Hi,
On 5 Mai, 14:54, Robert Luo <robort...@gmail.com> wrote:
> (defn repeated-seq
> [f start]
> (let [coll (f start)]
> (concat coll (lazy-seq (repeated-seq f (last coll))))))
>
> it is OK when I call it with:
> (repeated-seq #(range % 5) 0)
repeated-seq cannot do anything about the problem. You have to ensure
that your f is free of "overlap" (so to say). One way todo that in
your example is (repeated-seq #(-> % inc (range 5)) -1).
Also depending on the size of your intermediate seqs you might want to
roll your own concat or use knowledge of the underlying collection
type to avoid the slow last.
(defn roll-your-own-repeated-seq
[f init]
(let [step (fn step
[s]
(lazy-seq
(when-let [[fst & rst] s]
(if rst
(cons fst (step rst))
(cons fst (roll-your-own-repeated-seq f
fst))))))]
(lazy-seq
(step (seq (f init))))))
(defn vector-repeated-seq
[f init]
(lazy-seq
(let [v (f init)]
(when-let [s (seq v)]
(concat s (lazy-seq (vector-repeated-seq f (peek v))))))))
Hope this helps.
Sincerely
Meikel
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