A mapping function that allows splicing lists into the result. If fun returns a list whose first element is @ the following elements will be spliced into the list.

gistfile1.txt

(defun mapcar@ (fun seq)
  (let (result)
    (loop for elem in (reverse seq)
          for newelem = (funcall fun elem)
          if (and (listp newelem)
                  (eq (car newelem) '@))
          do (loop for newelem2 in (cdr newelem)
                   do (setq result (cons newelem2 result)))
          else do (setq result (cons newelem result)))
    result))

Actually forget it. Just realized it's probably easier to do it directly with a loop.