Pascal Bourguignon wrote:

> Here is for example, a function that is both iterative and
> recursive. but not stupid (even if it could be written better with
> LOOP):
>
> (defun find-depths (target list)
> "Returns a list of depths where occurences of TARGET are found in LIST"
> (let ((results '()))
> (dolist (item list (nreverse (mapcar (function 1+) results)))
> (cond
> ((eql target item)
> (push 0 results))
> ((listp item)
> (setf results (nreconc (find-depths target item) results)))))))
>
> C/USER[139]> (find-depths 'a '(a a ((a b (c a d))) a))
> (1 1 3 4 1)
> C/USER[140]> (find-depths 'a '(a (((a)))))
> (1 4)

Gauche Scheme

(define (find-depths target lst :optional (depth 1))
(append-map
(lambda (item)
(cond ((eqv? item target) (list depth))
((list? item) (find-depths target item (+ depth 1)))
(#t '())))
lst))

(find-depths 'a '(a a ((a b (c a d))) a))
===>
(1 1 3 4 1)

(find-depths 'a '(a (((a)))))
===>
(1 4)