Scala for-comprehension

comprehensions.scala

class Person(val name: String, val female: Boolean)

val people = List(
  new Person("Cliffy", false),
  new Person("Ewing", true),
  new Person("Tolkein", false),
  new Person("Donna", true))
  
  // Traverse the list and print the names
  for (person <- people)
    println(person.name)
    
  // Filter out females
  for (person: Person <- people
        if person.female)
      println(person.name)
        
  // Only return males called Tolkein
  for (person: Person <- people
        if !person.female
        if person.name.Contains("Tolkein"))
    println(person.name)
    
  // Variable's inside for-comps
  for {person: Person <- people
        if !person.female;
        name = person.name
        if name.contains("Tolkein")}
    println(name)
    
  // Yielding
  val names = for(person <- people) yield person.name
  
  // Yielding tuple
  val namesTuple = for(person <- people) yield (person.name, person.female)
  
  // Yielding tuple and variables
  val tuples = for { person: Person <- people
    female = person.female
    if !female
    name = person.name
    if name.contains("Tolkein")
  } yield (name,female)
  
  for (person <- tuples) println(person)
  
  val things = ()

  // Case classes
  abstract class Thing
  case class Foo(name: String) extends Thing
  case class Bar(arg: String, body: Thing) extends Thing
  case class Baz(f: Thing, v: Thing) extends Thing
  
  // No 'new' required
  Foo("x", Bar("y", Baz(Foo("x", Var("y")))))
  
  // Constructor variables are public
  val x = Foo("X")
  println(x.name)
  
  // Automatic equality
  val x1 = Foo("X")
  val x2 = Foo("X")
  val y1 = Foo("Y")
  println("" + x1 + " == " + x2 + "=> " + (x1 == x2))
  println("" + x1 + " == " + y1 + "=> " + (x1 == y1))

  // Pretty printer.
  object ThingTest {
    def printThing(thing: Thing) {
      thing match {
        case Foo(n) =>
          print(n)
        case Bar(x, b) =>
          print("^" + x + ".")
          printThing(b)
        case Baz(f,v) =>
          print("(")
          printThing(f)
          print(" ")
          printThing(v)
          print(")")
      }
    }
    
    def isIdentityBar(thing: Thing): Boolean = term match {
      case Bar(x, Foo(y)) if x == y => true
      case _ => false
    }
    
    val id = Bar("x", Foo("x"))
    val t = Bar("x", Bar("x", Baz(Foo("x"), Foo("y"))))
    printThing(t)
    println
    println(isIdentifyBar(id))
    println(isIdentityBar(t))
  }