Copyright	(C) 2025 - Eitan Chatav
License	BSD-style (see the file LICENSE)
Maintainer	Eitan Chatav <eitan.chatav@gmail.com>
Stability	provisional
Portability	non-portable
Safe Haskell	Safe-Inferred
Language	Haskell2010

Control.Lens.Wither

Contents

Wither
Combinators
Witheroid
Altar

Description

See Chris Penner, Composable Filters Using Witherable Optics

Synopsis

type Wither s t a b = forall f. Alternative f => (a -> f b) -> s -> f t
type AWither s t a b = (a -> Altar a b b) -> s -> Altar a b t
cloneWither :: AWither s t a b -> Wither s t a b
withered :: Witherable t => Wither (t a) (t b) a b
filtraversed :: (Filterable t, Traversable t) => Wither (t a) (t b) a b
filterOf :: Alternative m => Wither s t a a -> (a -> Bool) -> s -> m t
type Witheroid s t a b = forall p f. (Choice p, Alternative f) => p a (f b) -> p s (f t)
witherPrism :: APrism s t a b -> Witheroid s t a b
newtype Altar a b t = Altar {
- runAltar :: forall f. Alternative f => (a -> f b) -> f t
}

Wither

type Wither s t a b = forall f. Alternative f => (a -> f b) -> s -> f t Source #

Withers extends Traversals by filtering.

Every one of the following is a Wither.

type AWither s t a b = (a -> Altar a b b) -> s -> Altar a b t Source #

If you see AWither in a signature for a function, the function is expecting a Wither.

Combinators

cloneWither :: AWither s t a b -> Wither s t a b Source #

Clone AWither so that you can reuse the same monomorphically typed Wither for different purposes.

withered :: Witherable t => Wither (t a) (t b) a b Source #

Construct a Wither for a Witherable.

filtraversed :: (Filterable t, Traversable t) => Wither (t a) (t b) a b Source #

withered = filtraversed

filterOf :: Alternative m => Wither s t a a -> (a -> Bool) -> s -> m t Source #

Filter a traversed structure based on a predicate.

Witheroid

type Witheroid s t a b = forall p f. (Choice p, Alternative f) => p a (f b) -> p s (f t) Source #

Witheroids generalize Withers. Every Prism is a Witheroid.

witherPrism :: APrism s t a b -> Witheroid s t a b Source #

Prisms already capture the idea of success and failure, but they simply skip the traversal if the prism doesn't match. Lift prisms into withers such that they'll fail in a way that wither can catch.

Altar

newtype Altar a b t Source #

This is used to characterize Withers.

Constructors

Altar
Fields runAltar :: forall f. Alternative f => (a -> f b) -> f t

Instances

Instances details

Alternative (Altar a b) Source #
Instance details Defined in Control.Lens.Wither Methods empty :: Altar a b a0 # (<\|>) :: Altar a b a0 -> Altar a b a0 -> Altar a b a0 # some :: Altar a b a0 -> Altar a b [a0] # many :: Altar a b a0 -> Altar a b [a0] #
Applicative (Altar a b) Source #
Instance details Defined in Control.Lens.Wither Methods pure :: a0 -> Altar a b a0 # (<>) :: Altar a b (a0 -> b0) -> Altar a b a0 -> Altar a b b0 # liftA2 :: (a0 -> b0 -> c) -> Altar a b a0 -> Altar a b b0 -> Altar a b c # (>) :: Altar a b a0 -> Altar a b b0 -> Altar a b b0 # (<*) :: Altar a b a0 -> Altar a b b0 -> Altar a b a0 #
Functor (Altar a b) Source #
Instance details Defined in Control.Lens.Wither Methods fmap :: (a0 -> b0) -> Altar a b a0 -> Altar a b b0 # (<$) :: a0 -> Altar a b b0 -> Altar a b a0 #
Sellable (->) Altar Source #
Instance details Defined in Control.Lens.Wither Methods sell :: a -> Altar a b b #