src/Pure/PIDE/xml.scala

clarified treatment of empty markup;

/*  Title:      Pure/PIDE/xml.scala
    Author:     Makarius

Untyped XML trees and basic data representation.
*/

package isabelle

import scala.annotation.tailrec


object XML {
  /** XML trees **/

  /* datatype representation */

  type Attribute = Properties.Entry
  type Attributes = Properties.T

  trait Trav
  case class End(name: String) extends Trav

  sealed abstract class Tree extends Trav {
    override def toString: String = string_of_tree(this)
  }
  type Body = List[Tree]
  case class Elem(markup: Markup, body: Body) extends Tree with Trav {
    private lazy val hash: Int = (markup, body).hashCode()
    override def hashCode(): Int = hash

    def name: String = markup.name

    def update_attributes(more_attributes: Attributes): Elem =
      if (more_attributes.isEmpty) this
      else Elem(markup.update_properties(more_attributes), body)

    def + (att: Attribute): Elem = Elem(markup + att, body)
  }
  case class Text(content: String) extends Tree with Trav {
    private lazy val hash: Int = content.hashCode()
    override def hashCode(): Int = hash
  }

  def elem(markup: Markup): XML.Elem = XML.Elem(markup, Nil)
  def elem(name: String, body: Body): XML.Elem = XML.Elem(Markup(name, Nil), body)
  def elem(name: String): XML.Elem = XML.Elem(Markup(name, Nil), Nil)

  val no_text: Text = Text("")
  val newline: Text = Text("\n")

  def string(s: String): Body = if (s.isEmpty) Nil else List(Text(s))

  def enclose(bg: String, en:String, body: Body): Body =
    string(bg) ::: body ::: string(en)

  trait Traversal {
    def text(s: String): Unit
    def elem(markup: Markup, end: Boolean = false): Unit
    def end_elem(name: String): Unit

    def traverse(trees: List[Tree]): Unit = {
      @tailrec def trav(list: List[Trav]): Unit =
        list match {
          case Nil =>
          case Text(s) :: rest => text(s); trav(rest)
          case Elem(markup, body) :: rest =>
            if (markup.is_empty) trav(body ::: rest)
            else if (body.isEmpty) { elem(markup, end = true); trav(rest) }
            else { elem(markup); trav(body ::: End(markup.name) :: rest) }
          case End(name) :: rest => end_elem(name); trav(rest)
          case _ :: _ => ???
        }
      trav(trees)
    }
  }


  /* name space */

  object Namespace {
    def apply(prefix: String, target: String): Namespace =
      new Namespace(prefix, target)
  }

  final class Namespace private(prefix: String, target: String) {
    def apply(name: String): String = prefix + ":" + name
    val attribute: XML.Attribute = ("xmlns:" + prefix, target)

    override def toString: String = attribute.toString
  }


  /* wrapped elements */

  val XML_ELEM = "xml_elem"
  val XML_NAME = "xml_name"
  val XML_BODY = "xml_body"

  object Wrapped_Elem {
    def apply(markup: Markup, body1: Body, body2: Body): XML.Elem =
      XML.Elem(Markup(XML_ELEM, (XML_NAME, markup.name) :: markup.properties),
        XML.Elem(Markup(XML_BODY, Nil), body1) :: body2)

    def unapply(tree: Tree): Option[(Markup, Body, Body)] =
      tree match {
        case
          XML.Elem(Markup(XML_ELEM, (XML_NAME, name) :: props),
            XML.Elem(Markup(XML_BODY, Nil), body1) :: body2) =>
          Some(Markup(name, props), body1, body2)
        case _ => None
      }
  }

  object Root_Elem {
    def apply(body: Body): XML.Elem = XML.Elem(Markup(XML_ELEM, Nil), body)
    def unapply(tree: Tree): Option[Body] =
      tree match {
        case XML.Elem(Markup(XML_ELEM, Nil), body) => Some(body)
        case _ => None
      }
  }


  /* traverse text */

  def traverse_text[A](body: Body)(a: A)(op: (A, String) => A): A = {
    def traverse(x: A, t: Tree): A =
      t match {
        case XML.Wrapped_Elem(_, _, ts) => ts.foldLeft(x)(traverse)
        case XML.Elem(_, ts) => ts.foldLeft(x)(traverse)
        case XML.Text(s) => op(x, s)
      }
    body.foldLeft(a)(traverse)
  }

  def text_length(body: Body): Int = traverse_text(body)(0) { case (n, s) => n + s.length }
  def symbol_length(body: Body): Int = traverse_text(body)(0) { case (n, s) => n + Symbol.length(s) }


  /* text content */

  def content(body: Body): String = {
    val text = new StringBuilder(text_length(body))
    traverse_text(body)(()) { case (_, s) => text.append(s) }
    text.toString
  }

  def content(tree: Tree): String = content(List(tree))



