public RpnExpression Parse(string text)
{
Stack <RpnExpression> stack = new Stack <RpnExpression>();
string[] words = text.Split(' ');
foreach (string word in words)
{
RpnExpression leftHandSubexpression = null;
RpnExpression rightHandSubexpression = null;
switch (word)
{
case "+":
rightHandSubexpression = stack.Pop();
leftHandSubexpression = stack.Pop();
stack.Push(new Add(leftHandSubexpression, rightHandSubexpression));
break;
case "-":
rightHandSubexpression = stack.Pop();
leftHandSubexpression = stack.Pop();
stack.Push(new Substract(leftHandSubexpression, rightHandSubexpression));
break;
case "*":
rightHandSubexpression = stack.Pop();
leftHandSubexpression = stack.Pop();
stack.Push(new Multiply(leftHandSubexpression, rightHandSubexpression));
break;
case "/":
rightHandSubexpression = stack.Pop();
leftHandSubexpression = stack.Pop();
stack.Push(new Divide(leftHandSubexpression, rightHandSubexpression));
break;
default:
int number = int.Parse(word);
stack.Push(new Number(number));
break;
}
}
return(stack.Pop());
}
public Multiply(RpnExpression leftHandSubexpression, RpnExpression rightHandSubexpression)
{
this.leftHandSubexpression = leftHandSubexpression;
this.rightHandSubexpression = rightHandSubexpression;
}
public Divide(RpnExpression leftHandSubexpression, RpnExpression rightHandSubexpression)
{
this.leftHandSubexpression = leftHandSubexpression;
this.rightHandSubexpression = rightHandSubexpression;
}
public Substract(RpnExpression leftHandSubexpression, RpnExpression rightHandSubexpression)
{
this.leftHandSubexpression = leftHandSubexpression;
this.rightHandSubexpression = rightHandSubexpression;
}
