#!/usr/bin/perl
use strict;
use warnings;
use Algorithm::Combinatorics qw(variations_with_repetition);


my @data = qw(a b c);
my $iter = variations_with_repetition( \@data, $#data );

while ( my $c = $iter->next ) { 
    print @$c, "\n";
}

__END__

Output:
aa
ab
ac
ba
bb
bc
ca
cb
cc