在clojure中,如何测试是否已定义符号？

Question

我想看看符号是否已被"def"修改,但我看不到任何ifdef语法

Answer 1

user> (resolve 'foo)
nil
user> (def foo 3)
#'user/foo
user> (resolve 'foo)
#'user/foo

Answer 2

resolve或者ns-resolve可以做你想要的:

user> (def a 1)
#'user/a
user> (def b)
#'user/b
user> (resolve 'a)
#'user/a
user> (resolve 'b)
#'user/b
user> (resolve 'c)
nil

要获得布尔值:

user> (boolean (resolve 'b))
true

编辑:根据MayDaniel的评论,这不是你要求的,但它会让你到那里.这是bounded?(可能不是最好的名字)的实现:

(defn bounded? [sym]
  (if-let [v (resolve sym)]
    (bound? v)
    false))

user> (map bounded? ['a 'b 'c])
(true false false)