euler-problem-10.clj

(def seen-primes (atom []))

;; BUG: if composite c is larger than any p in known-primes-atom,
;; and (rem c p) != 0 for all p, then c would be seen as a prime, though
;; it is a composite number.
(defn memoized-prime? [known-primes-atom n]
  (if (< n 2)
    false
    (every? #(not (zero? (rem n %)))
            (for [d @known-primes-atom :when (< (* d d) n)] d))))

(defn memoizing-prime? [n]
  (if (memoized-prime? seen-primes n)
    (do
      (swap! seen-primes conj n)
      true)
    false))

(defn memoized-sum-primes [mx]
    (reduce + (for [x (range (inc mx)) :when (memoizing-prime? x)] x)))

(println (memoized-sum-primes 100))
(println (memoized-sum-primes 1000))
(println (memoized-sum-primes 10000))