Safe Haskell	None
Language	Haskell2010

Optics.At.Core

Contents

Type families
Ixed
At
Contains

Description

This module provides optics for Map and Set-like containers, including an AffineTraversal to traverse a key in a map or an element of a sequence:

>>> preview (ix 1) ['a','b','c']
Just 'b'

a Lens to get, set or delete a key in a map:

>>> set (at 0) (Just 'b') (Map.fromList [(0, 'a')])
fromList [(0,'b')]

and a Lens to insert or remove an element of a set:

>>> IntSet.fromList [1,2,3,4] & contains 3 .~ False
fromList [1,2,4]

The Optics.At module from optics-extra provides additional instances of the classes defined here.

Synopsis

type family Index (s :: Type) :: Type
type family IxValue (m :: Type) :: Type
class Ixed m where
- type IxKind (m :: Type) :: OpticKind
- ix :: Index m -> Optic' (IxKind m) NoIx m (IxValue m)
ixAt :: At m => Index m -> AffineTraversal' m (IxValue m)
class (Ixed m, IxKind m ~ An_AffineTraversal) => At m where
- at :: Index m -> Lens' m (Maybe (IxValue m))
at' :: At m => Index m -> Lens' m (Maybe (IxValue m))
sans :: At m => Index m -> m -> m
class Contains m where
- contains :: Index m -> Lens' m Bool

Type families

type family Index (s :: Type) :: Type Source #

Type family that takes a key-value container type and returns the type of keys (indices) into the container, for example Index (Map k a) ~ k. This is shared by Ixed, At and Contains.

Instances

type Index IntSet Source #
Instance details Defined in Optics.At.Core type Index IntSet = Int
type Index [a] Source #
Instance details Defined in Optics.At.Core type Index [a] = Int
type Index (Maybe a) Source #
Instance details Defined in Optics.At.Core type Index (Maybe a) = ()
type Index (Complex a) Source #
Instance details Defined in Optics.At.Core type Index (Complex a) = Int
type Index (Identity a) Source #
Instance details Defined in Optics.At.Core type Index (Identity a) = ()
type Index (NonEmpty a) Source #
Instance details Defined in Optics.At.Core type Index (NonEmpty a) = Int
type Index (IntMap a) Source #
Instance details Defined in Optics.At.Core type Index (IntMap a) = Int
type Index (Tree a) Source #
Instance details Defined in Optics.At.Core type Index (Tree a) = [Int]
type Index (Seq a) Source #
Instance details Defined in Optics.At.Core type Index (Seq a) = Int
type Index (Set a) Source #
Instance details Defined in Optics.At.Core type Index (Set a) = a
type Index (e -> a) Source #
Instance details Defined in Optics.At.Core type Index (e -> a) = e
type Index (a, b) Source #
Instance details Defined in Optics.At.Core type Index (a, b) = Int
type Index (UArray i e) Source #
Instance details Defined in Optics.At.Core type Index (UArray i e) = i
type Index (Array i e) Source #
Instance details Defined in Optics.At.Core type Index (Array i e) = i
type Index (Map k a) Source #
Instance details Defined in Optics.At.Core type Index (Map k a) = k
type Index (a, b, c) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c) = Int
type Index (a, b, c, d) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d) = Int
type Index (a, b, c, d, e) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d, e) = Int
type Index (a, b, c, d, e, f) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d, e, f) = Int
type Index (a, b, c, d, e, f, g) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d, e, f, g) = Int
type Index (a, b, c, d, e, f, g, h) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d, e, f, g, h) = Int
type Index (a, b, c, d, e, f, g, h, i) Source #
Instance details Defined in Optics.At.Core type Index (a, b, c, d, e, f, g, h, i) = Int

type family IxValue (m :: Type) :: Type Source #

Type family that takes a key-value container type and returns the type of values stored in the container, for example IxValue (Map k a) ~ a. This is shared by both Ixed and At.

