Data.List.NonEmpty.Compat

base-compat-0.14.1: A compatibility layer for base

Safe Haskell | Safe-Inferred
Language | Haskell2010

Data.List.NonEmpty.Compat

Contents

- The type of non-empty streams
- Non-empty stream transformations
- Basic functions
- Building streams
- Extracting sublists
- Sublist predicates
- "Set" operations
- Indexing streams
- Zipping and unzipping streams
- Converting to and from a list

Description

This backports the modern Data.Semigroup interface back to `base-4.9`/GHC 8.0.

Synopsis

- data NonEmpty a = a :| [a]
- map :: (a -> b) -> NonEmpty a -> NonEmpty b
- intersperse :: a -> NonEmpty a -> NonEmpty a
- scanl :: Foldable f => (b -> a -> b) -> b -> f a -> NonEmpty b
- scanr :: Foldable f => (a -> b -> b) -> b -> f a -> NonEmpty b
- scanl1 :: (a -> a -> a) -> NonEmpty a -> NonEmpty a
- scanr1 :: (a -> a -> a) -> NonEmpty a -> NonEmpty a
- transpose :: NonEmpty (NonEmpty a) -> NonEmpty (NonEmpty a)
- sortBy :: (a -> a -> Ordering) -> NonEmpty a -> NonEmpty a
- sortWith :: Ord o => (a -> o) -> NonEmpty a -> NonEmpty a
- length :: NonEmpty a -> Int
- compareLength :: NonEmpty a -> Int -> Ordering
- head :: NonEmpty a -> a
- tail :: NonEmpty a -> [a]
- last :: NonEmpty a -> a
- init :: NonEmpty a -> [a]
- singleton :: a -> NonEmpty a
- (<|) :: a -> NonEmpty a -> NonEmpty a
- cons :: a -> NonEmpty a -> NonEmpty a
- uncons :: NonEmpty a -> (a, Maybe (NonEmpty a))
- unfoldr :: (a -> (b, Maybe a)) -> a -> NonEmpty b
- sort :: Ord a => NonEmpty a -> NonEmpty a
- sortOn :: Ord b => (a -> b) -> NonEmpty a -> NonEmpty a
- reverse :: NonEmpty a -> NonEmpty a
- inits :: Foldable f => f a -> NonEmpty [a]
- inits1 :: NonEmpty a -> NonEmpty (NonEmpty a)
- tails :: Foldable f => f a -> NonEmpty [a]
- tails1 :: NonEmpty a -> NonEmpty (NonEmpty a)
- append :: NonEmpty a -> NonEmpty a -> NonEmpty a
- appendList :: NonEmpty a -> [a] -> NonEmpty a
- prependList :: [a] -> NonEmpty a -> NonEmpty a
- iterate :: (a -> a) -> a -> NonEmpty a
- repeat :: a -> NonEmpty a
- cycle :: NonEmpty a -> NonEmpty a
- unfold :: (a -> (b, Maybe a)) -> a -> NonEmpty b
- insert :: (Foldable f, Ord a) => a -> f a -> NonEmpty a
- some1 :: Alternative f => f a -> f (NonEmpty a)
- take :: Int -> NonEmpty a -> [a]
- drop :: Int -> NonEmpty a -> [a]
- splitAt :: Int -> NonEmpty a -> ([a], [a])
- takeWhile :: (a -> Bool) -> NonEmpty a -> [a]
- dropWhile :: (a -> Bool) -> NonEmpty a -> [a]
- span :: (a -> Bool) -> NonEmpty a -> ([a], [a])
- break :: (a -> Bool) -> NonEmpty a -> ([a], [a])
- filter :: (a -> Bool) -> NonEmpty a -> [a]
- partition :: (a -> Bool) -> NonEmpty a -> ([a], [a])
- group :: (Foldable f, Eq a) => f a -> [NonEmpty a]
- groupBy :: Foldable f => (a -> a -> Bool) -> f a -> [NonEmpty a]
- groupWith :: (Foldable f, Eq b) => (a -> b) -> f a -> [NonEmpty a]
- groupAllWith :: Ord b => (a -> b) -> [a] -> [NonEmpty a]
- group1 :: Eq a => NonEmpty a -> NonEmpty (NonEmpty a)
- groupBy1 :: (a -> a -> Bool) -> NonEmpty a -> NonEmpty (NonEmpty a)
- groupWith1 :: Eq b => (a -> b) -> NonEmpty a -> NonEmpty (NonEmpty a)
- groupAllWith1 :: Ord b => (a -> b) -> NonEmpty a -> NonEmpty (NonEmpty a)
- permutations :: [a] -> NonEmpty [a]
- permutations1 :: NonEmpty a -> NonEmpty (NonEmpty a)
- isPrefixOf :: Eq a => [a] -> NonEmpty a -> Bool
- nub :: Eq a => NonEmpty a -> NonEmpty a
- nubBy :: (a -> a -> Bool) -> NonEmpty a -> NonEmpty a
- (!!) :: HasCallStack => NonEmpty a -> Int -> a
- zip :: NonEmpty a -> NonEmpty b -> NonEmpty (a, b)
- zipWith :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c
- unzip :: Functor f => f (a, b) -> (f a, f b)
- fromList :: HasCallStack => [a] -> NonEmpty a
- toList :: NonEmpty a -> [a]
- nonEmpty :: [a] -> Maybe (NonEmpty a)
- xor :: NonEmpty Bool -> Bool

