using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var some =  Maybe<int>.Some(10);

        var none = Maybe<int>.None;

        var emptyList = new List<int>();

        var list = new List<int>{ 1, 2};

    }   

}

​

​

public interface Functor<F> 

{

    HKT<F, B> map<A,B>(Func<A,B> f, HKT<F,A> fa);

}

​

/*

public interface HKT<F,A>{}

​

public interface Functor<F> 

{

    FB map<A,B,FA,FB>(Func<A,B> f,FA fa)

        where FA : HKT<F, A>

        where FB : HKT<F, B>;

}

​

public class IsMaybe {}

​

*/

​

public struct Maybe<T> //: HKT<IsMaybe, T>

{

    public T Value { get; private set; }

    public bool HasValue { get; private set;}

    private Maybe(T val)

    {

        Value = val;

        HasValue = true;

    }

    public static Maybe<T> Some(T val){ return new Maybe<T>(val); }

    public static Maybe<T> None = new Maybe<T>();

}

​

public class FMaybe<T> : Functor<IsMaybe>

{

    public Maybe<B> map<A,B>(Func<A,B> f, Maybe<A> fa)

    {

    }

}

​

​