要在DrRacket中编写一个函数来从RES类型中提取RegE,可以按照以下步骤进行:
(define-struct RES (value))
(define-struct RegE (value))
(define (extract-RegE res)
(match res
[(RES r) (RegE r)]))
(check-expect (extract-RegE (RES 5)) (RegE 5))
完整的代码示例如下:
(define-struct RES (value))
(define-struct RegE (value))
(define (extract-RegE res)
(match res
[(RES r) (RegE r)]))
(check-expect (extract-RegE (RES 5)) (RegE 5))
在DrRacket中运行上述代码,将会得到期望的结果,并验证函数是否按预期工作。