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Scala example source code file (StrictTree.scala)

This example Scala source code file (StrictTree.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

boolean, equal, node, option, stricttree, stricttreeequal, vector

The StrictTree.scala Scala example source code

package scalaz

import scala.collection.mutable
import std.vector.{vectorInstance, vectorMonoid}

/**
  *
  * @param rootLabel The label at the root of this tree.
  * @param subForest The child nodes of this tree.
  * @tparam A
  */
case class StrictTree[A](
  rootLabel: A,
  subForest: Vector[StrictTree[A]]
) {

  import StrictTree._

  /**
    * Run a bottom-up algorithm.
    *
    * This is the framework for several stackless methods, such as map.
    *
    * @param reduce is a function from a label and its mapped children to the new result.
    */
  private[scalaz] def runBottomUp[B](
    reduce: A => mutable.Buffer[B] => B
  ): B = {
    val root = BottomUpStackElem[A, B](None, this)
    val stack = mutable.Stack[BottomUpStackElem[A, B]](root)

    while (stack.nonEmpty) {
      val here = stack.elems.head
      if (here.hasNext) {
        val child = here.next()
        val nextStackElem = BottomUpStackElem[A, B](Some(here), child)
        stack.push(nextStackElem)
      } else {
        //The "here" node is completed, so add its result to its parents completed children.
        val result = reduce(here.rootLabel)(here.mappedSubForest)
        here.parent.foreach(_.mappedSubForest += result)
        stack.pop()
      }
    }

    reduce(root.rootLabel)(root.mappedSubForest)
  }

  /** Maps the elements of the StrictTree into a Monoid and folds the resulting StrictTree. */
  def foldMap[B: Monoid](f: A => B): B =
    runBottomUp(foldMapReducer(f))

  def foldRight[B](z: B)(f: (A, => B) => B): B =
    Foldable[Vector].foldRight(flatten, z)(f)

  /** A 2D String representation of this StrictTree. */
  def drawTree(implicit sh: Show[A]): String = {
    toTree.drawTree
  }

  /** A histomorphic transform. Each element in the resulting tree
    * is a function of the corresponding element in this tree
    * and the histomorphic transform of its children.
    */
  def scanr[B](g: (A, Vector[StrictTree[B]]) => B): StrictTree[B] =
    runBottomUp(scanrReducer(g))

  /** Pre-order traversal. */
  def flatten: Vector[A] = {
    val stack = mutable.Stack(this)

    val result = mutable.Buffer.empty[A]

    while (stack.nonEmpty) {
      val popped = stack.pop()
      result += popped.rootLabel
      popped.subForest.reverseIterator.foreach(stack.push)
    }

    result.toVector
  }

  def size: Int = {
    val stack = mutable.Stack(this.subForest)

    var result = 1

    while (stack.nonEmpty) {
      val popped = stack.pop()
      result += popped.size
      stack.pushAll(popped.map(_.subForest))
    }

    result
  }

  /** Breadth-first traversal. */
  def levels: Vector[Vector[A]] = {
    val f = (s: Vector[StrictTree[A]]) => {
      Foldable[Vector].foldMap(s)((_: StrictTree[A]).subForest)
    }
    Vector.iterate(Vector(this), size)(f) takeWhile (!_.isEmpty) map (_ map (_.rootLabel))
  }

  def toTree: Tree[A] = {
    Tree.Node[A](rootLabel, subForest.toStream.map(_.toTree))
  }

  /** Binds the given function across all the subtrees of this tree. */
  def cobind[B](f: StrictTree[A] => B): StrictTree[B] = unfoldTree(this)(t => (f(t), t.subForest))

  def foldNode[Z](f: A => Vector[StrictTree[A]] => Z): Z =
    f(rootLabel)(subForest)

  def map[B](f: A => B): StrictTree[B] = {
    runBottomUp(mapReducer(f))
  }

  def flatMap[B](f: A => StrictTree[B]): StrictTree[B] = {
    runBottomUp(flatMapReducer(f))
  }

  def traverse1[G[_] : Apply, B](f: A => G[B]): G[StrictTree[B]] = {
    val G = Apply[G]

    subForest match {
      case Vector() => G.map(f(rootLabel))(Leaf(_))
      case x +: xs => G.apply2(f(rootLabel), NonEmptyList.nel(x, IList.fromFoldable(xs)).traverse1(_.traverse1(f))) {
        case (h, t) => Node(h, t.list.toVector)
      }
    }
  }

