code: def add_rec_new(self, k, val):
          
          self.rec_new(val)
          self[k] = val
          return val
docs: Recursively add a new value and its children to me, and assign a
          variable to it.
  
          Args:
              k (str): The name of the variable to assign.
              val (LispVal): The value to be added and assigned.
  
          Returns:
              LispVal: The added value.