Portability | portable |
---|---|
Stability | experimental |
Maintainer | libraries@haskell.org |
Safe Haskell | Trustworthy |
The Typeable
class reifies types to some extent by associating type
representations to types. These type representations can be compared,
and one can in turn define a type-safe cast operation. To this end,
an unsafe cast is guarded by a test for type (representation)
equivalence. The module Data.Dynamic uses Typeable for an
implementation of dynamics. The module Data.Data uses Typeable
and type-safe cast (but not dynamics) to support the "Scrap your
boilerplate" style of generic programming.
- class Typeable a where
- cast :: (Typeable a, Typeable b) => a -> Maybe b
- gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
- data TypeRep
- showsTypeRep :: TypeRep -> ShowS
- data TyCon
- tyConString :: TyCon -> String
- tyConPackage :: TyCon -> String
- tyConModule :: TyCon -> String
- tyConName :: TyCon -> String
- mkTyCon :: String -> TyCon
- mkTyCon3 :: String -> String -> String -> TyCon
- mkTyConApp :: TyCon -> [TypeRep] -> TypeRep
- mkAppTy :: TypeRep -> TypeRep -> TypeRep
- mkFunTy :: TypeRep -> TypeRep -> TypeRep
- splitTyConApp :: TypeRep -> (TyCon, [TypeRep])
- funResultTy :: TypeRep -> TypeRep -> Maybe TypeRep
- typeRepTyCon :: TypeRep -> TyCon
- typeRepArgs :: TypeRep -> [TypeRep]
- typeRepKey :: TypeRep -> IO TypeRepKey
- data TypeRepKey
- class Typeable1 t where
- class Typeable2 t where
- class Typeable3 t where
- class Typeable4 t where
- class Typeable5 t where
- class Typeable6 t where
- class Typeable7 t where
- gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
- gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
- typeOfDefault :: forall t a. (Typeable1 t, Typeable a) => t a -> TypeRep
- typeOf1Default :: forall t a b. (Typeable2 t, Typeable a) => t a b -> TypeRep
- typeOf2Default :: forall t a b c. (Typeable3 t, Typeable a) => t a b c -> TypeRep
- typeOf3Default :: forall t a b c d. (Typeable4 t, Typeable a) => t a b c d -> TypeRep
- typeOf4Default :: forall t a b c d e. (Typeable5 t, Typeable a) => t a b c d e -> TypeRep
- typeOf5Default :: forall t a b c d e f. (Typeable6 t, Typeable a) => t a b c d e f -> TypeRep
- typeOf6Default :: forall t a b c d e f g. (Typeable7 t, Typeable a) => t a b c d e f g -> TypeRep
The Typeable class
The class Typeable
allows a concrete representation of a type to
be calculated.
Type-safe cast
gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)Source
A flexible variation parameterised in a type constructor
Type representations
A concrete representation of a (monomorphic) type. TypeRep
supports reasonably efficient equality.
showsTypeRep :: TypeRep -> ShowSSource
tyConString :: TyCon -> StringSource
Deprecated: renamed to tyConName; tyConModule and tyConPackage are also available.
Observe string encoding of a type representation
tyConPackage :: TyCon -> StringSource
tyConModule :: TyCon -> StringSource
Construction of type representations
Deprecated: either derive Typeable, or use mkTyCon3 instead
Backwards-compatible API
:: String | package name |
-> String | module name |
-> String | the name of the type constructor |
-> TyCon | A unique |
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] -> TypeRepSource
Applies a type constructor to a sequence of types
mkFunTy :: TypeRep -> TypeRep -> TypeRepSource
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
typeRepTyCon :: TypeRep -> TyConSource
Observe the type constructor of a type representation
typeRepArgs :: TypeRep -> [TypeRep]Source
Observe the argument types of a type representation
typeRepKey :: TypeRep -> IO TypeRepKeySource
The other Typeable classes
Note: The general instances are provided for GHC only.
Variant for unary type constructors
Typeable1 [] | |
Typeable1 Ratio | |
Typeable1 StablePtr | |
Typeable1 IO | |
Typeable1 Ptr | |
Typeable1 FunPtr | |
Typeable1 Maybe | |
Typeable1 MVar | |
Typeable1 IORef | |
Typeable1 ForeignPtr | |
Typeable1 Weak | |
Typeable1 TVar | |
Typeable1 STM | |
Typeable1 Chan | |
Typeable1 SampleVar | |
Typeable1 Complex | |
Typeable1 Fixed | |
Typeable1 StableName | |
(Typeable2 s, Typeable a) => Typeable1 (s a) | One Typeable1 instance for all Typeable2 instances |
Variant for binary type constructors
Variant for 3-ary type constructors
Variant for 4-ary type constructors
Variant for 5-ary type constructors
Variant for 6-ary type constructors
Variant for 7-ary type constructors
Default instances
Note: These are not needed by GHC, for which these instances are generated by general instance declarations.
typeOfDefault :: forall t a. (Typeable1 t, Typeable a) => t a -> TypeRepSource
typeOf1Default :: forall t a b. (Typeable2 t, Typeable a) => t a b -> TypeRepSource
typeOf2Default :: forall t a b c. (Typeable3 t, Typeable a) => t a b c -> TypeRepSource
typeOf3Default :: forall t a b c d. (Typeable4 t, Typeable a) => t a b c d -> TypeRepSource
typeOf4Default :: forall t a b c d e. (Typeable5 t, Typeable a) => t a b c d e -> TypeRepSource
typeOf5Default :: forall t a b c d e f. (Typeable6 t, Typeable a) => t a b c d e f -> TypeRepSource