sub isa {
    my $obj = shift;
    my $base = ref($obj) || $obj;
    my $class = shift;
    my %is_seen;
    my @pkgs = ("UNIVERSAL", $base);
    no strict 'refs';
    while (scalar @pkgs) {
        my $pkg = pop @pkgs;
        return 1 if ($pkg eq $class);    # Found it!
        next if exists $is_seen{$pkg};   # Already processed this one
        ++$is_seen{$pkg};                # Mark this package seen
        push @pkgs, @{"${pkg}::ISA"};    # Append what this inherits from
    }
    # Searched the inheritance tree, failed to find it, so...
    return 0;
}