I was going to write "Tree traversal". Now I don't need to. Great example. Of course, it's possible to replace it with a loop, but if you can do it, you already know what recursion is and when it's good to use it.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]