# File lib/mail/parsers/rfc2822.rb, line 14
    def _nt_ALPHA
      start_index = index
      if node_cache[:ALPHA].has_key?(index)
        cached = node_cache[:ALPHA][index]
        @index = cached.interval.end if cached
        return cached
      end

      if has_terminal?('\G[a-zA-Z]', true, index)
        r0 = instantiate_node(SyntaxNode,input, index...(index + 1))
        @index += 1
      else
        r0 = nil
      end

      node_cache[:ALPHA][start_index] = r0

      r0
    end