Emulation of subkinds and subkind polymorphism.
Subkinds are the kind-level analog to subtypes. A kind denotes a set of types, and a subkind of some base kind denotes a subset of the base kind’s set of types. Haskell has no support for subkinds and subkind polymorphism. However, this package can be used to emulate subkinds of kind * and subkind variables.
To define a new subkind, the user declares a type that represents the subkind, and instantiates some classes. Afterwards, the user can declare types to be of that subkind and universally quantify over the inhabitants of the subkind. Since subkinds are represented by types, type-level polymorphism can be used to emulate kind-level polymorphism.
For detailed information, please refer to Section 6 of the paper Generic Record Combinators with Static Type Checking.