_nt_alternative (Treetop::Compiler::Metagrammar)

    # File lib/treetop/compiler/metagrammar.rb, line 1119
          def _nt_alternative
            start_index = index
            if node_cache[:alternative].has_key?(index)
              cached = node_cache[:alternative][index]
              @index = cached.interval.end if cached
              return cached
            end

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

            node_cache[:alternative][start_index] = r0

            return r0
          end