code: function onEachTopic(eachTopic) {
          return (data) => forum.Topic.parseExtended(data)
              .then((parsed) => eachTopic(parsed.topic, parsed.user, parsed.category));
      }
docs: Topic Processor
  
  @typedef {TopicProcesspr}
  @function
  
  @param {Topic} topic Topic to process
  @param {User} user Topic Opening User
  @param {Category} category The category `topic` belongs to
  @returns {Promise} Resolves on completion
   
  Create a function to process topic data using a Topic Processor
  
  @private
  
  @param {TopicProcessor} eachTopic Function to process topics
  @returns {function} Internal topic processing function