cprint {
  /* 
    static int ackermann_int(int a, int b) {
      if (a == 0)
        ret b+1;
      if (b == 0)
        ret ackermann_int(a-1, 1);
      ret ackermann_int(a-1, ackermann_int(a, b-1));
    }
  */

  srecord f_ackermann(int a, int b) implements VStack.Computable<Int> {
    void step(VStack stack, O subComputationResult) {
      if (!stack.justReturned) {
        if (a == 0)
          stack._return(b+1);
        else if (b == 0)
          stack.tailCall(new f_ackermann(a-1, 1);
        else
          stack.push(new f_ackermann(a, b-1));
      } else
        stack.tailCall(new f_ackermann(a-1, subComputationResult/Int));
    }
  }
  
  start-thread {
    print("Result: " + vStackComputeWithStats(new f_ackermann(2, 2)));
    
    // detailed run
    VStack stack = new(new f_ackermann(2, 2));
    printStruct(stack);
    while ping (stack.step()) {
      printStruct(stack);
      stack = restructure(stack); // persist to string and re-create
    }
  }
}