Scala example source code file (Iterable.scala)

This example Scala source code file (Iterable.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, foldable, iterable, iterableinstances, monoid, order, ordering, show

The Iterable.scala Scala example source code

package scalaz
package std

trait IterableInstances {

  implicit def iterableShow[CC[X] <: Iterable[X], A: Show]: Show[CC[A]] = new Show[CC[A]] {
    override def show(as: CC[A]) = "[" +: Cord.mkCord(",", as.map(Show[A].show(_)).toSeq:_*) :+ "]"
  }

  /** Lexicographical ordering */
  implicit def iterableOrder[A](implicit A: Order[A]): Order[Iterable[A]] = new Order[Iterable[A]] {
    def order(a1: Iterable[A], a2: Iterable[A]): Ordering = {
      import scalaz.Ordering._
      val i1 = a1.iterator
      val i2 = a2.iterator

      while (i1.hasNext && i2.hasNext) {
        val a1 = i1.next()
        val a2 = i2.next()

        val o = A.order(a1, a2)
        if (o != EQ) {
          return o
        }
      }
      anyVal.booleanInstance.order(i1.hasNext, i2.hasNext)
    }
  }

  implicit def iterableEqual[CC[X] <: Iterable[X], A: Equal]: Equal[CC[A]] = new Equal[CC[A]] {
    def equal(a1: CC[A], a2: CC[A]) = {
      val i1 = a1.iterator
      val i2 = a2.iterator
      var b = false

      while (i1.hasNext && i2.hasNext && !b) {
        val x1 = i1.next
        val x2 = i2.next

        if (!Equal[A].equal(x1, x2)) {
          b = true
        }
      }

      !(b || i1.hasNext || i2.hasNext)
    }
  }

  implicit def iterableSubtypeFoldable[I[X] <: Iterable[X]]: Foldable[I] = new Foldable[I] {
    def foldMap[A,B](fa: I[A])(f: A => B)(implicit F: Monoid[B]) = foldLeft(fa, F.zero)((x,y) => Monoid[B].append(x, f(y)))

    def foldRight[A, B](fa: I[A], b: => B)(f: (A, => B) => B) = fa.foldRight(b)(f(_, _))

    override def foldLeft[A, B](fa: I[A], b: B)(f: (B, A) => B): B = fa.foldLeft(b)(f)

    override def length[A](a: I[A]) = {
      var n = 0
      val i = a.iterator
      while (i.hasNext) {
        n = n + 1
        i.next
      }
      n
    }

    override def any[A](fa: I[A])(p: A => Boolean): Boolean =
      fa.exists(p)

    override def all[A](fa: I[A])(p: A => Boolean): Boolean =
      fa.forall(p)
  }
}

object iterable extends IterableInstances