;; 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 the authors. Full text is available for free at
;; http://www.gustavus.edu/+max/concrete-abstractions.html

;; Chapter 14: Object-Oriented Programming

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

(define-class
  'wizard
  auto-person-class
  '()
  '())

(class/set-method!
 wizard-class 'act
 (lambda (this)
   (let ((place (wizard/place this)))
     (let ((scrolls (filter scroll?
                            (place/contents place))))
       (if (and (not (null? scrolls))
                (not (eq? place chamber-of-wizards)))
           (begin
             (wizard/take this (car scrolls))
             (wizard/move-to this chamber-of-wizards)
             (wizard/lose this (car scrolls)))
           (auto-person^act this))))))