diff options
Diffstat (limited to 'src/clojure/contrib/lazy_seqs.clj')
| -rw-r--r-- | src/clojure/contrib/lazy_seqs.clj | 42 |
1 files changed, 25 insertions, 17 deletions
diff --git a/src/clojure/contrib/lazy_seqs.clj b/src/clojure/contrib/lazy_seqs.clj index 118a5602..cf83b5de 100644 --- a/src/clojure/contrib/lazy_seqs.clj +++ b/src/clojure/contrib/lazy_seqs.clj @@ -33,24 +33,32 @@ (ns clojure.contrib.lazy-seqs (:use clojure.contrib.def)) +; primes cannot be written efficiently as a function, because +; it needs to look back on the whole sequence. contrast with +; fibs and powers-of-2 which only need a fixed buffer of 1 or 2 +; previous values. (defvar primes - (lazy-cat [2 3 5 7] + (concat + [2 3 5 7] + (lazy-seq (let [primes-from - (fn primes-from [n [f & r]] - (if (some #(zero? (rem n %)) - (take-while #(<= (* % %) n) primes)) - (recur (+ n f) r) - (lazy-seq (cons n (primes-from (+ n f) r))))) - wheel (cycle [2 4 2 4 6 2 6 4 2 4 6 6 2 6 4 2 - 6 4 6 8 4 2 4 2 4 8 6 4 6 2 4 6 - 2 6 6 4 2 4 6 2 6 4 2 4 2 10 2 10])] - (primes-from 11 wheel))) - "A lazy sequence of all the prime numbers.") + (fn primes-from [n [f & r]] + (if (some #(zero? (rem n %)) + (take-while #(<= (* % %) n) primes)) + (recur (+ n f) r) + (lazy-seq (cons n (primes-from (+ n f) r))))) + wheel (cycle [2 4 2 4 6 2 6 4 2 4 6 6 2 6 4 2 + 6 4 6 8 4 2 4 2 4 8 6 4 6 2 4 6 + 2 6 6 4 2 4 6 2 6 4 2 4 2 10 2 10])] + (primes-from 11 wheel)))) + "Lazy sequence of all the prime numbers.") + +(defn fibs [] + "Returns a lazy sequence of all the Fibonacci numbers." + (map first (iterate (fn [[a b]] [b (+ a b)]) [0 1]))) + +(defn powers-of-2 [] + "Returns a lazy sequence of all the powers of 2" + (iterate #(bit-shift-left % 1) 1)) -(defvar fibs - (lazy-cat [0 1] (map + fibs (rest fibs))) - "A lazy sequence of all the fibonacci numbers.") -(defvar powers-of-2 - (lazy-seq (cons 1 (map #(bit-shift-left % 1) powers-of-2))) - "A lazy sequence of all the powers of 2") |