Comment by opnitro

Enforcing the type hints at runtime gets really expensive if you allow for complex/higher order types. Typed Racket has had trouble with this since it tries to actually be a sound gradual typing system. Interesting work here: https://dl.acm.org/doi/pdf/10.1145/3434334 on speeding it up via static analysis (figuring out what dynamic enforcement points you can statically eliminate).