• Subject: Re: Lua minus null (-0)
• From: David Kastrup <dak@...>
• Date: Thu, 09 Jun 2011 17:26:52 +0200

```Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br> writes:

>> #define lua_number2str(s,n)     sprintf((s), LUA_NUMBER_FMT, (n)+0.0)
>
> That seems to work but can be confusing as well:
> 	z=0 a=z b=-z print(a,b,a==b,1/a,1/b)
> now prints
> 	0	0	true	inf	-inf
> when it originally printed
> 	0	-0	true	inf	-inf
>

Well, so what?

Either case we have a==b, and 1/a ~= 1/b.  As long as a==b, the basic
surprise is f(a)~=f(b).  f(x)=1/x yields such a surprise,
f(x)=tostring(x) does, f(x)=x+0 does not, and f(x)=tostring(x+0) does
not, either.  I don't see how having -0 print differently when it
compares equal is of help.

It is not like

> z=1e-10 a=z b=z+1e-25 print(a,b,a==b,1/a,1/b)
1e-10   1e-10   false   10000000000     10000000000
> z=1e-10 a=z b=z+1e-24 print(a,b,a==b,1/a,1/b)
1e-10   1e-10   false   10000000000     9999999999.9999

are particularly surprising, either.  Why do we want differing print
representations for values comparing as equal when we don't even have
differing print representations for some values comparing as unequal?

--
David Kastrup

```