anchor.diff:  
   (defun maplist-into (result-list fn &rest lists)
     "A variation of map-into."
  -  ;; This is an inner loop.
  -  (declare #.*normal-optimize*)
     (let1 fn (ensure-function fn)
       (apply #'mapl
              (lambda (result &rest args)
  +             ;; This is an inner loop.
  +             (declare #.*normal-optimize*)
                (declare (dynamic-extent args))
                (setf (car result) (apply fn args)))
              result-list
  
positive.code:       (prog1
            (if seqs
                (pmap-into/parsed map-into result-seq fn seqs size parts-hint)
                (locally (declare #.*normal-optimize*)
                  (pmap-into/parsed map-into
                                    result-seq
                                    (lambda (x)
                                      (declare (ignore x))
                                      (funcall fn))
                                    (list result-seq)
                                    size
                                    parts-hint)))
          (when has-fill-p
            (setf (fill-pointer result-seq) size))))))
  
  
negative.code:   "A variation of (map nil ...)/mapc/mapl with size constrained.
  Without a result to delineate sublist boundaries, we must enforce them
  manually."
    (let1 index 0
      (apply map
             (lambda (&rest args)
               ;; This is an inner loop.
               (declare #.*normal-optimize*)
               (declare (dynamic-extent args))
               (when (eql index size)
                 (return-from map-iterate nil))
  