Implementing monads for C++ template metaprograms

摘要

C++ template metaprogramming is used in various application areas, such as expression templates, static interface checking, active libraries, etc. Its recognized similarities to pure functional programming languages - like Haskell - make the adoption of advanced functional techniques possible. Such a technique is using monads, programming structures representing computations. Using them actions implementing domain logic can be chained together and decorated with custom code. C++ template metaprogramming could benefit from adopting monads in situations like advanced error propagation and parser construction. In this paper we present an approach for implementing monads in C++ template metaprograms. Based on this approach we have built a monadic framework for C++ template metaprogramming. As real world examples we present a generic error propagation solution for C++ template metaprograms and a technique for building compile-time parser generators. All solutions presented in this paper are implemented and available as an open source library.