Since Haskell is statically typed, I think it's a feature, not a bug, that type parametricity is implemented at compile time. Also, I think what you're describ

Since Haskell is statically typed, I think it's a feature, not a bug, that type parametricity is implemented at compile time. Also, I think what you're describing is the difference between parametric polymorphism and ad-hoc polymorphism.