  def zip[B](b: StrictTree[B]): StrictTree[(A, B)] = {
    val root = ZipStackElem[A, B](None, this, b)
    val stack = mutable.Stack[ZipStackElem[A, B]](root)

    while (stack.nonEmpty) {
      val here = stack.elems.head
      if (here.hasNext) {
        val (childA, childB) = here.next()
        val nextStackElem = ZipStackElem[A, B](Some(here), childA, childB)
        stack.push(nextStackElem)
      } else {
        //The "here" node is completed, so add its result to its parents completed children.
        val result = StrictTree((here.a.rootLabel, here.b.rootLabel), here.mappedSubForest.toVector)
        here.parent.foreach(_.mappedSubForest += result)
        stack.pop()
      }
    }

    StrictTree((rootLabel, b.rootLabel), root.mappedSubForest.toVector)
  }

  /**
    * This implementation is 24x faster than the trampolined implementation for StrictTreeTestJVM's hashCode test.
    *
    * @return
    */
  override def hashCode(): Int = {
    runBottomUp(hashCodeReducer)
  }

  override def equals(obj: scala.Any): Boolean = {
    obj match {
      case other: StrictTree[A] =>
        StrictTree.badEqInstance[A].equal(this, other)
      case _ =>
        false
    }
  }
}

sealed abstract class StrictTreeInstances {
  implicit val strictTreeInstance: Traverse1[StrictTree] with Monad[StrictTree] with Comonad[StrictTree] with Align[StrictTree] with Zip[StrictTree] = new Traverse1[StrictTree] with Monad[StrictTree] with Comonad[StrictTree] with Align[StrictTree] with Zip[StrictTree] {
    def point[A](a: => A): StrictTree[A] = StrictTree.Leaf(a)
    def cobind[A, B](fa: StrictTree[A])(f: StrictTree[A] => B): StrictTree[B] = fa cobind f
    def copoint[A](p: StrictTree[A]): A = p.rootLabel
    override def map[A, B](fa: StrictTree[A])(f: A => B) = fa map f
    def bind[A, B](fa: StrictTree[A])(f: A => StrictTree[B]): StrictTree[B] = fa flatMap f
    def traverse1Impl[G[_]: Apply, A, B](fa: StrictTree[A])(f: A => G[B]): G[StrictTree[B]] = fa traverse1 f
    override def foldRight[A, B](fa: StrictTree[A], z: => B)(f: (A, => B) => B): B = fa.foldRight(z)(f)
    override def foldMapRight1[A, B](fa: StrictTree[A])(z: A => B)(f: (A, => B) => B) = (fa.flatten.reverse: @unchecked) match {
      case h +: t => t.foldLeft(z(h))((b, a) => f(a, b))
    }
    override def foldLeft[A, B](fa: StrictTree[A], z: B)(f: (B, A) => B): B =
      fa.flatten.foldLeft(z)(f)
    override def foldMapLeft1[A, B](fa: StrictTree[A])(z: A => B)(f: (B, A) => B): B = fa.flatten match {
      case h +: t => t.foldLeft(z(h))(f)
    }
    override def foldMap[A, B](fa: StrictTree[A])(f: A => B)(implicit F: Monoid[B]): B = fa foldMap f

    //This implementation is 14x faster than the trampolined implementation for StrictTreeTestJVM's align test.
    override def alignWith[A, B, C](f: (\&/[A, B]) => C): (StrictTree[A], StrictTree[B]) => StrictTree[C] = {
      (a, b) =>
        import StrictTree.AlignStackElem
        val root = AlignStackElem[A, B, C](None, \&/(a, b))
        val stack = mutable.Stack(root)

        while (stack.nonEmpty) {
          val here = stack.elems.head
          if (here.hasNext) {
            val nextChildren = here.next()
            val nextStackElem = AlignStackElem[A, B, C](Some(here), nextChildren)
            stack.push(nextStackElem)
          } else {
            //The "here" node is completed, so add its result to its parents completed children.
            val result = StrictTree[C](f(here.trees.bimap(_.rootLabel, _.rootLabel)), here.mappedSubForest.toVector)
            here.parent.foreach(_.mappedSubForest += result)
            stack.pop()
          }
        }

