use strict;

my @array = ["a","b","c","d"];
my $newlist = combine(2,@array);
foreach my $list (@$newlist)
{
    print "[" . join(",", @$list) . "]\n";
}


# takes a list of items
# returns a list of lists of those items for each combination
sub combine {
    my $length = shift;
    my $items = shift;    
    my @list;
    if ($length == 1)
    {
        foreach my $item (@$items)
        {
            push @list,[$item];
        }
    }
    else
    {
        my $l = length(@$items) + 1;
        foreach (0..$l)                     # once for each item
        {
            my $tempa = shift @$items;      # get first item(a)
            
            # get permutations for this set, but one 
            # shorter (without current item)
            my $templist = combine($length-1,$items);  
            foreach my $i (@$templist)
            {
                unshift @$i,$tempa;        
                push @list,$i;
            }
            push @$items,$tempa;
        }
    }
    return [@list];
}

1;