diff -r e10547372c41 -r e596a0b71f3c src/Pure/Thy/change.scala
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Thy/change.scala	Mon Jan 11 23:00:05 2010 +0100
@@ -0,0 +1,42 @@
+/*
+ * Changes of plain text
+ *
+ * @author Fabian Immler, TU Munich
+ * @author Makarius
+ */
+
+package isabelle
+
+
+class Change(
+  val id: Isar_Document.Document_ID,
+  val parent: Option[Change],
+  val edits: List[Text_Edit],
+  val result: Future[(List[Document.Edit], Document)])
+{
+  def ancestors: Iterator[Change] = new Iterator[Change]
+  {
+    private var state: Option[Change] = Some(Change.this)
+    def hasNext = state.isDefined
+    def next =
+      state match {
+        case Some(change) => state = change.parent; change
+        case None => throw new NoSuchElementException("next on empty iterator")
+      }
+  }
+
+  def join_document: Document = result.join._2
+  def is_assigned: Boolean = result.is_finished && join_document.assignment.is_finished
+
+  def edit(session: Session, edits: List[Text_Edit]): Change =
+  {
+    val new_id = session.create_id()
+    val result: Future[(List[Document.Edit], Document)] =
+      Future.fork {
+        val old_doc = join_document
+        old_doc.await_assignment
+        Document.text_edits(session, old_doc, new_id, edits)
+      }
+    new Change(new_id, Some(this), edits, result)
+  }
+}
\ No newline at end of file