in TextBuilder, forgot to build cursor when cursorIdx is over space, so now we build cursor when cursorIdx is over space

fcore/app-update.sml

@@ -19,14 +19,38 @@ struct
       (newApp, drawMsg)
     end
 
-  fun handleChr (app, chr) =
+  fun moveRight (app: app_type) =
     let
-      val chr = Char.toString chr ^ "\n"
-      val () = print chr
+      (* todo: proper implementation of moveRight
+       * currently, we also retrieve the newCursorIdx improperly.
+       * To do it properly, we have to look inside LineGap
+       * instead of just incrementing cursorIdx by 1.
+       * So:
+       * - Find newCursorIdx from LineGap
+       * *)
+
+      val {buffer, windowWidth, windowHeight, startLine, cursorIdx} = app
+
+      (* move LineGap to cursorIdx, which is necessary for finding newCursorIdx *)
+      val newBuffer = LineGap.goToIdx (cursorIdx, buffer)
+      (* todo: call to retrieve newCursorIdx should be below *)
+      val newCursorIdx = cursorIdx + 1
+
+      (* move LineGap to first line displayed on screen, and build new text *)
+      val newBuffer = LineGap.goToLine (startLine, newBuffer)
+      val drawMsg = TextBuilder.build
+        (startLine, cursorIdx, newBuffer, windowWidth, windowHeight)
+
+      val newApp = AppWith.bufferAndCursorIdx (app, newBuffer, newCursorIdx)
     in
-      (app, [])
+      (newApp, drawMsg)
     end
 
+  fun handleChr (app: app_type, chr) =
+    case chr of
+      #"l" => moveRight app
+    | _ => (app, [])
+
   fun update (app, msg) =
     case msg of
       RESIZE_EVENT (width, height) => resizeText (app, width, height)