null

Test whether the structure is empty. The default implementation is Left-associative and lazy in both the initial element and the accumulator. Thus optimised for structures where the first element can be accessed in constant time. Structures where this is not the case should have a non-default implementation.

Examples

Basic usage:

>>> null []
True

>>> null [1]
False

null is expected to terminate even for infinite structures. The default implementation terminates provided the structure is bounded on the left (there is a leftmost element).

>>> null [1..]
False

Test whether a list is empty.

>>> null []
True

>>> null [1]
False

>>> null [1..]
False

O(1) Test whether a ByteString is empty.

O(1) Test whether a ShortByteString is empty.

O(1) Tests whether a Text is empty or not.

O(1) Tests whether a Stream Char is empty or not. Properties

null . stream = null

Is the map empty?

Data.IntMap.null (empty)           == True
Data.IntMap.null (singleton 1 'a') == False

Is the set empty?

Is the map empty?

Data.Map.null (empty)           == True
Data.Map.null (singleton 1 'a') == False

Is this the empty sequence?

Is this the empty set?

Is the map empty?

Return True if this map is empty, False otherwise.

Return True if this set is empty, False otherwise.

>>> HashSet.null HashSet.empty
True

>>> HashSet.null (HashSet.singleton 1)
False

O(1). Determine if a Deque is empty.

>>> Control.Lens.Internal.Deque.null empty
True

>>> Control.Lens.Internal.Deque.null (singleton 1)
False

True if there are no values in the stream. This function does not modify the stream.

Checks if there are no more bytes in the underlying representation.

Test whether IOData is empty

Is the map empty?

Data.Word64Map.null (empty)           == True
Data.Word64Map.null (singleton 1 'a') == False

Is the set empty?

Returns true if the passed-in UUID is the nil UUID.

Check if a byte array is empty