lens-4.19.2: Lenses, Folds and Traversals
Copyright(C) 2012-16 Edward Kmett
LicenseBSD-style (see the file LICENSE)
MaintainerEdward Kmett <ekmett@gmail.com>
Stabilityexperimental
Portabilitynon-portable
Safe HaskellTrustworthy
LanguageHaskell2010

Control.Lens.At

Description

 
Synopsis

At

class Ixed m => 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 . traverse

Methods

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

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

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

Instances

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At IntSet # 
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At (Maybe a) # 
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at :: Index (Maybe a) -> Lens' (Maybe a) (Maybe (IxValue (Maybe a))) #

At (IntMap a) # 
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at :: Index (IntMap a) -> Lens' (IntMap a) (Maybe (IxValue (IntMap a))) #

Ord k => At (Set k) # 
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at :: Index (Set k) -> Lens' (Set k) (Maybe (IxValue (Set k))) #

(Eq k, Hashable k) => At (HashSet k) # 
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at :: Index (HashSet k) -> Lens' (HashSet k) (Maybe (IxValue (HashSet k))) #

Ord k => At (Map k a) # 
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at :: Index (Map k a) -> Lens' (Map k a) (Maybe (IxValue (Map k a))) #

(Eq k, Hashable k) => At (HashMap k a) # 
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at :: Index (HashMap k a) -> Lens' (HashMap k a) (Maybe (IxValue (HashMap k a))) #

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

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

sans k = at k .~ Nothing

iat :: At m => Index m -> IndexedLens' (Index m) m (Maybe (IxValue m)) #

An indexed version of at.

>>> Map.fromList [(1,"world")] ^@. iat 1
(1,Just "world")
>>> iat 1 %@~ (\i x -> if odd i then Just "hello" else Nothing) $ Map.empty
fromList [(1,"hello")]
>>> iat 2 %@~ (\i x -> if odd i then Just "hello" else Nothing) $ Map.empty
fromList []

Ixed

type family Index (s :: *) :: * #

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type Index ByteString # 
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type Index ByteString # 
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type Index IntSet # 
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type Index Text # 
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type Index Text # 
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type Index Text = Int
type Index [a] # 
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type Index [a] = Int
type Index (Maybe a) # 
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type Index (Maybe a) = ()
type Index (Complex a) # 
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type Index (Complex a) = Int
type Index (Identity a) # 
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type Index (Identity a) = ()
type Index (NonEmpty a) # 
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type Index (NonEmpty a) = Int
type Index (IntMap a) # 
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type Index (IntMap a) = Int
type Index (Tree a) # 
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type Index (Tree a) = [Int]
type Index (Seq a) # 
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type Index (Seq a) = Int
type Index (Set a) # 
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type Index (Set a) = a
type Index (HashSet a) # 
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type Index (HashSet a) = a
type Index (Vector a) # 
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type Index (Vector a) = Int
type Index (Vector a) # 
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type Index (Vector a) = Int
type Index (Vector a) # 
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type Index (Vector a) = Int
type Index (Vector a) # 
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type Index (Vector a) = Int
type Index (e -> a) # 
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type Index (e -> a) = e
type Index (a, b) # 
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type Index (a, b) = Int
type Index (UArray i e) # 
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type Index (UArray i e) = i
type Index (Array i e) # 
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type Index (Array i e) = i
type Index (Map k a) # 
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type Index (Map k a) = k
type Index (HashMap k a) # 
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type Index (HashMap k a) = k
type Index (a, b, c) # 
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type Index (a, b, c) = Int
type Index (a, b, c, d) # 
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type Index (a, b, c, d) = Int
type Index (a, b, c, d, e) # 
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type Index (a, b, c, d, e) = Int
type Index (a, b, c, d, e, f) # 
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type Index (a, b, c, d, e, f) = Int
type Index (a, b, c, d, e, f, g) # 
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type Index (a, b, c, d, e, f, g) = Int
type Index (a, b, c, d, e, f, g, h) # 
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type Index (a, b, c, d, e, f, g, h) = Int
type Index (a, b, c, d, e, f, g, h, i) # 
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type Index (a, b, c, d, e, f, g, h, i) = Int

type family IxValue (m :: *) :: * #

This provides a common notion of a value at an index that is shared by both Ixed and At.

