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)

I would like to know how would you write a function that consumes a restaurant and produces the total number of dishes the restaurant has. Like I take restaurant1, I get 6 dishes. Hope I am doing this right.

Answer 1

It’s simple, just use the accessor procedure to retrieve the list of dishes of a restaurant, and then the built-in procedure to determine the size (or “length”) of that list:

(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?

I’ll let you figure out the details, but remember – whenever you define a new struct using define-struct, an accessor procedure is automatically created for each of its fields. For example, the price of a dish is obtained by calling dish-price on a dish: (dish-price dish).