Saint: an API-generic type-safe interpreter

Paper in proceedings, 2019

Many programs written in the functional programming language Haskell take advantage of its advanced type system. Haskell's type system is very expressive and allows us to write interesting programs without sacrificing type safety. Haskell programs that expose its API to an open world, however, are faced with the problem of dynamic type checking. Existing techniques that address this problem, such as Typeable and Dynamic, are often closed and difficult to extend. We have constructed an extensible library for describing APIs using annotated type representations. As a result, API calls can be interpreted in a type-safe manner without any extra programming effort. In addition, the user has full control over the universe of allowed types, which helps to catch any misconceptions in an early stage. We have applied our technique to connect a real-world DSL (GRACe) to a JavaScript GUI.