Question

(define-struct restaurant (name address  lod))
(define-struct dish  (name main-ingredient price))

(define lod
  (list
   (make-dish "BNC" "pepper" 15.00)
   (make-dish  "BBQ" "sauce" 20.00)
   (make-dish "BAW" "vanilla" 18.00)
    (make-dish "ACA" "tomato" 15.00)
   (make-dish  "NAM" "onions" 25.00)
   (make-dish "PLA" "milk" 34.00)))

(define lod1
  (list
   (make-dish "AHSH" "carrots" 23.00)
   (make-dish  "PROA" "garlic" 21.00)
   (make-dish "MENE" "eggs" 16.00)
    (make-dish "SAYB" "water" 11.00)
   (make-dish  "WAFA" "chicken" 22.00)
   (make-dish "LDAFK" "chocolate" 10.00)))


(define Sky-Dragon (make-restaurant "Sky Dragon" "23 Cutoiut, NY"  lod))
(define Tomas (make-restaurant "Tomas" "34 Rossi, CA" lod1))


(define restaurant1 Sky-Dragon)
(define restaurant2 Tomas)

我想知道你如何编写一个消耗餐厅的功能，并产生餐厅的菜肴总数。就像我吃restaurant1，我得到6道菜。希望我这样做。

Answer 1

这很简单，只需使用访问程序来检索餐馆的菜肴列表，然后使用内置程序来确定该列表的大小（或“长度”）：

(define (number-of-dishes restaurant)
  (<???>                  ; how do we determine the size of a list?
    (<???> restaurant)))  ; how do we access a restaurant's list of dishes?

我会让你弄清楚细节，但请记住 - 无论何时使用define-struct定义新结构，都会自动为其每个字段创建一个访问程序。例如，通过price dish dish-price上的dish来获取(dish-price dish)的{{1}}。

消耗列表球拍

1 个答案: