns the name of the local variable. | |
| <p> | |
| See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about | |
| variable indices and names. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3> | |
| <p> | |
| Sets the metatable for the given <code>value</code> to the given <code>table</code> | |
| (which can be <b>nil</b>). | |
| Returns <code>value</code>. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3> | |
| <p> | |
| This function assigns the value <code>value</code> to the upvalue | |
| with index <code>up</code> of the function <code>f</code>. | |
| The function returns <b>nil</b> if there is no upvalue | |
| with the given index. | |
| Otherwise, it returns the name of the upvalue. | |
| <p> | |
| <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3> | |
| <p> | |
| Sets the given <code>value</code> as | |
| the Lua value associated to the given <code>udata</code>. | |
| <code>value</code> must be a table or <b>nil</b>; | |
| <code>udata</code> must be a full userdata. | |
| <p> | |
| Returns <code>udata</code>. | |
| <p> | |
| <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3> | |
| <p> | |
| If <code>message</code> is present but is neither a string nor <b>nil</b>, | |
| this function returns <code>message</code> without further processing. | |
| Otherwise, | |
| it returns a string with a traceback of the call stack. | |
| An optional <code>message</code> string is appended | |
| at the beginning of the traceback. | |
| An optional <code>level</code> number tells at which level | |
| to start the traceback | |
| (default is 1, the function calling <code>traceback</code>). | |
| <p> | |
| <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3> | |
| <p> | |
| Returns an unique identifier (as a light userdata) | |
| for the upvalue numbered <code>n</code> | |
| from the given function. | |
| <p> | |
| 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. | |
| <p> | |
| <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3> | |
| <p> | |
| Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code> | |
| refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>. | |
| <h1>7 – <a name="7">Lua Standalone</a></h1> | |
| <p> | |
| 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 <code>lua</code>, | |
| is provided with the standard distribution. | |
| The standalone interpreter includes | |
| all standard libraries, including the debug library. | |
| Its usage is: | |
| <pre> | |
| lua [options] [script [args]] | |
| </pre><p> | |
| The options are: | |
| <ul> | |
| <li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li> | |
| <li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em>;</li> | |
| <li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li> | |
| <li><b><code>-v</code>: </b> prints version information;</li> | |
| <li><b><code>-E</code>: </b> ignores environment variables;</li> | |
| <li><b><code>--</code>: </b> stops handling options;</li> | |
| <li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li> | |
| </ul><p> | |
| After handling its options, <code>lua</code> runs the given <em>script</em>, | |
| passing to it the given <em>args</em> as string arguments. | |
| When called without arguments, | |
| <code>lua</code> behaves as <code>lua -v -i</code> | |
| when the standard input (<code>stdin</code>) is a terminal, | |
| and as <code>lua -</code> otherwise. | |
| <p> | |
| When called without option <code>-E</code>, | |
| the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_2"><code>LUA_INIT_5_2</code></a> | |
| (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if it is not defined) | |
| before running any argument. | |
| If the variable content has the format <code>@<em>filename</em></code>, | |
| then <code>lua</code> executes the file. | |
| Otherwise, <code>lua</code> executes the string itself. | |
| <p> | |
| When called with option <code>-E</code>, | |
| besides ignoring <code>LUA_INIT</code>, | |
| Lua also ignores | |
| the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>, | |
| setting the values of | |
| <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a> | |
