map-utils: add deep-merge-with

src/clojure/contrib/map_utils.clj

@@ -34,4 +34,19 @@
   [map ks]
   (reduce safe-get map ks))
 
+; by Chouser:
+(defn deep-merge-with
+  "Like merge-with, but merges maps recursively, appling the given fn
+  only when there's a non-map at a particular level.
+
+  (deepmerge + {:a {:b {:c 1 :d {:x 1 :y 2}} :e 3} :f 4}
+               {:a {:b {:c 2 :d {:z 9} :z 3} :e 100}})
+  -> {:a {:b {:z 3, :c 3, :d {:z 9, :x 1, :y 2}}, :e 103}, :f 4}"
+  [f & maps]
+  (apply
+    (fn m [& maps]
+      (if (every? map? maps)
+        (apply merge-with m maps)
+        (apply f maps)))
+    maps))