using System;

using NCalc;

public class Program

{

    public static void Main()

    {

        NCalc.Expression.CacheEnabled = false;

        NCalc.Expression nCalcExpression = new NCalc.Expression("SubUpper(1, 4, 'to upper')");

        nCalcExpression.EvaluateFunction += delegate (string name, FunctionArgs args)

        {

            var parameters = args.EvaluateParameters();

            Console.WriteLine(string.Format("Calling {0} with {1} args. {2}", name, parameters.Length, string.Join(",", parameters)));

            var x = (string)parameters[2];

            args.Result = x.Substring((int)parameters[0], (int)parameters[1]).ToUpper();

        };

        var result = nCalcExpression.Evaluate();

        Console.WriteLine("Result is " + result);

    }

}