package trees.expressiontrees;

/**
 * This abstract class represents the nodes in an expression tree.
 */
public abstract class ExpressionNode {
    Token t;
	abstract double value();  // Return the value of this node.
 
} 

/**
 * Class to represent node holding an integer.
 */
class NumbNode extends ExpressionNode {
      
 	int number;  // The number in the node.
 
 	NumbNode(Operand op) {
 		number = op.value();
 	}

 	double value() {
 		return number;
 	}
} 

/**
 * Class to represent node holding an operation.
 */
class BinaryOpNode extends ExpressionNode {
    
	char op;        // The operator.
	ExpressionNode left;   // The left operand.
	ExpressionNode right;  // The right operand.

	BinaryOpNode(Operation op, ExpressionNode left, ExpressionNode right) {
		this.op = op.toString().charAt(0);
		this.left = left;
		this.right = right;
	}

	// To get the value, compute the value of the left and
    // right operands, and combine them with the operator.
	double value() {      
		double leftValue = left.value();
		double rightValue = right.value();
		switch ( op ) {
         	case '+':  return leftValue + rightValue;
         	case '-':  return leftValue - rightValue;
         	case '*':  return leftValue * rightValue;
         	case '/':  return leftValue / rightValue;
         	default:   return Double.NaN;  // Bad operator.
		}
	}
}