;; Änderung der Repräsentation von PRICES:

(define prices
  (lambda (drink)
    (cond
     ((equal? drink 'coke)
      100)
     ((equal? drink 'fanta)
      100)
     ((equal? drink 'karamalz)
      120)
     ((equal? drink 'black-bush)
      250)
     (error "unfound drink"))))

(define drink-price
  (lambda (drink prices)
    (prices drink)))