local Luan = require "luan:Luan.luan"
local error = Luan.error
local Io = require "luan:Io.luan"
local Http = require "luan:http/Http.luan"
local Shared = require "site:/lib/Shared.luan"
local head = Shared.head or error()
local docs_header = Shared.docs_header or error()
local show_toc = Shared.show_toc or error()
local show_content = Shared.show_content or error()


local content = {
	intro = {
		title = "Introduction"
		content = function()
%>
<p>
Luan is a high level programming language based on <a href="http://www.lua.org">Lua</a>.  A great strength of Lua is its simplicity and Luan takes this even further, being even simpler than Lua.  The goal is to provide a simple programming language for the casual programmer with as few concepts as possible so that one can quickly learn the language and then easily understand any code written in Luan.
</p>

<p>
Luan is implemented in Java and is tightly coupled with Java.  So it makes a great scripting language for Java programmers.
</p>

<p>
Unlike Lua which is meant to be embedded, Luan is meant to be a full scripting language.  This done not by adding features to Luan, but rather by providing a complete set of libraries.
</p>
<%
		end
	}
	basic = {
		title = "Basic Concepts"
		content = function()
%>
<p>
This section describes the basic concepts of the language.
</p>
<%
		end
		subs = {
			types = {
				title = "Values and Types"
				content = function()
%>
<p>
Luan 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>

<p>
All values in Luan 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>

<p>
There are eight basic types in Luan:
<em>nil</em>, <em>boolean</em>, <em>number</em>,
<em>string</em>, <em>binary</em>, <em>function</em>, <em>java</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>Nil</em> is implemented as the Java value <em>null</em>.
<em>Boolean</em> is the type of the values <b>false</b> and <b>true</b>.
<em>Boolean</em> is implemented as the Java class <em>Boolean</em>.
<em>Number</em> represents both
integer numbers and real (floating-point) numbers.
<em>Number</em> is implemented as the Java class <em>Number</em>.  Any Java subclass of <em>Number</em> is allowed and this is invisible to the Luan user.  Operations on numbers follow the same rules of
the underlying Java implementation.
<em>String</em> is implemented as the Java class <em>String</em>.
<em>Binary</em> is implemented as the Java type <em>byte[]</em>.
</p>

<p>
Luan can call (and manipulate) functions written in Luan and
functions written in Java (see <a href="#fn_calls">Function Calls</a>).
Both are represented by the type <em>function</em>.
</p>

<p>
The type <em>java</em> is provided to allow arbitrary Java objects to
be stored in Luan variables.
A <em>java</em> value is a Java object that isn't one of the standard Luan types.
Java values have no predefined operations in Luan,
except assignment and identity test.
Java values are useful when Java access is enabled in Luan.
</p>

<p>
The type <em>table</em> implements associative arrays,
that is, arrays that can be indexed not only with numbers,
but with any Luan value except <b>nil</b>.
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>

<p>
Tables are the sole data-structuring mechanism in Luan;
they can be used to represent ordinary arrays, sequences,
symbol tables, sets, records, graphs, trees, etc.
To represent records, Luan uses the field name as an index.
The language supports this representation by
providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>.
There are several convenient ways to create tables in Luan
(see <a href="#constructors">Table Constructors</a>).
</p>

<p>
We use the term <em>sequence</em> to denote a table where
the set of all positive numeric keys is equal to {1..<em>n</em>}
for some non-negative integer <em>n</em>,
which is called the length of the sequence (see <a href="#length">The Length Operator</a>).
</p>

<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="#fn_def">Function Definitions</a>).
</p>

<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).
In particular, floats with integral values
are equal to their respective integers
(e.g., <code>1.0 == 1</code>).
</p>

<p>
Luan values are <em>objects</em>:
variables do not actually <em>contain</em> values,
only <em>references</em> to them.
Assignment, parameter passing, and function returns
always manipulate references to values;
these operations do not imply any kind of copy.
</p>

<p>
The library function <a href="#Luan.type"><code>Luan.type</code></a> returns a string describing the type
of a given value.
</p>
<%
				end
			}
			env = {
				title = "Environments"
				content = function()
%>
<p>
The environment of a chunk starts with only one local variable: <code><a href="#require">require</a></code>.  This function is used to load and access libraries and other modules.  All other variables must be added to the environment using <a href="http://localhost:8080/manual.html#local_stmt">local declarations</a>.
</p>

