:: [a] -> a -> Int -package:MissingH

elemIndexJust op = fromJust . elemIndex op

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.

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 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

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).