64 lines
1.1 KiB
C#
64 lines
1.1 KiB
C#
using System;
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class Maybe<T>
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{
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public readonly static Maybe<T> Nothing = new Maybe<T> ();
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public T Value { get; private set; }
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public bool HasValue { get; private set; }
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Maybe ()
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{
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HasValue = false;
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}
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public Maybe (T value)
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{
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Value = value;
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HasValue = true;
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}
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public override string ToString ()
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{
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if (HasValue)
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return Value.ToString ();
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return string.Empty;
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}
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public Maybe<U> SelectMany<U> (Func<T, Maybe<U>> k)
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{
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if (!HasValue)
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return Maybe<U>.Nothing;
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return k (Value);
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}
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public Maybe<V> SelectMany<U, V> (
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Func<T, Maybe<U>> selector,
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Func<T, U, V> resultSelector)
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{
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if (!HasValue)
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return Maybe<V>.Nothing;
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Maybe<U> n = selector (Value);
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if (!n.HasValue)
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return Maybe<V>.Nothing;
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return resultSelector (Value, n.Value).ToMaybe ();
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}
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}
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static class MaybeExtensions
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{
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public static Maybe<T> ToMaybe<T> (this T value)
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{
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return new Maybe<T> (value);
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}
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}
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class Test
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{
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public static void Main ()
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{
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Console.WriteLine (
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from x in 1.ToMaybe ()
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from y in 2.ToMaybe ()
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from z in 3.ToMaybe ()
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select x + y + z);
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}
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}
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