这是一个明智的单子为可变的状态在Clojure?

我已经在clojure中尝试过monads,并提出了以下代码,其中一个单值/状态对由一个可变的clojure deftype对象表示。

由于对象是可变的,一个优势似乎是您可以编写一元代码,而无需一直构造新的结果对象。

不过,我对单子还很陌生,所以很想知道:

• 这个结构有意义吗?
• 它真的能像单子一样正常工作吗?

代码如下:

(defprotocol PStateStore 
  (set-store-state [ss v])
  (get-store-state [ss])
  (set-store-value [ss v])
  (get-store-value [ss]))

(deftype StateStore [^{:unsynchronized-mutable true} value 
                     ^{:unsynchronized-mutable true} state]
  PStateStore 
      (get-store-state [ss] (.state ss))
      (get-store-value [ss] (.value ss))
      (set-store-state [ss v] (set! state v))
      (set-store-value [ss v] (set! value v))

   Object
     (toString [ss] (str "value=" (.value ss) ", state=" (.state ss))))

(defn state-store [v s] (StateStore. v s))

(defmonad MStoredState
  [m-result (fn [v] 
              (fn [^StateStore ss] 
                  (do
                    (set-store-value ss v)
                    ss)))
   m-bind (fn [a f]
            (fn [^StateStore ss]
              (do
                (a ss)
                ((f (get-store-value ss)) ss))))])

; Usage examples

(def mb
  (domonad MStoredState
    [a (m-result 1)
     b (m-result 5)]
    (+ a b)))

(def ssa (state-store 100 101))

(mb ssa)

; => #<StateStore value=6, state=101>