Planner#parser can't parse TIMESTAMP() function

      FrameworkConfig coreConfig = Frameworks.newConfigBuilder().build();
      Planner corePlanner = Frameworks.getPlanner(coreConfig);
      corePlanner.parse("SELECT TIMESTAMP('2022-05-21 08:00:00'");
      // Caused by: org.apache.calcite.sql.parser.babel.ParseException: Incorrect syntax near the keyword 'TIMESTAMP' at line 1, column 8.

      FrameworkConfig babelConfig = Frameworks.newConfigBuilder()
          .parserConfig(SqlParser.Config.DEFAULT.withParserFactory(
              SqlBabelParserImpl.FACTORY))
          .build();
      Planner babelPlanner = Frameworks.getPlanner(babelConfig);
      babelPlanner.parse("SELECT TIMESTAMP('2022-05-21 08:00:00'");
      // Caused by: org.apache.calcite.sql.parser.babel.ParseException: Incorrect syntax near the keyword 'TIMESTAMP' at line 1, column 8

select timestamp('2022-05-21 08:00:00')
// result
timestamp('2022-05-21 08:00:00') 
2022-05-21 08:00:00

select timestamp('2022-05-21 08:00:00')
//ORA-00923: FROM keyword not found where expected

select timestamp('2022-05-21 08:00:00')
// Msg 195 Level 15 State 10 Line 1
// 'timestamp' is not a recognized built-in function name.