anchor.diff:             ,starttag
              (? (not ,tmplst)
                 (go ,endtag))
  -           (? (not (list? ,tmplst))
  -              (error "List expected instead of ~A." ,tmplst))
              (setq ,iter (car ,tmplst))
              ,@body
              (setq ,tmplst (cdr ,tmplst))
  
positive.code:   (let result (cons nil nil)
      (dolist (i lst (cdr result))
        (rplaca result
                (cdr (rplacd (| (car result) result)
                             (list (funcall func i))))))))
  
negative.code:         start
          (? (not i)
             (return (queue-list nl)))
          (? (not (car i))	    ; Break if any list has no more elements.
             (return nil))
          (enqueue nl (caar i))	; Add head of list to list of arguments
  