flexible deep merge implementation in clojure

deep_merge.clj

;;found here: https://github.com/metosin/ring-swagger/blob/1c5b8ab7ad7a5735624986bbb6b288aaf168d407/src/ring/swagger/common.clj#L53-L73

(defn deep-merge
  "Recursively merges maps.
   If the first parameter is a keyword it tells the strategy to
   use when merging non-map collections. Options are
   - :replace, the default, the last value is used
   - :into, if the value in every map is a collection they are concatenated
     using into. Thus the type of (first) value is maintained."
  {:arglists '([strategy & values] [values])}
  [& values]
  (let [[values strategy] (if (keyword? (first values))
                            [(rest values) (first values)]
                            [values :replace])]
    (cond
      (every? map? values)
      (apply merge-with (partial deep-merge strategy) values)

      (and (= strategy :into) (every? coll? values))
      (reduce into values)

      :else
      (last values))))