# Kind

### From HaskellWiki

Revision as of 19:58, 4 January 2006 by 67.170.82.162 (Talk)

**Kinds** classify types. Kinds are to types and type-constructors what types are to values.

Ordinary types have kind `*`. Type constructors have kind `P -> Q`, where `P` and `Q` are kinds. For instance:

Int :: * Maybe :: * -> * Maybe Bool :: * a -> a :: * [] :: * -> * (->) :: * -> * -> *

In Haskell 98, `*` is the only **inhabited kind**, that is, all values have types of kind `*`. GHC introduces another inhabited kind, `#`, for unboxed types.