add mutually recursive functions to skip to start of next line in text builder

fcore/text-builder.sml

@@ -94,7 +94,102 @@ struct
       , #cursorOnCharB env
       )
 
-  fun buildTextString
+  structure TextWithCursor =
+  struct
+    fun goToFirstLineAfter
+      (stl, ltl, posY, lineNumber, absIdx, cursorIdx, env, acc) =
+      case (stl, ltl) of
+        (shd :: stl, lhd :: ltl) =>
+          if Vector.length lhd > 0 then
+            let
+              val lineOffset = Vector.sub (lhd, 0)
+              val strPos = lineOffset + 1
+              val absIdx = absIdx + strPos
+              val posY = posY + TC.ySpace
+              val lineNumber = lineNumber + 1
+            in
+              build
+                ( strPos
+                , shd
+                , stl
+                , lhd
+                , ltl
+                , #startX env
+                , posY
+                , 0
+                , lineNumber
+                , absIdx
+                , cursorIdx
+                , env : env_data
+                , acc
+                )
+            end
+          else
+            (* keep looping until we find a linebreak *)
+            goToFirstLineAfter
+              ( stl
+              , ltl
+              , posY
+              , lineNumber
+              , absIdx + String.size shd
+              , cursorIdx
+              , env
+              , acc
+              )
+      | (_, _) => acc
+
+    and skipToColumnStart
+      (pos, str, stl, line, ltl, posY, lineNumber, absIdx, cursorIdx, env, acc) =
+      if Vector.length line = 0 then
+        let
+          (* get index of buffer after this string *)
+          val absIdx = absIdx - pos
+          val absIdx = absIdx + String.size str
+        in
+          goToFirstLineAfter
+            (stl, ltl, posY, lineNumber, absIdx, cursorIdx, env, acc)
+        end
+      else
+        (* bin search lines *)
+        let
+          val searchPos = BinSearch.equalOrMore (pos + 1, searchList)
+        in
+          if searchPos = Vector.length lines then
+            (* next line is not in this node *)
+            let
+              val absIdx = absIdx - pos
+              val absIdx = absIdx + String.size str
+            in
+              goToFirstLineAfter
+                (stl, ltl, posY, lineNumber, absIdx, cursorIdx, env, acc)
+            end
+          else
+            let
+              val lineOffset = Vector.sub (line, searchPos)
+              val newStrPos = lineOffset + 1
+              val absIdx = absIdx - pos + newStrPos
+              val posY = posY + TC.ySpace
+              val lineNumber = lineNumber + 1
+            in
+              build
+                ( newStrPos
+                , str
+                , stl
+                , line
+                , ltl
+                , #startX env
+                , posY
+                , 0
+                , lineNumber
+                , absIdx
+                , cursorIdx
+                , env
+                , acc
+                )
+            end
+        end
+
+    and build
       ( pos
       , str
       , stl
@@ -112,7 +207,7 @@ struct
       if pos = String.size str then
         case (stl, ltl) of
           (str :: stl, line :: ltl) =>
-          buildTextString
+            build
               ( 0
               , str
               , stl
@@ -150,7 +245,7 @@ struct
                 if absIdx = cursorIdx then makeCursor (posX, posY, env) :: acc
                 else acc
             in
-            buildTextString
+              build
                 ( pos + 1
                 , str
                 , stl
@@ -177,7 +272,7 @@ struct
               if nextLineNumber > #lastLineNumber env then
                 acc
               else
-              buildTextString
+                build
                   ( pos + 1
                   , str
                   , stl
@@ -203,7 +298,7 @@ struct
                 else
                   makeCursor (chr, posX, posY, env) :: acc
             in
-            buildTextString
+              build
                 ( pos + 1
                 , str
                 , stl
@@ -219,6 +314,7 @@ struct
                 , acc
                 )
             end
+  end
 
   fun buildTextString
     ( pos