Question

What I am trying to do is create a function zip (note now that this is not homework) that iterates through multiple lists simultaneously, applying a function to each list of elements, like so:

(zip f '(1 2 3) '(4 5 6) '(7 8 9)) = (list (f 1 4 7) (f 2 5 8) (f 3 6 9))
(zip f '(1 2 3 4) '(5 6) '(7 8 9)) = (list (f 1 5 7) (f 2 6 8))

Basically, it stops when any list runs out of elements. Here is my current attempt:

(defun zip (f &rest lists)
  (if (apply and lists) ; <- Here is where I think the problem is.
    (cons (apply f (mapcar #'car lists)) (zip f &rest (mapcar #'cdr lists)))
    nil))

I would like to know how fix the conditional statement to work with and, or something to that effect. I think the problem arises from and being a macro. I would also like to know if there is a built-in function for doing this already.

Answer 1

You are re-implementing mapcar

? (mapcar #'list '(1 2 3) '(4 5 6) '(7 8 9))
((1 4 7) (2 5 8) (3 6 9))
? (mapcar #'list '(1 2 3 4) '(5 6) '(7 8 9))
((1 5 7) (2 6 8))
? (mapcar #'+ '(1 2 3) '(4 5 6) '(7 8 9))
(12 15 18)
? (mapcar #'+ '(1 2 3 4) '(5 6) '(7 8 9))
(13 16)

BTW, the function you want in your code in place of all is and