# The type of non-empty streams

data NonEmpty a #

Non-empty (and non-strict) list type.

@since base-4.9.0.0

Constructors

a :| [a] infixr 5 |

#### Instances

Instances details

MonadZip NonEmpty | Since: base-4.9.0.0
Instance details Defined in Control.Monad.Zip Methods mzip :: NonEmpty a -> NonEmpty b -> NonEmpty (a, b) # mzipWith :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c # munzip :: NonEmpty (a, b) -> (NonEmpty a, NonEmpty b) #
Foldable1 NonEmpty | Since: base-4.18.0.0
Instance details Defined in Data.Foldable1 Methods fold1 :: Semigroup m => NonEmpty m -> m # foldMap1 :: Semigroup m => (a -> m) -> NonEmpty a -> m # foldMap1' :: Semigroup m => (a -> m) -> NonEmpty a -> m # toNonEmpty :: NonEmpty a -> NonEmpty a # maximum :: Ord a => NonEmpty a -> a # minimum :: Ord a => NonEmpty a -> a # head :: NonEmpty a -> a # last :: NonEmpty a -> a # foldrMap1 :: (a -> b) -> (a -> b -> b) -> NonEmpty a -> b # foldlMap1' :: (a -> b) -> (b -> a -> b) -> NonEmpty a -> b # foldlMap1 :: (a -> b) -> (b -> a -> b) -> NonEmpty a -> b # foldrMap1' :: (a -> b) -> (a -> b -> b) -> NonEmpty a -> b #
Eq1 NonEmpty | Since: base-4.10.0.0
Instance details Defined in Data.Functor.Classes Methods liftEq :: (a -> b -> Bool) -> NonEmpty a -> NonEmpty b -> Bool #
Ord1 NonEmpty | Since: base-4.10.0.0
Instance details Defined in Data.Functor.Classes Methods liftCompare :: (a -> b -> Ordering) -> NonEmpty a -> NonEmpty b -> Ordering #
Read1 NonEmpty | Since: base-4.10.0.0
Instance details Defined in Data.Functor.Classes Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (NonEmpty a) # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [NonEmpty a] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (NonEmpty a) # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [NonEmpty a] #
Show1 NonEmpty | Since: base-4.10.0.0
Instance details Defined in Data.Functor.Classes Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> NonEmpty a -> ShowS # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [NonEmpty a] -> ShowS #
Applicative NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods pure :: a -> NonEmpty a # (<*>) :: NonEmpty (a -> b) -> NonEmpty a -> NonEmpty b # liftA2 :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c # (*>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # (<*) :: NonEmpty a -> NonEmpty b -> NonEmpty a #
Functor NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> NonEmpty a -> NonEmpty b # (<$) :: a -> NonEmpty b -> NonEmpty a #
Monad NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b # (>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # return :: a -> NonEmpty a #
Foldable NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Foldable Methods fold :: Monoid m => NonEmpty m -> m # foldMap :: Monoid m => (a -> m) -> NonEmpty a -> m # foldMap' :: Monoid m => (a -> m) -> NonEmpty a -> m # foldr :: (a -> b -> b) -> b -> NonEmpty a -> b # foldr' :: (a -> b -> b) -> b -> NonEmpty a -> b # foldl :: (b -> a -> b) -> b -> NonEmpty a -> b # foldl' :: (b -> a -> b) -> b -> NonEmpty a -> b # foldr1 :: (a -> a -> a) -> NonEmpty a -> a # foldl1 :: (a -> a -> a) -> NonEmpty a -> a # toList :: NonEmpty a -> [a] # null :: NonEmpty a -> Bool # length :: NonEmpty a -> Int # elem :: Eq a => a -> NonEmpty a -> Bool # maximum :: Ord a => NonEmpty a -> a # minimum :: Ord a => NonEmpty a -> a # sum :: Num a => NonEmpty a -> a # product :: Num a => NonEmpty a -> a #