<p>
As will be discussed in <a href="#vars">Variables</a> and <a href=#assignment">Assignment</a>,
any reference to a free name
(that is, a name not bound to any declaration) <code>var</code>
can be syntactically translated to <code>_ENV.var</code> if <code>_ENV</code> is defined.
</p>
<%
				end
			}
			error = {
				title = "Error Handling"
				content = function()
%>
<p>
Luan code can explicitly generate an error by calling the
<a href="#Luan.error"><code>error</code></a> function.
If you need to catch errors in Luan,
you can use the <a href="#try">Try Statement</code></a>.
</p>

<p>
Whenever there is an error,
an <em>error table</em>
is propagated with information about the error.
See <a href="#Luan.new_error"><code>Luan.new_error</code></a>.
</p>
<%
				end
			}
			meta = {
				title = "Metatables and Metamethods"
				content = function()
%>
<p>
Every table in Luan can have a <em>metatable</em>.
This <em>metatable</em> is an ordinary Luan table
that defines the behavior of the original value
under certain special operations.
You can change several aspects of the behavior
of operations over a value by setting specific fields in its metatable.
For instance, when a table is the operand of an addition,
Luan checks for a function in the field "<code>__add</code>" of the table's metatable.
If it finds one,
Luan calls this function to perform the addition.
</p>

<p>
The keys in a metatable are derived from the <em>event</em> names;
the corresponding values are called <ii>metamethods</em>.
In the previous example, the event is <code>"add"</code>
and the metamethod is the function that performs the addition.
</p>

<p>
You can query the metatable of any table
using the <a href="#Luan.get_metatable"><code>get_metatable</code></a> function.
</p>

<p>
You can replace the metatable of tables
using the <a href="#Luan.set_metatable"><code>set_metatable</code></a> function.
</p>

<p>
A metatable controls how a table behaves in
arithmetic operations, bitwise operations,
order comparisons, concatenation, length operation, calls, and indexing.
</p>

<p>
A detailed list of events controlled by metatables is given next.
Each operation is identified by its corresponding event name.
The key for each event is a string with its name prefixed by
two underscores, '<code>__</code>';
for instance, the key for operation "add" is the
string "<code>__add</code>".
Note that queries for metamethods are always raw;
the access to a metamethod does not invoke other metamethods.
You can emulate how Luan queries a metamethod for an object <code>obj</code>
with the following code:
</p>

<pre>
     raw_get(get_metatable(obj) or {}, "__" .. event_name)
</pre>

<p>
Here are the events:
</p>

<ul>

<li><p>
<b>"add": </b>
the <code>+</code> operation.

If any operand for an addition is a table,
Luan will try to call a metamethod.
First, Luan will check the first operand (even if it is valid).
If that operand does not define a metamethod for the "<code>__add</code>" event,
then Luan will check the second operand.
If Luan can find a metamethod,
it calls the metamethod with the two operands as arguments,
and the result of the call
(adjusted to one value)
is the result of the operation.
Otherwise,
it raises an error.
</p></li>

<li><p>
<b>"sub": </b>
the <code>-</code> operation.
Behavior similar to the "add" operation.
</li>

<li><p><b>"mul": </b>
the <code>*</code> operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"div": </b>
the <code>/</code> operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"mod": </b>
the <code>%</code> operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"pow": </b>
the <code>^</code> (exponentiation) operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"unm": </b>
the <code>-</code> (unary minus) operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"concat": </b>
the <code>..</code> (concatenation) operation.
Behavior similar to the "add" operation.
</p></li>

<li><p>
<b>"len": </b>
the <code>#</code> (length) operation.
If there is a metamethod,
Luan calls it with the object as argument,
and the result of the call
(always adjusted to one value)
is the result of the operation.
If there is no metamethod but the object is a table,
then Luan uses the table length operation (see <a href="#length">The Length Operator</a>).
Otherwise, Luan raises an error.
</p></li>

<li><p>
<b>"eq": </b>
the <code>==</code> (equal) operation.
Behavior similar to the "add" operation,
except that Luan will try a metamethod only when the values
being compared are both tables
and they are not primitively equal.
The result of the call is always converted to a boolean.
</p></li>

