scolobbContracts in #Racket rock, you may even have fancy dependent contracts (like in dependent types) 🤗
https://docs.racket-lang.org/guide/contracts-general-functions.html
https://docs.racket-lang.org/guide/contracts-general-functions.html
Compared with ML-family strictly typed languages #haskell and #caml, contracts feel like writing parts of your own typechecker.
Disadvantage: you write your own typechecker.
Advantage: you don't need to write it all the time (gradual typing) and you choose the level of expressiveness as you want.
Feels great for research and prototyping.