| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Optics.AffineFold
Description
An
AffineFold
is a
Fold
that contains at most one
element, or a
Getter
where the function may be
partial.
Synopsis
- type AffineFold s a = Optic' An_AffineFold NoIx s a
- afolding :: (s -> Maybe a) -> AffineFold s a
- preview :: Is k An_AffineFold => Optic' k is s a -> s -> Maybe a
- previews :: Is k An_AffineFold => Optic' k is s a -> (a -> r) -> s -> Maybe r
- afoldVL :: ( forall f. Functor f => ( forall r. r -> f r) -> (a -> f u) -> s -> f v) -> AffineFold s a
- filtered :: (a -> Bool ) -> AffineFold a a
- atraverseOf_ :: ( Is k An_AffineFold , Functor f) => Optic' k is s a -> ( forall r. r -> f r) -> (a -> f u) -> s -> f ()
- isn't :: Is k An_AffineFold => Optic' k is s a -> s -> Bool
- afailing :: ( Is k An_AffineFold , Is l An_AffineFold ) => Optic' k is s a -> Optic' l js s a -> AffineFold s a
- data An_AffineFold :: OpticKind
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
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_≡idatraverseOf_.afoldVL≡id
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 NothingTrue
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
