sclass PrintingBitOutputStream > BitOutputStream {
  void writeBit(bool b) {
    print(b ? 1 : 0);
  }
  
  // little-endian (starts with lowest bit)
  void writeBits(int data, int nBits) {
    print("[" + n2_lpad(3, nBits) + "] " + littleEndianBitsToString(data, nBits));
  }
}