This documentation language has been developed as part of LDT, 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 string, number or nil. 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 require function on it-
This concept allow you to express :

• which type will be return by the require function for your module,
• which new global variables will be available after your module was loaded.
  

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 fields and functions to it. This is a way to express the creation of new global variables when a module is loaded.

List

A list is a sequence of values stored in a table under numeric indexes.

Map

A map is a set of key/value pairs stored in a table.

Type Extending

When a sub-type extend a super-type all super-type fields and functions are available from the sub-type.

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 #.

• #boolean
• #nil
• #number
• #string
• #table

Internal references

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

• #typename 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.

• modulename#typename will refer to type typename defined in module modulename.
• modulename#modulename will refer to type modulename returned in module modulename.

Structure types

Enables to describe list and map structures.

• #list<#valuetype> where #valuetype is the reference to the type contained in the list.
• #map<#keyvalue,#valuetype> where #valuetype is the reference to the type contained in the map and #keyvalue the reference of the type used to index map values.

Comments

You could describe explicitly all file API just with our documentation language. But LDT is able to guess quite a lot of this information from code. (see samples)

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 ---.

Special comments can contain a short and an long description. The short description start at the beginning of the comment and continue till . or ?. The long description is the text coming after. By the way, Markdown is supported in all descriptions.

Special comments are handled only if they describe a concept.

Note: All leading -'s in special comments are trimmed.

--------------------------------------------------------------------------------
-- Short description.
-- Long _markdown_ description

Note: _markdown_ is supposed to be interpreted by Markdown.

---
-- Short description.
-- Long description

--[[-
 Short description.
 Long description
]]

--- Short description. Long description

Type comment block

A type comment block is a special comment with a type declaration with @type key word followed by desired type name.

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename

Since 1.2: @list and @map tags. The list and map tags allow to describe if the type is used as a list or a map of elements.

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
-- @list <#valuetypename>

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
-- @map <#keytype,#valuetype>

Since 1.2: @extends tag. The extend tag allow to define that current type is extending the given super-type.

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
-- @extends anothermodule#supertype

Module comment block

Denoted by @module keyword and followed by a module name, a 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.

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename

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

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @return #modulename

---@type modulename

Note: We used #modulename to refer to a declared type, if you want to know more about it refer to 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.

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @return #string

Note: We used #string to refer to a primitive type.

Since 1.2: @list and @map tags. The list and map tags allow to describe if the module is used as a list or a map of elements.

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @list <#valuetype>

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @map <#keytype,#valuetype>

Since 1.2: @extends tag. The extend tag allow to define that current module is extending the given super-type.

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @extends anothermodule#supertype

Field comment block

The field block represents a field of a type. It is possible to declare one with @field keyword followed by optional 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.

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename
-- @field #string fieldname Field description

--------------------------------------------------------------------------------
-- Type short description.
-- Type long description
--
-- @type typename

---
-- Field description
--
-- @field [parent=#typename] #string fieldname 

Function comment block

The function comment block has to be attached to a type. Its keyword is @function. A function can have several parameters denoted by keyword @param, they can be optionally typed with a type reference and have an optional descriptions. Several @return 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 @return markup. Returned values can be optionally typed using a type reference.
Note: If the first @param is called self, LDT will show completion proposal without this parameter but using : invocation operator.

--------------------------------------------------------------------------------
-- 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

Note: It is also possible to document function for types which name contains ".".

--------------------------------------------------------------------------------
-- Function short description.
-- Function long description
--
-- @function [parent=#typeprefix.typename] functionname

Since 1.2: @callof tag. In Lua a table can be call using the metatable keyword __call. To set a type callable just add @callof #typename in the function behind the __call metamethod. The first param should be self and of the type given to callof.

--------------------------------------------------------------------------------
-- Function short description.
-- Function long description
--
-- @callof #typename
-- @param #typename self
-- @param #paramtype paramname

Global comment block

To declare a function or a field with a type reference as global, you just have to attach it to the global type.

--------------------------------------------------------------------------------
-- Field long description
--
-- @field [parent=#global] #string fieldname

--------------------------------------------------------------------------------
-- Function short description. Function long description
--
-- @function [parent=#global] functionname
-- @param self

Samples

Simple module sample

---
-- 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 #number n Parameter description
-- @return #number Typed return description
-- @return #nil, #string Traditional nil and error message
function M.functionname(n)
  if n then return n else return nil, "error" end
end
return M

---
-- Module short description.
-- Module _long description_
local M = {}

---
-- Field description
M.fieldname = 'field value'

---
-- Function short description.
-- Function long description
-- @param #number n Parameter description
-- @return #number Typed return description
-- @return #nil, #string Traditional nil and error message
function M.functionname(n)
  if n then return n else return nil, "error" end
end
return M

---
-- Module short description.
-- Module _long description_
--
-- @module modulename

