RE: Saving the lua state

[Luiz Henrique de Figueiredo <lhf@...>]

>From lua-l@tecgraf.puc-rio.br  Fri Jul 28 16:32:06 2000
>From: Falko Poiker <fpoiker@relic.com>

>Cool.  Save.lua has pretty much everything I need.

save.lua is meant only as an example, really.
You should adapt it to your uses, but it does show how to save a table and
global variables so that their values are restored when the file is loaded
later.

>What part of lua's design makes it "designed for" saving stuff?

Not for saving per se, but for allowing applications to easily read values of
its "control variables".
This is what we called "configuration" in the SEMISH'94 paper that described
Lua 1.1. See http://www.tecgraf.puc-rio.br/lua/semish94.html .
In such configuration files, there no need for control flow, but there is
a need for data structuring, hence tables.
So, support for configuration was one of design goals of Lua.
Of course, once you have this support, you have support for saving state,
because all you have to do is write a file that can be read later.

>In this simplistic example, I demonstrate something I haven't been
>able to achieve with lua yet, that is blocking functions.  Is 
>there a way to do this?  

No. You have to write your application in a different way, probably using
threads and the new multi-state API of Lua 4.0.

>According to the
>lua reference doc, you can only read an entire file, a string
>or a buffer, but since lua 4.0 is reentrant, there's no saying
>you can't read a file line by line.  Does this make sense?  Is
>line reading (through a buffer maybe?) possible for lua?

You can only load *complete* chunks.
You can load it line by line, but only if the lines make sense as a whole.
That's what the sample interpreter lua.c does.
In particular, you cannot load the body of a function line by line, sorry.
Again, it seems to me that you need multithreading.

>At any rate, the reason I wanted to save the lua state innards 
>(using the second form mentioned above) is because the player 
>may want to save his game while his soldier is "moving to" 
>his target.  Lua would then be in the middle of reading a file, 
>possibly needing a save of the innards of the lua state.

Like I said, it seems to me that this is mainly a question about the
*architecture* of your game and has not much to do with Lua.
But I'm not a game expert. Perhaps other people in this list can help here.
--lhf