begin coding functionality to move squares

fcore/move-mode.sml

@@ -0,0 +1,35 @@
+structure MoveMode =
+struct
+  open AppType
+  open InputMessage
+
+  fun makeBlankYAxis length =
+    Vector.tabulate (length, fn _ => {r = 0, g = 0, b = 0, a = 0})
+
+  fun moveImageUp (model: app_type) =
+    let
+      val {squares, ...} = model
+
+      val squares =
+        Vector.mapi
+          (fn (idx, yAxis) =>
+             if idx + 1 < Vector.length squares then
+               Vector.sub (squares, idx + 1)
+             else
+               makeBlankYAxis (Vector.length yAxis)) squares
+
+      val model = AppWith.squares (model, squares)
+    in
+      (model, [])
+    end
+
+  fun update (model, inputMsg) =
+    case inputMsg of
+      ARROW_UP => moveImageUp model
+    (*
+    | ARROW_LEFT => moveImageLeft model
+    | ARROW_RIGHT => moveImageRight model
+    | ARROW_DOWN => moveImageDown model
+    *)
+    | _ => (model, [])
+end