Project Euler #3 in Clojure

euler-3.clj

(defn primes-until
  "A tail-recursive primes generator that generates primes until
  <stop-pred> returns true.  <stop-pred> is a function that
  takes in the current candidate prime and the number of primes 
  generated so far and returns true or false."
  [stop-pred] 
  (defn rec
    "p: vector of primes found so far; i: candidate prime"
    [p i] (cond 
           (stop-pred i (count p)) p
           (let [root (. Math (sqrt i))] 
             (every? #(not= (rem i %) 0) (take-while #(<= % root) p))) (recur (conj p i) (inc i))
             true (recur p (inc i))))
  (rec [] 2))

(defn prime-factor
  "Find the prime factors of <i> using a collection of primes <p>.
  <f> is a list of prime factors found so far."
  [i p f]
  (cond (= i 1) f
	(= 0 (rem i (first p))) (recur (/ i (first p)) p (cons (first p) f))
	true (recur i (rest p) f)))

(prime-factor 600851475143 (primes-until (fn [i n] (> i 10000))) nil)