  /** string representation **/

  val header: String = "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n"

  class Output(builder: StringBuilder) extends Traversal {
    def string(str: String, permissive: Boolean = false): Unit = {
      if (str == null) { builder ++= str }
      else {
        for (c <- str) {
          c match {
            case '<' => builder ++= "&lt;"
            case '>' => builder ++= "&gt;"
            case '&' => builder ++= "&amp;"
            case '"' if !permissive => builder ++= "&quot;"
            case '\'' if !permissive => builder ++= "&apos;"
            case _ => builder += c
          }
        }
      }
    }

    override def text(str: String): Unit = string(str)

    override def elem(markup: Markup, end: Boolean = false): Unit = {
      builder += '<'
      builder ++= markup.name
      for ((a, b) <- markup.properties) {
        builder += ' '
        builder ++= a
        builder += '='
        builder += '"'
        string(b)
        builder += '"'
      }
      if (end) builder += '/'
      builder += '>'
    }

    def end_elem(name: String): Unit = {
      builder += '<'
      builder += '/'
      builder ++= name
      builder += '>'
    }

    def result(ts: List[Tree]): String = { traverse(ts); builder.toString }
  }

  def string_of_body(body: Body): String =
    if (body.isEmpty) ""
    else new Output(new StringBuilder).result(body)

  def string_of_tree(tree: XML.Tree): String = string_of_body(List(tree))

  def text(s: String): String = string_of_tree(XML.Text(s))



  /** cache **/

  object Cache {
    def make(
        compress: Compress.Cache = Compress.Cache.make(),
        max_string: Int = isabelle.Cache.default_max_string,
        initial_size: Int = isabelle.Cache.default_initial_size): Cache =
      new Cache(compress, max_string, initial_size)

    val none: Cache = make(Compress.Cache.none, max_string = 0)
  }

  class Cache(val compress: Compress.Cache, max_string: Int, initial_size: Int)
  extends isabelle.Cache(max_string, initial_size) {
    protected def cache_props(x: Properties.T): Properties.T = {
      if (x.isEmpty) x
      else
        lookup(x) match {
          case Some(y) => y
          case None => store(x.map(p => (Library.isolate_substring(p._1).intern, cache_string(p._2))))
        }
    }

    protected def cache_markup(x: Markup): Markup = {
      lookup(x) match {
        case Some(y) => y
        case None =>
          x match {
            case Markup(name, props) =>
              store(Markup(cache_string(name), cache_props(props)))
          }
      }
    }

    protected def cache_tree(x: XML.Tree): XML.Tree = {
      lookup(x) match {
        case Some(y) => y
        case None =>
          x match {
            case XML.Elem(markup, body) =>
              store(XML.Elem(cache_markup(markup), cache_body(body)))
            case XML.Text(text) => store(XML.Text(cache_string(text)))
          }
      }
    }

    protected def cache_body(x: XML.Body): XML.Body = {
      if (x.isEmpty) x
      else
        lookup(x) match {
          case Some(y) => y
          case None => x.map(cache_tree)
        }
    }

    // support hash-consing
    def tree0(x: XML.Tree): XML.Tree =
      if (no_cache) x else synchronized { lookup(x) getOrElse store(x) }

    // main methods
    def props(x: Properties.T): Properties.T =
      if (no_cache) x else synchronized { cache_props(x) }
    def markup(x: Markup): Markup =
      if (no_cache) x else synchronized { cache_markup(x) }
    def tree(x: XML.Tree): XML.Tree =
      if (no_cache) x else synchronized { cache_tree(x) }
    def body(x: XML.Body): XML.Body =
      if (no_cache) x else synchronized { cache_body(x) }
    def elem(x: XML.Elem): XML.Elem =
      if (no_cache) x else synchronized { cache_tree(x).asInstanceOf[XML.Elem] }
  }



  /** XML as data representation language **/

  abstract class Error(s: String) extends Exception(s)
  class XML_Atom(s: String) extends Error(s)
  class XML_Body(body: XML.Body) extends Error("")

  object Encode {
    type T[A] = A => XML.Body
    type V[A] = PartialFunction[A, (List[String], XML.Body)]
    type P[A] = PartialFunction[A, List[String]]


    /* atomic values */

    def long_atom(i: Long): String = Library.signed_string_of_long(i)

    def int_atom(i: Int): String = Library.signed_string_of_int(i)

    def bool_atom(b: Boolean): String = if (b) "1" else "0"

    def unit_atom(u: Unit) = ""


    /* structural nodes */

    private def node(ts: XML.Body): XML.Tree = XML.Elem(Markup(":", Nil), ts)

    private def vector(xs: List[String]): XML.Attributes =
      xs.zipWithIndex.map({ case (x, i) => (int_atom(i), x) })

    private def tagged(tag: Int, data: (List[String], XML.Body)): XML.Tree =
      XML.Elem(Markup(int_atom(tag), vector(data._1)), data._2)


