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package scalaz

import collection.generic.CanBuildFrom

/**
 * A Zero in type Z provides the identity element for the operation  { @link scalaz.Semigroup # append }
 * in the corresponding  { @link scalaz.Semigroup } in type Z.
 * 
 * ∀ a in S, append(a, zero) = a
 */
trait Zero[Z] {
  val zero: Z
}

trait Zeros {
  def zero[Z](z: Z): Zero[Z] = new Zero[Z] {
    val zero = z
  }

  /**
   * Returns the Zero element of type Z.
   * 

   * For example:
   * 
   *   (∅[Int], ∅: List[Int]) == (0, List.empty[Int])
   * 
   * @usecase def ∅[Z]: Z
   */
  def ∅[Z](implicit z: Zero[Z]): Z = z.zero

  /**
   * Alias for  { @link scalaz.Zeros # ∅ }
   */
  def mzero[Z](implicit z: Zero[Z]): Z = z.zero
}

object Zero {
  import Scalaz._
  import xml.{Elem, Node, NodeSeq}

  implicit def DigitZero: Zero[Digit] = zero(Digit._0)

  implicit def OrderingZero: Zero[Ordering] = zero(EQ)

  implicit def UnitZero: Zero[Unit] = zero(())

  implicit def StringZero: Zero[String] = zero("")

  implicit def IntZero: Zero[Int] = zero(0)

  implicit def IntMultiplicationZero: Zero[IntMultiplication] = zero(1 ∏)

  implicit def BooleanConjunctionZero: Zero[BooleanConjunction] = zero(true |∧|)

  implicit def BooleanZero: Zero[Boolean] = zero(false)

  implicit def CharZero: Zero[Char] = zero(0.toChar)

  implicit def CharMultiplicationZero: Zero[CharMultiplication] = zero(1.toChar ∏)

  implicit def ByteZero: Zero[Byte] = zero(0.toByte)

  implicit def ByteMultiplicationZero: Zero[ByteMultiplication] = zero(1.toByte ∏)

  implicit def LongZero: Zero[Long] = zero(0L)

  implicit def LongMultiplicationZero: Zero[LongMultiplication] = zero(1L ∏)

  implicit def ShortZero: Zero[Short] = zero(0.toShort)

  implicit def ShortMultiplicationZero: Zero[ShortMultiplication] = zero(1.toShort ∏)

  implicit def FloatZero: Zero[Float] = zero(0F)

  implicit def DoubleZero: Zero[Double] = zero(0D)

  implicit def BigIntegerZero = zero(java.math.BigInteger.valueOf(0))

  implicit def BigIntegerMultiplicationZero = zero(java.math.BigInteger.valueOf(1) ∏)

  implicit def BigIntZero: Zero[BigInt] = zero(BigInt(0))

  implicit def BigIntMutliplicationZero: Zero[BigIntMultiplication] = zero(BigInt(1) ∏)

  implicit def TraversableZero[CC <: Traversable[_]](implicit cbf: CanBuildFrom[Nothing, Nothing, CC]): Zero[CC] =
    zero(cbf.apply.result)

  // Not implicit to ensure implicitly[Zero[NodeSeq]].zero === NodeSeqZero.zero
  def NodeZero: Zero[Node] = new Zero[Node] {
    val zero = new Node {
      override def text = null

      override def label = null

      override def child = Nil
    }
  }

  // Not implicit to ensure implicitly[Zero[NodeSeq]].zero === NodeSeqZero.zero
  def ElemZero: Zero[Elem] = new Zero[Elem] {
    val zero = new Elem(null, null, scala.xml.Null, xml.TopScope, Nil: _*)
  }

  implicit def ZipStreamZero[A]: Zero[ZipStream[A]] = zero(zip(Stream.Empty))

  implicit def OptionZero[A]: Zero[Option[A]] = zero(None)

  implicit def FirstOptionZero[A]: Zero[FirstOption[A]] = zero(None)

  implicit def LastOptionZero[A]: Zero[LastOption[A]] = zero(None)

  implicit def LazyOptionZero[A]: Zero[LazyOption[A]] = zero(LazyOption.none)

  implicit def FirstLazyOptionZero[A]: Zero[FirstLazyOption[A]] = zero(LazyOption.none[A])

  implicit def LastLazyOptionZero[A]: Zero[LastLazyOption[A]] = zero(LazyOption.none[A])

  implicit def ArrayZero[A: Manifest]: Zero[Array[A]] = zero(new Array[A](0))

  implicit def EitherLeftZero[A, B](implicit bz: Zero[B]): Zero[Either.LeftProjection[A, B]] = zero(Right(∅[B]).left)

  implicit def EitherRightZero[A: Zero, B]: Zero[Either.RightProjection[A, B]] = zero(Left(∅[A]).right)