Traversable NonEmpty | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Data.Traversable Methods traverse :: Applicative f => (a -> f b) -> NonEmpty a -> f (NonEmpty b) # sequenceA :: Applicative f => NonEmpty (f a) -> f (NonEmpty a) # mapM :: Monad m => (a -> m b) -> NonEmpty a -> m (NonEmpty b) # sequence :: Monad m => NonEmpty (m a) -> m (NonEmpty a) #
Generic1 NonEmpty |
Instance details Defined in GHC.Internal.Generics Associated Types
type Rep1 NonEmpty | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep1 NonEmpty = D1 ('MetaData "NonEmpty" "GHC.Internal.Base" "ghc-internal" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 [])))
Methods from1 :: NonEmpty a -> Rep1 NonEmpty a # to1 :: Rep1 NonEmpty a -> NonEmpty a #
Semigroup (NonEmpty a) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (<>) :: NonEmpty a -> NonEmpty a -> NonEmpty a # sconcat :: NonEmpty (NonEmpty a) -> NonEmpty a # stimes :: Integral b => b -> NonEmpty a -> NonEmpty a #
Generic (NonEmpty a) |
Instance details Defined in GHC.Internal.Generics Associated Types
type Rep (NonEmpty a) | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep (NonEmpty a) = D1 ('MetaData "NonEmpty" "GHC.Internal.Base" "ghc-internal" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a])))
Methods from :: NonEmpty a -> Rep (NonEmpty a) x # to :: Rep (NonEmpty a) x -> NonEmpty a #
IsList (NonEmpty a) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.IsList Associated Types
type Item (NonEmpty a) |
Instance details Defined in GHC.Internal.IsList type Item (NonEmpty a) = a
Methods fromList :: [Item (NonEmpty a)] -> NonEmpty a # fromListN :: Int -> [Item (NonEmpty a)] -> NonEmpty a # toList :: NonEmpty a -> [Item (NonEmpty a)] #
Read a => Read (NonEmpty a) | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS (NonEmpty a) # readList :: ReadS [NonEmpty a] # readPrec :: ReadPrec (NonEmpty a) # readListPrec :: ReadPrec [NonEmpty a] #
Show a => Show (NonEmpty a) | @since base-4.11.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> NonEmpty a -> ShowS # show :: NonEmpty a -> String # showList :: [NonEmpty a] -> ShowS #
Eq a => Eq (NonEmpty a) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (==) :: NonEmpty a -> NonEmpty a -> Bool # (/=) :: NonEmpty a -> NonEmpty a -> Bool #
Ord a => Ord (NonEmpty a) | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods compare :: NonEmpty a -> NonEmpty a -> Ordering # (<) :: NonEmpty a -> NonEmpty a -> Bool # (<=) :: NonEmpty a -> NonEmpty a -> Bool # (>) :: NonEmpty a -> NonEmpty a -> Bool # (>=) :: NonEmpty a -> NonEmpty a -> Bool # max :: NonEmpty a -> NonEmpty a -> NonEmpty a # min :: NonEmpty a -> NonEmpty a -> NonEmpty a #
type Rep1 NonEmpty | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep1 NonEmpty = D1 ('MetaData "NonEmpty" "GHC.Internal.Base" "ghc-internal" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1 :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec1 [])))
type Rep (NonEmpty a) | @since base-4.6.0.0
Instance details Defined in GHC.Internal.Generics type Rep (NonEmpty a) = D1 ('MetaData "NonEmpty" "GHC.Internal.Base" "ghc-internal" 'False) (C1 ('MetaCons ":|" ('InfixI 'RightAssociative 5) 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 a) :*: S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 [a])))
type Item (NonEmpty a) |
Instance details Defined in GHC.Internal.IsList type Item (NonEmpty a) = a

