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 type-level 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.