java - Clojure : java. lang.Character 无法转换为 clojure.lang.IFn

Question

我只是想用 Clojure 写一个简单的小猜谜游戏，我得到了这个错误。我看不到我的 Character 在哪里被视为函数，因为结果输入也预测不应该存在这样的问题。这是代码:

(ns clojure.examples.hello
  (:gen-class))

(ns clojure-noob.core)

(defn takeFst [x n]
    (if (= n 0) () (cons (first x) (takeFst (rest x) (- n 1))))
)

(defn createSeq [elem n]
    (if (= n 0) () (cons elem (createSeq elem (- n 1))))
)

(defn fnEquals? [n]
    (fn [elem] (= elem n))
)

(defn removeEach [x elem]
    (remove (fnEquals? elem) x)
)

(defn containsString? [s ch]
    (not (empty? (filter true? (map = (createSeq ch (count s)) s))))
)

(defn akasztofa! [s lives]
    (println s)
    (if (and (not= () s) (not= lives 0))
        (
            (def guess (eval (read)))
            (if (containsString? s guess) (akasztofa! (removeEach s guess) lives) (akasztofa! s (- lives 1)))
        )
        ()
    )
)

(akasztofa! "hab" 10)

我得到的输出是这样的:

hab
(a b)
(b)
() 
Exception in thread "main" java.lang.ClassCastException: 
java.lang.Character cannot be cast to clojure.lang.IFn, compiling:
(/home/cicaharcos/Documents/Clojure/First/akasztofa/main.clj:38:1)

我的输入是:\h\a\b

Answer 1

错误来自尝试将字符作为函数求值，例如:

(\a) => Exception in thread "main" java.lang.ClassCastException: java.base/java.lang.Character cannot be cast to clojure.lang.IFn, 

我认为是 if 语句中的额外括号试图将字符作为函数求值。请记住，在 Clojure 中，括号不像在 Java 中那样“分组”，它们的意思是“函数调用”。

您的代码还有一些其他问题，值得注意的是对空列表使用 ()。您必须像这样引用列表:

'()

或者，更好的是，使用带方括号的空 vector (不需要引号):

 []

---

如果您使代码看起来像下面这样，它似乎可以工作:

(ns clojure.examples.hello
  (:gen-class))

(ns clojure-noob.core)

(defn takeFst [x n]
    (if (= n 0) [] (cons (first x) (takeFst (rest x) (- n 1))))
)

(defn createSeq [elem n]
    (if (= n 0) [] (cons elem (createSeq elem (- n 1))))
)

(defn fnEquals? [n]
    (fn [elem] (= elem n))
)

(defn removeEach [x elem]
    (remove (fnEquals? elem) x)
)

(defn containsString? [s ch]
    (not (empty? (filter true? (map = (createSeq ch (count s)) s))))
)

(defn akasztofa! [s lives]
    (println s)
    (if (and (not= [] s) (not= lives 0))
        (let [guess (eval (read))]
          (if (containsString? s guess)
            (akasztofa! (removeEach s guess) lives)
            (akasztofa! s (- lives 1))))
        [] ))

(akasztofa! "hab" 10)

结果:

hab
\h      ; <= user input plus <ret>
(a b)
\a      ; <= user input plus <ret>
(b)
\b      ; <= user input plus <ret>
()

---

清空列表:

使用count函数，可以看出问题:

demo.core=> (count ())
0

demo.core=> (count (\b))

ClassCastException java.base/java.lang.Character cannot be cast to clojure.lang.IFn  demo.core/eval16682 (form-init2403719904611886388.clj:1)

demo.core=> (count (1))

ClassCastException java.base/java.lang.Long cannot be cast to clojure.lang.IFn  demo.core/eval16686 (form-init2403719904611886388.clj:1)

demo.core=> (count '(\b))
1

所以你可以使用 () (未加引号)作为一个空列表(我忘记了)，但是如果它是非空的，它会失败，除非你引用它。使用 vector 更简单且不易出错:

demo.core=> (count [])
0
demo.core=> (count [\b])
1
demo.core=> (count [1])
1