Clojure的封閉不符合預期？

Question

的REPL預期返回5.

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

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

Answer 1

count時返回2不是一個可變變量所以(+ count 1)不改變其值。如果您想要突變，您可以將計數存儲在​​中並使用swap!進行更新：

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