Hi Lucas, lazy sequences, as the one produced by the map/filter construct, aren't realized at once. I. e. they are returned as a sequence, but your map and filter lambdas are only invoked once somebody looks at whats in the sequence. Usually, steps are evaluated in chunks of size 32.
Your filter lambda is depending on mutable Java map. When you count a lazy sequence, all elements are realized. So depending on whether you invoke count, the lambda will be invoked with a different version of the Java map. You should solve this by eliminating the mutable state Java map - it makes your filter lambda impure. Lazy evaluation does not work with impure functions. I'd recommend to learn about reduce, which will help you to write this much more concisely. Kind regards, Leon. On Saturday, April 22, 2017 at 2:41:09 PM UTC+2, Lucas Wiener wrote: > > Hi all, > > I'm working on solving the problem http://adventofcode.com/2016/day/11 , > and ran into some weird behaviour. I have solved the actual problem, so > let's not focus on it. > > Here's my code: > > (defn compute3 > {:test (fn [] > (is= (compute3 (create-state "F4 . . . . . " > "F3 . . . LG . " > "F2 . HG . . . " > "F1 E . HM . LM ")) > 11))} > [state] > (let [done-simple-state (state->simple-state (construct-finished-state > state)) > inner-fn (fn [states steps java-memory-map] > (println "On step" steps) > (println "Number of states" (count states)) > (let [next-states (->> states > (map (fn [state] > (->> (get-next-states > state) > (filter (fn [s] > (nil? (.get java-memory-map (state->simple-state s)))))))) > (flatten))] > ;; (println (count next-states)) <- Uncomment this > line to change the behavior > (if (.get java-memory-map done-simple-state) > steps > (do (doseq [next-state next-states] > (.put java-memory-map (state->simple-state > next-state) steps)) > (recur next-states (inc steps) > java-memory-map)))))] > (inner-fn [state] 0 (java.util.HashMap.)))) > > When running this in the repl I get the following output: > > On step 0 > Number of states 1 > On step 1 > Number of states 1 > On step 2 > Number of states 3 > On step 3 > Number of states 11 > On step 4 > Number of states 14 > On step 5 > Number of states 22 > On step 6 > Number of states 37 > On step 7 > Number of states 48 > On step 8 > Number of states 35 > On step 9 > Number of states 22 > On step 10 > Number of states 17 > On step 11 > Number of states 7 > > However, if I uncomment the println statement I get the following output > in the REPL: > > On step 0 > Number of states 1 > 1 > On step 1 > Number of states 1 > 3 > On step 2 > Number of states 3 > 11 > On step 3 > Number of states 11 > 15 > On step 4 > Number of states 15 > 28 > On step 5 > Number of states 28 > 63 > On step 6 > Number of states 63 > 107 > On step 7 > Number of states 107 > 90 > On step 8 > Number of states 90 > 82 > On step 9 > Number of states 82 > 115 > On step 10 > Number of states 115 > 81 > On step 11 > Number of states 81 > 110 > > Please note that "On step 4" prints "Number of states 14" and "Number of > states 15" differently. > > Any thoughts? > -- 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.
