diff --git a/dotscape b/dotscape
index ef0bc3d..22f50f8 100755
Binary files a/dotscape and b/dotscape differ
diff --git a/dotscape.mlb b/dotscape.mlb
index 43b2e0a..85cd649 100644
--- a/dotscape.mlb
+++ b/dotscape.mlb
@@ -18,7 +18,9 @@ functional-core/app-init.sml
 functional-core/app-with.sml
 
 message-types/input-msg.sml
+message-types/file-msg.sml
 message-types/draw-msg.sml
+message-types/update-msg.sml
 
 functional-core/app-update.sml
 
diff --git a/functional-core/app-update.sml b/functional-core/app-update.sml
index c594538..edb03b7 100644
--- a/functional-core/app-update.sml
+++ b/functional-core/app-update.sml
@@ -1,14 +1,16 @@
 signature APP_UPDATE =
 sig
   val update: AppType.app_type * InputMessage.t
-              -> AppType.app_type * DrawMessage.t
+              -> AppType.app_type * UpdateMessage.t
 end
 
 structure AppUpdate :> APP_UPDATE =
 struct
   open AppType
+
   open DrawMessage
   open InputMessage
+  open UpdateMessage
 
   fun mouseMoveOrRelease (model: app_type) =
     let
@@ -16,7 +18,7 @@ struct
       val drawVec = TriangleStage.toVector (model, drawVec)
       val drawMsg = DRAW_DOT drawVec
     in
-      (model, drawMsg)
+      (model, DRAW drawMsg)
     end
 
   fun mouseLeftClick (model: app_type) =
@@ -36,7 +38,7 @@ struct
               val model =
                 AppWith.addTriangleStage (model, newTriangleStage, newUndoTuple)
             in
-              (model, drawMsg)
+              (model, DRAW drawMsg)
             end
         | FIRST {x1, y1} =>
             let
@@ -48,7 +50,7 @@ struct
               val model =
                 AppWith.addTriangleStage (model, newTriangleStage, newUndoTuple)
             in
-              (model, drawMsg)
+              (model, DRAW drawMsg)
             end
         | SECOND {x1, y1, x2, y2} =>
             let
@@ -58,10 +60,10 @@ struct
               val drawVec = Triangles.toVector model
               val drawMsg = DRAW_TRIANGLES_AND_RESET_DOTS drawVec
             in
-              (model, drawMsg)
+              (model, DRAW drawMsg)
             end
       else
-        (model, NO_DRAW)
+        (model, NO_MAILBOX)
     end
 
   fun resizeWindow (model, width, height) =
@@ -79,7 +81,7 @@ struct
         RESIZE_TRIANGLES_DOTS_AND_GRAPH
           {triangles = triangles, graphLines = graphLines, dots = dots}
     in
-      (model, drawMsg)
+      (model, DRAW drawMsg)
     end
 
   fun undoAction model =
@@ -90,7 +92,7 @@ struct
           val model =
             AppWith.undo (model, NO_TRIANGLE, #triangles model, (x1, y1))
         in
-          (model, CLEAR_DOTS)
+          (model, DRAW CLEAR_DOTS)
         end
     | SECOND {x1, y1, x2, y2} =>
         (* Change FIRST to SECOND and redraw dots. *)
@@ -103,7 +105,7 @@ struct
           val drawVec = TriangleStage.firstToVector (x1, y1, emptyVec, model)
           val drawMsg = DRAW_DOT drawVec
         in
-          (model, drawMsg)
+          (model, DRAW drawMsg)
         end
     | NO_TRIANGLE =>
         (case #triangles model of
@@ -124,11 +126,11 @@ struct
                  DRAW_TRIANGLES_AND_DOTS
                    {triangles = newTriangleVec, dots = drawVec}
              in
-               (model, drawMsg)
+               (model, DRAW drawMsg)
              end
          | [] =>
              (* Can't undo, because there are no actions to undo. *)
-             (model, NO_DRAW))
+             (model, NO_MAILBOX))
 
   fun redoAction model =
     case #redo model of
@@ -147,7 +149,7 @@ struct
                val drawVec = TriangleStage.firstToVector (x, y, emptyVec, model)
                val drawMsg = DRAW_DOT drawVec
              in
-               (model, drawMsg)
+               (model, DRAW drawMsg)
              end
          | FIRST {x1, y1} =>
              (* add to triangle stage, redraw dots *)
@@ -162,7 +164,7 @@ struct
                  (x1, y1, x, y, emptyVec, model)
                val drawMsg = DRAW_DOT drawVec
              in
-               (model, drawMsg)
+               (model, DRAW drawMsg)
              end
          | SECOND {x1, y1, x2, y2} =>
              (* clear triangle stage, add to trinagle list and redraw triangles *)
@@ -177,11 +179,9 @@ struct
                val drawVec = Triangles.toVector model
                val drawMsg = DRAW_TRIANGLES_AND_RESET_DOTS drawVec
              in
-               (model, drawMsg)
+               (model, DRAW drawMsg)
              end)
-    | [] => 
-        (* Nothing to redo. *)
-        (model, NO_DRAW)
+    | [] => (* Nothing to redo. *) (model, NO_MAILBOX)
 
