permutations with repetition

A little Perl snippet that generates all the permutations with repetition allowed, using recursion:

#!/usr/bin/perl                                                                                                   
$max_length = 3;
@collection = ('A','B','C');

generate('');

sub generate {
    my ($val) = $_[0];
    my ($add) = $_[1];
    $val .= $add;

    my $item;

    if (length($val) > $max_length - 1) {
        print "$val \n";
    } else {
        foreach $item (@collection) {
            generate($val,$item);
        }
    }
}

Generates:

AAA
AAB
AAC
ABA
ABB
ABC
ACA
ACB
ACC
BAA
BAB
BAC
BBA
BBB
BBC
BCA
BCB
BCC
CAA
CAB
CAC
CBA
CBB
CBC
CCA
CCB
CCC