sub pack (@array) returns Array {
    my @unpacked = @array;
    my (@list, @packed);
    while @unpacked {
        @list.push(@unpacked.shift) while !@list || @list[0] eq @unpacked[0];
        @packed.push([@list]);
        @list = ();
    }
    return @packed;
}
pack(<a a a a b c c a a d e e e e>).perl.say;