Type.Reflection (original) (raw)

Contents

• The Typeable class
• Propositional equality
• Type representations
  • Type-Indexed
  • Quantified
• Type constructors
• Module names

Description

This provides a type-indexed type representation mechanism, similar to that described by,

• Simon Peyton-Jones, Stephanie Weirich, Richard Eisenberg, Dimitrios Vytiniotis. "A reflection on types."Proc. Philip Wadler's 60th birthday Festschrift, Edinburgh (April 2016). ([PDF](https:/_www.microsoft.com_en-us_research_wp-content_uploads_2016_08_dynamic.pdf))

The interface provides [TypeRep](Type-Reflection.html#t:TypeRep "Type.Reflection"), a type representation which can be safely decomposed and composed. See Data.Dynamic for an example of this.

Since: 4.10.0.0

Synopsis

• class Typeable (a :: k)
• typeRep :: Typeable a => TypeRep a
• withTypeable :: forall k (a :: k) rep (r :: TYPE rep). TypeRep a -> (Typeable a => r) -> r
• data a :~: b where
  • Refl :: a :~: a
• data a :~~: b where
  • HRefl :: a :~~: a
• data TypeRep a
• typeOf :: Typeable a => a -> TypeRep a
• pattern App :: forall k2 (t :: k2). () => forall k1 (a :: k1 -> k2) (b :: k1). t ~ a b => TypeRep a -> TypeRep b -> TypeRep t
• pattern Con :: forall k (a :: k). () => IsApplication a ~ "" => TyCon -> TypeRep a
• pattern Con' :: forall k (a :: k). () => IsApplication a ~ "" => TyCon -> [SomeTypeRep] -> TypeRep a
• pattern Fun :: forall k (fun :: k). () => forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (arg :: TYPE r1) (res :: TYPE r2). (k ~ Type, fun ~~ (arg -> res)) => TypeRep arg -> TypeRep res -> TypeRep fun
• typeRepTyCon :: TypeRep a -> TyCon
• rnfTypeRep :: TypeRep a -> ()
• eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2). TypeRep a -> TypeRep b -> Maybe (a :~~: b)
• typeRepKind :: TypeRep (a :: k) -> TypeRep k
• splitApps :: TypeRep a -> (TyCon, [SomeTypeRep])
• data SomeTypeRep where
  • SomeTypeRep :: forall k (a :: k). !(TypeRep a) -> SomeTypeRep
• someTypeRep :: forall proxy a. Typeable a => proxy a -> SomeTypeRep
• someTypeRepTyCon :: SomeTypeRep -> TyCon
• rnfSomeTypeRep :: SomeTypeRep -> ()
• data TyCon
• tyConPackage :: TyCon -> String
• tyConModule :: TyCon -> String
• tyConName :: TyCon -> String
• rnfTyCon :: TyCon -> ()
• data Module
• moduleName :: Module -> String
• modulePackage :: Module -> String
• rnfModule :: Module -> ()

The Typeable class

class Typeable (a :: k) Source #

The class [Typeable](Type-Reflection.html#t:Typeable "Type.Reflection") allows a concrete representation of a type to be calculated.

Minimal complete definition

typeRep#

Propositional equality

data a :~: b where infix 4 Source #

Propositional equality. If a :~: b is inhabited by some terminating value, then the type a is the same as the type b. To use this equality in practice, pattern-match on the a :~: b to get out the Refl constructor; in the body of the pattern-match, the compiler knows that a ~ b.

Since: 4.7.0.0

data a :~~: b where infix 4 Source #

Kind heterogeneous propositional equality. Like [:~:](Type-Reflection.html#t::-126-: "Type.Reflection"), a :~~: b is inhabited by a terminating value if and only if a is the same type as b.

Since: 4.10.0.0

Type representationsType-Indexed

data TypeRep a Source #

A concrete representation of a (monomorphic) type.[TypeRep](Type-Reflection.html#t:TypeRep "Type.Reflection") supports reasonably efficient equality.

pattern App :: forall k2 (t :: k2). () => forall k1 (a :: k1 -> k2) (b :: k1). t ~ a b => TypeRep a -> TypeRep b -> TypeRep t Source #

A type application.

For instance,

typeRep @(Maybe Int) === App (typeRep @Maybe) (typeRep @Int)

Note that this will also match a function type,

typeRep @(Int# -> Char)

App (App arrow (typeRep @Int#)) (typeRep @Char)

where arrow :: TypeRep ((->) :: TYPE IntRep -> Type -> Type).

pattern Con :: forall k (a :: k). () => IsApplication a ~ "" => TyCon -> TypeRep a Source #

Pattern match on a type constructor

pattern Con' :: forall k (a :: k). () => IsApplication a ~ "" => TyCon -> [SomeTypeRep] -> TypeRep a Source #

Pattern match on a type constructor including its instantiated kind variables.

For instance,

App (Con' proxyTyCon ks) intRep = typeRep @(Proxy @Int)

will bring into scope,

proxyTyCon :: TyCon ks == [someTypeRep Type] :: [SomeTypeRep] intRep == typeRep Int

QuantifiedType constructorsModule names

data Module #

Instances

Instances details