lazy.js

'use strict';

function generate(parent, name) {
  var node = new parent.constructor();

  Object.defineProperty(parent, name, {
    enumerable   : true,
    configurable : false,
    writable     : false,
    value        : node
  });

  return node;
}

function lazify(entity, axis) {
  Object.defineProperty(entity, axis, {
    configurable : true, enumerable : true,
    get : generate.bind(null, entity, axis)
  });
}

function List() {
  lazify(this, 'next');
}

function Tree() {
  lazify(this, 'left');
  lazify(this, 'right');
}

module.exports = {
  List : List,
  Tree : Tree
};