Hi, thank you for your response ! I know the '& args' notation, but I thought that this notation expected a collection *after *the &, so in the apply signature, we expect a fn, 4 args and then, a sequence.
In this call : (apply + 1 1 1 1 1 1 1 1 1 1 1 [2 3]), the & should be here : (apply + 1 1 1 1 *&* 1 1 1 1 1 1 1 [2 3]) If I understand what you're saying, all the parameters after the & and the [2 3] sequence is converted into a single sequence, thanks to the & ? Le mercredi 14 décembre 2016 10:25:39 UTC-5, James Reeves a écrit : > > Clojure functions can take a collection of arguments by using the "&" > symbol. So for instance: > > (defn print-all [& args] > (doseq [arg args] > (println arg))) > > If we run this function with: > > (print-all "Hello" "World") > > Then it will print: > > Hello > World > > But dealing with sequences has a cost to it. If print-all has only one > argument, then we can avoid the doseq. So we can optimise the function to > be more performant when we pass in only one argument: > > (defn print-all > ([x] > (println x)) > ([x & args] > (println x) > (doseq [arg args] > (println arg)))) > > Notice that if we pass it one argument, we just print it directly. Two or > more arguments goes into the doseq loop. > > Of course we could also add an optimisation for two arguments as well: > > (defn print-all > ([x] > (println x)) > ([x y] > (println x) > (println y)) > ([x y & args] > (println x) > (println y) > (doseq [arg args] > (println arg)))) > > Hopefully you can see why "apply" has five arities now. The first four are > just optimisations, so "apply" will be slightly faster if it has five or > fewer arguments. > > In most cases you don't need to use this technique because the performance > gain will be minimal. My print-all function above is probably going to > spend most of its time on I/O, making the optimisation all but useless in > my example. But clojure.core is used everywhere, so wringing an extra drop > of performance is often worth it. > > - James > > On 14 December 2016 at 13:14, Rafo Ufoun <raf.de...@gmail.com > <javascript:>> wrote: > >> Hi everyone, >> >> I'm new to clojure and I try to understand the apply function. >> >> From the clojure sources, I can see that there are several signatures for >> this method: with or without additional arguments before the sequence. >> >> According to these signatures, we can have 4 arguments MAX before getting >> the sequence of arguments (([^clojure.lang.IFn f a b c d & args]) >> >> However, (apply + 1 1 1 1 1 1 1 1 1 1 1 [2 3]) is a valid function call >> and I can get a result. >> At this point I'm not sure how this signature can accept so many argument >> before the [2 3] sequence. I think I miss a point but don't know what ! >> >> Thanks you, Rafi. >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@googlegroups.com >> <javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <javascript:> >> 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+u...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > > -- 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.
