build-protocol Clojure macro

Question

As a follow-up to my previous question, I am trying to write a macro that builds a defprotocol:

(build-protocol AProtocol
  [(a-method [this]) (b-method [this that])]
  (map (fn [name] `(~(symbol (str name "-method")) [~'this ~'that ~'the-other]))
    ["foo" "bar" "baz"])
  (map (fn [name] `(~(symbol (str name "-method")) [~'_]))
    ["hello" "goodbye"]))

should expand to

(defprotocol AProtocol
  (a-method [this])
  (b-method [this that])
  (foo-method [this that the-other])
  (bar-method [this that the-other])
  (baz-method [this that the-other])
  (hello-fn [_])
  (goodbye-fn [_]))

My attempt:

(defmacro build-protocol [name simple & complex]
  `(defprotocol ~name ~@simple
     ~@(loop [complex complex ret []]
         (if (seq complex)
           (recur (rest complex) (into ret (eval (first complex))))
           ret))))

and expansion (macroexpand-1 '(...)):

(clojure.core/defprotocol AProtocol
  (a-method [this])
  (b-method [this that])
  (foo-method [this that the-other])
  (bar-method [this that the-other])
  (baz-method [this that the-other])
  (hello-method [_])
  (goodbye-method [_]))

I'm not really happy about the eval. Also, the map expressions are pretty ugly. Is there a better way? Any and all comments welcome.

Once I get this working, I'm going to do a similar macro for (build-reify ...). I'm writing a rather large Swing application and have several components (JButtons, JCheckBoxes, etc.) that have almost identical method signatures and actions.

amalloy · Accepted Answer · 2011-06-20 15:47:57Z

2

I think you're doing it upside down. Specify the "-method" stuff first, wrapped in a container of some kind so build-protocol knows what's what, and let it do the map inside the macro. e.g:

(build-protocol AProtocol
  {[this that whatever] [foo bar baz],
   [_] [hello goodbye]}
  ; a-method and b-method...
)

answered Jun 20, 2011 at 15:47

amalloy

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5 Comments

Ralph Over a year ago

Interesting idea. I'll have to explore it.

amalloy Over a year ago

See, for example, github.com/amalloy/ordered/blob/develop/src/deftype/… - I wrote this over the weekend and checked it in this morning. It defines a new delegating-deftype (seen in use at github.com/amalloy/ordered/blob/develop/src/ordered/map.clj), in much the same way I recommended you do build-protocol.

amalloy Over a year ago

@Ralph I went ahead and implemented a rough draft of this for you so you can see what I mean: github.com/amalloy/build-protocol/blob/develop/src/…

Ralph Over a year ago

I looked at your example at github.com/amalloy/build-protocol/blob/develop/src/…. I like it. Thanks.

Ralph Over a year ago

I am getting ready to try a (grid-bag-panel...) following the example Stuart Sierra did in his blog (stuartsierra.com/2010/01/05/taming-the-gridbaglayout), but I have some ideas of my own. The best way to learn this stuff is to actually do it (reading only goes so far).

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