optics-core-0.1: Optics as an abstract interface: core definitions

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Core optic types and subtyping machinery.

This module contains the core Optic types, and the underlying machinery that we need in order to implement the subtyping between various different flavours of optics.

The composition operator for optics is also defined here.

This module is intended for internal use only, and may change without warning in subsequent releases.



newtype Optic (k :: *) (is :: [*]) s t a b Source #

Wrapper newtype for the whole family of optics.

The first parameter k identifies the particular optic kind (e.g. A_Lens or A_Traversal).

The parameter is is a list of types available as indices. This will typically be NoIx for unindexed optics, or WithIx for optics with a single index. See the "Indexed optics" section of the overview documentation in the Optics module of the main optics package for more details.

The parameters s and t represent the "big" structure, whereas a and b represent the "small" structure.




(LabelOptic name k s t a b, is ~ NoIx) => IsLabel name (Optic k is s t a b) Source # 
Instance details

Defined in Optics.Internal.Optic


fromLabel :: Optic k is s t a b #

type Optic' k is s a = Optic k is s s a a Source #

Common special case of Optic where source and target types are equal.

Here, we need only one "big" and one "small" type. For lenses, this means that in the restricted form we cannot do type-changing updates.

type Optic_ k p i j s t a b = Constraints k p => Optic__ p i j s t a b Source #

Type representing the various kinds of optics.

The tag parameter k is translated into constraints on p via the type family Constraints.

type Optic__ p i j s t a b = p i a b -> p j s t Source #

Optic internally as a profunctor transformation.

type NoIx = '[] Source #

An alias for an empty index-list

type WithIx i = '[i] Source #

Singleton index list

castOptic :: forall destKind srcKind is s t a b. Is srcKind destKind => Optic srcKind is s t a b -> Optic destKind is s t a b Source #

Explicit cast from one optic flavour to another.

The resulting optic kind is given in the first type argument, so you can use TypeApplications to set it. For example

 castOptic @A_Lens o

turns o into a Lens.

This is the identity function, modulo some constraint jiggery-pokery.

(%) :: (Is k m, Is l m, m ~ Join k l, ks ~ Append is js) => Optic k is s t u v -> Optic l js u v a b -> Optic m ks s t a b infixl 9 Source #

Compose two optics of compatible flavours.

Returns an optic of the appropriate supertype. If either or both optics are indexed, the composition preserves all the indices.

(%%) :: forall k is js ks s t u v a b. ks ~ Append is js => Optic k is s t u v -> Optic k js u v a b -> Optic k ks s t a b infixl 9 Source #

Compose two optics of the same flavour.

Normally you can simply use (%) instead, but this may be useful to help type inference if the type of one of the optics is otherwise under-constrained.

(%&) :: Optic k is s t a b -> (Optic k is s t a b -> Optic l js s' t' a' b') -> Optic l js s' t' a' b' infixl 9 Source #

Flipped function application, specialised to optics and binding tightly.

Useful for post-composing optics transformations:

>>> toListOf (ifolded %& ifiltered (\i s -> length s <= i)) ["", "a","abc"]

data IsProxy (k :: *) (l :: *) (p :: * -> * -> * -> *) Source #

Proxy type for use as an argument to implies.




class LabelOptic (name :: Symbol) k s t a b | name s -> k a, name t -> k b, name s b -> t, name t a -> s where Source #

Support for overloaded labels as optics. An overloaded label #foo can be used as an optic if there is an instance of LabelOptic "foo" k s t a b.

See Optics.Label for examples and further details.


labelOptic :: Optic k NoIx s t a b Source #

Used to interpret overloaded label syntax. An overloaded label #foo corresponds to labelOptic @"foo".

(LabelOptic name k s t a b, (TypeError ((((((((((((Text "No instance for LabelOptic " :<>: ShowType name) :<>: Text " ") :<>: QuoteType k) :<>: Text " ") :<>: QuoteType s) :<>: Text " ") :<>: QuoteType t) :<>: Text " ") :<>: QuoteType a) :<>: Text " ") :<>: QuoteType b) :$$: Text " (maybe you forgot to define it or misspelled a name?)") :: Constraint)) => LabelOptic name k s t a b Source #

If no instance matches, GHC tends to bury error messages "No instance for LabelOptic..." within a ton of other error messages about ambiguous type variables and overlapping instances which are irrelevant and confusing. Use overlappable instance providing a custom type error to cut its efforts short.

Instance details

Defined in Optics.Internal.Optic


labelOptic :: Optic k NoIx s t a b Source #

type LabelOptic' name k s a = LabelOptic name k s s a a Source #

Type synonym for a type-preserving optic as overloaded label.