anchor.diff:        (+ (count-structure (vm-current-environment vm))
            (count-structure (vm-stack vm))))))
   
  +(declaim (inline check-ticks-quota))
   (defun check-ticks-quota (vm)
     (declare (type vm vm)
              (optimize (speed 1) (safety 0)))
  
positive.code:                                         ; instructions, skip them.
             (handle-nop vm instruction))
            (t (error "Shovel internal WTF: unknown instruction '~a'." opcode)))))
      (locally
          (declare (inline increment-vm-ticks)
                   (optimize (speed 1)))
        (increment-vm-ticks vm)))
    (vm-is-live vm))
  
  (defun increment-vm-ticks (vm)
    (declare (type vm vm))
    (incf (vm-executed-ticks vm))
  
negative.code:                          :num-args (second args))
            (vm-stack vm))
      ;; for the pushed callable (5 fields)
      (increment-cells-quota vm 5)
      (inc-pc vm)))
  
  (defun handle-new-frame (vm instruction)
  