I needed to do an n-ary tree traversal recently with some Javascript code that I’m working on and I initially wrote an iterative n-ary tree-traversal algorithm (using a node stack with a while loop). I wanted to keep track of some extra (depth-dependent) data during the traversal and I didn’t like the way I was forced to do it with the iterative algorithm. I also didn’t feel like adding a new function to the namespace. Then I realized that you can create function-literals in Javascript and self-invoke them. So I ended up with the an anonymous self-invoked recursive function. Here’s the basic skeleton for an n-ary tree traversal (this one is pre-order):

(function(node){
    for(var i = 0; i < node.children.length; i++) {
         console.log(node.data);
         arguments.callee(node.children[i]);
    }
}(root));

You can also do a binary tree traversal (this one is also pre-order):

(function(node){
    if(node != null) {
       console.log(node.data);
       arguments.callee(node.left);
       arguments.callee(node.right);
    }
}(root));

Seems very elegant and also very Lisp-like to me (must be the parentheses!)