delete-chr (equivalent of vi's 'x' cmd) works fine now, except when deleting from the very first line, where first line may become invisible temporarily. I am not sure why that is happening but will find out.

fcore/app-update.sml

@@ -257,8 +257,7 @@ struct
          * when cursor is at start of line, and next chr is line break *)
         clearMode app
       else if cursorIsStart then
-        let val _ = print "260\n" in
+        clearMode app
-        clearMode app end
       else if nextIsEnd then
          let
           (* delete char at cursor and then decrement cursorIdx by 1
@@ -280,8 +279,6 @@ struct
          in
            (newApp, drawMsg)
          end
-      else if Cursor.isPrevChrStartOfLine (buffer, cursorIdx) then
-        clearMode app
       else
         let
           val newBuffer = LineGap.delete (cursorIdx, 1, buffer)