One other question occurs to me re your comment... It's worth understanding how to go back and forth between accumulator-style > and a lazy construction. You can convert the above non-lazy accumulator > version into a similar version that is lazy but has no risk of stack > overflow in the realization of that lazy flattened list: >
Why does going lazy avoid a stack overflow risk? Again, to answer my own question :-) ... The resultant flat list from my-flatten will be realized one element at a time. The call stack will be used during this process, but lazy-seq prevents it getting very deep. I think lazy-seq is a bit like a thunk (invoked via the seq call), except that it also caches the result. So its like the thunks in our trampolining, except that the "bouncing" doesn't occur eagerly as with trampolining, but only on-demand as a consumer traverses the flat list. Is this a good way of thinking about it? > > (defn my-flatten > [xs] > (if (empty? xs) () > (let [x (first xs), ys (rest xs)] > (if (sequential? x) > (if (seq x) > (recur (cons (first x) (cons (rest x) ys))) > (recur ys)) > (lazy-seq (cons x (my-flatten ys))))))) > > Basically, you just get rid of the accumulator, and in the place where you > would have conj'd in the next atomic element, you just build the lazy > sequence. > > -- 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.
