lens-3.8.7.3: Lenses, Folds and Traversals

Portability | non-portable
Stability | experimental
Maintainer | Edward Kmett <ekmett@gmail.com>
Safe Haskell | None

Data.Sequence.Lens

Description

Synopsis

- viewL :: Iso (Seq a) (Seq b) (ViewL a) (ViewL b)
- viewR :: Iso (Seq a) (Seq b) (ViewR a) (ViewR b)
- sliced :: Int -> Int -> IndexedTraversal' Int (Seq a) a
- slicedTo :: Int -> IndexedTraversal' Int (Seq a) a
- slicedFrom :: Int -> IndexedTraversal' Int (Seq a) a

# Documentation

viewL :: Iso (Seq a) (Seq b) (ViewL a) (ViewL b)

A `Seq` is isomorphic to a `ViewL`

    viewl m ≡ m ^. viewL

    >>> Seq.fromList [a,b,c] ^. viewL
    a :< fromList [b,c]

    >>> Seq.empty ^. viewL
    EmptyL

    >>> EmptyL ^. from viewL
    fromList []

    >>> review viewL $ a :< fromList [b,c]
    fromList [a,b,c]

viewR :: Iso (Seq a) (Seq b) (ViewR a) (ViewR b)

A `Seq` is isomorphic to a `ViewR`

    viewr m ≡ m ^. viewR

    >>> Seq.fromList [a,b,c] ^. viewR
    fromList [a,b] :> c

    >>> Seq.empty ^. viewR
    EmptyR

    >>> EmptyR ^. from viewR
    fromList []

    >>> review viewR $ fromList [a,b] :> c
    fromList [a,b,c]

sliced :: Int -> Int -> IndexedTraversal' Int (Seq a) a

Traverse all the elements numbered from `i` to `j` of a `Seq`

    >>> fromList [a,b,c,d,e] & sliced 1 3 %~ f
    fromList [a,f b,f c,d,e]

slicedTo :: Int -> IndexedTraversal' Int (Seq a) a

Traverse the first `n` elements of a `Seq`

    >>> fromList [a,b,c,d,e] ^.. slicedTo 2
    [a,b]

    >>> fromList [a,b,c,d,e] & slicedTo 2 %~ f
    fromList [f a,f b,c,d,e]

    >>> fromList [a,b,c,d,e] & slicedTo 10 .~ x
    fromList [x,x,x,x,x]

slicedFrom :: Int -> IndexedTraversal' Int (Seq a) a

Traverse all but the first `n` elements of a `Seq`

    >>> fromList [a,b,c,d,e] ^.. slicedFrom 2
    [c,d,e]

    >>> fromList [a,b,c,d,e] & slicedFrom 2 %~ f
    fromList [a,b,f c,f d,f e]

    >>> fromList [a,b,c,d,e] & slicedFrom 10 .~ x
    fromList [a,b,c,d,e]