src/Pure/General/value.scala

clarified rendering: entity acts as atomic notation / expression;

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

Plain values, represented as string.
*/

package isabelle


object Value {
  object Boolean {
    def apply(x: scala.Boolean): java.lang.String = x.toString
    def unapply(s: java.lang.String): Option[scala.Boolean] =
      s match {
        case "true" => Some(true)
        case "false" => Some(false)
        case _ => None
      }
    def parse(s: java.lang.String): scala.Boolean =
      unapply(s) getOrElse error("Bad boolean: " + quote(s))
  }

  object Nat {
    def unapply(bs: Bytes): Option[scala.Int] =
      if (bs.byte_iterator.forall(Symbol.is_ascii_digit)) unapply(bs.text)
      else None
    def unapply(s: java.lang.String): Option[scala.Int] =
      s match {
        case Int(n) if n >= 0 => Some(n)
        case _ => None
      }
    def parse(s: java.lang.String): scala.Int =
      unapply(s) getOrElse error("Bad natural number: " + quote(s))
  }

  object Int {
    def apply(x: scala.Int): java.lang.String = Library.signed_string_of_int(x)
    def unapply(s: java.lang.String): Option[scala.Int] =
      try { Some(Integer.parseInt(s)) }
      catch { case _: NumberFormatException => None }
    def parse(s: java.lang.String): scala.Int =
      unapply(s) getOrElse error("Bad integer: " + quote(s))
  }

  object Long {
    def apply(x: scala.Long): java.lang.String = Library.signed_string_of_long(x)
    def unapply(s: java.lang.String): Option[scala.Long] =
      try { Some(java.lang.Long.parseLong(s)) }
      catch { case _: NumberFormatException => None }
    def parse(s: java.lang.String): scala.Long =
      unapply(s) getOrElse error("Bad long integer: " + quote(s))
  }

  object Double {
    def apply(x: scala.Double): java.lang.String = x.toString
    def unapply(s: java.lang.String): Option[scala.Double] =
      try { Some(java.lang.Double.parseDouble(s)) }
      catch { case _: NumberFormatException => None }
    def parse(s: java.lang.String): scala.Double =
      unapply(s) getOrElse error("Bad real: " + quote(s))
  }

  object Seconds {
    def apply(t: Time): java.lang.String = {
      val s = t.seconds
      if (s.toInt.toDouble == s) s.toInt.toString else t.toString
    }
    def unapply(s: java.lang.String): Option[Time] = Double.unapply(s).map(Time.seconds)
    def parse(s: java.lang.String): Time =
      unapply(s) getOrElse error("Bad real (for seconds): " + quote(s))
  }
}