Scala example source code file (MixedBag.scala)

This example Scala source code file (MixedBag.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

arrow, free, functor, kleisli, mixedbag, pair, tree, unit, writer

The MixedBag.scala Scala example source code

package scalaz.example

import scalaz._

object MixedBag extends App {
  monoid()
  traverseBigList()
  traverseBigStream()
  tree()
  kleisiArrow()
  dListExample()

  def monoid() {
    import std.anyVal._
    import std.option._

    import syntax.monoid._

    1 |+| 2
    1 mappend 2
    some(1) |+| some(2)
    some(1) |+| mzero[Option[Int]]

    intInstance.semigroupSyntax.mappend(1, 2)
  }

  def traverseBigList() {
    import std.option._
    import std.list._
    import syntax.traverse._

    //    val xs: Option[List[Int]] = (1 to 100000).toList.traverse(x => some(x * 2))
    //    println(xs map (_ take 10))
    ()
  }

  def traverseBigStream() {
    import std.option._
    import std.stream._
    import syntax.traverse._

    (1 to 100000).toStream.traverse(x => none[Int])
    //    (1 to 100000).toStream.traverse(x => some(x * 2))
    ()
  }

  def tree() {
    import std.string._
    import syntax.semigroup._
    import syntax.equal._
    import syntax.tree._
    import syntax.traverse._
    import std.stream._

    val tree: Tree[Int] = 1.node(2.node(3.leaf), 4.leaf, 5.leaf)
    val r = tree.foldRight(".")((i, s) => i.toString |+| s)
    r assert_=== "12345."
    val f = tree.flatten.foldMap(_.toString)
    f assert_=== "12345"
    val m = tree.foldMap(_.toString)
    m assert_=== "12345"
  }

  def strictTree() {
    import std.string._
    import syntax.semigroup._
    import syntax.equal._
    import syntax.strictTree._
    import syntax.traverse._
    import std.vector._

    val tree: StrictTree[Int] = 1.strictNode(2.strictNode(3.strictLeaf), 4.strictLeaf, 5.strictLeaf)
    val r = tree.foldRight(".")((i, s) => i.toString |+| s)
    r assert_=== "12345."
    val f = tree.flatten.foldMap(_.toString)
    f assert_=== "12345"
    val m = tree.foldMap(_.toString)
    m assert_=== "12345"
  }

  def kleisiArrow() {
    import Kleisli._
    import std.option._
    import syntax.compose._

    val f = kleisli((i: Int) => some(i))
    f map (i => i * 2) map (x => println(x)) run 3

    val K = Arrow[λ[(α,β)=>Kleisli[Option,α,β]]]
    f >>> K.arr(i => i * 2) >>> K.arr(x => println(x)) run 3
  }

  def dListExample() {
    import DList._
    import syntax.monad._
    import syntax.writer._
    import WriterT._

    type Pair[+A] = (A, A)
    type Tree[A] = Free[Pair, A]

    implicit val pairFunctor: Functor[Pair] = new Functor[Pair] {
      def map[A, B](as: Pair[A])(f: A => B) =
        f(as._1) -> f(as._2)
    }

    def leaf[A](a: A): Tree[A] = Free.pure(a)
    def node[A](l: Tree[A], r: Tree[A]): Tree[A] = Free[Pair, A](l -> r)

    def flattenWriter[A](t: Tree[A]): DList[A] = {
      def flatten(t: Tree[A]): Writer[DList[A], Unit] = t.resume match {
        case \/-(a)     => DList(a).tell
        case -\/((x, y)) => flatten(x) >> flatten(y)
      }
      flatten(t).run._1
    }

    flattenWriter(node(node(leaf(1), leaf(3)), leaf(2))).toList
  }

  def zipper() {
    import scalaz.std.list

    val fileName = "abc.txt"

    val oldExtensionAndNewName: Option[(String, String)] = for {
      zipper <- list.toZipper(fileName.toList)

      // previousC from the first position rotates the focus to the last element
      zipperAtLast = zipper.previousC

      // focus on the first preceding character, if found, that `== '.'`
      zipperAtDot <- zipper.findPrevious(_ == '.')

      // Zipper#rights contains the elements to the right of the focus
      oldExtension = zipperAtDot.rights.mkString

      // Change the extension.
      changedExtZipper = zipperAtDot.copy(rights = "log".toStream)

      // Convert the Zipper back to a string
      newFileName = changedExtZipper.toStream.mkString
    } yield (oldExtension, newFileName)
  }
}