Question

The test function is as below:

(defun fab (n) 
    (let ((res '(1 1)))
        (loop for i from 2 to n do
            (nconc res (list (+ (nth (- i 2) res) (nth (- i 1) res)))))
        res))

$ecl

…
EECL (Embeddable Common-Lisp) 12.7.1 (git:UNKNOWN)

…

>(fab 10)
(1 1 2 3 5 8 13 21 34 55 89)
>(fab 20)
(1 1 2 3 5 8 13 21 34 55 89 2 3 5 8 13 21 34 55 89 144 91 5 8 13 21 34 55 89 144

Then i restart ECL

>(fab 20)
(1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765 10946)

It seems the “res” is not freed after the (fac 10) ?

Sincerely!

Answer 1

You should use (list 1 1) rather than '(1 1) in the let form. In Common Lisp, the effects of modifying literal objects are not defined.

(defun fib (n)
  (let ((res (list 1 1))) ; (list 1 1) instead of '(1 1)
    (loop for i from 2 to n
          do (nconc res (list (+ (nth (- i 2) res) (nth (- i 1) res)))))
    res))