sub RnR
{
        push my @list, @_;
        return sub
        {
                my $r = 1 + int rand(@list-1);

                # swap [0] with [$r]
                my $t = $list[$r];
                $list[$r] = $list[0];
                $list[0] = $t;

                return $t;
        }
}

# usage
my $rnr = RnR(qw(a b c d e f g));
print "next :", $rnr->(), "\n" for (1..20);