Moduleoptics-core-0.4.1.1Haskell2010

Optics.At.Core

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:

Example1 expression

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

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

Example1 expression

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

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

Example1 expression

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

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

3 classes
3 values

Packageoptics-core-0.4.1.1
Exports8
LanguageHaskell2010
LicenceBSD-3-Clause
SourceCore.hs

Type families

2 declarations

familytype family Index s

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.

Instances22Index, …

type Index IntSet = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (UArray i e) = iDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Complex a) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (IntMap a) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Map k a) = kDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Seq a) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Set a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Tree a) = [Int]Defined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Array i e) = iDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (NonEmpty a) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Identity a) = ()Defined in optics-core-0.4.1.1 · Optics.At.Core
type Index (Maybe a) = ()Defined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d, e) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d, e, f) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d, e, f, g) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d, e, f, g, h) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (a, b, c, d, e, f, g, h, i) = IntDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index (e -> a) = eDefined in optics-core-0.4.1.1 · Optics.At.Core
type Index [a] = IntDefined in optics-core-0.4.1.1 · Optics.At.Core

familytype family IxValue m

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.

Instances21IxValue, …

type IxValue IntSet = ()Defined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (UArray i e) = eDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (IntMap a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Map k a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Seq a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Set k) = ()Defined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Tree a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Array i e) = eDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (NonEmpty a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Identity a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (Maybe a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue (a0, a1, a2) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a) a
```
type IxValue (a0, a1, a2, a3) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a) a
```
type IxValue (a0, a1, a2, a3, a4) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a, a) a
```
type IxValue (a0, a1, a2, a3, a4, a5) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a, a, a) a
```
type IxValue (a0, a1, a2, a3, a4, a5, a6) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a, a, a, a) a
```
type IxValue (a0, a1, a2, a3, a4, a5, a6, a7) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a, a, a, a, a) a
```
type IxValue (a0, a1, a2, a3, a4, a5, a6, a7, a8) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a, a, a, a, a, a, a, a) a
```
type IxValue (a0, a2) = a0Defined in optics-core-0.4.1.1 · Optics.At.Core
```
ix :: Int -> AffineTraversal' (a, a) a
```
type IxValue (e -> a) = aDefined in optics-core-0.4.1.1 · Optics.At.Core
type IxValue [a] = aDefined in optics-core-0.4.1.1 · Optics.At.Core

Ixed

2 declarations

classclass Ixed m where

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.

Associated types

type family IxKind m :: OpticKind
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)
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.
Example1 expression
```
>>> [1,2,3,4] & ix 2 %~ (*10)[1,2,30,4]
```
Example1 expression
```
>>> "abcd" & ix 2 .~ 'e'"abed"
```
Example1 expression
```
>>> "abcd" ^? ix 2Just 'c'
```
Example1 expression
```
>>> [] ^? ix 2Nothing
```

Instances21Ixed, …

Ixed IntSetDefined in optics-core-0.4.1.1 · Optics.At.Core
Ord k => Ixed (Set k)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (IntMap a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (Seq a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (Tree a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (NonEmpty a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (Identity a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed (Maybe a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ixed [a]Defined in optics-core-0.4.1.1 · Optics.At.Core

Ix i => Ixed (Array i e)Defined in optics-core-0.4.1.1 · Optics.At.Core

arr ! i ≡ arr ^. ix i
arr // [(i,e)] ≡ ix i .~ e $ arr

Eq e => Ixed (e -> a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ord k => Ixed (Map k a)Defined in optics-core-0.4.1.1 · Optics.At.Core
(IArray UArray e, Ix i) => Ixed (UArray i e)Defined in optics-core-0.4.1.1 · Optics.At.Core
```
arr ! i ≡ arr ^. ix i
arr // [(i,e)] ≡ ix i .~ e $ arr
```
a0 ~ a1 => Ixed (a0, a1)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2) => Ixed (a0, a1, a2)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2, a0 ~ a3) => Ixed (a0, a1, a2, a3)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4) => Ixed (a0, a1, a2, a3, a4)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5) => Ixed (a0, a1, a2, a3, a4, a5)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5, a0 ~ a6) => Ixed (a0, a1, a2, a3, a4, a5, a6)Defined in optics-core-0.4.1.1 · Optics.At.Core
(a0 ~ a1, a0 ~ a2, a0 ~ a3, a0 ~ a4, a0 ~ a5, a0 ~ a6, a0 ~ a7) => Ixed (a0, a1, a2, a3, a4, a5, a6, a7)Defined in optics-core-0.4.1.1 · Optics.At.Core
(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)Defined in optics-core-0.4.1.1 · Optics.At.Core

valueixAt :: At m => Index m -> AffineTraversal' m (IxValue m)

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

At

3 declarations

classclass (Ixed m, IxKind m ~ An_AffineTraversal) => At m where

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))
Example1 expression
```
>>> Map.fromList [(1,"world")] ^. at 1Just "world"
```
Example1 expression
```
>>> at 1 ?~ "hello" $ Map.emptyfromList [(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.

Instances5At

At IntSetDefined in optics-core-0.4.1.1 · Optics.At.Core
Ord k => At (Set k)Defined in optics-core-0.4.1.1 · Optics.At.Core
At (IntMap a)Defined in optics-core-0.4.1.1 · Optics.At.Core
At (Maybe a)Defined in optics-core-0.4.1.1 · Optics.At.Core
Ord k => At (Map k a)Defined in optics-core-0.4.1.1 · Optics.At.Core

valueat' :: At m => Index m -> Lens' m (Maybe (IxValue m))

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

Example:

Example1 expression

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

Example1 expression

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

Example1 expression

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

Example1 expression

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

It also works as expected for other data structures:

Example1 expression

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

Example1 expression

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

valuesans :: At m => Index m -> m -> m

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

sans k = at k .~ Nothing

Contains

1 declaration

classclass Contains m where

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

Example1 expression

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

Example1 expression

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

Example1 expression

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

Instances2Contains

Contains IntSetDefined in optics-core-0.4.1.1 · Optics.At.Core
Ord a => Contains (Set a)Defined in optics-core-0.4.1.1 · Optics.At.Core