Never mind... I just used 'count'. And sorry to spam the group. On Oct 25, 10:44 am, Tim Robinson <tim.blacks...@gmail.com> wrote: > Good question. > > Also, I wonder if there are any existing realize type functions? > i.e. > (realize (filter ...)) > > or how would I realize without printing? > Tim > > On Oct 25, 10:12 am, "Marshall T. Vandegrift" <llas...@gmail.com> > wrote: > > > > > > > > > Tim Robinson <tim.blacks...@gmail.com> writes: > > > => (defn oops! [] > > > (let [x1 (atom (hash-map)) > > > v1 (filter > > > #(let [xv1 (@data %)] > > > (if (= xv1 "v1") > > > (swap! x1 assoc :k1 "other"))) > > > (keys @data)) > > > rxv (reset! flag @x1)] > > > (println v1))) > > > So why didn't the first version with deref work? > > > Because `filter' produces a lazy list, which isn't realized (and the > > side effects generated) until your call to `println'. > > > Furthermore, the documentation for `filter' explicitly notes that "pred > > must be free of side-effects." Looking at the implementation, I'm not > > sure why function-argument purity matters more for `filter' than any > > other sequence-generating higher-order function. Does anyone else know > > the reason? > > > -Marshall
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