On 6 September 2010 18:49, Robert McIntyre <r...@mit.edu> wrote: > I thought that since into uses reduce, it would be lazy, but I was wrong. > reduce just plows through everything with a non-lazy recursion.
Well, there's another reason in that the concept of a lazy map is problematic. In Clojure, at any rate, either you have a map or you don't -- it's always strict. > Why is reduce not lazy? The tail call in reduce is a call to itself, so it's pretty hard to imagine a meaningful way for it to be lazy -- it only has anything to return other than a result to a further call to reduce upon reaching the end of the sequence being reduced. Thus, it's purpose is fundamentally to go through the entire seq producing a single "end product". In contrast, a right fold's tail is a call to the reduction function with one of the arguments being a further call to foldr, so that can be made lazy in a sufficiently lazy language; but in Clojure, only seqs can be lazy, so that wouldn't really work either. Sincerely, Michał -- 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
