f# - 如何解决联合案例之间的循环引用？

Question

如何解决联合案例之间的循环引用？

type ModuleInfo = | Author of Name
                  | Section of Section
                  | Duration of Duration
                  | Url of string

我收到以下错误:

The type 'Section' is not defined.

代码如下:

module ManageModule.Entities

type FirstName = FirstName of string
type LastName = LastName of string

type Name = | First of FirstName
            | Last of LastName
            | Suffix of string option

type Duration = | Hours of int
                | Minutes of int
                | Seconds of int

type ModuleInfo = | Author of Name
                  | Section of Section
                  | Duration of Duration
                  | Url of string

type Module = Module of ModuleInfo
type Modules = Modules of ModuleInfo list

type Section = | Introduction of Module
               | Conclusion of Module

Answer 1

您可以使用和关键字:

type ModuleInfo = 
  | Author of Name
  | Section of Section
  | Duration of Duration
  | Url of string

and Module = Module of ModuleInfo
and Modules = Modules of ModuleInfo list

and Section = 
  | Introduction of Module
  | Conclusion of Module