# File lib/treetop/compiler/metagrammar.rb, line 1828
      def _nt_parenthesized_expression
        start_index = index
        if node_cache[:parenthesized_expression].has_key?(index)
          cached = node_cache[:parenthesized_expression][index]
          @index = cached.interval.end if cached
          return cached
        end

        i0, s0 = index, []
        if input.index('(', index) == index
          r1 = instantiate_node(SyntaxNode,input, index...(index + 1))
          @index += 1
        else
          terminal_parse_failure('(')
          r1 = nil
        end
        s0 << r1
        if r1
          r3 = _nt_space
          if r3
            r2 = r3
          else
            r2 = instantiate_node(SyntaxNode,input, index...index)
          end
          s0 << r2
          if r2
            r4 = _nt_parsing_expression
            s0 << r4
            if r4
              r6 = _nt_space
              if r6
                r5 = r6
              else
                r5 = instantiate_node(SyntaxNode,input, index...index)
              end
              s0 << r5
              if r5
                if input.index(')', index) == index
                  r7 = instantiate_node(SyntaxNode,input, index...(index + 1))
                  @index += 1
                else
                  terminal_parse_failure(')')
                  r7 = nil
                end
                s0 << r7
              end
            end
          end
        end
        if s0.last
          r0 = instantiate_node(ParenthesizedExpression,input, i0...index, s0)
          r0.extend(ParenthesizedExpression0)
          r0.extend(ParenthesizedExpression1)
        else
          self.index = i0
          r0 = nil
        end

        node_cache[:parenthesized_expression][start_index] = r0

        return r0
      end