add ability to move from normal mode to move mode, and from move mode back to normal mode

fcore/move-mode.sml

@@ -7,9 +7,6 @@ struct
 
   (* todo: resize message, escape button to go back to normal mode *)
 
-  fun makeBlankYAxis length =
-    Vector.tabulate (length, fn _ => {r = 0, g = 0, b = 0, a = 0})
-
   fun getDrawMsg (model: app_type) =
     let
       val
@@ -40,6 +37,9 @@ struct
       (model, [DRAW drawMsg])
     end
 
+  fun makeBlankYAxis length =
+    Vector.tabulate (length, fn _ => {r = 0, g = 0, b = 0, a = 0})
+
   fun moveImageUp (model: app_type) =
     let
       val {squares, ...} = model
@@ -79,8 +79,10 @@ struct
       val squares =
         Vector.mapi
           (fn (idx, yAxis) =>
-             if idx = 0 then makeBlankYAxis (Vector.length squares)
-             else Vector.sub (squares, idx - 1)) squares
+             if idx + 1 = Vector.length squares then
+               makeBlankYAxis (Vector.length squares)
+             else
+               Vector.sub (squares, idx + 1)) squares
 
       val model = AppWith.squares (model, squares)
     in
@@ -94,21 +96,25 @@ struct
       val squares =
         Vector.mapi
           (fn (idx, yAxis) =>
-             if idx + 1 = Vector.length squares then
-               makeBlankYAxis (Vector.length squares)
-             else
-               Vector.sub (squares, idx + 1)) squares
+             if idx = 0 then makeBlankYAxis (Vector.length squares)
+             else Vector.sub (squares, idx - 1)) squares
 
       val model = AppWith.squares (model, squares)
     in
       getDrawMsg model
     end
 
+  fun enterNormalMode model =
+    let val model = AppWith.mode (model, AppType.NORMAL_MODE)
+    in (model, [])
+    end
+
   fun update (model, inputMsg) =
     case inputMsg of
       ARROW_UP => moveImageUp model
     | ARROW_DOWN => moveImageDown model
     | ARROW_LEFT => moveImageLeft model
     | ARROW_RIGHT => moveImageRight model
+    | KEY_ESC => enterNormalMode model
     | _ => (model, [])
 end