Safe Haskell	None
Language	Haskell2010

Data.Type.Role.Phantom

Synopsis

class (forall a b. Coercible (f a) (f b)) => Phantom (f :: k -> l)
data Phantomicity (f :: k -> l) where
- Phantomicity :: Phantom f => Phantomicity f
applyPhantom :: Phantomicity f -> Coercion f g -> Coercion (f a) (g b)
class (forall a b. Coercible (f a) (f b) => Coercible a b) => NonPhantom (f :: k -> l)
data NonPhantomicity (f :: k -> l) where
- NonPhantomicity :: NonPhantom f => NonPhantomicity f
innerNonPhantom :: NonPhantomicity f -> Coercion (f a) (f b) -> Coercion a b

Documentation

class (forall a b. Coercible (f a) (f b)) => Phantom (f :: k -> l) Source #

A constraint witnessing that the next argument of the type constructor of the f type has phantom type role.

For example Proxy atomatically becomes an instance of this class.

Instances

(forall (a :: k) (b :: k). Coercible (f a) (f b)) => Phantom (f :: k -> l) Source #
Instance details Defined in Data.Type.Role.Phantom

data Phantomicity (f :: k -> l) where Source #

A datatype witness of the phantom type role.

Constructors

Saturate a coercion of a phantom datatype.

class (forall a b. Coercible (f a) (f b) => Coercible a b) => NonPhantom (f :: k -> l) Source #

A constraint witnessing that the next argument of the type constructor of the f type has a non-phantom (representational or nominal) type role.

For example Map and Maybe automatically become instances of this class.

Instances

(forall (a :: k) (b :: k). Coercible (f a) (f b) => Coercible a b) => NonPhantom (f :: k -> l) Source #
Instance details Defined in Data.Type.Role.Phantom

data NonPhantomicity (f :: k -> l) where Source #

A datatype witness of the non-phantom type role.

Constructors

Extract coercion from coercibility of types in a non-phantom position.