using System;

using System.Collections.Generic;

using System.Linq;

​

static int Add(int a, int b) => a + b;

​

var numbers = new int[]{ 1, 2, 3, 4, 5, 6};

​

var sum = reduce<int>(numbers, Add);

​

Console.WriteLine(sum);

​

/*----------------------------------------------------------*/

static T reduce<T>(IEnumerable<T> values, Func<T, T, T> reducer)

{

    if (!values.Any())

        return default;

    var enumerator = values.GetEnumerator();

    _ = enumerator.MoveNext();

    var current = enumerator.Current;

    T next;

    while (enumerator.MoveNext())

    {

        next = enumerator.Current;

        current = reducer(current, next);

    }

​

    return current;

}