        StrictTree(f(root.trees.bimap(_.rootLabel, _.rootLabel)), root.mappedSubForest.toVector)
    }

    override def zip[A, B](a: => StrictTree[A], b: => StrictTree[B]): StrictTree[(A, B)] = {
      a.zip(b)
    }
  }

  implicit def treeEqual[A](implicit A0: Equal[A]): Equal[StrictTree[A]] =
    new StrictTreeEqual[A] { def A = A0 }

  implicit def treeOrder[A](implicit A0: Order[A]): Order[StrictTree[A]] =
    new Order[StrictTree[A]] with StrictTreeEqual[A] {
      def A = A0
      import std.vector._
      override def order(x: StrictTree[A], y: StrictTree[A]) =
        A.order(x.rootLabel, y.rootLabel) match {
          case Ordering.EQ =>
            Order[Vector[StrictTree[A]]].order(x.subForest, y.subForest)
          case x => x
        }
    }



  /* TODO
  def applic[A, B](f: StrictTree[A => B]) = a => StrictTree.node((f.rootLabel)(a.rootLabel), implicitly[Applic[newtypes.ZipVector]].applic(f.subForest.map(applic[A, B](_)).?)(a.subForest ?).value)
   */
}

object StrictTree extends StrictTreeInstances {
  /**
   * Node represents a tree node that may have children.
   *
   * You can use Node for tree construction or pattern matching.
   */
  object Node {
    def apply[A](root: A, forest: Vector[StrictTree[A]]): StrictTree[A] = {
      StrictTree[A](root, forest)
    }

    def unapply[A](t: StrictTree[A]): Option[(A, Vector[StrictTree[A]])] = Some((t.rootLabel, t.subForest))
  }

  /**
   *  Leaf represents a a tree node with no children.
   *
   *  You can use Leaf for tree construction or pattern matching.
   */
  object Leaf {
    def apply[A](root: A): StrictTree[A] = {
      Node(root, Vector.empty)
    }

    def unapply[A](t: StrictTree[A]): Option[A] = {
      t match {
        case Node(root, Vector()) =>
          Some(root)
        case _ =>
          None
      }
    }
  }

  def unfoldForest[A, B](s: Vector[A])(f: A => (B, Vector[A])): Vector[StrictTree[B]] =
    s.map(unfoldTree(_)(f))

  def unfoldTree[A, B](v: A)(f: A => (B, Vector[A])): StrictTree[B] =
    f(v) match {
      case (a, bs) => Node(a, unfoldForest(bs)(f))
    }

  //Only used for .equals.
  private def badEqInstance[A] = new StrictTreeEqual[A] {
    override def A: Equal[A] = new Equal[A] {
      override def equal(a1: A, a2: A): Boolean = a1.equals(a2)
    }
  }

  /**
    * This implementation is 16x faster than the trampolined implementation for StrictTreeTestJVM's scanr test.
    */
  private def scanrReducer[A, B](
    f: (A, Vector[StrictTree[B]]) => B
  )(rootLabel: A
  )(subForest: mutable.Buffer[StrictTree[B]]
  ): StrictTree[B] = {
    val subForestVector = subForest.toVector
    StrictTree[B](f(rootLabel, subForestVector), subForestVector)
  }

  /**
    * This implementation is 10x faster than mapTrampoline for StrictTreeTestJVM's map test.
    */
  private def mapReducer[A, B](
    f: A => B
  )(rootLabel: A
  )(subForest: Seq[StrictTree[B]]
  ): StrictTree[B] = {
    StrictTree[B](f(rootLabel), subForest.toVector)
  }

  /**
    * This implementation is 9x faster than flatMapTrampoline for StrictTreeTestJVM's flatMap test.
    */
  private def flatMapReducer[A, B](
    f: A => StrictTree[B]
  )(root: A
  )(subForest: Seq[StrictTree[B]]
  ): StrictTree[B] = {
    val StrictTree(rootLabel0, subForest0) = f(root)
    StrictTree(rootLabel0, subForest0 ++ subForest)
  }

  /**
    * This implementation is 9x faster than the trampolined implementation for StrictTreeTestJVM's foldMap test.
    */
  private def foldMapReducer[A, B: Monoid](
    f: A => B
  )(rootLabel: A
  )(subForest: mutable.Buffer[B]
  ): B = {
    val mappedRoot = f(rootLabel)
    val foldedForest = Foldable[Vector].fold[B](subForest.toVector)

