Specifically, the type of a name depends on the type of the object. For example a Person with a Name would give a Persons-Name and a Dog with a Name would give a Dogs-Name.
One radically simple way to get that would be something like this (you can also use 'newtype' instead of 'data'): -- warning: untested code -- data (Eq b) => Named a b = Named a b equivalent :: Named a b -> Named c b -> Bool equivalent (Named _ a1 ) (Named _ a2) = (a1 == a2) Then you can check Persons-Name and Dogs-Name (Named Persons Name and Named Dogs Name) for equivalence based only on their values of Name type. Note that you can't use (==) from Eq class because Persons-Name and Dogs-Name are different types, and Eq class uses only one when instanciated. If you would like to use a equivalence relashionship that is not limited to your parametric type you could write a class like this: class Equivalent a b where equivalent :: a -> b -> Bool instance (Eq b) => Equivalent (Named a b) (Named c b) where ...
Thanks for your rapid feedback, I will study your code.
Instead, study Felipe's example. It shows a nice way to "attach" a name to anything, and shows some interesting classes you will like to learn. Best, Maurício