# File lib/treetop/compiler/metagrammar.rb, line 1031
      def _nt_parsing_expression
        start_index = index
        if node_cache[:parsing_expression].has_key?(index)
          cached = node_cache[:parsing_expression][index]
          if cached
            node_cache[:parsing_expression][index] = cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
            @index = cached.interval.end
          end
          return cached
        end

        i0 = index
        r1 = _nt_choice
        if r1
          r1 = SyntaxNode.new(input, (index-1)...index) if r1 == true
          r0 = r1
        else
          r2 = _nt_sequence
          if r2
            r2 = SyntaxNode.new(input, (index-1)...index) if r2 == true
            r0 = r2
          else
            r3 = _nt_primary
            if r3
              r3 = SyntaxNode.new(input, (index-1)...index) if r3 == true
              r0 = r3
            else
              @index = i0
              r0 = nil
            end
          end
        end

        node_cache[:parsing_expression][start_index] = r0

        r0
      end