Instances

type IxValue IntSet Source #
Instance details Defined in Optics.At.Core type IxValue IntSet = ()
type IxValue [a] Source #
Instance details Defined in Optics.At.Core type IxValue [a] = a
type IxValue (Maybe a) Source #
Instance details Defined in Optics.At.Core type IxValue (Maybe a) = a
type IxValue (Identity a) Source #
Instance details Defined in Optics.At.Core type IxValue (Identity a) = a
type IxValue (NonEmpty a) Source #
Instance details Defined in Optics.At.Core type IxValue (NonEmpty a) = a
type IxValue (IntMap a) Source #
Instance details Defined in Optics.At.Core type IxValue (IntMap a) = a
type IxValue (Tree a) Source #
Instance details Defined in Optics.At.Core type IxValue (Tree a) = a
type IxValue (Seq a) Source #
Instance details Defined in Optics.At.Core type IxValue (Seq a) = a
type IxValue (Set k) Source #
Instance details Defined in Optics.At.Core type IxValue (Set k) = ()
type IxValue (e -> a) Source #
Instance details Defined in Optics.At.Core type IxValue (e -> a) = a
type IxValue (a0, a2) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a2) = a0
type IxValue (UArray i e) Source #
Instance details Defined in Optics.At.Core type IxValue (UArray i e) = e
type IxValue (Array i e) Source #
Instance details Defined in Optics.At.Core type IxValue (Array i e) = e
type IxValue (Map k a) Source #
Instance details Defined in Optics.At.Core type IxValue (Map k a) = a
type IxValue (a0, a1, a2) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2) = a0
type IxValue (a0, a1, a2, a3) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3) = a0
type IxValue (a0, a1, a2, a3, a4) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3, a4) = a0
type IxValue (a0, a1, a2, a3, a4, a5) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3, a4, a5) = a0
type IxValue (a0, a1, a2, a3, a4, a5, a6) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3, a4, a5, a6) = a0
type IxValue (a0, a1, a2, a3, a4, a5, a6, a7) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a, a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3, a4, a5, a6, a7) = a0
type IxValue (a0, a1, a2, a3, a4, a5, a6, a7, a8) Source #	`ix` :: `Int` -> `AffineTraversal'` (a, a, a, a, a, a, a, a, a) a
Instance details Defined in Optics.At.Core type IxValue (a0, a1, a2, a3, a4, a5, a6, a7, a8) = a0

Ixed

class Ixed m where Source #

Provides a simple AffineTraversal lets you traverse the value at a given key in a Map or element at an ordinal position in a list or Seq.

Minimal complete definition

Nothing

Associated Types

type IxKind (m :: Type) :: OpticKind Source #

Type family that takes a key-value container type and returns the kind of optic to index into it. For most containers, it's An_AffineTraversal, Representable (Naperian) containers it is A_Lens, and multi-maps would have A_Traversal.

Methods

ix :: Index m -> Optic' (IxKind m) NoIx m (IxValue m) Source #

NB: Setting the value of this AffineTraversal will only set the value in at if it is already present.

If you want to be able to insert missing values, you want at.

>>> [1,2,3,4] & ix 2 %~ (*10)
[1,2,30,4]

>>> "abcd" & ix 2 .~ 'e'
"abed"

>>> "abcd" ^? ix 2
Just 'c'

>>> [] ^? ix 2
Nothing

ix :: (At m, IxKind m ~ An_AffineTraversal) => Index m -> Optic' (IxKind m) NoIx m (IxValue m) Source #

NB: Setting the value of this AffineTraversal will only set the value in at if it is already present.

If you want to be able to insert missing values, you want at.

>>> [1,2,3,4] & ix 2 %~ (*10)
[1,2,30,4]

>>> "abcd" & ix 2 .~ 'e'
"abed"

>>> "abcd" ^? ix 2
Just 'c'

