anchor.diff:    (with-output-to-string (str)
       (write-environment (vm-current-environment vm) vm str)))
   
  +(declaim (inline vm-not-finished))
   (defun vm-not-finished (vm)
     (and
      (< (vm-program-counter vm) (length (vm-bytecode vm)))
  
positive.code:          (push args (vm-stack vm))
           (incf (vm-program-counter vm))
           (if (stringp args)
               ;; 1 for the strings, the rest for the contents
               (increment-cells-quota vm (1+ (length args)))
  
               ;; for the pushed value
  
negative.code:          (count-structure (vm-stack vm))))))
  
  (defun step-vm (vm)
    (check-vm-without-error vm)
    (when (and (vm-total-ticks-quota vm)
               (>= (vm-executed-ticks vm)
  