elem package:rio

O(n) elem is the ByteString membership predicate.

Does the element occur in the structure? Note: elem is often used in infix form.

Examples

Basic usage:

>>> 3 `elem` []
False

>>> 3 `elem` [1,2]
False

>>> 3 `elem` [1,2,3,4,5]
True

For infinite structures, the default implementation of elem terminates if the sought-after value exists at a finite distance from the left side of the structure:

>>> 3 `elem` [1..]
True

>>> 3 `elem` ([4..] ++ [3])
* Hangs forever *

O(n) The elemIndex function returns the index of the first element in the given ByteString which is equal to the query element, or Nothing if there is no such element. This implementation uses memchr(3).

O(n) The elemIndexEnd function returns the last index of the element in the given ByteString which is equal to the query element, or Nothing if there is no such element. The following holds:

elemIndexEnd c xs = case elemIndex c (reverse xs) of
Nothing -> Nothing
Just i  -> Just (length xs - 1 - i)

O(n) The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order. This implementation uses memchr(3).

O(n) The elemIndex function returns the index of the first element in the given ByteString which is equal to the query element, or Nothing if there is no such element. This implementation uses memchr(3).

O(n) The elemIndexEnd function returns the last index of the element in the given ByteString which is equal to the query element, or Nothing if there is no such element. The following holds:

elemIndexEnd c xs = case elemIndex c (reverse xs) of
Nothing -> Nothing
Just i  -> Just (length xs - 1 - i)

O(n) The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order. This implementation uses memchr(3).

Return a list of this map's values. The list is produced lazily.

The elemIndex function returns the index of the first element in the given list which is equal (by ==) to the query element, or Nothing if there is no such element. For the result to be Nothing, the list must be finite.

Examples

>>> elemIndex 4 [0..]
Just 4

>>> elemIndex 'o' "haskell"
Nothing

>>> elemIndex 0 [1..]
* hangs forever *

The elemIndices function extends elemIndex, by returning the indices of all elements equal to the query element, in ascending order.

Examples

>>> elemIndices 'o' "Hello World"
[4,7]

>>> elemIndices 1 [1, 2, 3, 1, 2, 3]
[0,3]

Retrieve an element by its index, i.e. by its zero-based index in the sequence sorted by keys. If the index is out of range (less than zero, greater or equal to size of the map), error is called.

elemAt 0 (fromList [(5,"a"), (3,"b")]) == (3,"b")
elemAt 1 (fromList [(5,"a"), (3,"b")]) == (5, "a")
elemAt 2 (fromList [(5,"a"), (3,"b")])    Error: index out of range

Return all elements of the map in the ascending order of their keys. Subject to list fusion.

elems (fromList [(5,"a"), (3,"b")]) == ["b","a"]
elems empty == []

elemIndexL finds the leftmost index of the specified element, if it is present, and otherwise Nothing.

elemIndexR finds the rightmost index of the specified element, if it is present, and otherwise Nothing.

elemIndicesL finds the indices of the specified element, from left to right (i.e. in ascending order).

elemIndicesR finds the indices of the specified element, from right to left (i.e. in descending order).

An alias of toAscList. The elements of a set in ascending order. Subject to list fusion.

Retrieve an element by its index, i.e. by its zero-based index in the sorted sequence of elements. If the index is out of range (less than zero, greater or equal to size of the set), error is called.

elemAt 0 (fromList [5,3]) == 3
elemAt 1 (fromList [5,3]) == 5
elemAt 2 (fromList [5,3])    Error: index out of range