<li><p>
<b>"lt": </b>
the <code>&lt;</code> (less than) operation.
Behavior similar to the "add" operation.
The result of the call is always converted to a boolean.
</p></li>

<li><p>
<b>"le": </b>
the <code>&lt;=</code> (less equal) operation.
Unlike other operations,
The less-equal operation can use two different events.
First, Luan looks for the "<code>__le</code>" metamethod in both operands,
like in the "lt" operation.
If it cannot find such a metamethod,
then it will try the "<code>__lt</code>" event,
assuming that <code>a &lt;= b</code> is equivalent to <code>not (b &lt; a)</code>.
As with the other comparison operators,
the result is always a boolean.
</p></li>

<li>
<p>
<b>"index": </b>
The indexing access <code>table[key]</code>.
This event happens
when <code>key</code> is not present in <code>table</code>.
The metamethod is looked up in <code>table</code>.
</p>

<p>
Despite the name,
the metamethod for this event can be any type.
If it is a function,
it is called with <code>table</code> and <code>key</code> as arguments.
Otherwise
the final result is the result of indexing this metamethod object with <code>key</code>.
(This indexing is regular, not raw,
and therefore can trigger another metamethod if the metamethod object is a table.)
</p>
</li>

<li>
<p>
<b>"new_index": </b>
The indexing assignment <code>table[key] = value</code>.
Like the index event,
this event happens when
when <code>key</code> is not present in <code>table</code>.
The metamethod is looked up in <code>table</code>.
</p>

<p>
Like with indexing,
the metamethod for this event can be either a function or a table.
If it is a function,
it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments.
If it is a table,
Luan does an indexing assignment to this table with the same key and value.
(This assignment is regular, not raw,
and therefore can trigger another metamethod.)
</p>

<p>
Whenever there is a "new_index" metamethod,
Luan does not perform the primitive assignment.
(If necessary,
the metamethod itself can call <a href="#Luan.raw_set"><code>raw_set</code></a>
to do the assignment.)
</p>
</li>

<li><p>
<b>"gc":</b>
This is when a table is garbage collected.  When the table's <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#finalize()">finalize</a> method is called by the Java garbage collector, if there is a "<code>__gc</code>" metamethod then it is called with the table as a parameter.
</p></li>

</ul>
<%
				end
			}
			gc = {
				title = "Garbage Collection"
				content = function()
%>
<p>
Luan uses Java's garbage collection.
</p>
<%
				end
			}
		}
	}
	lang = {
		title = "The Language"
		content = function()
%>
<p>
This section describes the lexis, the syntax, and the semantics of Luan.
In other words,
this section describes
which tokens are valid,
how they can be combined,
and what their combinations mean.
</p>

<p>
Language constructs will be explained using the usual extended BNF notation,
in which
{<em>a</em>}&nbsp;means&nbsp;0 or more <em>a</em>'s, and
[<em>a</em>]&nbsp;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 &lsquo;<b>=</b>&rsquo;.
The complete syntax of Luan can be found in <a href="#9">&sect;9</a>
at the end of this manual.
</p>
<%
		end
		subs = {
			lex = {
				title = "Lexical Conventions"
				content = function()
%>
<p>
Luan ignores spaces and comments
between lexical elements (tokens),
except as delimiters between names and keywords.
Luan considers the end of a line to be the end of a statement.  This catches errors and encourages readability.  If you want to continue a statement on another line, you can use a backslash followed by a newline which will be treated as white space.
</p>

<p>
<em>Names</em>
(also called <em>identifiers</em>)
in Luan 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>

<p>
The following <em>keywords</em> are reserved
and cannot be used as names:
</p>

<p keywords>
	<span>and</span>
	<span>break</span>
	<span>catch</span>
	<span>continue</span>
	<span>do</span>
	<span>else</span>
	<span>elseif</span>
	<span>end_do</span>
	<span>end_for</span>
	<span>end_function</span>
	<span>end_if</span>
	<span>end_try</span>
	<span>end_while</span>
	<span>false</span>
	<span>finally</span>
	<span>for</span>
	<span>function</span>
	<span>if</span>
	<span>in</span>
	<span>local</span>
	<span>nil</span>
	<span>not</span>
	<span>or</span>
	<span>repeat</span>
	<span>return</span>
	<span>then</span>
	<span>true</span>
	<span>try</span>
	<span>until</span>
	<span>while</span>
</p>

