src/Pure/General/position.scala

decode_term: some context-sensitive markup;
more informative Markup.entity and Name_Space.markup_entry;
Markup.const: use "constant" to make it coincide with name space kind;

/*  Title:      Pure/General/position.scala
    Author:     Makarius

Position properties.
*/

package isabelle


object Position
{
  type T = List[(String, String)]

  val Line = new Markup.Int_Property(Markup.LINE)
  val Offset = new Markup.Int_Property(Markup.OFFSET)
  val End_Offset = new Markup.Int_Property(Markup.END_OFFSET)
  val File = new Markup.Property(Markup.FILE)
  val Id = new Markup.Long_Property(Markup.ID)

  object Range
  {
    def apply(range: Text.Range): T = Offset(range.start) ++ Offset(range.stop)
    def unapply(pos: T): Option[Text.Range] =
      (Offset.unapply(pos), End_Offset.unapply(pos)) match {
        case (Some(start), Some(stop)) if start <= stop => Some(Text.Range(start, stop))
        case (Some(start), None) => Some(Text.Range(start, start + 1))
        case _ => None
      }
  }

  object Id_Range
  {
    def unapply(pos: T): Option[(Long, Text.Range)] =
      (pos, pos) match {
        case (Id(id), Range(range)) => Some((id, range))
        case _ => None
      }
  }

  def purge(props: T): T = props.filterNot(p => Markup.POSITION_PROPERTIES(p._1))
}