#!/usr/bin/perl
use strict;
use warnings;

my $n = 3;
my @a = "a".."b";

my @b = vw_rep(\@a, $n); # variations with repetition (Algorithm::Combinatorics)

use Data::Dump; dd \@b;

sub vw_rep {
    my ($ref, $n) = @_;
    my @c;
    for my $k (0 .. $n-1) {
        my $L = 0;
        for (1 .. @$ref**$k) {
            for my $i (0 .. $#$ref) {
                for (1 .. @$ref**($n-1 - $k)) {
                    push @{ $c[$L++] }, $ref->[$i];
                }   
            }
        }
    }
    return @c;
}

__END__
C:\Old_Data\perlp>perl var_w_rep.pl
[
  ["a", "a", "a"],
  ["a", "a", "b"],
  ["a", "b", "a"],
  ["a", "b", "b"],
  ["b", "a", "a"],
  ["b", "a", "b"],
  ["b", "b", "a"],
  ["b", "b", "b"],
]