row-types-1.0.1.2: Open Records and Variants

Safe Haskell | None
Language | Haskell2010

Data.Row.Dictionaries

Contents

- Axioms
  - Helper Types
- Re-exports

Description

This module exports various dictionaries that help the type-checker when dealing with row-types.

For the various axioms, type variables are consistently in the following order:

- Any types that do not belong later.
- Labels

- Row-types

  - If applicable, the type in the row-type at the given label goes after each row-type
- Constraints

Synopsis

- uniqueMap :: forall {k1} {k2} (f :: k1 -> k2) (r :: Row k1). Dict (AllUniqueLabels (Map f r) ≈ AllUniqueLabels r)
- uniqueAp :: forall {k1} {k2} (fs :: Row (k1 -> k2)) (r :: Row k1). Dict (AllUniqueLabels (Ap fs r) ≈ AllUniqueLabels r)
- uniqueApSingle :: forall {a} {k} (x :: a) (r :: Row (a -> k)). Dict (AllUniqueLabels (ApSingle r x) ≈ AllUniqueLabels r)
- uniqueZip :: forall (r1 :: Row Type) (r2 :: Row Type). Dict (AllUniqueLabels (Zip r1 r2) ≈ (AllUniqueLabels r1, AllUniqueLabels r2))
- extendHas :: forall {k} (l :: Symbol) (t :: k) (r :: Row k). Dict ((Extend l t r .! l) ≈ t)
- mapHas :: forall {k} {b} (f :: k -> b) (l :: Symbol) (t :: k) (r :: Row k). ((r .! l) ≈ t) :- ((Map f r .! l) ≈ f t, (Map f r .- l) ≈ Map f (r .- l))
- apHas :: forall {k} {b} (l :: Symbol) (f :: k -> b) (ϕ :: Row (k -> b)) (t :: k) (ρ :: Row k). ((ϕ .! l) ≈ f, (ρ .! l) ≈ t) :- ((Ap ϕ ρ .! l) ≈ f t, (Ap ϕ ρ .- l) ≈ Ap (ϕ .- l) (ρ .- l))
- apSingleHas :: forall {a} {b} (x :: a) (l :: Symbol) (f :: a -> b) (r :: Row (a -> b)). ((r .! l) ≈ f) :- ((ApSingle r x .! l) ≈ f x, (ApSingle r x .- l) ≈ ApSingle (r .- l) x)
- mapExtendSwap :: forall {k} {b} (f :: k -> b) (ℓ :: Symbol) (τ :: k) (r :: Row k). Dict (Extend ℓ (f τ) (Map f r) ≈ Map f (Extend ℓ τ r))
- apExtendSwap :: forall {k} {b} (ℓ :: Symbol) (f :: k -> b) (fs :: Row (k -> b)) (τ :: k) (r :: Row k). Dict (Extend ℓ (f τ) (Ap fs r) ≈ Ap (Extend ℓ f fs) (Extend ℓ τ r))
- apSingleExtendSwap :: forall {a} {b} (τ :: a) (ℓ :: Symbol) (f :: a -> b) (r :: Row (a -> b)). Dict (Extend ℓ (f τ) (ApSingle r τ) ≈ ApSingle (Extend ℓ f r) τ)
- zipExtendSwap :: forall (ℓ :: Symbol) τ1 (r1 :: Row Type) τ2 (r2 :: Row Type). Dict (Extend ℓ (τ1, τ2) (Zip r1 r2) ≈ Zip (Extend ℓ τ1 r1) (Extend ℓ τ2 r2))
- mapMinJoin :: forall {k} {b} (f :: k -> b) (r :: Row k) (r' :: Row k). Dict ((Map f r .\/ Map f r') ≈ Map f (r .\/ r'))
- apSingleMinJoin :: forall {a} {b} (r :: Row (a -> b)) (r' :: Row (a -> b)) (x :: a). Dict ((ApSingle r x .\/ ApSingle r' x) ≈ ApSingle (r .\/ r') x)
- type FreeForall (r :: Row k) = Forall r (Unconstrained1 :: k -> Constraint)
- type FreeBiForall (r1 :: Row k1) (r2 :: Row k2) = BiForall r1 r2 (Unconstrained2 :: k1 -> k2 -> Constraint)
- freeForall :: forall {k} (r :: Row k) (c :: k -> Constraint). Forall r c :- Forall r (Unconstrained1 :: k -> Constraint)
- mapForall :: forall {k1} {k2} (f :: k1 -> k2) (ρ :: Row k1) (c :: k1 -> Constraint). Forall ρ c :- Forall (Map f ρ) (IsA c f)
- apSingleForall :: forall {k1} {k2} (a :: k1) (fs :: Row (k1 -> k2)) (c :: (k1 -> k2) -> Constraint). Forall fs c :- Forall (ApSingle fs a) (ActsOn c a)
- subsetJoin :: forall {k} (r1 :: Row k) (r2 :: Row k) (s :: Row k). Dict ((Subset r1 s, Subset r2 s) ≈ Subset (r1 .+ r2) s)
- subsetJoin' :: forall {k} (r1 :: Row k) (r2 :: Row k) (s :: Row k). Dict ((Subset r1 s, Subset r2 s) ≈ Subset (r1 .// r2) s)
- subsetRestrict :: forall {k} (r :: Row k) (s :: Row k) (l :: Symbol). Subset r s :- Subset (r .- l) s
- subsetTrans :: forall {k} (r1 :: Row k) (r2 :: Row k) (r3 :: Row k). (Subset r1 r2, Subset r2 r3) :- Subset r1 r3
- mapDifference :: forall {k} {b} (f :: k -> b) (r :: Row k) (r' :: Row k). Dict ((Map f r .\\ Map f r') ≈ Map f (r .\\ r'))
- apSingleDifference :: forall {a} {b} (r :: Row (a -> b)) (r' :: Row (a -> b)) (x :: a). Dict ((ApSingle r x .\\ ApSingle r' x) ≈ ApSingle (r .\\ r') x)
- class IsA (c :: k -> Constraint) (f :: k -> k1) (a :: k1) where
  - as :: As c f a
- data As (c :: k -> Constraint) (f :: k -> k1) (a :: k1) where
  - As :: forall {k} {k1} (c :: k -> Constraint) (f :: k -> k1) (a :: k1) (t :: k). (a ~ f t, c t) => As c f a
- class ActsOn (c :: (k -> k1) -> Constraint) (t :: k) (a :: k1) where
  - actsOn :: As' c t a
- data As' (c :: (k -> k1) -> Constraint) (t :: k) (a :: k1) where
  - As' :: forall {k} {k1} (c :: (k -> k1) -> Constraint) (f :: k -> k1) (a :: k1) (t :: k). (a ~ f t, c f) => As' c t a
- data Dict a where
  - Dict :: forall a. a => Dict a
- newtype a :- b = Sub (a => Dict b)
- class HasDict c e | e -> c where
  - evidence :: e -> Dict c
- (\\) :: HasDict c e => (c => r) -> e -> r
- withDict :: HasDict c e => e -> (c => r) -> r
- class Unconstrained
- class Unconstrained1 (a :: k)
- class Unconstrained2 (a :: k) (b :: k1)

