reify-let.clj

(defn ensure-initialized [p]
  (or (deref p 0 nil) (throw (IllegalStateException. "Method called on half-initialized object."))))

(defmacro reify-let 
 [name bindings & impls]
  (let [p (gensym "p")
        delegate (fn [x]
                   (if (seq? x)
                     (let [[method args] x]
                       `(~method ~args (~method (ensure-initialized ~p) ~@(next args))))  
                     x))
        shadow (fn [x]
                 (if (seq? x)
                   (let [[method args & body] x]
                     `(~method ~args (let [~(first args) ~name] ~@body)))
                   x))]
    `(let [~p (promise)
           ~name (reify ~@(map delegate impls))
           ~@bindings]
       (deliver ~p (reify ~@(map shadow impls)))
       ~name)))

;; usage
(reify-let self
  [context-map {:me self}]
  MyProtocol
  (do-that-thing [this event]
    (handle-event context-map event)))