Attribute grammars fly first-class... safer!: dealing with DSL errors in type-level programming

AspectAG is a domain specific language embedded in Haskell to represent modular attribute grammars. In AspectAG attribute grammar fragments can be defined independently (even in separate modules) and then combined in a safe way. This flexibility is achieved through the use of extensible records, which are implemented using type-level programming techniques. Type-level programming support has remarkably evolved in Haskell since the first version of AspectAG was designed; having incorporated new features like data promotion and kind polymorphism, among others, which allows to program in a "strongly typed" way at the level of types in a similar way as when programming at the level of values. In this paper we redefine AspectAG applying the new type-level programming techniques. As a consequence, we obtain a more robust system with better error messages.