Hello, This is my first post to this group. If my post or the tone of my post is not up to this communities standards, please give me feedback so that I can integrate with the community.
I'm coming from Scala-land. In Scala, there's a PartialFunction: http://www.scala-lang.org/archives/downloads/distrib/files/nightly/docs/library/index.html#scala.PartialFunction The key take-away for PartialFunctions is "... is a unary function where the domain does not necessarily include all values of type A." The ability to test a PartialFunction to see if the domain includes a particular value is very helpful. pf.isDefinedAt(x) allows testing to see if the function is defined at a given value of x. But a PartialFunction is a subclass of Function, so PartialFunctions can be applied: pf(x) The Scala compiler will take a pattern and turn it into a PartialFunction: def pf: PartialFunction[String, Number] = { case "" => 0 // special case blank to zero case x if isInt(x) => x.toInt case x if isDouble(x) => x.toDouble case x if isBigInt(x) => asBigInt(x) } Another property of PartialFunction is they can be composed: pf = pf1 orElse pf2 orElse pf3 // pf isDefinedAt any place any of the partial functions are defined We use PartialFunctions extensively in Lift to allow choosing if a particular URL should be served by Lift, if it should be served by a particular REST handler, etc. For example, defining a REST route in Lift: serve { case "api" :: "user" :: AsLong(userId) :: _ GetJson _ => User.find(userId).map(_.toJson) } As I've been learning Clojure in preparation for a presentation at Strange Loop and as part of a new project I've been working on ( http://blog.goodstuff.im/plugh), I am looking to bring the best things in Lift into the Clojure code I write. Clojure's pattern matching stuff is pretty nifty. I especially like how you can extract values out of a Map (this is *so* much more powerful that Scala's pattern matching, even with unapply... but I digress). So, I wrote a macro (it's my first, so feedback on the style for the macro itself): (defmacro match-func [& body] `(fn [~'x] (match [~'x] ~@body))) This creates a function that is the application of the match to a parameter, so: ((match-func [q :guard even?] (+ 1 q) [z] (* 7 z)) 33) ;; 231 I am struggling with the right style for how to create something that's both a function: (def my-test (match-func [q :guard even?] (+ 1 q) [z] (* 7 z))) (my-test 33) And also something that can be tested for definition at a given value. Put another way, if Clojure had something that's both a function and a thing that could be asked if it's defined for a given input, how would one in Clojure apply that thing and also ask that thing if it was defined? Thanks for reading my long question and I look forward to feedback. David -- Telegram, Simply Beautiful CMS https://telegr.am Lift, the simply functional web framework http://liftweb.net Follow me: http://twitter.com/dpp Blog: http://goodstuff.im -- -- 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/groups/opt_out.
