Copyright	(C) 2012-16 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	provisional
Portability	Rank2Types
Safe Haskell	None
Language	Haskell2010

Control.Lens.Equality

Contents

Type Equality
The Trivial Equality
Iso-like functions
Implementation Details

Description

Synopsis

type Equality (s :: k1) (t :: k2) (a :: k1) (b :: k2) = forall k3 (p :: k1 -> k3 -> Type) (f :: k2 -> k3). p a (f b) -> p s (f t)
type Equality' s a = Equality s s a a
type AnEquality (s :: k1) (t :: k2) (a :: k1) (b :: k2) = Identical a (Proxy b) a (Proxy b) -> Identical a (Proxy b) s (Proxy t)
type AnEquality' s a = AnEquality s s a a
data (a :: k) :~: (b :: k) where
- Refl :: forall k (a :: k). a :~: a
runEq :: AnEquality s t a b -> Identical s t a b
substEq :: forall s t a b rep (r :: TYPE rep). AnEquality s t a b -> ((s ~ a, t ~ b) => r) -> r
mapEq :: forall k1 k2 (s :: k1) (t :: k2) (a :: k1) (b :: k2) (f :: k1 -> Type). AnEquality s t a b -> f s -> f a
fromEq :: AnEquality s t a b -> Equality b a t s
simply :: forall p f s a rep (r :: TYPE rep). (Optic' p f s a -> r) -> Optic' p f s a -> r
simple :: Equality' a a
equality :: (s :~: a) -> (b :~: t) -> Equality s t a b
equality' :: (a :~: b) -> Equality' a b
withEquality :: forall s t a b rep (r :: TYPE rep). AnEquality s t a b -> ((s :~: a) -> (b :~: t) -> r) -> r
underEquality :: AnEquality s t a b -> p t s -> p b a
overEquality :: AnEquality s t a b -> p a b -> p s t
fromLeibniz :: (Identical a b a b -> Identical a b s t) -> Equality s t a b
fromLeibniz' :: ((s :~: s) -> s :~: a) -> Equality' s a
cloneEquality :: AnEquality s t a b -> Equality s t a b
data Identical a b s t where
- Identical :: Identical a b a b

Type Equality

type Equality (s :: k1) (t :: k2) (a :: k1) (b :: k2) = forall k3 (p :: k1 -> k3 -> Type) (f :: k2 -> k3). p a (f b) -> p s (f t) #

A witness that (a ~ s, b ~ t).

Note: Composition with an Equality is index-preserving.

type Equality' s a = Equality s s a a #

A Simple Equality.

type AnEquality (s :: k1) (t :: k2) (a :: k1) (b :: k2) = Identical a (Proxy b) a (Proxy b) -> Identical a (Proxy b) s (Proxy t) #

When you see this as an argument to a function, it expects an Equality.

type AnEquality' s a = AnEquality s s a a #

A Simple AnEquality.

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 #
Semigroupoid ((:~:) :: k -> k -> Type)
Instance details Defined in Data.Semigroupoid Methods o :: forall (j :: k0) (k1 :: k0) (i :: k0). (j :~: k1) -> (i :~: j) -> i :~: k1 #
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 #
NFData (a :~: b)	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods rnf :: (a :~: b) -> () #

runEq :: AnEquality s t a b -> Identical s t a b #

Extract a witness of type Equality.

substEq :: forall s t a b rep (r :: TYPE rep). AnEquality s t a b -> ((s ~ a, t ~ b) => r) -> r #

Substituting types with Equality.

mapEq :: forall k1 k2 (s :: k1) (t :: k2) (a :: k1) (b :: k2) (f :: k1 -> Type). AnEquality s t a b -> f s -> f a #

We can use Equality to do substitution into anything.

fromEq :: AnEquality s t a b -> Equality b a t s #

Equality is symmetric.

simply :: forall p f s a rep (r :: TYPE rep). (Optic' p f s a -> r) -> Optic' p f s a -> r #

This is an adverb that can be used to modify many other Lens combinators to make them require simple lenses, simple traversals, simple prisms or simple isos as input.

The Trivial Equality

simple :: Equality' a a #

Composition with this isomorphism is occasionally useful when your Lens, Traversal or Iso has a constraint on an unused argument to force that argument to agree with the type of a used argument and avoid ScopedTypeVariables or other ugliness.

`Iso`-like functions

equality :: (s :~: a) -> (b :~: t) -> Equality s t a b #

Construct an Equality from explicit equality evidence.

equality' :: (a :~: b) -> Equality' a b #

A Simple version of equality

withEquality :: forall s t a b rep (r :: TYPE rep). AnEquality s t a b -> ((s :~: a) -> (b :~: t) -> r) -> r #

A version of substEq that provides explicit, rather than implicit, equality evidence.

underEquality :: AnEquality s t a b -> p t s -> p b a #

The opposite of working overEquality is working underEquality.

overEquality :: AnEquality s t a b -> p a b -> p s t #

Recover a "profunctor lens" form of equality. Reverses fromLeibniz.

fromLeibniz :: (Identical a b a b -> Identical a b s t) -> Equality s t a b #

Convert a "profunctor lens" form of equality to an equality. Reverses overEquality.

The type should be understood as

fromLeibniz :: (forall p. p a b -> p s t) -> Equality s t a b

fromLeibniz' :: ((s :~: s) -> s :~: a) -> Equality' s a #

Convert Leibniz equality to equality. Reverses mapEq in Simple cases.

The type should be understood as

fromLeibniz' :: (forall f. f s -> f a) -> Equality' s a

cloneEquality :: AnEquality s t a b -> Equality s t a b #

Implementation Details

data Identical a b s t where #

Provides witness that (s ~ a, b ~ t) holds.