Clojure闭合不符合预期？

Question

当预期返回5时,repl返回2.

(defn counter [] 
  (let [count 1]
    (fn [] 
      (+ count 1)
    )
  )
)

(defn test-counter []
  (let [increment (counter)]
    (increment)
    (increment)
    (increment)
    (increment)
  )
)

Answer 1

count不是一个可变变量,所以(+ count 1)不会改变它的值.如果你想要变异,你可以将计数存储在一个atom并使用swap!以下方法更新它:

(defn counter []
  (let [count (atom 0)]
    (fn [] (swap! count inc))))