Clojure：使用Java Interop限制来保持纯度

Question

我有一个Clojure代码片段，它遵循第三方Java库中定义的Observer pattern，如下所示：

(defrecord RecordHandler []
  RecordListener
  (onMsg [this msg] (getValue msg)))

(defn read
  [file]
  (let [decoder (Decode.)
        broadcaster (MsgBroadcaster. decoder)
        handler (RecordHandler.)]
    (.addListener broadcaster handler)
    (.run broadcaster file)))

我希望能够在调用onMsg时收集每条记录的结果。我的主要限制是Decode，MsgBroadcaster和RecordListener接口都由第三方库定义，onMsg返回void。< / p>

如何在保持纯粹的同时收集每个广播的值RecordHandler？我当前的解决方案涉及将向量引用传递给RecordHandler的初始化并使用alter和conj，但这是修改引用，这似乎违反了不修改外部状态的想法。

(defrecord RecordHandler [memo]
  RecordListener
  (onMsg [this msg] 
    (dosync
      (alter memo conj (getValue msg))))

(defn read
  [file]
  (let [decoder (Decode.)
        broadcaster (MsgBroadcaster. decoder)
        memo (ref [])
        handler (RecordHandler. memo)]
    (.addListener broadcaster handler)
    (.run broadcaster file)))