Factoring constructor into the superclass

  abstract class AlgorithmState[ResultType](sum: Int) {
    def produce(option: Int)
  }

  class IntAlg(sum: Int) extends AlgorithmState[Int] (sum) {
    def produce(option: Int) = new IntAlg(sum - option)
   }

  class StringAlg(sum: Int) extends AlgorithmState[Int] (sum) {
    def produce(option: Int) = new StringAlg(sum - option)
   }

  // the produce method is identical for Str and Int algorithms. Can I move it into the abstract parent class?
  // How do I instantiate appropriate child objects?