Unfold in Clojure

unfold-examples.clj

(ns unfold-examples
  (:use [unfold-util]))

(defn unfold-tails [s]
  (unfold empty? identity rest s))

(defn unfold-map [f s]
  (unfold empty? #(f (first %)) rest s))

unfold-util.clj

;; Enrico Franchi (c) 2011
;; Released under the terms of the MIT License
;; http://www.opensource.org/licenses/mit-license.php 

(ns unfold-util
  (:use [clojure.test]))

(defn unfold
  ([p f g seed tail-g]
   (lazy-seq
     (if (p seed)
       (tail-g seed)
       (cons (f seed)
             (unfold p f g (g seed))))))
  ([p f g seed]
   (unfold p f g seed (fn [_] ()))))

(deftest standard-unfold []
  (is (= (set (unfold #(= 0 %) identity dec 10))
    (set (range 1 11)))))

(deftest infinite-unfold []
  (is (=
    (take 10 (unfold
      (fn [x] false)
      identity
      inc
      0))
    (take 10 (iterate inc 0)))))

(run-tests)