Copyright	(C) 2015-2021 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	None
Language	Haskell2010

Data.Constraint.Deferrable

Description

The idea for this trick comes from Dimitrios Vytiniotis.

Synopsis

newtype UnsatisfiedConstraint = UnsatisfiedConstraint String
class Deferrable p where
- deferEither :: (p => r) -> Either String r
defer :: forall p r. Deferrable p => (p => r) -> r
deferred :: forall p. Deferrable p :- p
data (a :: k1) :~~: (b :: k2) where
- HRefl :: forall k1 (a :: k1). a :~~: a
data (a :: k) :~: (b :: k) where
- Refl :: forall k (a :: k). a :~: a

Documentation

newtype UnsatisfiedConstraint Source #

Constructors

UnsatisfiedConstraint String

Instances

Instances details

Show UnsatisfiedConstraint Source #
Instance details Defined in Data.Constraint.Deferrable Methods showsPrec :: Int -> UnsatisfiedConstraint -> ShowS # show :: UnsatisfiedConstraint -> String # showList :: [UnsatisfiedConstraint] -> ShowS #
Exception UnsatisfiedConstraint Source #
Instance details Defined in Data.Constraint.Deferrable Methods toException :: UnsatisfiedConstraint -> SomeException # fromException :: SomeException -> Maybe UnsatisfiedConstraint # displayException :: UnsatisfiedConstraint -> String #

class Deferrable p where Source #

Allow an attempt at resolution of a constraint at a later time

Methods

deferEither :: (p => r) -> Either String r Source #

Resolve a Deferrable constraint with observable failure.

Instances

Instances details

Deferrable () Source #
Instance details Defined in Data.Constraint.Deferrable Methods deferEither :: (() => r) -> Either String r Source #
(Deferrable a, Deferrable b) => Deferrable (a, b) Source #
Instance details Defined in Data.Constraint.Deferrable Methods deferEither :: ((a, b) => r) -> Either String r Source #
(Typeable k, Typeable a, Typeable b) => Deferrable (a ~ b) Source #	Deferrable homogeneous equality constraints. Note that due to a GHC bug (https:/ghc.haskell.orgtracghcticket/10343), using this instance on GHC 7.10 will only work with `*`-kinded types.
Instance details Defined in Data.Constraint.Deferrable Methods deferEither :: (a ~ b => r) -> Either String r Source #
(Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c) Source #
Instance details Defined in Data.Constraint.Deferrable Methods deferEither :: ((a, b, c) => r) -> Either String r Source #
(Typeable i, Typeable j, Typeable a, Typeable b) => Deferrable (a ~~ b) Source #	Deferrable heterogenous equality constraints. Only available on GHC 8.0 or later.
Instance details Defined in Data.Constraint.Deferrable Methods deferEither :: (a ~~ b => r) -> Either String r Source #

defer :: forall p r. Deferrable p => (p => r) -> r Source #

deferred :: forall p. Deferrable p :- p Source #

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: base-4.10.0.0

Constructors

HRefl :: forall k1 (a :: k1). a :~~: a

Instances

Instances details

Category ((:~~:) :: k -> k -> Type)	Since: base-4.10.0.0
Instance details Defined in Control.Category Methods id :: forall (a :: k0). a :~~: a # (.) :: forall (b :: k0) (c :: k0) (a :: k0). (b :~~: c) -> (a :~~: b) -> a :~~: c #
TestCoercion ((:~~:) a :: k -> Type)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: forall (a0 :: k0) (b :: k0). (a :~~: a0) -> (a :~~: b) -> Maybe (Coercion a0 b) #
TestEquality ((:~~:) a :: k -> Type)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods testEquality :: forall (a0 :: k0) (b :: k0). (a :~~: a0) -> (a :~~: b) -> Maybe (a0 :~: b) #
NFData2 ((:~~:) :: Type -> Type -> Type)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods liftRnf2 :: (a -> ()) -> (b -> ()) -> (a :~~: b) -> () #
NFData1 ((:~~:) a :: Type -> Type)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods liftRnf :: (a0 -> ()) -> (a :~~: a0) -> () #
a ~~ b => Bounded (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods minBound :: a :~~: b # maxBound :: a :~~: b #
a ~~ b => Enum (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods succ :: (a :~~: b) -> a :~~: b # pred :: (a :~~: b) -> a :~~: b # toEnum :: Int -> a :~~: b # fromEnum :: (a :~~: b) -> Int # enumFrom :: (a :~~: b) -> [a :~~: b] # enumFromThen :: (a :~~: b) -> (a :~~: b) -> [a :~~: b] # enumFromTo :: (a :~~: b) -> (a :~~: b) -> [a :~~: b] # enumFromThenTo :: (a :~~: b) -> (a :~~: b) -> (a :~~: b) -> [a :~~: b] #
Eq (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods (==) :: (a :~~: b) -> (a :~~: b) -> Bool # (/=) :: (a :~~: b) -> (a :~~: b) -> Bool #
(Typeable i, Typeable j, Typeable a, Typeable b, a ~~ b) => Data (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Data Methods gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> (a :~~: b) -> c (a :~~: b) # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (a :~~: b) # toConstr :: (a :~~: b) -> Constr # dataTypeOf :: (a :~~: b) -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (a :~~: b)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (a :~~: b)) # gmapT :: (forall b0. Data b0 => b0 -> b0) -> (a :~~: b) -> a :~~: b # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> (a :~~: b) -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> (a :~~: b) -> r # gmapQ :: (forall d. Data d => d -> u) -> (a :~~: b) -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> (a :~~: b) -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> (a :~~: b) -> m (a :~~: b) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> (a :~~: b) -> m (a :~~: b) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> (a :~~: b) -> m (a :~~: b) #
Ord (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods compare :: (a :~~: b) -> (a :~~: b) -> Ordering # (<) :: (a :~~: b) -> (a :~~: b) -> Bool # (<=) :: (a :~~: b) -> (a :~~: b) -> Bool # (>) :: (a :~~: b) -> (a :~~: b) -> Bool # (>=) :: (a :~~: b) -> (a :~~: b) -> Bool # max :: (a :~~: b) -> (a :~~: b) -> a :~~: b # min :: (a :~~: b) -> (a :~~: b) -> a :~~: b #
a ~~ b => Read (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods readsPrec :: Int -> ReadS (a :~~: b) # readList :: ReadS [a :~~: b] # readPrec :: ReadPrec (a :~~: b) # readListPrec :: ReadPrec [a :~~: b] #
Show (a :~~: b)	Since: base-4.10.0.0
Instance details Defined in Data.Type.Equality Methods showsPrec :: Int -> (a :~~: b) -> ShowS # show :: (a :~~: b) -> String # showList :: [a :~~: b] -> ShowS #
a ~~ b => Boring (a :~~: b)	Heterogeneous type equality is `Boring` too.
Instance details Defined in Data.Boring Methods boring :: a :~~: b Source #
NFData (a :~~: b)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods rnf :: (a :~~: b) -> () #
HasDict (a ~~ b) (a :~~: b) Source #
Instance details Defined in Data.Constraint Methods evidence :: (a :~~: b) -> Dict (a ~~ b) Source #