| with the default paths defined in <code>luaconf.h</code>. | |
| <p> | |
| All options are handled in order, except <code>-i</code> and <code>-E</code>. | |
| For instance, an invocation like | |
| <pre> | |
| $ lua -e'a=1' -e 'print(a)' script.lua | |
| </pre><p> | |
| will first set <code>a</code> to 1, then print the value of <code>a</code>, | |
| and finally run the file <code>script.lua</code> with no arguments. | |
| (Here <code>$</code> is the shell prompt. Your prompt may be different.) | |
| <p> | |
| Before starting to run the script, | |
| <code>lua</code> collects all arguments in the command line | |
| in a global table called <code>arg</code>. | |
| The script name is stored at index 0, | |
| the first argument after the script name goes to index 1, | |
| and so on. | |
| Any arguments before the script name | |
| (that is, the interpreter name plus the options) | |
| go to negative indices. | |
| For instance, in the call | |
| <pre> | |
| $ lua -la b.lua t1 t2 | |
| </pre><p> | |
| the interpreter first runs the file <code>a.lua</code>, | |
| then creates a table | |
| <pre> | |
| arg = { [-2] = "lua", [-1] = "-la", | |
| [0] = "b.lua", | |
| [1] = "t1", [2] = "t2" } | |
| </pre><p> | |
| and finally runs the file <code>b.lua</code>. | |
| The script is called with <code>arg[1]</code>, <code>arg[2]</code>, ... | |
| as arguments; | |
| it can also access these arguments with the vararg expression '<code>...</code>'. | |
| <p> | |
| In interactive mode, | |
| if you write an incomplete statement, | |
| the interpreter waits for its completion | |
| by issuing a different prompt. | |
| <p> | |
| In case of unprotected errors in the script, | |
| the interpreter reports the error to the standard error stream. | |
| If the error object is a string, | |
| the interpreter adds a stack traceback to it. | |
| Otherwise, if the error object has a metamethod <code>__tostring</code>, | |
| the interpreter calls this metamethod to produce the final message. | |
| Finally, if the error object is <b>nil</b>, | |
| the interpreter does not report the error. | |
| <p> | |
| When finishing normally, | |
| the interpreter closes its main Lua state | |
| (see <a href="#lua_close"><code>lua_close</code></a>). | |
| The script can avoid this step by | |
| calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate. | |
| <p> | |
| 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 <code>#</code>. | |
| Therefore, Lua scripts can be made into executable programs | |
| by using <code>chmod +x</code> and the <code>#!</code> form, | |
| as in | |
| <pre> | |
| #!/usr/local/bin/lua | |
| </pre><p> | |
| (Of course, | |
| the location of the Lua interpreter may be different in your machine. | |
| If <code>lua</code> is in your <code>PATH</code>, | |
| then | |
| <pre> | |
| #!/usr/bin/env lua | |
| </pre><p> | |
| is a more portable solution.) | |
| <h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1> | |
| <p> | |
| Here we list the incompatibilities that you may find when moving a program | |
| from Lua 5.1 to Lua 5.2. | |
| You can avoid some incompatibilities by compiling Lua with | |
| appropriate options (see file <code>luaconf.h</code>). | |
| However, | |
| all these compatibility options will be removed in the next version of Lua. | |
| Similarly, | |
| all features marked as deprecated in Lua 5.1 | |
| have been removed in Lua 5.2. | |
| <h2>8.1 – <a name="8.1">Changes in the Language</a></h2> | |
| <ul> | |
| <li> | |
| The concept of <em>environment</em> changed. | |
| Only Lua functions have environments. | |
| To set the environment of a Lua function, | |
| use the variable <code>_ENV</code> or the function <a href="#pdf-load"><code>load</code></a>. | |
| <p> | |
| C functions no longer have environments. | |
| Use an upvalue with a shared table if you need to keep | |
| shared state among several C functions. | |
| (You may use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> to open a C library | |
| with all functions sharing a common upvalue.) | |
| <p> | |
| To manipulate the "environment" of a userdata | |
| (which is now called user value), | |
