View source for LDT/User Area/Documentation Language

This documentation language has been developed as part of Koneki, its main goal is to '''describe the API supplied by a file'''. It is strongly inspired by LDoc. Information given with this language is parsed by LDT and supply advanced features such as code completion and documentation view. Before diving into syntax, it is time to enumerate the underlying concepts, knowing them will enable you to write documentation more efficiently.

= Concepts =

Our documentation language introduce some concepts which may not be described explicitly in Lua, but help to defined the contract between the library provider and the user. 

== Type ==

This is the most important one. A compound ''type'' is a set of values, accessible through fields. It is not a primitive type like <code>string</code>, <code>number</code> or <code>nil</code>. Theses fields can point to functions, primitive values or other compound types.

It is the way to explicitly ensure the structure of a Lua table.

== Module ==

It is ''requireable'' entity - you can use the <tt>require</tt> function on it- <br>
This concept allow you to express :
* which ''type'' will be return by the <tt>require</tt> function for your module,
* which new global variables will be available after your module was loaded.<br>
Most of the time people refer to the returned type instance as module.

== Field ==

It is '''always''' a field of a ''type''. This is the way to ensure the presence of a value in a table which implement a type.

== Function ==

It is a special kind of ''field'' which can have parameters and return values, just as Lua functions. Both parameters and returned values can be typed. This concept allow to express a contract about which parameters suit a function and expected outputs.

== Global ==

When a module is required, it could modify the global environment. To handle those cases, the predefined type ''global'' is available. It is a reserved type which will be available everywhere, enabling you to attach field and function to it.
This is a way to express the creation of new global variables when module is loaded.

== Type references ==

It is often needed to refer to a type. There is a notation for this. It is based on types. So if you want to type a field, a function parameter or returned value, they are several kinds of references available.

=== Primitive references ===

Refer to Lua ''primitive types'', it is the type prefixed with <code>#</code>.

* <code>#boolean</code>
* <code>#nil</code>
* <code>#number</code>
* <code>#string</code>
* <code>#table</code>

=== Internal references ===

Enables to refer to types defined in current module, it is type name prefixed with <code>#</code>.

* <code>#typename</code> will refer to type ''typename'' defined in current module.

=== External references ===

Enables to refer to a type defined in another module, it is targeted module name followed by internal reference which could be used in targeted module.

* <code>modulename#typename</code> will refer to type ''typename'' defined in module ''modulename''.
* <code>modulename#modulename</code> will refer to type ''modulename'' returned in module ''modulename''.

= Comments =

It is the ''only source'' of information of our documentation language. So far, there is no inference from code. So all aspect of the API has to be described explicitly.

== Special comments ==

First of all, only ''special comments'' are parsed as part of Lua documentation. To mark your comment as special, just start it with <code>---</code>.

Special comments can contain a short and an long description. The ''short description'' start at the beginning of the comment and continue till <code>.</code> or <code>?</code>. The ''long description'' is the text coming after. By the way, [http://fr.wikipedia.org/wiki/Markdown Markdown]  is supported in ''all'' descriptions.

Special comments are handled '''only if they describe a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Concepts|concept]]'''.

'''Note''':  All leading <code>-</code>'s in special comments are trimmed.

<code><pre>
--------------------------------------------------------------------------------
-- Short description.
-- Long _markdown_ description
</pre></code>
<center><small>Special comment with trimmed first line </small></center>
'''Note''': <code>_markdown_</code> is supposed to be interpreted by [http://fr.wikipedia.org/wiki/Markdown Markdown].

<code><pre>
---
-- Short description.
-- Long description
</pre></code>
<center><small>Special comment composed of short comments format</small></center>

<code><pre>
--[[-
 Short description.
 Long description
]]
</pre></code>
<center><small> Special comment with long comment format</small></center>

<code><pre>--- Short description. Long description</pre></code>
<center><small> Special comment in one line</small></center>

== Type comment block ==

A [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type|type]] comment block is a ''special comment'' with a type declaration with <code>@type</code> key word followed by desired type name.

<code><pre>
--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
</pre></code>
<center><small>Sample of type declaration</small></center>

== Module comment block ==

Denoted by <code>@module</code> keyword and followed by a module name, a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Module|module]] is the type described in a file. This is why there should be only one module declaration per file. Here is the simplest way to declare a module. 

<code><pre>
--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
</pre></code>
<center><small>Sample of module declaration.</small></center>

When a module is declared, a type with its name is automatically created and returned. So, the following is equivalent to first module sample.

<code><pre>
--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @return #modulename

---@type modulename
</pre></code>
<center><small>Sample of verbose module declaration</small></center>
'''Note''': We used <code>#typename</code> to refer to a declared type, if you want to know more about it refer to [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type_references|type reference section]].

In previous sample, you may wonder in which case it could be of any use to return manually a type for a module. It is useful when you want to return a type different from the one automatically created.

<code><pre>
--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @return #string
</pre></code>
<center><small>Sample of module returning custom type</small></center>
'''Note''': We used <code>#string</code> to refer to a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Primitive_references|primitive type]].

== Field comment block ==

The field block represents a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Field|field of a type]]. It is possible to declare one with <code>@field</code> keyword followed by optional [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type_references|type reference]], field name and optional description.

There are two ways of defining a field, in its parent block type or in a separate documentation block where you have to mention field parent type.

