fclabels-2.0.3.2: First class accessor labels implemented as lenses.

Safe Haskell | Safe
Language | Haskell98

Data.Label.Partial

Contents

- Seemingly total modifications.
- Potentially removing modification.

Description

Monomorphic lenses where the getters and updates can potentially silently fail. Partial lenses are useful for creating accessor labels for multi constructor data types where projection and modification of fields will not always succeed.

Synopsis

- type (:~>) f o = Lens Partial f o
- type Partial = Kleisli Maybe
- lens :: (f -> Maybe o) -> ((o -> Maybe i) -> f -> Maybe g) -> (f -> g) :~> (o -> i)
- get :: ((f -> g) :~> (o -> i)) -> f -> Maybe o
- modify :: ((f -> g) :~> (o -> i)) -> (o -> i) -> f -> Maybe g
- set :: ((f -> g) :~> (o -> i)) -> i -> f -> Maybe g
- embed :: Lens (->) (f -> g) (Maybe o -> Maybe i) -> (f -> g) :~> (o -> i)
- set' :: ((f -> f) :~> (o -> o)) -> o -> f -> f
- modify' :: ((f -> f) :~> (o -> o)) -> (o -> o) -> f -> f
- update :: ((f -> b) :~> (o -> i)) -> (o -> Maybe i) -> f -> Maybe b

# Documentation

type (:~>) f o = Lens Partial f o #

Partial lens type for situations in which the accessor functions can fail.

type Partial = Kleisli Maybe #

Context that represents computations that might silently fail.

lens #

Arguments

:: (f -> Maybe o) | Getter.
-> ((o -> Maybe i) -> f -> Maybe g) | Modifier.
-> (f -> g) :~> (o -> i) |

Create a lens that can fail from a getter and a modifier that can themselves potentially fail.

get :: ((f -> g) :~> (o -> i)) -> f -> Maybe o #

Getter for a lens that can fail. When the field to which the lens points is not accessible the getter returns `Nothing`.

modify :: ((f -> g) :~> (o -> i)) -> (o -> i) -> f -> Maybe g #

Modifier for a lens that can fail. When the field to which the lens points is not accessible this function returns `Nothing`.

set :: ((f -> g) :~> (o -> i)) -> i -> f -> Maybe g #

Setter for a lens that can fail. When the field to which the lens points is not accessible this function returns `Nothing`.

embed :: Lens (->) (f -> g) (Maybe o -> Maybe i) -> (f -> g) :~> (o -> i) #

Embed a total lens that points to a `Maybe` field into a lens that might fail.

# Seemingly total modifications.

set' :: ((f -> f) :~> (o -> o)) -> o -> f -> f #

Like `set` but return behaves like the identity function when the field could not be set.

modify' :: ((f -> f) :~> (o -> o)) -> (o -> o) -> f -> f #

Like `modify` but return behaves like the identity function when the field could not be set.

# Potentially removing modification.

update :: ((f -> b) :~> (o -> i)) -> (o -> Maybe i) -> f -> Maybe b #

Like `modify`, but update allows, depending on the underlying lens, to remove items by modifying to `Nothing`.