gistfile1.as

  public static function getFirstPath (from:ClassType, to:ClassType):Option<Path> 
  {
    
    function loop(from:ClassType, to:ClassType, path:Path) 
    {
      trace(loop); // boom, loop is null in my case
      
      function findInSuperOrInterface () 
      {
        function findInSuper () 
        {
          var sc = from.superClass;
          return if (sc != null) loop(sc.t.get(), to, path.concat([SuperClass])) else None;
        }
        
        function findInInterfaces () 
        {
          function findInInterface (cur, index) return loop(cur.t.get(), to, path.concat([InterfaceAt(index)]));
          function findFirst (acc:Option<Path>, cur, index) return acc.orElse(findInInterface.partial1_2(cur, index));
          
          return from.interfaces.foldLeftWithIndex(findFirst, None);
        }
        return findInSuper().orElse(findInInterfaces);
      }
      
      return if (ClassTypes.eq(from, to)) Some(path) else findInSuperOrInterface();
    }
    trace(loop); // #function:3, everything is fine here
    return loop(from, to, []);
  }