complete implementation of rightwards navigation (viL)

fcore/cursor.sml

@@ -0,0 +1,30 @@
+structure Cursor =
+struct
+  (* Prerequisite: lineGap is moved to requested idx first *)
+  fun viL (lineGap: LineGap.t, cursorIdx) =
+    let
+      val {rightStrings, idx = bufferIdx, ...} = lineGap
+    in
+      case rightStrings of
+        hd :: tl =>
+          let
+            (* idx relative to this string *)
+            val strIdx = cursorIdx - bufferIdx
+          in
+            if strIdx < String.size hd - 2 then
+              (* increment if there is a character after where cursor is *)
+              cursorIdx + 1
+            else
+              (case tl of
+                 _ :: _ =>
+                   (* if there is another string after current head, we can increment cursorIdx *)
+                   bufferIdx + String.size hd - 1
+               | _ =>
+                   (* if there is no string after current head, return original cursorIdx *)
+                   cursorIdx)
+          end
+      | [] =>
+          (* return original cursorIdx if there is nothing to the right *)
+          cursorIdx
+    end
+end