anchor.diff:  
     int decimals = 0;
     int multi = 1;
  +  bool solved = false;
   
     BinaryOperation operation;
     var operands = new Queue<Term>();
  
positive.code:   CalculatorElement.created() : super.created();
  
    void number(Event e, var detail, ButtonElement target) {
      if (decimals > 0) {
        current = current + dec(multi) * dec(target.value) / dec(decimals);
        decimals *= 10;
  
negative.code:       throw 'Try again later, trying to figure out what went wrong.';
      } else {
        current = operands.removeFirst().evaluate();
        solved = true;
      }
    }
  
    void _prepareNextTerm(BinaryOperation operation) {
      operands.add(new NullaryTerm(current));
      operations.add(operation);
      solved = false;
      current = dec(0);
      decimals = 0;
      multi = 1;
  