Generic Generic Programming

Abstract. Generic programming (GP) is a form of abstraction in programming languages that serves to reduce code duplication by exploiting the regular struc-ture of algebraic datatypes. Over the years, several different approaches to GP in Haskell have surfaced. These approaches are often similar, but certain differ-ences make them particularly well-suited for one specific domain or application. As such, there is a lot of code duplication across GP libraries, which is rather unfortunate, given the original goals of GP. To address this problem, we define conversions from one popular GP library rep-resentation to several others. Our work unifies many approaches to GP, and sim-plifies the life of both library writers and users. Library writers can define their approach as a conversion from our library, obviating the need for writing meta-programming code for generation of conversions to and from the generic repre-sentation. Users of GP, who often struggle to find “the right approach ” to use, can now mix and match functionality from different libraries with ease, and need not worry about having multiple (potentially inefficient and large) code blocks for generic representations in different approaches.