using System;

using System.Linq;

using System.Collections.Generic;

​

​

//https://stackoverflow.com/questions/31166013/what-is-the-best-way-to-implement-a-rust-enum-in-c

​

public abstract record State(int Count);  // An abstract base state that tracks shared information, here the total number of iterations.

​

public sealed record InitialState(int Count) : State(Count) { public InitialState() : this(0) {}}

public record StateA(int Count, string Token, int InnerCount) : State(Count) { }

public record StateB(int Count, string Token) : State(Count);

public sealed record FinalState(int Count) : State(Count);

public sealed record ErrorState(int Count) : State(Count);

​

public class TestClass

{

    const string terminalString = "stop";

    IEnumerator<string> inputs = Enumerable.Range(1, 6).Select(i => "token " + i.ToString()).Concat(new [] {terminalString}).GetEnumerator();

    string GetNextToken()

    {

        inputs.MoveNext();

        return inputs.Current;

    }

    public void Test()

    {

        string terminalString = "stop";

        int maxIterations = 100;

        State state = new InitialState();

​

        // Negation pattern: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns#logical-patterns

        while (state is not FinalState && state is not ErrorState) 

        {

            // Get the next token

            string token = GetNextToken();

            // Do some work with the current state + next token

            Console.WriteLine("State = {0}", state);

​

            // Transition to the new state

            state = state switch // Switch Expression: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/switch-expression

            {

                var s when s.Count > maxIterations =>  // https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/switch-expression#case-guards

                    new ErrorState(s.Count + 1),

                InitialState s => 

                    new StateA(s.Count + 1, token, 0),

                StateA s when s is { InnerCount : > 3 } =>  //https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns#property-pattern

                    new StateB (s.Count + 1, token),

                StateA s =>

                    s with { Count = s.Count + 1, Token = token, InnerCount = s.InnerCount + 1 },  // https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/record#nondestructive-mutation

                StateB s when s.Token == terminalString =>

                    new FinalState(s.Count + 1),

                StateB  s =>

                    s with { Count = s.Count + 1, Token = token },

                _ => throw new Exception($"Unknown state {state}"),

            };

            // Do some additional work with the new state

        }

        Console.WriteLine("State = {0}", state);

    }

}

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Environment version: {0} ({1}), {2}\n", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

​

        new TestClass().Test();

    }

}