> a popular gradually typed language that natively allows writing both dynamic and type-safe code, allowing quick prototyping and then gradual refactor to type

> a popular gradually typed language that natively allows writing both dynamic and type-safe code, allowing quick prototyping and then gradual refactor to type safety. You mention it in your edit, but Crystal has been exactly that for me. A rubyist for a decade I found Crystal to have the type system I was expecting all along.