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!

(fn [s] (apply str (filter #(Character/isUpperCase %) s)))

#(apply
str (re-seq #"[A-Z]" %)))

Had to edit (tests 2 to
(__ "nothing") := "", cant think of any way to return no action for "" or nil?

(def __ #(loop [el (seq %)
                res ""]
           (if (nil? el)
             (str res)
             (recur (next el)
                    (if (Character/isUpperCase (first el))
                      (str res (first el))
                      res)))))

(def __ (fn [s]
          (->> s
               (filter (fn [c] (Character/isUpperCase c)))
               (apply str)
               )))