How is this done, I searched the source, but there was so much indirection I can't find it. I'm familiar with how Haskell does rfold vs lfold, but one of those does create allocations, they may be in the form of closures, but they are allocations none the less. So does fold use iterators or something?
Timothy On Fri, Sep 23, 2016 at 4:23 PM, Dragan Djuric <draga...@gmail.com> wrote: > fluokitten's fold is MUCH better than (map f a b) because it does NOT > create intermediate collections. just use (fold f a b) and it would fold > everything into one thing (in this case nil). If f is a function with side > effects, it will invoke them. No intermediate collection is created AND the > folding would be optimized per the type of a. > > On Friday, September 23, 2016 at 10:56:00 PM UTC+2, tbc++ wrote: >> >> How is fluokitten's fold any better than using seqs like (map f a b) >> would? Both create intermediate collections. >> >> On Fri, Sep 23, 2016 at 11:40 AM, Dragan Djuric <drag...@gmail.com> >> wrote: >> >>> If you do not insist on vanilla clojure, but can use a library, fold >>> from fluokitten might enable you to do this. It is similar to reduce, but >>> accepts multiple arguments. Give it a vararg folding function that prints >>> what you need and ignores the first parameter, and you'd get what you asked >>> for. >>> >>> >>> On Friday, September 23, 2016 at 7:15:42 PM UTC+2, Mars0i wrote: >>>> >>>> On Friday, September 23, 2016 at 11:11:07 AM UTC-5, Alan Thompson wrote: >>>>> >>>>> Huh. I was also unaware of the run! function. >>>>> >>>>> I suppose you could always write it like this: >>>>> >>>>> (def x (vec (range 3))) >>>>> (def y (vec (reverse x))) >>>>> >>>>> (run! >>>>> (fn [[x y]] (println x y)) >>>>> >>>>> (map vector x y)) >>>>> >>>>> >>>>> > lein run >>>>> 0 2 >>>>> 1 1 >>>>> 2 0 >>>>> >>>>> >>>> Yes. But that's got the same problem. Doesn't matter with a toy >>>> example, but the (map vector ...) could be undesirable with large >>>> collections in performance-critical code. >>>> >>>> although the plain old for loop with dotimes looks simpler: >>>>> >>>>> (dotimes [i (count x) ] >>>>> (println (x i) (y i))) >>>>> >>>>> >>>>> maybe that is the best answer? It is hard to beat the flexibility of a >>>>> a loop and an explicit index. >>>>> >>>> >>>> I agree that this is clearer, but it kind of bothers me to index >>>> through a vector sequentially in Clojure. We need indexing In Clojure >>>> because sometimes you need to access a vector more arbitrarily. If you're >>>> just walking the vector in order, we have better methods--as long as we >>>> don't want to walk multiple vectors in the same order for side effects. >>>> >>>> However, the real drawback of the dotimes method is that it's not >>>> efficient for the general case; it could be slow on lists, lazy sequences, >>>> etc. (again, on non-toy examples). Many of the most convenient Clojure >>>> functions return lazy sequences. Even the non-lazy sequences returned by >>>> transducers aren't efficiently indexable, afaik. Of course you can always >>>> throw any sequence into 'vec' and get out a vector, but that's an >>>> unnecessary transformation if you just want to iterate through the >>>> sequences element by element. >>>> >>>> If I'm writing a function that will plot points or that will write data >>>> to a file, it shouldn't be a requirement for the sake of efficiency that >>>> the data come in the form of vectors. I should be able to pass in the data >>>> in whatever form is easiest. Right now, if I wanted efficiency for walking >>>> through sequences in the same order, without creating unnecessary data >>>> structures, I'd have to write the function using loop/recur. On the other >>>> hand, if I wanted the cross product of the sequences, I'd use doseq and be >>>> done a lot quicker with clearer code. >>>> >>> -- >>> 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 >>> 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 >>> 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. >>> 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. > -- “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.
