Copyright	(C) 2012-14 Edward Kmett
License	BSD-style (see the file LICENSE)
Maintainer	Edward Kmett <ekmett@gmail.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell98

Control.Lens.At

Contents

At
Ixed
Contains

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

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
At (Maybe a)
At (IntMap a)
Ord k => At (Set k)
(Eq k, Hashable k) => At (HashSet k)
(Eq k, Hashable k) => At (HashMap k a)
Ord k => At (Map k a)

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

Ixed

type family Index s :: * Source

Instances

type Index ByteString = Int
type Index ByteString = Int64
type Index Text = Int
type Index Value = Text
type Index IntSet = Int
type Index Text = Int64
type Index [a] = Int
type Index (Maybe a) = ()
type Index (Complex a) = Int
type Index (Identity a) = ()
type Index (IntMap a) = Int
type Index (Set a) = a
type Index (Tree a) = [Int]
type Index (Seq a) = Int
type Index (NonEmpty a) = Int
type Index (HashSet a) = a
type Index (Vector a) = Int
type Index (Vector a) = Int
type Index (Vector a) = Int
type Index (Vector a) = Int
type Index (e -> a) = e
type Index (a, b) = Int
type Index (a, b) = Int
type Index (HashMap k a) = k
type Index (Map k a) = k
type Index (UArray i e) = i
type Index (Array i e) = i
type Index (a, b, c) = Int
type Index (a, b, c) = Int
type Index (a, b, c, d) = Int
type Index (a, b, c, d) = Int
type Index (a, b, c, d, e) = Int
type Index (a, b, c, d, e) = Int
type Index (a, b, c, d, e, f) = Int
type Index (a, b, c, d, e, f) = Int
type Index (a, b, c, d, e, f, g) = Int
type Index (a, b, c, d, e, f, g) = Int
type Index (a, b, c, d, e, f, g, h) = Int
type Index (a, b, c, d, e, f, g, h) = Int
type Index (a, b, c, d, e, f, g, h, i) = Int
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 = Word8
type IxValue ByteString = Word8
type IxValue Text = Char
type IxValue Value = Value
type IxValue IntSet = ()
type IxValue Text = Char
type IxValue [a] = a
type IxValue (Maybe a) = a
type IxValue (Identity a) = a
type IxValue (IntMap a) = a
type IxValue (Set k) = ()
type IxValue (Tree a) = a
type IxValue (Seq a) = a
type IxValue (NonEmpty a) = a
type IxValue (HashSet k) = ()
type IxValue (Vector a) = a
type IxValue (Vector a) = a
type IxValue (Vector a) = a
type IxValue (Vector a) = a
type IxValue (e -> a) = a
type IxValue (a, b) = a
type IxValue (HashMap k a) = a
type IxValue (Map k a) = a
type IxValue (UArray i e) = e
type IxValue (Array i e) = e
type IxValue (a, b, c) = a
type IxValue (a, b, c, d) = a
type IxValue (a, b, c, d, e) = a
type IxValue (a, b, c, d, e, f) = a
type IxValue (a, b, c, d, e, f, g) = a
type IxValue (a, b, c, d, e, f, g, h) = a
type IxValue (a, b, c, d, e, f, g, h, i) = a

class Ixed m where Source

This 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.

Methods

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

This 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.

NB: Setting the value of this AffineTraversal will only set the value in the Lens 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
Ixed ByteString
Ixed Text
Ixed Value
Ixed IntSet
Ixed Text
Ixed [a]
Ixed (Maybe a)
Ixed (Identity a)
Ixed (IntMap a)
Ord k => Ixed (Set k)
Ixed (Tree a)
Ixed (Seq a)
Ixed (NonEmpty a)
(Eq k, Hashable k) => Ixed (HashSet k)
Ixed (Vector a)
Unbox a => Ixed (Vector a)
Storable a => Ixed (Vector a)
Prim a => Ixed (Vector a)
Eq e => Ixed (e -> a)
(~) * a b => Ixed (a, b)
(Eq k, Hashable k) => Ixed (HashMap k a)
Ord k => Ixed (Map k a)
(IArray UArray e, Ix i) => Ixed (UArray i e)	arr `!` i ≡ arr 'Control.Lens.Getter.^.' `ix` i arr `//` [(i,e)] ≡ `ix` i `.~` e `$` arr
Ix i => Ixed (Array i e)	arr `!` i ≡ arr 'Control.Lens.Getter.^.' `ix` i arr `//` [(i,e)] ≡ `ix` i `.~` e `$` arr
((~) * a b, (~) * a c) => Ixed (a, b, c)
((~) * a b, (~) * a c, (~) * a d) => Ixed (a, b, c, d)
((~) * a b, (~) * a c, (~) * a d, (~) * a e) => Ixed (a, b, c, d, e)
((~) * a b, (~) * a c, (~) * a d, (~) * a e, (~) * a f) => Ixed (a, b, c, d, e, f)
((~) * a b, (~) * a c, (~) * a d, (~) * a e, (~) * a f, (~) * a g) => Ixed (a, b, c, d, e, f, g)
((~) * a b, (~) * a c, (~) * a d, (~) * a e, (~) * a f, (~) * a g, (~) * a h) => Ixed (a, b, c, d, e, f, g, h)
((~) * a b, (~) * a c, (~) * a d, (~) * a e, (~) * a f, (~) * a g, (~) * a h, (~) * a i) => Ixed (a, b, c, d, e, f, g, h, i)

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.

Contains

class Contains m where Source

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

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
Ord a => Contains (Set a)
(Eq a, Hashable a) => Contains (HashSet a)