Laurent PETIT a écrit : > 2009/4/23 Christophe Grand <christo...@cgrand.net>: > >> *Warning this message contains mutable state and may hurt functional >> sensibilities.* >> >> Ugly hack: >> >> (defn my-split-with [pred coll] >> (let [s (atom coll) >> p #(when-let [r (pred %)] (swap! s rest) r)] >> [(take-while p coll) (drop-while pred (lazy-seq @s))])) >> > > Cheater ! ;-) > > But there's still the problem of having the user being able to check > the second argument before having exhausted (if possible) the first... > and then having an infinite loop: e.g. (first (second (my-split-with > true? (repeat true))). >
I don't see the problem, it's like (dropwhile true? (repeat true)) you can't protect the user from himself. > And maybe calling swap! for each matched elem may be expensive ? > (That's a real question, I don't have any real idea, just a guess ...) > Neither do I. Updates to the atom are serialized by the lazy-seq realization, so we don't even need an atom: a simple volatile field should do the trick. No? > But wait ... the more I think about it, the more it appears to me > (though I can not prove it formally) that the problem requires > side-effect to be solved, either via the use of mutation, either via > the use of multiple threads for coordinating the feeding of 2 separate > sequences ? > I share your intuition on this. Christophe -- Professional: http://cgrand.net/ (fr) On Clojure: http://clj-me.blogspot.com/ (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 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 -~----------~----~----~----~------~----~------~--~---
