But my previous reply is a little content-free, as what you're really asking for is how we solve the same problem that typeclasses solve in Haskell.

Very briefly, there's two ways of asking whether a caller can change the type of a parameter. The normal way is to say, are all the possible values of the caller's type in the set of nouns that the parameter defines? This is what I call "geometric polymorphism."

But there's also "generic polymorphism," in which we ask: will the Nock code that was generated for the parameter type, actually work with the type we're calling it with? A really stupid way to ask this is to recompile the function, with the parameters exchanged for the arguments. The Hoon approach is a little bit smarter than this but not much.

So, with these two approaches, you basically get variance and genericity, which is all of polymorphism.