# Axioms

uniqueMap :: forall {k1} {k2} (f :: k1 -> k2) (r :: Row k1). Dict (AllUniqueLabels (Map f r) ≈ AllUniqueLabels r) #

Map preserves uniqueness of labels.

uniqueAp :: forall {k1} {k2} (fs :: Row (k1 -> k2)) (r :: Row k1). Dict (AllUniqueLabels (Ap fs r) ≈ AllUniqueLabels r) #

Ap preserves uniqueness of labels.

uniqueApSingle :: forall {a} {k} (x :: a) (r :: Row (a -> k)). Dict (AllUniqueLabels (ApSingle r x) ≈ AllUniqueLabels r) #

ApSingle preserves uniqueness of labels.

uniqueZip :: forall (r1 :: Row Type) (r2 :: Row Type). Dict (AllUniqueLabels (Zip r1 r2) ≈ (AllUniqueLabels r1, AllUniqueLabels r2)) #

Zip preserves uniqueness of labels.

extendHas :: forall {k} (l :: Symbol) (t :: k) (r :: Row k). Dict ((Extend l t r .! l) ≈ t) #

If we know that `r` has been extended with `l .== t`, then we know that this extension at the label `l` must be `t`.

mapHas :: forall {k} {b} (f :: k -> b) (l :: Symbol) (t :: k) (r :: Row k). ((r .! l) ≈ t) :- ((Map f r .! l) ≈ f t, (Map f r .- l) ≈ Map f (r .- l)) #