| use the new functions | |
| <a href="#lua_getuservalue"><code>lua_getuservalue</code></a> and <a href="#lua_setuservalue"><code>lua_setuservalue</code></a>. | |
| </li> | |
| <li> | |
| Lua identifiers cannot use locale-dependent letters. | |
| </li> | |
| <li> | |
| Doing a step or a full collection in the garbage collector | |
| does not restart the collector if it has been stopped. | |
| </li> | |
| <li> | |
| Weak tables with weak keys now perform like <em>ephemeron tables</em>. | |
| </li> | |
| <li> | |
| The event <em>tail return</em> in debug hooks was removed. | |
| Instead, tail calls generate a special new event, | |
| <em>tail call</em>, so that the debugger can know that | |
| there will not be a corresponding return event. | |
| </li> | |
| <li> | |
| Equality between function values has changed. | |
| Now, a function definition may not create a new value; | |
| it may reuse some previous value if there is no | |
| observable difference to the new function. | |
| </li> | |
| </ul> | |
| <h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2> | |
| <ul> | |
| <li> | |
| Function <code>module</code> is deprecated. | |
| It is easy to set up a module with regular Lua code. | |
| Modules are not expected to set global variables. | |
| </li> | |
| <li> | |
| Functions <code>setfenv</code> and <code>getfenv</code> were removed, | |
| because of the changes in environments. | |
| </li> | |
| <li> | |
| Function <code>math.log10</code> is deprecated. | |
| Use <a href="#pdf-math.log"><code>math.log</code></a> with 10 as its second argument, instead. | |
| </li> | |
| <li> | |
| Function <code>loadstring</code> is deprecated. | |
| Use <code>load</code> instead; it now accepts string arguments | |
| and are exactly equivalent to <code>loadstring</code>. | |
| </li> | |
| <li> | |
| Function <code>table.maxn</code> is deprecated. | |
| Write it in Lua if you really need it. | |
| </li> | |
| <li> | |
| Function <code>os.execute</code> now returns <b>true</b> when command | |
| terminates successfully and <b>nil</b> plus error information | |
| otherwise. | |
| </li> | |
| <li> | |
| Function <code>unpack</code> was moved into the table library | |
| and therefore must be called as <a href="#pdf-table.unpack"><code>table.unpack</code></a>. | |
| </li> | |
| <li> | |
| Character class <code>%z</code> in patterns is deprecated, | |
| as now patterns may contain '<code>\0</code>' as a regular character. | |
| </li> | |
| <li> | |
| The table <code>package.loaders</code> was renamed <code>package.searchers</code>. | |
| </li> | |
| <li> | |
| Lua does not have bytecode verification anymore. | |
| So, all functions that load code | |
| (<a href="#pdf-load"><code>load</code></a> and <a href="#pdf-loadfile"><code>loadfile</code></a>) | |
| are potentially insecure when loading untrusted binary data. | |
| (Actually, those functions were already insecure because | |
| of flaws in the verification algorithm.) | |
| When in doubt, | |
| use the <code>mode</code> argument of those functions | |
| to restrict them to loading textual chunks. | |
| </li> | |
| <li> | |
| The standard paths in the official distribution may | |
| change between versions. | |
| </li> | |
| </ul> | |
| <h2>8.3 – <a name="8.3">Changes in the API</a></h2> | |
| <ul> | |
| <li> | |
| Pseudoindex <code>LUA_GLOBALSINDEX</code> was removed. | |
| You must get the global environment from the registry | |
| (see <a href="#4.5">§4.5</a>). | |
| </li> | |
| <li> | |
| Pseudoindex <code>LUA_ENVIRONINDEX</code> | |
| and functions <code>lua_getfenv</code>/<code>lua_setfenv</code> | |
| were removed, | |
| as C functions no longer have environments. | |
| </li> | |
| <li> | |
| Function <code>luaL_register</code> is deprecated. | |
| Use <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> so that your module does not create globals. | |
| (Modules are not expected to set global variables anymore.) | |
| </li> | |
| <li> | |
| The <code>osize</code> argument to the allocation function | |
| may not be zero when creating a new block, | |
| that is, when <code>ptr</code> is <code>NULL</code> | |
