使用if定义函数时出错

Question

我们有一个简单的函数定义:

(defn calculate [d x y]
  ((if (and (== d 1) (== x 1) (== y 0))
     1
     0)))
(println (calculate 1 1 0))

但是这导致了这个错误:

Exception in thread "main" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke    (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at jline.ConsoleRunner.main(ConsoleRunner.java:69)
Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn
    at user$calculate.invoke(main.clj:13)
    at user$eval5.invoke(main.clj:17)
    at clojure.lang.Compiler.eval(Compiler.java:6465)
    at clojure.lang.Compiler.load(Compiler.java:6902)
    at clojure.lang.Compiler.loadFile(Compiler.java:6863)
    at clojure.main$load_script.invoke(main.clj:282)
    at clojure.main$script_opt.invoke(main.clj:342)
    at clojure.main$main.doInvoke(main.clj:426)
    at clojure.lang.RestFn.invoke(RestFn.java:408)
    at clojure.lang.Var.invoke(Var.java:401)
    at clojure.lang.AFn.applyToHelper(AFn.java:161)
    at clojure.lang.Var.applyTo(Var.java:518)
    at clojure.main.main(main.java:37)
    ... 5 more

(顺便说一句,线13是与线if和and).

与向量相同:

(defn calculate [vectorr]
  ((if (and (== (vectorr 0) 1) (== (vectorr 1) 1) (== (vectorr 2) 0))
     1
     0)))
(println (calculate [1 1 0]))

这导致:

Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

... 相同.

并附图:

(defn calculate [mapp]
  ((if (and (== (mapp :d) 1) (== (mapp :x) 1) (== (mapp :y) 0))
     1
     0)))
(println (calculate {:d 1 :x 1 :y 0}))

结果在同一条消息中:

Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to clojure.lang.IFn

我们认为与某些事情if或比较有关.我们尝试使用普通参数,矢量作为参数,并使用地图,显然,错误保持不变.

我们还尝试了许多其他变体,但没有对实际问题有更深入的了解.

Answer 1

你的函数体周围有一对额外的括号,这意味着你想调用结果if(它是1或0 - 即长).

它应该是:

(defn calculate [vectorr]
  (if (and (== (vectorr 0) 1) (== (vectorr 1) 1) (== (vectorr 2) 0))
     1
     0))