<p>
Luan 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.
</p>

<p>
The following strings denote other tokens:
</p>

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

<p>
Luan can specify any character in a literal string 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>\u<em>XXXX</em></code>,
where <em>XXXX</em> is a sequence of exactly four 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 sequence is to be followed by a digit,
it must be expressed using exactly three digits.)
</p>

<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 same level.
Literals in this bracketed form can run for several lines,
do not interpret any escape sequences,
and ignore long brackets of any other level.
Any kind of end-of-line sequence
(carriage return, newline, carriage return followed by newline,
or newline followed by carriage return)
is converted to a simple newline.
</p>

<p>
Any character in a literal string not
explicitly affected by the previous rules represents itself.
However, Luan 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>

<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
the five literal strings below denote the same string:
</p>

<pre>
     a = 'alo\n123"'
     a = "alo\n123\""
     a = '\97lo\10\04923"'
     a = [[alo
     123"]]
     a = [==[
     alo
     123"]==]
</pre>

<p>
A <em>numerical constant</em> (or <em>numeral</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>'.
Luan 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>'.
A numeric constant with a fractional dot or an exponent 
denotes a float;
otherwise it denotes an integer.
Examples of valid integer constants are
</p>

<pre>
     3   345   0xff   0xBEBADA
</pre>

<p>
Examples of valid float constants are
</p>

<pre>
     3.0     3.1416     314.16e-2     0.31416E1     34e1
     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.
</p>
<%
				end
			}
			vars = {
				title = "Variables"
				content = function()
%>
<p>
Variables are places that store values.
There are three kinds of variables in Luan:
global variables, local variables, and table fields.
</p>

<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):
</p>

<pre>
	var ::= Name
</pre>

<p>
Name denotes identifiers, as defined in <a href="#lex">Lexical Conventions</a>.
</p>

<p>
Local variables are <em>lexically scoped</em>:
local variables can be freely accessed by functions
defined inside their scope (see <a href="#visibility">Visibility Rules</a>).
</p>

<p>
Before the first assignment to a variable, its value is <b>nil</b>.
</p>

<p>
Square brackets are used to index a table:
</p>

<pre>
	var ::= prefixexp &lsquo;<b>[</b>&rsquo; exp &lsquo;<b>]</b>&rsquo;
</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="#meta">Metatables and Metamethods</a> for a complete description of the
<code>gettable_event</code> function.
This function is not defined or callable in Luan.
We use it here only for explanatory purposes.)
</p>

<p>
The syntax <code>var.Name</code> is just syntactic sugar for
<code>var["Name"]</code>:
</p>

<pre>
	var ::= prefixexp &lsquo;<b>.</b>&rsquo; Name
</pre>

<p>
Global variables are not available by default.  To enable global variable, you must define <code>_ENV</code> as a local variable whose value is a table.  If <code>_ENV</code> is not defined, then an unrecognized variable name will produce a compile error.  If <code>_ENV</code> is defined then an access to an unrecognized variable name will be consider a global variable.  So then an acces to 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="#env">Environments</a>).
</p>
<%
				end
			}
			stmt = {
				title = "Statements"
				content = function()
%>
<p>
Luan 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.
</p>
<%
				end
				subs = {
					blocks = {
						title = "Blocks"
						content = function()
%>
<p>
A block is a list of statements,
which are executed sequentially:
</p>

<pre>
	block ::= {stat}
</pre>

<p>
Luan 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:
</p>

<pre>
	stat ::= &lsquo;<b>;</b>&rsquo;
</pre>

<p>
A block can be explicitly delimited to produce a single statement:
</p>

<pre>
	stat ::= <b>do</b> block end_do
	end_do ::= <b>end_do</b> | <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="#control">Control Structures</a>).
</p>
<%
						end
					}
					chunks = {
						title = "Chunks"
						content = function()
%>
<p>
The unit of compilation of Luan is called a <em>chunk</em>.
Syntactically,
a chunk is simply a block:
</p>

<pre>
	chunk ::= block
</pre>

<p>
Luan handles a chunk as the body of an anonymous function
with a variable number of arguments
(see <a href="#fn_def">Function Definitions</a>).
As such, chunks can define local variables,
receive arguments, and return values.
</p>

<p>
A chunk can be stored in a file or in a string inside the host program.
To execute a chunk,
Luan first <em>loads</em> it,
compiling the chunk's code,
and then Luan executes the compiled code.
</p>
<%
						end
					}
					assignment = {
						title = "Assignment"
						content = function()
%>
<p>
Luan 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:
</p>

<pre>
	stat ::= varlist &lsquo;<b>=</b>&rsquo; explist
	varlist ::= var {&lsquo;<b>,</b>&rsquo; var}
	explist ::= exp {&lsquo;<b>,</b>&rsquo; exp}
</pre>

<p>
Expressions are discussed in <a href="#expressions">Expressions</a>.
</p>

<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="#expressions">Expressions</a>).
</p>

<p>
The assignment statement first evaluates all its expressions
and only then the assignments are performed.
Thus the code
</p>

<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&nbsp;4.
Similarly, the line
</p>

<pre>
     x, y = y, x
</pre>

<p>
exchanges the values of <code>x</code> and <code>y</code>,
and
</p>

<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>

<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="#meta">Metatables and Metamethods</a> for a complete description of the
<code>settable_event</code> function.
This function is not defined or callable in Luan.
We use it here only for explanatory purposes.)
</p>

<p>
An assignment to a global name <code>x = val</code>
is equivalent to the assignment
<code>_ENV.x = val</code> (see <a href="#env">Environments</a>).
Global names are only available when <code>_ENV</code> is defined.
</p>
<%
						end
					}
					control = {
						title = "Control Structures"
						content = function()
%>
<p>
The control structures
<b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and
familiar syntax:
</p>

<pre>
	stat ::= <b>while</b> exp <b>do</b> block end_while
	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] end_if
	end_while ::= <b>end_while</b> | <b>end</b>
	end_if ::= <b>end_if</b> | <b>end</b>
</pre>

<p>
Luan also has a <b>for</b> statement (see <a href="#for">For Statement</a>).
</p>

<p>
The condition expression of a
control structure must be a boolean.
Any other value type will produce an error.
This helps catch errors and makes code more readable.
</p>

<p>
In the <b>repeat</b>&ndash;<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>

<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:
</p>

<pre>
	stat ::= <b>break</b>
</pre>

<p>
A <b>break</b> ends the innermost enclosing loop.
</p>

<p>
The <b>continue</b> statement jumps to the beginning of a
<b>while</b>, <b>repeat</b>, or <b>for</b> loop for next iteration,
skipping the execution of statements inside the body of loop for the current iteration:
</p>

<pre>
	stat ::= <b>continue</b>
</pre>

<p>
The <b>return</b> statement is used to return values
from a function or a chunk
(which is an anonymous function).
Functions can return more than one value,
so the syntax for the <b>return</b> statement is
</p>

<pre>
	stat ::= <b>return</b> [explist] [&lsquo;<b>;</b>&rsquo;]
</pre>
<%
						end
					}
					["for"] = {
						title = "For Statement"
						content = function()
%>
<p>
The <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 <b>for</b> loop has the following syntax:
</p>

<pre>
	stat ::= <b>for</b> namelist <b>in</b> exp <b>do</b> block end_for
	namelist ::= Name {&lsquo;<b>,</b>&rsquo; Name}
	end_for ::= <b>end_for</b> | <b>end</b>
</pre>

<p>
A <b>for</b> statement like
</p>

<pre>
     for <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> in <em>exp</em> do <em>block</em> end
</pre>

<p>
is equivalent to the code:
</p>

<pre>
     do
       local <em>f</em> = <em>exp</em>
       while true do
         local <em>var_1</em>, &middot;&middot;&middot;, <em>var_n</em> = <em>f</em>()
         if <em>var_1</em> == nil then break end
         <em>block</em>
       end
     end
</pre>

<p>
Note the following:
</p>

<ul>
	<li>
		<code><em>exp</em></code> is evaluated only once.
		Its result is an <em>iterator</em> function.
	</li>
	<li>
		<code><em>f</em></code> is an invisible variable.
		The name is 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>
<%
						end
					}
					["try"] = {
						title = "Try Statement"
						content = function()
%>
<p>
The <b>try</b> statement has the same semantics as in Java.
</p>

