Variadic function with keyword arguments

Question

I'm a newbie to Clojure and I was wondering if there is a way to define a function that can be called like this:

(strange-adder 1 2 3 :strange true)

That is, a function that can receive a variable number of ints and a keyword argument.

I know that I can define a function with keyword arguments this way:

(defn strange-adder
  [a b c & {:keys [strange]}]
  (println strange)
  (+ a b c))

But now my function can only receive a fixed number of ints.

Is there a way to use both styles at the same time?

Answer 1

unfortunately, no.

The & destructuring operator uses everything after it on the argument list so it does not have the ability to handle two diferent sets of variable arity destructuring groups in one form.

one option is to break the function up into several arities. Though this only works if you can arrange it so only one of them is variadic (uses &). A more universal and less convenient solution is to treat the entire argument list as one variadic form, and pick the numbers off the start of it manually.

user> (defn strange-adder
        [& args]
         (let [nums (take-while number? args)
               opts (apply hash-map (drop-while number? args))
               strange (:strange opts)]
          (println strange)
              (apply + nums)))
#'user/strange-adder
user> (strange-adder 1 2 3 4 :strange 4)
4
10