semigroups-0.16.0.1: Anything that associates

Copyright (C) 2011-2014 Edward Kmett, (C) 2010 Tony Morris, Oliver Taylor, Eelis van der Weegen BSD-style (see the file LICENSE) Edward Kmett provisional portable Trustworthy Haskell98

Data.List.NonEmpty

Description

A NonEmpty list forms a monad as per list, but always contains at least one element.

Synopsis

# The type of non-empty streams

data NonEmpty a Source

Constructors

 a :| [a] infixr 5

Instances

 Monad NonEmpty Functor NonEmpty Applicative NonEmpty Foldable NonEmpty Traversable NonEmpty IsList (NonEmpty a) Eq a => Eq (NonEmpty a) Data a => Data (NonEmpty a) Ord a => Ord (NonEmpty a) Read a => Read (NonEmpty a) Show a => Show (NonEmpty a) Generic (NonEmpty a) NFData a => NFData (NonEmpty a) Hashable a => Hashable (NonEmpty a) Semigroup (NonEmpty a) Typeable (* -> *) NonEmpty type Rep (NonEmpty a) type Item (NonEmpty a) = a

# Non-empty stream transformations

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

Map a function over a NonEmpty stream.

intersperse :: a -> NonEmpty a -> NonEmpty a Source

'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 Source

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 Source

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 Source

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 Source

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

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 Source

sortBy for NonEmpty, behaves the same as sortBy

sortOn :: Ord o => (a -> o) -> NonEmpty a -> NonEmpty a Source

sortOn for NonEmpty, behaves the same as:

sortBy . comparing

# Basic functions

head :: NonEmpty a -> a Source

Extract the first element of the stream.

tail :: NonEmpty a -> [a] Source

Extract the possibly-empty tail of the stream.

last :: NonEmpty a -> a Source

Extract the last element of the stream.

init :: NonEmpty a -> [a] Source

Extract everything except the last element of the stream.

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

Prepend an element to the stream.

cons :: a -> NonEmpty a -> NonEmpty a Source

Synonym for <|.

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

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 Source

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

Sort a stream.

reverse a finite NonEmpty stream.

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

The inits function takes a stream xs and returns all the finite prefixes of xs.

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

The tails function takes a stream xs and returns all the suffixes of xs.

# Building streams

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

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 Source

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

cycle :: NonEmpty a -> NonEmpty a Source

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 Source

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 Source

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) Source

some1 x sequences x one or more times.

# Extracting sublists

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

take n xs returns the first n elements of xs.

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

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

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

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] Source

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

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

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

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

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]) Source

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

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

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

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

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] Source

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. For example, in list notation:

'group' \$ 'cycle' "Mississippi" = "M" : "i" : "ss" : "i" : "ss" : "i" : "pp" : "i" : "M" : "i" : ...

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

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

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

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) Source

groupBy1 is to group1 as groupBy is to group.

# Sublist predicates

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

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

# "Set" operations

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

The nub function removes duplicate elements from a list. In particular, it keeps only the first occurence 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 Source

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

# Indexing streams

(!!) :: NonEmpty a -> Int -> a Source

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) Source

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

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

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) Source

The unzip function is the inverse of the zip function.

# Functions on streams of characters

The words function breaks a stream of characters into a stream of words, which were delimited by white space.

Beware: if the input contains no words (i.e. is entirely whitespace), this will cause an error.

The unwords function is an inverse operation to words. It joins words with separating spaces.

Beware: the input ("" :| []) will cause an error.

The lines function breaks a stream of characters into a stream of strings at newline characters. The resulting strings do not contain newlines.

The unlines function is an inverse operation to lines. It joins lines, after appending a terminating newline to each.

# Converting to and from a list

fromList :: [a] -> NonEmpty a Source

Converts a normal list to a NonEmpty stream.

Raises an error if given an empty list.

toList :: NonEmpty a -> [a] Source

Convert a stream to a normal list efficiently.

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

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