Deriving a Relationship from a Single Example

Abstract

Given an appropriate domain specific language (DSL), it is possible to describe the relationship between Haskell data types and many generic functions, typically type-class instances. While describing the relationship is possible, it is not always an easy task. There is an alternative -simply give one example output for a carefully chosen input, and have the relationship derived.When deriving a relationship from only one example, it is important that the derived relationship is the intended one. We identify general restrictions on the DSL, and on the provided example, to ensure a level of predictability. We then apply these restrictions in practice, to derive the relationship between Haskell data types and generic functions. We have used our scheme in the DERIVE tool, where over 60% of type classes are derived from a single example.

Usage of generic programming on hackage

“…The derive library and preprocessing tool [17] is a relatively recent successor to DrIFT. Using derive is very similar to using DrIFT:…”

“…Generic programming language constructs, tools and libraries have been available in Haskell since the first published report on the programming language Haskell [7] via the deriving construct. In the early phase of generic programming, generic programming was available via extra language constructs [5,8,14], or preprocessing tools [17,20,24]. Later, generic programming libraries [1,3,12,13,18,23] were introduced, in many variants.…”

“…• how much the DrIFT [24] and derive [17] preprocessing tools are used. • the number of packages that depend on some generic programming tool or library to compile their sources.…”