匿名的記錄類型內識別聯合

Question

的F＃教程包括下面的代碼片段：

/// A record for a person's first and last name 
type Person = {  
    First : string 
    Last : string 
} 

/// define a discriminated union of 3 different kinds of employees 
type Employee = 
    | Engineer of Person 
    | Manager of Person * list<Employee>   // manager has list of reports 
    | Executive of Person * list<Employee> * Employee // executive also has an assistant 

是經理和執行被描述爲元組冒犯了我的感情（我很容易生氣）的事實。它讓我覺得不是非常有表現力。我試圖對其進行修改如下：

/// define a discriminated union of 3 different kinds of employees 
type Employee = 
    | Engineer of Person 
    | Manager of { Name: Person; Reports: Employee list }   // manager has list of reports 
    | Executive of { Name: Person; Reports: Employee list; Assistant: Employee} // executive also has an assistant 

可悲的是，經理和執行的定義現在給出一個錯誤：「該構建過時;考慮使用一個單獨的記錄類型，而不是」。好吧，看起來很公平，我們稱之爲ManagerType。但是請等待... ManagerType引用Employee（對於Reports部分），Employee引用ManagerType（對於Manager選項）。

這裏有解決方案嗎？兩個數據結構是不可能相互定義的？

Answer 1

您可以定義相互依賴的類型使用and：

type Employee = 
    | Engineer of Person 
    | Manager of Manager   // manager has list of reports 
    | Executive of Executive 
    and Manager = { Name: Person; Reports: Employee list } 
    and Executive = { Name: Person; Reports: Employee list; Assistant: Employee } 

Answer 2

如果您使用F＃3.1版，您可以使用named union fields ^[MSDN]（和保護你嬌嫩的感情）：

type Employee = 
    | Engineer of Person 
    | Manager of Name: Person * Reports: Employee list 
    | Executive of Name: Person * Reports: Employee list * Assistant: Employee 

Answer 3

相互遞歸類型的聲明與type ... = ... and ... = ...：

type Employee = 
    | Engineer of Person 
    | Manager of Manager 
    | Executive of Executive 
and Manager = { Name: Person; Reports: Employee list } 
and Executive = { Name: Person; Reports: Employee list; Assistant: Employee}