<code><pre>
--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
-- @field #string fieldname Field description
</pre></code>
<center><small>Sample of field declaration in parent type block</small></center>

<code><pre>
---
-- Type short description.
-- Type long description
--
-- @type typename

---
-- Field description
--
-- @field [parent=#typename] #string fieldname 
</pre></code>
<center><small>Sample of field declaration in dedicated block</small></center>

== Function comment block ==

The function comment block has to be attached to a type. Its keyword is <code>@function</code>. A [[Koneki/LDT/Technical_Documentation/Documentation_Language#Function|function]] can have several parameters denoted by keyword <code>@param</code>, they can be optionally typed with a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type_references|type reference]] and have an optional descriptions. Several <code>@return</code> cases are also possible, but ''LDT inference -which is used for code assistance- only handles the first one''. As Lua functions allow to return several values at once, it is possible to ''define several returned values'' per <code>@return</code> markup. Returned values can be optionally typed using a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type_references|type reference]].<br/>
'''Note''': If the first <code>@param</code> is called ''self'', LDT will show completion proposal without this parameter but using <code>:</code> invocation operator.

<code><pre>
--------------------------------------------------------------------------------
-- Function short description.
-- Function long description
--
-- @function [parent=#typename] functionname
-- @param self Parameter description
-- @param #string parametername Parameter description
-- @return #number Typed return description
-- @return #nil, #string Traditional nil and error message
-- @return Untyped return description
</pre></code>
<center><small>Sample of function declaration</small></center>

== Global comment block ==

To declare a function or a field with a [[Koneki/LDT/Technical_Documentation/Documentation_Language#Type_references|type reference]] as ''[[Koneki/LDT/Technical_Documentation/Documentation_Language#Global|global]]'', you just have to attach it to the <code>global</code> type.

<code><pre>
--------------------------------------------------------------------------------
-- Field long description
--
-- @field [parent=#global] #string fieldname

--------------------------------------------------------------------------------
-- Function short description. Function long description
--
-- @function [parent=#global] functionname
-- @param self
</pre></code>
<center><small>Sample of global field and function</small></center>

= Sample mixing code and comments =
<code><pre>
---
-- Module short description.
-- Module _long description_
--
-- @module modulename
local M = {}

---
-- Field description
--
-- @field [parent=#modulename] #string fieldname 
M.fieldname = 'field value'

---
-- Function short description.
-- Function long description
--
-- @function [parent=#modulename] functionname
-- @param self Parameter description
-- @return #number Typed return description
-- @return #nil, #string Traditional nil and error message
function M.functionname(self)
    return 0
end
return M
</pre></code>
<center><small>Sample of documented module</small></center>

== Short references ==

It is way to reference a types and their fields ''in a textual description''. You just have to surround a type reference with <code>@{}</code>. You can reference a types and their fields, functions are handled as a specific type of fields.

* Reference to types
** <code>@{#typename}</code> will refer to type ''typename'' defined in current module.
** <code>@{modulename}</code> will refer to module named ''modulename''.
** <code>@{modulename#typename}</code> will refer to type ''typename'' defined in module ''modulename''.
* Reference to fields
** <code>@{#typename.fieldname}</code> will refer to ''fieldname'' which could be a function or field attached to type ''typename'' defined in current module.
** <code>@{modulename#typename.fieldname}</code> will refer to ''fieldname'' which could be a function or field attached to type ''typename'' defined in ''modulename'' module.

<code><pre>
--------------------------------------------------------------------------------
-- Short description and reference to @{io#io.flush}.
--
-- @function [parent=#typename] functionname
</pre></code>
<center><small>Sample of type reference in a description</small></center>

'''Ambiguity'''

It is possible to use dots in type names, but then it becomes hard to differentiate type name from field name. Let's explained the ''default behavior'':
* Everything before ''#'' is module name
* Everything between ''#'' and last dot is type name.
* Everything after last dot is field name
So in <code>@{module.name#type.name.fieldname}</code> will refer to field ''fieldname'' of type named ''type.name'' from module ''module.name''.
Well, but what happens when we simply want to reference a type name containing dots? It is possible to surround type name with parenthesis to remove ambiguity.
* <code>@{modulenamed#(type.name).fieldname}</code> will refer to field named ''fieldname'' from type named ''type.name'' defined in module named ''modulename''.
* <code>@{modulenamed#(type.name)}</code> will refer to type named ''type.name'' from module named ''modulename''
* <code>@{#(type.name)}</code> will refer to type named ''type.name''.

= Limitations =

== Identifiers ==

Due to our way of parsing, is not possible to use tag names as identifiers. So assume that the following identifiers are reserved:

* field
* function
* module
* param
* return
* type

== Markdown ==

Markdown allows reusable element. As each description is parsed separately, you cannot reuse an element from another description.

== Inference ==

So far, all information about the documented module has to be explicitly described. There is no inference enabling us to extract documentation-valuable information from the code ... yet.

== Parsing ==

We use ''Metalua'' to parse comments, and it can't parse only comments. So if you write a documentation only file, ensure it contains a least a valid statement. Most of the time we use, <code>return nil</code> at end of file.

= Tips =

== Usage ==

When you have a comment block related to a concept, you can give one or several samples of how it should be used by using the <code>@usage</code> keyword.

<code><pre>
--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @usage local modulename = require 'modulename'
-- @usage require('modulename')
</pre></code>
<center><small>Sample of module declaration with usage markup.</small></center>