* Luke Evans
It's sometimes difficult to figure out a good choice when you're searching for a new feature/library (when you go beyond safety of the HP). I'm looking for a generic zipper to (hopefully) navigate over an AST… so a hetrogeneous structure.
It's probably sufficient to make this traversable in a fixed way, but a zipper seemed like a good idea. Google says there are lots of options (various papers and their related implementations etc).
I see a generic zipper in an 'syz' package that is based on generics, which looks like a nice choice as it's now easy to add the extension for deriving generics on ADTs. However, that package looks pretty old and unmaintained.
Does anyone have any suggestions/advice?
I plan to add an syz-like zipper to traverse-with-class[1] soon. The main advantage is that it'll let you to specify, via GTraversable instances, at which nodes it should "stop" and which nodes it should "skip". [1]: http://hackage.haskell.org/package/traverse-with-class For example, when you navigate around a list with syz, it'll "stop" at (:) and [] nodes, apart from the actual list elements, which may or may not be what you want. Apart from that, I am not aware of any problems with syz. Roman