Question: Lua Constructor Mechanism

[nelson@...]

Hi everyone,

Recently, I picked up some of the Lua related technical documents 
again, and I tried to figure out how Lua can benefit my current 
project. Regarding the article titled "SPE Paper" which is under the 
link: http://www.tecgraf.puc-rio.br/lua/spe.html

I was trying to play with Lua's simple constuctor mechanism, by using 
the example used in the document. Namely,

window1 = Window{ x = 200, y = 300, foreground = "blue" } 

which is the syntactic sugar for 

window1 = Window( { x = 200, y = 300, foreground = "blue" ) } with 
initailization.

However, I received following error message:
----------------------------------------------------------------------
> window1 = Window{ x = 200, y=300, foreground = "blue" }  
error: attempt to call global `Window' (a nil value)
stack traceback:
   1:  main of string "window1 = Window{ x = 200, y=300,foregroun..." 
at line 1
----------------------------------------------------------------------

I expected it should create a instance of "Window" Class (I think in  
C++. :) ) which internally creates table and the elements within. Of 
course, I can explicitly create table as a window object.
But, I am trying to use Lua to simulate C++ syntax for prototyping 
Therefore, I intend to try this interesting feature.

I wonder if there is anything need to be created / initailized before 
constructing a object/instance using lua's constructor mechanism??

Thanks in advance!! :)
And enjoy using Lua!!

Nelson