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Maybe monad in C#
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| using System; | |
| namespace Maybe | |
| { | |
| interface Maybe<T> | |
| { | |
| T Value(); | |
| bool HasValue(); | |
| Maybe<T> Bind(Func<T, Maybe<T>> f); | |
| } | |
| class Just<T> : Maybe<T> | |
| { | |
| private T _val; | |
| public Just(T val) // <- Unit | |
| { | |
| _val = val; | |
| } | |
| #region Maybe implementation | |
| public T Value () | |
| { | |
| return _val; | |
| } | |
| public bool HasValue() { return true; } | |
| 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 | |
| public T Value () | |
| { | |
| return default(T); | |
| } | |
| public bool HasValue() { return false; } | |
| public Maybe<T> Bind (Func<T, Maybe<T>> f) | |
| { | |
| return new Nothing<T>(); // don't care | |
| } | |
| #endregion | |
| } | |
| class MainClass | |
| { | |
| public static void Main (string[] args) | |
| { | |
| Maybe<int> m = new Just<int> (20); // <- unit, technical the constructor | |
| var res = m.Bind (x => new Just<int> (x + 4)) | |
| .Bind (x => new Just<int> (x * 100)) | |
| .Bind (x => { | |
| Console.WriteLine ("Value at this stage is: " + x.ToString()); // did something but didn't change the value... | |
| return new Just<int> (x); | |
| }) | |
| .Bind (x => x >= 2400 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x)); | |
| if (res.HasValue()) | |
| Console.WriteLine (res.Value()); | |
| else | |
| Console.WriteLine ("no value present"); | |
| Maybe<int> m2 = new Just<int> (20); | |
| var res2 = m2.Bind (x => new Just<int>(x - 10)) | |
| .Bind (x => new Just<int>(x * 100)) | |
| .Bind (x => { | |
| Console.WriteLine ("Value at this stage is: " + x.ToString()); | |
| return new Just<int> (x); | |
| }) | |
| .Bind (x => x >= 2400 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x)); | |
| if (res2.HasValue()) | |
| Console.WriteLine (res2.Value()); | |
| else | |
| Console.WriteLine ("no value present"); | |
| Maybe<int> m3 = new Just<int> (0); | |
| var res3 = m3.Bind (x => x == 0 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x)) | |
| .Bind (x => new Just<int> (50 / x)); | |
| if (res3.HasValue ()) | |
| Console.WriteLine (res3.Value ()); | |
| else | |
| Console.WriteLine ("Failed to divide by 0"); | |
| Maybe<int> m4 = new Just<int> (10); | |
| var res4 = m4.Bind (x => x == 0 ? (Maybe<int>)new Nothing<int> () : (Maybe<int>)new Just<int> (x)) | |
| .Bind (x => new Just<int> (50 / x)); | |
| if (m4.HasValue ()) | |
| Console.WriteLine (res4.Value ()); | |
| else | |
| Console.WriteLine ("Failed to divide by 10"); | |
| /* | |
| Value at this stage is: 2400 | |
| no value present | |
| Value at this stage is: 1000 | |
| 1000 | |
| Failed to divide by 0 | |
| 5 | |
| */ | |
| } | |
| } | |
| } |
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