Documentation

Return the last element and the rest.

Build a list with one element.

More precise type for snoc.

More precise type for groupBy'.

A variant of groupBy which applies the predicate to consecutive pairs. O(n).

Breaks a list just after an element satisfying the predicate is found.

>>> breakAfter even [1,3,5,2,4,7,8]
([1,3,5,2],[4,7,8])

Concatenate one or more non-empty lists.

Like union. Duplicates in the first list are not removed. O(nm).

Checks if all the elements in the list are equal. Assumes that the Eq instance stands for an equivalence relation. O(n).

Like catMaybes.

Like filter.

Like partitionEithers.

Like lefts.

Like rights.

Non-efficient, monadic nub. O(n²).

Like zipWithM.

Like zipWithM.

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

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

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

The unzip function is the inverse of the zip function.

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

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.

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

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

Convert a stream to a normal list efficiently.

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

take n xs returns the first n elements of xs.

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

Extract the possibly-empty tail of the stream.

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

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

sortWith for NonEmpty, behaves the same as:

sortBy . comparing

sortBy for NonEmpty, behaves the same as sortBy

Sort a stream.

some1 x sequences x one or more times.

Construct a NonEmpty list from a single element.

Since: base-4.15

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

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

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

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), ...]

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.

reverse a finite NonEmpty stream.

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

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

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)

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

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.

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

Map a function over a NonEmpty stream.

Number of elements in NonEmpty list.

Extract the last element of the stream.

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

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

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

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

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

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.

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

Extract everything except the last element of the stream.

Extract the first element of the stream.

groupWith1 is to group1 as groupWith is to group

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

groupBy1 is to group1 as groupBy is to group.

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

groupAllWith1 is to groupWith1 as groupAllWith is to groupWith

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

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

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" : ...

Converts a normal list to a NonEmpty stream.

Raises an error if given an empty list.

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

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

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

cycle xs returns the infinite repetition of xs:

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

Synonym for <|.

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

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

A monomorphic version of <> for NonEmpty.

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

Since: base-4.16

Prepend an element to the stream.

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.