progress towards saving export string in correct format (but note there is currently an exception somewhere because of changes; need to fix)

fcore/layer-tree.sml

@@ -46,6 +46,17 @@ struct
           foldl (f, right, acc)
         end
 
+  fun foldr (f, tree, acc) =
+    case tree of
+      LEAF => acc
+    | NODE {value, left, right, ...} =>
+        let
+          val acc = foldr (f, right, acc)
+          val acc = f (value, acc)
+        in
+          foldr (f, left, acc)
+        end
+
   fun map (f, tree) =
     case tree of
       LEAF => LEAF