From bd9392ec507de1ff8546f4acb0035e7972241b90 Mon Sep 17 00:00:00 2001
From: Sanchime <sanchime.qq.com>
Date: Sat, 14 May 2022 18:43:04 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=E5=85=8D=E8=B4=B9=E5=8D=95?=
 =?UTF-8?q?=E5=AD=90?=
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---
 Sanchime.Functional/Monads/FreeMonad.cs | 75 +++++++++++++++++++++++++
 Sanchime.Functional/Products/Coyo.cs    | 20 +++++++
 2 files changed, 95 insertions(+)
 create mode 100644 Sanchime.Functional/Monads/FreeMonad.cs
 create mode 100644 Sanchime.Functional/Products/Coyo.cs

diff --git a/Sanchime.Functional/Monads/FreeMonad.cs b/Sanchime.Functional/Monads/FreeMonad.cs
new file mode 100644
index 0000000..6721cd0
--- /dev/null
+++ b/Sanchime.Functional/Monads/FreeMonad.cs
@@ -0,0 +1,75 @@
+using Sanchime.Functional.Extensions;
+using static Sanchime.Functional.Extensions.TaskExtension;
+namespace Sanchime.Functional.Monads;
+
+public abstract class Free<T>
+{
+    public abstract R Match<R>(Func<T, R> Done, Func<Coyo<object, Free<T>>, R> More);
+
+}
+
+internal sealed class Done<T> : Free<T>
+{
+    public T Value { get; }
+
+    public Done(T value)
+        => Value = value;
+
+    public override R Match<R>(Func<T, R> Done, Func<Coyo<object, Free<T>>, R> More)
+        => Done(Value);
+}
+
+internal sealed class More<T> : Free<T>
+{
+    public Coyo<object, Free<T>> Next { get; }
+
+    public More(Coyo<object, Free<T>> next)
+        => Next = next;
+
+    public override R Match<R>(Func<T, R> Done, Func<Coyo<object, Free<T>>, R> More)
+        => More(Next);
+}
+
+/// <summary>
+/// 自由单子
+/// </summary>
+public static class FreeMonad
+{
+    /// <summary>
+    /// 自然变幻Return， 将值导入至Free的世界
+    /// </summary>
+    /// <param name="value">无状态的值</param>
+    /// <typeparam name="T"></typeparam>
+    /// <returns></returns>
+    public static Free<T> Return<T>(T value) 
+        => Done(value);
+
+    /// <summary>
+    /// 执行Free
+    /// </summary>
+    /// <param name="free">计算描述</param>
+    /// <param name="interpret">解释执行</param>
+    /// <typeparam name="T"></typeparam>
+    /// <returns></returns>
+    public static T Run<T>(this Free<T> free, Func<object, object> interpret)
+        => free.Match(val => val, coyo => Run(coyo.Func(interpret(coyo.Value)), interpret));
+
+    /// <summary>
+    /// 异步执行Free
+    /// </summary>
+    /// <param name="free">计算描述</param>
+    /// <param name="interpret">解释执行</param>
+    /// <typeparam name="T"></typeparam>
+    /// <returns></returns>
+    public static Task<T> Run<T>(this Free<T> free, Func<object, Task<object>> interpret)
+        => free.Match<Task<T>>(val => Async(val), async coyo => await Run(coyo.Func(await interpret(coyo.Value)),interpret));
+
+    public static Free<T> Of<T>(object op)
+        => More(Coyo.Of<object, T>(op).Map(val => Done<T>(val)));
+
+    internal static Free<T> Done<T>(T value) 
+        => new Done<T>(value);
+
+    internal static Free<T> More<T>(Coyo<object, Free<T>> value) 
+        => new More<T>(value);
+}
diff --git a/Sanchime.Functional/Products/Coyo.cs b/Sanchime.Functional/Products/Coyo.cs
new file mode 100644
index 0000000..c46971f
--- /dev/null
+++ b/Sanchime.Functional/Products/Coyo.cs
@@ -0,0 +1,20 @@
+namespace Sanchime.Functional.Products;
+
+public readonly struct Coyo<V, T>
+{
+    public V Value {get;}
+
+    public Func<object, T> Func { get; }
+
+    public Coyo(V value, Func<object, T> func)
+        => (Value, Func) = (value, func);
+}
+
+public static class Coyo
+{
+    public static Coyo<V, T> Of<V, T>(V value)
+        => new Coyo<V, T>(value, x => (T)x);
+
+    public static Coyo<V, R> Map<V, T, R>(this Coyo<V, T> @this, Func<T, R> mapping)
+        => new Coyo<V, R>(@this.Value, x => mapping(@this.Func(x)));
+}