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type IxValue ByteString # 
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type IxValue ByteString # 
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type IxValue IntSet # 
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type IxValue IntSet = ()
type IxValue Text # 
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type IxValue Text # 
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type IxValue [a] # 
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type IxValue [a] = a
type IxValue (Maybe a) # 
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type IxValue (Maybe a) = a
type IxValue (Identity a) # 
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type IxValue (Identity a) = a
type IxValue (NonEmpty a) # 
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type IxValue (NonEmpty a) = a
type IxValue (IntMap a) # 
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type IxValue (IntMap a) = a
type IxValue (Tree a) # 
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type IxValue (Tree a) = a
type IxValue (Seq a) # 
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type IxValue (Seq a) = a
type IxValue (Set k) # 
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type IxValue (Set k) = ()
type IxValue (HashSet k) # 
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type IxValue (HashSet k) = ()
type IxValue (Vector a) # 
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type IxValue (Vector a) = a
type IxValue (Vector a) # 
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type IxValue (Vector a) = a
type IxValue (Vector a) # 
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type IxValue (Vector a) = a
type IxValue (Vector a) # 
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type IxValue (Vector a) = a
type IxValue (e -> a) # 
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type IxValue (e -> a) = a
type IxValue (a, a2) #
ix :: Int -> Traversal' (a,a) a
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type IxValue (a, a2) = a
type IxValue (UArray i e) # 
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type IxValue (UArray i e) = e
type IxValue (Array i e) # 
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type IxValue (Array i e) = e
type IxValue (Map k a) # 
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type IxValue (Map k a) = a
type IxValue (HashMap k a) # 
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type IxValue (HashMap k a) = a
type IxValue (a, a2, a3) #
ix :: Int -> Traversal' (a,a,a) a
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type IxValue (a, a2, a3) = a
type IxValue (a, a2, a3, a4) #
ix :: Int -> Traversal' (a,a,a,a) a
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Defined in Control.Lens.At

type IxValue (a, a2, a3, a4) = a
type IxValue (a, a2, a3, a4, a5) #
ix :: Int -> Traversal' (a,a,a,a,a) a
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type IxValue (a, a2, a3, a4, a5) = a
type IxValue (a, a2, a3, a4, a5, a6) #
ix :: Int -> Traversal' (a,a,a,a,a,a) a
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Defined in Control.Lens.At

type IxValue (a, a2, a3, a4, a5, a6) = a
type IxValue (a, a2, a3, a4, a5, a6, a7) #
ix :: Int -> Traversal' (a,a,a,a,a,a,a) a
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Defined in Control.Lens.At

type IxValue (a, a2, a3, a4, a5, a6, a7) = a
type IxValue (a, a2, a3, a4, a5, a6, a7, a8) #
ix :: Int -> Traversal' (a,a,a,a,a,a,a,a) a
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Defined in Control.Lens.At

type IxValue (a, a2, a3, a4, a5, a6, a7, a8) = a
type IxValue (a, a2, a3, a4, a5, a6, a7, a8, a9) #
ix :: Int -> Traversal' (a,a,a,a,a,a,a,a,a) a
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Defined in Control.Lens.At

type IxValue (a, a2, a3, a4, a5, a6, a7, a8, a9) = a

class Ixed m where #

Provides a simple Traversal 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

Methods

ix :: Index m -> Traversal' m (IxValue m) #

NB: Setting the value of this Traversal 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.

>>> Seq.fromList [a,b,c,d] & ix 2 %~ f
fromList [a,b,f c,d]
>>> Seq.fromList [a,b,c,d] & ix 2 .~ e
fromList [a,b,e,d]
>>> Seq.fromList [a,b,c,d] ^? ix 2
Just c
>>> Seq.fromList [] ^? ix 2
Nothing

default ix :: (Applicative f, At m) => Index m -> LensLike' f m (IxValue m) #

Instances

Instances details
Ixed ByteString # 
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Defined in Control.Lens.At

Ixed ByteString # 
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Ixed IntSet # 
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Ixed Text # 
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Ixed Text # 
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Ixed [a] # 
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ix :: Index [a] -> Traversal' [a] (IxValue [a]) #

Ixed (Maybe a) # 
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ix :: Index (Maybe a) -> Traversal' (Maybe a) (IxValue (Maybe a)) #

Ixed (Identity a) # 
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ix :: Index (Identity a) -> Traversal' (Identity a) (IxValue (Identity a)) #

Ixed (NonEmpty a) # 
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ix :: Index (NonEmpty a) -> Traversal' (NonEmpty a) (IxValue (NonEmpty a)) #

Ixed (IntMap a) # 
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ix :: Index (IntMap a) -> Traversal' (IntMap a) (IxValue (IntMap a)) #

Ixed (Tree a) # 
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ix :: Index (Tree a) -> Traversal' (Tree a) (IxValue (Tree a)) #

Ixed (Seq a) # 
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ix :: Index (Seq a) -> Traversal' (Seq a) (IxValue (Seq a)) #

Ord k => Ixed (Set k) # 
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ix :: Index (Set k) -> Traversal' (Set k) (IxValue (Set k)) #

(Eq k, Hashable k) => Ixed (HashSet k) # 
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ix :: Index (HashSet k) -> Traversal' (HashSet k) (IxValue (HashSet k)) #

Unbox a => Ixed (Vector a) # 
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ix :: Index (Vector a) -> Traversal' (Vector a) (IxValue (Vector a)) #

Storable a => Ixed (Vector a) # 
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ix :: Index (Vector a) -> Traversal' (Vector a) (IxValue (Vector a)) #

Prim a => Ixed (Vector a) # 
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ix :: Index (Vector a) -> Traversal' (Vector a) (IxValue (Vector a)) #

Ixed (Vector a) # 
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ix :: Index (Vector a) -> Traversal' (Vector a) (IxValue (Vector a)) #

