为符号`with-redefs`连续返回不同的值(Clojure)

Question

我希望用来with-redefs模拟STDIN的用户输入.

首先,我正在测试不正确的输入,它应该重新询问用户输入.然后,应该给出正确的输入.

有没有办法用于with-redefs将不同的值绑定到给定的符号？

我正在尝试获得此功能:

(with-redefs [read-line (fn [] "HI")
              read-line (fn [] "OK")]
  (do (println (read-line)) ;; -> "HI"
      (println (read-line)))) ;; -> "OK"

Answer 1

不是特别的,但是你总是可以用某种状态'让兰比达'!

(let [a (atom ["a" "b"])]
  (defn f []
    (let [r (first @a)]
      (swap! a rest)
      r)))

(f) ;; "a"
(f) ;; "b"
(f) ;; nil

在你的特定情况下,有一个生成'有状态'函数的函数是有意义的,所以一个完整的例子是:

(defn maker [l]
  (let [a (atom l)]
    (fn []
      (let [r (first @a)]
        (swap! a rest)
        r))))

(with-redefs [read-line (maker ["HI" "OK"])]
  (do (println (read-line)) ;; -> "HI"
      (println (read-line)))) ;; -> "OK"