data (a :: k) :~: (b :: k) where infix 4 #

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: base-4.7.0.0

Constructors

Refl :: forall k (a :: k). a :~: a

Instances

Instances details

Category ((:~:) :: k -> k -> Type)	Since: base-4.7.0.0
Instance details Defined in Control.Category Methods id :: forall (a :: k0). a :~: a # (.) :: forall (b :: k0) (c :: k0) (a :: k0). (b :~: c) -> (a :~: b) -> a :~: c #
TestCoercion ((:~:) a :: k -> Type)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Coercion Methods testCoercion :: forall (a0 :: k0) (b :: k0). (a :~: a0) -> (a :~: b) -> Maybe (Coercion a0 b) #
TestEquality ((:~:) a :: k -> Type)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods testEquality :: forall (a0 :: k0) (b :: k0). (a :~: a0) -> (a :~: b) -> Maybe (a0 :~: b) #
NFData2 ((:~:) :: Type -> Type -> Type)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods liftRnf2 :: (a -> ()) -> (b -> ()) -> (a :~: b) -> () #
NFData1 ((:~:) a)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods liftRnf :: (a0 -> ()) -> (a :~: a0) -> () #
a ~ b => Bounded (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods minBound :: a :~: b # maxBound :: a :~: b #
a ~ b => Enum (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods succ :: (a :~: b) -> a :~: b # pred :: (a :~: b) -> a :~: b # toEnum :: Int -> a :~: b # fromEnum :: (a :~: b) -> Int # enumFrom :: (a :~: b) -> [a :~: b] # enumFromThen :: (a :~: b) -> (a :~: b) -> [a :~: b] # enumFromTo :: (a :~: b) -> (a :~: b) -> [a :~: b] # enumFromThenTo :: (a :~: b) -> (a :~: b) -> (a :~: b) -> [a :~: b] #
Eq (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods (==) :: (a :~: b) -> (a :~: b) -> Bool # (/=) :: (a :~: b) -> (a :~: b) -> Bool #
(a ~ b, Data a) => Data (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) -> (a :~: b) -> c (a :~: b) # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (a :~: b) # toConstr :: (a :~: b) -> Constr # dataTypeOf :: (a :~: b) -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (a :~: b)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (a :~: b)) # gmapT :: (forall b0. Data b0 => b0 -> b0) -> (a :~: b) -> a :~: b # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> (a :~: b) -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> (a :~: b) -> r # gmapQ :: (forall d. Data d => d -> u) -> (a :~: b) -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> (a :~: b) -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> (a :~: b) -> m (a :~: b) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> (a :~: b) -> m (a :~: b) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> (a :~: b) -> m (a :~: b) #
Ord (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods compare :: (a :~: b) -> (a :~: b) -> Ordering # (<) :: (a :~: b) -> (a :~: b) -> Bool # (<=) :: (a :~: b) -> (a :~: b) -> Bool # (>) :: (a :~: b) -> (a :~: b) -> Bool # (>=) :: (a :~: b) -> (a :~: b) -> Bool # max :: (a :~: b) -> (a :~: b) -> a :~: b # min :: (a :~: b) -> (a :~: b) -> a :~: b #
a ~ b => Read (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods readsPrec :: Int -> ReadS (a :~: b) # readList :: ReadS [a :~: b] # readPrec :: ReadPrec (a :~: b) # readListPrec :: ReadPrec [a :~: b] #
Show (a :~: b)	Since: base-4.7.0.0
Instance details Defined in Data.Type.Equality Methods showsPrec :: Int -> (a :~: b) -> ShowS # show :: (a :~: b) -> String # showList :: [a :~: b] -> ShowS #
a ~ b => Boring (a :~: b)	Homogeneous type equality is `Boring` too.
Instance details Defined in Data.Boring Methods boring :: a :~: b Source #
NFData (a :~: b)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods rnf :: (a :~: b) -> () #
HasDict (a ~ b) (a :~: b) Source #
Instance details Defined in Data.Constraint Methods evidence :: (a :~: b) -> Dict (a ~ b) Source #