Indexed Optics

[nomisRev]

Implement Indexed Optics in Arrow-optics. i.e. IndexedTraversal

It allows for working with traversable structures based on indexes, i.e. traverse a matrix diagonally (or any custom pattern).

References: https://github.com/hablapps/Monocle/blob/indexed/core/shared/src/main/scala/monocle/ITraversal.scala http://hackage.haskell.org/package/lens-4.17.1/docs/Control-Lens-Traversal.html#t:IndexedTraversal

The same can be done for other optics.