Dart: List directory recursively (tree, ls)

Dart: List directory recursively (tree, ls)

  ls(String where, [String prefix]) {
    if(prefix == null) {
      prefix = '';
    }
    var dir = new Directory(where);
    print(where);
    List contents = dir.listSync();
    for (var fileOrDir in contents) {
      if (fileOrDir is File) {
        print(fileOrDir.path);
      } else if (fileOrDir is Directory) {
        print(fileOrDir.path);
        ls(fileOrDir.path, prefix + '-');
      }
    }
  }