gistfile1.js

var doTree = function (tree, func) { 
    func (tree.value); 
    for (var child in tree.children) { doTree (child); } 
};

var makeNode = function (i) { return { value: i, children: [] };};

var numTree = { value: 42, children: [makeNode (1), makeNode (2)]};

var sumTree = function (i) { if (this.sum == undefined) this.sum = 0; else this.sum += i; };

doTree (numTree, sumTree);
print (sumTree.sum);