@hackage data-category0.2.0

Data-category is a collection of categories, and some categorical constructions on them.

You can restrict the types of the objects of your category by using a GADT for the arrow type. To be able to proof to the compiler that a type is an object in some category, objects also need to be represented at the value level. Therefore the Category class has an associated data type Obj. This which will often also be a GADT.

See the Monoid, Boolean and Product categories for some examples.