diff --git a/dotscape b/dotscape
index 320a3a3..97e65d8 100755
Binary files a/dotscape and b/dotscape differ
diff --git a/functional-core/app-init.sml b/functional-core/app-init.sml
index c6046e1..ae84282 100644
--- a/functional-core/app-init.sml
+++ b/functional-core/app-init.sml
@@ -8,7 +8,7 @@ struct
   open AppType
 
   fun helpFromWidthAndHeight
-    (windowWidth, windowHeight, wStart, wFinish, hStart, hFinish) =
+    (windowWidth, windowHeight, wStart, wFinish, hStart, hFinish) : app_type =
     let
       val xClickPoints = ClickPoints.generate (wStart, wFinish)
       val yClickPoints = ClickPoints.generate (hStart, hFinish)
@@ -24,6 +24,8 @@ struct
       , yClickPoints = yClickPoints
       , graphLines = graphLines
       , undo = []
+      , mouseX = 0.0
+      , mouseY = 0.0
       }
     end
 
diff --git a/functional-core/app-type.sml b/functional-core/app-type.sml
index bfe5ef8..18d5c50 100644
--- a/functional-core/app-type.sml
+++ b/functional-core/app-type.sml
@@ -24,6 +24,8 @@ sig
     , yClickPoints: Real32.real vector
     , graphLines: Real32.real vector
     , undo: (Real32.real * Real32.real) list
+    , mouseX: Real32.real
+    , mouseY: Real32.real
     }
 end
 
@@ -61,5 +63,7 @@ struct
     , yClickPoints: Real32.real vector
     , graphLines: Real32.real vector
     , undo: (Real32.real * Real32.real) list
+    , mouseX: Real32.real
+    , mouseY: Real32.real
     }
 end
diff --git a/functional-core/app-update.sml b/functional-core/app-update.sml
index 1b06f29..f985547 100644
--- a/functional-core/app-update.sml
+++ b/functional-core/app-update.sml
@@ -1,7 +1,7 @@
 signature APP_UPDATE =
 sig
-  val update: AppType.app_type * Real32.real * Real32.real * InputMessage.t
-              -> AppType.app_type * DrawMessage.t * Real32.real * Real32.real
+  val update: AppType.app_type *  InputMessage.t
+              -> AppType.app_type * DrawMessage.t
 end
 
 structure AppUpdate :> APP_UPDATE =
@@ -10,9 +10,18 @@ struct
   open DrawMessage
   open InputMessage
 
-  fun mouseMoveOrRelease (model: app_type, mouseX, mouseY) =
+  fun mouseMoveOrRelease (model: app_type) =
     let
-      val {xClickPoints, yClickPoints, windowWidth, windowHeight, ...} = model
+      val
+        { xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , mouseX
+        , mouseY
+        , ...
+        } = model
+
       val (drawVec, _, _) = ClickPoints.getClickPosition
         ( mouseX
         , mouseY
@@ -27,12 +36,21 @@ struct
       val drawVec = TriangleStage.toVector (model, drawVec)
       val drawMsg = DRAW_BUTTON drawVec
     in
-      (model, drawMsg, mouseX, mouseY)
+      (model, drawMsg)
     end
 
-  fun mouseLeftClick (model: app_type, mouseX, mouseY) =
+  fun mouseLeftClick (model: app_type) =
     let
-      val {xClickPoints, yClickPoints, windowWidth, windowHeight, ...} = model
+      val
+        { xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , mouseX
+        , mouseY
+        , ...
+        } = model
+
       val (buttonVec, hpos, vpos) = ClickPoints.getClickPosition
         ( mouseX
         , mouseY
@@ -57,7 +75,7 @@ struct
               val model =
                 AppWith.newTriangleStage (model, newTriangleStage, newUndoTuple)
             in
-              (model, drawMsg, mouseX, mouseY)
+              (model, drawMsg)
             end
         | FIRST {x1, y1} =>
             let
@@ -70,7 +88,7 @@ struct
               val model =
                 AppWith.newTriangleStage (model, newTriangleStage, newUndoTuple)
             in
-              (model, drawMsg, mouseX, mouseY)
+              (model, drawMsg)
             end
         | SECOND {x1, y1, x2, y2} =>
             let
@@ -80,13 +98,13 @@ struct
               val drawVec = Triangles.toVector model
               val drawMsg = DRAW_TRIANGLES_AND_RESET_BUTTONS drawVec
             in
-              (model, drawMsg, mouseX, mouseY)
+              (model, drawMsg)
             end
       else
-        (model, NO_DRAW, mouseX, mouseY)
+        (model, NO_DRAW)
     end
 