>>> [] ^? ix 2
Nothing

Instances

Ixed IntSet Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind IntSet :: OpticKind Source # Methods ix :: Index IntSet -> Optic' (IxKind IntSet) NoIx IntSet (IxValue IntSet) Source #
Ixed [a] Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind [a] :: OpticKind Source # Methods ix :: Index [a] -> Optic' (IxKind [a]) NoIx [a] (IxValue [a]) Source #
Ixed (Maybe a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Maybe a) :: OpticKind Source # Methods ix :: Index (Maybe a) -> Optic' (IxKind (Maybe a)) NoIx (Maybe a) (IxValue (Maybe a)) Source #
Ixed (Identity a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Identity a) :: OpticKind Source # Methods ix :: Index (Identity a) -> Optic' (IxKind (Identity a)) NoIx (Identity a) (IxValue (Identity a)) Source #
Ixed (NonEmpty a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (NonEmpty a) :: OpticKind Source # Methods ix :: Index (NonEmpty a) -> Optic' (IxKind (NonEmpty a)) NoIx (NonEmpty a) (IxValue (NonEmpty a)) Source #
Ixed (IntMap a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (IntMap a) :: OpticKind Source # Methods ix :: Index (IntMap a) -> Optic' (IxKind (IntMap a)) NoIx (IntMap a) (IxValue (IntMap a)) Source #
Ixed (Tree a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Tree a) :: OpticKind Source # Methods ix :: Index (Tree a) -> Optic' (IxKind (Tree a)) NoIx (Tree a) (IxValue (Tree a)) Source #
Ixed (Seq a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Seq a) :: OpticKind Source # Methods ix :: Index (Seq a) -> Optic' (IxKind (Seq a)) NoIx (Seq a) (IxValue (Seq a)) Source #
Ord k => Ixed (Set k) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Set k) :: OpticKind Source # Methods ix :: Index (Set k) -> Optic' (IxKind (Set k)) NoIx (Set k) (IxValue (Set k)) Source #
Eq e => Ixed (e -> a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (e -> a) :: OpticKind Source # Methods ix :: Index (e -> a) -> Optic' (IxKind (e -> a)) NoIx (e -> a) (IxValue (e -> a)) Source #
a0 ~ a1 => Ixed (a0, a1) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1) :: OpticKind Source # Methods ix :: Index (a0, a1) -> Optic' (IxKind (a0, a1)) NoIx (a0, a1) (IxValue (a0, a1)) Source #
(IArray UArray e, Ix i) => Ixed (UArray i e) Source #	arr `!` i ≡ arr `^.` `ix` i arr `//` [(i,e)] ≡ `ix` i `.~` e `$` arr
Instance details Defined in Optics.At.Core Associated Types type IxKind (UArray i e) :: OpticKind Source # Methods ix :: Index (UArray i e) -> Optic' (IxKind (UArray i e)) NoIx (UArray i e) (IxValue (UArray i e)) Source #
Ix i => Ixed (Array i e) Source #	arr `!` i ≡ arr `^.` `ix` i arr `//` [(i,e)] ≡ `ix` i `.~` e `$` arr
Instance details Defined in Optics.At.Core Associated Types type IxKind (Array i e) :: OpticKind Source # Methods ix :: Index (Array i e) -> Optic' (IxKind (Array i e)) NoIx (Array i e) (IxValue (Array i e)) Source #
Ord k => Ixed (Map k a) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (Map k a) :: OpticKind Source # Methods ix :: Index (Map k a) -> Optic' (IxKind (Map k a)) NoIx (Map k a) (IxValue (Map k a)) Source #
(a0 ~ a1, a0 ~ a2) => Ixed (a0, a1, a2) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2) :: OpticKind Source # Methods ix :: Index (a0, a1, a2) -> Optic' (IxKind (a0, a1, a2)) NoIx (a0, a1, a2) (IxValue (a0, a1, a2)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3) => Ixed (a0, a1, a2, a3) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3) -> Optic' (IxKind (a0, a1, a2, a3)) NoIx (a0, a1, a2, a3) (IxValue (a0, a1, a2, a3)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4) => Ixed (a0, a1, a2, a3, a4) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3, a4) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3, a4) -> Optic' (IxKind (a0, a1, a2, a3, a4)) NoIx (a0, a1, a2, a3, a4) (IxValue (a0, a1, a2, a3, a4)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5) => Ixed (a0, a1, a2, a3, a4, a5) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3, a4, a5) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3, a4, a5) -> Optic' (IxKind (a0, a1, a2, a3, a4, a5)) NoIx (a0, a1, a2, a3, a4, a5) (IxValue (a0, a1, a2, a3, a4, a5)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5, a0 ~ a6) => Ixed (a0, a1, a2, a3, a4, a5, a6) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3, a4, a5, a6) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3, a4, a5, a6) -> Optic' (IxKind (a0, a1, a2, a3, a4, a5, a6)) NoIx (a0, a1, a2, a3, a4, a5, a6) (IxValue (a0, a1, a2, a3, a4, a5, a6)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5, a0 ~ a6, a0 ~ a7) => Ixed (a0, a1, a2, a3, a4, a5, a6, a7) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3, a4, a5, a6, a7) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3, a4, a5, a6, a7) -> Optic' (IxKind (a0, a1, a2, a3, a4, a5, a6, a7)) NoIx (a0, a1, a2, a3, a4, a5, a6, a7) (IxValue (a0, a1, a2, a3, a4, a5, a6, a7)) Source #
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5, a0 ~ a6, a0 ~ a7, a0 ~ a8) => Ixed (a0, a1, a2, a3, a4, a5, a6, a7, a8) Source #
Instance details Defined in Optics.At.Core Associated Types type IxKind (a0, a1, a2, a3, a4, a5, a6, a7, a8) :: OpticKind Source # Methods ix :: Index (a0, a1, a2, a3, a4, a5, a6, a7, a8) -> Optic' (IxKind (a0, a1, a2, a3, a4, a5, a6, a7, a8)) NoIx (a0, a1, a2, a3, a4, a5, a6, a7, a8) (IxValue (a0, a1, a2, a3, a4, a5, a6, a7, a8)) Source #

