On Sat, Jan 8, 2011 at 3:11 PM, Laurent PETIT <laurent.pe...@gmail.com> wrote: > 2011/1/8 Ken Wesson <kwess...@gmail.com> >> >> On Sat, Jan 8, 2011 at 2:09 PM, Laurent PETIT <laurent.pe...@gmail.com> >> wrote: >> > 2011/1/8 Ken Wesson <kwess...@gmail.com> >> >> >> >> On Sat, Jan 8, 2011 at 12:33 PM, Stuart Halloway >> >> <stuart.hallo...@gmail.com> wrote: >> >> > One goal of resource scopes [1] is to help with scoping activities at >> >> > the REPL. That said, I think this is a "ramping up" problem -- I >> >> > rarely if >> >> > ever hit it anymore. >> >> > >> >> > Stu >> >> > >> >> > [1] http://dev.clojure.org/display/design/Resource+Scopes >> >> >> >> Eww. >> >> >> >> The more I think about it, the more I'm convinced that it's far >> >> preferable to use a pure functional approach. Instead of fixing >> >> >> >> (defn foo [x] >> >> (with-open [bar (baz x)] >> >> (make-some-lazy-seq bar))) >> >> >> >> (map do-something-with (foo quux)) >> >> >> >> -> IOException: stream closed >> >> >> >> with "resource scopes", or even with >> >> >> >> (defn foo [x] >> >> (with-open [bar (baz x)] >> >> (doall (make-some-lazy-seq bar)))) >> >> >> >> (map do-something-with (foo quux)) >> >> >> >> isn't the truly functional way to use HOF like this? >> >> >> >> (defn foo [x processor] >> >> (with-open [bar (baz x)] >> >> (processor (make-some-lazy-seq bar)))) >> >> >> >> (foo quux #(map do-something-with %)) >> > >> > With the implicit assumption that your processor is not lazy itself ... >> >> Yes, obviously. I figure it could be anything from (doall (take 5 >> ...)) to (reduce #(assoc ...) {} ...) or whatnot, resulting in a >> number, a map, a short eager seq, or some such. After all you are >> querying the file for something, boiling it down to something, aren't >> you? (first (filter identity (map #(re-matches ...) (line-seq ...)))) >> perhaps, to emit the first occurrence of some pattern in a text file? >> Whatever. > > > So we can altogether get rid of the concept of lazy seq, following your > argument :)
Of course not. It's still useful all the way up to the point that the result is obtained and distilled down. But using a passed-in function that consumes it while the with-open or binding is still in effect makes more sense than making the latter's effect somehow linger in the lazy-seq, given the difficulties the latter creates both with implementation and avoiding surprising behavior. -- 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
