:: a -> [a] -> Int -package:base-prelude

elemIndexJust op = fromJust . elemIndex op

Returns a count of the number of times the given element occured in the given list.

Like elemRIndex, but returns -1 if there is nothing found.

countElem gets the number of occurrences of the specified element. Example:

countElem 'o' "foo bar" == 2

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 *

Returns the rightmost index of the given element in the given 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. For the result to be Nothing, the list must be finite.

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

O(n) Yield Just the index of the first occurrence of the given element or Nothing if the vector does not contain the element. This is a specialised version of findIndex.

A generalised variant of elemIndex. O(n).

Find position of a value in a list. Used to change metavar argument indices during assignment. reverse is necessary because we are directly abstracting over the list.