Sums of Products: A Tutorial about Generics and Barbies
This is a port of Haskell’s generics-sop library, where data types are represented as n-ary sums over n-ary products. Such a generic representation is useful for two reasons: First, and most important, it allows us to automatically derive interface implementations with a minimal amount of code for a large set of data types. Second, the combinators provided by this library present a powerful toolkit for manipulating data types when in their generic form.
In this tutorial, we address both aspects of generic programming in the SOP style, while showing at the same time, how a minimal amount of reflection code can be used to fully automatize the deriving of several interface implementations all at once using elaborator reflection.