elemIndex -package:utf8-string package:rio

elemIndex :: Word8 -> ByteString -> Maybe Int
rio RIO.ByteString
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).
elemIndex :: Word8 -> ByteString -> Maybe Int64
rio RIO.ByteString.Lazy
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).
elemIndex :: Eq a => a -> [a] -> Maybe Int
rio RIO.List
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. 
>>> elemIndex 4 [0..]
Just 4
elemIndex :: (Vector v a, Eq a) => a -> v a -> Maybe Int
rio RIO.Vector
O(n) Yield Just the index of the first occurence of the given element or Nothing if the vector does not contain the element. This is a specialised version of findIndex.
elemIndex :: Eq a => a -> Vector a -> Maybe Int
rio RIO.Vector.Boxed
O(n) Yield Just the index of the first occurence of the given element or Nothing if the vector does not contain the element. This is a specialised version of findIndex.
elemIndex :: (Storable a, Eq a) => a -> Vector a -> Maybe Int
rio RIO.Vector.Storable
O(n) Yield Just the index of the first occurence of the given element or Nothing if the vector does not contain the element. This is a specialised version of findIndex.
elemIndex :: (Unbox a, Eq a) => a -> Vector a -> Maybe Int
rio RIO.Vector.Unboxed
O(n) Yield Just the index of the first occurence of the given element or Nothing if the vector does not contain the element. This is a specialised version of findIndex.
elemIndexEnd :: Word8 -> ByteString -> Maybe Int
rio RIO.ByteString
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 ==
(-) (length xs - 1) `fmap` elemIndex c (reverse xs)
elemIndexEnd :: Word8 -> ByteString -> Maybe Int64
rio RIO.ByteString.Lazy
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 ==
(-) (length xs - 1) `fmap` elemIndex c (reverse xs)
elemIndexL :: Eq a => a -> Seq a -> Maybe Int
rio RIO.Seq
elemIndexL finds the leftmost index of the specified element, if it is present, and otherwise Nothing.
elemIndexR :: Eq a => a -> Seq a -> Maybe Int
rio RIO.Seq
elemIndexR finds the rightmost index of the specified element, if it is present, and otherwise Nothing.