lens-1.9: Lenses, Folds and Traversals

Portability portable provisional Edward Kmett Safe-Infered

Data.List.Lens

Contents

Description

Traversals for manipulating parts of a list.

Synopsis

# Documentation

_head :: Simple Lens [a] aSource

A lens reading and writing to the head of a non-empty list

````>>> ````[1,2,3]^._head
```1
```

_tail :: Simple Lens [a] [a]Source

A lens reading and writing to the tail of a non-empty list

````>>> ````_tail .~ [3,4,5] \$ [1,2]
```[1,3,4,5]
```

_last :: Simple Lens [a] aSource

A lens reading and writing to the last element of a non-empty list

````>>> ````[1,2]^._last
```2
```

_init :: Simple Lens [a] [a]Source

A lens reading and replacing all but the a last element of a non-empty list

````>>> ````[1,2,3,4]^._init
```[1,2,3]
```

interspersed :: a -> Getter [a] [a]Source

Obtain a version of the list with the supplied value interspersed.

````>>> ````"abcde"^.interspersed ','
```"a,b,c,d,e"
```
``` xs^.interspersed a = intersperse a xs
```

intercalated :: [a] -> Getter [[a]] [a]Source

Obtain a version of the list with the supplied value intercalated

# Traversals

traverseList :: IndexedTraversal Int [a] [b] a bSource

Indexed traversal of a list. The position in the list is available as the index.

The traversal for reading and writing to the head of a list

The position of the head in the original list (0) is available as the index.

````>>> ````traverseHead +~ 1 \$ [1,2,3]
```[2,2,3]
```
``` traverseHead :: Applicative f => (a -> f a) -> [a] -> f [a]
```

Traversal for editing the tail of a list.

The position of each element in the original list is available as the index.

````>>> ````traverseTail +~ 1 \$ [1,2,3]
```[1,3,4]
```
``` traverseTail :: Applicative f => (a -> f a) -> [a] -> f [a]
```

Traverse all but the last element of a list

The position of each element is available as the index.

````>>> ````traverseInit +~ 1 \$ [1,2,3]
```[2,3,3]
```
``` traverseInit :: Applicative f => (a -> f a) -> [a] -> f [a]
```

Traverse the last element in a list.

The position of the last element in the original list is available as the index.

````>>> ````traverseLast +~ 1 \$ [1,2,3]
```[1,2,4]
```
``` traverseLast :: Applicative f => (a -> f a) -> [a] -> f [a]
```