Visitor pattern: Number arithmetics based on input

Let's say we have the following data hierarchy in C# to evaluate mathematic (prefix) expressions in int arithmetics:

abstract class Expression {
        public abstract int Evaluate();
}

class ValueExpression : Expression {
    public int Value {
        get;
    }

    public sealed override int Evaluate() {
        return Value;
    }
}

abstract class OperatorExpression : Expression {
    // ...
}

abstract class BinaryExpression : OperatorExpression {
    protected Expression op0, op1;

    public Expression Op0 {
        get { return op0; }
        set { op0 = value; }
    }

    public Expression Op1 {
        get { return op1; }
        set { op1 = value; }
    }

    public sealed override int Evaluate() {
        return Evaluate(op0.Evaluate(), op1.Evaluate());
    }

    protected abstract int Evaluate(int op0Value, int op1Value);
}

sealed class PlusExpression : BinaryExpression {
    protected override int Evaluate(int op0Value, int op1Value) {
        return checked(op0Value + op1Value);
    }
} // and more operators...

How could I use the visitor pattern to evaluate an expression and write out a result as int or double based on the user input? I thought I might write a Visitor class that holds double result; and each Visit(...) would evaluate the (sub)expression using double arithmetics and then I would convert the result to int if needed. But is this the best solution to this using visitor pattern? What if I wanted to use long later on? It would be necessary to modify the classes by non-trivial amount of code, or? (Note: I would like to use visitor pattern (and not the dynamic one) and not any generic code.)