Copyright | (C) 2015-2016 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 |
The idea for this trick comes from Dimitrios Vytiniotis.
Synopsis
- newtype UnsatisfiedConstraint = UnsatisfiedConstraint String
- class Deferrable p where
- deferEither :: proxy p -> (p => r) -> Either String r
- defer :: forall p r proxy. Deferrable p => proxy p -> (p => r) -> r
- deferred :: forall p. Deferrable p :- p
- defer_ :: forall p r. Deferrable p => (p => r) -> r
- deferEither_ :: forall p r. Deferrable p => (p => r) -> Either String r
- data (a :: k1) :~~: (b :: k2) :: forall k1 k2. k1 -> k2 -> Type where
- data (a :: k) :~: (b :: k) :: forall k. k -> k -> Type where
Documentation
newtype UnsatisfiedConstraint Source #
Instances
Show UnsatisfiedConstraint Source # | |
Defined in Data.Constraint.Deferrable showsPrec :: Int -> UnsatisfiedConstraint -> ShowS # show :: UnsatisfiedConstraint -> String # showList :: [UnsatisfiedConstraint] -> ShowS # | |
Exception UnsatisfiedConstraint Source # | |
class Deferrable p where Source #
Allow an attempt at resolution of a constraint at a later time
deferEither :: proxy p -> (p => r) -> Either String r Source #
Resolve a Deferrable
constraint with observable failure.
Instances
Deferrable () Source # | |
Defined in Data.Constraint.Deferrable deferEither :: proxy () -> (() -> r) -> Either String r Source # | |
(Deferrable a, Deferrable b) => Deferrable (a, b) Source # | |
Defined in Data.Constraint.Deferrable deferEither :: proxy (a, b) -> ((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 |
Defined in Data.Constraint.Deferrable deferEither :: proxy (a ~ b) -> ((a ~ b) -> r) -> Either String r Source # | |
(Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c) Source # | |
Defined in Data.Constraint.Deferrable deferEither :: proxy (a, b, c) -> ((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. |
Defined in Data.Constraint.Deferrable |
defer :: forall p r proxy. Deferrable p => proxy p -> (p => r) -> r Source #
Defer a constraint for later resolution in a context where we want to upgrade failure into an error
deferred :: forall p. Deferrable p :- p Source #
defer_ :: forall p r. Deferrable p => (p => r) -> r Source #
deferEither_ :: forall p r. Deferrable p => (p => r) -> Either String r Source #
A version of deferEither
that uses visible type application in place of a Proxy
.
Only available on GHC 8.0 or later.
data (a :: k1) :~~: (b :: k2) :: forall k1 k2. k1 -> k2 -> Type 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
Instances
Category ((:~~:) :: k -> k -> Type) | Since: base-4.10.0.0 |
TestCoercion ((:~~:) a :: k -> Type) | Since: base-4.10.0.0 |
Defined in Data.Type.Coercion | |
TestEquality ((:~~:) a :: k -> Type) | Since: base-4.10.0.0 |
Defined in Data.Type.Equality | |
NFData2 ((:~~:) :: Type -> Type -> Type) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
NFData1 ((:~~:) a :: Type -> Type) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
a ~~ b => Bounded (a :~~: b) | Since: base-4.10.0.0 |
a ~~ b => Enum (a :~~: b) | Since: base-4.10.0.0 |
Defined in Data.Type.Equality succ :: (a :~~: b) -> a :~~: b # pred :: (a :~~: b) -> 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 |
(Typeable i, Typeable j, Typeable a, Typeable b, a ~~ b) => Data (a :~~: b) | Since: base-4.10.0.0 |
Defined in Data.Data 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 :: (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 |
a ~~ b => Read (a :~~: b) | Since: base-4.10.0.0 |
Show (a :~~: b) | Since: base-4.10.0.0 |
NFData (a :~~: b) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
HasDict (a ~~ b) (a :~~: b) Source # | |
data (a :: k) :~: (b :: k) :: forall k. k -> k -> Type 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
Instances
Category ((:~:) :: k -> k -> Type) | Since: base-4.7.0.0 |
TestCoercion ((:~:) a :: k -> Type) | Since: base-4.7.0.0 |
Defined in Data.Type.Coercion | |
TestEquality ((:~:) a :: k -> Type) | Since: base-4.7.0.0 |
Defined in Data.Type.Equality | |
NFData2 ((:~:) :: Type -> Type -> Type) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
NFData1 ((:~:) a) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
a ~ b => Bounded (a :~: b) | Since: base-4.7.0.0 |
a ~ b => Enum (a :~: b) | Since: base-4.7.0.0 |
Defined in Data.Type.Equality | |
Eq (a :~: b) | Since: base-4.7.0.0 |
(a ~ b, Data a) => Data (a :~: b) | Since: base-4.7.0.0 |
Defined in Data.Data 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 :: (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 |
Defined in Data.Type.Equality | |
a ~ b => Read (a :~: b) | Since: base-4.7.0.0 |
Show (a :~: b) | Since: base-4.7.0.0 |
NFData (a :~: b) | Since: deepseq-1.4.3.0 |
Defined in Control.DeepSeq | |
HasDict (a ~ b) (a :~: b) Source # | |