   fun toggleGraph (model: app_type) =
     if #showGraph model then
@@ -189,7 +189,7 @@ struct
         val model = AppWith.graphVisibility (model, false)
         val drawMsg = DRAW_GRAPH (Vector.fromList [])
       in
-        (model, drawMsg)
+        (model, DRAW drawMsg)
       end
     else
       let
@@ -197,7 +197,7 @@ struct
         val graphLines = GraphLines.generate model
         val drawMsg = DRAW_GRAPH graphLines
       in
-        (model, drawMsg)
+        (model, DRAW drawMsg)
       end
 
   fun update (model: app_type, inputMsg) =
diff --git a/imperative-shell/draw-thread.sml b/imperative-shell/draw-thread.sml
index 7a04a2f..caebf41 100644
--- a/imperative-shell/draw-thread.sml
+++ b/imperative-shell/draw-thread.sml
@@ -150,18 +150,7 @@ struct
                    , triangleDrawObject
                    , triangleDrawLength
                    )
-               end
-           | NO_DRAW =>
-               run
-                 ( drawMailbox
-                 , window
-                 , graphDrawObject
-                 , drawGraphLength
-                 , dotDrawObject
-                 , dotDrawLength
-                 , triangleDrawObject
-                 , triangleDrawLength
-                 ))
+               end)
     else
       Glfw.terminate ()
 end
diff --git a/imperative-shell/update-thread.sml b/imperative-shell/update-thread.sml
index e86fd22..9a2a3d7 100644
--- a/imperative-shell/update-thread.sml
+++ b/imperative-shell/update-thread.sml
@@ -1,18 +1,32 @@
-structure UpdateThread =
+signature UPDATE_THREAD =
+sig
+  val run:
+      InputMessage.t Mailbox.mbox
+    * DrawMessage.t Mailbox.mbox
+    * AppType.app_type
+    -> unit
+end
+
+structure UpdateThread :> UPDATE_THREAD =
 struct
   open CML
+  open UpdateMessage
 
-  local
-    fun loop (inputMailbox, drawMailbox, model) =
-      let
-        val inputMsg = Mailbox.recv inputMailbox
-        val (model, drawMsg) = AppUpdate.update (model, inputMsg)
-        val _ = Mailbox.send (drawMailbox, drawMsg)
-      in
-        loop (inputMailbox, drawMailbox, model)
-      end
-  in
-    fun run (inputMailbox, drawMailbox, initial) =
-      loop (inputMailbox, drawMailbox, initial)
-  end
+  fun handleMsg (drawMailbox, updateMsg) =
+    case updateMsg of
+      DRAW drawMsg => Mailbox.send (drawMailbox, drawMsg)
+    | FILE fileMsg => ()
+    | NO_MAILBOX => ()
+
+  fun loop (inputMailbox, drawMailbox, model) =
+    let
+      val inputMsg = Mailbox.recv inputMailbox
+      val (model, updateMsg) = AppUpdate.update (model, inputMsg)
+      val _ = handleMsg (drawMailbox, updateMsg)
+    in
+      loop (inputMailbox, drawMailbox, model)
+    end
+
+  fun run (inputMailbox, drawMailbox, initial) =
+    loop (inputMailbox, drawMailbox, initial)
 end
diff --git a/message-types/draw-msg.sml b/message-types/draw-msg.sml
index 8a6495d..a7e9b96 100644
--- a/message-types/draw-msg.sml
+++ b/message-types/draw-msg.sml
@@ -12,7 +12,6 @@ sig
       , dots: Real32.real vector
       }
   | CLEAR_DOTS
-  | NO_DRAW
 end
 
 structure DrawMessage :> DRAW_MESSAGE =
@@ -29,5 +28,4 @@ struct
       , dots: Real32.real vector
       }
   | CLEAR_DOTS
-  | NO_DRAW
 end
diff --git a/message-types/io-msg.sml b/message-types/file-msg.sml
similarity index 79%
rename from message-types/io-msg.sml
rename to message-types/file-msg.sml
index 5d27022..6b1e462 100644
--- a/message-types/io-msg.sml
+++ b/message-types/file-msg.sml
@@ -1,4 +1,4 @@
-signature IO_MESSAGE =
+signature FILE_MESSAGE =
 sig
   datatype t =
     SAVE_TRIANGLES of AppType.triangle list
@@ -6,7 +6,7 @@ sig
   | IMPORT_FILE
 end
 
-structure IoMessage :> IO_MESSAGE =
+structure FileMessage :> FILE_MESSAGE =
 struct
   datatype t =
     SAVE_TRIANGLES of AppType.triangle list
diff --git a/message-types/update-msg.sml b/message-types/update-msg.sml
new file mode 100644
index 0000000..870cfa8
--- /dev/null
+++ b/message-types/update-msg.sml
@@ -0,0 +1,7 @@
+signature UPDATE_MESSAGE =
+sig
+  datatype t = DRAW of DrawMessage.t | FILE of FileMessage.t | NO_MAILBOX
+end
+
+structure UpdateMessage :> UPDATE_MESSAGE =
+struct datatype t = DRAW of DrawMessage.t | FILE of FileMessage.t | NO_MAILBOX end