Clojure: determine if a function exists

问题:

how can i know if a function name provided as string is callable or not in the current context? something like:

(callable? "asdasd") ;; false
(callable? "filter") ;; true

thanks

回答1:

You are looking for resolve,

(resolve (symbol "asd"))

returns nil

(resolve (symbol "filter"))

return #'clojure.core/filter

To check if a var is a function (credit goes to @amalloy):

(-> s symbol resolve deref ifn?)

回答2:

Chances are if you need this, you're doing something wrong, but...

(defn callable? 
  [s] 
  (let [obj (try (eval (symbol s)) (catch Exception e))]
  (and obj (fn? obj))))

回答3:

(defn callable? [name]      
   (clojure.test/function? (symbol name)))

UPD. I found out that fn? checks only for interface Fn and doesn't work for resolved symbol. Though, clojure.test/function? does what is needed, so I updated an example.