Created
December 27, 2015 16:37
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Maybe Monad take 2
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| using System; | |
| namespace Maybe | |
| { | |
| abstract class Maybe<T> { | |
| public static Maybe<T> Return(T val) | |
| { | |
| return new Just<T> (val); | |
| } | |
| #region Monad implementation | |
| abstract public T Value (); | |
| abstract public bool HasValue (); | |
| abstract public Maybe<T> Bind (Func<T, Maybe<T>> f); | |
| #endregion | |
| } | |
| class Just<T> : Maybe<T> | |
| { | |
| private T _val; | |
| public Just(T val) // <- Unit | |
| { | |
| _val = val; | |
| } | |
| #region Maybe implementation | |
| override public T Value () | |
| { | |
| return _val; | |
| } | |
| override public bool HasValue() { return true; } | |
| override public Maybe<T> Bind (Func<T, Maybe<T>> f) // <- Bind | |
| { | |
| return f (_val); | |
| } | |
| #endregion | |
| } | |
| class Nothing<T> : Maybe<T> | |
| { | |
| public Nothing() {} // <- Unit | |
| #region Maybe implementation | |
| override public T Value () | |
| { | |
| return default(T); | |
| } | |
| override public bool HasValue() { return false; } | |
| override public Maybe<T> Bind (Func<T, Maybe<T>> f) | |
| { | |
| return new Nothing<T>(); // don't care | |
| } | |
| #endregion | |
| } | |
| class MainClass | |
| { | |
| public static void printVal<T>(Maybe<T> m) | |
| { | |
| if (m.HasValue()) Console.WriteLine (m.Value()); | |
| else Console.WriteLine ("no value present"); | |
| } | |
| public static Maybe<int> Example1(int val) | |
| { | |
| return Maybe<int>.Return(val) | |
| .Bind (x => Maybe<int>.Return(x + 4)) | |
| .Bind (x => Maybe<int>.Return(x * 100)) | |
| .Bind (x => x >= 2400 ? (Maybe<int>)Maybe<int>.Return(x) : (Maybe<int>)new Nothing<int>()); | |
| } | |
| public static Maybe<int> Example2(int val) | |
| { | |
| return Maybe<int>.Return(val) | |
| .Bind (x => x == 0 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)Maybe<int>.Return (x)) | |
| .Bind (x => Maybe<int>.Return (50 / x)); | |
| } | |
| public static void Main (string[] args) | |
| { | |
| printVal<int> (Example1 (20)); | |
| printVal<int> (Example1 (10)); | |
| printVal<int> (Example2 (0)); | |
| printVal<int> (Example2 (10)); | |
| /* | |
| 2400 | |
| no value present | |
| no value present | |
| 5 | |
| */ | |
| } | |
| } | |
| } |
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