This allows us to derive `Map f r .! l ≈ f t` from `r .! l ≈ t`

apHas :: forall {k} {b} (l :: Symbol) (f :: k -> b) (ϕ :: Row (k -> b)) (t :: k) (ρ :: Row k). ((ϕ .! l) ≈ f, (ρ .! l) ≈ t) :- ((Ap ϕ ρ .! l) ≈ f t, (Ap ϕ ρ .- l) ≈ Ap (ϕ .- l) (ρ .- l)) #

This allows us to derive `Ap ϕ ρ .! l ≈ f t` from `ϕ .! l ≈ f` and `ρ .! l ≈ t`

apSingleHas :: forall {a} {b} (x :: a) (l :: Symbol) (f :: a -> b) (r :: Row (a -> b)). ((r .! l) ≈ f) :- ((ApSingle r x .! l) ≈ f x, (ApSingle r x .- l) ≈ ApSingle (r .- l) x) #

This allows us to derive `ApSingle r x .! l ≈ f x` from `r .! l ≈ f`

mapExtendSwap :: forall {k} {b} (f :: k -> b) (ℓ :: Symbol) (τ :: k) (r :: Row k). Dict (Extend ℓ (f τ) (Map f r) ≈ Map f (Extend ℓ τ r)) #

Proof that the `Map` type family preserves labels and their ordering.

apExtendSwap :: forall {k} {b} (ℓ :: Symbol) (f :: k -> b) (fs :: Row (k -> b)) (τ :: k) (r :: Row k). Dict (Extend ℓ (f τ) (Ap fs r) ≈ Ap (Extend ℓ f fs) (Extend ℓ τ r)) #

Proof that the `Ap` type family preserves labels and their ordering.

apSingleExtendSwap :: forall {a} {b} (τ :: a) (ℓ :: Symbol) (f :: a -> b) (r :: Row (a -> b)). Dict (Extend ℓ (f τ) (ApSingle r τ) ≈ ApSingle (Extend ℓ f r) τ) #

Proof that the `ApSingle` type family preserves labels and their ordering.

zipExtendSwap :: forall (ℓ :: Symbol) τ1 (r1 :: Row Type) τ2 (r2 :: Row Type). Dict (Extend ℓ (τ1, τ2) (Zip r1 r2) ≈ Zip (Extend ℓ τ1 r1) (Extend ℓ τ2 r2)) #

Proof that the `Ap` type family preserves labels and their ordering.

mapMinJoin :: forall {k} {b} (f :: k -> b) (r :: Row k) (r' :: Row k). Dict ((Map f r .\/ Map f r') ≈ Map f (r .\/ r')) #

Map distributes over MinJoin

apSingleMinJoin :: forall {a} {b} (r :: Row (a -> b)) (r' :: Row (a -> b)) (x :: a). Dict ((ApSingle r x .\/ ApSingle r' x) ≈ ApSingle (r .\/ r') x) #

ApSingle distributes over MinJoin

type FreeForall (r :: Row k) = Forall r (Unconstrained1 :: k -> Constraint) #

`FreeForall` can be used when a `Forall` constraint is necessary but there is no particular constraint we care about.

type FreeBiForall (r1 :: Row k1) (r2 :: Row k2) = BiForall r1 r2 (Unconstrained2 :: k1 -> k2 -> Constraint) #

`FreeForall` can be used when a `BiForall` constraint is necessary but there is no particular constraint we care about.

freeForall :: forall {k} (r :: Row k) (c :: k -> Constraint). Forall r c :- Forall r (Unconstrained1 :: k -> Constraint) #

Allow any `Forall` over a row-type, be usable for `Unconstrained1`.

mapForall :: forall {k1} {k2} (f :: k1 -> k2) (ρ :: Row k1) (c :: k1 -> Constraint). Forall ρ c :- Forall (Map f ρ) (IsA c f) #

This allows us to derive a `Forall (Map f r) ..` from a `Forall r ..`.

apSingleForall :: forall {k1} {k2} (a :: k1) (fs :: Row (k1 -> k2)) (c :: (k1 -> k2) -> Constraint). Forall fs c :- Forall (ApSingle fs a) (ActsOn c a) #

This allows us to derive a `Forall (ApSingle f r) ..` from a `Forall f ..`.

subsetJoin :: forall {k} (r1 :: Row k) (r2 :: Row k) (s :: Row k). Dict ((Subset r1 s, Subset r2 s) ≈ Subset (r1 .+ r2) s) #

