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)

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