There is a -0 too

Signed zeroes exist in the mpfr library - and are therefore accessible to perl via Math::MPFR:

C:\_32>perl -MMath::MPFR -e "$z=Math::MPFR->new(0);$z/=-1;print $z"
-0
[download]

They don't seem to be accessible via either Math::Pari or Math::BigFloat

C:\_32>perl -MMath::Pari -e "$x=PARI(0);$x/=-1;print $x"
0
C:\_32>perl -MMath::BigFloat -e "$z=Math::BigFloat->new(0);$z/=-1;prin
+t $z"
0
[download]

can you overload unary plus?

I don't think so. Even if you could, returning '+0' would not use the overloaded '+' subroutine - overloading works only with blessed objects (and 0 is not a blessed object :-)

Cheers,
Rob