---
-- Field description
--
-- @field [parent=#modulename] #string fieldname 

---
-- Function short description.
-- Function long description
--
-- @function [parent=#modulename] functionname
-- @param #number n Parameter description
-- @return #number Typed return description
-- @return #nil, #string Traditional nil and error message
return nil

Object-oriented sample

--- A module that allow to manage geometry shapes
-- @module geometry
local M = {}

--- A rectangle 
-- @type rectangle
-- @field #number x 
-- @field #number y 
-- @field #number width
-- @field #number height
local R = {x=0, y=0, width=100, height=100, }

--- Move the rectangle
-- @function [parent=#rectangle] move
-- @param self
-- @param x
-- @param y
function R.move(self,x,y)
  self.x = self.x + x
  self.y = self.y + y
end

--- Create a new rectangle
-- @function [parent=#geometry] newRectangle
-- @param x
-- @param y
-- @param width
-- @param height
-- @return #rectangle the created rectangle
function M.newRectangle(x,y,width,height)
  local newrectangle = {x=x,y=y,width=width,height=height}
    
  -- Set to new rectangle the properties of a rectangle
  setmetatable(newrectangle, {__index = R})
  return newrectangle
end

return M

--- A module that allow to manage geometry shapes
local M = {}

--- A rectangle 
-- @type rectangle
local R = {x=0, y=0, width=100, height=100, }

--- Move the rectangle
function R.move(self,x,y)
  self.x = self.x + x
  self.y = self.y + y
end

--- Create a new rectangle
-- @return #rectangle the created rectangle
function M.newRectangle(x,y,width,height)
  local newrectangle = {x=x,y=y,width=width,height=height}
    
  -- set to new rectangle the properties of a rectangle
  setmetatable(newrectangle, {__index = R})
  return newrectangle
end

return M

Callof sample

The @callof tag is only available since the v1.2

--- A module that allow to manage circle shapes
-- @module circleModule
local M = {}
 
--- A circle
-- @type circle
local C = {radius=0, x=0, y=100}
 
--- Move the circle
-- @function [parent=#circle] move
function C.move(self,x,y)
  self.x = self.x + x
  self.y = self.y + y
end
 
--- Create a new circle
-- @callof #circleModule
-- @return #circle the created cicle
local function new(self,radius,x,y)
  local newcircle = {radius=radius,x=x,y=y}
 
  -- Set to new circle the properties of a circle
  setmetatable(newcircle, {__index = C})
  return newcircle
end

setmetatable(M,{__call=new})
 
return M

local circlemodule = require "circleModule"

local firstcircle = circlemodule(10,0,0)
local secondcircle = circlemodule(50,10,0)

firstcircle.radius = 20

List and Map samples

The @list and @map tags are only available since the v1.2

---
-- A simple addressbook module
--
-- @module addressbook
-- @list <#contact>
local M = {}

--- @type contact
-- @field #string name Contact full name
-- @field #number phone Contact landline

function M.empty()
  return M[1] == nil
end

function M:add(name,phonenumber)
  table.insert(self,{name = name, phone = phonenumber})
end

---
-- @return #contact
-- @return nil, errormsg
function M:find(name)
  for _, contact in pairs(self) do
    if (contact.name == name) then
      return contact
    end
  end
  return nil, string.format("No contact found under the name %s", name)
end

return M

---
-- System made of users
--
-- @module system
-- @map <#string, #user> users All users sorted by identifier
local M = { }

---
-- User description at system level
--
-- @type user
-- @field #string name User full name
-- @field #number rights
local users = { }

---
-- Sanity checks
function M.checks()
  if not (M.root and M.root.rights == 777) then
    error('No root user found.')
  end
end

return M

Extends sample

The @extends tag is only available since the v1.2

---
-- @module mymath
-- @extends math#math
local M = require "math"

--- Generate a Fibonacci sequence
-- @param #number n the size of sequence (10 by default)
-- @return #list<#number>
function M.fibonacci(n)
  assert(n>0)
  local size = n or 10
  local sequence = {}

  for i = 1,size do
    if (i == 1) then
      sequence[i] = 0
    elseif (i == 2) then
      sequence[i] = 1
    else
      sequence[i] = sequence[i-1] + sequence[i-2]
    end
  end

  return sequence
end

return M

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 @{}. You can reference a types and their fields, functions are handled as a specific type of fields.

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

Note: So far, there are no short references for globals.

--------------------------------------------------------------------------------
-- Short description. Long description with a reference to @{io#io.flush}.
--
-- @function [parent=#typename] functionname

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 @{module.name#type.name.fieldname} 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.

• @{modulenamed#(type.name).fieldname} will refer to field named fieldname from type named type.name defined in module named modulename.
• @{modulenamed#(type.name)} will refer to type named type.name from module named modulename
• @{#(type.name)} will refer to type named type.name.

Limitations

Markdown

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

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, return nil 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 @usage keyword.

--------------------------------------------------------------------------------
-- Module short description.
-- Module long description
--
-- @module modulename
-- @usage local modulename = require 'modulename'
-- @usage require('modulename')