public RpnExpression Parse(string text)
{
Stack <RpnExpression> stack = new Stack <RpnExpression>();
string[] words = text.Split(' ');
foreach (var word in words)
{
RpnExpression lhs = null, rhs = null;
switch (word)
{
case "+":
rhs = stack.Pop();
lhs = stack.Pop();
stack.Push(new Add(lhs, rhs));
break;
case "-":
rhs = stack.Pop();
lhs = stack.Pop();
stack.Push(new Subtract(lhs, rhs));
break;
case "*":
rhs = stack.Pop();
lhs = stack.Pop();
stack.Push(new Multiply(lhs, rhs));
break;
case "/":
rhs = stack.Pop();
lhs = stack.Pop();
stack.Push(new Divide(lhs, rhs));
break; //Above are Non-Terminal expression
default:
int number = int.Parse(word);
stack.Push(new Number(number));
break; //This is terminal expression
}
}
return(stack.Pop());
}
public Multiply(RpnExpression lhs, RpnExpression rhs)
{
_lhs = lhs;
_rhs = rhs;
}
public Divide(RpnExpression lhs, RpnExpression rhs)
{
_lhs = lhs;
_rhs = rhs;
}
public Subtract(RpnExpression lhs, RpnExpression rhs)
{
_lhs = lhs;
_rhs = rhs;
}
public Add(RpnExpression lhs, RpnExpression rhs)
{
_lhs = lhs;
_rhs = rhs;
}