Two rows are subsets of a third if and only if their disjoint union is a subset of that third.

subsetJoin' :: forall {k} (r1 :: Row k) (r2 :: Row k) (s :: Row k). Dict ((Subset r1 s, Subset r2 s) ≈ Subset (r1 .// r2) s) #

If two rows are each subsets of a third, their join is a subset of the third

subsetRestrict :: forall {k} (r :: Row k) (s :: Row k) (l :: Symbol). Subset r s :- Subset (r .- l) s #

If a row is a subset of another, then its restriction is also a subset of the other

subsetTrans :: forall {k} (r1 :: Row k) (r2 :: Row k) (r3 :: Row k). (Subset r1 r2, Subset r2 r3) :- Subset r1 r3 #

Subset is transitive

mapDifference :: forall {k} {b} (f :: k -> b) (r :: Row k) (r' :: Row k). Dict ((Map f r .\\ Map f r') ≈ Map f (r .\\ r')) #

Map distributes over Difference

apSingleDifference :: forall {a} {b} (r :: Row (a -> b)) (r' :: Row (a -> b)) (x :: a). Dict ((ApSingle r x .\\ ApSingle r' x) ≈ ApSingle (r .\\ r') x) #

ApSingle distributes over Difference

## Helper Types

class IsA (c :: k -> Constraint) (f :: k -> k1) (a :: k1) where #

A class to capture the idea of `As` so that it can be partially applied in a context.

Methods

as :: As c f a #

#### Instances

Instances details

c a => IsA (c :: k1 -> Constraint) (f :: k1 -> k2) (f a :: k2) # |
Instance details Defined in Data.Row.Dictionaries Methods as :: As c f (f a) #

data As (c :: k -> Constraint) (f :: k -> k1) (a :: k1) where #

This data type is used to for its ability to existentially bind a type variable. Particularly, it says that for the type `a`, there exists a `t` such that `a ~ f t` and `c t` holds.

Constructors

As :: forall {k} {k1} (c :: k -> Constraint) (f :: k -> k1) (a :: k1) (t :: k). (a ~ f t, c t) => As c f a |

class ActsOn (c :: (k -> k1) -> Constraint) (t :: k) (a :: k1) where #

A class to capture the idea of `As'` so that it can be partially applied in a context.

Methods

actsOn :: As' c t a #

#### Instances

Instances details

c f => ActsOn (c :: (k1 -> k2) -> Constraint) (t :: k1) (f t :: k2) # |
Instance details Defined in Data.Row.Dictionaries Methods actsOn :: As' c t (f t) #

data As' (c :: (k -> k1) -> Constraint) (t :: k) (a :: k1) where #

Like `As`, but here we know the underlying value is some `f` applied to the given type `a`.

Constructors

As' :: forall {k} {k1} (c :: (k -> k1) -> Constraint) (f :: k -> k1) (a :: k1) (t :: k). (a ~ f t, c f) => As' c t a |

# Re-exports

data Dict a where #

Values of type ``Dict` p` capture a dictionary for a constraint of type `p`.

e.g.

    Dict :: Dict (Eq Int)

captures a dictionary that proves we have an:

    instance Eq Int

Pattern matching on the `Dict` constructor will bring this instance into scope.