-  fun resizeWindow (model, mouseX, mouseY, width, height) =
+  fun resizeWindow (model, width, height) =
     let
       val model = AppWith.windowResize (model, width, height)
       val triangles = Triangles.toVector model
@@ -95,15 +113,15 @@ struct
         RESIZE_TRIANGLES_BUTTONS_AND_GRAPH
           {triangles = triangles, graphLines = graphLines}
     in
-      (model, drawMsg, mouseX, mouseY)
+      (model, drawMsg)
     end
 
-  fun undoAction (model, mouseX, mouseY) =
+  fun undoAction model =
     case #triangleStage model of
       FIRST {x1, y1} =>
         (* Change FIRST to NO_TRIANGLE and clear buttons. *)
         let val model = AppWith.replaceTriangleStage (model, NO_TRIANGLE)
-        in (model, CLEAR_BUTTONS, mouseX, mouseY)
+        in (model, CLEAR_BUTTONS)
         end
     | SECOND {x1, y1, x2, y2} =>
         (* Change FIRST to SECOND and redraw buttons. *)
@@ -115,7 +133,7 @@ struct
             TriangleStage.firstToVector (x1, y1, Vector.fromList [], model)
           val drawMsg = DRAW_BUTTON drawVec
         in
-          (model, drawMsg, mouseX, mouseY)
+          (model, drawMsg)
         end
     | NO_TRIANGLE =>
         (case #triangles model of
@@ -135,19 +153,21 @@ struct
                  DRAW_TRIANGLES_AND_BUTTONS
                    {triangles = newTriangleVec, buttons = drawVec}
              in
-               (model, drawMsg, mouseX, mouseY)
+               (model, drawMsg)
              end
          | [] =>
              (* Can't undo, because there are no actions to undo. *)
-             (model, NO_DRAW, mouseX, mouseY))
+             (model, NO_DRAW))
 
-  fun update (model: app_type, mouseX, mouseY, inputMsg) =
+  fun update (model: app_type, inputMsg) =
     case inputMsg of
       MOUSE_MOVE {x = mouseX, y = mouseY} =>
-        mouseMoveOrRelease (model, mouseX, mouseY)
-    | MOUSE_LEFT_RELEASE => mouseMoveOrRelease (model, mouseX, mouseY)
-    | MOUSE_LEFT_CLICK => mouseLeftClick (model, mouseX, mouseY)
+        let val model = AppWith.mousePosition (model, mouseX, mouseY)
+        in mouseMoveOrRelease model
+        end
+    | MOUSE_LEFT_RELEASE => mouseMoveOrRelease model
+    | MOUSE_LEFT_CLICK => mouseLeftClick model
     | RESIZE_WINDOW {width, height} =>
-        resizeWindow (model, mouseX, mouseY, width, height)
-    | UNDO_ACTION => undoAction (model, mouseX, mouseY)
+        resizeWindow (model, width, height)
+    | UNDO_ACTION => undoAction model
 end
diff --git a/functional-core/app-with.sml b/functional-core/app-with.sml
index d95d720..e062ecd 100644
--- a/functional-core/app-with.sml
+++ b/functional-core/app-with.sml
@@ -22,6 +22,9 @@ sig
     * Real32.real
     * (Real32.real * Real32.real)
     -> AppType.app_type
+
+  val mousePosition: AppType.app_type * Real32.real * Real32.real
+                     -> AppType.app_type
 end
 
 structure AppWith :> APP_WITH =
@@ -40,7 +43,10 @@ struct
         , windowHeight
         , graphLines
         , undo
+        , mouseX
+        , mouseY
         } = app
+
       val newUndo = xyTuple :: undo
     in
       { triangleStage = newTriangleStage
@@ -51,6 +57,8 @@ struct
       , windowHeight = windowHeight
       , graphLines = graphLines
       , undo = newUndo
+      , mouseX = mouseX
+      , mouseY = mouseY
       }
     end
 
