use Math::Combinatorics qw(combine);

my @data       = qw(A B C);
my @frequency  = qw(3 2 1);
my $racklength = 2;

my $combinat = Math::Combinatorics->new(count   => $racklength,
                                      data      => [@data],     
                                      frequency => [@frequency],
                                     );

while(my @combo = $combinat->next_multiset){
    print join(' ', @combo)."\n";
}