= Kind Annotations =

== Brief explanation ==

In Haskell 98, each type constructor and variable has a kind.
Though the Report uses a notation for kinds, they do not appear in Haskell source.

GHC permits types and new type constructors and variables to be annotated with a kind signature, e.g.
{{{
type T (f :: * -> *) = f Int
}}}

== References ==
 * [http://www.haskell.org/onlinereport/decls.html#sect4.1.1 Kinds] in the Haskell 98 report
 * [http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html#sec-kinding Explicitly-kinded quantification] in the GHC User's Guide

== Tickets ==
[[TicketQuery(description~=KindAnnotations)]]

== Pros ==
 * Allows more machine-checked documentation.
 * Haskell 98 defaults kinds to `*`, which is a nuisance if you want a higher kind.
   Kind annotations remove the need for awkward workarounds like dummy data constructors.
   See KindInference for alternative solutions to this problem.

== Cons ==
 * con

== Proposal ==

To adopt explicit kind annotations as part of the language, more or less exactly as GHC permits.