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  • Re: flatten

    From B. Pym@Nobody447095@here-nor-there.org to comp.lang.lisp on Mon Aug 4 06:42:46 2025
    From Newsgroup: comp.lang.lisp

    John Thingstad wrote:

    As a sidenote I played around with ways of counting leaves

    (defun count-leaves (list)
    (loop for element in list summing
    (if (listp element) (count-leaves element) 1)))

    (defun count-leaves (element)
    (typecase element
    (list (reduce #'+ (mapcar #'count-leaves element)))
    (atom 1)))

    Here I clearly prefer the first as it is MUCH more efficient (and also slightly terser).

    This is slightly faster than the LOOP version.

    (defun count-leaves3 (seq)
    (do ((sum 0
    (let ((e (pop seq)))
    (+ sum (if (listp e)(count-leaves3 e) 1)))))
    ((not seq) sum)))
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