attempt.lisp

(defun event-p (x) t) ;; constantly t
(defun key-p (x) t)   ;; constantly t

;; w/o defpattern
(match event
  ((and (sdl:event- (type (eq :key-down-event)))
       ;;^^^^^^^^^^ this specify the container type
                   ;;^^^^ this is a slot
                   ;;      ^^^^^^^^^^^^^^^^^^ and this specifies the type of the slot.
        (sdl::key-  (key (eq :sdl-key-z)) state)))
   (format t "Z: ~A~%" state))
  ((and (sdl:event- (type (eq :key-down-event)))
        (sdl::key-  state)))
   (format t "Down: ~A~%" state)))
  ((and (sdl:event- (type (eq :key-up-event)))
        (sdl::key-  state)))
   (format t "UP: ~A~%" state)))

;; generalize it into defpattern
(defpattern sdl-event (type key state)
  `(and (sdl:event- (type (eq ,type)))
        (sdl::key-  (key (eq ,key)) ,state)))

;; w/ defpattern
(match event
  ((sdl-event :key-down-event :sdl-key-z state)
   (format t "Z: ~A~%" state))
  ((sdl-event :key-down-event _ state)
   (format t "Down: ~A~%" state)))
  ((sdl-event :key-up-event _ state)
   (format t "UP: ~A~%" state)))