<pre>
	stat ::= <b>try</b> block [<b>catch</b> Name block] [<b>finally</b> block] end_try
	end_try ::= <b>end_try</b> | <b>end</b>
</pre>
<%
						end
					}
					fn_stmt = {
						title = "Function Calls as Statements"
						content = function()
%>
<p>
To allow possible side-effects,
function calls can be executed as statements:
</p>

<pre>
	stat ::= functioncall
</pre>

<p>
In this case, all returned values are thrown away.
Function calls are explained in <a href="#fn_calls">Function Calls</a>.
</p>
<%
						end
					}
					logical_stmt = {
						title = "Logical Statement"
						content = function()
%>
<p>
<a href="#logical_ops">Logical expressions</a> can be statements.
This is useful in cases like this:
</p>

<pre>
	x==5 or error "x should be 5"
</pre>
<%
						end
					}
					local_stmt = {
						title = "Local Declarations"
						content = function()
%>
<p>
Local variables can be declared anywhere inside a block.
The declaration can include an initial assignment:
</p>

<pre>
	stat ::= <b>local</b> namelist [&lsquo;<b>=</b>&rsquo; explist]
</pre>

<p>
If present, an initial assignment has the same semantics
of a multiple assignment (see <a href="#assignment">Assignment</a>).
Otherwise, all variables are initialized with <b>nil</b>.
</p>

<p>
A chunk is also a block (see <a href="#chunks">Chunks</a>),
and so local variables can be declared in a chunk outside any explicit block.
</p>

<p>
The visibility rules for local variables are explained in <a href="#visibility">Visibility Rules</a>.
</p>
<%
						end
					}
					template_stmt = {
						title = "Template Statements"
						content = function()
%>
<p>Template statements provide the full equivalent of <a href="http://en.wikipedia.org/wiki/JavaServer_Pages">JSP</a> but in a general way.  Template statements write to standard output.  For example:</p>
</p>

<pre>
	local name = "Bob"
	%&gt;
	Hello &lt;%= name %&gt;!
	Bye &lt;%= name %&gt;.
	&lt;%
</pre>

<p>
is equivalent to the code:
</p>

<pre>
	local name = "Bob"
	require("luan:Io.luan").stdout.write( "Hello ", name , "!\nBye ", name , ".\n" )
</pre>
<%
						end
					}
				}
			}
			expressions = {
				title = "Expressions"
				content = function()
%>
<p>
The basic expressions in Luan are the following:
</p>

<pre>
	exp ::= prefixexp
	exp ::= <b>nil</b> | <b>false</b> | <b>true</b>
	exp ::= Numeral
	exp ::= LiteralString
	exp ::= functiondef
	exp ::= tableconstructor
	exp ::= &lsquo;<b>...</b>&rsquo;
	exp ::= exp binop exp
	exp ::= unop exp
	prefixexp ::= var | functioncall | &lsquo;<b>(</b>&rsquo; exp &lsquo;<b>)</b>&rsquo;
</pre>

<p>
Numerals and literal strings are explained in <a href="#lex">Lexical Conventions</a>;
variables are explained in <a href="#vars">Variables</a>;
function definitions are explained in <a href="#fn_def">Function Definitions</a>;
function calls are explained in <a href="#fn_calls">Function Calls</a>;
table constructors are explained in <a href="#constructors">Table Constructors</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="#fn_def">Function Definitions</a>.
</p>

<p>
Binary operators comprise arithmetic operators (see <a href="#arithmetic">Arithmetic Operators</a>),
relational operators (see <a href="#relational">Relational Operators</a>), logical operators (see <a href="#logical_ops">Logical Operators</a>),
and the concatenation operator (see <a href="#concatenation">Concatenation</a>).
Unary operators comprise the unary minus (see <a href="#arithmetic">Arithmetic Operators</a>),
the unary logical <b>not</b> (see <a href="#logical_ops">Logical Operators</a>),
and the unary <em>length operator</em> (see <a href="#length">The Length Operator</a>).
</p>

