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mecdemort/prime?.clj

Created March 16, 2011 02:31
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prime?.clj
(use '[clojure.contrib.lazy-seqs :only [primes]]
'[clojure.set])
(def prime?
(let [mem (ref #{})
primes (ref primes)]
(fn [n]
(if (< n (first @primes))
(@mem n)
(let [[mems ps] (split-with #(<= % n) @primes)]
(dosync
(ref-set primes ps)
((commute mem union (set mems)) n)))))))
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