普通类型:在普通类型的DrRacket中使用定义类型的嵌套结构

Question

我尝试使用#lang plai-typed用DrRacket编写简单的模式匹配器，如下所示：

#lang plai-typed

(define-type Activity
  [kind (type : string) (description : string)]
)

(define-type Hacktivity
   [activity1 (activity : Activity)]
   [activity2 (activity : Activity)]
   [activity3 (activity : Activity)]
)

(define (good? [h : Hacktivity]) : boolean
    (type-case Hacktivity h
        [activity1 (activity) (string=? activity-kind-type "Analyze")]
        [activity2 (activity) (string=? "Analyze" "Analyze")]    
        [activity3 (activity) (string=? "Analyze" "Analyze")]
    )
)

然而，不能正确地理解“活动-种类-类型”部分。任何帮助都是非常感谢的。提前谢谢。

Answer 1

我可以用下面的方法解决这个问题：

#lang plai-typed

(define-type Activity
    [kind (type : string) (description : string)]
)
(define-type Hacktivity
    [activity1 (activity : Activity)]
    [activity2 (activity : Activity)]
    [activity3 (activity : Activity)]
)
(define analyze : Activity (kind "Analyze" "Test description"))
(define hack : Hacktivity (activity1 analyze))

(define (good? [h : Hacktivity]) : boolean
    (type-case Hacktivity h
      [activity1 (activity)
                 (type-case Activity activity
                   [kind (type description) (string=? type "Analyze")])]
      [activity2 (activity)
                 (type-case Activity activity
                   [kind (type description) (string=? type "Analyze")])]
      [activity3 (activity)
                 (type-case Activity activity
                   [kind (type description) (string=? type "Analyze")])])
  )

如果您有嵌套类型定义，则需要以嵌套方式应用type-case。