Thanks for the input. Didn't know that I was multiply-evaluating f. The reason why I wrote a macro instead of a function is because 'get' and 'duplicate' are not declared in any common superclass of the different buffers, so I was getting lots of reflection!
Are there alternatives to the macro that avoid reflection? Thanks On Oct 18, 2012 7:33 PM, "Alan Malloy" <a...@malloys.org> wrote: > As a general-macro aside, you are multiply-evaluating the `f` > argument, by expanding it in-place inside the recursive clause. This > is almost certainly not what you want, and you could avoid it by > starting with (let [f# ~f] ...). Better still, ask why this is a macro > at all. This should really just be a function, because you don't > introduce any new syntax, and you don't delay evaluation of anything. > > On Oct 18, 2:56 pm, Bruno França dos Reis <bfr...@gmail.com> wrote: > > Damn, just noticed a small mistake in the macro: I use the original > buffer, > > not the duplicated one. Here's the correct version: > > > > (defmacro buffer-reduce [b f val] > > `(let [b# (.duplicate ~b)] > > (loop [remaining# (.remaining b#) > > result# ~val] > > (if (zero? remaining#) > > result# > > (recur (dec remaining#) (~f result# (.get b#))))))) > > > > (extend-protocol clojure.core.protocols/CollReduce > > java.nio.ByteBuffer > > (coll-reduce [b f] (coll-reduce b f (f))) > > (coll-reduce [b f val] (buffer-reduce b f val)) > > > > java.nio.LongBuffer > > (coll-reduce [b f] (coll-reduce b f (f))) > > (coll-reduce [b f val] (buffer-reduce b f val)) > > > > ; ... other kinds of buffer ... > > ) > > > > Sorry for that. > > > > On Thursday, October 18, 2012 6:50:07 PM UTC-3, Bruno França dos Reis > wrote: > > > > > > > > > > > > > > > > > > > > > Hello! > > > > > I've recently started playing with Clojure, and a couple of days ago > I've > > > been pointed to Reducers in Clojure 1.5 after a discussion on #clojure > at > > > Freenode. > > > > > I've read Rich's posts announcing the Reducers library, and he says > that > > > there's a ***lack of reducible IO sources***. I'm working on a project > > > that in which I analyze lots of data (from huge files on disk), and I'm > > > frequently doing "reduce" operations on it. I began by writing a custom > > > sequence, that after I transformed in a custom reducible collection. > But > > > I've just noticed that I could encapsulate it on a kind of reducible IO > > > source. > > > > > I'm writing this message to share the code I wrote relating to > reducible > > > IO sources, if anybody sees any use for it. The idea is to make the > ***NIO > > > Buffers reducible***, so that you can open huge files as **memory > mapped > > > files**, which are instances of `ByteBuffer`. You can then obtain > > > instances of other buffers, say, `LongBuffer` (which is what I'm using > on > > > my current project), which are also reducible: > > > > > (defmacro buffer-reduce [b f val] > > > `(let [b# (.duplicate ~b)] > > > (loop [remaining# (.remaining b#) > > > result# ~val] > > > (if (zero? remaining#) > > > result# > > > (recur (dec remaining#) (~f result# (.get ~b))))))) > > > > > (extend-protocol clojure.core.protocols/CollReduce > > > java.nio.ByteBuffer > > > (coll-reduce [b f] (coll-reduce b f (f))) > > > (coll-reduce [b f val] (buffer-reduce b f val)) > > > > > java.nio.LongBuffer > > > (coll-reduce [b f] (coll-reduce b f (f))) > > > (coll-reduce [b f val] (buffer-reduce b f val)) > > > > > ; ... other kinds of buffer ... > > > ) > > > > > Hope this might be useful for someone. > > > > > Bruno > > -- > 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 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
