kindtypes

Kindtypes refer to concepts in type theory and language design that involve kinds—the types of type constructors—and, in some discussions, treating or manipulating those kinds as part of the type system. The idea centers on extending or generalizing how kinds are used, often by enabling kind polymorphism or by allowing higher-level abstractions that operate over kinds themselves.

In many statically typed languages, kinds classify types. The simplest kind, often denoted by *, is the kind of concrete types. Type constructors have other kinds, such as * -> * for a one-argument type constructor (for example, a list type constructor) or even higher kinds like (* -> *) -> *. Kindtypes describe patterns and abstractions that can vary over these kinds, enabling more flexible generic programming and the ability to write code that is parameterized over the kind of its type arguments.

Core ideas associated with kindtypes include higher-kinded types, where type constructors themselves are parameters, and kind polymorphism, where abstractions can be general over kinds. Related language features include type-level functions, data kinds (promoting data to the kind level), and type families or associated types, which perform computations at the type level. Together, these enable advanced forms of code reuse and generic design, allowing libraries to be written in a way that is agnostic to the exact kind of their type arguments.

Challenges include increased language complexity, more difficult type errors, and the need for sophisticated type inference and tooling. Conceptual clarity about the distinction between kinds and types remains important for maintainability.

See also: Kinds, Higher-kinded types, Type-level programming, Data kinds, Type families, Type classes.