/*  Title:      Pure/library.scala

    Author:     Makarius

Basic library.

*/

package isabelle

import java.lang.System

object Library

{

  /* reverse CharSequence */

  class Reverse(text: CharSequence, start: Int, end: Int) extends CharSequence

  {

    require(0 <= start && start <= end && end <= text.length)

    def this(text: CharSequence) = this(text, 0, text.length)

    def length: Int = end - start

    def charAt(i: Int): Char = text.charAt(end - i - 1)

    def subSequence(i: Int, j: Int): CharSequence =

      if (0 <= i && i <= j && j <= length) new Reverse(text, end - j, end - i)

      else throw new IndexOutOfBoundsException

    override def toString: String =

    {

      val buf = new StringBuilder(length)

      for (i <- 0 until length)

        buf.append(charAt(i))

      buf.toString

    }

  }

  /* timing */

  def timeit[A](e: => A) =

  {

    val start = System.currentTimeMillis()

    val result = Exn.capture(e)

    val stop = System.currentTimeMillis()

    System.err.println((stop - start) + "ms elapsed time")

    Exn.release(result)

  }

}