ixAt :: At m => Index m -> AffineTraversal' m (IxValue m) Source #

A definition of ix for types with an At instance. This is the default if you don't specify a definition for ix.

At

class (Ixed m, IxKind m ~ An_AffineTraversal) => At m where Source #

At provides a Lens that can be used to read, write or delete the value associated with a key in a Map-like container on an ad hoc basis.

An instance of At should satisfy:

ix k ≡ at k % _Just

Methods

at :: Index m -> Lens' m (Maybe (IxValue m)) Source #

>>> Map.fromList [(1,"world")] ^. at 1
Just "world"

>>> at 1 ?~ "hello" $ Map.empty
fromList [(1,"hello")]

Note: Usage of this function might introduce space leaks if you're not careful to make sure that values put inside the Just constructor are evaluated. To force the values and avoid such leaks, use at' instead.

Note: Map-like containers form a reasonable instance, but not Array-like ones, where you cannot satisfy the Lens laws.

Instances

At IntSet Source #
Instance details Defined in Optics.At.Core Methods at :: Index IntSet -> Lens' IntSet (Maybe (IxValue IntSet)) Source #
At (Maybe a) Source #
Instance details Defined in Optics.At.Core Methods at :: Index (Maybe a) -> Lens' (Maybe a) (Maybe (IxValue (Maybe a))) Source #
At (IntMap a) Source #
Instance details Defined in Optics.At.Core Methods at :: Index (IntMap a) -> Lens' (IntMap a) (Maybe (IxValue (IntMap a))) Source #
Ord k => At (Set k) Source #
Instance details Defined in Optics.At.Core Methods at :: Index (Set k) -> Lens' (Set k) (Maybe (IxValue (Set k))) Source #
Ord k => At (Map k a) Source #
Instance details Defined in Optics.At.Core Methods at :: Index (Map k a) -> Lens' (Map k a) (Maybe (IxValue (Map k a))) Source #

at' :: At m => Index m -> Lens' m (Maybe (IxValue m)) Source #

Version of at strict in the value inside the Just constructor.

Example:

>>> (at () .~ Just (error "oops") $ Nothing) `seq` ()
()

>>> (at' () .~ Just (error "oops") $ Nothing) `seq` ()
*** Exception: oops
...

>>> view (at ()) (Just $ error "oops") `seq` ()
()

>>> view (at' ()) (Just $ error "oops") `seq` ()
*** Exception: oops
...

It also works as expected for other data structures:

>>> (at 1 .~ Just (error "oops") $ Map.empty) `seq` ()
()

>>> (at' 1 .~ Just (error "oops") $ Map.empty) `seq` ()
*** Exception: oops
...

sans :: At m => Index m -> m -> m Source #

Delete the value associated with a key in a Map-like container

sans k = at k .~ Nothing

Contains

class Contains m where Source #

This class provides a simple Lens that lets you view (and modify) information about whether or not a container contains a given Index. Instances are provided for Set-like containers only.

Methods

contains :: Index m -> Lens' m Bool Source #

>>> IntSet.fromList [1,2,3,4] ^. contains 3
True

>>> IntSet.fromList [1,2,3,4] ^. contains 5
False

>>> IntSet.fromList [1,2,3,4] & contains 3 .~ False
fromList [1,2,4]

Instances

Contains IntSet Source #
Instance details Defined in Optics.At.Core Methods contains :: Index IntSet -> Lens' IntSet Bool Source #
Ord a => Contains (Set a) Source #
Instance details Defined in Optics.At.Core Methods contains :: Index (Set a) -> Lens' (Set a) Bool Source #