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Scala example source code file (Optional.scala)

This example Scala source code file (Optional.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

a\,x, boolean, maybe, optional

The Optional.scala Scala example source code

package scalaz

////
/** Abstraction over a container/context which may or may not provide a value.
  *
  * @tparam F the container/context type
  *
  * @see [[syntax.OptionalOps]]
  */
////
trait Optional[F[_]]  { self =>
  ////

  /** If `fa` has an `a`, return it; otherwise it must be universally
    * quantified.
    */
  def pextract[B, A](fa: F[A]): F[B] \/ A

  // derived functions

  /** Returns the value within the context if defined or else the value of `default`. */
  def getOrElse[A](fa: F[A])(default: => A): A = pextract(fa) | default

  /** Returns `true` if a value is defined within the context. */
  def isDefined[A](fa: F[A]): Boolean = pextract(fa).isRight

  /** Returns `true` if a value is defined within the context. This is an alias for `isDefined`. */
  final def nonEmpty[A](fa: F[A]): Boolean = isDefined(fa)

  /** Returns `true` if no value is defined within the context. */
  final def isEmpty[A](fa: F[A]): Boolean = ! isDefined(fa)

  /** Returns given context if it is defined or else the value of the `alternative`. */
  def orElse[A](fa: F[A])(alternative: => F[A]): F[A] =
    if (isDefined(fa)) fa else alternative

  /** Returns `some` if this context is defined, otherwise `none`. */
  def ?[A,X](fa: F[A])(some: => X, none: => X): X =
    if (isDefined(fa)) some else none

  // conversions

  /** Returns this context converted to the `Option` context. */
  def toOption[A](fa: F[A]): Option[A] = pextract(fa).toOption

  /** Returns this context converted to the `Maybe` context. */
  def toMaybe[A](fa: F[A]): Maybe[A] = pextract(fa).toMaybe

  ////
  val optionalSyntax = new scalaz.syntax.OptionalSyntax[F] { def F = Optional.this }
}

object Optional {
  @inline def apply[F[_]](implicit F: Optional[F]): Optional[F] = F

  ////

  ////
}

Other Scala examples (source code examples)

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my book on functional programming

 

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