Monads!

monad01 - unit.cs

void Main()
{
	"Hello".Unit().Dump();
	5.Unit().Dump();
	DateTime.Today.Unit().Dump();
	new List<char> { 'a', 'b' }.Unit().Dump();
	(3 * 1.5).Unit().Dump();
}

public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> Unit<T>(this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>(this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
}

monad02 - bind.cs

void Main()
{
	4.Unit()
		.Bind(x => (x * 2.5).Unit())
		.Dump();
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> Unit<T>(this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>(this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
}

monad03 - multibind lambda.cs

void Main()
{
	4.Unit()
		.Bind(x => (x * 2.5).Unit())
		.Dump();
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> Unit<T>(this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>(this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
}

monad04 - ToIdentity and SelectMany.cs

void Main()
{
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
}

monad05 - SelectMany lambda.cs

void Main()
{
	5.ToIdentity()
		.SelectMany(x => 9.ToIdentity(), (x,y) => (x+y))
	.Dump();
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
}

monad06 - SelecMany query.cs

void Main()
{
	(
		from x in 5.ToIdentity()
		from y in 9.ToIdentity()
		select (x + y)
	).Dump();	
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
}

monad07 - IEnumerable.cs

void Main()
{
	(
		from x in new[] { 1, 2 }
		from y in new List<int> { 3, 4, 5}
		select (x + y)
	).Dump();	
}

// Define other methods and classes here
public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
}

monad08 - Maybe.cs

void Main()
{
	
}

// Define other methods and classes here

public class Maybe<T>
{
	public readonly static Maybe<T> Nothing = new Maybe<T>();
	public T Value { get; }
	public bool HasValue { get;}
	public Maybe() {HasValue=false;}
	public Maybe(T value) { Value = value; HasValue=true;}
}

public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
	
	public static Maybe<T> ToMaybe<T>          (this T m) => new Maybe<T>(m);
	public static Maybe<U> Bind<T,U>           (this Maybe<T> m, Func<T,Maybe<U>> k) => m.HasValue ? k(m.Value) : Maybe<U>.Nothing;
	public static Maybe<V> SelectMany<T,U,V>   (this Maybe<T> m, Func<T,Maybe<U>> k, Func<T,U,V> s) => k(m.Value).HasValue ? s(m.Value, k(m.Value).Value).ToMaybe() : Maybe<V>.Nothing
}

monad09 - Maybe examples.cs

void Main()
{
	(
	 from x in 5.ToMaybe()
	 from y in 9.ToMaybe()
	 select x + y
	 ).Dump();

	(
	from x in Maybe<int>.Nothing
	from y in 9.ToMaybe()
	select x + y
	).Dump();

	(
	from x in 5.ToMaybe()
	from y in Maybe<int>.Nothing
	select x + y
	).Dump();

	(
	from x in 5.ToMaybe()
	from y in 9.ToMaybe()
	from z in new Maybe<int>()
	select x + y + z
	).Dump();
}

// Define other methods and classes here

public class Maybe<T>
{
	public readonly static Maybe<T> Nothing = new Maybe<T>();
	public T Value { get; }
	public bool HasValue { get;}
	public Maybe() {HasValue=false;}
	public Maybe(T value) { Value = value; HasValue=true;}
}

public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
	
	public static Maybe<T> ToMaybe<T>          (this T m) => new Maybe<T>(m);
	public static Maybe<U> Bind<T,U>           (this Maybe<T> m, Func<T,Maybe<U>> k) => m.HasValue ? k(m.Value) : Maybe<U>.Nothing;
	public static Maybe<V> SelectMany<T,U,V>   (this Maybe<T> m, Func<T,Maybe<U>> k, Func<T,U,V> s) => m.Bind(k).HasValue ? s(m.Value, m.Bind(k).Value).ToMaybe() : Maybe<V>.Nothing;
}

monad10 - Maybe composition.cs

void Main()
{
	(
	 from x in 5.ToMaybe()
	 from y in 9.ToMaybe()
	 select x + y
	 ).Dump();

	(
	 from x in DateTime.Now.Millisecond.ToMaybe()
	 from y in ExcludePairs(x)
	 from z in Times2(y).ToMaybe()
	 select x+y+z
	).Dump();
}

// Define other methods and classes here
public static int Times2(int x) => x * 2;
public static Maybe<int> ExcludePairs(int x) => x % 2 == 0 ? Maybe<int>.Nothing : x.ToMaybe();

public class Maybe<T>
{
	public readonly static Maybe<T> Nothing = new Maybe<T>();
	public T Value { get; }
	public bool HasValue { get;}
	public Maybe() {HasValue=false;}
	public Maybe(T value) { Value = value; HasValue=true;}
}

public class Identity<T>
{
	public T Value {get;}
	public Identity(T value) {Value=value;}
}

public static class MonadHelper
{
	public static Identity<T> ToIdentity<T>    (this T t) => new Identity<T>(t);
	public static Identity<U> Bind<T,U>        (this Identity<T> id, Func<T, Identity<U>> k) => k(id.Value);
	public static Identity<V> SelectMany<T,U,V>(this Identity<T> id, Func<T, Identity<U>> k, Func<T,U,V> s) => s(id.Value, k(id.Value).Value).ToIdentity();
	
	public static Maybe<T> ToMaybe<T>          (this T m) => new Maybe<T>(m);
	public static Maybe<U> Bind<T,U>           (this Maybe<T> m, Func<T,Maybe<U>> k) => m.HasValue ? k(m.Value) : Maybe<U>.Nothing;
	public static Maybe<V> SelectMany<T,U,V>   (this Maybe<T> m, Func<T,Maybe<U>> k, Func<T,U,V> s) => m.Bind(k).HasValue ? s(m.Value, m.Bind(k).Value).ToMaybe() : Maybe<V>.Nothing;
}