lens-4.15.3: 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
LanguageHaskell98

Control.Lens.At

Contents

Description

 

Synopsis

At

class Ixed m => 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 . traverse

Minimal complete definition

at

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

Instances

At IntSet Source # 
At (Maybe a) Source # 

Methods

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

At (IntMap a) Source # 

Methods

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

Ord k => At (Set k) Source # 

Methods

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

(Eq k, Hashable k) => At (HashSet k) Source # 

Methods

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

Ord k => At (Map k a) Source # 

Methods

at :: Index (Map k a) -> Lens' (Map k a) (Maybe (IxValue (Map k a))) Source #

(Eq k, Hashable k) => At (HashMap k a) Source # 

Methods

at :: Index (HashMap k a) -> Lens' (HashMap k a) (Maybe (IxValue (HashMap k a))) Source #

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

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

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 :: *) :: * Source #

Instances

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

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

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

Instances

type IxValue ByteString Source # 
type IxValue ByteString Source # 
type IxValue IntSet Source # 
type IxValue IntSet = ()
type IxValue Text Source # 
type IxValue Text Source # 
type IxValue [a] Source # 
type IxValue [a] = a
type IxValue (Maybe a) Source # 
type IxValue (Maybe a) = a
type IxValue (Identity a) Source # 
type IxValue (Identity a) = a
type IxValue (NonEmpty a) Source # 
type IxValue (NonEmpty a) = a
type IxValue (IntMap a) Source # 
type IxValue (IntMap a) = a
type IxValue (Tree a) Source # 
type IxValue (Tree a) = a
type IxValue (Seq a) Source # 
type IxValue (Seq a) = a
type IxValue (Set k) Source # 
type IxValue (Set k) = ()
type IxValue (HashSet k) Source # 
type IxValue (HashSet k) = ()
type IxValue (Vector a) Source # 
type IxValue (Vector a) = a
type IxValue (Vector a) Source # 
type IxValue (Vector a) = a
type IxValue (Vector a) Source # 
type IxValue (Vector a) = a
type IxValue (Vector a) Source # 
type IxValue (Vector a) = a
type IxValue (e -> a) Source # 
type IxValue (e -> a) = a
type IxValue (a, a2) Source # 
type IxValue (a, a2) = a
type IxValue (UArray i e) Source # 
type IxValue (UArray i e) = e
type IxValue (Array i e) Source # 
type IxValue (Array i e) = e
type IxValue (Map k a) Source # 
type IxValue (Map k a) = a
type IxValue (HashMap k a) Source # 
type IxValue (HashMap k a) = a
type IxValue (a, a2, a3) Source # 
type IxValue (a, a2, a3) = a
type IxValue (a, a2, a3, a4) Source # 
type IxValue (a, a2, a3, a4) = a
type IxValue (a, a2, a3, a4, a5) Source # 
type IxValue (a, a2, a3, a4, a5) = a
type IxValue (a, a2, a3, a4, a5, a6) Source # 
type IxValue (a, a2, a3, a4, a5, a6) = a
type IxValue (a, a2, a3, a4, a5, a6, a7) Source # 
type IxValue (a, a2, a3, a4, a5, a6, a7) = a
type IxValue (a, a2, a3, a4, a5, a6, a7, a8) Source # 
type IxValue (a, a2, a3, a4, a5, a6, a7, a8) = a
type IxValue (a, a2, a3, a4, a5, a6, a7, a8, a9) Source # 
type IxValue (a, a2, a3, a4, a5, a6, a7, a8, a9) = a

class Ixed m where Source #

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.

Methods

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

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

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

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

Instances

Ixed ByteString Source # 
Ixed ByteString Source # 
Ixed IntSet Source # 
Ixed Text Source # 
Ixed Text Source # 
Ixed [a] Source # 

Methods

ix :: Index [a] -> Traversal' [a] (IxValue [a]) Source #

Ixed (Maybe a) Source # 

Methods

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

Ixed (Identity a) Source # 
Ixed (NonEmpty a) Source # 
Ixed (IntMap a) Source # 

Methods

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

Ixed (Tree a) Source # 

Methods

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

Ixed (Seq a) Source # 

Methods

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

Ord k => Ixed (Set k) Source # 

Methods

ix :: Index (Set k) -> Traversal' (Set k) (IxValue (Set k)) Source #

(Eq k, Hashable k) => Ixed (HashSet k) Source # 

Methods

ix :: Index (HashSet k) -> Traversal' (HashSet k) (IxValue (HashSet k)) Source #

Ixed (Vector a) Source # 

Methods

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

Storable a => Ixed (Vector a) Source # 

Methods

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

Unbox a => Ixed (Vector a) Source # 

Methods

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

Prim a => Ixed (Vector a) Source # 

Methods

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

Eq e => Ixed (e -> a) Source # 

Methods

ix :: Index (e -> a) -> Traversal' (e -> a) (IxValue (e -> a)) Source #

(~) * a a2 => Ixed (a, a2) Source # 

Methods

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

(IArray UArray e, Ix i) => Ixed (UArray i e) Source #
arr ! i ≡ arr ^. ix i
arr // [(i,e)] ≡ ix i .~ e $ arr

Methods

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

Methods

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

Ord k => Ixed (Map k a) Source # 

Methods

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

(Eq k, Hashable k) => Ixed (HashMap k a) Source # 

Methods

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

((~) * a a2, (~) * a a3) => Ixed (a, a2, a3) Source # 

Methods

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

((~) * a a2, (~) * a a3, (~) * a a4) => Ixed (a, a2, a3, a4) Source # 

Methods

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

((~) * a a2, (~) * a a3, (~) * a a4, (~) * a a5) => Ixed (a, a2, a3, a4, a5) Source # 

Methods

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

((~) * a a2, (~) * a a3, (~) * a a4, (~) * a a5, (~) * a a6) => Ixed (a, a2, a3, a4, a5, a6) Source # 

Methods

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

((~) * a a2, (~) * a a3, (~) * a a4, (~) * a a5, (~) * a a6, (~) * a a7) => Ixed (a, a2, a3, a4, a5, a6, a7) Source # 

Methods

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)) Source #

((~) * a a2, (~) * a a3, (~) * a a4, (~) * a a5, (~) * a a6, (~) * a a7, (~) * a a8) => Ixed (a, a2, a3, a4, a5, a6, a7, a8) Source # 

Methods

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)) Source #

((~) * 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) Source # 

Methods

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)) Source #

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

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

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 Source #

This class provides a simple Lens that lets you view (and modify) information about whether or not a container contains a given Index.

Minimal complete definition

contains

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

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

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]