primes.clj

(ns net.abhinavsarkar
  (:use
    [clojure.contrib.math :only (sqrt ceil)]
    [clojure.contrib.import-static]))

(import-static java.lang.Integer parseInt)

(declare primes)

(defn- divisible? [x y] (zero? (mod x y)))

(defn prime-divisors [n]
  (filter (partial divisible? n)
    (take-while #(<= % (ceil (sqrt n))) primes)))

(def prime?
  (memoize
    (fn [n]
      (cond
        (= n 1) false
        (some #(= n %) [2 3 5 7]) true
        (some (partial divisible? n) [2 3 5 7]) false
        (not-any? #(zero? (mod (% n) 6)) [inc dec]) false
        :else (empty? (prime-divisors n))))))

(def primes
  (let [odds (iterate #(+ % 2) 3)]
    (cons 2 (filter prime? odds))))

(defn primes-between [start, end]
  (let [
    start-012?
      (some #(= start %) [0 1 2])
    first-candidate
      (cond
        start-012? 3
        (prime? start) start
        (divisible? start 2) (inc start)
        :else (+ start 2))
    candidates
      (iterate #(+ % 2) first-candidate)
    real-candidates
      (if start-012?
        (cons 2 candidates)
        candidates)]
    (filter prime?
      (take-while #(<= % end) real-candidates))))

(defn main []
  (let [[x y] (map #(parseInt %) *command-line-args*)]
    (doseq [p (primes-between x y)] (println p))))

(main)