code: function(obj, visitor, leafMemo, context) {
        var reducer = function(value, key, parent, subResults) {
          return visitor(subResults || leafMemo, value, key, parent);
        };
        return walkImpl(obj, this._traversalStrategy, null, reducer, context, true);
      }
docs: Builds up a single value by doing a post-order traversal of `obj` and calling the `visitor` function on each object in the tree. For leaf objects, the `memo` argument to `visitor` is the value of the `leafMemo` argument to `reduce`. For non-leaf objects, `memo` is a collection of the results of calling `reduce` on the object's children.