command-line parser DSL

  root := help:
      root.print_help()
      exit(-2)
  help := '-h'
  help += '--help'

  root += version:
      root.print_version()
      exit(-1)
  version := '-v'
  version += '--version'

  root += command
  root += 'help' command:
      command.print_help()
  root += command '--help' => 'help' command

  root += 'version' command:
      command.print_version()
  root += command '--version' => 'version' command:

  command := 'node' node
  command.node := 'list':
      node_list()

  command.node += 'attach' name connect_string optional(force):
      if node.is_available(node_name):
        message = 'node "%s" is already defined' % name
        if force:
          root.warning('%s, would be replaced' % message)
        else:
          root.error(message)
      node_attach(name, connect_string)

  command.node.connect_string := user host port:
    return dict(user=user, host=host, port=port)

  command.node.connect_string.user := '([a-z]+[a-z0-9._]*)@':
    return args[1]

  host := '[a-z]+[a-z0-9._]*'
  host +=  '(digit{1,3})\.(digit{1,3})\.(digit{1,3})\.(digit{1,3})':
    result = []
    for byte in args[1:]:
      if int(byte) > 255:
        root.error('invalid ip address')
      else:
        result.append(int(byte))
    return args[0]
  command.node.connect_string.port := '(digit)+:' :
    if int(args) > 2**16:
        root.error('too big port number')
    else:
        return int(args)

  command.node.detach := 'detach' name optional(force):
      if not node.is_available(node_name):
          message = 'node "%s" did not found' % name
          if force:
              root.warning(message)
              node_detach(name)
          else:
              root.error(message)
      else:
          node_detach(name)

  name := simple_name
  name += complex_name
  simple_name := '[a-zA-Z]+[a-zA-Z0-9]*'
  complex_name := '"([a-zA-Z]+[a-zA-Z0-9 ])*"':
      return args[1]