src/Pure/General/linear_set.scala

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/General/linear_set.scala	Tue Sep 01 11:52:19 2009 +0200
@@ -0,0 +1,103 @@
+/*  Title:      Pure/General/linear_set.scala
+    Author:     Makarius
+
+Sets with canonical linear order, or immutable linked-lists.
+*/
+package isabelle
+
+
+object Linear_Set
+{
+  def empty[A]: Linear_Set[A] = new Linear_Set[A]
+  def apply[A](elems: A*): Linear_Set[A] =
+    (empty[A] /: elems) ((s, elem) => s + elem)
+
+  class Duplicate(s: String) extends Exception(s)
+  class Undefined(s: String) extends Exception(s)
+
+  private def make[A](first: Option[A], last: Option[A], b: Map[A, A]): Linear_Set[A] =
+    new Linear_Set[A] {
+      override val first_elem = first
+      override val last_elem = last
+      override val body = b
+    }
+}
+
+
+class Linear_Set[A] extends scala.collection.immutable.Set[A]
+{
+  /* representation */
+
+  val first_elem: Option[A] = None
+  val last_elem: Option[A] = None
+  val body: Map[A, A] = Map.empty
+
+
+  /* basic methods */
+
+  def next(elem: A) = body.get(elem)
+  def prev(elem: A) = body.find(_._2 == elem).map(_._1)
+  override def isEmpty: Boolean = !last_elem.isDefined
+  def size: Int = if (isEmpty) 0 else body.size + 1
+
+  def empty[B] = Linear_Set.empty[B]
+
+  def contains(elem: A): Boolean =
+    !isEmpty && (last_elem.get == elem || body.isDefinedAt(elem))
+
+  private def _insert_after(hook: Option[A], elem: A): Linear_Set[A] =
+    if (contains(elem)) throw new Linear_Set.Duplicate(elem.toString)
+    else hook match {
+      case Some(hook) =>
+        if (!contains(hook)) throw new Linear_Set.Undefined(hook.toString)
+        else if (body.isDefinedAt(hook))
+          Linear_Set.make(first_elem, last_elem, body - hook + (hook -> elem) + (elem -> body(hook)))
+        else Linear_Set.make(first_elem, Some(elem), body + (hook -> elem))
+      case None =>
+        if (isEmpty) Linear_Set.make(Some(elem), Some(elem), Map.empty)
+        else Linear_Set.make(Some(elem), last_elem, body + (elem -> first_elem.get))
+    }
+
+  def insert_after(hook: Option[A], elems: Seq[A]): Linear_Set[A] =
+    elems.reverse.foldLeft (this) ((ls, elem) => ls._insert_after(hook, elem))
+
+  def +(elem: A): Linear_Set[A] = _insert_after(last_elem, elem)
+
+  def delete_after(elem: Option[A]): Linear_Set[A] =
+    elem match {
+      case Some(elem) =>
+        if (!contains(elem)) throw new Linear_Set.Undefined(elem.toString)
+        else if (!body.isDefinedAt(elem)) throw new Linear_Set.Undefined(null)
+        else if (body(elem) == last_elem.get) Linear_Set.make(first_elem, Some(elem), body - elem)
+        else Linear_Set.make(first_elem, last_elem, body - elem - body(elem) + (elem -> body(body(elem))))
+      case None =>
+        if (isEmpty) throw new Linear_Set.Undefined(null)
+        else if (size == 1) empty
+        else Linear_Set.make(Some(body(first_elem.get)), last_elem, body - first_elem.get)
+    }
+
+  def delete_between(from: Option[A], to: Option[A]): Linear_Set[A] = {
+    if(!first_elem.isDefined) this
+    else {
+      val next = if (from == last_elem) None
+                 else if (from == None) first_elem
+                 else from.map(body(_))
+      if (next == to) this
+      else delete_after(from).delete_between(from, to)
+    }
+  }
+
+  def -(elem: A): Linear_Set[A] =
+    if (!contains(elem)) throw new Linear_Set.Undefined(elem.toString)
+    else delete_after(body find (p => p._2 == elem) map (p => p._1))
+
+  def elements = new Iterator[A] {
+    private var next_elem = first_elem
+    def hasNext = next_elem.isDefined
+    def next = {
+      val elem = next_elem.get
+      next_elem = if (body.isDefinedAt(elem)) Some(body(elem)) else None
+      elem
+    }
+  }
+}
\ No newline at end of file