Rcmd::Handler - Internal class with miscellaneous interfaces to R language.

 Intended for internal use only. Super class for the core. Provides 
 the native methods.

    my $R_OUTPUT;

    # trap STDERR output from R
    open TMPOUT, '>&', STDERR; close STDERR; open STDERR, '>',\$ R_OUTPUT;

    # call 'library()' method
    my $rcmd= Rcmd->new(); $rcmd->exec('library()');

    # re-open STDERR
    close STDERR; open STDERR, '>&TMPOUT'; close TMPOUT;

    my @pkg_list;
    for my $line (split /\n/, $R_OUTPUT) {
	my ($pkg)= split /\s+/, $line;
	push @pkg_list, $pkg if $pkg;
    }

    return @pkg_list;

    return -1 unless $_[0];
    return -1 unless ref $_[0] eq 'ARRAY';

    my @array= @{+shift};
    return -1 unless $array[0];

    # array is continuous scale (0) or nominal scale (1)
    my $is_nominal= 0;
    for (0 .. ($#array > 9 ? 9 : $#array)) {
        my $item= $array[$_];
        next unless $item;

        if (($item ^ $item) eq '0') { # $item is number
            next;
        } else { # $item is not number
            $is_nominal = 1; # nominal scale
            last;
        }
    }

    return $is_nominal;