optics-core-0.4.1.1: Optics as an abstract interface: core definitions
Safe HaskellSafe-Inferred
LanguageHaskell2010

Optics.AffineFold

Description

An AffineFold is a Fold that contains at most one element, or a Getter where the function may be partial.

Synopsis

Formation

type AffineFold s a = Optic' An_AffineFold NoIx s a Source #

Type synonym for an affine fold.

Introduction

afolding :: (s -> Maybe a) -> AffineFold s a Source #

Create an AffineFold from a partial function.

>>> preview (afolding listToMaybe) "foo"
Just 'f'

Elimination

preview :: Is k An_AffineFold => Optic' k is s a -> s -> Maybe a Source #

Retrieve the value targeted by an AffineFold.

>>> let _Right = prism Right $ either (Left . Left) Right
>>> preview _Right (Right 'x')
Just 'x'
>>> preview _Right (Left 'y')
Nothing

previews :: Is k An_AffineFold => Optic' k is s a -> (a -> r) -> s -> Maybe r Source #

Retrieve a function of the value targeted by an AffineFold.

Computation

preview (afolding f) ≡ f

Additional introduction forms

afoldVL :: (forall f. Functor f => (forall r. r -> f r) -> (a -> f u) -> s -> f v) -> AffineFold s a Source #

Obtain an AffineFold by lifting traverse_ like function.

afoldVL . atraverseOf_id
atraverseOf_ . afoldVLid

Since: 0.3

filtered :: (a -> Bool) -> AffineFold a a Source #

Filter result(s) of a fold that don't satisfy a predicate.

Additional elimination forms

atraverseOf_ :: (Is k An_AffineFold, Functor f) => Optic' k is s a -> (forall r. r -> f r) -> (a -> f u) -> s -> f () Source #

Traverse over the target of an AffineFold, computing a Functor-based answer, but unlike atraverseOf do not construct a new structure.

Since: 0.3

isn't :: Is k An_AffineFold => Optic' k is s a -> s -> Bool Source #

Check to see if this AffineFold doesn't match.

>>> isn't _Just Nothing
True

The negation of this operator is is from Optics.Core.Extras.

Monoid structure

AffineFold admits a monoid structure where afailing combines folds (returning a result from the second fold only if the first returns none) and the identity element is ignored (which returns no results).

Note: There is no summing equivalent that returns an AffineFold, because it would not need to return more than one result.

There is no Semigroup or Monoid instance for AffineFold, because there is not a unique choice of monoid to use that works for all optics, and the (<>) operator could not be used to combine optics of different kinds.

afailing :: (Is k An_AffineFold, Is l An_AffineFold) => Optic' k is s a -> Optic' l js s a -> AffineFold s a infixl 3 Source #

Try the first AffineFold. If it returns no entry, try the second one.

>>> preview (ix 1 % re _Left `afailing` ix 2 % re _Right) [0,1,2,3]
Just (Left 1)
>>> preview (ix 42 % re _Left `afailing` ix 2 % re _Right) [0,1,2,3]
Just (Right 2)

Subtyping

data An_AffineFold :: OpticKind Source #

Tag for an affine fold.

Instances

Instances details
Is A_Getter An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints A_Getter p => r) -> Constraints An_AffineFold p => r Source #

Is A_Lens An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints A_Lens p => r) -> Constraints An_AffineFold p => r Source #

Is A_Prism An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints A_Prism p => r) -> Constraints An_AffineFold p => r Source #

Is A_ReversedPrism An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints A_ReversedPrism p => r) -> Constraints An_AffineFold p => r Source #

Is An_AffineFold A_Fold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints An_AffineFold p => r) -> Constraints A_Fold p => r Source #

Is An_AffineTraversal An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints An_AffineTraversal p => r) -> Constraints An_AffineFold p => r Source #

Is An_Iso An_AffineFold Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

implies :: forall (p :: Type -> Type -> Type -> Type) r. (Constraints An_Iso p => r) -> Constraints An_AffineFold p => r Source #

k ~ A_Fold => JoinKinds A_Fold An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_Fold p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds A_Getter An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_Getter p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds A_Lens An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_Lens p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds A_Prism An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_Prism p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds A_ReversedPrism An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_ReversedPrism p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ A_Fold => JoinKinds A_Traversal An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints A_Traversal p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ A_Fold => JoinKinds An_AffineFold A_Fold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_Fold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold A_Getter k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_Getter p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold A_Lens k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_Lens p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold A_Prism k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_Prism p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold A_ReversedPrism k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_ReversedPrism p) => r) -> Constraints k p => r Source #

k ~ A_Fold => JoinKinds An_AffineFold A_Traversal k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints A_Traversal p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold An_AffineTraversal k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints An_AffineTraversal p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineFold An_Iso k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineFold p, Constraints An_Iso p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_AffineTraversal An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_AffineTraversal p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

k ~ An_AffineFold => JoinKinds An_Iso An_AffineFold k Source # 
Instance details

Defined in Optics.Internal.Optic.Subtyping

Methods

joinKinds :: forall (p :: Type -> Type -> Type -> Type) r. ((Constraints An_Iso p, Constraints An_AffineFold p) => r) -> Constraints k p => r Source #

(s ~ t, a ~ b) => IxOptic An_AffineFold s t a b Source # 
Instance details

Defined in Optics.Indexed.Core

Methods

noIx :: forall (is :: IxList). NonEmptyIndices is => Optic An_AffineFold is s t a b -> Optic An_AffineFold NoIx s t a b Source #

(s ~ t, a ~ b) => ToReadOnly An_AffineFold s t a b Source # 
Instance details

Defined in Optics.ReadOnly

Associated Types

type ReadOnlyOptic An_AffineFold Source #

Methods

getting :: forall (is :: IxList). Optic An_AffineFold is s t a b -> Optic' (ReadOnlyOptic An_AffineFold) is s a Source #

type ReadOnlyOptic An_AffineFold Source # 
Instance details

Defined in Optics.ReadOnly