> if something is, say, a functor then you know what sort of things you can do with that value

Sure. Because you memorized all the functor methods and remembered that there is a functor instance defined for the data type at hand… ;-)

> Unfortunately this wouldn't be very idiomatic in Haskell, maybe in Idris with |> this would make more sense?

Or you could just admit that the "OOP style syntax" is superior. (I'm not saying that OOP is superior, though)