    import 'dart:io' show File;
    /**
     * print a number
     * "helo"
     * 'string'
     */

    const List<int> list = [1];

    String s = '''
    Multline string single quote
    ''';

    String d = '''
    Multline string double quote
    ''';

    enum Enum { one, two }

    class SimpleClass {}

    abstract class Interface extends SimpleClass {}

    final class Dummy {}

    Stream<int> gen() async* {
      for (int i = 0; i < 100; ++i) {
        yield switch (i) {
          1 => 1,
          _ => throw "Invalid",
        };
        yield i;
      }
    }

    Future<int> printNum(int anum) async {
      print("This is a $anum\n");
      print('This is a $anum\n \'world\'');
      if (anum == 1) {
        switch (anum) {
          case 1:
            return 3;
          default:
            // do while
            do {
              anum--;
            } while (anum < 0);
            // while
            while (anum > 0) {
              anum--;
            }
            break;
        }
        return 1;
      } else {
        return 2;
      }
    }

    // What are you doing?
    void main() {
      final int nn = 10;
      double dd = 1.5;
      double de = double.nan;
      bool boolean = true;
      printNum(nn);
    }