2011/1/8 Ken Wesson <kwess...@gmail.com> > 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. > >
I understand the desire. I question the generality. ;) -- 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
