Re: advice needed about macro for proxy with argument

[Meikel Brandmeyer]

Hi,

Am 25.08.2009 um 20:09 schrieb rb:

Here is what I've done for now:

(defmacro deflistener [ interfaces trigger-args & body]
 `(proxy [ ~...@interfaces ] [] (trigger [...@trigger-args] ~...@body))
)

Which can be used like this:
( deflistener (Signal1$Listener) (mouse-event)  (.setText result-text
(.getText line-edit)) ))

I would rewrite it as follows:

    (defmacro create-listener
      [interfaces args & body]
      `(proxy ~interfaces [] (trigger ~args ~...@body)))



Then with the above changes the call looks like

    (create-listener [inter faces] [a b c] (do-stuff a b c))

First the macro doesn't "def" something global. So it should not be called deflistener. Compare with create-struct and defstruct. This is more idiomatic Clojure. (Effectively you can specify a vector in your version also, but seems like waste to define vector which is thrown away just to define another vector with the same contents. I find this not very elegant)

It takes as arguments
* the list of interfaces it implements (currently necessary for
http://www.assembla.com/spaces/clojure/tickets/181)

?? You always have to specify the interfaces, no?

* the list of arguments passed to the trigger method implemented
* the body of the implementation of trigger

Here are the questions that arise:

* I thought I could and should do away with trigger-args, but if I use
gensyms in the macro to define the arguments received by trigger, how
can I get to the argument values in the code of the method?

You cannot get rid of the argument vector.

* if it implements  SignalX$Listener, trigger takes X arguments. How
can implement that with one macro, and still have access to these
arguments in the forms I pass as body of trigger?

You could pass the body as a fn.

    (defmacro create-listener
      [x f]
      (let [args (take x (repeatedly gensym))]


And call it like

    (create-listener 2 (fn [a b] ...))



Hope this helps.

Sincerely
Meikel

`(proxy [~(symbol (str "Signal" x "$Listener"))] [] (trigger [...@args] (~f ~...@args))))) Whether this is better than the above.... I would prefer the first solution.

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