play with objects

Hello guys,
can I ask you for help regarding my problem?

I would like to create shop with cars. Then I will create two cars and I will put these cars to slot "cars" to my shop. I want to create method which will take cost of all cars from my shop and give back some number. could you advice pls ?

(defclass autoshop () ((cars :initform nil :accessor cars)
                   (name :initarg :name :reader name) ))

(defclass automobile ()
  ((car_name   :initform nil :accessor car_name)
   (cost :initform nil :accessor cost)))

>(setf greencar (make-instance 'autoshop))   
>(setf (slot-value greencar 'name) 'Green_car_shop)

.....my shop will be called 'Green_car_shop'

first car:

>(setf audi (make-instance 'automobile))
>(setf (slot-value audi 'car_name) 'AudiA3)
>(setf (slot-value audi 'cost) 10000)

result:

#<AUTOMOBILE 2183BD67> is an AUTOMOBILE
CAR_NAME      AUDIA3
COST          10000

second car:

>(setf bmw (make-instance 'automobile))
>(setf (slot-value bmw 'cost) 12000)
>(setf (slot-value bmw 'car_name) 'BmwM3)

result:

#<AUTOMOBILE 21854D3B> is an AUTOMOBILE
CAR_NAME      BMWM3
COST          12000

Then I will put these cars to my shop:

>(push bmw (slot-value greencar 'cars))
>(push audi (slot-value greencar 'cars))

results:

#<AUTOSHOP 2180F753> is an AUTOSHOP
CARS      (#<AUTOMOBILE 2183BD67> #<AUTOMOBILE 21854D3B>)
NAME      GREEN_CAR_SHOP

How to continue pls? In case of these 2 cars, it should return 22000. when I will put there third car with cost 11000, cost will be 33000.

(defmethod cost_of_all_cars ((autoshop autoshop))
 ????????????
  )

For example:

(defmethod cost_of_all_cars ((autoshop autoshop))
  (list (cars autoshop)) )

CL-USER 33 > (cost_of_all_cars greencar)
((#<AUTOMOBILE 2183BD67> #<AUTOMOBILE 21854D3B>))

but how to get in to the slots called cost and calculate costs of all cars?

any idea pls?

Use LOOP or DOLIST to iterate over the cars in the shop. Then use your COST accessor or call (slot-value car 'cost) to get the cost of each car, summing that cost into a central accumulator variable.

nuntius wrote:Use LOOP or DOLIST to iterate over the cars in the shop. Then use your COST accessor or call (slot-value car 'cost) to get the cost of each car, summing that cost into a central accumulator variable.

thanks nuntius, working.. . Loop was good choise. thx man . Im beginner and I didn't know this function/macro..