# Non-empty stream transformations

map :: (a -> b) -> NonEmpty a -> NonEmpty b #

Map a function over a `NonEmpty` stream.

intersperse :: a -> NonEmpty a -> NonEmpty a #

'intersperse x xs' alternates elements of the list with copies of `x`.

    intersperse 0 (1 :| [2,3]) == 1 :| [0,2,0,3]

scanl :: Foldable f => (b -> a -> b) -> b -> f a -> NonEmpty b #

`scanl` is similar to `foldl`, but returns a stream of successive reduced values from the left:

    scanl f z [x1, x2, ...] == z :| [z `f` x1, (z `f` x1) `f` x2, ...]

Note that

    last (scanl f z xs) == foldl f z xs.

scanr :: Foldable f => (a -> b -> b) -> b -> f a -> NonEmpty b #

`scanr` is the right-to-left dual of `scanl`. Note that

    head (scanr f z xs) == foldr f z xs.

scanl1 :: (a -> a -> a) -> NonEmpty a -> NonEmpty a #

`scanl1` is a variant of `scanl` that has no starting value argument:

    scanl1 f [x1, x2, ...] == x1 :| [x1 `f` x2, x1 `f` (x2 `f` x3), ...]

scanr1 :: (a -> a -> a) -> NonEmpty a -> NonEmpty a #

`scanr1` is a variant of `scanr` that has no starting value argument.

transpose :: NonEmpty (NonEmpty a) -> NonEmpty (NonEmpty a) #

`transpose` for `NonEmpty`, behaves the same as `transpose` The rows/columns need not be the same length, in which case > transpose . transpose /= id

sortBy :: (a -> a -> Ordering) -> NonEmpty a -> NonEmpty a #

`sortBy` for `NonEmpty`, behaves the same as `sortBy`

sortWith :: Ord o => (a -> o) -> NonEmpty a -> NonEmpty a #

`sortWith` for `NonEmpty`, behaves the same as:

    sortBy . comparing

# Basic functions

length :: NonEmpty a -> Int #

Number of elements in `NonEmpty` list.

compareLength :: NonEmpty a -> Int -> Ordering #

Use `compareLength` `xs` `n` as a safer and faster alternative to `compare` (`length` `xs`) `n`. Similarly, it's better to write `compareLength xs 10 == LT` instead of `length xs < 10`.

While `length` would force and traverse the entire spine of `xs` (which could even diverge if `xs` is infinite), `compareLength` traverses at most `n` elements to determine its result.

    >>> compareLength ('a' :| []) 1
    EQ
    >>> compareLength ('a' :| ['b']) 3
    LT
    >>> compareLength (0 :| [1..]) 100
    GT
    >>> compareLength undefined 0
    GT
    >>> compareLength ('a' :| 'b' : undefined) 1
    GT

Since: 4.21.0.0

head :: NonEmpty a -> a #

Extract the first element of the stream.

tail :: NonEmpty a -> [a] #

Extract the possibly-empty tail of the stream.

last :: NonEmpty a -> a #

Extract the last element of the stream.

init :: NonEmpty a -> [a] #

Extract everything except the last element of the stream.

singleton :: a -> NonEmpty a #

Construct a `NonEmpty` list from a single element.

