Question

我在这里问一个特定的话题 - 我在网上找到的信息很少。我正在实现一个F＃版本的Minimax算法。我现在遇到的问题是我要比较我的树叶（下面的数据结构）。正在搜索VS给我的错误，我得到了这样的东西：

我曾经拥有的树型：

type TreeOfPosition =
    | LeafP   of Position
    | BranchP of Position * TreeOfPosition list

和实施IComparable的临终关怀

type staticValue = int
[<CustomEquality;CustomComparison>]
type TreeOfPosition =
    | LeafP   of Position * staticValue
    | BranchP of Position * TreeOfPosition list

    override x.Equals(yobj) = 
        match yobj with
        | :? TreeOfPosition as y -> (x = y)
        | _ -> false

    override x.GetHashCode() = hash (x)
    interface System.IComparable with
        member x.CompareTo yobj =
            match yobj with
            | :? TreeOfPosition as y -> compare (x) (y)
            | _ -> invalidArg "yobj" "cannot compare value of different types"

最后，我只想通过其静态值（在其他函数中计算）得到LeafP列表的最大值（和最小值）。

上面的代码编译。无论如何测试：

let p = new Position()
p.Add(1,BLACK)
let a = LeafP(p,1)
let b = LeafP(p,2)

let biger = compare a b
printf "%d" biger

我在GetHashCode的覆盖中的“|：？TreeOfPosition as y - ＆gt; compare（x）（y）”中得到了一个System.StackOverflowException。

我在hubfs.net（http://cs.hubfs.net/forums/thread/15891.aspx）中有一个帖子，我正在讨论我的Minimax。在这里，您可以找到我最新的代码（http://www.inf.ufrgs.br/~pmdusso/works/Functional_Implementation_Minimax_FSharp.htm）

提前致谢，

Pedro Dusso

嗯，我清楚地理解了这个想法，但我不能让它发挥作用。记住我想从叶子列表（“List.max”：P）获取具有最大静态值的叶子，我认为实现CompareTo或Equals将使List.max工作在他们身上，对吗？我写了这样的事情：

let mycompare x y = 
  match x, y with
  // Compare values stored as part of your type
  | LeafP(_, n1), LeafP(_, n2) -> compare n1 n2
  //| BranchP(_, l1), BranchP(_, l2) -> compare l1 l2 //I do not need Branch lists comparison
  | _ -> 0 // or 1 depending on which is list...

[< CustomEquality;CustomComparison >]
type TreeOfPosition =
    | LeafP   of Position * int
    | BranchP of Position * TreeOfPosition list

    override x.Equals(yobj) = 
       match yobj with
       | :? TreeOfPosition as y -> (x = y)
       | _ -> false

    override x.GetHashCode() = hash (x)
    interface System.IComparable with
       member x.CompareTo yobj = 
          match yobj with 
          | :? TreeOfPosition as y -> mycompare x y
          | _ -> invalidArg "yobj" "cannot compare value of different types"

我以这种方式安排功能的问题是：

1）模式鉴别器'LeafP'未定义（LeafP红色下划线）

2）（77,39）：错误FS0039：未定义值或构造函数'mycompare'，当我尝试ALT ENTER时，此消息出现在我的F＃Interactive中。位置{77,39}对应于mycompare调用的开始（在GetHashCode中）。

我做错了什么？我能做得更好吗？

非常感谢，

Pedro Dusso

编辑3 - 解决了

是的！我完成了最终工作的答案！

最终的代码在这里：

[<CustomEquality;CustomComparison>]
type TreeOfPosition =
    | LeafP   of Position * int
    | BranchP of Position * TreeOfPosition list

    //Func: compare
    //Retu: -1: first parameter is less than the second
    //       0: first parameter is equal to the second
    //       1: first parameter is greater than the second
    static member mycompare (x, y) = 
        match x, y with
        // Compare values stored as part of your type
        | LeafP(_, n1), LeafP(_, n2) -> compare n1 n2
        | _ -> 0 // or 1 depending on which is list...

    override x.Equals(yobj) = 
        match yobj with
        | :? TreeOfPosition as y -> (x = y)
        | _ -> false

    override x.GetHashCode() = hash (x)
    interface System.IComparable with
       member x.CompareTo yobj = 
          match yobj with 
          | :? TreeOfPosition as y -> TreeOfPosition.mycompare(x, y)
          | _ -> invalidArg "yobj" "cannot compare value of different types"

感谢您的反馈！

Pedro Dusso

Answer 1

首先，您获得了异常，因为compare函数调用了您正在比较的值的CompareTo方法（即x.ComaperTo(y)）。您在compare的自定义实现中使用CompareTo进行比较的值是您要求比较的值（由运行时），因此这会导致堆栈溢出。

实施CompareTo或Equals的常用方法是仅比较您在类型中存储的某些值。例如，你可以这样写：

编辑：您可以编写辅助函数mycopare来进行比较（或者您只需更改CompareTo实现）。但是，如果你想使用一个函数，你需要在类型声明中移动它（以便它知道类型 - 注意在F＃中，声明的顺序很重要！）

写作的一种方式是：

[<CustomEquality; CustomComparison >] 
type TreeOfPosition = 
  | LeafP   of Position * int 
  | BranchP of Position * TreeOfPosition list 

  override x.Equals(yobj) =  
     match yobj with 
     | :? TreeOfPosition as y -> 
        // TODO: Check whether both y and x are leafs/branches
        // and compare their content (not them directly)
     | _ -> false 
  override x.GetHashCode() = // TODO: hash values stored in leaf/branch

  interface System.IComparable with 
     member x.CompareTo yobj =  

       // Declare helper function inside the 'CompareTo' member
       let mycompare x y = 
         match x, y with
         // Compare values stored as part of your type
         | LeafP(_, n1), LeafP(_, n2) -> compare n1 n2
         | BranchP(_, l1), BranchP(_, l2) -> compare l1 l2
         | _ -> -1 // or 1 depending on which is list...

       // Actual implementation of the member
       match yobj with 
       | :? TreeOfPosition as y -> mycompare x y
       | _ -> invalidArg "yobj" "cannot compare value of different types"

这样可行，因为每次调用compare只会获取部分数据，因此您可以取得一些进展。

在F＃元组中使用CustomComparison和CustomEquality实现自定义比较

1 个答案: