zipper

inspired by Greg Meredith's blog post and Jesper Nordenberg's comment i implemented some code generation which allows navigating trees of caseclasses and performing functional updates on them.
Here's an example. Suppose we model the state of a pacman game the following way:

scala> @zip case class Pacman(lives: Int = 3, superMode: Boolean = false)
scala> @zip case class Game(state: Symbol = 'pause, pacman: Pacman = Pacman())
scala> val g = Game() g: Game = Game('pause,Pacman(3,false))

Changing the game state to 'run is simple using the copy method:

scala> val g1 = g.copy(state = 'run) g1: Game = Game('run,Pacman(3,false))

However, changing pacman's super mode is much more cumbersome (and it gets worse for deeper structures):

scala> val g2 = g1.copy(pacman = g1.pacman.copy(superMode = true)) g2: Game = Game('run,Pacman(3,true))

Using the compiler-generated location classes this gets much easier:

scala> val g3 = g1.loc.pacman.superMode set true g3: Game = Game('run,Pacman(3,true))

What happens? For a case class "@zip case class C(x: A, y: B)", suppose T is another case class annotated with @zip, U is any other type, the compilergenerates:

class CLoc[T, P <: Loc[T, _, _]](v: C, f: C => Option[P]) extends Loc[T, C, P](v, f) { self =>  override def copy(v: C) = new CLoc[T, P](v, f)   def x: ALoc[T, CLoc[T, P]] = new ALoc[T, CLoc[T, P]](v.x, (x: A) => {    Some(self.copy(v.copy(x = x)))   })  def y: Loc[T, B, CLoc[T, P]] = new Loc[T, B, CLoc[T, P]](v.y, (y: B) => {     Some(self.copy(v.copy(y = y)))  }) }

in the class C

def loc = new CLoc[C, Nothing](this, v => None)

The class Loc is defined in the library as

/**  * T: top type * E: element type of this location  * P: parent location type */ class Loc[T, E, P <: Loc[T, _, _]](v: E, f: E => Option[P]) {  def up: Option[P] = f(v)   def top: T = up match {    case Some(p) => p.top     case _ => v.asInstanceOf[T]  }   def copy(v: E): Loc[T, E, P] = new Loc[T, E, P](v, f)  def set(v: E) = copy(v).top }

The prototype is on github, many things are not worked out yet e.g. generic case classes, case classes without copy method or name clashes.
Comments welcome :)Lukas