gistfile1.clj

(defn unfold
  "Next and done? are functions that operate on a seed. next should return a pair, [value new-seed]; the value half of the pair is inserted into the resulting list, while the new-seed is used to continue unfolding. Notably, the value is never passed as an argument to either next or done?."
  [next done? seed]
  (map first
       (rest
        (take-while (comp (complement done?) second)
                    (iterate (comp next second)
                             [nil seed])))))

(defn fibs []
  (unfold (fn [[a b]] [a [b (+ a b)]]) (constantly false) [0 1]))

user> (take 10 (fibs))
(0 1 1 2 3 5 8 13 21 34)