In #Clojure Rich mentioned today that we can define our own data structures on top of the existing ones. Maybe someone wants/needs his own version of vectors that rearrange automatically in some specific order or whatever.
If I now want to add something that works nearly like lists, but a little bit different, and for which I can use all functions that work for lists, I will have to use a proxy. Chris Houser implemented a little helper tool: http://paste.lisp.org/display/67122#1 Now what I would like to see are some minimal examples on how to do that. Lists are a good candidate as they only have 6 methods which we need to implement: user> (show clojure.lang.IPersistentList) === #=clojure.lang.IPersistentList === [ 0] cons : interface clojure.lang.IPersistentCollection (1) [ 1] count : int (0) [ 2] empty : interface clojure.lang.IPersistentCollection (0) [ 3] peek : class java.lang.Object (0) [ 4] pop : interface clojure.lang.IPersistentStack (0) [ 5] seq : interface clojure.lang.ISeq (0) nil The numbers in parens at the end tell us how many parameters the methods should have. They have a hidden one more. We can magically use “this”. Here is what I tried: user> (defn make-lyst [& items] (proxy [clojure.lang.IPersistentList] [] (cons [obj] (cons obj this)) (count [] (count this)) (empty [] ()) (peek [] 5) (pop [] 6) (seq [] this))) As I found no examples yet, I was hoping this would return an instance of my own list type. (make-lyst 1 2 3) would print like normal lists: (1 2 3) And it would use the cons function of lists, dito for counting. (empty lyst) would return an empty IPersistentList, peek always a 5, pop always a 6 and seq the list object itself. But unfortunately (make-lyst 1 2 3) ==> java.lang.ClassCastException: clojure.lang.Proxy__5307 cannot be cast to clojure.lang.ISeq Any ideas how this should be done so that it will work? --~--~---------~--~----~------------~-------~--~----~ 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 To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
