The shapely-data package
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
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.
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|Dependencies||base (<5), proxy-kindness (==0.1), tagged, template-haskell (==2.*) [details]|
|Source repository||head: git clone https://github.com/jberryman/shapely-data.git -b master|
|Uploaded||Sun Dec 22 23:32:01 UTC 2013 by BrandonSimmons|
|Downloads||457 total (5 in the last 30 days)|
|Status||Docs available [build log]
Successful builds reported [all 1 reports]
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