rendezvous with cassidoo challenge: 22.09.04

from_to.clj

(ns from-to
  (:require [clojure.test :refer [deftest is]]))

(defn from-to [lower upper]                                                                      
  (let [gen (atom (dec lower))]                                                                  
    (fn []                                                                                       
      (when (< @gen upper)                                                                       
        (swap! gen inc)                                                                          
        (deref gen)))))                                                                          
                                                                                                 
(deftest from-to-test                                                                            
  (let [gen (from-to 5 7)]                                                                       
    (is (= 5 (gen)))                                                                             
    (is (= 6 (gen)))                                                                             
    (is (= 7 (gen)))                                                                             
    (is (= nil (gen)))))