I see. You are right. A function passed to swap! must return only poped value, so peeked element from a queue is used only for side-effect in the function.
2011/11/10 Allen Johnson <akjohnso...@gmail.com>: > Although now I see that this usage is breaking the "side-effect free" > rule. So actually this is probably not what you want to do. :) > > Now I'm with you and thinking that atoms are not a proper fit for > PersistentQueue. Maybe someone from the conj can shed some light on > this. > > Allen > > On Wed, Nov 9, 2011 at 8:56 PM, Allen Johnson <akjohnso...@gmail.com> wrote: >> In your example yes, but you could make it atomic by placing the >> functionality in a function of it's own: >> >> ;; queue processing actions >> (defn process-item [queue] >> (println "Processed item:" (peek queue)) >> (pop queue)) >> >> ;; usage >> (let [queue (atom (into PersistentQueue/EMPTY [1 2 3]))] >> (swap! queue process-item) ; prints 1 >> (swap! queue process-item) ; prints 2 >> (swap! queue process-item)) ; prints 3 >> >> Probably better examples but that's the basic idea. >> >> Allen >> >> On Wed, Nov 9, 2011 at 8:46 PM, Takahiro Hozumi <fat...@googlemail.com> >> wrote: >>> Hi, >>> >>> To avoid peeking same element of a queue, I think PersistentQueue must >>> be stored in ref not atom. >>> Is this correct? >>> >>> ;;Ref: safe >>> (dosync >>> (let [item (peek @r)] >>> (alter r pop) >>> item)) >>> >>> ;Atom: unsafe >>> (let [item (peek @a)] >>> (swap! a pop) >>> item)) >>> >>> Thanks. >>> >>> -- >>> 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 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 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