Eq e => Ixed (e -> a) # 
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ix :: Index (e -> a) -> Traversal' (e -> a) (IxValue (e -> a)) #

a ~ a2 => Ixed (a, a2) # 
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ix :: Index (a, a2) -> Traversal' (a, a2) (IxValue (a, a2)) #

(IArray UArray e, Ix i) => Ixed (UArray i e) #
arr ! i ≡ arr ^. ix i
arr // [(i,e)] ≡ ix i .~ e $ arr
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Defined in Control.Lens.At

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ix :: Index (UArray i e) -> Traversal' (UArray i e) (IxValue (UArray i e)) #

Ix i => Ixed (Array i e) #
arr ! i ≡ arr ^. ix i
arr // [(i,e)] ≡ ix i .~ e $ arr
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Defined in Control.Lens.At

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ix :: Index (Array i e) -> Traversal' (Array i e) (IxValue (Array i e)) #

Ord k => Ixed (Map k a) # 
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ix :: Index (Map k a) -> Traversal' (Map k a) (IxValue (Map k a)) #

(Eq k, Hashable k) => Ixed (HashMap k a) # 
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Defined in Control.Lens.At

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ix :: Index (HashMap k a) -> Traversal' (HashMap k a) (IxValue (HashMap k a)) #

(a ~ a2, a ~ a3) => Ixed (a, a2, a3) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3) -> Traversal' (a, a2, a3) (IxValue (a, a2, a3)) #

(a ~ a2, a ~ a3, a ~ a4) => Ixed (a, a2, a3, a4) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4) -> Traversal' (a, a2, a3, a4) (IxValue (a, a2, a3, a4)) #

(a ~ a2, a ~ a3, a ~ a4, a ~ a5) => Ixed (a, a2, a3, a4, a5) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4, a5) -> Traversal' (a, a2, a3, a4, a5) (IxValue (a, a2, a3, a4, a5)) #

(a ~ a2, a ~ a3, a ~ a4, a ~ a5, a ~ a6) => Ixed (a, a2, a3, a4, a5, a6) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4, a5, a6) -> Traversal' (a, a2, a3, a4, a5, a6) (IxValue (a, a2, a3, a4, a5, a6)) #

(a ~ a2, a ~ a3, a ~ a4, a ~ a5, a ~ a6, a ~ a7) => Ixed (a, a2, a3, a4, a5, a6, a7) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4, a5, a6, a7) -> Traversal' (a, a2, a3, a4, a5, a6, a7) (IxValue (a, a2, a3, a4, a5, a6, a7)) #

(a ~ a2, a ~ a3, a ~ a4, a ~ a5, a ~ a6, a ~ a7, a ~ a8) => Ixed (a, a2, a3, a4, a5, a6, a7, a8) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4, a5, a6, a7, a8) -> Traversal' (a, a2, a3, a4, a5, a6, a7, a8) (IxValue (a, a2, a3, a4, a5, a6, a7, a8)) #

(a ~ a2, a ~ a3, a ~ a4, a ~ a5, a ~ a6, a ~ a7, a ~ a8, a ~ a9) => Ixed (a, a2, a3, a4, a5, a6, a7, a8, a9) # 
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Defined in Control.Lens.At

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ix :: Index (a, a2, a3, a4, a5, a6, a7, a8, a9) -> Traversal' (a, a2, a3, a4, a5, a6, a7, a8, a9) (IxValue (a, a2, a3, a4, a5, a6, a7, a8, a9)) #

ixAt :: At m => Index m -> Traversal' 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.

iix :: Ixed m => Index m -> IndexedTraversal' (Index m) m (IxValue m) #

An indexed version of ix.

>>> Seq.fromList [a,b,c,d] & iix 2 %@~ f'
fromList [a,b,f' 2 c,d]
>>> Seq.fromList [a,b,c,d] & iix 2 .@~ h
fromList [a,b,h 2,d]
>>> Seq.fromList [a,b,c,d] ^@? iix 2
Just (2,c)
>>> Seq.fromList [] ^@? iix 2
Nothing

Contains

class 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.

Methods

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

>>> 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

Instances details
Contains IntSet # 
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Defined in Control.Lens.At

Ord a => Contains (Set a) # 
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Defined in Control.Lens.At

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contains :: Index (Set a) -> Lens' (Set a) Bool #

(Eq a, Hashable a) => Contains (HashSet a) # 
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Defined in Control.Lens.At

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contains :: Index (HashSet a) -> Lens' (HashSet a) Bool #

icontains :: Contains m => Index m -> IndexedLens' (Index m) m Bool #

An indexed version of contains.

>>> IntSet.fromList [1,2,3,4] ^@. icontains 3
(3,True)
>>> IntSet.fromList [1,2,3,4] ^@. icontains 5
(5,False)
>>> IntSet.fromList [1,2,3,4] & icontains 3 %@~ \i x -> if odd i then not x else x
fromList [1,2,4]
>>> IntSet.fromList [1,2,3,4] & icontains 3 %@~ \i x -> if even i then not x else x
fromList [1,2,3,4]