static S listSomeFiles(File[] files) {
  ret listSomeFiles(asList(files));
}

static S listSomeFiles(L<File> files) {
  new StringBuilder buf;
  for (File f : files) {
    boolean isDir = f.isDirectory();
    S line = (isDir ? "D" : "F") + " " + f.getName();
    if (!isDir) {
      long size = f.length();
      S suffix = "B";
      if (size >= 1024*1024) {
        size = (size+1024*1024-1) / (1024*1024);
        suffix = "MB";
      } else if (size >= 1024) {
        size = (size+1024-1) / 1024;
        suffix = "KB";
      }
      line += " (" + size + " " + suffix + ")";
    }
    buf.append(line).append("\n");
  }
  ret str(buf);
}