function ascentManager(oboeBus, handlers){
   "use strict";
   
   var listenerId = {},
       ascent;

   function stateAfter(handler) {
      return function(param){
         ascent = handler( ascent, param);
      }
   }
   
   for( var eventName in handlers ) {

      oboeBus(eventName).on(stateAfter(handlers[eventName]), listenerId);
   }
   
   oboeBus(NODE_SWAP).on(function(newNode) {
      
      var oldHead = head(ascent),
          key = keyOf(oldHead),
          ancestors = tail(ascent),
          parentNode;

      if( ancestors ) {
         parentNode = nodeOf(head(ancestors));
         parentNode[key] = newNode;
      }
   });

   oboeBus(NODE_DROP).on(function() {

      var oldHead = head(ascent),
          key = keyOf(oldHead),
          ancestors = tail(ascent),
          parentNode;

      if( ancestors ) {
         parentNode = nodeOf(head(ancestors));
 
         delete parentNode[key];
      }
   });

   oboeBus(ABORTING).on(function(){
      
      for( var eventName in handlers ) {
         oboeBus(eventName).un(listenerId);
      }
   });   
}
A bridge used to assign stateless functions to listen to clarinet.

As well as the parameter from clarinet, each callback will also be passed
the result of the last callback.

This may also be used to clear all listeners by assigning zero handlers:

   ascentManager( clarinet, {} )