El viernes 24 de febrero de 2012 18:46:03 UTC+1, Cedric Greevey escribió: > > On Fri, Feb 24, 2012 at 11:30 AM, JuanManuel Gimeno Illa wrote: > > > I think it would be better to create the lazy-seq over a function that > uses > > the pieces in order to not to explode input with partition-all and > > de-explode it with map-first before the recursive call. > > That hangs on the case > > (first (second (split-at-subsequence [1 2] (range)))) > > again. I don't know why; from what I can see, it shouldn't, since > everything seems sufficiently lazy. > My third version does this and I think does not hang on the example.
Maybe could also use some optimization: > > (defn split-at-subsequence [mark input] > (when-let [sequence (seq input)] > (let [len (count mark) > pieces (partition-all len 1 sequence) > step (fn step [rst-input] > (when rst-input > (lazy-seq > (let [[fst rst] (split-with #(not= mark %) rst-input)] > (cons fst (step (nthnext rst len)))))))] > (map #(map first %) (remove nil? (map seq (step pieces))))))) > > This avoids computing len and pieces and (map first ...) over and > over, and uses nthnext instead of drop to save some calls to seq. > > The > split-with could be replaced by a loop to save traversing part of the > sequence twice, but then it would definitely be impossible to fix the > hang with (first (second (split-at-subsequence [1 2] (range)))). > What I don't understand of your solution is the (map seq (step pieces)) because for me it is clear that each of the sequences generated by step is a seq, so why do you need to seq it? It's probably possible to do quite a bit better, though, perhaps by > using Boyer-Moore, though I'm not sure how easily Boyer-Moore can be > made lazy, especially lazy enough to avoid than hang. > Interesting .... Juan Manuel -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
