(defparameter *day17-rocks*
  (list (make-array '(1 4) :element-type 'boolean :initial-contents '((T T T T)))
        (make-array '(3 3) :element-type 'boolean :initial-contents '((NIL T NIL)
                                                                      ( T  T  T )
                                                                      (NIL T NIL)))
        (make-array '(3 3) :element-type 'boolean :initial-contents '((NIL NIL  T )
                                                                      (NIL NIL  T )
                                                                      ( T   T   T )))
        (make-array '(4 1) :element-type 'boolean :initial-contents '((T) (T) (T) (T)))
        (make-array '(2 2) :element-type 'boolean :initial-contents '((T T) (T T)))))

(defun day17-print-rock (rock)
  (loop with (height width) = (array-dimensions rock)
        for row from 0 below height
        do (loop for col from 0 below width
                 do (format T "~a" (if (aref rock row col) #\# #\.)))
        do (format T "~%")))