code: def expect_keyword(parser, value):
      # type: (Parser, str) -> Token
      
      token = parser.token
      if token.kind == TokenKind.NAME and token.value == value:
          advance(parser)
          return token
  
      raise GraphQLSyntaxError(
          parser.source,
          token.start,
          u'Expected "{}", found {}'.format(value, get_token_desc(token)),
      )
docs: If the next token is a keyword with the given value, return that
      token after advancing the parser. Otherwise, do not change the parser
      state and return False.