| Copyright | (c) The University of Glasgow CWI 2001--2017 |
|---|---|
| License | BSD-style (see the file libraries/base/LICENSE) |
| Maintainer | libraries@haskell.org |
| Stability | experimental |
| Portability | non-portable (requires GADTs and compiler support) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
Type.Reflection
Contents
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).
The interface provides TypeRep, a type representation which can
be safely decomposed and composed. See Data.Dynamic for an example of this.
Since: 4.10.0.0
- class Typeable (a :: k)
- typeRep :: Typeable a => TypeRep a
- withTypeable :: forall a r. TypeRep a -> (Typeable a => r) -> r
- data a :~: b where
- data (a :: k1) :~~: (b :: k2) where
- data TypeRep (a :: k)
- 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). TyCon -> TypeRep a
- pattern Con' :: forall k (a :: k). 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
The class Typeable allows a concrete representation of a type to
be calculated.
Minimal complete definition
typeRep#
withTypeable :: forall a r. TypeRep a -> (Typeable a => r) -> r #
Propositional equality
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
Instances
| Category k ((:~:) k) # | Since: 4.7.0.0 |
| TestEquality k ((:~:) k a) # | Since: 4.7.0.0 |
| TestCoercion k ((:~:) k a) # | Since: 4.7.0.0 |
| (~) k a b => Bounded ((:~:) k a b) # | Since: 4.7.0.0 |
| (~) k a b => Enum ((:~:) k a b) # | Since: 4.7.0.0 |
| Eq ((:~:) k a b) # | |
| ((~) * a b, Data a) => Data ((:~:) * a b) # | Since: 4.7.0.0 |
| Ord ((:~:) k a b) # | |
| (~) k a b => Read ((:~:) k a b) # | Since: 4.7.0.0 |
| Show ((:~:) k a b) # | |
data (a :: k1) :~~: (b :: k2) where infix 4 #
Kind heterogeneous propositional equality. Like '(:~:)', a :~~: b is
inhabited by a terminating value if and only if a is the same type as b.
Since: 4.10.0.0
Instances
| Category k ((:~~:) k k) # | Since: 4.10.0.0 |
| TestEquality k ((:~~:) k1 k a) # | Since: 4.10.0.0 |
| TestCoercion k ((:~~:) k1 k a) # | Since: 4.10.0.0 |
| (~~) k1 k2 a b => Bounded ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
| (~~) k1 k2 a b => Enum ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
| Eq ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
| (Typeable * i2, Typeable * j2, Typeable i2 a, Typeable j2 b, (~~) i2 j2 a b) => Data ((:~~:) i2 j2 a b) # | Since: 4.10.0.0 |
| Ord ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
| (~~) k1 k2 a b => Read ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
| Show ((:~~:) k1 k2 a b) # | Since: 4.10.0.0 |
Type representations
Type-Indexed
A concrete representation of a (monomorphic) type.
TypeRep 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 #
A type application.
For instance,
typeRep @(Maybe Int) === App (typeRep @Maybe) (typeRep @Int)
Note that this will never match a function type (e.g. Int -> Char).
pattern Con' :: forall k (a :: k). TyCon -> [SomeTypeRep] -> TypeRep a #
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
@
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 #
The function type constructor.
For instance,
typeRep @(Int -> Char) === Fun (typeRep @Int) (typeRep @Char)
typeRepTyCon :: TypeRep a -> TyCon #
Observe the type constructor of a type representation
rnfTypeRep :: TypeRep a -> () #
Helper to fully evaluate TypeRep for use as NFData(rnf) implementation
Since: 4.8.0.0
eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2). TypeRep a -> TypeRep b -> Maybe (a :~~: b) #
Type equality
Since: 4.10
typeRepKind :: TypeRep (a :: k) -> TypeRep k #
Observe the kind of a type.
splitApps :: TypeRep a -> (TyCon, [SomeTypeRep]) #
Quantified
data SomeTypeRep where #
A non-indexed type representation.
Constructors
| SomeTypeRep :: forall k (a :: k). !(TypeRep a) -> SomeTypeRep |
Instances
| Eq SomeTypeRep # | |
| Ord SomeTypeRep # | |
| Show SomeTypeRep # | Since: 4.10.0.0 |
someTypeRep :: forall proxy a. Typeable a => proxy a -> SomeTypeRep #
Takes a value of type a and returns a concrete representation
of that type.
Since: 4.7.0.0
someTypeRepTyCon :: SomeTypeRep -> TyCon #
Observe the type constructor of a quantified type representation.
rnfSomeTypeRep :: SomeTypeRep -> () #
Helper to fully evaluate SomeTypeRep for use as NFData(rnf)
implementation
Since: 4.10.0.0
Type constructors
tyConPackage :: TyCon -> String #
tyConModule :: TyCon -> String #
Module names
moduleName :: Module -> String #
modulePackage :: Module -> String #