<p>
Both function calls and vararg expressions can result in multiple values.
If a function call is used as a statement (see <a href="#fn_stmt">Function Calls as Statements</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,
Luan 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>

<p>
Here are some examples:
</p>

<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.)
</p>
<%
				end
				subs = {
					arithmetic = {
						title = "Arithmetic Operators"
						content = function()
%>
<p>
Luan supports the following arithmetic operators:
</p>

<ul>
<li><b><code>+</code>: </b>addition</li>
<li><b><code>-</code>: </b>subtraction</li>
<li><b><code>*</code>: </b>multiplication</li>
<li><b><code>/</code>: </b>division</li>
<li><b><code>%</code>: </b>modulo</li>
<li><b><code>^</code>: </b>exponentiation</li>
<li><b><code>-</code>: </b>unary minus</li>
</ul>

<p>
Addition, subtraction, multiplication, division, and unary minus are the same as these operators in Java.  Exponentiation uses Java's <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html#pow(double,%20double)">Math.pow</a> function.
</p>

<p>
Modulo is defined as the remainder of a division
that rounds the quotient towards minus infinite (floor division).
(The Java modulo operator is not used.)
</p>
<%
						end
					}
					conversions = {
						title = "Coercions and Conversions"
						content = function()
%>
<p>
Luan generally avoids automatic conversions.
String concatenation automatically converts all of its arguments to strings.
</p>

<p>
Luan provides library functions for explicit type conversions.
</p>
<%
						end
					}
					relational = {
						title = "Relational Operators"
						content = function()
%>
<p>
Luan supports the following relational operators:
</p>

<ul>
	<li><b><code>==</code>: </b>equality</li>
	<li><b><code>~=</code>: </b>inequality</li>
	<li><b><code>&lt;</code>: </b>less than</li>
	<li><b><code>&gt;</code>: </b>greater than</li>
	<li><b><code>&lt;=</code>: </b>less or equal</li>
	<li><b><code>&gt;=</code>: </b>greater or equal</li>
</ul>

<p>
These operators always result in <b>false</b> or <b>true</b>.
</p>

<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.
Strings, numbers, and binary values are compared in the obvious way (by value).
</p>

<p>
Tables
are compared by reference:
two objects are considered equal only if they are the same object.
Every time you create a new table,
it is different from any previously existing table.
Closures are also compared by reference.
</p>

<p>
You can change the way that Luan compares tables
by using the "eq" metamethod (see <a href="#meta">Metatables and Metamethods</a>).
</p>

<p>
Java values are compared for equality with the Java <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#equals(java.lang.Object)"><code>equals</code></a> method.
</p>

<p>
Equality comparisons do not convert strings to numbers
or vice versa.
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>

<p>
The operator <code>~=</code> is exactly the negation of equality (<code>==</code>).
</p>

<p>
The order operators work as follows.
If both arguments are numbers,
then they are compared following
the usual rule for binary operations.
Otherwise, if both arguments are strings,
then their values are compared according to the current locale.
Otherwise, Luan tries to call the "lt" or the "le"
metamethod (see <a href="#meta">Metatables and Metamethods</a>).
A comparison <code>a &gt; b</code> is translated to <code>b &lt; a</code>
and <code>a &gt;= b</code> is translated to <code>b &lt;= a</code>.
</p>
<%
						end
					}
				}
			}
		}
	}
}


return function()
	Io.stdout = Http.response.text_writer()
%>
<!doctype html>
<html>
	<head>
<%		head() %>
		<title>Luan Reference Manual</title>
		<style>
			p[keywords] {
				font-family: monospace;
				margin-left: 40px;
				max-width: 700px;
			}
			p[keywords] span {
				display: inline-block;
				width: 100px;
			}
		</style>
	</head>
	<body>
<%		docs_header() %>
		<div content>
			<h1><a href="manual.html">Luan Reference Manual</a></h1>
			<p small>
				Original copyright &copy; 2015 Lua.org, PUC-Rio.
				Freely available under the terms of the
				<a href="http://www.lua.org/license.html">Lua license</a>.
				Modified for Luan.
			</p>
			<hr>
			<h2>Contents</h2>
			<div toc>
<%			show_toc(content) %>
			</div>
			<hr>
<%			show_content(content,2) %>
		</div>
	</body>
</html>
<%
end