Francis is correct, and I want to make a point about something he said. If you are mapping over two collections at once, you will either be using Java iterators, or you will be creating lazy sequences when you walk over the input collections. Sure, how many lazy sequences are create here and there can be tweaked, but it is *impossible* on the JVM to walk two data structures at the same time and not build sequences unless you drop to Java iterators. So I have to say yet again "No extra sequence building involved," is not technically true. Fluokitten's functions are calling next/first on a vector which causes the creation of a lazy sequence, sure there may be one less allocation (no extra sequence is being produced as the output of this operation), but the statement that it does "NOT create intermediate collections" is false.
There are ways we could speed up iteration over collections, but in the end I recommend benchmarking. Unless your collection is a set of primitive numbers the overhead of other operations (assoc, get, etc) is going to be much more expensive than simply walking a lazy seq. In my experience, and depending on the domain, optimizing lazy seq creation is almost always optimizing in the wrong place. There are places where switching to the iteration methods improves performance, but benchmark your code and see before adopting any non-standard methods wholesale. Timothy On Sat, Sep 24, 2016 at 1:00 AM, Dragan Djuric <draga...@gmail.com> wrote: > Now I am on the REPL, and the solution is straightforward: > > (foldmap op nil println [1 2 3] [4 5 6]) > > gives: > > 1 4 > 2 5 > 3 6 > nil > > The first function is a folding function. In this case we can use op, a > monoid operation. Since nil is also a monoid, everything will be folded to > nil. The second part is a function that maps inputs to the monoid that we > need (nil in this case). println does just this, and does the side effect > that you asked for. No extra sequence building involved, and we do not need > to write extra functions. > > On Saturday, September 24, 2016 at 2:42:16 AM UTC+2, Mars0i wrote: >> >> Thanks everyone--I'm very much appreciating the discussion, though I'm >> not sure I follow every point. >> >> Dragan, thank you very much for suggesting (and writing) foldmap. Very >> nice. I certainly don't mind using a library, though I still think there >> ought to be something like what I've described in the language core. >> >> Francis, thanks for separating out the different types of intermediate >> collections. I'm not entirely clear on type 1. It sounds like those are >> just collections that are already there before processing them. Or are you >> saying that Clojure has to convert them to a seq as such? Why would doseq >> have to do that, for example? >> >> It's an understatement to say that my understanding of monads, monoids, >> etc. is weak. Haven't used Haskell in years, and I never understood >> monads, etc.. They seem trivial or/and or deeply mysterious. One day I'll >> have to sit down and figure it out. For foldmap, I don't understand what >> the first function argument to foldmap is supposed to do, but it's easy >> enough to put something there that does nothing. >> > -- > 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. > -- “One of the main causes of the fall of the Roman Empire was that–lacking zero–they had no way to indicate successful termination of their C programs.” (Robert Firth) -- 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.
