Get the Caps – Rich 4Clojure Problem 29 – See: https://github.com/PEZ/rich4clojure

rich4clojure_easy_problem_029.clj

(ns rich4clojure.easy.problem-029
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Get the Caps =
;; By 4Clojure user: dbyrne
;; Difficulty: Easy
;; Tags: [strings]
;; 
;; Write a function which takes a string and returns a new
;; string containing only the capital letters.

(def __ :tests-will-fail)

(comment
  
  )

(tests
  (__ "HeLlO, WoRlD!") := "HLOWRD"
  (__ "nothing") :=
  (__ "$#A(*&987Zf") := "AZ")

;; To participate, fork:
;; https://github.com/PEZ/rich4clojure

;; Post your solution below, please!

(defn filter-upper
  "takes a string and returns a new string containing only the capital letters"
  [s]
  (apply str (re-seq #"[A-Z]" s)))