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Language	Haskell2010

Optic.Prism.Cons

Contents

Cons

Synopsis

class Cons s t a b | s -> a, t -> b, s b -> t, t a -> s where
(<|) :: Cons s s a a => a -> s -> s
cons :: Cons s s a a => a -> s -> s
uncons :: Cons s s a a => s -> Maybe (a, s)
_head :: Cons s s a a => Traversal' s a
_tail :: Cons s s a a => Traversal' s s
pattern (:<) :: forall b a. Cons b b a a => a -> b -> b

Cons

class Cons s t a b | s -> a, t -> b, s b -> t, t a -> s where #

This class provides a way to attach or detach elements on the left side of a structure in a flexible manner.

Minimal complete definition

_Cons

Methods

_Cons :: Prism s t (a, s) (b, t) #

_Cons :: Prism [a] [b] (a, [a]) (b, [b])
_Cons :: Prism (Seq a) (Seq b) (a, Seq a) (b, Seq b)
_Cons :: Prism (Vector a) (Vector b) (a, Vector a) (b, Vector b)
_Cons :: Prism' String (Char, String)
_Cons :: Prism' Text (Char, Text)
_Cons :: Prism' ByteString (Word8, ByteString)

Instances

Cons ByteString ByteString Word8 Word8
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism ByteString ByteString (Word8, ByteString) (Word8, ByteString) #
Cons ByteString ByteString Word8 Word8
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism ByteString ByteString (Word8, ByteString) (Word8, ByteString) #
Cons Text Text Char Char
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism Text Text (Char, Text) (Char, Text) #
Cons Text Text Char Char
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism Text Text (Char, Text) (Char, Text) #
Cons [a] [b] a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism [a] [b] (a, [a]) (b, [b]) #
Cons (ZipList a) (ZipList b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (ZipList a) (ZipList b) (a, ZipList a) (b, ZipList b) #
Cons (Seq a) (Seq b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (Seq a) (Seq b) (a, Seq a) (b, Seq b) #
(Prim a, Prim b) => Cons (Vector a) (Vector b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (Vector a) (Vector b) (a, Vector a) (b, Vector b) #
(Storable a, Storable b) => Cons (Vector a) (Vector b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (Vector a) (Vector b) (a, Vector a) (b, Vector b) #
(Unbox a, Unbox b) => Cons (Vector a) (Vector b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (Vector a) (Vector b) (a, Vector a) (b, Vector b) #
Cons (Vector a) (Vector b) a b
Instance details Defined in Control.Lens.Cons Methods _Cons :: Prism (Vector a) (Vector b) (a, Vector a) (b, Vector b) #

(<|) :: Cons s s a a => a -> s -> s infixr 5 #

cons an element onto a container.

This is an infix alias for cons.

>>> a <| []
[a]

>>> a <| [b, c]
[a,b,c]

>>> a <| Seq.fromList []
fromList [a]

>>> a <| Seq.fromList [b, c]
fromList [a,b,c]

cons :: Cons s s a a => a -> s -> s infixr 5 #

cons an element onto a container.

>>> cons a []
[a]

>>> cons a [b, c]
[a,b,c]

>>> cons a (Seq.fromList [])
fromList [a]

>>> cons a (Seq.fromList [b, c])
fromList [a,b,c]

uncons :: Cons s s a a => s -> Maybe (a, s) #

Attempt to extract the left-most element from a container, and a version of the container without that element.

>>> uncons []
Nothing

>>> uncons [a, b, c]
Just (a,[b,c])

_head :: Cons s s a a => Traversal' s a #

A Traversal reading and writing to the head of a non-empty container.

>>> [a,b,c]^? _head
Just a

>>> [a,b,c] & _head .~ d
[d,b,c]

>>> [a,b,c] & _head %~ f
[f a,b,c]

>>> [] & _head %~ f
[]

>>> [1,2,3]^?!_head
1

>>> []^?_head
Nothing

>>> [1,2]^?_head
Just 1

>>> [] & _head .~ 1
[]

>>> [0] & _head .~ 2
[2]

>>> [0,1] & _head .~ 2
[2,1]

This isn't limited to lists.

For instance you can also traverse the head of a Seq:

>>> Seq.fromList [a,b,c,d] & _head %~ f
fromList [f a,b,c,d]

>>> Seq.fromList [] ^? _head
Nothing

>>> Seq.fromList [a,b,c,d] ^? _head
Just a

_head :: Traversal' [a] a
_head :: Traversal' (Seq a) a
_head :: Traversal' (Vector a) a

_tail :: Cons s s a a => Traversal' s s #

A Traversal reading and writing to the tail of a non-empty container.

>>> [a,b] & _tail .~ [c,d,e]
[a,c,d,e]

>>> [] & _tail .~ [a,b]
[]

>>> [a,b,c,d,e] & _tail.traverse %~ f
[a,f b,f c,f d,f e]

>>> [1,2] & _tail .~ [3,4,5]
[1,3,4,5]

>>> [] & _tail .~ [1,2]
[]

>>> [a,b,c]^?_tail
Just [b,c]

>>> [1,2]^?!_tail
[2]

>>> "hello"^._tail
"ello"

>>> ""^._tail
""

This isn't limited to lists. For instance you can also traverse the tail of a Seq.

>>> Seq.fromList [a,b] & _tail .~ Seq.fromList [c,d,e]
fromList [a,c,d,e]

>>> Seq.fromList [a,b,c] ^? _tail
Just (fromList [b,c])

>>> Seq.fromList [] ^? _tail
Nothing

_tail :: Traversal' [a] [a]
_tail :: Traversal' (Seq a) (Seq a)
_tail :: Traversal' (Vector a) (Vector a)

pattern (:<) :: forall b a. Cons b b a a => a -> b -> b infixr 5 #