An Inherently-Typed Formalization for Featherweight Java

Featherweight Java is one of the most popular calculi which specify object-oriented programming features. It has been used as the basis for investigating novel language functionalities, as well as to specify and understand the formal properties of existing features for languages in this paradigm. However, when considering mechanized formalization, it is hard to find an implementation for languages with complex structures and binding mechanisms as Featherweight Java. In this paper we explore an inherently-typed approach to formalize Featherweight Java, implementing the static and dynamic semantics in Agda using dependent types, and then replicating it in Coq (the latter using the Equations plug-in). Using this approach, the interpreter is correct by construction, since the type checker of the host language is responsible for verifying type safety, thus avoiding repetitions of proofs and error checking.