Necessary variables in let, Tabby A.I suggest with Clojure

Code

;; necessary_variables_in_let.clj

(def string "rgaraga4agjrj4rikllmrfmghjqwwrwengek")

(defn sieve [string]
  (let [first-4-letters (take 4 string)
        unique-letters (set first-4-letters)
        length (count unique-letters)]
    (if (= length 4)
      (clojure.string/join "" first-4-letters)
      (if (= length 0)
        (println "Nothing found")
        (recur (rest string))))))

(defn sieve-2 [string]
  (let [first-4-letters (take 4 string)
        length (->> first-4-letters
                    set
                    count)]
    (if (= length 4)
      (clojure.string/join "" first-4-letters)
      (if (= length 0)
        (println "Nothing found")
        (recur (rest string))))))

(defn number-of-unique-letters [string]
  (->> string
       set
       count))

(defn sieve-3 [string]
  (let [first-4-letters (take 4 string)
        length (number-of-unique-letters first-4-letters)]
    (if (= length 4)
      (clojure.string/join "" first-4-letters)
      (if (= length 0)
        (println "Nothing found")
        (recur (rest string))))))

(sieve-3 "abracadabra")