anchor.diff:    "A variation of (map nil ...)/mapc/mapl with size constrained.
   Without a result to delineate sublist boundaries, we must enforce them
   manually."
  -  ;; This is an inner loop.
  -  (declare #.*normal-optimize*)
     (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))
  
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: 
  (defun maplist-into (result-list fn &rest lists)
    "A variation of map-into."
    (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
  