Aspects for Stages: Cross Cutting Concerns for Metaprograms

In multi-stage languages the program code is finalized though a sequence of transformations defined in the program itself, a process known as staging, with stages also referred as metaprograms. Since stages are essentially programs, they may also require application of aspectoriented methods to handle crosscutting concerns, something not considered or supported in existing aspect systems. We introduce aspect-oriented support for multi-stage languages by identifying three aspect types for the staging pipeline, namely pre-, inand poststaging. We discuss their implementation in a language supporting compile-time metaprogramming, where aspects are realized as batches of AST transformation metaprograms, accompanied by an AOP-specific library. We also provide example scenarios where the proposed aspect types may be used in practice. Finally, we show how full-scale source-level aspect debugging is facilitated during the program compilation process.