Functional prototypes for generic C++ libraries: a transformational approach based on higher-order, typed signatures

This paper presents a method for developing generic C++ software libraries from functional prototypes, based on program transformation. More precisely, the type signatures of generic functions, i.e., functions parameterized on types, are transformed. This transformation maps typelevel expressions from functional higher-order, typed languages to type-level expressions in C++. In particular, type-level functional constructs such as higher-order functions and type constructors, are mapped to type parameters of generics that are constrained with appropriate concepts. The core of the transformation is a novel form of "defunctionalization" at the level of types. To make the transformation retargetable, we based it on two kernel languages that can be bound to different functional and object-oriented languages. For this paper, we use bindings to Haskell as front end and C++ with concepts as back end. Our transformational approach presents an alternative to a language extension and is useful particularly for functional prototyping where functional features are employed at specification time. We illustrate our approach by a case study: we show how we developed a generic C++ library for vulnerability modeling in the context of global change from a functional prototype in Haskell.