BinaryOpNode.cs


namespace ExpressionParser
{
   // A binary operator node. Supports +, -, *, and /.
   public class BinaryOpNode : ExpressionNode
   {
      private ExpressionNode _left;
      private ExpressionNode _right;
      private TokenType _operator;
      public BinaryOpNode(ExpressionNode left, TokenType op, ExpressionNode right)
      {
         _left = left;
         _operator = op;
         _right = right;
      }
      public override object Evaluate(Dictionary<string, object> variables)
      {
         object leftVal  = _left.Evaluate(variables);
         object rightVal = _right.Evaluate(variables);

         switch (_operator)
         {
            case TokenType.Plus:
               if (Parser.IsNumeric(leftVal) && Parser.IsNumeric(rightVal))
                  return Convert.ToDouble(leftVal) + Convert.ToDouble(rightVal);
               throw new Exception("The '+' operator requires both operands to be numeric.");
            case TokenType.Minus:
               if (Parser.IsNumeric(leftVal) && Parser.IsNumeric(rightVal))
                  return Convert.ToDouble(leftVal) - Convert.ToDouble(rightVal);
               throw new Exception("The '-' operator requires both operands to be numeric.");
            case TokenType.Multiply:
               if (Parser.IsNumeric(leftVal) && Parser.IsNumeric(rightVal))
                  return Convert.ToDouble(leftVal) * Convert.ToDouble(rightVal);
               throw new Exception("The '*' operator requires both operands to be numeric.");
            case TokenType.Divide:
               if (Parser.IsNumeric(leftVal) && Parser.IsNumeric(rightVal))
               {
                  double denominator = Convert.ToDouble(rightVal);
                  if (denominator == 0)
                     throw new Exception("Division by zero.");
                  return Convert.ToDouble(leftVal) / denominator;
               }
               throw new Exception("The '/' operator requires both operands to be numeric.");
            default:
               throw new Exception($"Unsupported binary operator: {_operator}");
         }
      }
   }
}