feat: add ability to dispatch a update function

src/types.tsx

@@ -99,9 +99,12 @@ export type NavigationHelpers<
   ParamList extends ParamListBase = ParamListBase
 > = {
   /**
-   * Dispatch an action to the router.
+   * Dispatch an action or an update function to the router.
+   * The update function will receive the current state,
    */
-  dispatch(action: NavigationAction): void;
+  dispatch(
+    action: NavigationAction | ((state: NavigationState) => NavigationState)
+  ): void;
 
   /**
    * Navigate to a route in current navigation tree.

src/useNavigationBuilder.tsx

@@ -180,8 +180,12 @@ export default function useNavigationBuilder(
   );
 
   const helpers = React.useMemo((): NavigationHelpers => {
-    const dispatch = (action: NavigationAction) => {
+    const dispatch = (
-      if (!onAction(action)) {
+      action: NavigationAction | ((state: NavigationState) => NavigationState)
+    ) => {
+      if (typeof action === 'function') {
+        setState(action(getState()));
+      } else if (!onAction(action)) {
         throw new Error(
           `No navigators are able to handle the action "${action.type}".`
         );
@@ -206,7 +210,7 @@ export default function useNavigationBuilder(
       ),
       dispatch,
     };
-  }, [onAction, parentNavigationHelpers, router.actionCreators]);
+  }, [getState, onAction, parentNavigationHelpers, router, setState]);
 
   const navigation = React.useMemo(
     () => ({