memberGet method
Fetch a member by the varName, in the form of
object.varName
varName must be of String type.
Implementation
@override
dynamic memberGet(String varName, {String? from}) {
  switch (varName) {
    case 'int.fromEnvironment':
      return (HTEntity entity,
              {List<dynamic> positionalArgs = const [],
              Map<String, dynamic> namedArgs = const {},
              List<HTType> typeArgs = const []}) =>
          int.fromEnvironment(positionalArgs[0],
              defaultValue: namedArgs['defaultValue']);
    case 'int.parse':
      return (HTEntity entity,
              {List<dynamic> positionalArgs = const [],
              Map<String, dynamic> namedArgs = const {},
              List<HTType> typeArgs = const []}) =>
          int.tryParse(positionalArgs[0], radix: namedArgs['radix']);
    default:
      throw HTError.undefined(varName);
  }
}