LambdaIntro.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;

namespace LambdaTest2
{
    class Program
    {
        static void Main(string[] args)
        {
            var digits = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

            // we can now query this list with LINQ methods
            // e.g. digits.Where(...)
            // Where() is a templated LINQ method (templated on the type of data source you have) 
            // In this case, since we have a list of integers -- the argument to Where() must be 
            // a function that takes an int and returns a bool (or, a Func<int, bool>)
            // That function is evaluated for each item in the list, items that return true are 
            // kept, items that return false are discarded.

            // you can pass in a function that's defined elsewhere (as in IsEven(..) defined below
            var evenDigits = digits.Where(IsEven);
            evenDigits.ToList().ForEach((input) => Console.Write($"  {input}"));
            Console.WriteLine();

            // OR you can define the function inline with a lambda
            var evenDigitsLambda = digits.Where((input) => (input % 2) == 0);
            evenDigitsLambda.ToList().ForEach((input) => Console.Write($"  {input}"));
            Console.WriteLine();

            // the above two options are equivalent -- but the lambda is often preferred
            // because it is more compact, and keeps the logic right where it's being used

            // the function delegate would be more common if the same logic is reused in many places.
            // You can also combine the two using good judgement, as in:
            var evenDigitsGreaterThan3AndLessThan7 = digits.Where((input) => IsEven(input) && IsLessThanSeven(input) && IsGreaterThanThree(input));
            evenDigitsGreaterThan3AndLessThan7.ToList().ForEach((input) => Console.Write($"  {input}"));
            Console.WriteLine();

            Console.ReadKey();

            // that gives you a TON of flexibility to define core reusable logic, and compose it in different ways
        }


        private static bool IsEven(int input)
        {
            return (input % 2) == 0;
        }
        private static bool IsGreaterThanThree(int input)
        {
            return input > 3;
        }
        private static bool IsLessThanSeven(int input)
        {
            return input < 7;
        }
    }
}