Some C# Insanity

using System;
using System.CodeDom;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CodeRetreate
{
    public static class CodeRetreat
    {
        public static int Sum(int a, int b)
        {
            return SumRec(a, b, 0, false);
        }

        public static int Substract(int a, int b)
        {
            return Sum(a, Sum(~b, 1));
        }

        private static int SumRec(int a, int b, int index, bool overflow)
        {
            return IF(index == sizeof(int)*8, () => a, () =>
            {
                var bita = ((a >> index) & 1) == 1;
                var bitb = ((b >> index) & 1) == 1;
                a = IF(bita ^ bitb ^ overflow,
                    () => a | (1 << index),
                    () => a & ~(1 << index));
                overflow = bita & overflow | bitb & overflow | bita & bitb;
                return SumRec(a, b, index + 1, overflow);
            });
        }

        public static int SumByPairs(int[] array, int l, int r)
        {
            return IF(Substract(r, l) <= 1, () => array[l], () =>
            {
                var centerIndex = (int) Math.Pow(2, Math.Truncate(Math.Log(Substract(r, l), 2)));
                IF(Sum(l, centerIndex) == r, () => centerIndex /= 2, () => { });
                centerIndex = Sum(centerIndex, l);
                var leftValue = SumByPairs(array, l, centerIndex);
                var rightValue = SumByPairs(array, centerIndex, r);
                return IF(leftValue > rightValue,
                    () => Substract(leftValue, rightValue),
                    () => Sum(leftValue, rightValue));
            });
        }

        public static void IF(bool condition, Action actionIfTrue, Action actionIfFalse)
        {
            var actions = new[] {actionIfFalse, actionIfTrue};
            actions[Convert.ToInt32(condition)]();
        }

        public static T IF<T>(bool condition, Func<T> actionIfTrue, Func<T> actionIfFalse)
        {
            var actions = new[] {actionIfFalse, actionIfTrue};
            return actions[Convert.ToInt32(condition)]();
        }
    }

    class Program
    {
        static void Main()
        {
            var data = new[] {1, 2, 3, 4, 5, 6, 7, 8, 9};
            var sum = 0;
            for (var i = 0; i < data.Length; i = CodeRetreat.Sum(i, 1))
                sum = CodeRetreat.Sum(sum, data[i]);
            Console.WriteLine(sum);

            var sumAndSubstract = data[0];
            for (var i = 1; i < data.Length; i = CodeRetreat.Sum(i, 1))
                sumAndSubstract = CodeRetreat.IF(data[i] > data[i - 1],
                    () => CodeRetreat.Sum(sumAndSubstract, data[i]),
                    () => CodeRetreat.Substract(sumAndSubstract, data[i]));
            Console.WriteLine(sumAndSubstract);

            var sumByPairs = CodeRetreat.SumByPairs(data, 0, data.Length);
            Console.WriteLine(sumByPairs);
        }
    }
}