common lisp - Scope of variables inside functions -

common lisp - Scope of variables inside functions -

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why function homecoming different value every time? 4 answers unexpected persistence of info [duplicate] 1 reply

i have written function returns prime factorization of numbers n less 20. function uses allow create list of exponents, , increments exponents when finds n divisible prime.

in lisp interpreter (both gcl , clisp), when phone call next function once, right factorization when phone call sec time, sum of factorizations of first , sec function - isn't scope of exponents limited within of let!? why isn't exponents beingness re-assigned value '(0 0 0 0 0 0 0 0)? how can re-write function withstand multiple calls?

(setf primes '(2 3 5 7 11 13 17 19)) (defun factorize (n) (let ((exponents '(0 0 0 0 0 0 0 0))) (loop 0 (- (length primes) 1) (loop while (and (= (mod n (nth primes)) 0) (not (= n 1))) (incf (nth exponents)) (setf n (/ n (nth primes))))) (return-from factorize exponents)))

output:

>(factorize 10) ;; first time (1 0 1 0 0 0 0 0) ;; 2^1*5*1 = 10, right >(factorize 10) (2 0 2 0 0 0 0 0) ;; wrong >(factorize 10) (3 0 3 0 0 0 0 0)

the list '(0 0 0 0 0 0 0 0) stored literal, , modifying literal undefined behaviour. should use

(let ((exponents (copy-list '(0 0 0 0 0 0 0 0))))

to create re-create of literal every time need it, or alternatively

(let ((exponents (list 0 0 0 0 0 0 0 0)))

btw, utilize

(defparameter *primes* '(2 3 5 7 11 13 17 19))

rather setf @ top level. note * signs convention indicate special variable.

common-lisp literals