IEnumerable<int> nums = Enumerable.Range(0, 10);
var sum = nums.Aggregate(
    seed: 0,
    func: (accumulator, val) => {
        Console.WriteLine($"Acc: {accumulator}, Val: {val} => {accumulator+val}");
        return accumulator + val;
    }
);
Console.WriteLine("Sum: " + sum);