  implicit def EitherZero[A: Zero, B]: Zero[Either[A, B]] = zero(Left(∅[A]))

  implicit def MapZero[K, V: Zero]: Zero[Map[K, V]] = zero(Map.empty[K, V])

  implicit def IndSeqZero[A]: Zero[IndSeq[A]] = zero(IndSeq.apply[A]())

  implicit def Tuple2Zero[A, B](implicit az: Zero[A], bz: Zero[B]): Zero[(A, B)] =
    zero((az.zero, bz.zero))

  implicit def Tuple3Zero[A, B, C](implicit az: Zero[A], bz: Zero[B], cz: Zero[C]): Zero[(A, B, C)] =
    zero((az.zero, bz.zero, cz.zero))

  implicit def Tuple4Zero[A, B, C, D](implicit az: Zero[A], bz: Zero[B], cz: Zero[C], dz: Zero[D]): Zero[(A, B, C, D)] =
    zero((az.zero, bz.zero, cz.zero, dz.zero))

  implicit def Function1ABZero[A, B: Zero]: Zero[A => B] = zero((_: A) => ∅[B])

  implicit def EndoZero[A]: Zero[Endo[A]] = zero(EndoTo(identity(_: A)))

  implicit def DualZero[A: Zero]: Zero[Dual[A]] = zero(∅[A] σ)

  implicit def FingerTreeZero[V, A](implicit m: Reducer[A, V]): Zero[FingerTree[V, A]] = {
    zero(FingerTree.empty)
  }

  implicit def ZeroKleisliZero[M[_], A, B](implicit z: Zero[M[B]]): Zero[Kleisli[M, A, B]] = zero(☆((_: A) => ∅[M[B]]))

  import concurrent.Strategy
  import concurrent.Strategy.Id

  implicit def StrategyZero[A]: Zero[Strategy] = zero(Id)

  import java.util._
  import java.util.concurrent._

  implicit def JavaArrayListZero[A]: Zero[ArrayList[A]] = zero(new ArrayList[A])

  implicit def JavaHashMapZero[K, V]: Zero[HashMap[K, V]] = zero(new HashMap[K, V])

  implicit def JavaHashSetZero[A]: Zero[HashSet[A]] = zero(new HashSet[A])

  implicit def JavaHashtableZero[K, V]: Zero[Hashtable[K, V]] = zero(new Hashtable[K, V])

  implicit def JavaIdentityHashMapZero[K, V] = zero(new IdentityHashMap[K, V])

  implicit def JavaLinkedHashMapZero[K, V]: Zero[LinkedHashMap[K, V]] = zero(new LinkedHashMap[K, V])

  implicit def JavaLinkedHashSetZero[A]: Zero[LinkedHashSet[A]] = zero(new LinkedHashSet[A])

  implicit def JavaLinkedListZero[A]: Zero[LinkedList[A]] = zero(new LinkedList[A])

  implicit def JavaPriorityQueueZero[A]: Zero[PriorityQueue[A]] = zero(new PriorityQueue[A])

  implicit def JavaStackZero[A]: Zero[Stack[A]] = zero(new Stack[A])

  implicit def JavaTreeMapZero[K, V]: Zero[TreeMap[K, V]] = zero(new TreeMap[K, V])

  implicit def JavaTreeSetZero[A]: Zero[TreeSet[A]] = zero(new TreeSet[A])

  implicit def JavaVectorZero[A]: Zero[Vector[A]] = zero(new Vector[A])

  implicit def JavaWeakHashMapZero[K, V]: Zero[WeakHashMap[K, V]] = zero(new WeakHashMap[K, V])

  implicit def JavaArrayBlockingQueueZero[A]: Zero[ArrayBlockingQueue[A]] = zero(new ArrayBlockingQueue[A](0))

  implicit def JavaConcurrentHashMapZero[K, V]: Zero[ConcurrentHashMap[K, V]] = zero(new ConcurrentHashMap[K, V])

  implicit def JavaConcurrentLinkedQueueZero[A]: Zero[ConcurrentLinkedQueue[A]] = zero(new ConcurrentLinkedQueue[A])

  implicit def JavaCopyOnWriteArrayListZero[A]: Zero[CopyOnWriteArrayList[A]] = zero(new CopyOnWriteArrayList[A])

  implicit def JavaCopyOnWriteArraySetZero[A]: Zero[CopyOnWriteArraySet[A]] = zero(new CopyOnWriteArraySet[A])

  implicit def JavaLinkedBlockingQueueZero[A]: Zero[LinkedBlockingQueue[A]] = zero(new LinkedBlockingQueue[A])

  implicit def JavaSynchronousQueueZero[A]: Zero[SynchronousQueue[A]] = zero(new SynchronousQueue[A])
}