my $error = '';
    if ( $toggle !~ /^\d+$/ or $toggle == 0 ) {
        $error = "The first argument to &alternate must be a positive integer: $toggle\n";
    }
    if ( ! @$items ) {
        $error .= "The second argument to &alternate must be an array reference.";
    }
    die $error if $error;

##</code><code>##

die "Toggle not greater than 0" unless $toggle > 0;