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;;;                     General Game Definitions                     ;;;
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;;;; Classes

;;; All game objects are subclasses of this.
(defclass <game-object> ()
  ;; symbol used by players to refer to the object
  (nickname    :type      <symbol>
               :accessor  nick
               :initarg   :nick)
  ;; its printed name
  (name        :type      <string>
               :accessor  name
               :initarg   :name)
  ;; a longer description - a list of strings
  (description :type      <list>
               :accessor  description
               :initarg   :description
               :initvalue '()))

;;; Objects that contain other objects.
(defclass <container> (<game-object>)
  (contents :type      <list> ; (of <game-object>s)
            :accessor  contents
            :initarg   :contents
            :initvalue '()))

;;; Objects that can be in containers.
(defclass <contained> (<game-object>)
  (location :type      <game-object>
            :accessor  location
            :initarg   :location))


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;;;; Interface

;;; Use this to show an object with its nickname so players know how to
;;; refer to this object.
(defgeneric (name+nick game-object))

;;; This function gets a list of <game-object>s and returns the one with
;;; the given nickname, or #f of none found.
;;; (define (nick-find nickname list) ...)

;;; Move an object to a different location.
(defgeneric (transfer obj source target))


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;;;; Implementation

;;; This specialize the way that <contained> objects are created -
;;; updating the holding container automatically.
;;; initialize is a built-in standard generic that is called on every
;;; object that is created, so you must call the next method to do what
;;; it was supposed to do, then add stuff.
(defmethod (initialize (o <contained>) initargs)
  (call-next-method)                    ; must call this
  ;; this prevents errors when there is no initial location value
  ;; (slot-bound can test if there is any value in the location slot)
  (when (slot-bound? o 'location)
    (set! (contents (location o)) (cons o (contents (location o))))))

;;; Using this method will produce uniform output that players can use.
(defmethod (name+nick (obj <game-object>))
  (add (name obj) " [" (as <string> (nick obj)) "]"))

;;; Search for an object by its nickname, nickname can be anything, but
;;; only symbols will be found.
(define (nick-find nickname list)
  (find-if (lambda (x) (eq? (nick x) nickname)) list))

;;; Move an object to a different location.  Using only this method to
;;; make sure that you don't get inconsistencies.
(defmethod (transfer
            (obj <contained>) (from <container>) (to <container>))
  (unless (eq? from to)
    (set! (contents from) (remq obj (contents from)))
    (set! (location obj) to)
    (set! (contents to) (cons obj (contents to)))))