code: def fold(self, elems):
          
  
          lhs, rhs = elems
  
          if isinstance(lhs, Constant):
              return [rhs if lhs.value else lhs]
  
          return [Instructions([lhs, JumpIfNot(len(rhs) + 1), pop, rhs])]
docs: Perform constant folding.  If the result of applying the
          operator to the elements would be a fixed constant value,
          returns the result of applying the operator to the operands.
          Otherwise, returns an instance of ``Instructions`` containing
          the instructions necessary to apply the operator.
  
          :param elems: A list (or list-like object) containing the
                        elements.
  
          :returns: A list of one element, containing the instructions
                    necessary to implement the operator.