;; ====== Problem 5.2 ======
;; creation of predicates

;; categorie=?: product symbol -> bool
;;
;; example: (categorie=? tea 'drink) ergibt true
(define (categorie=? prod categ)
  (if (symbol=? (product-categorie prod) categ) true
      false)
  )

;; cheaper?: product number -> bool
;;
;; example: (cheaper? apple 0.5) ergibt false
(define (cheaper? prod value)
  (if (< (product-price prod) value) true
      false)
  )

(check-expect (categorie=? apple 'fruit) true)
(check-expect (categorie=? tea 'fruit) false)
(check-expect (cheaper? apple 0.5) false)
(check-expect (cheaper? banana 55) true)