ACL2

(defun replace-ints (x)

(cond ((endp x) nil)

((integerp (car x))
(cons 'I
(replace-ints (cdr x))))

(t
(cons (car x)
(replace-ints (cdr x))))))

>>4
Vile, disgusting shit. Even Racket least allows using only round brackets, and any code can be purified using simple find-and-replace. This, however, makes a syntactic difference between [] and (). Call it however you want, but it sure as hell isn't Lisp.