License	BSD-style (see the LICENSE file in the distribution)
Maintainer	libraries@haskell.org
Stability	experimental
Portability	not portable
Safe Haskell	None
Language	Haskell2010

Data.Type.Coercion

Description

Definition of representational equality (Coercion).

Since: base-4.7.0.0

Synopsis

data Coercion a b where
- Coercion :: Coercible a b => Coercion a b
coerceWith :: Coercion a b -> a -> b
gcoerceWith :: Coercion a b -> (Coercible a b => r) -> r
sym :: Coercion a b -> Coercion b a
trans :: Coercion a b -> Coercion b c -> Coercion a c
repr :: (a :~: b) -> Coercion a b
class TestCoercion f where
- testCoercion :: f a -> f b -> Maybe (Coercion a b)

Documentation

data Coercion a b where #

Representational equality. If Coercion a b is inhabited by some terminating value, then the type a has the same underlying representation as the type b.

To use this equality in practice, pattern-match on the Coercion a b to get out the Coercible a b instance, and then use coerce to apply it.

Since: base-4.7.0.0

Constructors

Coercion :: Coercible a b => Coercion a b

Instances

Category (Coercion :: k -> k -> Type) #	Since: base-4.7.0.0
Instance details Defined in Control.Category Methods id :: Coercion a a # (.) :: Coercion b c -> Coercion a b -> Coercion a c #
TestCoercion (Coercion a :: k -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: Coercion a a0 -> Coercion a b -> Maybe (Coercion a0 b) #
Coercible a b => Bounded (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods minBound :: Coercion a b # maxBound :: Coercion a b #
Coercible a b => Enum (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods succ :: Coercion a b -> Coercion a b # pred :: Coercion a b -> Coercion a b # toEnum :: Int -> Coercion a b # fromEnum :: Coercion a b -> Int # enumFrom :: Coercion a b -> [Coercion a b] # enumFromThen :: Coercion a b -> Coercion a b -> [Coercion a b] # enumFromTo :: Coercion a b -> Coercion a b -> [Coercion a b] # enumFromThenTo :: Coercion a b -> Coercion a b -> Coercion a b -> [Coercion a b] #
Eq (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods (==) :: Coercion a b -> Coercion a b -> Bool Source # (/=) :: Coercion a b -> Coercion a b -> Bool Source #
(Coercible a b, Data a, Data b) => Data (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> Coercion a b -> c (Coercion a b) # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Coercion a b) # toConstr :: Coercion a b -> Constr # dataTypeOf :: Coercion a b -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Coercion a b)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Coercion a b)) # gmapT :: (forall b0. Data b0 => b0 -> b0) -> Coercion a b -> Coercion a b # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Coercion a b -> r # gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Coercion a b -> r # gmapQ :: (forall d. Data d => d -> u) -> Coercion a b -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Coercion a b -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Coercion a b -> m (Coercion a b) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Coercion a b -> m (Coercion a b) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Coercion a b -> m (Coercion a b) #
Ord (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods compare :: Coercion a b -> Coercion a b -> Ordering Source # (<) :: Coercion a b -> Coercion a b -> Bool Source # (<=) :: Coercion a b -> Coercion a b -> Bool Source # (>) :: Coercion a b -> Coercion a b -> Bool Source # (>=) :: Coercion a b -> Coercion a b -> Bool Source # max :: Coercion a b -> Coercion a b -> Coercion a b Source # min :: Coercion a b -> Coercion a b -> Coercion a b Source #
Coercible a b => Read (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods readsPrec :: Int -> ReadS (Coercion a b) # readList :: ReadS [Coercion a b] # readPrec :: ReadPrec (Coercion a b) # readListPrec :: ReadPrec [Coercion a b] #
Show (Coercion a b) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods showsPrec :: Int -> Coercion a b -> ShowS # show :: Coercion a b -> String # showList :: [Coercion a b] -> ShowS #

coerceWith :: Coercion a b -> a -> b #

Type-safe cast, using representational equality

gcoerceWith :: Coercion a b -> (Coercible a b => r) -> r #

Generalized form of type-safe cast using representational equality

Since: base-4.10.0.0

sym :: Coercion a b -> Coercion b a #

Symmetry of representational equality

trans :: Coercion a b -> Coercion b c -> Coercion a c #

Transitivity of representational equality

repr :: (a :~: b) -> Coercion a b #

Convert propositional (nominal) equality to representational equality

class TestCoercion f where #

This class contains types where you can learn the equality of two types from information contained in terms. Typically, only singleton types should inhabit this class.

Methods

testCoercion :: f a -> f b -> Maybe (Coercion a b) #

Conditionally prove the representational equality of a and b.

Instances

TestCoercion (Coercion a :: k -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: Coercion a a0 -> Coercion a b -> Maybe (Coercion a0 b) #
TestCoercion ((:~:) a :: k -> Type) #	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: (a :~: a0) -> (a :~: b) -> Maybe (Coercion a0 b) #
TestCoercion ((:~~:) a :: k -> Type) #	Since: base-4.10.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: (a :~~: a0) -> (a :~~: b) -> Maybe (Coercion a0 b) #