Scala example source code file (SyntaxUsage.scala)

This example Scala source code file (SyntaxUsage.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

app, int, list, none, option, some, stream, syntaxusage

The SyntaxUsage.scala Scala example source code

package scalaz.example

object SyntaxUsage extends App {

  val o1: Option[Int] = Some(0)
  val o2: Option[Option[Int]] = Some(Some(0))
  val l1: List[String] = List("one")
  val l2: List[List[String]] = List(List("one"))

  syntax1()
  syntax2()
  syntax3()
  stdSyntax()
  stdSyntaxUeber()

  def typed[T](t: T) = ()

  // Use the syntax only for Monad[Option]
  // This includes the syntax for the parent type classes.
  def syntax1() {
    import scalaz._

    // Import type class instances for Option, and the
    // Monad syntax for Option.
    import std.option._
    import std.option.optionInstance.monadSyntax._
    val x = 1.point
    val y = point(1)
    typed[Option[Int]](x)
    typed[Option[Int]](x)

    o1 >>= (x => if (x == 0) Some(0) else None)
    o2.join
  }

  // Use two different instances, and the syntax for all Monads
  def syntax2() {
    import scalaz._

    // Import type class instances for Option and List
    import std.option._
    import std.list._

    // Implicit conversions from M[A] => BindV[M, A], etc.
    import syntax.monad._

    o1 >>= (x => if (x == 0) Some(0) else None)
    o2.join
    l2.join

    1.point[Option]
  }

  def syntax3() {
    import scalaz._

    // Import all type class instances
    import Scalaz._

    o1 >>= (x => if (x == 0) Some(0) else None)
    o2.join
    l2.join

    o2.tuple(o2)
  }

  def stdSyntax() {
    import scalaz.Tags.Last
    import scalaz.std.anyVal._
    import scalaz.std.stream.streamSyntax._

    val interleaved = Stream(1, 3, 5).interleave(Stream(2, 4, 6))

    import scalaz.std.list._
    import scalaz.std.option._
    import scalaz.std.option.optionSyntax._
    import scalaz.syntax.monoid._
    import scalaz.syntax.equal._

    val lists: List[Int] = some(1).orEmpty[List]
    Last.unwrap((some(1).last |+| some(2).last)) assert_=== some(2)
  }

  def stdSyntaxUeber() {
    // Scalaz 6 Style: import everything: type class instances, implicit conversions
    // to the syntax wrappers, general functions.
    import scalaz._
    import scalaz.Scalaz._

    // prefix style function call `op(args)`
    orEmpty[Int, List](some(1))

    // syntax to provide `x.op(args)`
    some(1).orEmpty[List]

    Tag.unwrap((some(1).last |+| some(2).last)) assert_=== some(2)
    some(some(1)).join assert_=== some(1)

    List(1, 2, 3).powerset.join

    import Kleisli._

    val k = kleisli((a: Int) => some(0))
    kleisliArrow[Option].compose(k, k)
    k >>> k

    List(some(0)).sequence
  }
}