> (defn dec-or-dissoc! [key] > (dosync > (let [n (@*counts* key)] > (if (< 1 n) > (alter *counts* assoc key (dec n)) > (alter *counts* dissoc key)))))
> Is it true that in that case, one would have to use "ensure" to make the > operation correct? I don't think ensure is necessary here, coz the *counts* gets altered in all cases. Whereas consider this: (defn dec-or-dissoc! [key] (dosync (let [n (@*counts* key)] (when (< 1 n) (alter *counts* assoc key (dec n)))))) In this case I think ensure is necessary. Now consider this, (defn dec-or-dissoc! [key] (dosync (alter *counts* (fn [m] (let [n (m key)] (when (< 1 n) (assoc m key (dec n)))))))) In this case ensure is not necessary. -- 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