I'm very impressed by this solution, and it's author, but completely unimpressed by the people who voted the solution "best practice". While it is certainly clever, I wouldn't say a recursive solution is exactly "best practice". I was thought in A&D to avoid recursion wherever possible. Typically this sort of thing will crowd the stack with the return adresses and parameters of outer calls. It is very functional in style though. So kudos, once again, for cleverness.