Data.Typeable

Copyright	(c) The University of Glasgow, CWI 2001--2004
License	BSD-style (see the file libraries/base/LICENSE)
Maintainer	[email protected]
Stability	experimental
Portability	portable
Safe Haskell	Trustworthy
Language	Haskell2010

The Typeable class

class Typeable a Source

The class Typeable allows a concrete representation of a type to be calculated.

typeRep :: forall proxy a. Typeable a => proxy a -> TypeRep Source

Takes a value of type a and returns a concrete representation of that type.

Since: 4.7.0.0

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

For backwards compatibility

typeOf :: forall a. Typeable a => a -> TypeRep Source

typeOf1 :: forall t a. Typeable t => t a -> TypeRep Source

typeOf2 :: forall t a b. Typeable t => t a b -> TypeRep Source

typeOf3 :: forall t a b c. Typeable t => t a b c -> TypeRep Source

typeOf4 :: forall t a b c d. Typeable t => t a b c d -> TypeRep Source

typeOf5 :: forall t a b c d e. Typeable t => t a b c d e -> TypeRep Source

typeOf6 :: forall t a b c d e f. Typeable t => t a b c d e f -> TypeRep Source

typeOf7 :: forall t a b c d e f g. Typeable t => t a b c d e f g -> TypeRep Source

type Typeable1 a = Typeable a Source

type Typeable2 a = Typeable a Source

type Typeable3 a = Typeable a Source

type Typeable4 a = Typeable a Source

type Typeable5 a = Typeable a Source

type Typeable6 a = Typeable a Source

type Typeable7 a = Typeable a Source

Type-safe cast

cast :: forall a b. (Typeable a, Typeable b) => a -> Maybe b Source

The type-safe cast operation

eqT :: forall a b. (Typeable a, Typeable b) => Maybe (a :~: b) Source

Extract a witness of equality of two types

Since: 4.7.0.0

gcast :: forall a b c. (Typeable a, Typeable b) => c a -> Maybe (c b) Source

A flexible variation parameterised in a type constructor

Generalized casts for higher-order kinds

gcast1 :: forall c t t' a. (Typeable t, Typeable t') => c (t a) -> Maybe (c (t' a)) Source

Cast over k1 -> k2

gcast2 :: forall c t t' a b. (Typeable t, Typeable t') => c (t a b) -> Maybe (c (t' a b)) Source

Cast over k1 -> k2 -> k3

A canonical proxy type

data Proxy t Source

A concrete, poly-kinded proxy type

Type representations

data TypeRep Source

A concrete representation of a (monomorphic) type. TypeRep supports reasonably efficient equality.

typeRepFingerprint :: TypeRep -> Fingerprint Source

Observe the Fingerprint of a type representation

Since: 4.8.0.0

rnfTypeRep :: TypeRep -> () Source

Helper to fully evaluate TypeRep for use as NFData(rnf) implementation

Since: 4.8.0.0

showsTypeRep :: TypeRep -> ShowS Source

data TyCon Source

An abstract representation of a type constructor. TyCon objects can be built using mkTyCon.

tyConFingerprint :: TyCon -> Fingerprint Source

Since: 4.8.0.0

tyConString :: TyCon -> String Source

Observe string encoding of a type representation

tyConPackage :: TyCon -> String Source

Since: 4.5.0.0

tyConModule :: TyCon -> String Source

Since: 4.5.0.0

tyConName :: TyCon -> String Source

Since: 4.5.0.0

rnfTyCon :: TyCon -> () Source

Helper to fully evaluate TyCon for use as NFData(rnf) implementation

Since: 4.8.0.0

Construction of type representations

mkTyCon3 Source

Builds a TyCon object representing a type constructor. An implementation of Data.Typeable should ensure that the following holds:

 A==A' ^ B==B' ^ C==C' ==> mkTyCon A B C == mkTyCon A' B' C'

mkTyConApp :: TyCon -> [TypeRep] -> TypeRep Source

Applies a monomorphic type constructor to a sequence of types

mkAppTy :: TypeRep -> TypeRep -> TypeRep Source

Adds a TypeRep argument to a TypeRep.

mkFunTy :: TypeRep -> TypeRep -> TypeRep Source

A special case of mkTyConApp, which applies the function type constructor to a pair of types.

Observation of type representations

splitTyConApp :: TypeRep -> (TyCon, [TypeRep]) Source

Splits a type constructor application. Note that if the type construcotr is polymorphic, this will not return the kinds that were used. See splitPolyTyConApp if you need all parts.

funResultTy :: TypeRep -> TypeRep -> Maybe TypeRep Source

Applies a type to a function type. Returns: Just u if the first argument represents a function of type t -> u and the second argument represents a function of type t. Otherwise, returns Nothing.

typeRepTyCon :: TypeRep -> TyCon Source

Observe the type constructor of a type representation

typeRepArgs :: TypeRep -> [TypeRep] Source

Observe the argument types of a type representation