[Dev-luatex] Minimal example of using mplib in luatex

[Nicola]

Hi,
can someone show me a minimal example of how to embed a MetaPost figure 
into a (La)TeX document using LuaTeX (along the lines of embedded 
MetaPost code in ConTeXt)? Provided that that's the goal of mplib, of 
course... I'm using the latest LuaTeX as of today (0.40.6 beta). This is 
where I've got so far:

\documentclass{article}
\usepackage[english,italian]{babel}
\begin{document}
\directlua{
local mplib = require('mplib') 
local mp = mplib.new ({ ini_version = false, mem_name = 'plain' }) 
if mp then 
   local l = mp:execute([[ 
      beginfig(1); 
         fill fullcircle scaled 20; 
      endfig; 
   ]]) 
   if l and l.fig then 
      print (l.fig[1]:postscript()) 
   end 
   mp:finish(); 
end
}

\end{document}

This compiles successfully (with pdflualatex), but it does not generate 
any output figure. How do I generate an output figure and/or how do I 
include it into the document?

Besides, is it possible to use mplib with Lua (not LuaTeX)? If so, how?

Thanks,
Nicola