    Monoid[B].append(mappedRoot, foldedForest)
  }

  private def hashCodeReducer[A](root: A)(subForest: Seq[Int]): Int = {
    root.hashCode ^ subForest.hashCode
  }

  private case class BottomUpStackElem[A, B](
    parent: Option[BottomUpStackElem[A, B]],
    tree: StrictTree[A]
  ) extends Iterator[StrictTree[A]] {
    private val subIterator = tree.subForest.iterator

    def rootLabel = tree.rootLabel

    val mappedSubForest: mutable.Buffer[B] = mutable.Buffer.empty

    override def hasNext: Boolean = subIterator.hasNext

    override def next(): StrictTree[A] = subIterator.next()
  }

  private case class ZipStackElem[A, B](
    parent: Option[ZipStackElem[A, B]],
    a: StrictTree[A],
    b: StrictTree[B]
  ) extends Iterator[(StrictTree[A], StrictTree[B])] {
    private val zippedSubIterator =
      a.subForest.iterator.zip(b.subForest.iterator)

    val mappedSubForest: mutable.Buffer[StrictTree[(A, B)]] = mutable.Buffer.empty

    override def hasNext: Boolean = zippedSubIterator.hasNext

    override def next(): (StrictTree[A], StrictTree[B]) = zippedSubIterator.next()
  }

  private[scalaz] case class AlignStackElem[A, B, C](
    parent: Option[AlignStackElem[A, B, C]],
    trees: \&/[StrictTree[A], StrictTree[B]]
  ) extends Iterator[\&/[StrictTree[A], StrictTree[B]]] {
    private val iterators =
      trees.bimap(_.subForest.iterator, _.subForest.iterator)

    val mappedSubForest: mutable.Buffer[StrictTree[C]] = mutable.Buffer.empty

    def whichHasNext: \&/[Boolean, Boolean] =
      iterators.bimap(_.hasNext, _.hasNext)

    override def hasNext: Boolean =
      whichHasNext.fold(identity, identity, _ || _)

    override def next(): \&/[StrictTree[A], StrictTree[B]] =
      whichHasNext match {
        case \&/(true, true) =>
          iterators.bimap(_.next(), _.next())

        case \&/(true, false) | \&/.This(true) =>
          \&/.This(iterators.onlyThis.get.next())

        case \&/(false, true) | \&/.That(true) =>
          \&/.That(iterators.onlyThat.get.next())

        case _ =>
          throw new NoSuchElementException("reached iterator end")
      }
  }

  implicit def ToStrictTreeUnzip[A1, A2](root: StrictTree[(A1, A2)]): StrictTreeUnzip[A1, A2] =
    new StrictTreeUnzip[A1, A2](root)

}

private trait StrictTreeEqual[A] extends Equal[StrictTree[A]] {
  def A: Equal[A]

  private case class EqualStackElem(
    a: StrictTree[A],
    b: StrictTree[A]
  ) {
    val aSubIterator =
      a.subForest.iterator

    val bSubIterator =
      b.subForest.iterator
  }

  //This implementation is 4.5x faster than the trampolined implementation for StrictTreeTestJVM's equal test.
  override final def equal(a1: StrictTree[A], a2: StrictTree[A]): Boolean = {
    val root = EqualStackElem(a1, a2)
    val stack = mutable.Stack[EqualStackElem](root)

    while (stack.nonEmpty) {
      val here = stack.elems.head
      if (A.equal(here.a.rootLabel, here.b.rootLabel)) {
        val aNext = here.aSubIterator.hasNext
        val bNext = here.bSubIterator.hasNext
        (aNext, bNext) match {
          case (true, true) =>
            val childA = here.aSubIterator.next()
            val childB = here.bSubIterator.next()
            val nextStackElem = EqualStackElem(childA, childB)
            stack.push(nextStackElem)
          case (false, false) =>
            stack.pop()
          case _ =>
            return false
        }
      } else return false
    }

    true
  }
}

final class StrictTreeUnzip[A1, A2](val root: StrictTree[(A1, A2)]) extends AnyVal {
  private def unzipCombiner(rootLabel: (A1, A2))(accumulator: Seq[(StrictTree[A1], StrictTree[A2])]): (StrictTree[A1], StrictTree[A2]) = {
    (StrictTree(rootLabel._1, accumulator.map(_._1).toVector), StrictTree(rootLabel._2, accumulator.map(_._2).toVector))
  }

  /** Turns a tree of pairs into a pair of trees. */
  def unzip: (StrictTree[A1], StrictTree[A2]) = {
    root.runBottomUp[(StrictTree[A1], StrictTree[A2])](unzipCombiner)
  }
}

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