Since: base-4.15

(<|) :: a -> NonEmpty a -> NonEmpty a infixr 5 #

Prepend an element to the stream.

cons :: a -> NonEmpty a -> NonEmpty a #

Synonym for `<|`.

uncons :: NonEmpty a -> (a, Maybe (NonEmpty a)) #

`uncons` produces the first element of the stream, and a stream of the remaining elements, if any.

unfoldr :: (a -> (b, Maybe a)) -> a -> NonEmpty b #

The `unfoldr` function is analogous to Data.List's `unfoldr` operation.

sort :: Ord a => NonEmpty a -> NonEmpty a #

Sort a stream.

sortOn :: Ord b => (a -> b) -> NonEmpty a -> NonEmpty a #

Sort a `NonEmpty` on a user-supplied projection of its elements. See `sortOn` for more detailed information.

#### Examples

Expand

    >>> sortOn fst $ (2, "world") :| [(4, "!"), (1, "Hello")]
    (1,"Hello") :| [(2,"world"),(4,"!")]

    >>> sortOn length $ "jim" :| ["creed", "pam", "michael", "dwight", "kevin"]
    "jim" :| ["pam","creed","kevin","dwight","michael"]

#### Performance notes

Expand

This function minimises the projections performed, by materialising the projections in an intermediate list.

For trivial projections, you should prefer using `sortBy` with `comparing`, for example:

    >>> sortBy (comparing fst) $ (3, 1) :| [(2, 2), (1, 3)]
    (1,3) :| [(2,2),(3,1)]

Or, for the exact same API as `sortOn`, you can use `sortBy . comparing`:

    >>> (sortBy . comparing) fst $ (3, 1) :| [(2, 2), (1, 3)]
    (1,3) :| [(2,2),(3,1)]

`sortWith` is an alias for `sortBy . comparing`.

Since: base-4.20.0.0

reverse :: NonEmpty a -> NonEmpty a #

`reverse` a finite NonEmpty stream.

inits :: Foldable f => f a -> NonEmpty [a] #

The `inits` function takes a stream `xs` and returns all the finite prefixes of `xs`, starting with the shortest. The result is `NonEmpty` because the result always contains the empty list as the first element.

    inits [1,2,3] == [] :| [[1], [1,2], [1,2,3]]
    inits [1] == [] :| [[1]]
    inits [] == [] :| []

inits1 :: NonEmpty a -> NonEmpty (NonEmpty a) #

The `inits1` function takes a `NonEmpty` stream `xs` and returns all the `NonEmpty` finite prefixes of `xs`, starting with the shortest.

    inits1 (1 :| [2,3]) == (1 :| []) :| [1 :| [2], 1 :| [2,3]]
    inits1 (1 :| []) == (1 :| []) :| []

Since: base-4.18

tails :: Foldable f => f a -> NonEmpty [a] #

The `tails` function takes a stream `xs` and returns all the suffixes of `xs`, starting with the longest. The result is `NonEmpty` because the result always contains the empty list as the last element.

    tails [1,2,3] == [1,2,3] :| [[2,3], [3], []]
    tails [1] == [1] :| [[]]
    tails [] == [] :| []

tails1 :: NonEmpty a -> NonEmpty (NonEmpty a) #

The `tails1` function takes a `NonEmpty` stream `xs` and returns all the non-empty suffixes of `xs`, starting with the longest.

    tails1 (1 :| [2,3]) == (1 :| [2,3]) :| [2 :| [3], 3 :| []]
    tails1 (1 :| []) == (1 :| []) :| []

Since: base-4.18

append :: NonEmpty a -> NonEmpty a -> NonEmpty a #

A monomorphic version of `<>` for `NonEmpty`.

