diff -r 2bf8cfc98c4d -r 9c1173a7e4cb src/Tools/VSCode/src/line.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Tools/VSCode/src/line.scala	Mon Dec 19 20:27:49 2016 +0100
@@ -0,0 +1,151 @@
+/*  Title:      Tools/VSCode/src/line.scala
+    Author:     Makarius
+
+Line-oriented text.
+*/
+
+package isabelle.vscode
+
+
+import isabelle._
+
+import scala.annotation.tailrec
+
+
+object Line
+{
+  /* position */
+
+  object Position
+  {
+    val zero: Position = Position(0, 0)
+  }
+
+  sealed case class Position(line: Int, column: Int)
+  {
+    def line1: Int = line + 1
+    def column1: Int = column + 1
+    def print: String = line1.toString + ":" + column1.toString
+
+    def compare(that: Position): Int =
+      line compare that.line match {
+        case 0 => column compare that.column
+        case i => i
+      }
+
+    private def advance[A](iterator: Iterator[A], is_newline: A => Boolean): Position =
+    {
+      var l = line
+      var c = column
+      for (x <- iterator) {
+        if (is_newline(x)) { l += 1; c = 0 } else c += 1
+      }
+      Position(l, c)
+    }
+
+    def advance(text: String): Position =
+      if (text.isEmpty) this else advance[Char](text.iterator, _ == '\n')
+
+    def advance_symbols(text: String): Position =
+      if (text.isEmpty) this else advance[Symbol.Symbol](Symbol.iterator(text), Symbol.is_newline _)
+
+    def advance_codepoints(text: String): Position =
+      if (text.isEmpty) this else advance[Int](Word.codepoint_iterator(text), _ == 10)
+  }
+
+
+  /* range (right-open interval) */
+
+  sealed case class Range(start: Position, stop: Position)
+  {
+    if (start.compare(stop) > 0)
+      error("Bad line range: " + start.print + ".." + stop.print)
+
+    def print: String = start.print + ".." + stop.print
+  }
+
+
+  /* document with newline as separator (not terminator) */
+
+  object Document
+  {
+    val empty: Document = new Document("", Nil)
+
+    def apply(lines: List[Line]): Document =
+      if (lines.isEmpty) empty
+      else new Document(lines.mkString("", "\n", ""), lines)
+
+    def apply(text: String): Document =
+      if (text.contains('\r'))
+        apply(Library.cat_lines(Library.split_lines(text).map(Library.trim_line(_))))
+      else if (text == "") Document.empty
+      else new Document(text, Library.split_lines(text).map(Line(_)))
+  }
+
+  final class Document private(val text: String, val lines: List[Line])
+  {
+    override def toString: String = text
+
+    override def equals(that: Any): Boolean =
+      that match {
+        case other: Document => lines == other.lines
+        case _ => false
+      }
+    override def hashCode(): Int = lines.hashCode
+
+    private def position(advance: (Position, String) => Position, offset: Text.Offset): Position =
+    {
+      @tailrec def move(i: Text.Offset, lines_count: Int, lines_rest: List[Line]): Position =
+      {
+        lines_rest match {
+          case Nil => require(i == 0); Position(lines_count, 0)
+          case line :: ls =>
+            val n = line.text.length
+            if (ls.isEmpty || i <= n) advance(Position(lines_count, 0), line.text.substring(n - i))
+            else move(i - (n + 1), lines_count + 1, ls)
+        }
+      }
+      move(offset, 0, lines)
+    }
+
+    def position(i: Text.Offset): Position = position(_.advance(_), i)
+    def position_symbols(i: Text.Offset): Position = position(_.advance_symbols(_), i)
+    def position_codepoints(i: Text.Offset): Position = position(_.advance_codepoints(_), i)
+
+    // FIXME symbols, codepoints
+    def offset(pos: Position): Option[Text.Offset] =
+    {
+      val l = pos.line
+      val c = pos.column
+      if (0 <= l && l < lines.length) {
+        val line_offset =
+          if (l == 0) 0
+          else (0 /: lines.take(l - 1))({ case (n, line) => n + line.text.length + 1 })
+        if (c <= lines(l).text.length) Some(line_offset + c) else None
+      }
+      else None
+    }
+  }
+
+
+  /* line text */
+
+  val empty: Line = new Line("")
+  def apply(text: String): Line = if (text == "") empty else new Line(text)
+}
+
+final class Line private(val text: String)
+{
+  require(text.forall(c => c != '\r' && c != '\n'))
+
+  lazy val length_symbols: Int = Symbol.iterator(text).length
+  lazy val length_codepoints: Int = Word.codepoint_iterator(text).length
+
+  override def equals(that: Any): Boolean =
+    that match {
+      case other: Line => text == other.text
+      case _ => false
+    }
+  override def hashCode(): Int = text.hashCode
+  override def toString: String = text
+}