data-accumulating-spike.clj

(def append-fn #(conj (or % []) %2))                                                     
                                                                                         
(deftest append-fn-test                                                                  
  (testing "works as advertised"                                                         
    (is (= {:a {:b 1 :c [2]}} (update-in {:a {:b 1}} [:a :c] append-fn 2)))              
    (is (= {:a {:b 1 :c [2 3]}} (update-in {:a {:b 1 :c [2]}} [:a :c] append-fn 3))) ) ) 
                                                                                         
(def prepend-fn #(into [%2] (or % [])))                                                  
                                                                                         
(deftest prepend-fn-test                                                                 
  (testing "works as advertised"                                                         
    (is (= {:a {:b 1 :c [2]}} (update-in {:a {:b 1}} [:a :c] prepend-fn 2)))             
    (is (= {:a {:b 1 :c [2 3]}} (update-in {:a {:b 1 :c [3]}} [:a :c] prepend-fn 2))) ) )