locked-magic-door-failed.rkt

#lang racket

(define the-key 'the-key)
(define the-spell-book 'the-spell-book)

(define person%
  (class object%
    (init-field items h)
    (super-new)         
    
    (define/public (has-item item)
      (member item items))

    (define/public (height)
      h)
    ))

(define door<%> (interface () can-open can-pass))

(define door-mixin
  (mixin () (door<%>)
    (super-new)
    
    (define/public (can-open p)
      (println "door% can-open")
      #t)
    
    (define/public (can-pass p)
      (println "door% can-pass")
      #t)
    ))

(define secure-door<%> (interface (door<%>) needed-item))

(define secure-mixin
  (mixin (door<%>) (secure-door<%>)
    (super-new)

    (define/public (needed-item) ;; error??
      (println "secure-mixin needed-item")
      #f)

    (define/override (can-open p)
      (println "secure-mixin can-open")
      (define item (needed-item))
      (cond
        ((not (send p has-item item)) (printf "You don't have the Key ~v\n" item)
                                      #f)
        (else (printf "Using Key... ~v\n" item)
              (super can-open p))))
    ))

(define locked-needed-mixin
  (mixin (secure-door<%>) (secure-door<%>)
    (super-new)
    (define/override (needed-item)
      (println "locked-needed-mixin neededItem")
      the-key)
    ))

(define magic-needed-mixin
  (mixin (secure-door<%>) (secure-door<%>)
    (super-new)
    (define/override (needed-item)
      (println "magic-needed-mixin neededItem")
      the-spell-book)
    ))

(define door%
  (door-mixin object%))

(define locked-mixin (compose locked-needed-mixin secure-mixin))
(define magic-mixin (compose magic-needed-mixin secure-mixin))

(define locked-magic-mixin (compose locked-mixin magic-mixin))
(define locked-magic-door% (locked-magic-mixin door%))


(define door (new locked-magic-door%))
(send door can-open (new person% [items (list the-key the-spell-book)] [h 0.5]))

; class*: superclass already contains method
;   superclass: #<class:...agic-door-failed.rkt:62:2>
;   method name: needed-item
;   class name: ...agic-door-failed.rkt:36:2

https://www.mail-archive.com/racket-users@googlegroups.com/msg44893.html