gistfile1.cs

using System;

namespace Data
{
  
  public struct Maybe<T> where T : class
  {

    public static implicit operator Maybe<T> (T value)
    {
      return new Maybe<T> (value);
    }

    T value;

    Maybe (T value)
    {
      this.value = value;
    }

    public bool IsNull    { get { return value == null; } }
    public bool IsNotNull { get { return value != null; } }

    public T Value {
      get {
        if (IsNull) throw new NullReferenceException ();
        return value;
      }
    }

    public T Out ()
    {
      if (IsNull) throw new NullReferenceException ();
      return value;
    }

    public T Out (T alt)
    {
      if (alt == null)
        throw new NullReferenceException ("alternative value cannot be null");

      return IsNotNull ? value : alt;
    }

    public R Out<R> (R alt, Func<T, R> f) where R : class
    {
      if (alt == null)
        throw new NullReferenceException ("alternative value cannot be null");

      return IsNotNull ? f (value) : alt;
    }
    
    public Maybe<R> Bind<R> (Func<T, Maybe<R>> f) where R : class
    {
      return IsNotNull ? f (value) : null;
    }

    public Maybe<R> Map<R> (Func<T, R> f) where R : class
    {
      return Bind (t => new Maybe<R> (f (t)));
    }

    public override string ToString()
    {
      return Out ("(null)", t => t.ToString ());
    }
  }
}