Hi, the naming of your args [x r] is a bit confusing as x is usually the second item and the first is often caled acc (and it's also the argument passed to the completing arity (1-arg)).
However acc is a name inherited from reduce and does not really represent its actual purpose. *You have to consider acc as an opaque linear value storing the state of the transducing context.* Here are my rules to write a transducer: 0-arg: always call (rf) -- nothing much to do as depending on how the transducer is used it may not even be called (eg transduce with init value) 1-arg: it's an opportunity to flush state of the current transducer, so several calls to the downstream rf with 2 args is possible. However one should always end by calling the 1-arg arity of rf. There's no guarantee it will be called (eg sequence or chan) 2-arg: don't forget to think about how to handle reduced values (unwrap, rewrap or porpagate) Hope this helps. Christophe On Tue, Sep 5, 2017 at 11:00 AM, Peter Hull <peterhul...@gmail.com> wrote: > On Tuesday, 5 September 2017 00:07:07 UTC+1, Alex Miller wrote: >> >> When you say "the" answer here, that doesn't make sense to me. >> > Nor me. But, I think I've got it now, thanks for your help. The question I > should have asked was "what is the purpose of the ([x] ...) arity in an > eduction?" I wish I could phrase my questions as clearly as you phrase > your answers! > > >> The termination value in an eduction is just a nil, so x is nil in the >> ([x] ...) arity. >> > > I couldn't understand why, in eduction, the function was being called > with arity 1 at all if the result was not being used. Is this so that > stateful transducers can 'clean up' their state in some way at the end? > > > -- > 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. > -- On Clojure http://clj-me.cgrand.net/ Clojure Programming http://clojurebook.com Training, Consulting & Contracting http://lambdanext.eu/ -- 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.
