@Override
        public double applyAsDouble(double left, double right) {
            MapContext context = new MapContext();
            if (arguments.size() > 0)
                context.put(arguments.get(0), left);
            if (arguments.size() > 1)
                context.put(arguments.get(1), right);
            return evaluate(context).asDouble();
        }
Returns this as a double binary operator

@throws IllegalStateException if this has more than two arguments
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/LambdaFunctionNode.java