2009/5/18 Konrad Hinsen <konrad.hin...@laposte.net>: > > On May 18, 2009, at 11:58, Adrian Cuthbertson wrote: > >> I know I keep plugging this - sorry - but it just keeps surfacing >> as a solution; >> >> (lcm 4 6) >> 12 >> (binding [clojure.contrib.math/gcd (fn [a b] 1)] (lcm 4 6)) >> 24 > > Such a use of binding will lead to bad surprises as soon as you use > it with lazy sequences:
And there's also the problem that bindings do not "traverse" threads, even if one thread is just used as a "technical thread" (e.g. a thread from a pool of threads). So if e.g. some code works without parallelism, it may well not work anymore if one piece on the call chain is delivered with a new version that uses parallel computing (e.g. starts using pmap instead of map). > > (map #(lcm % 6) (range 6)) > -> (0 6 6 6 12 30) > > (binding [clojure.contrib.math/gcd (fn [a b] 1)] > (map #(lcm % 6) (range 6))) > -> (0 6 6 6 12 30) > > You have to use doall to get the result you expect: > > (binding [clojure.contrib.math/gcd (fn [a b] 1)] > (doall (map #(lcm % 6) (range 6)))) > -> (0 6 12 18 24 30) > > The reason is that the temporary binding remains active only while > map creates the lazy sequence that it returns, but it is no longer > active when the actual elements of the lazy sequence are evaluated. > > More details and examples in my blog post: > http://onclojure.com/2009/05/06/simulating-dynamic-scoping/ > > Konrad. > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