    /* representation of standard types */

    val tree: T[XML.Tree] = (t => List(t))

    val properties: T[Properties.T] =
      (props => List(XML.Elem(Markup(":", props), Nil)))

    val string: T[String] = (s => if (s.isEmpty) Nil else List(XML.Text(s)))

    val long: T[Long] = (x => string(long_atom(x)))

    val int: T[Int] = (x => string(int_atom(x)))

    val bool: T[Boolean] = (x => string(bool_atom(x)))

    val unit: T[Unit] = (x => string(unit_atom(x)))

    def pair[A, B](f: T[A], g: T[B]): T[(A, B)] =
      (x => List(node(f(x._1)), node(g(x._2))))

    def triple[A, B, C](f: T[A], g: T[B], h: T[C]): T[(A, B, C)] =
      (x => List(node(f(x._1)), node(g(x._2)), node(h(x._3))))

    def list[A](f: T[A]): T[List[A]] =
      (xs => xs.map((x: A) => node(f(x))))

    def option[A](f: T[A]): T[Option[A]] = {
      case None => Nil
      case Some(x) => List(node(f(x)))
    }

    def variant[A](fs: List[V[A]]): T[A] = {
      case x =>
        val (f, tag) = fs.iterator.zipWithIndex.find(p => p._1.isDefinedAt(x)).get
        List(tagged(tag, f(x)))
    }
  }

  object Decode {
    type T[A] = XML.Body => A
    type V[A] = PartialFunction[(List[String], XML.Body), A]
    type P[A] = PartialFunction[List[String], A]


    /* atomic values */

    def long_atom(s: String): Long =
      try { java.lang.Long.parseLong(s) }
      catch { case e: NumberFormatException => throw new XML_Atom(s) }

    def int_atom(s: String): Int =
      try { Integer.parseInt(s) }
      catch { case e: NumberFormatException => throw new XML_Atom(s) }

    def bool_atom(s: String): Boolean =
      if (s == "1") true
      else if (s == "0") false
      else throw new XML_Atom(s)

    def unit_atom(s: String): Unit =
      if (s == "") () else throw new XML_Atom(s)


    /* structural nodes */

    private def node(t: XML.Tree): XML.Body =
      t match {
        case XML.Elem(Markup(":", Nil), ts) => ts
        case _ => throw new XML_Body(List(t))
      }

    private def vector(atts: XML.Attributes): List[String] =
      atts.iterator.zipWithIndex.map(
        { case ((a, x), i) => if (int_atom(a) == i) x else throw new XML_Atom(a) }).toList

    private def tagged(t: XML.Tree): (Int, (List[String], XML.Body)) =
      t match {
        case XML.Elem(Markup(name, atts), ts) => (int_atom(name), (vector(atts), ts))
        case _ => throw new XML_Body(List(t))
      }


    /* representation of standard types */

    val tree: T[XML.Tree] = {
      case List(t) => t
      case ts => throw new XML_Body(ts)
    }

    val properties: T[Properties.T] = {
      case List(XML.Elem(Markup(":", props), Nil)) => props
      case ts => throw new XML_Body(ts)
    }

    val string: T[String] = {
      case Nil => ""
      case List(XML.Text(s)) => s
      case ts => throw new XML_Body(ts)
    }

    val long: T[Long] = (x => long_atom(string(x)))

    val int: T[Int] = (x => int_atom(string(x)))

    val bool: T[Boolean] = (x => bool_atom(string(x)))

    val unit: T[Unit] = (x => unit_atom(string(x)))

    def pair[A, B](f: T[A], g: T[B]): T[(A, B)] = {
      case List(t1, t2) => (f(node(t1)), g(node(t2)))
      case ts => throw new XML_Body(ts)
    }

    def triple[A, B, C](f: T[A], g: T[B], h: T[C]): T[(A, B, C)] = {
      case List(t1, t2, t3) => (f(node(t1)), g(node(t2)), h(node(t3)))
      case ts => throw new XML_Body(ts)
    }

    def list[A](f: T[A]): T[List[A]] =
      (ts => ts.map(t => f(node(t))))

    def option[A](f: T[A]): T[Option[A]] = {
      case Nil => None
      case List(t) => Some(f(node(t)))
      case ts => throw new XML_Body(ts)
    }

    def variant[A](fs: List[V[A]]): T[A] = {
      case List(t) =>
        val (tag, (xs, ts)) = tagged(t)
        val f =
          try { fs(tag) }
          catch { case _: IndexOutOfBoundsException => throw new XML_Body(List(t)) }
        f(xs, ts)
      case ts => throw new XML_Body(ts)
    }
  }
}