| (see <a href="#lua_Alloc"><code>lua_Alloc</code></a>). | |
| Use only the test <code>ptr == NULL</code> to check whether | |
| the block is new. | |
| </li> | |
| <li> | |
| Finalizers (<code>__gc</code> metamethods) for userdata are called in the | |
| reverse order that they were marked for finalization, | |
| not that they were created (see <a href="#2.5.1">§2.5.1</a>). | |
| (Most userdata are marked immediately after they are created.) | |
| Moreover, | |
| if the metatable does not have a <code>__gc</code> field when set, | |
| the finalizer will not be called, | |
| even if it is set later. | |
| </li> | |
| <li> | |
| <code>luaL_typerror</code> was removed. | |
| Write your own version if you need it. | |
| </li> | |
| <li> | |
| Function <code>lua_cpcall</code> is deprecated. | |
| You can simply push the function with <a href="#lua_pushcfunction"><code>lua_pushcfunction</code></a> | |
| and call it with <a href="#lua_pcall"><code>lua_pcall</code></a>. | |
| </li> | |
| <li> | |
| Functions <code>lua_equal</code> and <code>lua_lessthan</code> are deprecated. | |
| Use the new <a href="#lua_compare"><code>lua_compare</code></a> with appropriate options instead. | |
| </li> | |
| <li> | |
| Function <code>lua_objlen</code> was renamed <a href="#lua_rawlen"><code>lua_rawlen</code></a>. | |
| </li> | |
| <li> | |
| Function <a href="#lua_load"><code>lua_load</code></a> has an extra parameter, <code>mode</code>. | |
| Pass <code>NULL</code> to simulate the old behavior. | |
| </li> | |
| <li> | |
| Function <a href="#lua_resume"><code>lua_resume</code></a> has an extra parameter, <code>from</code>. | |
| Pass <code>NULL</code> or the thread doing the call. | |
| </li> | |
| </ul> | |
| <h1>9 – <a name="9">The Complete Syntax of Lua</a></h1> | |
| <p> | |
| Here is the complete syntax of Lua in extended BNF. | |
| (It does not describe operator precedences.) | |
| <pre> | |
| chunk ::= block | |
| block ::= {stat} [retstat] | |
| stat ::= ‘<b>;</b>’ | | |
| varlist ‘<b>=</b>’ explist | | |
| functioncall | | |
| label | | |
| <b>break</b> | | |
| <b>goto</b> Name | | |
| <b>do</b> block <b>end</b> | | |
| <b>while</b> exp <b>do</b> block <b>end</b> | | |
| <b>repeat</b> block <b>until</b> exp | | |
| <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | | |
| <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> | | |
| <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | | |
| <b>function</b> funcname funcbody | | |
| <b>local</b> <b>function</b> Name funcbody | | |
| <b>local</b> namelist [‘<b>=</b>’ explist] | |
| retstat ::= <b>return</b> [explist] [‘<b>;</b>’] | |
| label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ | |
| funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] | |
| varlist ::= var {‘<b>,</b>’ var} | |
| var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name | |
| namelist ::= Name {‘<b>,</b>’ Name} | |
| explist ::= exp {‘<b>,</b>’ exp} | |
| exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | ‘<b>...</b>’ | functiondef | | |
| prefixexp | tableconstructor | exp binop exp | unop exp | |
| prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ | |
| functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args | |
| args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | String | |
| functiondef ::= <b>function</b> funcbody | |
| funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> | |
| parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ | |
| tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ | |
| fieldlist ::= field {fieldsep field} [fieldsep] | |
| field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp | |
| fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ | |
| binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ | ‘<b>..</b>’ | | |
| ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ | | |
| <b>and</b> | <b>or</b> | |
| unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’ | |
| </pre> | |
| <p> | |
| <HR> | |
| <SMALL CLASS="footer"> | |
| Last update: | |
| Thu Mar 21 12:58:59 BRT 2013 | |
| </SMALL> | |
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