Refer to - http://wiki.infinitegrid.org/index.php/LuaSL_-_New_scripting_engine

LuaSL is a Lua based LSL scripting engine that will aim for LSL
compatability first, then adding Lua extensions.  It aims to replace the
woeful XEngine from OpenSim, and at a later stage, be the basis for a
client side scripting engine.


Design.
-------

The basic design will be made up as I go along, but so far I have this -

An object is a file system directory, full of LSL scripts as text files,
notecards as text files, animations as BVH (or later BVJ) files, etc. 
There will be some sort of metadata in place.

A parser parses an LSL script, validating it and reporting errors.

A preprocessor takes the result of the parse, and converts it into Lua
source.  Each LSL script becomes a Lua state.  LSL states are handled as
Lua tables, with each LSL state function being a table function in a
common metatable.  LL and OS functions are likely to be C functions. 
Careful testing should be done with LuaJIT FFI, sandboxing, and
performance testing.

The Lua source is compiled by the Lua compiler.

LuaJIT is used as the Lua compiler, library, and runtime.

Luaproc is used to start up operating system threads and hand Lua
states between them.

Nails is used to pump commands in and out of the LuaSL system.  Incoming
commands invoke LSL events via the LuaSL state metatable.  LL and OS
functions that impact the world will be converted to nails commands sent
to the command pump.

A watchdog thread is used to make sure no LuaSL script spends forever
processing any event.

Some form of serialization will need to be created for saving script
state during shutdowns, passing script state to other threads /
processes / computers.


Test harness.
-------------

I'll build a test harness.  It will be based on EFL Edje Lua, with
buttons for triggering LSL events, SL style dialogs, and other goodies.

The initial goal will be to run standard MLP scripts.  They have minimal
interface to the world, and exercise quite a bit of the rest of LSL. 
They are also quite common, and sometimes responsible for a lot of the
script running load.  Gotta start somewhere, so start with the ~run
script.

Various eina logging domains will be used to handle whisper, say, shout,
etc.

Performance testing will have to be done on 5000 scripts, to see how
that compares against XEngine.


Parser.
-------

The SL viewer code includes a flex/bison based parser that generates C++
code that depends on various other bits of LL source code.  It's GPL 2,
though the flex and bison source files includes no license text.

Flex is BSD and written in C.  Bison is GNU (GPL 3 since 2.4.1, 2.3 is
GPL2) and written in C.  It used to include info that stuff generated by
bison had to be GPL.  Berkeley YACC is public domain, and written in C. 
There is also btyacc, based on the berkeley version, but with some
useful extras.  btyacc version 3 (the version coming from my version of
Ubuntu) apparently no longer supports C, only C++.  It's written in C
though.

Let's see if flex and btyacc will do the trick, and output C.

Might be best to have the LSL to Lua converter as a seperate executable.