// -----------------------------------------------------------------------------
//
//  Scalax - The Scala Community Library
//  Copyright (c) 2005-8 The Scalax Project. All rights reserved.
//
//  The primary distribution site is http://scalax.scalaforge.org/
//
//  This software is released under the terms of the Revised BSD License.
//  There is NO WARRANTY.  See the file LICENSE for the full text.
//
// -----------------------------------------------------------------------------

package scalax.rules;

/** Represents the combined value of two rules applied in sequence.
 *
 * @see the Scala parser combinator
 */
case class ~[+A, +B](_1 : A, _2 : B) {
  override def toString = "(" + _1 + " ~ " + _2 + ")"
}
  
sealed abstract class Result[+Out, +A, +X] {
  def map[B](f : A => B) : Result[Out, B, X]
  def mapOut[Out2](f : Out => Out2) : Result[Out2, A, X]
  def map[Out2, B](f : (Out, A) => (Out2, B)) : Result[Out2, B, X]
  def flatMap[Out2, B](f : (Out, A) => Result[Out2, B, Nothing]) : Result[Out2, B, X]
  def orElse[Out2 >: Out, B >: A](other : => Result[Out2, B, Nothing]) : Result[Out2, B, X]
}

case class Success[+Out, +A](out : Out, value : A) extends Result[Out, A, Nothing] {
  def map[B](f : A => B) = Success(out, f(value))
  def mapOut[Out2](f : Out => Out2) = Success(f(out), value)
  def map[Out2, B](f : (Out, A) => (Out2, B)) = f(out, value) match { case (out2, b) => Success(out2, b) }
  def flatMap[Out2, B](f : (Out, A) => Result[Out2, B, Nothing]) = f(out, value)
  def orElse[Out2 >: Out, B >: A](other : => Result[Out2, B, Nothing]) = this
}

case object Failure extends Result[Nothing, Nothing, Nothing] {
  def map[B](f : Nothing => B) = this
  def mapOut[Out2](f : Nothing => Out2) = this
  def map[Out2, B](f : (Nothing, Nothing) => (Out2, B)) = this
  def flatMap[Out2, B](f : (Nothing, Nothing) => Result[Out2, B, Nothing]) = this
  def orElse[Out2, B](other : => Result[Out2, B, Nothing]) = other
}

case class Error[+X](x : X) extends Result[Nothing, Nothing, X] {
  def map[B](f : Nothing => B) = this
  def mapOut[Out2](f : Nothing => Out2) = this
  def map[Out2, B](f : (Nothing, Nothing) => (Out2, B)) = this
  def flatMap[Out2, B](f : (Nothing, Nothing) => Result[Out2, B, Nothing]) = this
  def orElse[Out2, B](other : => Result[Out2, B, Nothing]) = other
}