anchor.diff:  
   ;; main is a grid hash, other is a grid hash
   (defun grid-combine-fun (main other offset-x offset-y)
  -  (declare (optimize (debug 3)))
     (let ((w (@ main :width))
           (h (@ main :height)))
       (with main :v
  
positive.code:   (@ (@ grid :v) (+ x (* y (@ grid :width)))))
  
  (defun do-grid-fun-aux (grid val fn x y width)
    (declare (optimize (debug 3)))
     (let ((v (@ grid :v)))
       (if (>= y (@ grid :height))
         val
  
negative.code: 
  ;; executes against game when drop-counter hits zero
  (defun drop-block-one (game)
    (let* ((fb (@ game :fb))
           (dropped-fb (with fb :y (1+ (@ fb :y)))))
      (if (legal-block-position game dropped-fb)
  