i am not trying anything, i just want to figure out what happens. this is my output for the "print" version: user=> (defmulti fac print) (defmethod fac 1 [_] 1) (defmethod fac :default [n] (*' n (fac (dec n)))) #'user/fac #<MultiFn clojure.lang.MultiFn@1afb02d> #<MultiFn clojure.lang.MultiFn@1afb02d> user=> (fac 1) 10-1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18-19-20-21-22-23-24-25-26-27-28-....until stackoverflow
2013/6/22 Chris Bilson <cbil...@pobox.com> > Dennis Haupt <d.haup...@gmail.com> writes: > > > i was taking a look at multimethods: > > (defmulti fac int) > > (defmethod fac 1 [_] 1) > > (defmethod fac :default [n] (*' n (fac (dec n)))) > > > > this works > > > > however, this also works: > > > > (defmulti fac print) > > (defmethod fac 1 [_] 1) > > (defmethod fac :default [n] (*' n (fac (dec n)))) > > This definately does not work when I try it: > > user> (defmulti fac print) > #<Var@6427854d: #<MultiFn clojure.lang.MultiFn@4bddef9a>> > nil > user> (defmethod fac 1 [_] 1) > #<MultiFn clojure.lang.MultiFn@4bddef9a> > nil > user> (fac 1) > IllegalArgumentException No method in multimethod 'fac' for dispatch > value: null clojure.lang.MultiFn.getFn (MultiFn.java:160) > 1 > > The second arg to defmulti's job is to decide which method to call. The > print function always produces nil, so you would need a defmethod for > dispatch value nil to use print as a dispatch function: > > user> (defmethod fac nil [_] 2) > #<MultiFn clojure.lang.MultiFn@4bddef9a> > nil > user> (fac 1) > 12 > nil > > Notice the "12": the "1" is from print and the "2" is the value the > method produced. > > Are you trying to print the dispatch values so you can see them for > tracing or something? If so, you could try something like: > > user> (defn inspect [& stuff] > (println "inspect: " stuff) > (first stuff)) > #<Var@5b1413a8: > #<user$eval336$inspect__337 user$eval336$inspect__337@68903261>> > nil > user> (inspect 1) > inspect: (1) > 1 > nil > user> (defmulti fac2 inspect) > nil > nil > user> (defmethod fac2 1 [_] 1) > #<MultiFn clojure.lang.MultiFn@e2df60d> > nil > user> (fac2 1) > inspect: (1) > 1 > nil > user> > > > -- > -- > 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.
