The real power comes, when you can express: var age: 18 ... 120; This is more than 50 years old Pascal. As far as I know the only mainstream language that

The real power comes, when you can express: var age: 18 ... 120; This is more than 50 years old Pascal. As far as I know the only mainstream language that supports this in its type system (and compile-time checked) today is Ada[1]. Blows my mind. I never got over the loss when I switched to C. [1] I think you could convince Rust to do something pretty close but a bit uglier syntax-wise.