impure->pure-function.clj

(require '[clojure.test :refer [is]])

(defn random-beatle []
  (case (rand-int 4)
    0 "John"
    1 "Paul"
    2 "George"
    3 "Ringo"))

(defn hello-beatle [get-beatle]
  (str "Hello " (get-beatle)))

;; pass in a stub
(is (= "Hello George" (hello-beatle (fn [] "George"))))

;; or use constantly to create a stub
(is (= "Hello George" (hello-beatle (constantly "George"))))

;; we can use this to build a new function
(defn hello-random-beatle []
  (hello-beatle random-beatle))

;; or we can use partial to create a new function
(def hello-random-beatle (partial hello-beatle random-beatle))