public static MRInstruction[] parseMixedInstructions(String str)
      throws DMLUnsupportedOperationException, DMLRuntimeException {
    if (str == null || str.isEmpty()) return null;

    Instruction[] inst = InstructionParser.parseMixedInstructions(str);
    MRInstruction[] mrinst = new MRInstruction[inst.length];
    for (int i = 0; i < inst.length; i++) {
      mrinst[i] = (MRInstruction) inst[i];
    }

    return mrinst;
  }