I'm not adverse to a purely intellectual challenge.

But the specification of what is and what is not zero doesn't seem to comply with any either real-world or rational definition that I can think of. I cannot think of any existing implementation that would interprete "0" as zero, and not "00" or "0 ". Nor can I see any rational for doing so.

Without some logic as to why these arbitrary rules have been picked, you might as well do:

#! perl -slw
use strict;
use feature qw[ state ];
use Scalar::Util qw[ dualvar ];


my @true = ( 0, "0", 0.0, Scalar::Util::dualvar( 0, 1 ) );
my @false = (
    1, "foo", "00", "0 ", undef, "",
    Scalar::Util::dualvar( 1, 0 ), "0.0"
);

sub isZero {
    state %isZero;
    unless( %isZero ) {
        $isZero{ $_ } = 1 for @true;
        $isZero{ $_ } = 0 for @false;
    }
    return $isZero{ $_ } if exists $isZero{ $_ };
    die "Don't know";
}


print "$_ : ", isZero( $_ ) for @true;
print "$_ : ", isZero( $_ ) for @false;
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As it can be infinitely extended to deal with any set of illogical rules.