I think this <https://github.com/plumatic/plumbing/blob/318af7798bb701607aaae8639d12829014941184/src/plumbing/core.cljx#L182> will do it:
(lazy-cat (first coll) (when-let [n (next coll)] (lazy-flatten n)))) On Tuesday, November 21, 2017 at 2:34:15 PM UTC-8, Matt Anderson wrote: > > I have a function that is returning a lazy-seq of lazy-seq's. > > > (seq (seq [1 2 3]) (seq [4 5 6]) ...) > > > The end-user API, however, should be able to get back a lazy-seq of the > individual items across all lazy-seq's--essentially a flattening of the > output of my function--instead of the "top level" seqs. > > > (seq [1 2 3 4 5 6 ...]) > > Each of the internal lazy-seq's is expensive in terms of memory usage so > I'd like to only "load" one at a time. I've been trying to find a way to > only calculate one of the top-level lazy-seq's at a time and then not > "take" the next until the user gets to the end of the first and needs the > first item from the next (eg: (seq [4 5 6]) doesn't get calculated until we > have consumed 3 and are asking for the next), but haven't found a way to do > it. Best I've gotten is "loading" 2 "top level" seqs at a time and I'm > afraid that may be the best I get, but I thought it might be an exercise > worth presenting in case anyone had ideas. Here's a contrived example: > > > (defn lazy-flatten > > [coll] > > (when-let [s (seq coll)] > > (lazy-seq > > (if (seq? (first s)) > > (concat (lazy-flatten (first s)) (lazy-flatten (rest s))) > > (cons (first s) (lazy-flatten (rest s))))))) > > (->> (repeatedly > (fn [] > (println "New seq...") > (map (fn [x] + x (rand-int 10)) (range 4)))) > lazy-flatten > (take 1)) > > > > Prints: > > > New seq... > > New seq... > > => (8) > > > I realize this is because 2 items must be taken for "concat", so there > would need to be another approach (this was just my best shot > implementation). > > > Any ideas on how to get the bottom form to only print 1 "New seq..."? > -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
