Clojure: What does [_] do in a Functions Argument List?

Question

I am working through the joy of clojure and am wondering what the _ syntax does in a functions argument vector.

Example:

(def available-processors
           


        

Answer 1

Nothing special about it, it is just a convention for naming something that you don't care about, but still it is a name and can be used like a normal name.

(defn hello [_] (+ 1 _))
(hello 10)

UPDATE

Doing this:

(defn hello [a a]  (+ a a))

doesn't produce an error and hence you can use as many _ as you want ;).

NOTE: The above isn't the case with Scheme or CL... Hmm what was the rational behind it in clojure then???