Lua & cpp! (Re: Lua constants?)

[Asko Kauppi <asko.kauppi@...>]

I've thought of adding CPP (c preprocessor) support to loading lua 
scripts. It would simply feed them through the cpp first, then to lua. 
This would allow:
	#if 0 	(for commenting out blocks)
	#if HAVE_SOMETHING
	...and all the rest

There's (presumably) a ready-made hook for this in Lua 5.0 somewhere, 
so no patching would be necessary.

Anyone already done this?

-ak


Ando Sonenblick kirjoittaa maanantaina, 4. elokuuta 2003, kello 20:19:

> Gang,
>
> I know lua has no preprocessor, but is there a way to implement 
> constants in
> lua?
>
> I'm setting up a table, currently with hard coded numbers:
>
> t = {
>     a = function() Dispatch(100) end,
>     b = function() Dispatch(101) end,
>     c = function() Dispatch(102) end
>     }
>
> (Dispatch is a registered C routine to do the internal dispatching in 
> my
> app.)
>
> I'd like the flexibility of defining a base number (eg 100) and the 
> rest be
> offsets so that if I need to shift the entire range of numbers, I need 
> only
> change one.
>
> For example
>
> base = 100
>
> t = {
>     a = function() Dispatch(base) end,
>     b = function() Dispatch(base + 1) end,
>     c = function() Dispatch(base + 2) end
>     }
>
> I know I can do the above, but I don't want the extra bit of variable 
> look
> up and math on each call... I want "base + x" to be resolved at 
> compile time
> into a number constant.
>
> Is this possible?
>
> If not, I may implement my own preprocessor to do what I need.  One 
> question
> about that:
>
> If I replace instances of base with a constant number:
>
> t = {
>     a = function() Dispatch(100) end,
>     b = function() Dispatch(100 + 1) end,
>     c = function() Dispatch(100 + 2) end
>     }
>
> And then have lua compile that, is the compile process smart enough to
> collapse the contant math into a single contant: such as
>
> t = {
>     a = function() Dispatch(100) end,
>     b = function() Dispatch(101) end,
>     c = function() Dispatch(102) end
>     }
>
> Or if I call b, will it perform 100 + 1 and than pass that to Dispatch?
>
> Thx,
> Ando
>
>
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> www.spritec.com