Your problem with recur is because you can only recur from the tail position.
> On Sep 23, 2015, at 12:28, nchurch <nchubr...@gmail.com> wrote: > > Yeah, it consumes stack just like the Clojurescript version of Iterate. I'm > curious if anyone knows how to avoid this. The Clojure version of Iterate is > Java; and for some reason 'recur' can't be used inside of lazy-cat (not > really documented, but apparently true). > >> On Tuesday, September 22, 2015 at 9:21:57 PM UTC-7, Max Countryman wrote: >> I wonder if something like this is a little easier to read? >> >> (defn generate >> ([f coll] >> (generate f coll (reverse coll))) >> ([f coll args] >> (let [next-val (apply f args)] >> (lazy-cat coll (generate f [next-val] (conj (butlast args) >> next-val)))))) >> >> Where your Fibonacci example becomes: >> >> (take 100 (generate +’ [1 1])) >> >> As for your other questions, I can’t be of much help. But isn’t there >> nontrivial memory overhead to consider with this approach? >> >> >>> On Sep 22, 2015, at 18:19, nchurch <nchu...@gmail.com> wrote: >>> >>> I was going through 4clojure (highly recommended!) and doing the Fibonacci >>> exercise. It occurred to me that the iterate function could be generalized >>> in a reasonable way, so that the next value is generated by applying the >>> function to the last N items so far, where N is the number of initial >>> arguments beyond the function. Thus: >>> >>> (generate inc 1) >>> >>> works just like iterate, while >>> >>> (generate + 1 1) >>> >>> generates the Fibonacci sequence. >>> >>> Here's the code: >>> >>> (defn generate >>> [f & more] >>> (letfn [(recurse >>> [coll args] >>> (let [next-val (apply f args)] >>> (lazy-cat coll (recurse [next-val] (conj (butlast args) >>> next-val)))))] >>> (recurse more (reverse more)))) >>> >>> Code is also on Github. >>> >>> I see this as part of a larger class of generalized sequence functions: for >>> instance, extra arguments in a function given to reduce could refer to N >>> arguments back in the sequence (might be useful, for instance, in smoothing >>> a sequence of values using an average). >>> >>> Questions: is there an existing home for this kind of functionality? And >>> could the above code be improved? (I just used the definition of iterate >>> as a starting point.) >>> >>> >>> >>> >>> -- >>> 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. > > -- > 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. -- 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.
