It's about the ability, not the reality. As Racket, the base language can have no explicit rules for any type systems to be embedded. There can be more powerful

It's about the ability, not the reality. As Racket, the base language can have no explicit rules for any type systems to be embedded. There can be more powerful candidates, e.g. Kernel: https://web.cs.wpi.edu/~jshutt/kernel.html https://web.cs.wpi.edu/~jshutt/kernel.html. Racket is special because its designers provide dedicated support of language-oriented programming. But that is about ecosystems, not typesystems.