Convert decimal number to octal in Lisp

Question

I'm trying to write a function in Common Lisp to convert a base 10 number into a base 8 number, represented as a list, recursively.

Here's what I have so far:

(defun base8(n)
(cond
    ((zerop (truncate n 8)) (cons n nil))
    ((t) (cons (mod n 8) (base8 (truncate n 8))))))

This function works fine when I input numbers < 8 and > -8, but the recursive case is giving me a lot of trouble. When I try 8 as an argument (which should return (1 0)), I get an error Undefined operator T in form (T).

Thanks in advance.

Answer 1

Just for fun, here's a solution without recursion, using built-in functionality:

(defun base8 (n)
  (reverse (coerce (format nil "~8R" n) 'list)))