Having spent quite a bit of time recently dissecting transducers <http://beickhoff.github.io/posts/2016-05-27-deconstructing-transducers.html>, I'd tend to agree with Tim: core transducers will probably give you most of what you want. I'd also agree that writing macros should be your last resort. But maybe the core function completing is very close to what you're looking for...
clojure.core/completing ([f] [f cf]) Takes a reducing function f of 2 args and returns a fn suitable for transduce by adding an arity-1 signature that calls cf (default - identity) on the result argument. On Friday, June 10, 2016 at 2:07:58 PM UTC-4, Travis Daudelin wrote: > > Hi all! > > I'm current working on a project where I am ingesting events off a stream > and processing them. There are many many steps involved in the processing > component, so I am choosing to write the steps as a series of transducers > (because, hey, they're super cool!). Here's the problem though, after > writing the first 2 processing steps I'm noticing that all of them are > going to look very similar: > > (defn a-step-transducer > [] > (fn [reducing-fn] > (fn > ([] (reducing-fn)) > ([result] (reducing-fn result)) > ([[guid-state processed-events :as result] event] > ;; step-specific logic > )))) > > Given how many steps I am planning to write, this is a ton of boilerplate! > So, my first thought was to use a macro to abstract away all this > boilerplate. Now, I have to admit that Clojure is my first Lisp, so I'm > really not sure I fully understand when or why to use macros to do things. > My current understanding is that macros are a kind of "template" for code, > so something like this where I don't want to write the same function > structure over and over seems like a decent use case for macros (feel free > to correct me if I'm totally off on this). Here is my first attempt: > > (defmacro deftransducer > [body] > `(fn [reducing-fn] > (fn > ([] (reducing-fn)) > ([result] (reducing-fn result)) > ([[guid-state processed-events :as result] event] > ~@body)))) > > The idea here being that in body I can reference the variables defined by > the macro like reducing-fn, result, event, etc. Of course, I quickly > found out that this doesn't work: > > storm-etl.entry-processing> (deftransducer "something") > CompilerException java.lang.RuntimeException: Can't use qualified name as > parameter: storm-etl.entry-processing/reducing-function > > Some quick googling tells me that the solution to this is to use gensyms > for these variable names, but that would defeat the whole purpose of this > because I want to be able to reference those variables from within the code > that I pass to my macro. Is this an appropriate use case for macros or am I > way off base? Is there an alternative approach that would be recommended? > -- 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 unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
