code: @Override
      public R visitProvides(ProvidesTree node, P p) {
          R r = scan(node.getServiceType(), p);
          r = scanAndReduce(node.getDescription(), p, r);
          return r;
      }
docs: {@inheritDoc} This implementation scans the children in left to right order.
  
  @param node  {@inheritDoc}
  @param p  {@inheritDoc}
  @return the result of scanning