    >>> append (1 :| []) (2 :| [3])
    1 :| [2,3]

Since: base-4.16

appendList :: NonEmpty a -> [a] -> NonEmpty a #

Attach a list at the end of a `NonEmpty`.

    >>> appendList (1 :| [2,3]) []
    1 :| [2,3]

    >>> appendList (1 :| [2,3]) [4,5]
    1 :| [2,3,4,5]

Since: base-4.16

prependList :: [a] -> NonEmpty a -> NonEmpty a #

Attach a list at the beginning of a `NonEmpty`.

    >>> prependList [] (1 :| [2,3])
    1 :| [2,3]

    >>> prependList [negate 1, 0] (1 :| [2, 3])
    -1 :| [0,1,2,3]

Since: base-4.16

# Building streams

iterate :: (a -> a) -> a -> NonEmpty a #

``iterate` f x` produces the infinite sequence of repeated applications of `f` to `x`.

    iterate f x = x :| [f x, f (f x), ..]

repeat :: a -> NonEmpty a #

``repeat` x` returns a constant stream, where all elements are equal to `x`.

cycle :: NonEmpty a -> NonEmpty a #

``cycle` xs` returns the infinite repetition of `xs`:

    cycle (1 :| [2,3]) = 1 :| [2,3,1,2,3,...]

unfold :: (a -> (b, Maybe a)) -> a -> NonEmpty b #

`unfold` produces a new stream by repeatedly applying the unfolding function to the seed value to produce an element of type `b` and a new seed value. When the unfolding function returns `Nothing` instead of a new seed value, the stream ends.

insert :: (Foldable f, Ord a) => a -> f a -> NonEmpty a #

``insert` x xs` inserts `x` into the last position in `xs` where it is still less than or equal to the next element. In particular, if the list is sorted beforehand, the result will also be sorted.

some1 :: Alternative f => f a -> f (NonEmpty a) #

``some1` x` sequences `x` one or more times.

# Extracting sublists

take :: Int -> NonEmpty a -> [a] #

``take` n xs` returns the first `n` elements of `xs`.

drop :: Int -> NonEmpty a -> [a] #

``drop` n xs` drops the first `n` elements off the front of the sequence `xs`.

splitAt :: Int -> NonEmpty a -> ([a], [a]) #

``splitAt` n xs` returns a pair consisting of the prefix of `xs` of length `n` and the remaining stream immediately following this prefix.

    'splitAt' n xs == ('take' n xs, 'drop' n xs)
    xs == ys ++ zs where (ys, zs) = 'splitAt' n xs

takeWhile :: (a -> Bool) -> NonEmpty a -> [a] #

``takeWhile` p xs` returns the longest prefix of the stream `xs` for which the predicate `p` holds.

dropWhile :: (a -> Bool) -> NonEmpty a -> [a] #

``dropWhile` p xs` returns the suffix remaining after ``takeWhile` p xs`.

span :: (a -> Bool) -> NonEmpty a -> ([a], [a]) #

``span` p xs` returns the longest prefix of `xs` that satisfies `p`, together with the remainder of the stream.

    'span' p xs == ('takeWhile' p xs, 'dropWhile' p xs)
    xs == ys ++ zs where (ys, zs) = 'span' p xs

break :: (a -> Bool) -> NonEmpty a -> ([a], [a]) #

The ``break` p` function is equivalent to ``span` (not . p)`.

filter :: (a -> Bool) -> NonEmpty a -> [a] #

``filter` p xs` removes any elements from `xs` that do not satisfy `p`.

partition :: (a -> Bool) -> NonEmpty a -> ([a], [a]) #

The `partition` function takes a predicate `p` and a stream `xs`, and returns a pair of lists. The first list corresponds to the elements of `xs` for which `p` holds; the second corresponds to the elements of `xs` for which `p` does not hold.

