Thanks! We're working on extending the system to support more advanced type systems. In theory, the current system could already support these kinds of features (but not in quite as slick a way as modern languages, most likely), but it would be very cumbersome, so the work is in trimming down the formalization and taking advantage of new abstractions. Check out the implementation for a look at how defining the actual language (and typing rules) works currently https://github.com/jeprinz/pantograph/blob/main/src/Language...