# File lib/treetop/compiler/metagrammar.rb, line 1158
      def _nt_alternative
        start_index = index
        if node_cache[:alternative].has_key?(index)
          cached = node_cache[:alternative][index]
          if cached
            cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
            @index = cached.interval.end
          end
          return cached
        end

        i0 = index
        r1 = _nt_sequence
        if r1
          r0 = r1
        else
          r2 = _nt_primary
          if r2
            r0 = r2
          else
            @index = i0
            r0 = nil
          end
        end

        node_cache[:alternative][start_index] = r0

        r0
      end