petekneller

/**
 * Part Zero : 10:15 Saturday Night
 *
 * (In which we will see how to let the type system help you handle failure)...
 *
 * First let's define a domain. (All the following requires scala 2.9.x and scalaz 6.0)
 */

import scalaz._
import Scalaz._

petekneller

/*
The Oracle Java enum Planets example using the Klang DIY Enum, modified to include ordering.
*/
object KlangEnumPlanets extends App {

  trait Enum { //DIY enum type
    import java.util.concurrent.atomic.AtomicReference //Concurrency paranoia

    type EnumVal <: Value //This is a type that needs to be found in the implementing class

petekneller

trait Enum { //DIY enum type
  import java.util.concurrent.atomic.AtomicReference //Concurrency paranoia

  type EnumVal <: Value //This is a type that needs to be found in the implementing class

  private val _values = new AtomicReference(Vector[EnumVal]()) //Stores our enum values

  //Adds an EnumVal to our storage, uses CCAS to make sure it's thread safe, returns the ordinal
  private final def addEnumVal(newVal: EnumVal): Int = { import _values.{get, compareAndSet => CAS}
    val oldVec = get

petekneller

package demo

import scalaz._
import scalaz.syntax._
import scalaz.effect.IO
import scalaz.effect.IO._
import scalaz.syntax.std.either._

object Demo {
  type M[A] = EitherT[IO, Throwable, A]

petekneller

import scalaz.effect.IO
import scalaz.{EitherT, Monad}

object Program extends ProgramInstances {
  def apply[A](a: A): Program[A] = Program[A](EitherT.right[IO, Throwable, A](IO(a)))
}

trait ProgramInstances {
  implicit object ProgramMonad extends Monad[Program] {
    override def point[A](a: => A): Program[A] = Program[A](a)

petekneller

// No case classes
object Consoles {

  trait ConsoleAlg[F[_]] {
    def readLine: F[Option[String]]

    def printLine(line: String): F[Unit]
  }

  trait Console[+A] {

petekneller

/** GADTs in Scala and their limitations */

/** Background: what is an algebraic data type (ADT) ? 
  * ADT: (possibly) recursive datatype with sums and products
  * In scala - a trait with case classes (case class is product, subtyping is sum) 
  */

/** Motivation: untyped embedded DSL doesn't prevent nonsensical expressions */
sealed trait Expr { 
  def apply(other: Expr) = Ap(this, other)

petekneller

class A
class A2 extends A
class B

trait M[X]

//
// Upper Type Bound
//
def upperTypeBound[AA <: A](x: AA): A = x