public class CalculatorVisitor extends CalculatorParserBaseVisitor<Double> {
    @Override
    public Double visitTimesdiv(CalculatorParser.TimesdivContext ctx) {
        double left = visit(ctx.expression(0));
        double right = visit(ctx.expression(1));

        if (ctx.op.getType() == CalculatorParser.TIMES) {
            return left * right;
        } else {
            return left / right;
        }
    }
    
    @Override
    public Double visitPlusminus(CalculatorParser.PlusminusContext ctx) {
        double left = visit(ctx.expression(0));
        double right = visit(ctx.expression(1));

        if (ctx.op.getType() == CalculatorParser.PLUS) {
            return left + right;
        } else {
            return left - right;
        }
    }

    @Override
    public Double visitRealval(CalculatorParser.RealvalContext ctx) {
        return Double.parseDouble(ctx.REALVAL().getText());
    }

    @Override
    public Double visitPival(CalculatorParser.PivalContext ctx) {
        return Math.PI;
    }
    
    
    @Override
    public Double visitParens(CalculatorParser.ParensContext ctx) {
        return visit(ctx.expression());
    }
}