@@ -65,6 +73,8 @@ struct
         , windowHeight
         , graphLines
         , undo
+        , mouseX
+        , mouseY
         } = app
     in
       { triangleStage = newTriangleStage
@@ -75,6 +85,8 @@ struct
       , windowHeight = windowHeight
       , graphLines = graphLines
       , undo = undo
+      , mouseX = mouseX
+      , mouseY = mouseY
       }
     end
 
@@ -90,6 +102,8 @@ struct
         , windowHeight
         , graphLines
         , undo
+        , mouseX
+        , mouseY
         } = app
     in
       { triangleStage = newTriangleStage
@@ -100,6 +114,8 @@ struct
       , windowHeight = windowHeight
       , graphLines = graphLines
       , undo = undo
+      , mouseX = mouseX
+      , mouseY = mouseY
       }
     end
 
@@ -115,6 +131,8 @@ struct
         , windowHeight
         , graphLines
         , undo
+        , mouseX
+        , mouseY
         } = app
 
       val newTriangle = {x1 = x1, y1 = y1, x2 = x2, y2 = y2, x3 = x3, y3 = y3}
@@ -123,12 +141,14 @@ struct
     in
       { triangleStage = NO_TRIANGLE
       , triangles = newTriangles
+      , undo = newUndo
       , xClickPoints = xClickPoints
       , yClickPoints = yClickPoints
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , graphLines = graphLines
-      , undo = newUndo
+      , mouseX = mouseX
+      , mouseY = mouseY
       }
     end
 
@@ -145,6 +165,8 @@ struct
         , triangles
         , triangleStage
         , undo
+        , mouseX
+        , mouseY
         } = app
       val xClickPoints = ClickPoints.generate (wStart, wFinish)
       val yClickPoints = ClickPoints.generate (hStart, hFinish)
@@ -160,6 +182,8 @@ struct
       , windowWidth = windowWidth
       , windowHeight = windowHeight
       , undo = undo
+      , mouseX = mouseX
+      , mouseY = mouseY
       }
     end
 
@@ -185,4 +209,33 @@ struct
         helpWindowResize
           (app, windowWidth, windowHeight, 0, windowWidth, hStart, hFinish)
       end
+
+  fun mousePosition (app: app_type, mouseX, mouseY) =
+    let
+      val
+        { mouseX = _
+        , mouseY = _
+        , triangles
+        , triangleStage
+        , xClickPoints
+        , yClickPoints
+        , windowWidth
+        , windowHeight
+        , graphLines
+        , undo
+        } = app
+
+    in
+      { mouseX = mouseX
+      , mouseY = mouseY
+      , triangles = triangles
+      , triangleStage = triangleStage
+      , xClickPoints = xClickPoints
+      , yClickPoints = yClickPoints
+      , windowWidth = windowWidth
+      , windowHeight = windowHeight
+      , graphLines = graphLines
+      , undo = undo
+      }
+    end
 end
diff --git a/imperative-shell/event-loop.sml b/imperative-shell/event-loop.sml
index 0b070e8..3736efc 100644
--- a/imperative-shell/event-loop.sml
+++ b/imperative-shell/event-loop.sml
@@ -4,18 +4,17 @@ struct
   open DrawMessage
 
   local
-    fun loop (inputMailbox, drawMailbox, mouseX, mouseY, model) =
+    fun loop (inputMailbox, drawMailbox, model) =
       let
         val inputMsg = Mailbox.recv inputMailbox
-        val (model, drawMsg, mouseX, mouseY) =
-          AppUpdate.update (model, mouseX, mouseY, inputMsg)
+        val (model, drawMsg) = AppUpdate.update (model, inputMsg)
         val _ = Mailbox.send (drawMailbox, drawMsg)
       in
-        loop (inputMailbox, drawMailbox, mouseX, mouseY, model)
+        loop (inputMailbox, drawMailbox, model)
       end
   in
     fun update (inputMailbox, drawMailbox, initial) =
-      loop (inputMailbox, drawMailbox, 0.0, 0.0, initial)
+      loop (inputMailbox, drawMailbox, initial)
   end
 
   fun draw