On Thu, Jul 9, 2009 at 12:10, Mike<cki...@gmail.com> wrote: > > I wanted to grab bytes out of a stream, and didn't see an analogue to > reader from duck-streams, so I made my own: > > (defn byte-seq > "Returns the bytes from stream as a lazy sequence of ints. > stream must implement java.io.InputStream." > [#^java.io.InputStream stream] > (lazy-seq > (let [b (. stream (read))] > (if (>= b 0) > (cons b (byte-seq stream)))))) > > Then I did a simple lazy operation on a stream of bytes, say, to drop > the first 5: > > (with-open [st (FileInputStream. "mike.clj")] (drop 5 (byte-seq st))) > > I was a little surprised at first getting java.io.IOException: Bad > file descriptor, but of course it hit me: the laziness persists well > beyond the .close() in the with-open. > > I modified my byte-seq to close the stream when EOF is reached, but > this is an awful ugly solution having the inner thing know when to > close the outer concern's thing. (What if the outer thing wants to > rewind? etc.) > > Is there a pattern out there in Clojure for handling laziness at the > same time as handling resource lifecycle (with-open, etc.)? >
I'd just like to pile-on to say that I ran into the same question last night in a slightly different form. I have a file containing a sequence of clojure forms, which I want to read in sequentially. I don't have to have them all in memory at the same time for my task. A lazy sequence which yielded parsed forms while consuming bytes from the underlying file would be a perfect solution, but I ran into the same issue. I close the file when EOF is reached. I can (but don't yet, because it was a quick hack late at night) catch IOExceptions and close the underlying file under those circumstances, but this is ugly. What happens if the caller grabs such a lazy sequence and then just drops it on the floor? Does the file ever get closed before the VM exits? Do InputStreams register a finalizer? Needed: a pattern for handing a lazy sequence backed by a closeable resource. // ben --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
