merge for clojure that doesn't overwrite existing values with nil values

safe-merge.clj

(require '[clojure.core.match :refer [match]])

(defn discard-nils [a b]
  (match [a b]
         [_ nil] a
         :else b))

(def safe-merge (partial merge-with discard-nils))

;; examples

(safe-merge {:a 1 :b 1} {:a 5 :b nil} {:a nil :b 3})
;; => {:a 5, :b 3}

(merge {:a 1 :b 1} {:a 5 :b nil} {:a nil :b 3})

;; => {:a nil, :b 3}

(safe-merge {:a 1 :b nil} {:a nil :b 4 :c 5 :d nil})

;; => {:a 1, :b 4, :c 5, :d nil}

(merge {:a 1 :b nil} {:a nil :b 4 :c 5 :d nil})

;; => {:a nil, :b 4, :c 5, :d nil}

(def safe-merge (partial merge-with #(or %2 %1)))