add count to 'x' command, allowing [count] chars to be deleted

fcore/app-update.sml

@@ -233,9 +233,23 @@ struct
     end
 
   (* equivalent of vi's 'x' command *)
-  fun deleteChr (app: app_type, count) =
+  fun helpDeleteChr (app: app_type, buffer, cursorIdx, count) =
+    if count = 0 then
+      let
+        val {startLine, windowWidth, windowHeight, ...} = app
+
+        val buffer = LineGap.goToLine (startLine, buffer)
+        val newApp = AppWith.bufferAndCursorIdx
+          (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
+
+        val drawMsg = 
+          TextBuilder.build
+            (startLine, cursorIdx, buffer, windowWidth, windowHeight)
+      in
+        (newApp, drawMsg)
+      end
+    else
       let
-      val {buffer, cursorIdx, startLine, windowWidth, windowHeight, ...} = app
         val buffer = LineGap.goToIdx (cursorIdx, buffer)
 
         (* Explanation of how Vi's 'x' command behaves:
@@ -268,33 +282,20 @@ struct
               orelse cursorIdx = 0 then
                 cursorIdx
               else cursorIdx - 1
-
-           val buffer = LineGap.goToLine (startLine, buffer)
-           val newApp = AppWith.bufferAndCursorIdx
-             (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
-
-           val drawMsg = 
-             TextBuilder.build
-               (startLine, cursorIdx, buffer, windowWidth, windowHeight)
           in
-           (newApp, drawMsg)
+            helpDeleteChr (app, buffer, cursorIdx, count - 1)
           end
        else
          let
            val buffer = LineGap.delete (cursorIdx, 1, buffer)
-
-          val buffer = LineGap.goToLine (startLine, buffer)
-          val newApp = AppWith.bufferAndCursorIdx
-            (app, buffer, cursorIdx, NORMAL_MODE "", startLine)
-
-          val drawMsg = 
-            TextBuilder.build
-              (startLine, cursorIdx, buffer, windowWidth, windowHeight)
          in
-        (newApp, drawMsg)
+            helpDeleteChr (app, buffer, cursorIdx, count - 1)
          end
       end
 
+  fun deleteChr (app: app_type, count) =
+    helpDeleteChr (app, #buffer app, #cursorIdx app, count)
+
   (* number of characters which are integers *)
   fun getNumLength (pos, str) =
     if pos = String.size str then