> > Why does `alter-var-root` here seem to succeed, but have no effect?
What you want is: (set! *print-level* 2) But, this will not work 100% of the time, and sometimes you might want alter-var-root. Here's the trick. *print-level* is a dynamic Var. Alter-var-root only changes the root value of a Var, it can not change a dynamically binded value: (def ^:dynamic x "I am root!") x ; => "I am root!" (binding [x "I am dynamically binded!"] x) ; => "I am dynamically binded!" (alter-var-root #'x (constantly "I've had my root altered!")) x ; => "I've had my root altered!" (binding [x "I am dynamically binded!"] x) ; => "I am dynamically binded!" So where is *print-level* binded you ask? Well, that depends on how you bootstrapped Clojure. Most of the time, such as when using lein, or clojure.main, those things will wrap your entire code in a binding, and they will bind a certain number of default dynamic var such as *print-level*. You can see the code for clojure.main here: https://github.com/clojure/clojure/blob/master/src/clj/clojure/main.clj#L76 So in your case, you're probably bootstrapping Clojure using a mechanism that binds *print-level*, thus changing its root has no effect in your code, you have to change its binding, and the function to do that is set!. On Monday, 24 July 2017 07:12:05 UTC-7, Rob Nikander wrote: > > I think in my case here the easiest thing will be to remove the cycles, > but still I'd like to understand a couple things... > > On Sunday, July 23, 2017 at 10:12:46 PM UTC-4, Didier wrote: >> >> I'm not sure I can fully help without you explaining more what you're >> doing. It sounds like you've got a collection or container type which has >> an implementation of print that loops over its elements, and calls print on >> them. So if you have a cycle, the print will go on forever until memory >> runs out. >> > > My container type (the tree node) is simply the standard clojure map. > > If you're using a standard type, you might be able to limit *print-level* >> <https://clojuredocs.org/clojure.core/*print-level*>. Most Clojure >> collections will limit how deep they print based on the value of this >> global dynamic Var. >> > > Okay, *print-level* works but it looks like I have to call print myself. I > can't rely on the REPL to print it. > > (binding [*print-level* 2] (println (find-route "/reports"))) ; okay > > Why does `alter-var-root` here seem to succeed, but have no effect? > > (alter-var-root #'*print-level* (constantly 2)) > => 2 > *print-level* > => nil > (find-route "/reports") > stack overflow > > > -- 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/d/optout.
