Rather dubious struct-based stuff all plumbed through

RaftFable/src/App.fs

@@ -64,7 +64,8 @@ module App =
                 | RegisterClientResponse.Success client ->
                     try
                         clients.Add (client, HashSet ())
-                    with :? ArgumentException ->
+                    with _ ->
+                        // This is ArgumentException, but Fable can't type-test that
                         failwith "TODO: got a response a second time - need to handle this in the UI"
                 | RegisterClientResponse.NotLeader hint -> failwith "TODO: asked a non-leader, have to handle it"
             )
@@ -157,7 +158,7 @@ module App =
                 ActionHistory = []
             }
 
-        (promise { return () }, userPrefs.Value.ActionHistory)
+        (promise { return () }, newPrefs.ActionHistory)
         ||> List.fold (fun (inPromise : Promise<unit>) action ->
             promise {
                 let! _ = inPromise

RaftFable/src/Ui.fs

@@ -402,13 +402,20 @@ module Ui =
         : Result<UserPreferences<'a>, string>
         =
         let actionHistory =
-            ui.ActionHistoryList.value.Split "\n"
-            |> Seq.filter (not << System.String.IsNullOrEmpty)
-            |> Seq.map (
-                NetworkAction.tryParse<'a> parse None handleRegisterClientResponse handleClientDataResponse clusterSize
-            )
-            |> Result.allOkOrError
-            |> Result.map List.ofSeq
+            let arr = ResizeArray ()
+
+            for i in StringSplitEnumerator.make '\n' ui.ActionHistoryList.value do
+                if not (EfficientString.isEmpty i) then
+                    NetworkAction.tryParse<'a>
+                        parse
+                        None
+                        handleRegisterClientResponse
+                        handleClientDataResponse
+                        clusterSize
+                        i
+                    |> arr.Add
+
+            Result.allOkOrError arr |> Result.map List.ofSeq
 
         match actionHistory with
         | Result.Ok actionHistory ->