shapely-data (hackage): shapely-data is a library for working with algebraic datatypes in a simple generic form made up of haskell's primitive product, sum and unit types: (,), Either, and (), providing something like light-weight Structural Typing.  The library was not designed to facilitate generic traversals or abstraction over different recursion schemes, but rather to (from most to least important)  Provide a good story for (,)Either as a lingua franca/ generic representation that other library writers can use without dependencies, encouraging abstractions in terms of products and sums  Support algebraic operations on ADTs, making types composable  Support powerful, typed conversions between Shapely types  Influences  I've taken lots of inspiration, code, names, ideas, and type-level programming techniques from, in particular  Oleg Kiselyov's HList work  Edward Kmett's "categories" package  Chris Taylor's "Algebra of Algebraic Datatypes" series at http://chris-taylor.github.io/blog/2013/02/10/the-algebra-of-algebraic-data-types/  Issues and Limitations:  massage does not support mutually-recursive types and other more complicated recursion schemes, nor type application.  While all classes except Shapely are considered closed, we don't do any tricks to enforce that in the API yet.  In fancier functions that use type equality (e.g. coerce), types need to be unambiguous so type signatures are sometimes required.  type errors, especially in massage and coerce, can be cryptic  TH deriving hasn't been considered for fancier types like GADTs, existential types, etc. some of which may have sensible Shapely instances  Performance hasn't been tested at all yet.
Keywords: bsd3|data|generics|library