Type systems for the masses: deriving soundness proofs and efficient checkers

Sylvia Grewe, Sebastian Erdweg, Pascal Wittmann, Mira Mezini. Type systems for the masses: deriving soundness proofs and efficient checkers. In Gail C. Murphy, Guy L. Steele Jr., editors, 2015 ACM International Symposium on New Ideas, New Paradigms, and Reflections on Programming and Software, Onward! 2015, Pittsburgh, PA, USA, October 25-30, 2015. pages 137-150, ACM, 2015. [doi]


The correct definition and implementation of non-trivial type systems is difficult and requires expert knowledge, which is not available to developers of domain-specific languages (DSLs) in practice. We propose Veritas, a workbench that simplifies the development of sound type systems. Veritas provides a single, high-level specification language for type systems, from which it automatically tries to derive soundness proofs and efficient and correct type-checking algorithms. For verification, Veritas combines off-the-shelf automated first-order theorem provers with automated proof strategies specific to type systems. For deriving efficient type checkers, Veritas provides a collection of optimization strategies whose applicability to a given type system is checked through verification on a case-by-case basis. We have developed a prototypical implementation of Veritas and used it to verify type soundness of the simply-typed lambda calculus and of parts of typed SQL. Our experience suggests that many of the individual verification steps can be automated and, in particular, that a high degree of automation is possible for type systems of DSLs.