Integrate with the notion of Lens

[johnynek]

http://twanvl.nl/blog/haskell/isomorphism-lenses

I think something like:

// Type inference should work without having to specify R in the below unless there are multiple valid bijections
object Lens {
  def get[A,B](a: A)(implicit bij: Bijection[A,(B,_)]): B = bij(a)._1
  def modify[A,B,R](a: A)(update: B => B)(implicit bij: Bijection[A,(B,R)]): A = {
    val decons = bij(a)
    bij.invert((update(decons._1), decons._2))
  }
  def set[A,B,R](a: A, b: B)(implicit bij: Bijection[A,(B,R)]): A = {
    val decons = bij(a)
    bij.invert((b, decons._2))
  } 
}

This relies on having good bijections from A into each of it's parts. It would be great if we could have a way to signify that (B,R) could really be any tuple of B with any other items (e.g. (B,R1,R2,R3...) would work.

[sritchie]

http://twanvl.nl/blog/haskell/isomorphism-lenses
http://www.cis.upenn.edu/~bcpierce/papers/lenses-etapsslides.pdf -- awesome