Constructors

Dict :: forall a. a => Dict a |

#### Instances

Instances details

() :=> (Semigroup (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Semigroup (Dict a) #
() :=> (Show (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Show (Dict a) #
() :=> (Eq (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Eq (Dict a) #
() :=> (Ord (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Ord (Dict a) #
a :=> (Monoid (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: a :- Monoid (Dict a) #
a :=> (Bounded (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: a :- Bounded (Dict a) #
a :=> (Enum (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: a :- Enum (Dict a) #
a :=> (Read (Dict a)) |
Instance details Defined in Data.Constraint Methods ins :: a :- Read (Dict a) #
HasDict a (Dict a) |
Instance details Defined in Data.Constraint Methods evidence :: Dict a -> Dict a #
c => Boring (Dict c) |
Instance details Defined in Data.Constraint Methods boring :: Dict c #
NFData (Dict c) |
Instance details Defined in Data.Constraint Methods rnf :: Dict c -> () #
a => Monoid (Dict a) |
Instance details Defined in Data.Constraint Methods mempty :: Dict a # mappend :: Dict a -> Dict a -> Dict a # mconcat :: [Dict a] -> Dict a #
Semigroup (Dict a) |
Instance details Defined in Data.Constraint Methods (<>) :: Dict a -> Dict a -> Dict a # sconcat :: NonEmpty (Dict a) -> Dict a # stimes :: Integral b => b -> Dict a -> Dict a #
(Typeable p, p) => Data (Dict p) |
Instance details Defined in Data.Constraint Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Dict p -> c (Dict p) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Dict p) # toConstr :: Dict p -> Constr # dataTypeOf :: Dict p -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Dict p)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Dict p)) # gmapT :: (forall b. Data b => b -> b) -> Dict p -> Dict p # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Dict p -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Dict p -> r # gmapQ :: (forall d. Data d => d -> u) -> Dict p -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Dict p -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Dict p -> m (Dict p) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Dict p -> m (Dict p) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Dict p -> m (Dict p) #
a => Bounded (Dict a) |
Instance details Defined in Data.Constraint Methods minBound :: Dict a # maxBound :: Dict a #
a => Enum (Dict a) |
Instance details Defined in Data.Constraint Methods succ :: Dict a -> Dict a # pred :: Dict a -> Dict a # toEnum :: Int -> Dict a # fromEnum :: Dict a -> Int # enumFrom :: Dict a -> [Dict a] # enumFromThen :: Dict a -> Dict a -> [Dict a] # enumFromTo :: Dict a -> Dict a -> [Dict a] # enumFromThenTo :: Dict a -> Dict a -> Dict a -> [Dict a] #
a => Read (Dict a) |
Instance details Defined in Data.Constraint Methods readsPrec :: Int -> ReadS (Dict a) # readList :: ReadS [Dict a] # readPrec :: ReadPrec (Dict a) # readListPrec :: ReadPrec [Dict a] #
Show (Dict a) |
Instance details Defined in Data.Constraint Methods showsPrec :: Int -> Dict a -> ShowS # show :: Dict a -> String # showList :: [Dict a] -> ShowS #
Eq (Dict a) |
Instance details Defined in Data.Constraint Methods (==) :: Dict a -> Dict a -> Bool # (/=) :: Dict a -> Dict a -> Bool #
Ord (Dict a) |
Instance details Defined in Data.Constraint Methods compare :: Dict a -> Dict a -> Ordering # (<) :: Dict a -> Dict a -> Bool # (<=) :: Dict a -> Dict a -> Bool # (>) :: Dict a -> Dict a -> Bool # (>=) :: Dict a -> Dict a -> Bool # max :: Dict a -> Dict a -> Dict a # min :: Dict a -> Dict a -> Dict a #

newtype a :- b infixr 9 #

This is the type of entailment.

`a `:-` b` is read as `a` "entails" `b`.

With this we can actually build a category for `Constraint` resolution.

e.g.

Because ``Eq` a` is a superclass of ``Ord` a`, we can show that ``Ord` a` entails ``Eq` a`.

Because `instance `Ord` a => `Ord` [a]` exists, we can show that ``Ord` a` entails ``Ord` [a]` as well.

This relationship is captured in the `:-` entailment type here.

Since `p `:-` p` and entailment composes, `:-` forms the arrows of a `Category` of constraints. However, `Category` only became sufficiently general to support this instance in GHC 7.8, so prior to 7.8 this instance is unavailable.

But due to the coherence of instance resolution in Haskell, this `Category` has some very interesting properties. Notably, in the absence of `IncoherentInstances`, this category is "thin", which is to say that between any two objects (constraints) there is at most one distinguishable arrow.

This means that for instance, even though there are two ways to derive ``Ord` a `:-` `Eq` [a]`, the answers from these two paths _must_ by construction be equal. This is a property that Haskell offers that is pretty much unique in the space of languages with things they call "type classes".

What are the two ways?

Well, we can go from ``Ord` a `:-` `Eq` a` via the superclass relationship, and then from ``Eq` a `:-` `Eq` [a]` via the instance, or we can go from ``Ord` a `:-` `Ord` [a]` via the instance then from ``Ord` [a] `:-` `Eq` [a]` through the superclass relationship and this diagram by definition must "commute".

Diagrammatically,

                       Ord a
                   ins /     \ cls
                      v       v
                Ord [a]     Eq a
                   cls \     / ins
                        v   v
                       Eq [a]

This safety net ensures that pretty much anything you can write with this library is sensible and can't break any assumptions on the behalf of library authors.

