=> (future (swap! atom inc 0)) #<core$future_call$reify__6267@38db2b7e: :pending>
=> @(future (swap! atom inc 0)) ClassCastException clojure.core$atom cannot be cast to clojure.lang.Atom clojure.core/swap! (core.clj:2161) (both in ccw, but i notice that the first statement does throw in lein repl) guessing the error is actually thrown in that thread, but nobody can see it unless they are trying to deref it in current thread or something else along those lines On Tue, May 21, 2013 at 1:01 PM, Colin Yates <colin.ya...@gmail.com> wrote: > Hi all, > > If the function executed in a future throws an error it is printed out in > the repl immediately. If that function is executed in a future which > itself is executed in a future then it isn't. > > For example, imagine somebody wrote the following code (please, suspend > belief and just accept people do do this when learning Clojure :)): > > [code] > ;; some silly code > user> (swap! atom inc 0) > ClassCastException clojure.core$atom cannot be cast to clojure.lang.Atom > clojure.core/swap! (core.clj:2161) > ;; silly code wrapped in a future > user> (future (swap! atom inc 0)) > ClassCastException clojure.core$atom cannot be cast to clojure.lang.Atom > clojure.core/swap! (core.clj:2161) > ;; silly code wrapped in a future wrapped in a future > user> (future (future (swap! atom inc 0))) > #<core$future_call$reify__6267@11e55d39: :pending> > user> > [/code] > > My understanding is that future executes its delegate in a separate > thread, hence the "(future (swa...))" code prints out the exception almost > immediately. I don't understand why the nested future doesn't print out > the error though as it should surely be executed almost immediately as well? > > Of course, if you dereference the call then it prints out the stack trace. > > As to why you would want a future in a future...that is a different kettle > of fish :). > > -- > -- > 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 unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- 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 unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