    'partition' p xs = ('filter' p xs, 'filter' (not . p) xs)

group :: (Foldable f, Eq a) => f a -> [NonEmpty a] #

The `group` function takes a stream and returns a list of streams such that flattening the resulting list is equal to the argument. Moreover, each stream in the resulting list contains only equal elements, and consecutive equal elements of the input end up in the same stream of the output list. For example, in list notation:

    >>> group "Mississippi"
    ["M", "i", "ss", "i", "ss", "i", "pp", "i"]

groupBy :: Foldable f => (a -> a -> Bool) -> f a -> [NonEmpty a] #

`groupBy` operates like `group`, but uses the provided equality predicate instead of `==`.

groupWith :: (Foldable f, Eq b) => (a -> b) -> f a -> [NonEmpty a] #

`groupWith` operates like `group`, but uses the provided projection when comparing for equality

groupAllWith :: Ord b => (a -> b) -> [a] -> [NonEmpty a] #

`groupAllWith` operates like `groupWith`, but sorts the list first so that each equivalence class has, at most, one list in the output

group1 :: Eq a => NonEmpty a -> NonEmpty (NonEmpty a) #

`group1` operates like `group`, but uses the knowledge that its input is non-empty to produce guaranteed non-empty output.

groupBy1 :: (a -> a -> Bool) -> NonEmpty a -> NonEmpty (NonEmpty a) #

`groupBy1` is to `group1` as `groupBy` is to `group`.

groupWith1 :: Eq b => (a -> b) -> NonEmpty a -> NonEmpty (NonEmpty a) #

`groupWith1` is to `group1` as `groupWith` is to `group`

groupAllWith1 :: Ord b => (a -> b) -> NonEmpty a -> NonEmpty (NonEmpty a) #

`groupAllWith1` is to `groupWith1` as `groupAllWith` is to `groupWith`

permutations :: [a] -> NonEmpty [a] #

The `permutations` function returns the list of all permutations of the argument.

Since: base-4.20.0.0

permutations1 :: NonEmpty a -> NonEmpty (NonEmpty a) #

`permutations1` operates like `permutations`, but uses the knowledge that its input is non-empty to produce output where every element is non-empty.

    permutations1 = fmap fromList . permutations . toList

Since: base-4.20.0.0

# Sublist predicates

isPrefixOf :: Eq a => [a] -> NonEmpty a -> Bool #

The `isPrefixOf` function returns `True` if the first argument is a prefix of the second.

# "Set" operations

nub :: Eq a => NonEmpty a -> NonEmpty a #

The `nub` function removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element. (The name `nub` means 'essence'.) It is a special case of `nubBy`, which allows the programmer to supply their own inequality test.

nubBy :: (a -> a -> Bool) -> NonEmpty a -> NonEmpty a #

The `nubBy` function behaves just like `nub`, except it uses a user-supplied equality predicate instead of the overloaded `==` function.

# Indexing streams

(!!) :: HasCallStack => NonEmpty a -> Int -> a infixl 9 #

`xs !! n` returns the element of the stream `xs` at index `n`. Note that the head of the stream has index 0.

Beware: a negative or out-of-bounds index will cause an error.

# Zipping and unzipping streams

zip :: NonEmpty a -> NonEmpty b -> NonEmpty (a, b) #

The `zip` function takes two streams and returns a stream of corresponding pairs.

zipWith :: (a -> b -> c) -> NonEmpty a -> NonEmpty b -> NonEmpty c #

The `zipWith` function generalizes `zip`. Rather than tupling the elements, the elements are combined using the function passed as the first argument.

unzip :: Functor f => f (a, b) -> (f a, f b) #

The `unzip` function is the inverse of the `zip` function.

# Converting to and from a list

fromList :: HasCallStack => [a] -> NonEmpty a #

Converts a normal list to a `NonEmpty` stream.

Raises an error if given an empty list.

toList :: NonEmpty a -> [a] #

Convert a stream to a normal list efficiently.

nonEmpty :: [a] -> Maybe (NonEmpty a) #

`nonEmpty` efficiently turns a normal list into a `NonEmpty` stream, producing `Nothing` if the input is empty.

xor :: NonEmpty Bool -> Bool #

Compute n-ary logic exclusive OR operation on `NonEmpty` list.