wrap helper functions to 'insert' inside 'local ... in ... end' to semantically convey that these helper functions are never used elsewhere

src/line_gap.sml

@@ -107,6 +107,8 @@ struct
       else helpBinSearch (findNum, lines, 0, Vector.length lines - 1)
   end
 
+  (* Helper functions for insertion operation. *)
+  local
     fun insWhenIdxAndCurIdxAreEqual
       ( newString
       , newLines
@@ -247,7 +249,8 @@ struct
                           Vector.sub (newLines, (idx - midpoint) - 1)
                           + String.size strSub1
                         else
-                        Vector.sub (leftLinesHd, (idx - Vector.length newLines))
+                          Vector.sub
+                            (leftLinesHd, (idx - Vector.length newLines))
                           + String.size newString
                     )
                 else
@@ -271,7 +274,8 @@ struct
               (* Implicit: a binSearch match was found. *)
               let
                 val newLeftLinesLength = midpoint + 1 + Vector.length newLines
-              val newLeftLines = Vector.tabulate (newLeftLinesLength, fn idx =>
+                val newLeftLines =
+                  Vector.tabulate (newLeftLinesLength, fn idx =>
                     if idx <= midpoint then
                       Vector.sub (leftLinesHd, idx)
                     else
@@ -414,10 +418,16 @@ struct
                * under the limit. 
                * *)
               (case (rightStrings, rightLines) of
-               (rightStringsHd :: rightStringsTl, rightLinesHd :: rightLinesTl) =>
+                 ( rightStringsHd :: rightStringsTl
+                 , rightLinesHd :: rightLinesTl
+                 ) =>
                    if
                      isInLimit
-                     (leftStringsHd, rightStringsHd, leftLinesHd, rightLinesHd)
+                       ( leftStringsHd
+                       , rightStringsHd
+                       , leftLinesHd
+                       , rightLinesHd
+                       )
                    then
                      let
                        val prevLine = curLine - Vector.length leftLinesHd
@@ -432,8 +442,9 @@ struct
                                  Vector.sub (leftLinesHd, idx)
                                else
                                  Vector.sub
-                                 (rightLinesHd, idx - Vector.length leftLinesHd)
+                                   ( rightLinesHd
-                               + String.size leftStringsHd
+                                   , idx - Vector.length leftLinesHd
+                                   ) + String.size leftStringsHd
                            )
                      in
                        moveLeftAndIns
@@ -568,7 +579,8 @@ struct
           then
             (* Join three strings together. *)
             let
-            val newRightStringsHd = String.concat [strSub1, newString, strSub2]
+              val newRightStringsHd =
+                String.concat [strSub1, newString, strSub2]
               val newRightLinesHd =
                 if Vector.length rightLinesHd > 0 then
                   Vector.tabulate
@@ -743,7 +755,11 @@ struct
                  (leftStringsHd :: leftStringsTl, leftLinesHd :: leftLinesTl) =>
                    if
                      isInLimit
-                     (leftStringsHd, rightStringsHd, leftLinesHd, rightLinesHd)
+                       ( leftStringsHd
+                       , rightStringsHd
+                       , leftLinesHd
+                       , rightLinesHd
+                       )
                    then
                      let
                        val nextLine = curLine + Vector.length rightLinesHd
@@ -757,8 +773,9 @@ struct
                                  Vector.sub (leftLinesHd, idx)
                                else
                                  Vector.sub
-                                 (rightLinesHd, idx - Vector.length leftLinesHd)
+                                   ( rightLinesHd
-                               + String.size leftStringsHd
+                                   , idx - Vector.length leftLinesHd
+                                   ) + String.size leftStringsHd
                            )
                      in
                        moveRightAndIns
@@ -873,7 +890,7 @@ struct
           , rightStrings
           , rightLines
           )
-
+  in
     fun insert (idx, newString, buffer: t) =
       let
         val newLines = countLineBreaks newString
@@ -890,6 +907,7 @@ struct
           , #rightLines buffer
           )
       end
+  end
 
 
   (* TEST CODE *)