Result with Error monad test with C# 7 pattern matching

ResultErr.cs

using System;

namespace MonadTest
{
    public interface IResult<E>
    {
        E Error { get; }
    }

    public abstract class Result<E> : IResult<E>
    {
        public abstract E Error { get; }

        public static IResult<E> Ok() => new Ok<E>();
        public static IResult<E> Err(E error) => new Err<E>(error);
    }

    public sealed class Ok<E> : Result<E>
    {
        public override E Error => throw new NotSupportedException();
    }

    public sealed class Err<E> : Result<E>
    {
        public override E Error { get; }

        public Err(E error)
        {
            Error = error;
        }
    }
    
    class Program
    {
        public static IResult<string> GetResult(bool isOk)
        {
            return isOk ? 
            Result<string>.Ok():
            Result<string>.Err("Ooops we got error");
        }

        static void Main(string[] args)
        {
            var res = GetResult(false);

            switch (res)
            {
                case Ok<string> ok:
                    Console.WriteLine("Everything is fine");
                    break;
                case Err<string> err:
                    Console.WriteLine(err.Error);
                    break;
            }
        }
    }
}