A, right. Silly me. This is something I have trouble remembering. For some reason when you use regular concat, the error message is helpful (can't recur from non-tail position); with lazy-cat it shows a mismatch of argument numbers.
On Wednesday, September 23, 2015 at 2:10:47 PM UTC-7, Max Countryman wrote: > > Your problem with recur is because you can only recur from the tail > position. > > On Sep 23, 2015, at 12:28, nchurch <nchu...@gmail.com <javascript:>> > 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 <https://github.com/nchurch/generate>. >> >> 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 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.
