;; This file contains excerpts from the textbook Concrete
;; Abstractions: An Introduction to Computer Science Using Scheme, by
;; Max Hailperin, Barbara Kaiser, and Karl Knight, Copyright (c) 1998
;; by Brooks/Cole Publishing Company. This file may not be reproduced
;; or redistributed other than for use with that textbook.

;; Chapter 14: Object-Oriented Programming

;; 14.5  An Application: Adventures in the Imaginary Land of Gack

(define-class
  'witch
  auto-person-class
  '()
  '(curse))
(class/set-method!
 witch-class 'act
 (lambda (this)
   (let ((victim (random-element
                  (witch/other-people-at-same-place this))))
     (if victim
         (witch/curse this victim)
         (auto-person^act this)))))

(class/set-method!
 witch-class 'curse
 (lambda (this person)
   (let ((person-name (person/name person)))
     (person/say this
                 (list
                  "Hah hah hah, I'm going to turn you into a frog"
                  person-name))
     (turn-into-frog person)
     (person/say this
                 (list "Hee hee" person-name
                       "looks better in green!")))))

(define turn-into-frog
  (lambda (person)
    (for-each (lambda (item) (person/lose person item))
              (person/possessions person))
    (person/say person '("Ribbitt!"))
    (person/move-to person pond)
    (registry/remove registry person)))