Hi,

On 8 Apr., 15:02, Alfredo <alfredo.dinap...@gmail.com> wrote:

> I know that it's a user's choice, but I'm wondering if it's possibile
> to offer a "+" function that it's extended to other datatypes -with or
> without protocols - and still able to be applied to Numbers :)

Yes. It is. Just provide it in your namespace. You showed already how.

(ns your.library
  (:refer-clojure :rename {+ core-+})
  (:import
    clojure.lang.IPersistentVector
    clojure.lang.ISeq))

(defprotocol Addable
 (+ [t1 t2]))

(extend-protocol Addable
  String
  (+ [s1 s2] (str s1 s2))
  IPersistentVector
  (+ [v1 v2] (into v1 v2))
  ISeq
  (+ [s1 s2] (concat s1 s2))
  Number
  (+ [n1 n2] (core-+ n1 n2)))

This gives:
your.library=> (+ 1 2)
3
your.library=> (+ "a" "b")
"ab"
your.library=> (+ [1 2] [3 4])
[1 2 3 4]
your.library=> (+ (list 1 2) (list 3 4))
(1 2 3 4)

I'm not sure it's advisable, though. I think adding numbers has
nothing to with catenating strings. You should probably choose a name
like append, concat or into.

Sincerely
Meikel

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