/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2010, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala.util.parsing.input


/** An interface for streams of values that have positions.
 *
 * @author Martin Odersky, Adriaan Moors
 */
abstract class Reader[+T] {

  /** If this is a reader over character sequences, the underlying char sequence 
   *  If not, throws a <code>NoSuchMethodError</code> exception.
   */
  def source: java.lang.CharSequence = 
    throw new NoSuchMethodError("not a char sequence reader")

  def offset: Int =
    throw new NoSuchMethodError("not a char sequence reader")

   /** Returns the first element of the reader
    */
  def first: T

  /** Returns an abstract reader consisting of all elements except the first 
   * 
   * @return If <code>atEnd</code> is <code>true</code>, the result will be
   *         <code>this'; otherwise, it's a <code>Reader</code> containing
   *         more elements.
   */
  def rest: Reader[T]
  
  /** Returns an abstract reader consisting of all elements except the first
   *  <code>n</code> elements.
   */ 
  def drop(n: Int): Reader[T] = {
    var r: Reader[T] = this
    var cnt = n
    while (cnt > 0) {
      r = r.rest; cnt -= 1
    }
    r
  }

  /** The position of the first element in the reader
   */
  def pos: Position

  /** true iff there are no more elements in this reader 
   */
  def atEnd: Boolean
}
