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NonEmpty

Import NonEmpty when a sequence must contain at least one value.

Type and constructor​

NonEmpty​

data NonEmpty a = NonEmpty a [a].

The public constructor stores the guaranteed head followed by an ordinary list tail. The same name refers to the type and its constructor.

NonEmpty​

The constructor is available to patterns.

Construction and conversion​

nonEmptySingleton​

nonEmptySingleton :: a -> NonEmpty(a).

nonEmptyFromList​

nonEmptyFromList :: [a] -> Maybe(NonEmpty(a)).

Returns Nothing for []; otherwise stores the list head and tail without traversing them. This is O(1).

nonEmptyToList​

nonEmptyToList :: NonEmpty(a) -> [a].

nonEmptyPrepend​

nonEmptyPrepend :: a -> NonEmpty(a) -> NonEmpty(a).

Adds a new first value in O(1).

nonEmptyAppendList​

nonEmptyAppendList :: NonEmpty(a) -> [a] -> NonEmpty(a).

Appends an ordinary list after the non-empty sequence. This is O(n) in the original sequence tail.

Access​

nonEmptyHead​

nonEmptyHead :: NonEmpty(a) -> a.

Total and O(1).

nonEmptyTail​

nonEmptyTail :: NonEmpty(a) -> [a].

The result may be empty. This is O(1).

nonEmptyLast​

nonEmptyLast :: NonEmpty(a) -> a.

Returns the final value. The function is total and O(n).

nonEmptyLength​

nonEmptyLength :: NonEmpty(a) -> Int.

Returns the number of values, which is always at least one. This is O(n).

Transforming and folding​

nonEmptyMap​

nonEmptyMap :: (a -> b) -> NonEmpty(a) -> NonEmpty(b).

Transforms every value in order and preserves non-emptiness. This is O(n) plus callback work.

nonEmptyFoldLeft​

nonEmptyFoldLeft :: (b -> a -> b) -> b -> NonEmpty(a) -> b.

Combines values from head to last, beginning with the supplied accumulator. This is O(n) plus callback work.

nonEmptyFoldRight​

nonEmptyFoldRight :: (a -> b -> b) -> b -> NonEmpty(a) -> b.

Combines values from last to head, beginning with the supplied terminal value. This is O(n) plus callback work.