On Fri, Jan 06, 2012 at 09:28:21PM +0000, Tom Doris wrote:
My questions are: 1) I presume this approach has been explored and probably there is a well thought through library of helper classes and functions already out there, can someone please point me to it?
One package which I think is similar is http://hackage.haskell.org/package/has
2) I don't know much about Haskell generics, but for product types in which all contained values are distinct types, it should be possible to automatically derive instances of Extract, since there's never ambiguity as to which field you want from a container if you've specified the type of value you want, is this possible, and if so does it already exist?
It's easy to extract a field of a certain type using a generic traversal (of the sort found in packages like uniplate or syb). To automatically derive instances of Extract I think you would have to use Template Haskell.
3) In type theory, are product types consisting of distinct member types considered special in any way? i.e. does the concept have a name and what special properties do they have?
Not that I know of. -Brent