Constructors

Sub (a => Dict b) |

#### Instances

Instances details

Category (:-) | Possible since GHC 7.8, when `Category` was made polykinded.
Instance details Defined in Data.Constraint Methods id :: a :- a # (.) :: (b :- c) -> (a :- b) -> a :- c #
() :=> (Show (a :- b)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Show (a :- b) #
() :=> (Eq (a :- b)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Eq (a :- b) #
() :=> (Ord (a :- b)) |
Instance details Defined in Data.Constraint Methods ins :: () :- Ord (a :- b) #
a => HasDict b (a :- b) |
Instance details Defined in Data.Constraint Methods evidence :: (a :- b) -> Dict b #
a => NFData (a :- b) |
Instance details Defined in Data.Constraint Methods rnf :: (a :- b) -> () #
(Typeable p, Typeable q, p => q) => Data (p :- q) |
Instance details Defined in Data.Constraint Methods gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> (p :- q) -> c (p :- q) # gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (p :- q) # toConstr :: (p :- q) -> Constr # dataTypeOf :: (p :- q) -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (p :- q)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (p :- q)) # gmapT :: (forall b. Data b => b -> b) -> (p :- q) -> p :- q # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> (p :- q) -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> (p :- q) -> r # gmapQ :: (forall d. Data d => d -> u) -> (p :- q) -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> (p :- q) -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> (p :- q) -> m (p :- q) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> (p :- q) -> m (p :- q) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> (p :- q) -> m (p :- q) #
Show (a :- b) |
Instance details Defined in Data.Constraint Methods showsPrec :: Int -> (a :- b) -> ShowS # show :: (a :- b) -> String # showList :: [a :- b] -> ShowS #
Eq (a :- b) | Assumes `IncoherentInstances` doesn't exist.
Instance details Defined in Data.Constraint Methods (==) :: (a :- b) -> (a :- b) -> Bool # (/=) :: (a :- b) -> (a :- b) -> Bool #
Ord (a :- b) | Assumes `IncoherentInstances` doesn't exist.
Instance details Defined in Data.Constraint 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 #

class HasDict c e | e -> c where #

Witnesses that a value of type `e` contains evidence of the constraint `c`.

Mainly intended to allow (`\\`) to be overloaded, since it's a useful operator.

Methods

evidence :: e -> Dict c #

#### Instances

Instances details

HasDict a (Dict a) |
Instance details Defined in Data.Constraint Methods evidence :: Dict a -> Dict a #
a => HasDict b (a :- b) |
Instance details Defined in Data.Constraint Methods evidence :: (a :- b) -> Dict b #
HasDict (Typeable k, Typeable a) (TypeRep a) |
Instance details Defined in Data.Constraint Methods evidence :: TypeRep a -> Dict (Typeable k, Typeable a) #
HasDict (Coercible a b) (Coercion a b) |
Instance details Defined in Data.Constraint Methods evidence :: Coercion a b -> Dict (Coercible a b) #
HasDict (a ~ b) (a :~: b) |
Instance details Defined in Data.Constraint Methods evidence :: (a :~: b) -> Dict (a ~ b) #
HasDict (a ~~ b) (a :~~: b) |
Instance details Defined in Data.Constraint Methods evidence :: (a :~~: b) -> Dict (a ~~ b) #

(\\) :: HasDict c e => (c => r) -> e -> r infixl 1 #

Operator version of `withDict`, with the arguments flipped

withDict :: HasDict c e => e -> (c => r) -> r #

From a `Dict`, takes a value in an environment where the instance witnessed by the `Dict` is in scope, and evaluates it.

Essentially a deconstruction of a `Dict` into its continuation-style form.

Can also be used to deconstruct an entailment, `a `:-` b`, using a context `a`.

    withDict :: Dict c -> (c => r) -> r
    withDict :: a => (a :- c) -> (c => r) -> r

class Unconstrained #

A null constraint

#### Instances

Instances details

Unconstrained # |
Instance details Defined in Data.Row.Internal

class Unconstrained1 (a :: k) #

A null constraint of one argument

#### Instances

Instances details

Unconstrained1 (a :: k) # |
Instance details Defined in Data.Row.Internal

class Unconstrained2 (a :: k) (b :: k1) #

A null constraint of two arguments

#### Instances

Instances details

Unconstrained2 (a :: k1) (b :: k2) # |
Instance details Defined in Data.Row.Internal