Saint: An API-Generic Type-Safe Interpreter

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