Continued Fractions

(defun continued-fraction (real)
  (multiple-value-bind (integer-part fractional-part)
      (floor (rationalize real))
    (cons integer-part (if (zerop fractional-part)
               nil
               (continued-fraction (/ 1 fractional-part))))))
What does /prog/ think? Am I shooting myself in the foot by just throwing rationalize in there and hoping it works out?

1)

(defun foo (a b c &aux (sum (+ a b c)))
 ...)

is like

(defun foo (a b c)
 (let* ((sum (+ a b c)))
  ...))

most lispers consider it bad style

2)
ensure is a CL naming convention, without years of experience (with other CL libraries) you wouldn't understand it.

3)
zerop is fail, sorry but it fucking is
where is my
ONEP TWOP THREEP etc?