Re: Zero as False

[Paige DePol <lual@...>]

Replying to myself just to add one change also required for making Zero as False work.

In the luaK_goiftrue function in lparser.c one line needs to be changed:

FROM: case VK: case VKNUM: case VTRUE: {
  TP: case VTRUE: {

This way constants and numbers will be checked if they are numeric 0 or not.

Again, if anyone knows why this is a bad idea (other than because it changes the semantics of the language, but remember I am creating a new variant of Lua so that is not a problem) please let me know.

So far, however, it does seem to work quite well, and since 0 has been false for as long as I have been coding it just makes me happy to have it work that way in my scripting language as well! ;)

~pmd~



On Nov 18, 2013, at 12:30 PM, Paige DePol <lual@serfnet.org> wrote:

> So, I was poking around in the Lua 5.2 code and I found this in lobject.h:
> 
> #define l_isfalse(o)	(ttisnil(o) || (ttisboolean(o) && bvalue(o) == 0))
> 
> Since I am in the process of heavily hacking Lua (and in the process creating a scripting language for my game engine) I decided I really wanted numeric '0' to also be false.
> 
> To that end I changed the above macro as follows:
> 
> #define l_isfalse(o)	(ttisnil(o) || (ttisnumber(o) && nvalue(o) == 0) || \
>                                       (ttisboolean(o) && bvalue(o) == 0) )
> 
> Not surprisingly this works very well, numeric zero is now a false value and logic statements now work as expected when the result of an expression is zero. 
> 
> I grep'd 'l_isfalse' and can not see anywhere that this change would adversely affect anything in the Lua core itself. So, if anyone else is working on a Lua variant and would like zero to be false, this seems to be the ticket!
> 
> This, of course, breaks with the official Lua rules, however, I am not too concerned about that. I am using Lua as the base for a scripting language I am calling LUNiA (my game engine is called ONiA).
> 
> Just thought I would share the discovery and see if anyone knows anything I missed that makes this change a bad idea.
> 
> ~pmd~