-;; A very simple defstruct built on lists. It supports just slot with
-;; an optional default initform, and it will create a constructor,
-;; predicate and accessors for you.
-(defmacro def!struct (name &rest slots)
- (unless (symbolp name)
- (error "It is not a full defstruct implementation."))
- (let* ((name-string (symbol-name name))
- (slot-descriptions
- (mapcar (lambda (sd)
- (cond
- ((symbolp sd)
- (list sd))
- ((and (listp sd) (car sd) (cddr sd))
- sd)
- (t
- (error "Bad slot accessor."))))
- slots))
- (predicate (intern (concat name-string "-P"))))
- `(progn
- ;; Constructor
- (defun ,(intern (concat "MAKE-" name-string)) (&key ,@slot-descriptions)
- (list ',name ,@(mapcar #'car slot-descriptions)))
- ;; Predicate
- (defun ,predicate (x)
- (and (consp x) (eq (car x) ',name)))
- ;; Copier
- (defun ,(intern (concat "COPY-" name-string)) (x)
- (copy-list x))
- ;; Slot accessors
- ,@(with-collect
- (let ((index 1))
- (dolist (slot slot-descriptions)
- (let* ((name (car slot))
- (accessor-name (intern (concat name-string "-" (string name)))))
- (collect
- `(defun ,accessor-name (x)
- (unless (,predicate x)
- (error ,(concat "The object is not a type " name-string)))
- (nth ,index x)))
- ;; TODO: Implement this with a higher level
- ;; abstraction like defsetf or (defun (setf ..))
- (collect
- `(define-setf-expander ,accessor-name (x)
- (let ((object (gensym))
- (new-value (gensym)))
- (values (list object)
- (list x)
- (list new-value)
- `(progn
- (rplaca (nthcdr ,',index ,object) ,new-value)
- ,new-value)
- `(,',accessor-name ,object)))))
- (incf index)))))
- ',name)))
-
-