What does the % character mean in the re-frame todomvc app todo-item function?

Question

The re-frame todomvc views namespace contains a function todo-item which contains the following snippet:

(when @editing
         [todo-edit {:class "edit"
                     :title title
                     :on-save #(dispatch [:save id %])
                     :on-stop #(reset! editing false)}])

the :on-save key is passed to and used in the todo-input function which contains the following snippet:

let [val (atom title)
        stop #(do (reset! val "")
                  (if on-stop (on-stop)))
        save #(let [v (-> @val str clojure.string/trim)]
               (if-not (empty? v) (on-save v))
               (stop))]

What is the meaning of the % character in the first snippet:

:on-save #(dispatch [:save id %])

and how should I interpret in the second snippet:

(on-save v)

?

Find the todomvc views namespace here.

Answer 1

It is shorthand for this inline anonymous function definition

(fn [x] 
  (dispatch [:save id x]))

For more info please see:

• https://clojuredocs.org/clojure.core/fn
• https://clojure.org/reference/reader#_dispatch