David, maybe I don't understand your example well, but anyway, here are my remarks / concerns:
* You're example is not at all exempt from multithreading: you use futures, and in the real scenario, the calls to deliver would have to occur from a thread able to pull from or be notified by the progress of the tests * If one wants all the graphical values to be update "on the fly", then one will have to place the calls to deref in independent threads, wouldn't it be too heavy to have so many threads (perhaps 100, 10000 ?) just for updating a single node of a tree in the overall application ? 2010/1/22 David Nolen <dnolen.li...@gmail.com>: > They are actually useful even outside the context of concurrency. For > example perhaps you have a recursive data structure that represents a series > of unit tests and unit test suites. You would like to do two things: > 1. Render out the nested structure of the tests that will be executed for > the user > 2. Render out the test results as they complete > With out promises you would have to traverse this data structure twice. Once > to render it for the user and a second time to show the results. With > promises you only need to traverse the data structure one time. In the > traversal you create promises for the test results as well as created a > flattened list of the tests to run. > In the following imagine that each test returns 0 or 1 depending on > pass/fail (I haven't bothered to make a recursive data structure here, but > the general point should be clear I hope). > (def x (promise)) > (def y (promise)) > (def z (promise)) > (def passed (promise)) > (defmacro future-out [& body] > `(let [out# *out*] > (future > (binding [*out* out#] > ~...@body)))) > (future-out > (deliver passed (reduce + (map deref [x y z]))) > (println "passed:" passed)) > (future-out (println "x:" @x)) > (future-out (println "y:" @y)) > (future-out (println "z:" @z)) > (deliver x 1) > (deliver y 0) > (deliver z 1) > Pretty useful I say :) > On Thu, Jan 21, 2010 at 6:19 AM, Baishampayan Ghose <b.gh...@ocricket.com> > wrote: >> >> Hello, >> >> I am trying to understand the use-cases of the new promise/deliver >> feature in Clojure. I have tried using them, and they seem to be >> pretty straight-forward to use, but unfortunately I haven't been able >> to understand its use-cases. >> >> It would be great if someone pointed out some example usage of >> promise/deliver. >> >> Regards, >> BG >> >> -- >> Baishampayan Ghose >> >> -- >> 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
