Sound gradual typing is nominally alive and well

Recent research has identified significant performance hurdles that sound gradual typing needs to overcome. These performance hurdles stem from the fact that the run-time checks gradual type systems insert into code can cause significant overhead. We propose that designing a type system for a gradually typed language hand in hand with its implementation from scratch is a possible way around these and several other hurdles on the way to efficient sound gradual typing. Such a design process also highlights the type-system restrictions required for efficient composition with gradual typing. We formalize the core of a nominal object-oriented language that fulfills a variety of desirable properties for gradually typed languages, and present evidence that an implementation of this language suffers minimal overhead even in adversarial benchmarks identified in earlier work.