support transforms to NONE for set-elem and map-key

src/clj/com/rpl/specter.cljc

@@ -870,7 +870,8 @@
 
 (defrichnav
   ^{:doc "Navigates to the given key in the map (not to the value). Navigates only if the
-          key currently exists in the map."}
+          key currently exists in the map. Can transform to NONE to remove the key/value
+          pair from the map."}
   map-key
   [key]
   (select* [this vals structure next-fn]
@@ -881,14 +882,17 @@
   (transform* [this vals structure next-fn]
     (if (contains? structure key)
       (let [newkey (next-fn vals key)
-            oldval (get structure key)]
-        (-> structure (dissoc key) (assoc newkey oldval))
-        )
+            dissoced (dissoc structure key)]
+        (if (identical? NONE newkey)
+          dissoced
+          (assoc dissoced newkey (get structure key))
+          ))
       structure
       )))
 
 (defrichnav
-  ^{:doc "Navigates to the given element in the set only if it exists in the set."}
+  ^{:doc "Navigates to the given element in the set only if it exists in the set.
+          Can transform to NONE to remove the element from the set."}
   set-elem
   [elem]
   (select* [this vals structure next-fn]
@@ -898,7 +902,12 @@
       ))
   (transform* [this vals structure next-fn]
     (if (contains? structure elem)
-      (-> structure (disj elem) (conj (next-fn vals elem)))
+      (let [newelem (next-fn vals elem)
+            removed (disj structure elem)]
+        (if (identical? NONE newelem)
+          removed
+          (conj removed newelem)
+          ))
       structure
       )))
 

test/com/rpl/specter/core_test.cljc

@@ -1531,12 +1531,14 @@
   (is (= {:c 3} (setval (s/map-key :a) :b {:c 3})))
   (is (= {:b 2} (setval (s/map-key :a) :b {:a 2})))
   (is (= {:b 2} (setval (s/map-key :a) :b {:a 2 :b 1})))
+  (is (= {:b 2} (setval (s/map-key :a) s/NONE {:a 1 :b 2})))
   )
 
 (deftest set-elem-test
   (is (= #{:b :d} (setval (s/set-elem :a) :x #{:b :d})))
   (is (= #{:x :a} (setval (s/set-elem :b) :x #{:b :a})))
   (is (= #{:a} (setval (s/set-elem :b) :a #{:b :a})))
+  (is (= #{:b} (setval (s/set-elem :a) s/NONE #{:a :b})))
   )
 
 #?(:clj