anchor.diff:    deps
     writes)
   
  -(defun %op (result-types body args)
  +(defun %%op (result-types body args)
     (let ((results (mapcar (lambda (type)
                              (vval type))
                            result-types)))
  
positive.code:             for i upfrom 0
              do (insert-write val i))
        new)))
  
negative.code:                   (load-op
                     (let ((var (load-op-var op)))
                       `((,(vval-name var)) (,(vval-type var))
                         (aref vec (+ start ,(load-op-idx op))))))
                    (store-op
                     `(() () (setf (aref vec (+ start ,(store-op-idx op)))
                                   ,(let ((var (store-op-var op)))
                                      (if (vval-p var)
                                          (vval-name var)
  